Sf2 Text Book

>>>

Kerry Whalley Carol Neville Peter Roberson Greg Rickard Geoff Phillips Faye Jeffery Karin Johnstone

Sydney, Melbourne, Brisbane, Perth and associated companies around the world

Pearson Education Australia A division of Pearson Australia Group Pty Ltd Level 9, 5 Queens Road Melbourne 3004 Australia www.pearsoned.com.au/schools Offices in Sydney, Brisbane and Perth, and associated companies throughout the world. Copyright © Pearson Education Australia 2005 First published 2005 All rights reserved. Except under the conditions described in the Copyright Act 1968 of Australia and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner. Designed by Polar Design Edited by Writers Reign Illustrated by Wendy Gorton and Bruce Rankin Prepress work by The Type Factory Set in Melior 10 pt Produced by Pearson Education Australia Printed in Hong Kong National Library of Australia Cataloguing-in-Publication data: Science Focus 2. Includes index. For secondary school students. ISBN 0 1236 0445 1. 1. Science - Textbooks. I. Whalley, Kerry.

500

ii

2

Atoms

29

2.1 Elements, compounds and mixtures 2.2 Physical and chemical change 2.3 Inside atoms Science focus: Atomic models Chapter review

30 38 46 50 53

3

Microbes

55

3.1 What is a microbe? 3.2 Reproduction in microbes 3.3 Friend or foe? Chapter review

56 64 70 76

4

Body systems

78

4.1 4.2 4.3 4.4 4.5

79 89 98 108 111 118 122

Food Digestion Blood and circulation Excretion: getting rid of wastes Respiratory systems Science focus: Spare parts Chapter review

UNIT

12 15 22 28

5.1 Static electricity 5.2 Moving electricity 5.3 Using electricity Science focus: Solar challenge Chapter review

126 133 141 147 150

6

Ecology

152

UNIT

Science focus: Scientific method: the path to greater understanding 1.3 Better measurements 1.4 Scientific conventions Chapter review

125

6.1 Ecosystems 6.2 Physical attributes of an ecosystem 6.3 Food chains and food webs:

153 159

interactions of life

165

6.4 Effects of human civilisation on the ecosystem Science focus: The right balance — a human problem Chapter review

179 184

7

Plant systems

185 186 191 201 206

UNIT

3 7

Electricity

7.1 Plant transport systems 7.2 Photosynthesis and respiration 7.3 Leaves

8

Astronomy

Chapter review

UNIT

1.1 What, why and how? 1.2 Scientific research

UNIT

2

UNIT

Science skills

UNIT

1

5

8.1 8.2 8.3 8.4

9

Team research project

UNIT

iv v viii 1

UNIT

Acknowledgements Introduction Curriculum grids Verbs

9.1 Teamwork and topics 9.2 Planning your investigation 9.3 Testing and evaluation

Space rocks The night sky The Milky Way and other galaxies Satellites and remote sensing Chapter review

Chapter review

Index

171

208 209 214 220 225 231

232 233 237 243 247 249

iii

We would like to thank the following for permission to reproduce photographs, texts and illustrations.

NASA: figures SF 5.3c, 8.0.1, 8.1.1, 8.3.4, 8.3.5, 8.3.6, 8.3.7, 8.4.0, 8.4.6, 8.4.7, 8.4.10, 8.4.11; Glen Research Center, figure 8.4.2.

Andromeda Oxford Limited: Based on original artwork from Ecology & Environment: The Cycles of Life by Sally Morgan, Oxford University Press NY ©Andromeda Oxford Limited 1995, figure 6.3.4.

The National Library of Australia: figure SF 6.5; John Allcot, figure SF 6.4.

Anglo-Australian Observatory / David Malin Images: figures 8.2.2, 8.3.1. ANT Photo Library: ©B.G. Thomson, figure 6.1.5; ©M.J. Tyler, figure 6.4.7. Auscape International Photo Library: ©Andrew Henley, figure 6.4.6. Australian Associated Press: figure 2.1.3. Australian Picture Library: figures 1.3.14, 3.1.6, SF 6.1a, SF 6.1b, SF 6.3, 7.0.1, 7.2.7, 7.3.4; Hulton-Deutsch Collection/Corbis, figure 1.1.1a; Hermann/Starke, figure 2.2.2; Digital Art, figure 3.1.14; Lester V. Bergman/ Corbis, figures 3.2.5b, 4.3.11; Lester Lefkowitz, figure 4.0.1; Paul A. Souders, figure 5.1.7; John Carnemolla, figure 6.1.8; Galen Rowell, figure 6.2.5; Jonathan Blair, figure 6.2.7; Michael & Patricia Fogden, figure 6.3.9. Dr Charles Vacanti: provided by Pearson Asset Library, figure SF 4.3. Coo-ee Picture Library: figure 6.1.4. CSIRO Publishing: figure 6.1.7, 8.2.8; ©CSIRO Human Nutrition and The Cancer Council South Australia Reproduced from 12345+ Food and Nutrition Plan (K Baghurst et al., 1990) by permission of CSIRO Australia and The Cancer Council South Australia, figure 4.1.4. Dorling Kindersley: figures 2.1.2c, 5.0.1; Max Alexander, figure 2.1.2a; Erik Svensson & Jeppe Wikstrom, figure 2.1.2b; Steve Gorton, 4.3.1; Andy Crawford, figure 4.4.1; Based on original artwork from Nature Encyclopedia by David Burnie, Jonathan Elphic et al, figure 6.1.2. Fundamental Photographs: NYC © Richard Menga, figure 2.2.4. Getty: figure 6.1.3. Global Publishing: Based on original artwork from Anatomica: The Complete Reference Guide to the Human Body, figure SF 4.5. HarperCollins Publishers Ltd: figure 1.3.11. Dr Ian Jamie: figure 1.1.2. Kerry Whalley: figures 9.1.3, 9.2.1, 9.2.4, 9.3.1a, 9.3.1b, 9.4.1.

iv

Oxford University Press: copyright © from The Young Oxford Book of Ecology by Michael Scott (OUP, 1996), reprinted by permission of Oxford University Press, figure 6.4.2. Pearson Education Australia: Anna Small, figures 2.2.1, SF 5.3a; Elizabeth Anglin, figures 1.1.4, 2.1.5, 2.1.11c, 3.1.3, 3.1.9, 3.1.15, 3.3.2, 3.3.3, 3.3.6, 4.1.1, 4.1.2, 4.1.3, 4.3.22, SF 5.1, SF 5.3d, 8.1.3; Karly Abery, figures 3.1.10c, 3.3.1; Kim Nolan, figure 3.3.8; Tricia Confoy, figure 2.2.3. Photolibrary: figures 1.1.1b, 1.1.1c, 2.0.1, 2.1.2d, 2.1.6, 2.3.3, 3.0.1, 3.1.4, 3.2.8, 3.3.9a, 3.3.9b, 3.3.9c, 4.3.4, 4.3.6, 4.3.19, 4.4.4, 5.2.9, 6.1.6, 6.2.1, 6.2.4, 6.3.10, 7.1.7, 7.2.1, 7.2.2, 7.3.2, 8.1.2, 8.1.4, 8.1.5, 8.1.7, 8.2.4, 8.2.6, 8.3.3, 8.4.5, 8.4.9, 9.2.2; Graham J. Hills, figure 2.1.8; Dr Tony Brain & David Parker, figure 3.1.1; Samuel Ashfield, figure 3.1.2; Jackie Lewin, EM Unit, Royal Free Hospital, figure 3.1.8; Susumu Nishinaga, figure 3.1.10d; Sinclair Stammers, figure 3.1.11; Astrid & Hanns-Frieder Michler, figure 3.1.12a; Laguna Design, figure 3.1.12b; David Scharf, figure 3.2.1b; Claude Nuridsany & Marie Perennou, figure 3.2.4; Jean-Loup Charmet, figure 3.3.5; John Heseltine, figure 3.3.7; National Cancer Institute, figure 4.3.2; Du Cane Medical Imaging Limited, figure 4.4.2; Alred Pasieka, figure 4.5.2; Klaus Guldbrandsen, figure SF 4.2; James KingHolmes, figure SF 4.4; Volker Steger, figure 6.3.5; Sheila Terry, figure 6.3.8; Dr Jeremy Burgess, figures 7.1.3, 7.2.4; St Mary’s Hospital Medical School, figure 9.3.2. Skymaps.com: figure 8.2.7. Thomson Learning: Based on original artwork from The Joy of Chemistry, 1st Edition ©1976, reprinted with permission of Brooks/Cole, an imprint of the Wadsworth Group, a division of Thomson Learning, figure 1.3.9. World Solar Challenge: figures SF 5.6a, SF 5.6b, SF 5.6c. Every effort has been made to trace and acknowledge copyright. However, should any infringement have occurred, the publishers tender their apologies and invite the copyright owners to contact them.

The Science Focus series has been written for the NSW Science syllabus, stages 4 and 5. It includes material that addresses the learning outcomes in the domains of knowledge, understanding and skills. Each chapter addresses at least one prescribed focus area in detail. The content is presented through many varied contexts to engage students in seeing the relationship between science and their everyday lives. By learning from the Science Focus series students will become confident, creative, responsible and scientifically literate members of society.

Coursebook The coursebook consists of nine chapters with the following features. Chapter opening pages include: • the key prescribed focus area for the chapter • outcomes presented in a way that students can easily understand • pre quiz questions to stimulate interest and test prior knowledge. Chapter units open with a ‘context’ to encourage students to make meaning of science in terms of their everyday experiences. The units also reinforce contextual learning by presenting theory, photos, illustrations and ‘science focus’ segments in a format that is easy to read and follow.

Each PFA has one Science Focus special feature which uses a contextual approach to focus specifically on the outcomes of that PFA. Student activities on these pages allow further investigation and exploration of the material covered.

Each unit ends with a set of questions. These begin with straightforward ‘checkpoint’ questions that build confidence, leading to ‘think’, ‘analyse’ and ‘skills’ questions that require further thought and application. Questions incorporate the syllabus ‘verbs’ so that students can begin to practise answering questions as required in examinations in later years. The extension questions can be set for further exploration and assignment work and include a variety of structured tasks including research, creative writing and Internet activities suitable for all students. Extension questions cater for a range of learning styles using the multiple intelligences approach, and may be used for extending more able students.

v

Key numeracy and literacy tasks are indicated with icons. Practical activities follow the questions. These are placed at the end of the unit to allow teachers to choose when and how to best incorporate the Prac 1 Unit 1.2 practical work. Cross-references to practical activities within DYO the units signal suggested points for practical work. Some practical activities are ‘design-your-own’ (DYO) tasks. Chapter review questions follow the last unit in each chapter. These cover all chapter outcomes in a variety of question styles to provide opportunities for all students to consolidate new knowledge and skills.

The use of the Aboriginal flag in the coursebook denotes material that is included to cover Aboriginal perspectives in science.

Companion Website The Companion Website contains a wealth of support material for students and teachers, which has been written to enhance the content covered in the coursebook.

vi

Online review questions Auto-correcting chapter review questions can be used as a diagnostic tool or for revision at school or home, and include: • multiple choice • labelling • matching • fill in the blanks.

Destinations A list of reviewed websites is available— these relate directly to chapter content for students to access. Technology activities These are activities that apply and review concepts covered in the chapters. They are designed for students to work independently, and include: • animations to develop key skills and knowledge in a stimulating, visual way • drag-and-drop activities to improve basic understandings in a fun way • interactives to enhance the learning of content in an interactive way.

Homework Book The Homework Book provides a structured program to complement the coursebook. These homework activities: • cover various skills required in the syllabus • offer consolidation of key content and interesting extension activities • provide revision activities for each chapter, including the construction of a glossary • cater for a multiple intelligences approach through varied activities • have ‘Worksheet’ icons in the coursebook to denote when a homework activity is available.

Teacher resource centre A wealth of teacher support material is provided and is password-protected. It includes: • a chapter test for each chapter, in MS Word to allow editing by the teacher • coursebook answers • Homework Book answers • teaching programs

Worksheet 1.5 Sci-skills crossword

Teacher resource pack Material in the teacher resource pack consists of a printout and electronic copy on CD. It includes: • curriculum correlation grids mapped in detail to the NSW syllabus • chapter-based teaching programs • contextual teaching programs • coursebook answers • chapter tests in MS Word • Homework Book answers.

Worksheet 4.3 The heart

vii

Science Focus 2

Stage 4 Syllabus Correlation

A fully mapped and detailed correlation of the stage 4 curriculum outcomes is available in the Science Focus 2 Teacher Resource.

chapter

1 23456789

outcomes

Science skills 4.1

Atoms

Microbes

Body systems

Electricity

Ecology

Plant systems

Astronomy

Team research project

▲

▲

4.2

▲

▲ ▲

4.3

▲

▲

4.4

▲ ▲

4.5

▲

▲

•

4.6

•

4.7

•

4.8

•

• •

4.9

•

4.10 4.11 4.12

• • • • • • • • •

4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21

• • • • • • •

4.22 4.23

• • •

4.24 4.25 4.26 4.27 Note:

viii

• •

• • • • • • • • • • • •

• • • • • • • • • •

• •

• • • • • • • • • • • •

▲ indicates the Key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Areas.

• • • • • • • • • •

• • •

• • • •

• • • •

• • • • •

• • • • • • • • • • •

• •

• • • • • • • • • • • • • •

Verbs Science Focus 2 uses the following verbs in the student activities. Account

account for: state reasons for; report on give an account of: narrate a series of events or transactions

Analyse

identify components and the relationships among them; draw out and relate implications

Apply

use, utilise, employ in a particular situation

Assess

make a judgement of value, quality, outcomes, results or size

Calculate

determine from given facts, figures or information

Extrapolate

infer from what is known

Identify

recognise and name

Investigate

plan, inquire into and draw conclusions

Justify

support an argument or conclusion

List

write down phrases only, without further explanation

Modify

change in form or amount in some way

Outline

sketch in general terms; indicate the main features of

Predict

suggest what may happen based on available information

Clarify

make clear or plain

Classify

arrange or include in classes/categories

Compare

show how things are similar or different

Present

provide information for consideration

Construct

make; build; put together items or arguments

Propose

Contrast

show how things are different or opposite

put forward (eg a point of view, idea, argument, suggestion) for consideration or action

Deduce

draw conclusions

Recall

Define

state meaning and identify essential qualities

present remembered ideas, facts or experiences

Demonstrate

show by example

Record

store information and observations for later

Describe

provide characteristics and features

Recount

retell a series of events

Discuss

identify issues and provide points for and/or against

Research

investigate through literature or practical investigation

Distinguish

recognise or note/indicate as being distinct or different from; note differences between

State

provide information without further explanation

Summarise

express concisely the relevant details

Evaluate

make a judgement based on criteria; determine the value of

Examine

inquire into

Explain

relate cause and effect; make the relationships between things evident; provide the ‘why’ and/or ‘how’

1

Science skills Key focus area:

4.2, 4.13, 4.14, 4.15, 4.17, 4.18, 4.19

Outcomes

>>> The nature and practice of science

By the end of this chapter you should be able to: ask questions that can be tested or investigated plan investigations, identifying what type of information or data needs to be collected and why identify variables that need to be controlled identify dependent and independent variables in experiments plan a procedure for performing a fair test perform experiments and record observations and measurements accurately organise data in various forms, including tables and graphs identify relationships, patterns and contradictions in information and data analyse results

Pre quiz

comment on the accuracy and meaning of observations and results.

1 What is a scientist? 2 Name as many different areas of work done by scientists as you can.

3 How do scientists go about their work? 4 What is a variable? 5 How do scientists ensure that their work is accurate?

6 How do scientists communicate their ideas to each other?

>>>

1

3.1 UNIT

UNIT

context

1.1 The world often seems to be a very confusing place: there seem to be so many mysterious things going on around us. Albert Einstein said that the job of scientists was to coordinate our experiences of the world and try to fit them into some logical system.

Asking questions Poisoned! Sir Isaac Newton (1642–1727) developed many laws in science and mathematics, but spent much of his time with the ancient art of alchemy. He was trying to change common metals into pure gold! Other scientists often found Newton extremely childish and difficult to work with and it is now thought that the fumes from his alchemy experiments were slowly poisoning him. In the laboratory scientists must take care with the chemicals they use, particularly fumes. What rules about chemicals should you obey in the laboratory?

a

Fig 1.1.1

Scientists ask ‘What, why and how?’ about the natural world. What protects some people from catching chicken pox? Why is the sky blue, not green? How do birds know the direction in which they should migrate? Why did the chicken cross the road? They also ask ‘How does this information connect with the information we already know?’.

Prac 1 p. 5

b

Prac 2 p. 6

We live in a technological world where we use machines and equipment every day. Most of us have no idea how these work, but someone invented them and others improved them so that they became small, cheap and reliable enough to have in homes, schools, factories, farms and businesses. Scientists ask ‘What, why and how?’ when they want to invent something new or improve current technology. Newer but not better What causes poor reception on your TV? Why does your computer crash? How can we make an alarm that alerts a surgeon that a patient is waking up during an operation? The answers to these questions can sometimes be found in written resources such as textbooks or the Internet. Other answers can be found out only by doing first-hand investigations or experiments. This is the job of a scientist.

The scientists of the electronics industry usually aim to develop parts that are smaller, faster and more powerful. There is, however, a growing demand for the large and clumsy valves of old. Top recording studios often use them since it is thought that sound quality is better than with modern electronic components. The radiation from X-rays can ‘knock out’ modern electronics, so medical laboratories use valves to keep equipment running. Fighter aircraft often use valves to avoid being ‘knocked out’ of the air by radiation from a possible nuclear explosion in war.

c

You may have heard about Einstein, and Newton, but what did a Howard Florey, b Marie Curie and c Charles Darwin do? Which of them was Australian?

3

What, why and how?

a 55 5

A sheep’s burp When a sheep farts or burps, it releases methane, a greenhouse gas that contribute s to global warming. Each sheep releases about 25 litres of methane each day! CSIR O scientists designed the device shown in Figure 1.1.2. to measure the amount of gas emitted without harming the sheep. This device is the result of scientists asking: What is the problem? Why is it occurring? How are we going to solve it?

10 50 45 40

b 80 10

15 75 70 65

8 Record the measurement shown on each of the micrometer scales illustrated at right.

Fig 1.1.2

UNIT

1.1

[ Questions ]

9 Draw the shaft and barrel of a micrometer showing a measurement of 12.87 mm.

30

35

25 20 15

Fig 1.1.3

Checkpoint 1 List three things about the natural world that confuse you. 2 Construct a ‘what, why and how?’ question about each of the things that confuses you. 3 Describe how you would go about finding an answer to each of your questions. 4 Contrast the methods you listed in question 3 with the methods used by workers who aren’t scientists.

Think 5 Construct a two- or three-frame cartoon that explains how to use a micrometer. Hint: Check Prac 1 on page 5. 6 State whether the following statements are true or false. a Scientists carry out experiments on what confuses them about the world. b A micrometer is used to measure thick objects. c The barrel of a micrometer usually has markings from 0 to 100. Hint: Check Prac 1 on page 5. d The measurements that you control should always go on the vertical axis of a graph. e Points on a graph should be joined up dot-to-dot.

Skills 7 Construct a diagram of a micrometer and label the parts.

4

c

[ Extension ] Investigate 1 There are many other instruments that can measure small quantities very accurately. Research information on: a other devices that are used to measure thicknesses and distances accurately b how the world’s most accurate clock works c how very small quantities of chemical pollutants are measured d how small signals from space are ‘amplified’ so that they can be measured. 2 Research a vernier caliper to find out what it measures and how its scale works. Include a diagram and description in your response. 3 Some scientific discoveries, such as the discovery of penicillin, are made by accident. a Research the discovery of penicillin and describe who discovered it, when and how; what it is used for and its importance to society. b Imagine that you are the person who discovered penicillin. Write a letter to the Royal Society of Medicine outlining your discovery.

UNIT

1.1 Creative writing The big flash! A massive and blinding white light blasts planet Earth. You get up and go to school the next day, but something odd happens in Science. The pages in your textbook and workbook are all blank. Your Science teacher just mumbles, not knowing what to say. That night there are news reports of scientists going to their laboratories having no idea why they are there. It seems that all the scientific knowledge of the world has been erased and

UNIT

1.1

needs to be learnt again. In a piece of writing explain what troubles humans will get into in the next week without any idea of science, its inventions or how the world works. Write it as either: • an essay • a series of newspaper front pages • a timeline starting from the big flash.

[ Practical activities ]

This micrometer reads 26.32 mm.

A useful tool: the micrometer Prac 1 Unit 1.1

Aim To use a device that can accurately measure the thickness of objects to within a fraction of a millimetre

Fig 1.1.5

40

10

15

20

Equipment

25

35

barrel reads 32

30

Micrometer, various common school items 25 shaft reads between 26 and 27

barrel (usually numbered from 0 to 100). Read the millimetre measurement off the shaft of the micrometer. 3 Along the shaft is a line. Read off the barrel measurement where it meets the barrel (it will be a number between 0 and 100).

Fig 1.1.4

A micrometer

Method 1 To take a measurement, place the object in the opening of the micrometer and screw down the barrel until the knob starts to slip. Do not overtighten; you don’t want to squash the object. 2 There are two measurement scales—one on the shaft (in millimetres just like a ruler) and another on the rotating

4 Use a micrometer to measure the: • thickness of your little finger • thickness of this textbook • thickness of five sheets of paper • diameter of the ball of a ballpoint pen • thickness of a pencil • thickness of a coin.

Questions 1 Compare and contrast the use of a micrometer with the use of a ruler for the measurements in the experiment. 2 Propose a method in which a normal ruler could be used for the measurements in the experiment.

5

>>>

What, why and how?

Prac 2 Unit 1.1

Does nature follow rules?

5 Use the micrometer to measure the thickness of the branch at each marking.

Aim To investigate how a tree grows and see if it

6 Have all partners in your group measure the diameters at each marking too.

follows any rules of nature

1 m ruler/tape measure, micrometer, permanent marker or chalk

7 Cross out any measurements that are very different from the rest, then calculate the average diameter for each marking.

Method

Questions

Equipment

1 Collect a branch or long twig from a tree, preferably an old twig from the ground. The branch needs to be 80 cm to 1 m long and no more than 2 cm thick at its base. It should not be broken off before its small end. 2 Strip the branch of any side twigs and leaves. 3 Make ten regularly spaced markings with the permanent marker or chalk along the length of the branch. The spacing must be the same for each marking, so you should make them 8 to 10 cm apart.

1 Identify which set of measurements, ‘Distance along the branch’ or ‘Diameter of the branch’, is the controlled measurement. 2 Plot the controlled measurements on the horizontal axis on a sheet of graph paper. Markings along each axis should be equal and evenly spaced. Each axis should have a label and correct units. 3 Construct a line graph to show your results.

markings

twig

micrometer

4 Assess whether there is a pattern to nature by examining whether the graph obtained approximates a smooth curve or a straight line. 5 Are there some points on the graph that are out of pattern? If so, examine the twig used in the experiment and propose a reason for them being ‘out’—for example, there may be a split, knot or side branch at that spot.

8 to 10 cm regular spacing

Fig 1.1.6

Checking if there is a growth rule

4 Construct a table or spreadsheet like that shown opposite. You need 11 lines.

6

Distance of marking (cm)

Diameter or thickness (mm)

Average diameter or thickness (mm)

UNIT

context

1. 2 Scientists generally do not perform just one experiment: they usually carry out many experiments, all of them investigating the one topic. These experiments are often done by a team of people all collecting different pieces of information to help solve a puzzle. This is called scientific research. Research can take a long time as experiments do not always

give the desired results the first time. It can take many years just to make a simple discovery. Many discoveries occur by chance, as a scientist notices something unusual and tries to work out what it was. Scientific research requires great patience, persistence and creativity.

The research journey Research normally starts with observations made in everyday life or maybe by accident. An observation is a fact and can be either qualitative (described and written down in words only) or quantitative (measured and stated as numbers). There is no guesswork in observations. You use your fives senses to observe and record observations accurately. You should check your observations a number of times to be sure you have not made Ancient any errors. The recording and observations reporting of your results will In the year 5 BC Chinese astronomers noted that allow other scientists to repeat there was a star burning your research. with unusual brightness Observations lead to for 70 days. What they saw was probably questions about what was the exploding star or observed. supernova Aquilae. Many Look at the following believe that 5 BC was also the year of the birth problem that confronted a of Jesus Christ. Was the Year 8 student during the star that led the three last school holidays. His wise men to Bethlehem observations led to the actually the supernova seen in China? questions ‘what, why and how?’. Carl and his friends went camping for a week over the school holidays. When they collapsed the tent to go home Carl found that the grass under the floor of the tent had gone a yellowwhite colour and was dying. Carl wondered what had caused the apparent death of the grass.

Observation: grass goes yellow-white in colour when it is covered.

Fig 1.2.1

When scientists are confronted with a problem they make logical explanations or inferences about what they observed. Carl and his friends thought about it carefully. They came up with a list of factors that may have affected the grass in the week it was covered by the tent. • • • • •

It was trampled badly in the week. It didn’t like the black colour of the plastic tent floor. It received no water. It didn’t receive any sunlight. It didn’t like the smell of his socks when he took them off at night (all his mates complained about that too!).

7

>>>

Scientific research

tested at a time. Otherwise they would not be able to work out which variable caused the effect. The variable that is changed in an experiment is also known as the independent variable. Scientists ask four questions when they are planning an experiment. • What is being tested? (the aim) • What is being changed? (the independent variable) • What is going to be kept the same? (the controlled variables) • What is going to be measured or recorded? (the dependent variable) The results obtained depend upon what Prac 2 p. 11 we change. Therefore what we measure or record is called the dependent variable. Factors that might have affected the grass

Fig 1.2.2

Scientists also try to fit the new observation with what they know already about similar situations. Carl knew from his science classes that plants need sunlight and carbon dioxide gas from the air to make energy and stay alive. A lack of carbon dioxide was another possible factor.

These factors are known as variables. Some of Carl’s variables were downright silly. After thinking more scientifically about it, Carl decided that the most important factors were the lack of sunlight and water. But which one of these was more important?

Prac 1 p. 10

Scientists then make a hypothesis, a prediction or ‘educated guess’ about what they might find in an experiment or what might have caused the observations. A hypothesis is something that can be tested by an experiment. Carl thought that the lack of sunlight was probably the most likely reason the grass was dying. This was his hypothesis.

Scientists then develop questions regarding the problem. These questions can become the aim for experiments. Carl planned two experiments. In the first he tried to find out if a lack of water would cause the grass to die in a week. In the second he asked, ‘Does a lack of sunlight kill grass in one week?’.

These were the aims of his experiments. Good scientists run fair tests. They carefully plan their experiments so that only one variable will be

8

Carl grew four identical patches of grass. The same type and amount of grass was in each patch—the controlled variables. In each experiment he was careful to change only one variable at a time, keeping everything else the same. •

Experiment 1: Carl watered two pieces the same. One patch was left in the sun (this one is called the ‘control’) and the other was covered by black plastic. • Experiment 2: The other two patches were placed side by side in the sun. One was watered regularly (the control) while the other was kept dry. Carl found that a lack of water made the grass go brown, not yellow. The lack of sunlight caused the grass to first go yellow, with some blades then turning white. These were his observations.

From observations and measurements, a conclusion can be made that should prove the hypothesis to be right or wrong. Carl’s conclusion was that the grass died because of a lack of sunlight. His hypothesis seemed to be correct.

Did scientists create AIDS? A virus called SIV has always infected the monkeys of Africa, but they never became ill from it. Most scientists believe SIV sprang from monkey to human from a scratch or from eating infected monkey meat. The SIV then mutated to become HIV, the virus that causes AIDS. Some think, however, that infected monkey kidneys were used in the development of a polio vaccine called CHAT. Polio was devastating the world in the 1950s and the experimental CHAT vaccine was given to thousands of people in Africa between 1957 and 1960. The first outbreaks of AIDS were in the same region that the vaccine was given, the first death being in 1959. Did the CHAT vaccine cause the AIDS outbreak? Did scientists take enough care in their research? As scientists we have a responsibility to take extreme care in everything we do.

UNIT

1.2

Controlling variables in an experiment

Fig 1.2.3

Worksheet 1.1 Carl’s new experiments

UNIT

1.2

[ Questions ]

Checkpoint

Think

1 Define the following terms: a observations d hypothesis b qualitative e variable c inference f controlled variable.

5 You arrive home after a large storm and notice that the television set isn’t working. There is a puddle of water on top of it and another underneath it. a Summarise your observations. b Describe inferences you can make from the observations. c Predict what may happen to the television set and the house.

2 State whether the following statements are true or false. a Research is a number of experiments run on the same topic. b Observations involve guesswork. c A hypothesis can be tested with an experiment. d A variable is the same as an inference. e ‘The grass is yellow’ is a qualitative observation. f ‘The grass grew 5 mm in a day’ is a qualitative observation. g Controlled variables are variables that are not changed in an experiment.

6 Fi and Cathy were in an egg-and-spoon race (see Figure 1.2.4). a Identify the variables in the race. Fig 1.2.4

3 List the three questions regarding well-designed experiments that need to be addressed. 4 Explain why only one variable should be tested at a time.

>> 9

>>>

Scientific research

b Assess whether it was a fair race. c Describe ways of making it a fair race.

Create

Analyse 7 Referring to Carl’s experiments on factors that affect the growth of grass: a identify the two variables tested by Carl b list other variables that could affect the growth of the grass under the tent c outline previous knowledge used by Carl. 8 Referring to Carl’s research: a propose a heading for the research project b construct an introductory sentence explaining why the research was being performed c propose aims for the research and the two experiments d draw conclusions from the two experiments and from the research project.

Investigate 9 Carl wondered whether the grass under the tent would die or whether it would recover. Design a controlled experiment to test a hypothesis he could make about this extra question.

UNIT

1.2

10 ‘I’m red with a cream-coloured interior. I grow on a tree and can be eaten. What am I?’ Select an item from the categories listed below, describe it and have a partner deduce what it is. a a food b a tool of some sort c a piece of furniture

d an animal or insect e a sport.

[ Extension ] Investigate Choose one of the occupations listed below. Research what areas of science a person would need to know to work effectively and safely in that occupation. Present your findings as a pamphlet to be displayed in the careers information centre in your school.

DYO

• • • • • •

Architect Laser eye surgeon Chemist Optometrist Firefighter Car mechanic

[ Practical activities ]

• • • • • •

Which variable caused more water to rise?

Fig 1.2.5

Happy birthday to you! pan

Aim To observe and interpret what happens when a candle is burnt in a sealed space

matches D RE S

Equipment

AD

HE

Prac 1 Unit 1.2

glass

6–8 birthday candles and matches, plasticine or Blu-tack, 2 elastic bands, a shallow pan, 1 gas jar or tall narrow drinking glass

candles

plasticine elastic band

Method 1 Construct a two-column results table or spreadsheet with the headings ‘Number of candles’ and ‘Rise in height (mm)’. 2 Make a small mound of plasticine or Blu-tack in the centre of the pan and then fill the pan with water. 3 Stick one candle in the plasticine. Place the gas jar or glass over the candle. 4 Place one elastic band around the glass at the level of the water.

10

Aircraft refueller Structural engineer Nurse Racing car driver Pilot Physiotherapist

elastic bands

water

5 Remove the jar, light the candle and quickly place the jar over the candle. 6 Allow the candle to burn until it goes out. Wait a short while and observe what happens to the water level. 7 Place the other elastic band over the glass at the new water level. 8 Measure the change in water level and record the measurements in the table. 9 Repeat the experiment with two, then three, five and seven candles. 10 Plot a line graph showing what happened to the height the water rose as more candles were added. 11 Use the graph to predict the water rise for four, six and eight candles. 12 Run the experiment again for four, six and eight candles to check your predictions.

UNIT

1.2 Questions 1 From the list below, identify the variable which probably had the most effect on the change in water level: the volume or depth of water in the tray, the height and diameter of the gas jar, the number or colour of the candles, the amount of plasticine or Blu-tack.

Flameout! When candles burn, wax melts and some of it vaporises into a gas. The flame you see is actually burning wax vapour. If you blow the candle out, a trail of smoke will rise from the wick. This too is wax vapour but it is unburnt. Can you relight a candle by setting fire to its smoke? Try lighting a candle, then blowing it out. Slowly lower a lit match down the smoke trail. The flame will jump down the smoke to relight the candle. Test how far it can jump.

2 Identify the chosen variable and the controlled variable in this experiment. 3 Propose reasons for the rise in water level in the jar. 4 Identify any trend evident from the graph which shows a relationship between the variables you plotted.

Why do cooks add salt to water? Prac 2 Unit 1.2

Aim To investigate why cooks usually add salt to water when cooking vegetables, pasta or rice thermometer

Equipment 3 x 100 mL beakers, 100 mL measuring cylinder, Bunsen burner, bench mat, retort stand, bossheads and clamps, gauze mat, thermometer, timer, table salt, beam balance or electronic scale

Method 1 Set up the Bunsen burner with a beaker containing 60 mL of water.

no salt then 2 g salt then 4 g salt

100 mL beaker

60 mL water

retort stand

2 Heat the water and record the temperature every 30 seconds until the water boils. 3 Add 2 g of salt to another 60 mL of water and repeat the experiment with the same Bunsen flame. 4 Repeat with 4 g of salt. 5 Record your results in a table or spreadsheet like this: Time (s)

Temperature (°C) No salt

2 g salt

4 g salt

0 30 60

Questions 1 Were the observations made qualitative or quantitative? Justify your answer.

Why do cooks add salt?

Fig 1.2.6

2 Based on your observations, deduce why cooks add salt to water. 3 Extension: Construct a line graph for the temperatures recorded without any salt. On the same graph plot heating curves for the beaker with 2 g and 4 g of salt added.

11

Science focus: Scientific method: the path to greater understanding Prescribed focus area: The nature and practice of science Why use the scientific method?

The first and most important step

Humans have always asked questions and sought to understand the observations they make. This desire to understand the world around them led the Ancient Greeks to develop the term scientia (to know) and to make the first steps towards a study of what we now call science. Initially people gained an understanding by simply thinking about a problem and coming up with an explanation! Over time, however, they began to want deeper understandings and began to conduct experiments. Through the work of Galileo and Newton, the scientific method was formalised and became the accepted technique for testing and proving ideas in science. Experiments became so important because they provided evidence to support the answers to questions.

Designing the right experiment that will be a valid test of the hypothesis is a very important skill for a scientist. The experiment can be considered the most important component of the scientific method because a well-designed experiment produces and confirms results and knowledge that scientists can trust to be accurate. It provides supportive evidence. If the experiment produces results that disagree with the hypothesis, this results in a downward path and the scientist must develop a new hypothesis. If the experiments produce results that agree with the hypothesis, further experiments are conducted to continue to test whether the hypothesis is true.

Climbing the mountain towards true understanding Figure SF 1.1 indicates how the scientific method has steadily led to humans gaining an increased understanding. The quest for knowledge can be viewed as similar to climbing a mountain.

Starting the climb As shown in the diagram, at the beginning of the path up the mountain the scientist asks questions in an attempt to explain observations or problems. The scientist comes up with an idea as a possible answer to the question, usually supported by observations and current knowledge. This idea becomes known as a hypothesis. Experiments must then be designed to allow the hypothesis to be tested.

12

Going up! If, after many experiments have been conducted and all have shown the hypothesis to be correct, the scientist climbs further up the mountain, and the idea becomes a theory. A theory is an explanation of an idea that is supported by a large amount of evidence and testing. A theory can lead to the development of a model. Models provide scientists and others with a clearer way to describe or explain their understanding. A model might not match exactly what is really going on, but it can be used to help us understand and predict what will happen in other situations, just like a model of a planned aircraft helps engineers better understand the real thing. As models develop and research continues, the new scientific understandings lead to another path resulting in technology that usually improves our lives.

New level of understanding Greater knowledge

Design and engineering

Law

Technology released to benefit humans

Model or theory found to apply and hold true in many areas of scientific study

Applications to serve humans

RESEARCH including mathematical predictions from theory or model

Model Theory Confirmation by many experiments

Hypothesis supported by experiments

New or contradictory predictions

New or unexpected observations Modified or new hypothesis

Experiment

Design experimental test for hypothesis or prediction

Hypothesis not supported by experiments New hypothesis

Problem, question, observation

Idea hypothesis

A mountain of research: the scientific method

Fig SF 1.1

13

Sometimes scientists develop a theory that is found to apply in many areas of scientific research, and is always proven true in every experiment. These very significant and important pieces of knowledge and understanding become known as laws and provide a solid base for scientists doing their work.

Slipping down … Sometimes, just when scientists think that they have a full understanding of an idea, the experiments—or sometimes mathematical predictions—show that the theory is not really the whole story, or in some cases, is completely wrong. This leads to a very steep slide back down the mountain to the development of a new hypothesis. This new hypothesis must then go through scientific method again before it is accepted as a replacement for old theories.

Onward and upward The scientific method has its ups and downs, but has been a powerful tool in increasing our understanding of the world around us. The strength of this method is based on the evidence gained from experiments. The scientific method has allowed us to gain a greater understanding, which has led to developments that have improved our quality of life. With continued research and experiment the quest to reach the top of the mountain continues.

A scientist in the lab

14

Fig SF 1.2

[ Student activities ] 1 a Investigate further the meanings of the following terms: hypothesis, experiment, theory, law, model. b Construct a table to summarise your findings, including a definition and example of each term. 2 When discussing the scientific method, many scientists claim ‘There is no such thing as a scientific fact!’. a Justify this statement by writing a paragraph to clarify your ideas. b Organise a class debate about this topic. 3 The Gravitation Theory developed by Isaac Newton in the 17th century is still discussed in science classrooms. Yet, for scientists working in modern research, Newton’s theory has been replaced. a Based on your understanding of scientific method, propose possible reasons why Newton’s Gravitation Theory: i is no longer used by scientists doing research into gravity ii is still taught in Science classes in schools. b List the possible reasons you have proposed and share your findings with the other groups. c Write a paragraph to present your own view and explain why you have made your choice. 4 a Investigate at least three scientific laws. b State the law in the scientific language used in your source (be sure to include your reference). c In your own words construct a simple description to allow you to clearly explain each law to your classmates. d Choose one of the laws you have found and construct a model to help you explain the law to others.

UNIT

context

1. 3 Accurate measurements are often impossible to make. Estimates are often the best we can do. If you wanted to know the amount of water in Sydney Harbour you would need to estimate it since there is no accurate way

Mistakes and errors Mistakes are things that could have been avoided if you took a little more care. They can include: • careless reading of a measurement • incorrect recording of a measurement • spillage of material • use of the wrong piece of equipment. Errors are things that are unavoidable. They are usually small and are not your fault. Errors will always happen and it doesn’t matter how careful you are. Nothing is exact. Even ‘accurate’ measurements are in fact estimates, all because of errors. Common errors are: • parallax error Your eye can never be exactly over the marking of a measuring device. Everyone looks at markings at slightly different angles so everyone will take slightly different readings.

Fig 1.3.1

Reduce parallax errors by keeping your eye in line with the measurement.

READING TOOHIGH ALWAYS MEASURE THELEVELAT THEBOTTOM OFTHECURVE MENISCUS

CORRECT READING M,



READING TOOLOW

of measuring it. The number of people in a shopping mall would constantly change as people left and new people arrived. An exact count would be near impossible.

• reading errors Measurements often fall between the markings of a measuring device. Some estimation is required for you to take your measurement.

0 cm 1

2

3

4

Not quite 6 cm long, but is it 5.7, 5.8 or 5.9 cm?

• instrument errors Sometimes the instrument you are using is faulty and will never give the correct reading. Some instruments give correct readings only at certain temperatures and will give small errors if used at any other temperature. A metal ruler expands when hot, causing the markings to move further apart. This makes measurements taken on a hot day slightly smaller than those made on a cold day. • human reaction time A stopwatch normally reads to one-hundredth of a second

5

6

7

Fig 1.3.2

100 milliseconds away from death Detailed studies by Saab have shown that a head-on collision of a car with a solid wall takes less than 100 milliseconds, or 0.1 s. How does this compare with your reaction time? If less, then the car accident is over before you can react to it! There is no chance of ‘getting ready’ or bracing to avoid injury—a good case for wearing seatbelts.

15

>>>

Better measurements

0 cm 1

2

3

4

5

6

7

metal rulers contract on cold days

0 cm

1

2

3

4

5

6

7

metal rulers expand when hot

Fig 1.3.3

Same match, different days, different measurements

(0.01 s). Humans are not as accurate as this: we simply can’t react quickly enough. Measurements of time will vary among people because we all have different reaction times. Data loggers have faster reaction time than humans and are more accurate, but there Prac 1 p. 19 are still errors involved.

Repeated measurements Because errors always exist, people can measure the same thing differently. So who has taken the ‘correct’ measurement? They all have! Unless someone made a silly mistake there is no wrong answer. Repeating measurements is a good way to improving accuracy. Once a collection of different measurements is taken, an average or mean can be obtained. To find an average: 1 add all the measurements together to get a total 2 divide this total by the number of measurements taken. Various members of a group measured the length of a mouse’s tail and each got different results: • Anna 8.1 cm • Lee 8.4 cm • Millai 8.5 cm • Nicole 8.2 cm • Steve 12.9 cm. Steve’s result is too far away from the rest of the results. It looks like he made a mistake so his result should be ignored.

16

Everyone will get slightly different measurements.

Fig 1.3.4

To obtain the most accurate measurement it is best to average the other four results; that is, add the four results: 8.1 + 8.4 + 8.2 + 8.5 = 33.2 and divide the total by the number of readings: 33.2 ÷ 4 = 8.3 cm Notice that no one in the group actually took a measurement that was the same as the average.

Prac 2 p. 20

A little give and take It is often useful to write measurements with an estimation of how big the error might be. We allow a little ‘give and take’ by showing the error as ± (standing for ‘plus or minus’). The exact measurement shown in Figure 1.3.5 needs a little guesswork. Although it looks as if it should be about 27°C it could be a little higher or lower, perhaps as much as 1°C. The measurement could

27 ± 1°C

35 30 25  15 10 5 0 ºC

Fig 1.3.5

be written as 27°C ‘give or take’ 1°C. Scientists write this as 27 ± 1°C. The mouse-tail measured earlier averaged 8.3 centimetres even though no one actually measured it as that. The mouse-tail could be said to be between 8.1 and 8.5 centimetres. This could be written as 8.3 centimetres ‘give Prac 3 p. 20 or take’ 0.2 centimetres, or 8.3 ± 0.2 cm.

1

Compare an error with a mistake.

2

Explain why it is difficult to avoid errors.

3

Outline four different types of errors.

4

Why do scientists use different procedures to avoid or minimise errors? Justify your answer.

Skills

1.3 UNIT

6 From the following, identify the measurements that could be taken accurately: a the number of kangaroos in Australia b the number of kangaroos in the zoo c the length of the science laboratory at school d the number of cloudy days in the next month e the number of students who buy chips at the school canteen. 7 Classify the following as either mistakes or errors. a Mia poured water from a measuring cylinder but could not get every drop out. b Kim spilt some of the chemicals he was to use in an experiment. c Johnno didn’t bother cleaning the dirt off the beam balance he used. d Sara found it difficult to decide on measurements that fell between the markings on a tape measure. e Micha’s electronic scale was reading 0.1 g when empty and he didn’t ‘zero’ it.

Worksheet 1.2 Extreme units

[ Questions ]

Checkpoint

Think 5 State whether the following statements are true or false. a All measurements are exact. b An average can also be called the mode. c A mistake is an error. d A measurement of 56 ± 2°C actually goes from 58°C to 56°C. e Human reactions are always fast and accurate.

UNIT

1.3

8 Calculate the average of these values to obtain the most accurate measurement. a 39 mm, 38 mm, 40 mm, 41 mm, 40 mm b 25.3°C, 26.8°C, 27.5°C c 45 mL, 47 mL, 46 mL, 58 mL (be careful here!) 9 For each example in Figure 1.3.6, describe the type of error made.

Fig 1.3.6

>> 17

>>>

Better measurements

Fig 1.3.8

10 a Define ‘±’. b Record the following measurements with a ± error.

17 0

18 0

190

20 0

a

16 0

4 3

15 0

2

12

0

13

0

14

0

1

90

10

0

11

0

b

70

80

c

160

60

180

mm 10

20

30

40

50

60

100 120 140 80

40

200 220

20 0

km/h

240

Fig 1.3.7

[ Extension ] Investigate 1 Conduct research to find the ‘correct operating temperatures’ for the following apparatus: a 250 mL beaker b 100 mL measuring cylinder c school electronic balance. 2 Police often give accurate estimates of crowd numbers at sporting events. a Explain how you could determine the number of people in the photo in Figure 1.3.8 without counting each person. b Use your method to estimate the number of people in Figure 1.3.8.

18

3 Use your method to estimate numbers in the following examples: a the number of grains of sand that would fit in a shoebox filled with sand b the number of leaves on a tree c the number of words and individual letters printed in this chapter. 4 Use the diagram in Figure 1.3.9 to explain the difference between accuracy and precision. 5 a Research and summarise what is meant by the ‘frequency’ of a pendulum. b Propose a way of measuring the frequency of a pendulum. c Design an experiment to investigate your method of measurement. DYO

Action 6 Examine each of the following instruments to find the smallest markings or divisions on them: a digital stopwatch b normal ruler c tape measure d thermometer e kitchen scale.

UNIT

1.3 Fig 1.3.9 good accuracy poor precision

good precision poor accuracy

good accuracy good precision bad news

UNIT

1.3

[ Practical activities ]

Measuring reaction time

Fig 1.3.10

How quickly can you react? Prac 1 Unit 1.3

Aim To find your reaction time

ruler

Equipment Ruler (for most people a 30 cm ruler will do), access to a calculator

Method 1 Hold a metre ruler vertically, with the zero level with the top of your partner’s hand.

have your fingers level with zero

2 Without warning, let go of the ruler. Your partner must catch it as quickly as possible. 3 Note the reading of the ruler (in centimetres) level with the top of your partner’s open hand.

the ruler has dropped 22 cm

4 Have two trial runs and then record the next three runs. Experiment

Distance ruler dropped (cm)

Average ruler drop (cm)

Average reaction time (s)

No distractions No warnings With countdown With distractions

>> 19

Better measurements

5 Calculate the reaction time by dividing the average ruler drop by 490. Now ‘square root’ ( ) your answer. The final answer is the time in seconds that your partner took to react. 6 Repeat the experiment, but this time count down (5–4–3–2–1) before dropping the ruler. 7 Try again, but this time get another student to distract your partner, by talking to them, tickling them, etc.

>>> Questions 1 Identify the degree of accuracy of a normal stopwatch. 2 Contrast the reaction time with the accuracy of a stopwatch. 3 Identify factors that affected the reaction time in this experiment. 4 Outline factors that affect your reaction time in everyday life.

Repeated measurements Aim To examine why taking a number of Prac 2 Unit 1.3

measurements is important

Equipment Measuring tape, thermometer, stopwatch

Method 1 Measure each of the following as carefully as you can. Have each member of your group do the same: • the length of the laboratory • the temperature of tap water • the number of heartbeats in a minute. • the time it takes for a pen to drop 2 m to the floor.

• the time it takes for a flat piece of A4 paper to flutter from a height of 2 m to the floor. 2 Calculate the average for each measurement. 3 Record this average with a ± error.

Chaos at play! Have you ever noticed that professional tennis players are always ‘on their toes’ when they are about to receive a serve? The unstable nature of their footing seem s to quicken their response, making them more likely to return the ball. Accurate measurements of heartbeats show that they are roughly the same, but are all slightly different. The slightly unstable beat helps keep our heart ‘on its toes’. It can then respond to any sudden need for increased blood supply when we exercise. This is the scientific theory called chaos at work.

Introduction to the pendulum Prac 3 Unit 1.3

A pendulum is a mass (called a bob) attached to a rod, chain or rope, which swings back and forth repeatedly.

The period of a pendulum is the time it takes to complete one entire swing, back and forth. A grandfather clock has a pendulum that keeps the clock on time. Many machines have ‘arms’ and parts that also act like pendulums. Their timing is important and scientists must know what affects the period so that these machines and devices stay accurate. Important variables that could logically affect the period are: • the length of the string • the mass of the bob (sometimes incorrectly called its weight) • the angle of the bob from vertical at the start. In this experiment you will see if the mass has any effect on period.

20

Fig 1.3.11

Pendulums are everywhere!

Aim To investigate the effect of changing the mass of the

UNIT

1.3 6 Plot a graph of period versus mass, with mass on the horizontal axis.

bob on a pendulum

Equipment

Use these axis markings

Fig 1.3.13

Materials to construct a pendulum, stopwatch or appropriate data-logging equipment, clock or watch, protractor (optional)

string

Period (s)

boss head and clamp

retort stand

0

Mass (g)

bob

7 Draw a line or curve of best fit for the points.

1 period

Questions 1 Describe variables that you controlled in this experiment. 2 Identify the dependent and independent variables. Fig 1.3.12

Is the mass an important variable?

3 Describe how you made sure the angle was always the same. 4 Explain why ten periods were measured rather than just one.

Method 1 Before you start you need to decide: • what masses should be used (50 g masses, paper clips, metal washers?) • what length your pendulum is to be • what angle your pendulum needs to be swung from each time and a method of making sure it is always the same.

5 Identify other variables that could affect the period. (Think about the bob and the string itself.) A practical pendulum

Fig 1.3.14

2 Construct a results table or spreadsheet like the following: Mass

Time for 10 swings (s)

Average time for 10 swings (s)

Period (s)

Mass 1 Mass 2 …

3 Tie one mass on the end of the pendulum, measure the length of the pendulum and hold the mass out to the angle you have decided on. 4 Let go and time ten complete swings. 5 Put your results in the table, add another mass and repeat. Keep adding until you have tested five different masses.

21

UNIT

>>>

context

1. 4 Scientists follow conventions or ‘rules’ when they present their data, graphs and reports. This is so that other scientists know exactly what was observed, and how the information was interpreted. It also allows them to repeat the experiment if necessary. As a scientist you should follow these conventions too.

Organising results ‘Data’ is the word used for a lot of measurements or observations. Data is usually placed in a table (tabulated), sometimes as a computer spreadsheet or database. This makes any patterns that may exist more obvious. Headings and units should be at the top of each column.

Drawing line graphs

What do you write in a report? When you write a report you need to include the following: • a heading, the date of the experimental work and a list of partners who assisted you • your aim—statement of what you intended to do or find out • a hypothesis (optional)—prediction or ‘educated guess’ about what you thought might be found out • a list of equipment or materials used • your method—explanation of what was done in the experiment, including the quantities used. A diagram can be useful here too • your results and observations—complete list of measurements and observations that were taken, preferably displayed in a table • a discussion or analysis, in which you discuss what you think your results show. This also includes what you have found about the experiment from secondary sources. It could include graphs, ideas for further experiments, a description of problems encountered and what was done to overcome them • a conclusion—summary of what was found out in the experiment. It must be short and must relate to the aim. A report sometimes ends with a list of all resources used in gathering information about the experiment. This is called a bibliography.

22

Patterns become even more obvious when data is plotted as a line graph. Line graphs can be used to predict patterns and measurements that were never actually taken in the experiment. Pie charts, bar graphs and histograms are useful but cannot be used to predict missing measurements. When drawing a line graph you must always include: • a heading, explaining what the graph is about • ruled vertical and horizontal axes • labels and units on the axes • regular markings for the scale along the axes • all your points clearly marked on the graph itself. The independent variable is placed on the the horizontal axis. The independent variable is the variable you have chosen to change in your experiment. You decide how large it should be and how much it should change by. The number of days after birth is the independent variable in Figure 1.4.1. The dependent variable is placed on the vertical axis. This is the variable that depends upon the independent variable and Prac 1 is measured throughout the experiment. p. 26 In Figure 1.4.1, the length of the mouse is the dependent variable. All experiments include errors, and connecting up the points in a dot-to-dot manner suggests that there is no error. It is more sensible to draw a straight line or smooth curve approximately through the ‘centre’ of

Fig 1.4.1

A line of best fit is not dot-to-dot

70 Length of baby mouse as it grows

Length of mouse (mm)

65 dependent variable— 60 changes 55 naturally 50 45

line of best fit

40 35 30 25

UNIT

1. 4 your points: this is called the line of best fit or curve of best fit. Patterns and results can then be predicted. You can predict extra results by continuing the shape of the line or curve. This is called extrapolation. In Figure 1.4.2 the curve has been extrapolated to allow us to predict that the temperature Prac 2 Prac 3 p. 26 p. 27 after 15 minutes would be 22°C.

Describing patterns Graphs of straight lines or smooth curves indicate that there is a pattern, rule or relationship between the variables that you tested. Some ways of describing these rules are shown in Figure 1.4.3.

20

Graphs showing common relationships

15

Fig 1.4.3

10

y

5 0

0

1

2

3

4

5 6 Days after birth

y

y

7 8 9 10 independent variable— you choose how big

x

100 The cooling curve of water 90

Could be described as a linear relationship (y doubles if x doubles).

x As x gets bigger y gets much bigger (y more than doubles if x doubles).

x As x gets bigger, y gets bigger but then levels out.

80

Worksheet 1.3 Graphing skills

Temperature (ºC)

70

Using and converting metric units

60

curve of best fit

50 extrapolation (logical extension of graph)

40 30 20 10 0

0

1

Fig 1.4.2

2

3

4

5

6 7 8 9 10 11 12 13 14 15 Time (minutes)

Line graphs can be used to predict missing values. For example, the temperature was 32°C at 8 minutes, and took 41/2 minutes to reach 48°C. What do you predict the temperature to be at 15 minutes?

Scientific measurements are based on the metric system. Length is measured in metres (m), mass in grams (g) and volume in litres (L). Other units, such as newtons (N) for weight and force, and joules (J) for energy, depend on these units. Sometimes measurements are too big or too small to be sensibly measured with these units. Other units have been developed from them using a series of prefixes. The prefixes you have probably already met are centi, milli and kilo in units such as centimetre or cm (100 are required to make up a metre),

The size of a smell A smell might be invisible but is actually particles of the material that made the smell, dissolving in the thin layer of mucus in the nose. A frightening thought considering what we smell each day! A typical smell has a mass of only 760 ng or 760 billionths 1 of a gram. This is about /5 the t (the insec est mass of the small parasite wasp) but 10 000 times heavier than the lightest virus. This means that we cannot possibly smell a virus like the common cold.

23

>>>

Scientific conventions Prefix symbol

Name of prefix

Size

Decimal notation

Example

G

Giga

one billion

1 000 000 000

GL

M

Mega

one million

1 000 000

ML

d

deci

one-tenth

1/10 = 0.1

dL

µ

micro

one-millionth

1/1 000 000 = 0.000 001

µm

n

nano

one-billionth

1/1 000 000 000 = 0.000 000 001

nm

millilitre or mL (one thousand make up one litre) and kilogram or kg (equal to a thousand grams). You have probably never heard of the other prefixes, although all of them are used for very small or very large Prac 4 p. 27 quantities. Worksheet 1.4 Body mass index

UNIT

1. 4

[ Questions ]

10 Metric prefixes are not usually used for time. State the following ‘metric time units’ in seconds (s): a 1 kilosecond or 1 ks b 1 centiminute or 1 cmin c 1 kiloday or 1 kd d 1 megasecond or 1 Ms.

Analyse 11 Sam measured the times it took for a feather and a stone to fall from different heights so that she could compare them. She obtained the graph shown in Figure 1.4.4.

Checkpoint Sam’s graph

1 Define the following terms: a convention d relationship b hypothesis e bibliography. c line of best fit

Fig 1.4.4

2.6 Drop times 2.4

2 Describe the type of information found in the discussion section of an experiment.

2.2

3 List all the details that must be included on a graph. 2.0

4 Propose the correct axis for the independent variable on a graph.

1.8

5 Explain the usefulness of the metric system in science.

7 Propose two places where diagrams would be useful in an experimental report. 8 Explain why scientists use line graphs more often than pie charts and bar graphs.

24

1.6 Time to drop (s)

6 Describe how a line of best fit is obtained when drawing a graph.

feather

1.4 1.2 1.0 0.8

Think

0.6

9 Modify the following values to make the conversions shown: a 5 ML into litres b 375 mL into litres c 500 000 mm into metres d 6 000 000 000 nm into metres.

0.4

stone

0.2 0

0

1

2

3

4

Height of drop (m)

5

d Extrapolate the height that the feather and the stone were dropped from, given the following times. i 0.5 s ii 1.2 s iii 1.9 s. e Extrapolate the graph to find the values of the following measurements: i time taken to drop the feather 5 m ii time taken to drop the stone 5 m iii the position of the feather after 2.5 s. f Draw conclusions from the experiment.

Skills

Fig 1.4.6

100 90 80 70 60 50 21.3 15.5 9.1 7.8 3.2 0

12 a Examine Figure 1.4.5 and assess whether all the data for the points plotted is reliable. b Copy the graph onto graph paper and construct a line of best fit. c Propose a title for the graph.

1

2

3

4

5 6 7 Seconds

8

9 10

[ Extension ] 1 Research and present information about the following features of the metric system. Include a bibliography in the information presented. a Outline where, when and why the metric system was developed. b Describe how the length of a metre was originally determined. c Use an example to explain what a measurement ‘standard’ is.

50 40 30 20 10 0

0

Investigate

60

Mass (kg)

c Construct a correct version of the graph.

Temperature

a Propose an aim for Sam’s experiment. b Construct a table of results for the experiment. c Use the graph to identify the drop time for the feather and stone from these heights: i 1.5 m ii 2.5 m iii 3500 mm.

UNIT

1. 4

0

1

2

3

4 5 6 7 Time (min)

8

9 10

Fig 1.4.5 13 a Identify five mistakes in the plotting of the graph in Figure 1.4.6. b Decide whether the independent variable is plotted on the correct axis. Justify your answer.

2 Carry out research to identify the metric units used for the following measurements: a air pressure b force c energy d electrical current e electrical voltage. 3 Describe where the following units are used: a megatonne (Mt) b decibel (dB) c gigabyte (Gb).

25

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Scientific conventions

[ Practical activities ] How does length affect a pendulum?

Prac 1 Unit 1.4

Aim To investigate if the length of a pendulum affects its period

8 Make another column in your table. Use a calculator to take the square root ( ) of the lengths you used and enter these into the new column.

Equipment Materials to construct a pendulum, stopwatch or appropriate data-logging equipment, clock or watch, protractor (optional)

Method 1 You need to keep constant the mass and the angle from which the pendulum is swung. Decide what values you will use.

9 Plot a new graph of period versus square root length.

2 Decide on the lengths that you will test. At least five different lengths should be tested. 3 You need to repeat measurements for the time taken for ten complete swings. Decide how many times you will repeat each experiment. 4 Construct a table or spreadsheet for the measurements you take. 5 Perform the experiment, recording the time taken. 6 Calculate the average time for ten swings and for one swing (the period). 7 Plot a graph of period versus length.

Length

Fig 1.4.7

Plotting period against square root length

Questions 1

Discuss any precautions taken in the experiment to reduce errors.

2

Identify the controlled variables.

3

Identify the independent and dependent variables.

4

Use the shape of the curve obtained in the graph to outline any relationship evident between the dependent and independent variables.

5

Draw conclusions from the data obtained.

Extension One aim of a scientist when analysing results is to try and get a straight line when plotting graphs. If you didn’t get a straight line then try this.

Period (s)

UNIT

1. 4

Does the angle matter? Prac 2 Unit 1.4

Aim To investigate the effect of angle on the period of a pendulum Equipment

Materials to construct a pendulum, stopwatch or appropriate data-logging equipment, protractor

Method 1 Bigger angles could mean longer periods, shorter periods or no change in period. Construct your hypothesis about the effect of angle on period. 2 Design an experiment to test your hypothesis. 3 Construct a graph showing the relationship between period and angle of pendulum swing.

26

Questions 1 Outline how you controlled variables that you did not want to test. 2 Does the shape of the graph support your hypothesis? Justify your answer. 3 Propose further questions that arise from this experiment.

Foucault’s pendulum A pendulum looks as if it never changes direction. This is because most pendulums are short and all pendulums eventually stop due to air resistance. As a pendulum moves back and forth, the Earth is slowly spinning underneath. If the pendulum kept going we would see it slowly change direction. After 24 hours it would return to its original orientation. A pendulum that does this is called Foucault’s pendulum.

Other pendulums to try

Complex pendulums

UNIT

1. 4 Fig 1.4.8

Aim To investigate different pendulums Prac 3 Unit 1.4

Equipment bridge pendulum

Materials to construct a pendulum, stopwatch

Method 1 Construct one of the pendulums shown. DYO

2 Identify two variables that you think could affect the period. 3 Design two experiments that test those variables.

chain pendulum

double pendulum

4 Report on your findings, including a graph for each experiment.

Drop time Prac 4 Unit 1.4

Aim To investigate the variables in the drop time of a parachute. Equipment

Lightweight materials (such as tissue paper, plastic sheet (garbage bags), newspaper), fine cotton, hole punch, sticky tape, small masses (plasticine or paper clips are ideal), electronic balance, stopwatch

3 Describe the shape of all graphs you plotted. 4 From the shape of the graphs describe any patterns in the relationships between variables.

Method

5 Use the information obtained from graphs to draw conclusions for both experiments.

1 Brainstorm a list of variables that could affect the drop time of a parachute. 2 Select the two variables that your group thinks will have the most effect. 3 Design two experiments that will test your two variables. Remember to keep everything else the same.

light materials, eg paper, plastic chute sticky tape reinforcing

4 When constructing your chutes, reinforce the string holes with patches of sticky tape. 5 Drop your chutes from a height of at least 2 m. 6 Make repeated measurements of the time the chutes take to hit the ground, recording the measurements in a table or spreadsheet. 7 Write a report of your research, including a line graph for each experiment.

stopwatch

2m or more

Questions mass

1 Identify the variables that may be important in this experiment. 2 Explain why you chose the variables you tested and not others. Fig 1.4.9

Testing parachutes

27

>>> Chapter review [ Summary questions ] 1 Contrast the work of scientists with that of other workers. 2 Identify two examples of each of the following types of observations: e made with the sense a qualitative of hearing only b quantitative f made with the sense c visual of taste or smell only. d made with the sense of touch only 3 Contrast each of the following terms: a an experiment and research b a qualitative and a quantitative observation c an aim and a hypothesis d an error and a mistake.

Australia we eat 13 500 kJ. Many claim that Australians eat more than the recommended allowance. Justify this statement. 14 Recommend appropriate metric units for the following measurements: a the length of a sugar ant b the amount of water in Botany Bay c the distance from here to the next galaxy. 15 Design a controlled experiment that would test the hypothesis that adding salt to water causes an increase in the boiling point of water.

[ Interpreting questions ] Fig 1.5.1

4 Draw diagrams to explain the following types of errors: a parallax errors b reading errors. 5 Use an example to contrast a dependent with an independent variable.

7 In order, list the features normally included in an experimental report.

[ Thinking questions ] 8 Sarah wrote the length of an insect as 2.1 ± 0.1 cm. State the biggest and the smallest length of the insect. 9 Record the following measurements correctly showing the errors. a The time a stone took to drop to the ground was measured by Kim as 2.5 seconds, give or take half a second. b Jess measured the temperature that salt water boiled at as somewhere between 102°C and 108°C. 10 Calculate the average value for the following measurements. a 87 mL, 90 mL, 86 mL and 93 mL b 115 g, 123 g and 125 g. 11 Propose a reason for all scientists using the same units for their measurements. 12 One of the most powerful cars built in Australia was the 285 kW HSV Clubsports R8. Calculate the car’s power in watts. 13 The World Health Organization recommends that people should eat 10.9 MJ of food each day. On average in

28

60 50 Sound intensity

6 Use an example to explain how human reflex can add errors to an experiment.

70

40 30 20 10 0

0

1

2 3 Distance (m)

4

5

16 Copy Figure 1.5.1 into your workbook and: a identify the independent variable b identify the variable that changed naturally c identify what is missing from the axes d construct a table of results for the experiment e construct a line or curve of best fit through the data f predict the sound intensities for the following distances: i 1.5 m iii 350 cm v 0 m. ii 2.8 m iv 6000 mm g predict the distances for the following sound intensities: iii 20 i 45 iv 55. ii 32 Worksheet 1.5 Sci skills crossword Worksheet 1.6 Sci-words

>>>

2

Atoms Key focus areas:

>>> The nature and practice of science >>> The history of science

distinguish between an atom, a molecule and a lattice recall the symbols of some elements write the formulae for some simple compounds identify whether a change in a substance is due to a physical or a chemical change write simple word equations to describe a chemical change classify chemical reactions into one of four types identify ways in which chemical reactions can be sped up.

ferret, ferocious or iron?

2 Which do you think is the symbol for chlorine? C, Ca, Cl or Co?

3 Are you making a new substance when you add water to cordial?

4 List what is produced when paper is burnt.

5 Why are vegetables stored in the refrigerator?

6 Which do you think will relieve a headache more quickly: a whole aspirin tablet or the same tablet crushed?

7 ‘You can easily see an atom with an ordinary microscope.’ True or false?

Pre quiz

1 Do you think the symbol Fe stands for

Outcomes

distinguish between an element, a compound and a mixture

4.1, 4.2, 4.7.4, 4.7.5, 4.7.6, 5.7.1, 5.7.2, 5.7.3

By the end of this chapter you should be able to:

UNIT

>>>

context

2.1 In the fourth century BC, Greek philosophers thought that everything was made from four basic ingredients: earth, air, fire and water. We now know that all matter is made from basic ingredients. These are not the ingredients of the ancients, however, but ‘elements’—around one hundred of them. These elements make up the planets and the stars and every substance that we see, breathe, drink and use. They even make up our bodies.

Teacher demonstration Your teacher may conduct a demonstration in a fume cupboard, showing how sugar may be broken down by concentrated sulfuric acid. The acid breaks the sugar down into water vapour, carbon and other substances. The water vapour bubbles through the carbon to produce an impressive black cone of charcoal. Warning: This demonstration must be done in a fume cupboard, as the fumes produced may trigger respiratory problems. Safety goggles must be worn.

Elements An element is an absolutely pure substance that cannot be broken down into other substances. If you were asked to name some pure substances, you might mention substances such as plastic, paper, air and sugar—however, none of these are elements! The reason—they can all be broken down into simpler substances. There are several possible ways to break down a substance, such as burning or using acids or other chemicals. When plastic, wood or paper are burnt, they break down to reveal the carbon within them. Carbon is an element, as it cannot be broken down any further. Some other elements are aluminium, copper, oxygen, sodium and chlorine. The periodic table (to be studied in The most ents elem detail next year) is a abundant Prac 1 The most abundant complete list of all p.36 element on Earth is the known elements. oxygen, which There are 92 naturally constitutes about the of cent per 47 occurring elements, most of Earth. Next is silicon which were discovered in (28 per cent of the Earth), the last 400 years, and over followed by aluminium iron then 20 synthetic elements. cent) per (8 (5 per cent).

30

sulfuric acid

sugar beaker

Fig 2.1.1

Concentrated acid may be used to break down sugar into carbon and other substances.

These have never been found in nature but were created by scientists in the laboratory. Many of the synthetic elements are unstable and exist for only a few seconds after being created. Some elements are listed in Figure 2.1.2.

Phosphorus discovered in P!

Each element has a unique The Hindenburg explodes. symbol made up of one or In medieval times, people called two letters. Carbon has the alchemists worked on potions symbol C. Because carbon and spells. They attempted to er’s uses the single letter C, find the legendary ‘philosoph stone’ that would turn base chlorine is given a different metals such as lead into gold. symbol, Cl. Cobalt has the A German alchemist, Henry symbol Co. The first letter of Brand, was working on an he when n potio life’ of ‘elixir a symbol is always a capital, extracted from urine an element while the second is always that glowed in the dark! He in lower case. But what had accidentally discovered given adays (now s about copper? C and Co have phosphoru the symbol P). been used already! Many elements get their symbols from Latin or Greek words. Copper’s symbol, Cu, is taken from the Latin word for copper—cuprium. The names of some The Hindenburg elements are not at all obvious initially—sodium The Hindenburg airship (or Zeppelin) was filled with the element hydrogen, has the symbol Na, from the Latin word natrium. and exploded in 1937 with the loss Potassium’s symbol, K, comes from the Latin of 35 lives. Hydrogen reacts with word kalium, while gold’s symbol, Au, comes oxygen in the air. It burns explosively, from the Latin word for the metal, aurum. producing lots of energy and water. Worksheet 2.1 Fig 2.1.2

UNIT

2 .1 Fig 2.1.3

The elements

Some elements and their symbols

Element

Symbol

Element

Symbol

Aluminium

Al

Lead

Pb

Americium

Am

Magnesium

Mg

Barium

Ba

Mercury

Hg

Boron

B

Neon

Ne

Calcium

Ca

Nickel

Ni

Carbon

C

Oxygen

O

Chlorine

Cl

Platinum

Pt

Chromium

Cr

Plutonium

Pu

Copper

Cu

Potassium

K

Einsteinium

Es

Radium

Ra

Europium

Eu

Sodium

Na

Fluorine

F

Silver

Ag

Gold

Au

Sulfur

S

Helium

He

Tin

Sn

Hydrogen

H

Titanium

Ti

Iodine

I

Tungsten

W

Iron

Fe

Uranium

U

Krypton

Kr

Zinc

Zn

31

>>>

Elements, compounds and mixtures Metal and non-metal elements Of the 106 known elements, 84 are metals and 22 are non-metals.

Elements

Metallic elements

Solid

Liquid

(Iron, Magnesium) (Mercury)

Non-metallic elements

Solid

Liquid

Gas

(Carbon) (Bromine) (Oxygen)

Metals and non-metals are classified according to their properties.

Fig 2.1.4

All metallic elements are solids at room temperature except for mercury, which is a liquid. The properties of metallic elements make them very useful to humans. For example, aluminium is used to form cooking utensils, copper for electrical wires and plumbing pipes, while mercury is used in thermometers. Fig 2.1.5

Many useful products are made of metals.

Fig 2.1.6

The sulfur shown is a typical example of a non-metal.

Sulfur displays all the typical properties of a nonmetal. It is used for making sulfuric acid and fertilisers, it has antibacterial and antifungal properties and its compounds are used to preserve food.

The different properties of metals and non-metals Metals

Properties

Non-metals

solid (except mercury)

physical state

solid liquid or gas

shiny

appearance

dull

high

melting point

low

high

density

low

malleable

malleability (ability to be shaped)

brittle (easily broken)

ductile

ductility (ability to be stretched into wires)

no

good

conductivity

poor

Atoms Non-metallic elements can exist as solids, liquids or gases. They are also very useful to humans. Nitrogen gas is used for making fertilisers, carbon (diamond) for jewellery and cutting tools, and carbon (graphite) for bicycle frames and as a lubricant.

32

Imagine you wish to share a thin sheet of gold equally among your class. You begin to divide it by cutting it up with a very fine, sharp knife. Of course, the small pieces you cut off from the original sheet are still gold. Now imagine these

Fig 2.1.9

UNIT

2 .1 Common molecules

gold bar

O

O

H

H C H H H

O

H oxygen 02

water H2O

methane CH4

O O Cu

O

many more divisions

an atom

O

S

C

O

carbon dioxide CO2

O copper sulfate CuSO4

The smallest piece of gold possible is an atom of gold.

Fig 2.1.7

smaller pieces are divided into tiny pieces to be shared among everyone in your year level. If the slicing continues, how far could you go before the pieces of gold could not be divided any further? Eventually you must get to the smallest piece possible. This ‘smallest piece’ is called an atom, in this case an atom of gold. The word ‘atom’ comes from the Greek word atomos, meaning ‘that which cannot be divided’. In other words, an atom is the smallest piece of a substance that is still that substance. The element gold (symbol Au) is simply lots and lots of individual atoms of gold. We represent atoms pictorially as spheres. Only recently has it been possible to observe atoms using powerful electron microscopes.

structures called lattices. Special forces called atomic bonds hold the atoms together. Water is perhaps the most famous molecule—each water molecule is made up of two hydrogen atoms and one oxygen atom, hence the familiar chemical symbol for water—H2O. A compound consists of a number of identical molecules or a lattice containing different atoms joined or ‘bonded’ together. A glass of the compound water contains billions of water molecules. The compound sodium chloride (table salt) consists of grains made up of a lattice of sodium and chlorine atoms held together by atomic bonds.

lattice

molecular

oxygen atom hydrogen atom

Fig 2.1.8

Gold atoms are distinguishable in this electron microscope photograph.

water (H2O)

chloride atom sodium atom

sodium chloride (NaCl)

Two types of compound—molecular and lattice

Fig 2.1.10

Compounds Virtually everything is made of atoms, but since there are only about 100 different Prac 2 atoms, how are there millions of different p. 37 substances in the world? The answer lies in the fact that atoms usually link to form small groups called molecules, or larger

Millions of compounds are possible since there are so many ways the 100 or so different types of atoms can be combined. Compounds usually have quite different properties (eg colour, texture, smell, density) than the elements whose atoms they contain. For example, the

33

>>>

Elements, compounds and mixtures Fig 2.1.11

Compound formulas

Some compounds

Scientists use a shorthand way of describing which atoms are bonded in a molecule or lattice. They write chemical formulas using element symbols, with subscripts to show how many of each atom there are in the compound. Water has two atoms of the element hydrogen and one atom of the element oxygen, so its formula could logically be written as H2O1. Scientists never include the subscript 1 and so the formula for water becomes H2O. The following table gives the formulas for some Prac 3 compounds. p. 37

compound water is a liquid at room temperature. Water (H2O) contains atoms of the elements hydrogen and oxygen, which exist in air as colourless gases, quite different from water! Sodium is an explosive metal and chlorine is a poisonous gas but these elements combine to form sodium chloride (NaCl), a solid that we safely sprinkle on food.

Body elements Our bodies are made up of only 16 different elements, but these 16 elements form hundreds of different compounds.

34

Molecules of elements Some molecules contain only one type of atom. Oxygen atoms can join together in pairs to form oxygen molecules. Hydrogen gas is composed of pairs of hydrogen atoms.

Our bodies contain hundreds of different compounds, as do trees, the Earth’s crust and the many human-made or synthetic materials, such as medicines and plastics. Worksheet 2.2 Body elements

Compound (common name)

Scientific name

Water

Dihydrogen oxide

Oxygen

Formula

Structure

Number of atoms of each type per group

H2O

Molecule

2 hydrogen 1 oxygen

Oxygen

O2

Molecule

2 oxygen

Ozone

Ozone

O3

Molecule

3 oxygen

Table salt

Sodium chloride

NaCl

Lattice

1 sodium 1 chlorine

Natural gas

Methane

CH4

Molecule

1 carbon 4 hydrogen

Hydrochloric acid

Hydrogen chloride

HCl

Molecule

1 hydrogen 1 chlorine

Quartz

Silicon dioxide

SiO2

Lattice

1 silicon 2 oxygen

Sugar

Sucrose

C12H22O11

Molecule

12 carbon 22 hydrogen 11 oxygen

Petrol

Octane

C8H18

Molecule

8 carbon 18 hydrogen

Rust

Iron oxide

Fe2O3

Lattice

2 iron 3 oxygen

Mixtures A mixture contains two or more substances (elements or compounds) simply mixed together. These substances are not bonded together and no new substance is formed when they are combined. This also means that a mixture can easily be separated

UNIT

2 .1 into its ingredients using simple techniques such as filtration or evaporation. Several methods of separating mixtures are discussed in Science Focus 1, Chapter 3. Soft drink is an example of a mixture. It contains sugar, water, flavouring, colouring and carbon dioxide gas. Worksheet 2.3 Elements wordfind How many different elements and different compounds are in this mixture?

UNIT

2 .1

Fig 2.1.12

A strawberry milkshake is a mixture of milk and flavouring, which themselves are mixtures of water, fats and sugars.

[ Questions ]

Fig 2.1.13

Checkpoint Elements 1 Clarify what is meant by the term ‘element’. 2 Identify methods that can be used to break down substances into elements. 3 State the number of naturally occurring elements. 4 Identify the two most abundant elements in the Earth’s crust. 5 Outline the properties of metals. 6 Identify two metals and state their uses. 7 Repeat questions 5 and 6 for non-metals.

Atoms 8 Define the term ‘atom’. 9 Describe the connection between atoms and elements.

Compounds 10 Define the term ‘compound’. 11 Using examples, identify the two types of compound structures.

Mixtures 12 Define the term ‘mixture’. 13 Distinguish between mixtures, elements and compounds.

Think 14 List the name and symbol of three elements starting with C. 15 List six elements with single-letter symbols. 16 List the name and symbol for three elements whose names are unlike their symbol.

17 Identify the names of the following elements: a Pt c Fe b Hg d K. 18 Identify the symbols for the following elements: a hydrogen c sulfur b helium d sodium. 19 Identify an element named after: a a place c a planet. b a person 20 For each of the following examples assess whether a mixture or a compound is formed. a Cordial is diluted with water. b Toast is burnt. c Caramel topping is added to milk to make a milkshake. d White PVA glue combines with air to form a hard, clear substance. e An iron nail rusts. 21 Identify two compounds that have a lattice structure. 22 State whether you would use a metal or non-metal for the following items. Justify your choice in each case. a b c d

ship’s hull fishing rod electrical wires barbecue hot plate.

Analyse 23 Use the information in the table on page 34 to construct diagrams of four different molecules.

>> 35

>>>

Elements, compounds and mixtures

24 Using the descriptions given, classify each substance as a metal or non-metal, and identify the element if possible. a I am used to make bicycle frames. I am light in weight but very strong. I can be polished to a shiny finish. b I have a density so low that I am found in the air. I am used by your body to make energy. c I am a solid that breaks easily. I am used to make fertilisers and I am found in gases that smell like rotten eggs. My colour is yellow. d I can be stretched into wires used to carry electricity. I am also used to make water pipes and can be easily bent in different directions. e I am a liquid that is used in thermometers. Although I look very shiny and pretty I am highly poisonous.

[ Extension ] Investigate 1 Choose an element and describe the following information: a b c d e

Action

Skills

2 Obtain or observe samples of ten elements from everyday life and construct a table listing name, symbol and appearance.

25 Use diagrams to contrast a molecular compound with a mixture.

3 Visit the chemistry department of a university or museum and examine samples of elements.

Creative writing

UNIT

DYO

Surf

Imagine that you have just discovered a new element. Present the following information about the element, using a creative format, such as a poster or website. a Describe how the element was made. b Propose a name and symbol for the element. c Describe some physical and chemical properties of the element. d Outline some potential uses for the element.

2.1

history of the element’s discovery uses for the element how the element is obtained relevant safety issues physical properties that make the element useful.

4 The alchemists played an important role in the development of chemistry as a subject. Research the contributions made by alchemists by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 2 and clicking on the destinations button. Construct a drawing to illustrate an alchemist at work.

[ Practical activities ] Fig 2.1.14

Breaking down substances Prac 1 Unit 2.1

Aim To identify elements in various substances Equipment

Small samples of various materials (paper, plastic straw, aluminium foil, wood (eg toothpick), cloth, green leaf, wool, cotton wool, bread), Bunsen burner, heat-proof mat, metal tongs, safety glasses, squares of contact adhesive to stick samples into workbook

Method 1 Hold a sample in the metal tongs and place part (but not all) of it in a blue Bunsen burner flame. The sample should be small enough to later stick into your workbook without causing too much of a bulge. Warning: Use a fume cupboard if testing plastic or other substances that produce dangerous fumes.

36

2 Allow the sample to burn only partially before removing it from the flame. If it does not burn, withdraw it from the flame after a couple of seconds.

3 After withdrawing the sample from the flame, put out any flame on the sample (eg by prodding with the tongs, blowing or using water). 4 When cool, stick the sample into your workbook. 5 Repeat steps 1 to 4 for the other samples.

UNIT

2 .1 Questions 1 Record your results in a table, describing observations made for each sample. 2 a List any observations that were common to each sample tested. b Use observations to identify an element common to several samples.

Mathomat molecules Aim To construct diagrams of molecules Prac 2 Unit 2.1

Equipment A Mathomat or similar template

Method 1 Construct diagrams of as many atom combinations as possible using Mathomat circles (let each different circle represent a different atom). You may not use more than four identical circles in each combination. 2 Colour each different size circle a particular colour. A few possibilities are shown opposite.

Fig 2.1.15

Questions 1 State the number of molecular combinations made. 2 Compare the number of ‘atoms’ with the number of ‘molecules’.

Flame tests Prac 3 Unit 2.1

Aim To identify various elements using the flame test Equipment Paperclips, tongs, Bunsen burner, heat-proof mat, beaker of water, various chloride salts (eg strontium chloride, sodium chloride, copper chloride, potassium chloride), watch-glass

Method 1 Obtain a tiny sample (enough to cover a match head) of one of the chemicals on a watch-glass. 2 Fill a clean beaker with water. 3 Dip one end of a paperclip into the water, then into the chemical so some of the chemical sticks to the paperclip. Fig 2.1.16

4 Set the Bunsen burner to a blue flame. 5 Using tongs, place the end of the paperclip containing the chemical into the flame and observe the colour produced. (See Figure 2.1.16.)

Questions

6 Rinse the beaker and fill it with clean water. Obtain a new paperclip.

2 For each chemical identify which elements give rise to colour.

7 Repeat steps 1 to 6 for the other chemicals.

3 Describe how flame tests can be used to identify elements in a compound.

Extension Your teacher will supply some unknown samples for you to test. Use your results to identify the elements in the unlabelled samples.

1 Record your results in a table. Include the scientific names of each chemical.

4 New water and a new paperclip were used for each chemical you tested. Explain why this is important. 5 Propose a use for this technique, drawing on the experience gained in this experiment.

37

>>>

UNIT

context

2.2 Changes are occurring to the substances around us all of the time. These changes may be as simple as a change in shape, such as when an aluminium can is squashed. Some substances are broken into smaller pieces—a window is smashed, sugar dissolves in hot coffee. In some cases, changes produce new substances—petrol

Exploding fireworks involve physical and chemical changes.

38

Fig 2.2.1

explodes to form different gases; iron rusts, producing an orange-red flaky substance very different from the original silvery grey metal. Changes can be classified as physical or chemical.

Physical change A physical change occurs when a substance changes, but no new substance is formed. Physical changes occur when the state of a substance changes (eg melting, evaporation, freezing, condensing) or a substance is crushed, ground or cut into smaller pieces. The following are examples of physical change. • A plate is dropped and shatters. • Ice melts. • Water boils.

Fig 2.2.2

Frozen carbon dioxide in water undergoes a physical change from solid to gas.

• • • • • •

Milo dissolves in hot milk. Grass is mown. Branches of a tree are mulched. A metal knife is sharpened. Finger nails are filed down. Breakfast cereal goes soggy.

Chemical change A chemical change or chemical reaction occurs whenever a new substance forms. When a substance forms that looks different or acts very differently from what was there before, then the chemical change is very obvious. Sometimes, however, the change is more difficult to observe. The only indication may be a change in colour, the production of heat or light or a drop in the temperature of the material. The following are examples of chemical change. • Wood burns to form charcoal (carbon). • A green tomato ripens and turns red. • An egg is cooked to become a white and yellow solid. • Vegetable scraps in the compost bin decompose to produce a rich soil. • A dead mouse stuck in the wall of a house begins to smell awful. • A metal panel on a car rusts. • Fireworks explode. • Concrete hardens.

UNIT

2 .2 Types of chemical reaction There are various types of chemical reaction but in all cases the substances present before the chemical reaction has occurred are called the reactants. The chemicals formed by the reaction are called the products. You can represent a chemical reaction using a simple word equation, in which reactants are written on the left and an arrow points to the products formed. reactants

→ products

Chemical reactions can be classified into four different types.

Combination reactions In all combination reactions the two or more reactants join together to form one new substance. A common combination reaction is rusting of a metal. Rust (iron oxide) is produced by a chemical reaction between iron and oxygen. The reactants (iron and oxygen) combine to form the product iron oxide or rust. In this reaction the word equation would be: iron + oxygen (reactants)

→ iron oxide (product)

Combination reactions are also called synthesis reactions. Worksheet 2.4 Combination reactions

Fig 2.2.3

Rusting is a chemical change.

Decomposition reactions Chemical reactions do not always need two reactants. Sometimes, one is enough. A single reactant can break down or decompose to form two or more new substances. For example, light breaks down silver chloride to form two substances—silver and chlorine. Silver chloride is used to coat photographic film, producing a dark image when light causes it to break down. Water can be broken down using electricity to produce oxygen gas and hydrogen gas. water (reactant)

→

oxygen gas + hydrogen gas (products)

Precipitation reactions Sometimes a solid forms when two solutions are mixed together. This solid is called a precipitate. Because precipitates do not dissolve in water (they are insoluble), this type of reaction is a useful way of removing certain chemicals from a solution.

39

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Physical and chemical change

through its air hole to produce carbon dioxide, water vapour and heat energy. methane + oxygen

Prac 2 p. 43

→ carbon dioxide + water

Word equations In their word equations, scientists often use the symbols (s), (l) and (g) to indicate whether the reactants and products are solid, liquid or gas respectively. The symbol (aq), short for ‘aqueous’, indicates that the atoms or molecules are dissolved in water. Some more examples appear below. Corrosion of aluminium: aluminium (s) + oxygen (g)

Prac 3 p. 44

→ aluminium oxide (s)

Combustion of coal gas (ethane): ethane (g) + oxygen (g)

→ carbon dioxide (g) + water (g)

Dissolving magnesium in acid: Fig 2.2.4

magnesium + hydrochloric (s) acid (l)

A precipitation reaction

Some precipitates are very colourful and are often used as paint pigments.

No—this doesn’t involve flames inside us! Glucose (a type of sugar produced when food is broken down) undergoes combustion during digestion by combining with oxygen carried in our blood to produce carbon dioxide, water vapour and heat. The carbon dioxide then gets carried back to our lungs to be breathed out. This kind of combustion is sometimes called respiration.

Prac 1 p. 43

Combustion reactions happen whenever something burns or explodes. They involve a substance reacting with oxygen, usually from the air around it. New (often gaseous) substances form, accompanied by the release of heat and/or light, sometimes as a flame or explosive flash. When magnesium ribbon burns, it combines with oxygen in the air to produce a white powder, magnesium oxide.

magnesium metal + oxygen gas

→ magnesium oxide powder

Carbon may be burnt to produce carbon dioxide gas. carbon + oxygen

→ carbon dioxide

A Bunsen burner works due to the reaction of methane gas from a gas tap with oxygen drawn

40

hydrogen + magnesium (g) chloride (aq)

Extracting copper from a compound:

Combustion reactions Combustion in our bodies

→

copper + sulfate (aq)

iron (s)

→

copper (s)

+

iron sulfate (aq)

Decomposition of silver chloride by light: silver chloride (s)

→ silver (s) + chlorine (g)

A precipitation reaction: silver sodium + nitrate (aq) chloride (aq)

silver → chloride (s)

+

sodium nitrate (aq)

Speeding up reactions When fireworks explode, the rate of reaction is very fast: the fireworks chemicals are used almost all at once, In contrast, iron rusts at a very slow rate. The rate of a reaction can be determined by observing how quickly products are produced or how quickly reactants disappear. Do scientists have a method of controlling reaction rates? If you examine the factors that affect reactions rates you will see that control is possible. Reaction rate can be affected by: • the amount or concentration of reactants Example: A stain may be removed more quickly by adding more stain remover, or a more concentrated stain remover. Reason: More molecules are available to take part in the reaction, so products are produced more quickly.

• temperature Examples: Fruit ripens more quickly in warmer weather; food keeps longer when stored cool in a refrigerator. Reason: Reactants move more quickly at higher temperatures and have more energy available to break bonds between Prac 4 atoms to allow the formation of new p. 44 substances. • the extent of the surface area Example: Lots of small pieces of iron (eg iron filings) react more quickly with acid than the same amount of iron present as a single lump. Reason: A lot of small pieces of iron have a greater surface area than one big Prac 5 block, allowing more atoms of iron to be p. 45 exposed to the acid. • catalysts (helper chemicals) Example: In a car’s catalytic converter, the element rhodium helps harmful exhaust fumes react with oxygen to produce less harmful products. Reason: The rhodium attracts the harmful gases and oxygen so more of each gas comes together and reacts. The rhodium does not actually react Hardening fillings with either gas; it just speeds al Dentists use a speci paste to fill holes in up the reaction by getting more teeth. The paste is then molecules to come together. by

UNIT

2 .2 Enzymes Special types of catalysts called enzymes are found in our bodies. Digestive enzymes help break down large molecules such as starch into smaller molecules such as glucose. Think of the enzymes as a pair of scissors and the starch molecule as a string of beads being cut by the enzyme into small beads (the glucose). This allows the starch to be more easily digested and ultimately be used by body cells. Like all catalysts, digestive enzymes do not combine with other atoms or molecules; they simply help the chemical reactions to occur more Prac 6 p. 45 quickly. Fig 2.2.5

Enzymes breaking up a starch molecule

starch molecule enzyme cuts bonds in starch molecule

hardened quickly using ultraviolet (UV) light as a catalyst.

UNIT

2.2

Types of chemical reaction

[ Questions ]

Checkpoint Physical change 1 Define what is meant by the term ‘physical change’. 2 State two examples of a physical change.

Chemical change 3 Use an example to define what is meant by the term ‘chemical change’.

6 List the four types of chemical reactions. 7 Recall the name given to the ‘ingredients’ of a chemical reaction. 8 Clarify what is meant by the term ‘precipitate’.

Word equations 9 Explain what is meant by each of the following when written in chemical equations: (s), (l), (g), (aq), →.

Speeding up reactions 10 Identify an example of a fast reaction and an example of a slow reaction. 11 Recall four ways of increasing the speed of a chemical reaction.

4 Recall the signs that could indicate that a chemical change is happening.

12 Define the term ‘catalyst’.

5 Outline two examples of chemical reactions happening around your home.

13 Outline the effect of an enzyme on the speed of digestion.

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41

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Physical and chemical change

Analyse

Think 14 Classify the following examples as physical or chemical changes. a A prisoner breaks up rocks. b Leaves turn red in autumn. c Food is digested and waste is expelled from your body. d A puddle of water evaporates. e Juice is squeezed from a lemon. f Rain turns the surface of a sports ground to mud. g Sugar and water are heated in a saucepan to produce caramel. h Sawdust is produced when a circular saw cuts timber. i A match is struck and burns. j Margarine melts in a frypan. k Butter burns in a frypan. l Bread goes mouldy. m Water freezes to make ice cubes. n After being stored in a cellar for ten years, a bottle of red wine tastes like vinegar. 15 a Describe the change or changes observed when a candle burns. b Classify each change observed as physical or chemical. 16 Contrast the effectiveness of a finely ground headache tablet with a solid tablet. 17 Predict the effect of each of the following on a wood fire heater. a A log is chopped into several small pieces before being added to the fire. b A vent is closed so less air gets to the fire. 18 Reaction rates slow as time goes on. Explain why.

Skills 20 Copy the following word equation and identify the reactant(s) and the product(s). hydrogen + chlorine → hydrogen chloride 21 Copy and complete the following chemical equations by identifying the missing reactant and products. a sodium chloride + silver nitrate → ________ ________ + ________ ________ b copper oxide + hydrogen → water (or hydrogen oxide) + ______ c zinc + sulfur → ______ sulfide d _________ + _________ → calcium oxide 22 Construct word equations for each of the following. a A strip of magnesium burns and combines with oxygen to produce magnesium oxide powder. b Hydrogen and oxygen gas explode together to form water vapour. c A lump of sodium dissolves in water to produce sodium hydroxide solution and hydrogen gas. d Solid mercury oxide is broken down into liquid mercury and oxygen gas.

Create 23 Construct models that illustrate the four ways of speeding up chemical reactions.

[ Extension ] Investigate

Surf

1 Baking soda reacts quickly with vinegar. a Design an experiment to investigate this chemical reaction. b Describe a method to prove that the gas produced is carbon dioxide. c Explain how the gas produced makes the reaction useful in baking cakes.

2 Research one or more of the following chemical reactions by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 2 and clicking on the destinations button.

DYO

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19 A catalyst is used in a reaction. Identify which of the following best describes the amount of catalyst left at the end of the reaction compared to the amount present at the start: A none B less C the same D more E depends on the type of reaction.

a Describe the new substances formed when food decomposes.

b Describe how to ensure vegetable scraps produce good compost suitable for the garden. c Outline the physical and chemical changes involved in the production of sheet metal from raw materials. d Describe the process of galvanising used to prevent rust. e Outline some uses for exothermic and endothermic reactions. f Describe the role of several enzymes used by the human body. g Examine the role of enzymes sometimes used in washing powders.

UNIT

2.2

UNIT

2 .2 Project Rusty nails

DYO

Design an experiment to compare the rate at which iron nails rust in the following conditions: nail partly under water, nail fully under water, nail in salty water, nail in water with a crushed vitamin C tablet (hint: vitamin C is an ‘antioxidant’).

[ Practical activities ] A precipitation reaction Aim To make and observe a precipitate

Prac 1 Unit 2.2

Equipment Potassium iodide solution, lead nitrate solution, filter paper, funnel, conical flask, matches, tongs

Method Warning: The chemicals used and formed in this experiment are poisonous. Handle with care. Inform your teacher immediately if there are any spills and follow the instructions on disposal methods.

4 Use filter paper, a conical flask and a funnel to filter out the precipitate. 5 If possible, leave the solution filtering overnight.

Questions 1 Observe and describe the appearance of the precipitate. 2 Given that one part of each reactant’s name is involved propose a name for the precipitate.

1 Place 2 cm of potassium iodide solution in a test tube.

3 Based on the answer given in question 2 state the names of the ions left in solution.

2 Add a similar amount of lead nitrate solution.

4 Construct a word equation for the reaction.

3 Leave the test tube to stand in a rack for several minutes and observe the contents.

5 Determine whether the reaction is a physical or chemical change and justify your choice.

Teacher demonstration—burning magnesium Prac 2 Unit 2.2

Your teacher will demonstrate the combustion of magnesium.

Warning: Do not look directly at the magnesium as it burns. Burning magnesium produces intense white light. Teacher: wear safety goggles.

Questions

3 The new substance produced in this reaction is magnesium oxide. Propose possible sources of the oxygen. 4 If the magnesium and magnesium oxide were accurately weighed, predict which would be heavier and why. 5 Construct a word equation for the reaction. 6 Determine whether the reaction is a physical or chemical change and justify your choice.

1 Contrast the appearance of the magnesium before and after the reaction. 2 Outline any evidence that a new substance has been formed.

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Physical and chemical change

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Coating nails

test tube rack

Aim To extract copper from a compound Prac 3 Unit 2.2

Equipment Small iron nails, copper sulfate solution, copper nitrate solution, 3 test tubes, test tube rack

Method 1 Place water in one test tube, copper sulfate solution in another and copper nitrate solution in another, and place the tubes in a rack. 2 Place one iron nail in each test tube. 3 Leave the test tubes to stand for 5 minutes or more, and preferably overnight.

Questions 1 Observe the test tubes and describe which solution produced the thickest coating on a nail.

water

copper sulfate solution

copper nitrate solution

Fig 2.2.6 2 Propose a purpose for the test tube containing a nail and water. 3 Use your observations to justify the nature of the coatings formed on the nails.

Reaction rate—effect of temperature and concentration Prac 4 Unit 2.2

Aim To investigate the effect of

Fig 2.2.7

10 mL hydrochloric acid

temperature and concentration on reaction rate

Equipment Sodium thiosulfate (‘hypo’) solution (0.1M), hydrochloric acid (1M), hydrochloric acid (2M), cold water, hot water, conical flask, measuring cylinder (10 mL), large beaker, safety glasses, timer timer

observe cross

Method 1 Place 50 mL of hypo solution into a conical flask.

50 mL hypo solution

2 Sit the conical flask in a beaker of cold water (put ice blocks in the water if they are available) for 5 minutes. 3 Remove the conical flask from the beaker and dry its base. 4 Draw a cross on a piece of white paper and place the conical flask on top of the cross.

44

7 Repeat steps 1 to 5, but use 2M hydrochloric acid.

5 Add 10 mL of hydrochloric acid (1M strength) to the conical flask, and time how long it takes before you can no longer see the cross under the base of the flask. (Alternatively, use a light sensor on one side of the flask and a light source on the other to measure the amount of light transmitted through the contents of the flask as the reaction progresses. Note the time taken for the cloudiness or ‘turbidity’ of the solution to stabilise.)

2 Using your own observations, explain how the concentration of the hydrochloric acid affected reaction rate.

6 Repeat steps 1 to 5, but use hot water at step 2 instead of cold.

3 Predict whether these conclusions might apply to all reactions.

Questions 1 Using your own observations, explain how temperature affected reaction rate in this experiment.

UNIT

2 .2 Reaction rate—effect of surface area Fig 2.2.8

Aim To investigate the effect of surface area on Prac 5 Unit 2.2

reaction rate

Equipment stirring rod

2 Alka Seltzer tablets, water, 2 beakers (250 mL), 100 mL measuring cylinder, 2 stirring rods, mortar and pestle or other grinding tools, timer

Method 1 Accurately measure 100 mL of water in each beaker. 2 Grind one of the Alka Seltzer tablets into a fine powder. 3 Place a whole tablet in one beaker and, at the same time, the crushed tablet in the other beaker, stirring for a few seconds.

whole tablet

crushed tablet

4 Record the time taken for each to finish reacting with the water.

Questions

2 Based on your observations, explain the effect of greater surface area on the rate of this reaction.

1 Determine which tablet (crushed or whole) had the greater surface area and justify your answer.

3 Identify the factors that should be kept the same for both beakers.

Reaction rate—effect of catalysts and enzymes Prac 6 Unit 2.2

Aim To investigate the effects of catalyst and enzymes on reaction rate hydrogen peroxide

Equipment 4 test tubes, test tube rack, fresh hydrogen peroxide solution, manganese (IV) dioxide, small piece of fresh liver, small piece of apple or potato, wax taper, safety glasses

Method 1 Place a small piece of liver in a test tube. 2 Place some manganese dioxide in another test tube. 3 Place a small piece of apple or potato in another test tube. 4 One-quarter fill another test tube with hydrogen peroxide only. Hydrogen peroxide slowly decomposes into water and bubbles of oxygen. Can you see any bubbles of oxygen forming? 5 Place the lighted wax taper into the tube and observe what happens to the flame.

hydrogen peroxide only

liver

manganese dioxide

piece of apple or potato

Fig 2.2.9

6 Add the same amount of hydrogen peroxide to the other test tubes and observe carefully, comparing rates of bubble formation in all three test tubes.

2 Use your observations to determine whether liver and manganese dioxide were left in the test tubes or consumed by the reaction. Justify your answer.

Questions

3 Compare the effect of the apple or potato with that of the manganese dioxide.

1 Use your observations to assess which test tube produced oxygen most rapidly.

4 Predict whether cooked liver would produce the same results.

45

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UNIT

2.3 negatively charged electrons

context

The original idea of a small particle called the atom came from the ancient Greeks, some 2000 years ago. Over the last two hundred years scientists have been discovering what is in these atoms and how they came into being. Their aim is still the same as the ancient Greeks—to find simple patterns that explain the complexity of nature.

positive ‘dough’ solid ball model Dalton (1808)

plum pudding model Thomson (1904)

nucleus (+) empty space

Atomic history There have been a number of theories about the structure of atoms and several Nobel prizes awarded to researchers. Here are some key dates.

Bohr escape During World War II, Niels Bohr escaped Germanoccupied Denmark, fleeing to America, where he assisted with bomb research.

electron (–) nuclear model (Rutherford 1911)

nuclear model with electron ‘shells’ Bohr (1913)

A history of atomic models

Fig 2.3.1

about 350 BC

The ancient Greeks believe that atoms are solid balls of matter.

1808

John Dalton (an English chemist) supports the idea of atoms as solid balls.

1897

Sir Joseph John Thomson (Great Britain) discovers electrons. The electron is the first known particle that is smaller than an atom.

1903

Sir Joseph John Thomson proposes the ‘plum pudding’ model of a positively charged ‘dough’ with negatively charged electrons embedded in it.

1908

New Zealand born physicist and student of Thomson, Ernest Rutherford, wins the Nobel prize for chemistry ‘for investigations into the disintegration of the elements, and the chemistry of radioactive substances’.

1911

Ernest Rutherford proposes a nuclear model in which negatively charged electrons orbit a positive nucleus, with most of the atom being empty space. This was discovered in his famous gold foil experiment.

1913

Ernest Rutherford discovers that hydrogen is the smallest atom. Niels Bohr, a Danish physicist and assistant to Rutherford, extends Rutherford’s model to include electron shells—regions in which a given number of electrons may move.

46

1914

Ernest Rutherford discovers the proton, although he did not name it until 1920.

1920

Ernest Rutherford proposes the existence of a ‘neutron’.

1922

Niels Bohr wins Nobel Prize for Physics ‘for investigations of the structure of the atoms and their radiation’.

1932

James Chadwick (Great Britain) discovers neutrons.

Atoms are mainly empty space! Working with two other scientists, Geiger and Marsden, Ernest Rutherford experimented with firing tiny positively charged particles (called alpha particles) at thin gold foil. Amazingly, many of the alpha particles went straight through the gold foil, some not even moving from their path! This suggested to Rutherford that most of an atom was empty space, allowing the alpha particles to go straight through. Some of the alpha particles were scattered, however, and Rutherford suggested that this was because they were repelled by a concentration of positive charges in the centre of an atom. In 1911 he presented his theory of the atom as consisting of a small, dense positively charged nucleus with negatively charged electrons orbiting the nucleus. Fig 2.3.2

Rutherford’s alpha particles and gold foil experiment

alpha particle source

Atomic structure The model of the atom used today is the Rutherford– Bohr model. This model has a central nucleus made up of positively charged particles, known as protons, and particles which are neutral (no charge), known as neutrons. This nucleus is orbited at high speed by much smaller negatively charged particles known as electrons. Protons and neutrons have about the same mass, while electrons have about 1/2000th the mass of protons and neutrons. Though the protons (+) and electrons (–) have opposite charges, the size of the charge is the same for each. An atom has an equal number of protons and electrons, so the positive and negative charges balance each other to produce a neutral atom (one with no overall charge). The simplest atom A hydrogen atom Fig 2.3.4 is the hydrogen atom, whose nucleus electron contains only a single proton, orbited by a lone electron. Diagrams of the next three simplest atoms are shown in proton Figure 2.3.5.

gold foil detector screen

Working small, thinking big

Scientists are now trying to manipulate indiv idual atoms and molecules. This has only become possible recently with the devel opment of new technology that allows us to see and move individual atoms. It is very difficult to build something from atoms. Imagine wearing oven mitts and trying to build something out of LEGO blocks! Working with atoms on this scale is called nanotechnology. Nanotechnology offers much potential for building nano-sized machines. For example, it is hoped that one day tiny nano bots could be injected into the blood, travel around and kill off bacteria and virus es, or investigate illness, sending information back to the doctor to make a diagnosis. Useful nanotechnology already exists. The Australian-designed Biosensor enables doctors to obtain results from blood tests in less than five minutes. Nano technology also has the potential to make computers super-fast and small.

Fig 2.3.3

This scanning tunnelling micrograph (STM) shows carbon nanotubes. It is hoped that these could be used as conducting wires for heat or electricity. They are one-billionth the thickness of a human hair. Individual atoms can be seen as bumps on the surface of the tubes.

47

UNIT

2 .3

>>>

Inside atoms Fig 2.3.5

Number of protons = number of electrons = atomic number

Helium, lithium and beryllium atoms

Number of neutrons = mass number – atomic number

Figure 2.3.6 indicates that the atomic number of a potassium atom is 19 and the mass number is 39. We therefore know that this particular potassium atom has:

nucleus

Number of protons = 19 = atomic number Number of electrons = number of protons = atomic number = 19 Number of neutrons = mass number – atomic number = 39 – 19 = 20

helium lithium

Worksheet 2.5 Atomic graphs (extension)

beryllium Key:

proton (+)

Electron shells

neutron (no charge) electron (-)

Scientists use two special numbers to describe atoms: • the atomic number is the number of protons in the nucleus • the mass number is the number of protons and neutrons in the nucleus. This means that the atomic number of hydrogen is 1, with helium, lithium and beryllium having atomic numbers of 2, 3, and 4 respectively. Scientists use the notation shown in Figure 2.3.6 to describe how many protons, neutrons and electrons are in an atom’s structure:

mass number

39 19

K

atomic number

= number of protons + number of neutrons

Bohr improved Rutherford’s model Weird particles of the atom by explaining how Scientists believe that other subatomic particles exist electrons orbit around the nucleus. besides protons, neutrons He suggested that they orbit in and electrons. These other special regions, or shells, around the particles, some of which have yet to be discovered, nucleus. Only two electrons can fit include quarks, leptons, in the innermost shell of any atom, neutrinos, gravitons, then up to eight in each of the next bosons, photons and two shells for elements up to atomic gluons. number 20. The shells closest to the nucleus are ‘filled’ first. This may be compared to filling spaces on a bookshelf—you might fill the bottom shelf first, then only move up as each lower shelf is filled. The sodium atom in Figure 2.3.7 has 11 electrons. Two of these electrons orbit in the inner shell and eight in the next shell, leaving one electron to orbit in the third shell.

nucleus containing 11 protons and 12 neutrons

symbol for potassium

= number of protons

23

Na

11

How does this information tell us there are 20 neutrons in a potassium atom?

11P 12N

Fig 2.3.6

If you know the atomic number of an atom, you automatically know the number of protons it has. Atoms are neutral and so the number of electrons is the same as the number of protons. To find the number of neutrons, you subtract the atomic number from the mass number.

48

shell 1 contains 2 electrons (max. 2)

shell 3 contains 1 electron (max. 8)

Three electron shells in a sodium atom— the inner two are filled to capacity

shell 2 contains 8 electrons (max. 8)

Fig 2.3.7

UNIT

2. 3

[ Questions ]

Checkpoint Atomic history 1 Outline the origin of the term ‘atom’. 2 List the following in date order. Start with the earliest atomic theory: Rutherford, Dalton, Thomson, Bohr. 3 Recall three Nobel prize winners involved in developing atomic theory. 4 Recall what the dough represents in the ‘plum pudding’ model. 5 Explain what the sultanas and raisins would represent in the ‘plum pudding’ model. 6 Describe the evidence that led Rutherford to believe there was positive charge at the centre of the atom. 7 Recall the date of discovery of each subatomic particle: a protons b neutrons c electrons.

Atomic structure

12 Chlorine has a mass number of 35 and an atomic number of 17. How many of each of the following does one atom of chlorine contain? a protons b neutrons c electrons. 13 Atoms are described as being made up mainly of empty space. Evaluate how correct this statement is by outlining the structure of an atom.

Skill 14 Construct diagrams of the following atoms showing the particles in the nucleus and the location of electrons in shells. a

11 5

B

b

27 13

Al

[ Extension ] Investigate

8 State which particles contribute most to the mass of an atom. 9 State whether the following statements are true or false. a The atomic number is the same as the number of protons. b The atomic number is the same as the number of electrons. c The mass number is equal to the number of neutrons. d The mass number is the number of particles in the nucleus. 10 State the charge on the following subatomic particles: a an electron b a neutron c a proton.

Think 11 In your workbook, construct a table like the one below, filling in the missing information for the first 20 elements.

Atomic number

UNIT

2 .3

Mass number

Element

1 Construct a timeline of key events in the development of atomic models. 2 Research and summarise information about other subatomic particles such as quarks. 3 Research and summarise information about isotopes of elements and how an element becomes radioactive.

Action 4 Use a spreadsheet to construct a database of elements showing atomic and mass number and electron shell information. Produce several printouts based on different sorting methods. Worksheet 2.6 The periodic table

Number of protons per atom

Number of electrons per atom

Number of neutrons per atom

Hydrogen Helium Lithium Beryllium

49

Science focus: Atomic models Prescribed focus area: The history of science

Matter considered to be made up of EARTH, WATER, FIRE and AIR. Alchemists try to transmute or change metals into gold. Scientific method develops in 16th century.

Ancient Greek philosopher, DEMOCRITUS (born about 460 BC) describes matter as made up of ‘indivisibles’ (atomis). These particles were extremely tiny, absolutely solid objects that were eternal.

1808 English chemist, John DALTON revives the Atomis idea and describes matter as made of solid, indivisible particles he called atoms. Dalton created a list of the different known atoms or elements. Radioactivity discovered and used to explore the structure of atoms.

Small, extremely dense nucleus with all positive charge of atom and majority of mass. 1911 New Zealand physicist, Ernest RUTHERFORD analyses experimental results using radio active particles to study atoms. He describes the ‘nuclear’ atom. His model of the atom had a tiny, very dense, positively charged nucleus about 1 ten-thousandth the diameter of the atom. The very tiny negative electrons orbited around the nucleus like tiny planets. The atom was mainly empty space.

Tiny electrons moving quickly in orbits around nucleus. Take up the space occupied by the atom.

e– e–

e–

+

1932 A new model was developed from previous ideas but with changes based on the contributions of several scientists including Louis Debroglie, James Chadwick, Werner Heisenberg, Erwin Schrödinger and Paul Dirac. The nucleus is where most of the mass of an atom is found and contains the protons and neutrons. The number of protons in the nucleus determines what element the atom is. The electrons exist in very definite areas (or energy levels) around the nucleus. The movement of electrons are difficult to show on a diagram as they take up an area of space, and do not have a set orbit like the Bohr model. Electrons in different energy levels have a definite amount of energy (quantised) which allows them to stay there.

Today The standard model is still based on the previous model but has more complex arrangement of electrons around the atoms.

50

e–

Small, extremely dense nucleus containing protons (positive charge) and neutrons (neutral). Represents nearly all the mass of the atom.

+

Negative electrons exist in ‘quantised energy levels. Electrons are shown as a ‘charge cloud’ that shows where an electron may be found in an area of space called an energy level.

Empty atoms! Atoms are so small it takes about 10 millio n of them lined up side by side to stretch one millim etre. Nearly all the mass of an atom is due to the nucleus, but the diameter of the nucleus is ONLY abou t one-ten-thousandth of the diameter of the atom. Atoms really are vacant space!

Extensive studies of chemistry and matter through experiments. New elements discovered and electricity becomes readily available. Electron identified as being present in atoms of all elements.

1903 English physicist, Joseph John THOMSON describes atoms as like a plum pudding or raisin cake. The atom was a heavy positive pudding with the light negatively charged electrons embedded in it. Dynamides moving quickly within space occupied by atom. Positive pudding makes up most of atom. Very light, negatively charged electrons embedded in pudding. 1904 German physicist Philip LENARD describes atoms as mainly empty space filled with fast-moving, neutral particles he called dynamides. These dynamides were made up of a heavier positive particle joined with a negative electron. Quantum theory is developed. It indicates that a particle (such as an electron) will have a set amount of energy.

Tiny, negative electrons orbit at very definite positions with ‘quantised’ energy.

Small, extremely dense nucleus with all positive charge of atom and majority of mass. Quantum mechanics is developed using quantum theory, Chadwick discovers and identifies neutron.

1913 Danish physicist, Niels BOHR, applies his own ideas to the electrons of the Rutherford nuclear atom. His new model has the electrons in orbits where they are only able to exist at very definite positions with a very definite energy (quantised). This uses quantum theory, which implies that particles have set amounts of energy.

Fig SF 2.1

51

[ Student activities ] 1 a State two things that are the basically the same for all the models described on pages 50–51. Outline reasons for your choices. b Discuss your answers with a partner to compare your ideas. c Compare your results with other groups and compile a class summary of the features of different models of the atom that have remained the same. 2 a The table below summarises the basic parts found in the current model of the atom. Copy and complete the table by choosing the correct description from the list provided to fill each box. Energy levels around nucleus Negative 1.0 Neutron Central, dense core Positive approx. 1/2000 neutral (none)

Name

Where found in an atom

Nucleus Proton

In the nucleus In the nucleus

Electrons

b Based on the models of the atom, explain why atoms of the different elements have different masses. 3 The existence of the neutron was suggested by Ernest Rutherford in 1920 but wasn’t finally discovered by experiments until James Chadwick did his Nobel prize-winning work in 1932. a Propose reasons why the neutron was suggested by Rutherford before it had been actually identified. b Discuss with a partner reasons why the neutron was very difficult to detect and record your ideas.

52

4 In small groups, research the following very famous experiments: i the alpha-particle scattering from gold foil used by Ernest Rutherford to develop his nuclear model for atoms ii the discovery and verification of the neutron by James Chadwick. For each experiment: a create a demonstration or model to demonstrate how each experiment was conducted b compare the experiments and make a list of the similarities and differences between them. 5 Chadwick’s and Rutherford’s experiments provided a new and very useful technique to explore atoms. This led to the creation of the particle accelerator. Research particle accelerators and then: a use pictures to demonstrate how a particle accelerator works b outline some uses and benefits of particle accelerators.

Electrical charge

Relative mass (compared to a proton taken as 1.0)

Positive

Depends upon atom 1.0

Chapter review [ Thinking questions ]

[ Summary questions ]

9 Explain why the following metals and non-metals are 1 Identify the correct statement. In a chemical change: able to be used for the purpose shown in the table: A only pure substances combine B no new substances are formed Metal Use Non-metal Use C one new substance is formed copper electrical wires diamond cutting tools D one or more new substances are silver jewellery liquid nitrogen freezing warts formed. 2 Identify which of the following is the most pure: A an element B a compound C a mixture D sugar.

aluminium

aeroplane frames

3 Recall the symbols for the following elements: a carbon b aluminium c gold d tin. 4 Recall the names of the elements that have these symbols: a Ag b Fe c Cu d B. 5 Describe the charge and relative size of subatomic particles found in the atom. 6 Construct a table to compare the properties of metals and non-metals.

sulfur

food preservative

10 Some eggs are to be scrambled for breakfast. They are broken and milk is added. After being thoroughly mixed, they are cooked by stirring continually in a hot pan. They are then eaten and digested. Describe the physical and chemical changes involved from start to finish. 11 Contrast a combination with a decomposition reaction. 12 Think of an everyday chemical change and propose an example of a word equation for the reaction involved. 13 Explain whether each of the following would most likely speed up, slow down or not affect the reaction. a More wood is added to a fire. b The gas control is set to low on a cooktop when a stirfry is being prepared. c A ‘chlorine tablet’ is added to a spa instead of the same chemical in powder form. d Your digestive system releases enzymes.

7 Identify three metals and their uses. 8 State whether the following statements are true or false. a The nucleus is the central region of an atom. b Any number of electrons can orbit in the innermost shell of an atom. c Only two protons may orbit in the innermost shell surrounding an atom. d Electrons are incredibly small compared to neutrons and protons.

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53

>>> Chapter review [ Interpreting questions ] 14 Use this list to classify each of the following diagrams: atom, element, compound, molecule, mixture.

16 For each of the following atoms calculate the number of protons and neutrons. a

56 26

Fe

b

64 29

Cu

c

127 53

I

d

238 92

U

Worksheet 2.7 Atoms crossword Worksheet 2.8 Sci-words A

B

C

D

E

15 Copy the following diagram and identify the parts of the helium atom.

+ +

helium

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3

Microbes Key focus area:

>>> The implications of science for society and the environment

classify microbes as fungi, bacteria, protists or viruses describe how big microbes are describe some of the ways in which microbes are studied explain how microbes reproduce

Outcomes

explain what a microbe is

4.4, 4.8.3

By the end of this chapter you should be able to:

identify ways in which microbes can be useful or harmful.

photograph at left could be happening in your intestine right now. True or false?

2 What is your idea of a ‘germ’? 3 What has the least germs, your computer mouse or your toilet?

4 Why do we fart? 5 Bacteria are found in yogurt. Does that mean the yogurt is ‘off’?

6 Mouldy bread provided the first antibiotic. True or false?

7 Why are you unlikely to catch chicken pox twice?

8 Why does food go bad and why do we get ill from it?

Pre quiz

1 What’s happening in the

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UNIT

context

3.1 When you think of ‘germs’ you probably only think of something invisible that can make you sick. Germs, however, are living things: they need food and somewhere to live, they reproduce and eventually they die. Scientists have developed ways of studying and classifying germs. New and improved microscopes have led to many exciting discoveries about these invisible organisms, which can be both our friends and our foes.

Microbes The scientifically correct term for ‘germs’ is microorganisms, which is often shortened to microbes. Microbes are singlecelled living organisms that are usually too small to be seen with the naked eye. Figure 3.1.1 shows rod-shaped bacterial microbes sitting on the tip of a pin. A non-living object such as a pin that can carry diseasecausing microbes is called a fomite.

There is a large variety of microorganisms, which scientists classify into five groups: bacteria, fungi, protozoa, algae and viruses.

Prac 1 p. 62

Observing microbes Scientists who study microorganisms are known as microbiologists. They carry out a wide range of tasks using specialised equipment and simple experimental techniques.

Poo on your toothbrush! One scientist in the USA has found that if you flush the toilet with the lid up, bacteria from your poo will be released into the air. There they will float around for up to an hour before dropping and settling upon something … maybe your toothbrush!

Fig 3.1.2

Coloured scanning electron micrograph of rodshaped bacteria on the tip of a household pin

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That stinks! The number of microbes in and on your body is larger than the number of human body cells that you are made of! The intestines contain more bacteria than the total number of people who have ever lived. Each gram of poo (the correct term is faeces) you produce contains 100 000 000 000 microbes. This means that human adults poo their own weight in bacteria each year!

Fig 3.1.1

Microbiologists commonly use petri dishes. Petri dishes are used to grow or culture microbes for study and experimentation. Here bacteria are being collected from a petri dish for further testing.

Microbes are very, very small—normal units such as the metre and even the millimetre are far too big to measure them. Instead, other smaller units based on the metre are used. To understand these units, you need to know their conversions:

Metric units of length

Fig 3.1.3

Metric unit

Meaning of prefix

Metric equivalent

1 kilometre (km)

k = kilo = 1000

1000 m

1 metre (m)

no prefix needed

Standard unit of length

1 centimetre (cm)

c = centi = 1/100

0.01 m

1 millimetre (mm)

m = milli = 1/1000

0.001 m

1 micrometre (µm)

µ = micro = 1/1 000 000

0.000001 m

1 nanometre (nm)

n = nano = 1/1 000 000 000

0.000000001 m

UNIT

3 .1 Parts of a light microscope eye piece (ocular lens)

barrel

objective lens stage

The comparative sizes of a range of items are shown in the table below. Different types of microbes are shaded.

diaphragm light

clips arm coarse focusing knob fine focusing knob

Relationship between sizes of various objects and microbes base

Object

Size

Method of viewing

Kelp

1 metre (m)

Human eye

Red algae

10 centimetre (cm)

Human eye

Fungal hyphae

1 centimetre (cm)

Human eye

Fungal spore

1 millimetre (mm)

Human eye

Protozoa

100 micrometre (µm)

Light microscope

Bacteria

1 micrometre (µm)

Light microscope

Virus

100 nanometre (nm)

Electron microscope

Large molecules

1 nanometre (nm)

Electron microscope

Electron microscopes (see Figure 3.1.4) are used to view objects that are smaller than 0.2 millimetres, such as viruses or cell organelles. They magnify in the range of 10 000 to 100 000 times. The only problem is that the images made are black and white, and live specimens cannot be viewed. Sometimes the images are coloured to highlight features.

Microbes range in size from a tiny 0.000001 metre (1 micrometre) for a protozoa to an even tinier 0.0000001 metre (100 nanometres) for a virus. Although they are microbes too, many fungi such as mushrooms are large enough to be seen easily with the naked eye.

Microscopes There are many types of modern microscopes that can be used to view microbes. Figure 3.1.3 shows a typical light microscope that is capable of magnifying 40 times using low power or 400 times using high power.

Prac 2 p. 63

A microbiologist using an electron microscope

Fig 3.1.4

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What is a microbe?

Belches and farts!

Bacteria A bacterium is a simple cell that is made up of a cell wall, cell membrane and cytoplasm. Bacteria do not have a nucleus like animal and plant cells. Some bacteria have tails, known as flagella, for movement. A typical bacterial cell

Fig 3.1.5

flagellum

cytoplasm

cocci

cell membrane

spirilla

cell wall

The human body is home to many bacteria—inside and out. Bacteria live in your nose, on your skin, in your blood and intestines—everywhere! Many of these bacteria do not cause you any harm and actually help you stay healthy. They help stop other harmful bacteria invading by taking up the available space. Other bacteria are less friendly: Zits! those under your arms cause body Staphylococcus aureus on odour and those in your mouth can bacteria normally live the skin and in the nose, cause bad breath,

throat and large intestine. But if these bacteria build up in a blocked skin pore, pus forms and the result is a zit!

Bacteria come in many sizes and shapes. The three basic shapes are cocci (spherical), bacillus (rod-shaped) and spirilla (spiral).

Depending on the microbes involved, the result of digestion may be waste gas. Methanogens are bacteria that live in the intestines and which produce carbon dioxide, hydrogen and methane gas. These microbes can produce up to two litres of gas each day, which then exits the body in some unpleasant way!

Pimples are caused by bacteria infecting the skin.

bacilli

Fig 3.1.7

Common shapes of bacteria

Fig 3.1.6

This spiral bacterium (shown in blue) is normally found attached to the wall of a person’s intestine (pink).

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Fig 3.1.8

Yum, tasty bacteria! Not all bacteria leave a bad taste in your mouth. Many bacteria, such as Lactobacillus acidophilus and Lactobacillus casei are used to make yogurt and drinks such as Yakult, while other bacteria are used to make cheese.

UNIT

3 .1 others are poisonous. Moulds grow on decaying food and damp surfaces such as bathroom walls. We use yeast to make foods and drinks like bread, cereals, wine and beer. Although fungi often look like plants they are not. They feed on dead and decaying material, helping to return nutrients to the Prac 3 p. 63 natural cycles of the environment.

Protists

Fig 3.1.9

Protists (sometimes called protozoa) are singlecelled organisms that live in water and areas of high moisture. If you look at a drop of pond water under the microscope you are likely to see some amazing protists. Some protists, such as euglena, are plant-like because they contain chlorophyll and make their own food. Euglena move rapidly using their whip-like tails or flagella.

Yakult contains a high concentration of beneficial bacteria.

Fungi There are a huge variety of fungi that you come across in your daily life. Mushrooms and toadstools are probably the best known fungi and come in many colours, shapes and sizes. Some are edible while

Prac 3 p. xx

a

c

Fig 3.1.10

b

d Different types of fungi: a Fungi on a rotting log; b Toadstool; c Mould on a lemon; d Bread mould close up

Euglena are plant protists. These are magnified x90 under a light microscope. Note the green chloroplasts in their cells and flagella for movement.

Fig 3.1.11

Amoeba and paramecium are examples of singlecelled animals that catch and eat their own food from the water around them. Paramecium have tiny hair-like cilia on their outside that beat back and forth, allowing them to move. Amoeba have no definite shape, and flow rather than swim. An amoeba extends a part of its cell body outward in the direction that it wants to move. The cell contents flow into this part of the cell. The part of the cell that extends outwards is called a false foot or pseudopod. Giardia and cryptosporidium are two protists that can cause diarrhoea, vomiting and severe illness. They are commonly tested for in drinking water, the results

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What is a microbe?

A typical virus

Fig 3.1.13

protein coat

chemical with instructions for making new viruses

a

Fig 3.1.12

b Animal protists under a light microscope: a Amoeba at 85X showing the false feet; b Paramecium

being recorded as the number of microorganisms found in each 100 litres of water. Chlorine kills these protists and chlorine levels are increased in drinking water if these microbes are discovered. Prac 4 p. 63

Viruses Virus is the Latin word for ‘poison’— viruses cause many illnesses. Viruses are much smaller than other Mad Cow Disease Some diseases are not microbes and must be viewed under caused by microbes at the electron microscope. Viruses all. Prions are pieces of are unlike other living things. Their are and in prote infectious responsible for diseases structure consists of a protein coat such as Mad Cow Disease. surrounding a chemical that contains Cows with this disease the instructions for building a new seem to go mad as parts virus. This chemical is commonly of their brain stop working. This protein can be known as DNA or RNA. The protein transferred to humans if coat is able to take on many shapes. they eat infected beef. Brain The polyhedral shape shown in damage is usually severe. Fig. 3.1.13 is very common.

UNIT

3.1

Fig 3.1.14

Worksheet 3.1 The size of microbes

[ Questions]

Checkpoint Microbes 1 Define the term ‘microbe’. 2 State whether the following statements are true or false. a All microbes cause disease. b Microbes cannot be seen with the naked eye. c All non-living objects are free of microbes.

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A model of the virus that causes AIDS, showing its inner structure

Observing microbes 3 In order to observe most microbes special instruments are needed. Identify two suitable instruments. 4 State which groups of microbes are visible with the human eye and which groups are not.

Microscopes 5 Identify the main parts of the microscope in Fig. 3.1.15.

Fig 3.1.15

UNIT

3 .1 Think 16 Contrast the characteristics of a bacterium with those of a protist.

A

17 It is difficult to classify viruses as living organisms. Propose some reasons why they may be considered living organisms. 18 Identify the disease not caused by a microbe: A Mad Cow Disease C acne. B AIDS B

G

19 Identify the type of microscope used to observe: a live cells of paramecium c bacteria. b a virus

H

20 Propose reasons why a telephone handset, a computer keyboard and a computer mouse often have far more bacteria than the toilet bowl at home.

C D E

I

21 Explain why you should wash your hands after going to the toilet.

Skills F

6 Recall the magnification range achieved by the electron microscope.

22 Three different surfaces in a classroom were wiped with sterilised damp cotton buds. The cotton buds were wiped over agar jelly in petri dishes. The diagram below shows the results after the petri dishes were incubated for three days.

Bacteria 7 Modify the following statements so that they are correct. a Bacteria consist of a cell wall, cell membrane and nucleus. b All bacteria cause disease. c Bacteria have only one basic shape. 8 List three types of bacteria, based on shape.

Fungi

A desk

B pen

9 List three different types of fungi, giving an example of each. 10 Outline how fungi obtain their nutrients.

Protists 11 Define the term ‘protist’.

C door handle

12 Describe three ways that protists may move. Fig 3.1.16

13 Identify two protists that are monitored in drinking water.

Viruses 14 State whether the following statements are true or false. a Viruses contain instructions for building new viruses. b Like bacteria, viruses have cell walls. c The word ‘virus’ is a Latin word that means ‘helpful to humans’. 15 Outline two features that make a virus different from other microbes.

a Compare the three sets of results. b Draw a conclusion for the experiment. 23 Calculate the correct answer to fill in the blank space. a 1 mm = ________m b 1 ________ = 0.000000001 m c 1 mm = _________ nm

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What is a microbe?

[ Extension ] Investigate

chapter 3 and clicking on the destinations button. Select one example of each type of microbe (bacteria, fungi, virus, and protist). Research your microbes and summarise your information about each, covering the details below. Then combine your information sheets into a class reference booklet: a scientific and common names b labelled diagram c preferred environment d advantages or disadvantages of the microbe to its environment and humans.

1 a Construct an illustrated timeline showing the main events in the discovery of the microscope and electron microscope. b Outline the impact of each discovery on the understanding of microbes. 2 Construct a poster using diagrams to explain how a light microscope magnifies.

Surf 3 Research more about microbes by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting

3. 1 UNIT

[ Practical activities ] SAFETY ALERT: Check with all students whether there are any allergies to products used or produced by the experiments in this chapter. Remind students not to breathe in any products produced and to wash their hands thoroughly with antibacterial soap after each experiment.

Fun with fomites Prac 1 Unit 3.1

Aim To observe microbes found on everyday objects Equipment

Sterile petri dishes containing nutrient agar, sticky tape, permanent markers, cotton buds, antibacterial soap

Method 1 Discuss and select a range of appropriate fomite samples. Use only everyday objects such as pens, door knobs, seats, desk tops or hand rails. Warning: Do not take samples from a toilet, your mouth, other body parts or unhygienic places as this could lead to growing dangerous bacteria that can cause serious illness. 2 Expose agar plates to a variety of everyday objects. This may be done by leaving the lid off for a period of time, wiping a cotton bud on an object and then onto the agar, or pressing an object such as a leaf onto the agar.

62

3 Place the lid on the agar and seal with sticky tape immediately. 4 Write your name, the fomite tested and the date around the edge of the underside of the plate. 5 Incubate samples overnight, upside down at 35°C. 6 Observe samples without opening plates. Warning: Lids must not be removed. 7 Record results using a table which includes labelled diagrams.

Questions 1 Compare and contrast results for the range of non-living objects sampled. 2 Evaluate whether non-living objects are ‘germ’ free.

Bacteria and fungi under the microscope Prac 2 Unit 3.1

Aim To observe bacteria and fungi using a microscope

UNIT

3 .1 Pond life Aim To observe and identify some protists present in pond water

Prac 4 Unit 3.1

Equipment

Mouldy bread, agar plates from previous prac, stereo microscope, microscope lamp if needed, forceps

Pond water, droppers, monocular microscope, microscope slides, cover slips, probes, gelatin (3 g in 100 mL water), neutral red or methylene blue stain

Method

Method

Equipment

1 Set up a microscope to focus on low power. 2 Use forceps to place a small piece of mould on a glass slide. 3 Observe the mould under the microscope and draw your observations. Record the magnification used on your diagram. 4 Observe the agar plates from Prac 1 under the microscope. Warning : Lids must not be removed from agar plates.

Questions

1 Place a drop of pond water on a slide and lower the cover slip using a probe. 2 Observe protists under low power of the microscope. 3 Record your observations using labelled diagrams. 4 To aid observation, a drop of gelatin solution can be added to the slide to slow down the movement of the protists. To enhance the visibility of structures a drop of neutral red or methylene blue stain can be placed on a slide, left to dry, and then a drop of pond water added. Some common protists that you may see in pond water

1 Contrast bacterial and fungal specimens on the agar plates. 2 Compare your observations of bread mould and any fungus on the agar plates.

flagella

Prac 3 Unit 3.1

Equipment

cilla

nucleus cell wall chloroplast

Paramecium

Chlamydomonas gullet

Various types of fungus—mushrooms, food mould, yeast solution, monocular microscope, microscope slides, stereo microscope, hand lens

eye spot

pseudopodium cytoplasm

chloroplast

Method 1 Mushrooms and mould can be viewed using microscopes and hand lenses. 2 Yeast can be viewed on a microscope slide using a microscope. 3 Draw diagrams of all specimens observed and label any features you can identify.

Questions 1 Contrast each of the different types of fungus observed. 2 Describe the structural features of mould.

cytoplasm

oral groove

nucleus

Observing fungi Aim To observe a variety of fungi

Fig 3.1.17

nucleus flagellum nucleus

cell wall Amoeba

Euglena

Questions 1 Describe any features you observe that help the protists to move. 2 Given the observations made of the pond water when viewed under a microscope, evaluate the suitability of pond water for human consumption. 3 Propose a method for measuring the size of the protists observed in the experiment.

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UNIT

context

3. 2 Remember the last time you got sick? You were probably feeling okay one day and very bad the next. It is amazing how fast illness can occur once a microbe has entered your body. It is all to do with how microbes reproduce. In only a few hours a single

Bacterial reproduction Bacteria reproduce by cell division or binary fission. This kind of reproduction does not need females and males. Instead, a parent cell divides to become two identical daughter cells. Figure 3.2.1 shows Fig 3.2.1

Fully grown cell

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Bacteria dividing by binary fission

DNA copies and divides

Crosswall starts to constrict

2 daughter cells produced, identical to parent cell

bacterium can become millions! The more bacteria there are, the sicker you get. And just to make it more difficult for you, the microbes making you sick don’t want to leave: your body is the perfect home for them—warm and comfortable, with lots of food available.

the stages involved in binary fission as well as a scanning electron micrograph of a single bacterium dividing. Some bacteria can undergo binary fission in as little as 20 minutes, but most take between one and three hours to reproduce. The daughter cells divide just as quickly. If the time for reproduction is every 20 minutes, then at this rate a single bacterium will become a colony of over one million in seven hours, making you very sick! Bacteria grow and reproduce very rapidly only when the conditions are right. All bacteria need moist and warm environments—many find the core temperature of 37°C of the human body ideal. These simple growth conditions also mean that we can grow bacteria very easily in the laboratory for our own use. We also need to supply the correct food source. Your body has ways to fight bacteria and overcome infection. Sometimes, if an infection is quite bad, extra help will be needed. This is when you need to take antibiotics. Antibiotics are chemicals or drugs that kill bacteria, usually by destroying their cell walls. Any bacteria that survive, Bad breath however, will probably be The stink of morning resistant to the antibiotic. breath occurs due to bacteria building up during They will then start to the night at the back of the breed and the infection will tongue. These bacteria are continue. The antibiotic is able to reproduce more then not effective any more easily as less saliva is produced during sleep. and a new drug-resistant The recommended cure— ‘strong’ strain of bacteria morning mouthwash! will have developed.

UNIT

3.2 A fungi way to reproduce

20 min

40 min

60 min

80 min

100 min

120 min

The number of individual bacteria can increase very quickly through binary fission, even after a few generations.

1 Branch grows upward from hyphae

2 Sporangium (spore case) begins to develop

Fig 3.2.2

Fungi such as mushrooms are moulds made up of thread-like structures that have a furry appearance. In mushrooms these threads grow underneath the mushroom and into the ground, so you usually do not see them. The threads are known as hyphae. Hyphae grow into the food and digest nutrients for further growth. Fungi such as mushrooms and moulds have two ways of reproducing. 1 A piece of fungus made up of hyphae breaks off and begins to grow. 2 The hyphae produce spores. These spores form in a capsule called a sporangium that grows upwards from the hyphae. When mature the sporangium bursts open, releasing the spores into the air. Spores are able to exist for long periods of time until they find the right place to grow. They are much like the seeds of a plant. The part of the mushroom that you eat is really just a big sporangium, preparing its spores to release into Prac 1 p. 69 the air.

3 Mature sporangium contains spores

4 Sporangium bursts, releasing spores

Feeding hyphae grow into food source

Reproduction and growth in fungi

Fig 3.2.3

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Reproduction in microbes

Explosive diarrhoea!

Reproduction of protists Like bacteria, protists are able to reproduce by binary fission.

Reproduction of paramecium and amoeba

Fig 3.2.6

Some protists, such as giardia, can produce a protective capsule called a cyst. A cyst is like an egg that can survive in tough conditions. It hatches only when conditions are right for growth. This makes it difficult to remove protists in drinking water because cysts can survive water disinfecting. Symptoms of infection by giardia are stomach cramp, vomiting, explosive diarrhoea and the production of huge amounts of gas that smells like sulfur.

Paramecium

Fig 3.2.4

Under the light microscope it is easy to see the sporangia and hyphae of bread mould.

Nucleus begins division

Parent cell

Another group of fungi known as yeasts reproduce by budding. The parent cell forms a ‘bud’ on its outer surface and a copy of everything in the cell is moved into it. A cell wall then forms between the bud and the parent cell, and the bud breaks away. Figure 3.2.5 shows an example of yeast cells budding. Here it is possible to identify the parent cells, buds forming and bud scars. Prac 1

Nucleus continues to divide and cell wall constricts

Daughter cells

Amoeba

p. 69

Parent cell

Fig 3.2.5

Bud begins to form on parent cell

a

66

Nucleus begins division

a Yeast cells reproduce by budding. b The yeast cells in this image can be seen in various stages of the budding process.

Nucleus copies and divides. The bud receives a copy

Bud now becomes a separate daughter cell

Budding produces chains of cells

b

Nucleus divides

Cell wall constricts

Daughter cells

UNIT

3.2 Viruses invade! A virus is only able to reproduce inside a host cell. A host cell is any cell that the virus invades and takes over. When a virus comes into contact with a host cell, it hijacks the cell, forcing it to become a virus factory. When the host cell is full of new viruses it bursts open, releasing the viruses, which then go on to infect more cells. A virus can lay dormant—or asleep—for many years without a host cell.

Virus attaches to cell

Virus hijacks cell, making it produce new viruses

Cell bursts open, releasing new viruses. Cell is killed and viruses infect new cells

Reproduction of a virus

Fig 3.2.7

Antibiotics kill only bacteria. Consequently they do not work against viruses. Instead, our bodies have an immune system that builds antibodies to destroy the invading virus. You have very few of these antibodies when you are young, and so you get sick with all sorts of viruses such as colds, chicken pox, measles and mumps. Your body builds antibodies to fight every time a new virus enters. This takes time and you get sick. However, once you have these antibodies it is unlikely that you will get ill with that virus again. The antibodies are there and are ready to fight at the first sign of invasion. Vaccinations ‘infect’ you with

Fig 3.2.8

When you are vaccinated you may be injected with a harmless version of a virus that makes your immune system produce antibodies ready to fight the real virus.

something very similar to a virus. This could be a modified virus or a harmless virus that is very similar in shape to one that is nasty. Your body is ‘bluffed’ into making antibodies that then protect you from the real disease. You might be asking why you keep getting colds when the antibodies built from your first cold should be protecting you. All viruses can mutate, The life of a virus? making slightly different Normally living things can versions of the same virus move, feed, excrete waste, produce energy, grow, and and the antibodies made for respond to things around one version might not fight them. The only one of another version of same virus. these things that a virus can do is reproduce, and it Unfortunately, the cold virus needs to take over a living mutates very quickly. This cell to do it! Because of means that although you are this some scientists argue that viruses are not living. probably safe from last year’s Others say they are. What version of the cold, you do you think? could catch this year’s ‘new improved’ version. Worksheet 3.2 Bacterial growth

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Reproduction in microbes

UNIT

3.2

[ Questions ]

Checkpoint Bacterial reproduction 1 Define the following terms: parent cell, daughter cell, antibiotic. 2 Construct a diagram to describe the process of binary fission. 3 Identify two benefits that binary fission give bacteria and their reproduction. 4 Outline the conditions needed for bacteria to grow.

A fungi way to reproduce 5 Draw a labelled diagram to demonstrate the structure of fungi. 6 Outline the role of the hyphae. 7 Outline two ways in which fungi can reproduce. 8 Describe the stages of budding in yeast.

Reproduction of protists 9 Copy and modify the following statements so that they are correct: a Protists reproduce by a process known as budding. b Cysts kill protists c Water that contains giardia is safe to drink. 10 Draw a diagram to demonstrate how amoeba reproduce.

Viruses invade! 11 Define the term ‘host cell’. 12 State whether the following statements are true or false: a The host cell is able to destroy a virus. b Viruses can reproduce only within a host cell. c A host cell makes copies of the virus before bursting open. d Antibiotics can kill a virus. 13 Outline why: a you probably won’t get chicken pox if you’ve already had it b vaccination can protect you from getting ill from a virus.

Think 14 Microbes have survived and flourished over billions of years. Propose a reason for their success. 15 If microbes are able to reproduce so rapidly, propose reasons why they have not overrun the planet.

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16 State whether the following statements are true or false. a Viruses and bacteria reproduce in the same way. b Yeast reproduces using binary fission. c Bacteria grow best on moist rather than dry skin. 17 Compare viral and bacterial reproduction. 18 Chicken meat sitting out of the refrigerator for a short time can be safe to eat, but after only a few hours on the bench it may no longer be able to be eaten. a Explain why this is the case. b Explain how a refrigerator helps keep food fresh. 19 You see only a small part of the organism when you look at a mushroom. Explain why.

Analyse 20 The amount of bacteria in saliva samples before and after using various mouthwashes was determined by collecting saliva and growing colonies on agar plates. The plates were incubated for 48 hours at 37°C and the following results were recorded. Colonies counted before using mouthwash

Colonies counted after using mouthwash

Mouthwash 1

25

10

Mouthwash 2

11

14

Mouthwash 3

9

6

a State an aim for the experiment. b Identify which mouthwash was not effective in reducing bacteria. c Propose reasons why this mouthwash increased the amount of bacteria in saliva. d Draw a conclusion from the data about the most effective mouthwash.

Skills 21 a If a single bacterium reproduced every 20 minutes, calculate how many there would be after two hours. b Construct a line graph showing the number of bacteria formed each half hour for two hours. c Use the graph to explain why bacteria can make you sick within one day. d Use the graph to predict the bacterial population after five hours.

UNIT

3.2 [ Extension ] Investigate

Action

1 Bacteria and protozoa can cause food poisoning in humans due to their fast rate of reproduction. Investigate a microbe that causes food poisoning and: a describe the conditions that may cause bacteria to grow to levels that cause food poisoning b outline the main ways that food poisoning occurs and how microbes are transmitted between people and food c outline how to handle food in order to avoid food poisoning d present your information as a brochure to teach people about how to avoid food poisoning.

2 Plan an excursion, or obtain information, from Sydney Water, or your local town water supplier in order to identify the measures taken to stop microbes contaminating the water supply.

3.2

Creative writing Write a short story about a microbe and its reproduction. Compile the stories written by each class member and present information as a book with a collective title.

UNIT

[ Practical activities ] SAFETY ALERT: Check with all students whether there are any allergies to products used or produced by the experiments in this chapter. Remind students not to breathe in any products produced and to wash their hands thoroughly with antibacterial soap after each experiment.

Prac 1 Unit 3.2

Fungal reproduction

Budding yeast

Aim To observe the stages of fungal reproduction

Aim To observe yeast cells reproducing by the process of budding

Equipment Samples of mould, forceps, glass slides, stereomicroscopes, disinfectant

Method 1 Using forceps, place small samples of mould on a microscope slide. A cover slip will not be required. Warning: Avoid inhaling or skin contact with moulds as they can cause allergies and/or disease. 2 Using a stereo-microscope, examine the mould for evidence of spores and mycelia. 3 Draw a diagram that shows as much of the structure of fungi as possible. 4 Clean your hands and working area with disinfectant.

Questions 1 Use your results to explain the stages in fungal reproduction. 2 Outline the advantages of this type of reproduction.

Prac 2 Unit 3.2

Equipment Freshly made yeast/sugar solution, microscope slides, cover slips, probes, droppers, tissues, microscopes

Method 1 Add a drop of yeast/sugar solution to the microscope slide. 2 Gently lower a cover slip onto it using the probe. 3 Draw out excess yeast solution using a tissue. 4 Focus the microscope slide under low power, then increase to high power. 5 Find an area to view and draw five different examples of yeast budding.

Questions 1 Which type of microorganism would you classify yeast as? 2 Explain why sugar was added to the yeast solution. 3 Use your results to explain how yeast reproduces. 4 Based upon observations in this experiment, evaluate budding as a means of reproduction.

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UNIT

context

3.3 Microbes are not all bad—they can actually serve us well. Bacteria can provide us with food and drinks. They help garbage and compost to decompose, and they keep the soil fertile. They are even used to make some very important medicines and scientists are trying to find ways of making viruses that can enter cells and help cure diseases such as cancer!

Good and bad bacteria Compost bins are amazing: all sorts of vegetable food scraps are thrown in and they break down into compost for the garden. Bacteria helps to break down matter that was once living or was once part of a living organism. This decomposition occurs everywhere: in the garden, in the soil, in decaying animal remains and in the waste of animals. Decomposition is important for two reasons. It returns nutrients to the soil that can then be used by plants and it rids the Earth of dead plants, animals and their waste. Imagine the Earth if nothing decomposed! Everything that has ever died would still be here! All their waste would be here too!



Fig 3.3.1

70

Bacteria and fungi help break down food and garden waste in compost.

It would be fair to say, however, that protists and viruses are more foe than friend, as they are responsible for a large number of diseases.

Bacteria are used in the treatment of industrial waste and to break down human faeces in sewage. Scientists are trying to find bacteria that can break down oil, so that they could then be used to clean up oil spills. Decomposition is not always a good thing. Bacteria will begin to decompose and ruin food if you leave it out of the fridge for too long. As they work, the bacteria produce toxins (or poisonous chemicals). If you eat the food, these toxins can make you violently ill. This is known as food poisoning.

Fig 3.3.2

Keeping food in the refrigerator slows down the growth of bacteria and reduces the risk of food poisoning.

Some bacteria can destroy food while others are used to make it. Yogurt, yogurt drinks and cheese all need bacteria in their production. To make yogurt, bacteria are added that use the sugar in the milk as food, turning the milk sour. Yogurt is often sweetened to take away the sour taste of natural yogurt. The right bacteria must be chosen as there are bacteria that cause food such as milk to go sour, but taste terrible and may cause food poisoning.

To make cheese, rennin (a chemical from a sheep’s stomach) is added to milk, causing it to clot and form curds and whey. The solid curds are removed from the liquid (whey), by filtering. The curds are ripened by the addition of bacteria or fungi that feed on the curd, giving it flavour. The holes in Swiss cheese are caused by bacteria releasing gas as they Prac 1 p. 75 ripen the cheese.

The friendly peanut In agriculture, bacteria assist with the supply of nitrogen in the soil. Nitrogen is used by plants for growth and so is very important. Nitrogenfixing bacteria take nitrogen from the air and put it in the soil in a form that plants can use. These bacteria often live in nodules on the roots of plants such as beans, peanuts and native wattle trees.

Bacteria are used to produce many foods.

Fig 3.3.3

UNIT

3 .3 Bacteria can be used to produce hormones for medical purposes and some drugs, such as insulin for people with diabetes. They can also introduce resistance to disease in plants. Since the discovery of antibiotics, medical science has found ways to cure many of the diseases caused by bacteria. A minor but infected scratch was once quite deadly, since nothing could stop the infection from spreading. With antibiotics, few people now die from these type of bacterial infections. The Black Death Antibiotics have almost In the 1300s Europe’s population eradicated many serious was devastated by a plague known as the Black Death, so bacterial diseases and plagues called because of the purplishsuch as the Black Death. A black appearance of the skin of disadvantage of antibiotics, its victims. It took 500 years for Europe’s population to return to however, is that bacteria can the level it had been before the become resistant to them and plague hit. Strange methods were therefore even more deadly. often used to ward off the illness,

including such practices as monks whipping themselves in village squares. The real culprit, bacteria transmitted by fleas living on rats, was yet to be discovered.

Bacteria carried by fleas caused the plague or Black Death, which killed one-quarter of the population of Europe. Antibiotics have controlled this bacterial disease but outbreaks still sometimes occur.

Fig 3.3.5

Fungi to eat, fungi that kill Fig 3.3.4

Antibiotics are able to kill a large number of bacteria. Unnecessary use and incomplete use can lead to the breeding of drug-resistant bacteria.

One of the most famous uses for a fungus was discovered by accident. In 1928, Alexander Fleming, a Scottish physician and bacteriologist, discovered that mould had contaminated some agar plates that he was using to grow bacteria. On closer inspection,

71

>>>

Friend or foe? Tasty truffles There are many fungi that can be safely eaten, the mushroom being the most common. There are many different types of edible mushrooms and the truffle is by far the rarest and most expensive. Highly prized by chefs for their unique flavour, truffles grow beneath the ground and only at certain times of the year. Because they are hidden from view, trained sniffer pigs or dogs are used to find the truffles. The truffles look more like a lump of dirt than a fungi, but they taste fantastic!

Fleming noticed that the bacteria around the mould had stopped growing. The mould was a bread mould, Penicillium notatum, commonly called penicillin. Penicillin was the first antibiotic and is now commonly used to treat many bacterial infections. Some people are allergic to penicillin, however, and penicillin is not effective for all the different bacterial infections that exist. For these reasons, many different antibiotics have been developed. Yeast is a useful fungus used in the production of bread, wine and beer. Fig 3.3.6

the glucose in fruit, vegetables or cereal grains, making alcohol as a product. Any type of fruit, vegetables or grains can be used, although grapes (producing wine), potatoes (vodka), barley (beer) and wheat (whisky) are most commonly used. Yeast will even work on the glucose in cactus to make tequila. The process is more commonly known as fermentation. Its word equation is: glucose

→ alcohol + carbon dioxide + energy

The carbon dioxide produced by the yeast causes the bubbles in beer and champagne. In wine this gas is allowed to escape before the wine is placed in a bottle.

Fig 3.3.7

The yeast on these grapes will give the wine flavour while converting sugar in the grapes to alcohol.

Prac 2 p. 76

Some breads and the yeast used to produce them

Yeasts make energy through a process called respiration in which glucose is used to produce carbon dioxide, water and energy. If the respiration requires oxygen it is called aerobic respiration and has the word equation: glucose + oxygen

→ carbon dioxide + water + energy

This is what occurs in yeast in the making of bread. It is the bubbles of carbon dioxide produced that cause the bread to rise and give it a spongy look. Anaerobic respiration occurs in the absence of oxygen. Under these conditions, yeast will feed on

72

The bubbles in champagne are caused by the build-up of carbon dioxide gas from the respiration reaction of yeast and the glucose in grapes.

Fig 3.3.8

Fungi are not always friendly. They are responsible for quite a range of fungal diseases. Some examples, shown in Figure 3.3.9, include thrush, tinea (sometimes called athlete’s foot) and ringworm. Fungal diseases are usually easily treated with antifungal powders or creams.

UNIT

3 .3 Viruses The self-destructing potato Geneticists have created a potato that can self-destruct in the face of its fungal enemy. If the fungus attacks, the potato sacrifices itself and takes the fungus with it, preventing it from spreading.

If a human, animal or plant gets sick, it is usually because a virus has invaded it. Billions of dollars are spent each year on learning more about viruses and ways to control them. The flu (influenza) is one example of a common disease caused by a virus. Some beneficial uses for viruses are now being investigated. Recently in a medical breakthrough, a virus was injected into a brain tumour in a human. The virus killed the cancerous cells, reducing the size of the tumour, and the person survived. Who knows what other great ways viruses may be used in the future? Worksheet 3.3 Preserving foods

Fig 3.3.9

a Severe oral thrush. b Athlete’s foot between the toes. c Ringworm

a

UNIT

3.3

Worksheet 3.4 Disease

b

c

[ Questions ]

Checkpoint Good and bad bacteria 1 State whether the following statements are true or false. a Bacteria are always harmful. b Decomposing bacteria help break down food waste to form compost. c Nitrogen-fixing bacteria help plants to grow by supplying nutrients to the soil. d Yogurt is made using bacteria but cheese is made by a virus. 2 List two ways that bacteria benefit human society.

Fungi to eat, fungi that kill 3 a List three types of useful fungi. b Outline how each fungi is used.

4 Modify the following statements so that they are correct. a Penicillin is an antibiotic that is produced by a yeast. b Alcohol is produced by aerobic respiration of yeast. c Thrush, tinea and ringworm are caused by the same fungi. 5 a Construct a word equation for aerobic respiration. b Construct a word equation for anaerobic respiration. c Identify which of these equations is also called fermentation.

Viruses 6 Outline how viruses might be used to actually benefit humans. >>

73

Friend or foe?

Think 7 Compare the word equations for aerobic and anaerobic respiration, outlining at least two differences. 8 Wine is produced by fermentation. Outline the requirements and products of this process. 9 Explain how a microbe is useful in each of the following cases: a making bread b making yogurt c making wine d treating sewage e composting.

>>> 12 From what you have learnt about the reproduction of viruses in the previous unit, predict how a virus injected into a tumour will kill the cancerous cells. 13 Wine and champagne are both produced by fermentation. Explain why wine has no bubbles, but champagne does.

Analyse 14 All cheeses are made with bacteria, yet they have many different styles and flavours. Explain how this is achieved.

10 Explain why bread appears frothy.

15 a Outline some effects on society of disease-causing microbes. b Present two examples to support your answer.

11 Propose how bacteria could be useful in cleaning up oil spills.

16 Evaluate overall whether microbes are friends or foes to society.

[ Extension ] Investigate

Surf

1 Choose one particular type of cheese that is made using a fungus. a Research how the cheese is made. b Construct a poster explaining the steps in making the cheese. c Outline the role played by the fungus in developing that type of cheese. d Explain how the temperature affects the product. e If the cheese is hard or soft, explain how this is accomplished.

6 Find out more about the Black Death by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button. a Describe three things that people of the time suspected were causes of the Black Death and the actions that were taken to avoid the disease. b Take a pilgrimage during the time of the Black Plague at the link supplied above. Describe the outcome of your journey.

2 a Research how yogurt is made and outline the steps involved. b The milk used to make yogurt is chemically changed. Explain the chemical change using equations, and clarify the role and type of bacteria needed to make yogurt. 3 Investigate a disease caused by microbes, such as influenza, AIDS, hepatitis or polio. You teacher will give you many other examples. Produce a report outlining the cause, symptoms and signs, cures and treatments.

Action 4 Organise an excursion to a factory or institute that makes cheese or yogurt. 5 Use antibiotic test rings and agar plates to design experiments testing the effectiveness of antibiotics.

74

Creative writing Imagine that all of the world’s decomposing microbes have disappeared. Write a story in order to describe what the world has become.

3. 3

UNIT

3 .3 UNIT

[ Practical activities ] SAFETY ALERT: Check with all students whether there are any allergies to products used or produced by the experiments in this chapter. Remind students not to breathe in any products produced and to wash their hands thoroughly with antibacterial soap after each experiment.

Getting cheesy Prac 1 Unit 3.3

Aim To model the process of cheese making by making curd cheese Equipment Culture of microbes, rennin, 500 mL pasteurised milk, lemon juice, disinfectant, thermometer, sieve, muslin, cotton scissors

6 Strain the contents of beaker A into a 20 cm square of muslin placed in a sieve. Tie the corners of the muslin and hang in refrigerator until next lesson. Alternatively, strain the contents as shown in Figure 3.3.10. 7 Repeat with beaker B, using a new piece of muslin. 8 Next lesson strain beaker C through the muslin. 9 Open and compare the three muslin bags containing samples of curd cheese.

Method 1 Place the milk in a clean beaker and heat to 40°C.

Warning: Do not taste cheese as contamination is likely under school laboratory conditions.

2 Divide the milk evenly into three 250 mL beakers. 3 Add 15 mL of lemon juice to beaker A and leave for 15 minutes.

Questions

4 Add 5 mL of rennin to beaker B and also leave for 15 minutes.

1 Compare and contrast the three samples of curd cheese.

5 Add the cultured microbes to beaker C when it is at 30°C and leave overnight at 30°C. Disinfect all surfaces in contact with microbes and wash hands.

2 Propose reasons why rennin and lemon juice make the cheese curdle. 3 Identify ways in which this experiment models real cheese making.

solid cheese

rubber band

muslin cloth filter

liquid beaker

Fig 3.3.10

75

Friend or foe?

Bread making Prac 2 Unit 3.3

Aim To identify a suitable temperature for the action of yeast in bread making Equipment Yeast suspension, sugar, flour, a range of beakers and measuring cylinders, stopwatch, balance, graph paper

DYO

Method 1 Research the most effective temperature for yeast production. 2 Construct a hypothesis to test the aim. 3 Design a method, including such things as: • which temperatures should be tested • how to keep the experiment at the chosen temperatures • what equipment will be required (Hint: Think about how the measuring cylinder would be useful.) • which measurements would be helpful to enable the results to be graphed (Hint: Think about a way of having a dependent variable and an independent variable.) • what quantities of flour, sugar, and yeast suspension to use • how to record and plot your results on a graph.

>>> Chapter review [ Summary questions ] 1 Define the following terms: microorganism, budding, binary fission, fermentation, antibiotic, mould, flagella, fomite, decomposition. 2 Modify the following statements so that they are correct. a Protists are many-celled animals found in water. b Light microscopes are used to study viruses. c Yeast reproduces by means of binary fission. 3 Use an example and equation to clarify the term ‘anaerobic respiration’. 4 Construct a diagram to show fungal reproduction. 5 Microbes are studied by growing cultures on agar in Petri dishes. Outline three safety precautions required for such experiments. 6 Outline one use for each type of microbe. 7 Identify two types of microscopes that would be suitable for observing fungi. 8 Copy and complete the following table to summarise how microbes reproduce. Microbe type

You may need to do some pretests to work out some of this information accurately.

Questions 1 Analyse the graph(s) and describe any patterns that seem evident.

Example

Method of reproduction

E.coli Fungi Protist

Budding Amoeba Influenza

2 Discuss your results and decide whether the hypothesis written has been proven or disproved. 3 Discuss any steps taken to make results reliable as well as any improvements in the experiment design to help reliability. 4 Describe how the variables were kept constant in the experiment. 5 Draw a conclusion for the experiment.

[ Thinking questions ] 9 Identify two microbes that you may expect to find in pond water. 10 Food is more likely to ‘go off’ on a hot day than on a cold one. Explain why. 11 State whether these statements about protists are true or false. a Protists can produce cysts that are like eggs. b Amoeba have cilia for movement. c Drinking water containing protists can cause diarrhoea and vomiting.

76

12 Use an example to justify how microbes can be both friend and foe. 13 Spa baths that are rarely emptied (eg external spas and those in gyms) need to have their chlorine levels regularly checked. Account for this fact given that most bacteria multiply Microbe type best at temperatures around 37°C. 14 Discuss the effectiveness of reproduction by binary fission.

Bacteria

15 Use the concept of mutation to explain why people catch colds each year.

Fungi

16 Construct a diagram to explain how a virus reproduces.

22 Copy and complete the following table to summarise the benefits and problems to society of each type of microbe. Try to use some specific examples in your summary. Benefits

Problems and cost to society

Making foods such as yogurt and cheese.

Protist Virus

17 Draw the shapes of bacteria and identify each by name. 18 Describe how yeast is used in making bread. 19 Outline how bacteria are important in ‘cleaning up’ the environment.

Cause many diseases and illness that kill many people every year. Many people miss work. costs society a lot of money in Worksheet 3.4 MicrobesThis crossword medical research.

Worksheet 3.5 Sci-words

Worksheet 3.5 Microbes crossword

[ Interpreting questions ]

Worksheet 3.6 Sci-words

20 Construct a key to classify each of the four classes of microorganisms. 21 Figure 3.4.1 shows a paramecium. Use the diagram and scale to calculate the length of the paramecium in nanometers.

0

25 µm

Fig 3.4.1

77

>>>

Body systems Key focus area:

>>> The applications and uses of science >>> Current issues, research and

4.3, 4.5, 4.8.1, 4.8.4, 4.8.5

Outcomes

developments in science

By the end of this chapter you should be able to: identify the foods required for good health list the main systems in the body that enable it to function properly describe how cells obtain their nutrients and get rid of their waste label diagrams of the digestive, circulatory, excretory and respiratory systems

Pre quiz

identify the major organs of each system and their function.

1 Why is food a little like petrol? 2 Your stomach has a very dangerous acid in it. Why isn’t this a problem?

3 What tube runs the length of your body with openings at both ends?

4 Blood is red so why do your veins look blue?

5 What is your resting pulse rate? 6 How much urine can your bladder hold?

7 What exactly does smoking do to the lungs?

4

3.1 UNIT

UNIT

context

4.1 We need fuel to be able to do all the things we want to do. For us, the fuel is food. It provides energy for movement and the production of heat, just as petrol provides energy for a car to run. A car needs more than just fuel, however. It also requires oil,

brake fluid, water and air filters. Our bodies also need other substances to maintain health and make new cells to enable growth and repair of body tissue. To maintain a healthy intake of food we need to include water, fibre and nutrients in our diet.

Carbohydrates

Water Water is an important part Six elephants During a lifetime, a human of body cells and makes up being will consume around about two-thirds of the body. 30 tonnes of food—that’s Water is a reactant in many about the same as the mass of six elephants! of the chemical reactions that take place inside us. It is also required to dissolve other chemicals, so that they can be easily transported around the body by blood. In fact, blood is almost all water (90 per cent). Lack of water (dehydration) can cause low blood pressure and become life-threatening.

These include starches and sugars, and are our main source of energy. Carbohydrates are made from carbon, hydrogen and oxygen. The body converts most carbohydrates into glucose, which is then transported to body cells for use. Excess glucose is converted to body fat and stored. Foods rich in carbohydrates

Fig 4.1.1

Fibre Fibre (sometimes called roughage) is found in the cell walls of plants such as cereals, vegetables, fruit, nuts and seeds. Though fibre is not fully broken down during digestion, it assists by providing bulk, which speeds the movement of matter through our intestines. Without fibre, undigested food would spend too much time in the large intestine, and too much water would be removed, resulting in harder, drier faeces and constipation (difficulty passing faeces). Fibre also soaks up some poisonous wastes for removal from our bodies. Research has indicated that a lack of fibre in the diet increases the risk of diseases such as bowel cancer. Processing of foods often removes fibre, which is found in the bran surrounding grains such as wheat.

Nutrients There are five main nutrients—carbohydrates, lipids, proteins, vitamins and minerals.

Lipids Lipids are fats and oils. These are a rich source of energy, containing twice as much energy as carbohydrates. Fat is stored under the skin as an energy reserve, and to provide insulation against loss of body heat. Fats contain important vitamins, and are used for making cell membranes and nerve cells.

79

>>>

Food Foods rich in lipids

Fig 4.1.2

Fig 4.1.3

Proteins Proteins are body-building compounds—the raw materials required for growth and repair of damaged or worn-out tissues (eg when a wound heals). Proteins provide only 10 per cent of the body’s energy. A lack of protein can lead to a disease called kwashiorkor, which generally affects children between 1 and 3 years old. In severe cases, muscles waste away and body fluids accumulate in the skin, causing

80

Foods rich in proteins

swelling. This is why starving children in poor nations often appear thin, but have swollen stomachs.

Vitamins Vitamins provide no energy, but are needed in small amounts to speed up various chemical reactions in the body and to maintain good health. Lack of vitamins or other nutrients can result in what are known as deficiency diseases. Excess vitamin intake can also cause problems.

Vitamin

Some sources

Important for

Deficiency may cause

A

Milk, dairy products, eggs, carrots, oranges, butter, margarine, green vegetables, fish liver oil, liver

Healthy skin, eyes, bones and teeth, lining of digestive and respiratory systems, pregnancy and foetal development

Poor vision in dim light, retarded growth, infections

B1 (thiamine)

Milk, meat, liver, kidney, wholegrain breads, wheat germ, bran, brown rice, beans, peas, nuts, pasta, fish

Helps body release energy from food

Fatigue, muscle cramps, nausea, beriberi (symptoms: muscular weakness, paralysis, heart failure), nervous disorders

B2 (riboflavin)

Milk, cheese, eggs, meat, kidney, liver, whole grains and cereals, fish, cheese

Healthy skin, eyes and tissue, helps body obtain energy from food

Greasy and scaly skin, mouth sores, poor growth

B3 (niacin)

Wholegrain breads and cereals, potatoes, eggs, liver, lean meat, poultry, fish, nuts, leafy vegetables

Healthy skin, helps body obtain energy from food

Pellagra (symptoms: skin rashes, diarrhoea, weakness, loss of appetite, mental illness)

B6

Wholegrain breads and cereals, chicken, pork, liver, fish, potatoes, eggs, cabbage, bananas

Healthy teeth and gums, red blood cells and blood vessels, helps digest protein

Weakness, poor appetite, infection, dermatitis, anaemia (lack of oxygen in red blood cells)

B12

Meat, fish, liver, milk, eggs, cheese, green vegetables

Formation of red and white blood cells, healthy nerves, skin, hair

Loss of appetite, headache, nausea, diarrhoea, fatigue, confusion, loss of memory, depression

Vitamin

Some sources

Important for

Deficiency may cause

C

Oranges, lemons, grapefruit, green peppers, blackcurrants, strawberries, tomatoes, potatoes, green vegetables

Healthy bones, teeth and tissues, wound healing

Scurvy (symptoms: bleeding gums and internal organs, easy bruising, depression)

D

Milk, margarine, butter, sardines, salmon, tuna, liver, egg yolk, also made by the body in sunlight

Helps the body use calcium and phosphorus for healthy teeth and bones, healthy nervous and immune systems

Children: rickets (symptoms: bones become soft and bend under the body’s weight) Adults: bone pain, muscle weakness, increased risk of osteoporosis, arthritis and cancer

E

Bread, butter, margarine, egg yolk, cereals, nuts, leafy green vegetables

Protects cells against damage by certain chemicals

Deficiency rare, irritability, anaemia, increased risk of heart disease, cancer, premature ageing

K

Cauliflower, cabbage, broccoli, turnip, cereal, eggs, green vegetables, pork, liver, also made by bacteria in the gut

Blood clotting, kidney function

Bleeding, bruising

Pantothenic acid

Cereals, vegetables, liver, heart, kidney, eggs, fish

Healthy red blood cells, immune system, nervous system, release of energy from food

Deficiency rare, greying of hair, decreased growth

Vitamin H (biotin)

Liver, egg yolk, peanuts, mushrooms, bananas, grapefruit, watermelon

Immune system, release of energy from food, helps the body use protein, healthy hair

Loss of appetite, dermatitis, muscle pain, decreased immunity, tiredness

Folic acid

Wholemeal bread, nuts, peas, egg yolk, mushrooms, green leafy vegetables

Healthy red blood cells, bones and hair, healthy immune, nervous and digestive systems, important during pregnancy

Increased risk of heart disease, mood and gastrointestinal disorders

UNIT

4.1

Minerals eys! Blimey—lim sailors with the is gl ges, En h

voya fruits During long e given rations of citrus er ck of w la y by av N Royal vy caused em from scur only used, and so th t ec ot pr to mm mes were co glish. vitamin C. Li e a nickname for the En m ca ‘limeys’ be

Mineral

Prac 1 p. 86

Prac 2 p. 87

Minerals are elements or other chemically simple substances that are also required for healthy growth and to avoid deficiency diseases. Minerals that are needed in larger amounts are called major elements, whereas those needed in smaller amounts are called trace elements. As with vitamins, health problems can be caused by too little or too much of some minerals.

Some sources

Important for

Deficiency may cause

Calcium

Milk, cheese, dairy products, tinned salmon, peanuts, tofu

Healthy bones and teeth, muscle contractions, heart, nervous system, blood clotting

Nerve and bone disorders, osteoporosis, rickets, insomnia

Sodium and chlorine

Table salt (sodium chloride), green vegetables

Water balance in the body, muscle contractions, transmission of nerve impulses, production of stomach acid

Deficiency rare (excess more likely); apathy, loss of appetite, vomiting, muscle cramps

Phosphorus

Milk, cereals, wholegrain breads, vegetables

Healthy bones, energy production

Weakness, loss of appetite, bone pain and joint soreness

Sulfur

Shellfish, beef, eggs, chicken, pork

Formation of keratin, a protein found in hair and nails

Beriberi, but deficiency is unlikely with a normal healthy diet

Major elements

81

>>>

Food Mineral

Some sources

Important for

Deficiency may cause

Potassium

Meat, fruit and vegetables, grilled snapper, raisins, orange juice, peanuts, ham

Water balance in the body, heart, blood vessels

High blood pressure

Magnesium

Cheese, nuts, green vegetables, whole grains

Energy, healthy muscles, bones, heart and blood vessels

Fatigue, mental and heart problems

Boron

Avocado, red kidney beans, prunes, chickpeas, raisins, apricots, red grapes

Healthy bones and joints

Osteoporosis, arthritis

Cobalt

Meat, fish, liver, milk, eggs, cheese, green vegetables

Formation of red and white blood cells; healthy nerves, skin, hair

Loss of appetite, headache, nausea, diarrhoea, fatigue, confusion, loss of memory, depression

Copper

Liver, peanuts, walnuts, sesame seeds, sardines

Healthy bones, joints, skin, blood vessels, blood cells

Anaemia, tissue defects, heart disease

Fluorine

Tap water, sea food, cereals, fruit

Helps tooth enamel to resist decay

Increased risk of tooth decay

Iodine

Water, fish, iodised table salt

Growth and development

Hyperthyroidism (overactivity of the thyroid gland resulting in cells functioning at an increased rate), goitre

Iron

Red meat, liver, cereals, green vegetables

Energy, oxygen transport in blood and storage in muscles

Fatigue, reduced resistance to infection, anaemia

Zinc

Meat, green vegetables

Energy, detoxification of chemicals such as alcohol, healthy brain, bones, teeth, skin, reproductive and immune systems

Skin problems, reproductive defects, loss of eye function, osteoporosis

Trace elements

Worksheet 4.1 Analyse this!

A balanced diet We all have our favourite foods, so why can’t we survive eating just these? The reason is Hunger hormone that our bodies need the many Hormones are chemical different nutrients provided messengers produced the When body. the by by a range of foods. We also amount of glucose in the need to eat these foods in blood drops to a certain the correct proportions. in level, the hormone insul Various dietary guidelines is released into the bloodstream. This triggers have been produced that the feeling of hunger. recommend how much of for It may take 20 minutes blood the different categories of food in levels se gluco to begin rise again after we should eat. One set of eating, so it is possible guidelines produced by the to overeat! CSIRO divides foods into

82

the six groups shown in Figure 4.1.4. It is called the 12345+ plan, and the 1, 2, 3 and so on refer to the number of daily servings that are recommended for adults from each group. As a teenagers, you have different nutritional requirements from adults. The recommended daily servings for 12- to 15-year-olds are shown below. Nutrient

Males

Females

Protein

51 grams

50 grams

Vitamin C

30 milligrams

30 milligrams

Calcium

1200 milligrams

1000 milligrams

Iron

12 milligrams

12 milligrams

Sodium

920–2300 milligrams

920–2300 milligrams

indulgences or extras

UNIT

4.1 no more than 2

No-fat water Water contains no fat nor any other food type, and so contributes zero kilojoules to your diet. Water is, however, used by the body in many ways, so try to drink at least a litre a day.

1 serve

meat and alternatives

2 serves

milk and milk products

3 serves

fruits

4 serves

vegetables

breads and cereals

Fig 4.1.4

5+ serves

Energy Energy in food We need food for energy. Just how much is provided by each particular food may be measured in experiments. Packaged foods now provide a nutrition information table displaying energy per serving and per 100 grams. If you eat food containing significantly more energy than you actually use, your body stores it as additional body fat. Many people use the energy content of foods, measured in kilojoules (kJ), as one of the guiding factors in developing their diet.

Food

Average daily energy requirements (megajoules)

The CSIRO’s recommendations for healthy eating

The recommended energy intake according to age is shown in the table opposite. A megajoule equals 1000 kilojoules or one million joules.

Age

Male

Female

10

8.6

7.8

11

9.3

8.2

12

9.5

8.6

13

10.4

9.0

14

11.2

9.2

15

11.8

9.3

16

12.5

9.4

17

12.8

9.4

Sample menus The table below gives the nutritional and energy content of a single serving of selected foods.

Energy (kJ)

Carbohydrate (g)

Protein (g)

Fats (g)

Bran cereal

298

21

4

0.5

Coco Puffs

462

25

1.5

0.4

Milk

630

11

8

8.2

Bread (slice)

294

13

3

58

3

466

26

Vitamin C (mg)

Calcium (mg)

Iron (mg)

100

15

4.5

15

5

1.8

2.3

91

0.1

1

0

18

0.9

0

0

3

1

0.05

1.7

0.1

109

27

0.2

Breakfast

Jam (teaspoon) Orange juice

83

>>>

Food Food

Energy (kJ)

Carbohydrate (g)

Protein (g)

Fats (g)

Vitamin C (mg)

Calcium (mg)

Iron (mg)

0.9

Lunch Bread (slice)

294

13

3

1

0

18

Margarine (teaspoon)

143

0

0

3.8

0

0

Can of soft drink

668

40

0.1

0.1

0

11

0.1

Biscuits (3)

588

18

2

7

0

5

0.8

Apple

340

21

0.3

0.5

7.8

10

0.3

Hamburger

1300

40

35

3

35

3.0

French fries

950

24

2.6

13

10

10

0.5

Ice-cream cone

777

30

4.3

4.2

0

183

0.1

1352

0

26.4

0

7

2.0

Spaghetti with meat sauce

886

26

8.5

8.1

5

28

2.2

Pizza (1/8 of large)

643

18

7.8

4.4

5

144

0.7

Boiled potato

487

27

2.3

0.1

10

10

0.4

French fries

950

24

2.6

10

10

0.5

Peas (1/2 cup)

281

13

4.3

0.2

11

22

1.2

95

5

0.5

0

3

19

0.4

235

15

0.6

0

3

10

0.3

15

0

Evening meal Porterhouse steak

Carrots (1/2 cup) Fruit salad

Prac 3 p. 88

Using energy The table at right shows the approximate energy used in one hour by an adult doing various activities.

Brain drain Around 25 per cent of the body’s energy is used in the ? brain. Can you suggest why

84

20

Activity

Energy used per hour (kJ)

Sleeping

250

Sitting

370

Writing

500

Walking

1000

Cycling (slow)

1000

Cleaning

1000

Jogging

1380

Running fast

1680

Dancing

1720

Heavy manual labour

1890

Climbing stairs

2770

13

Eating disorders Magazines, advertising, television and films tend to promote unrealistically thin bodies as the ideal body shape for women and overly muscular, athletic bodies for men. Unfortunately, this places unnecessary pressure on young people to try to be like this also. Although less pressure is placed on young men, the numbers of males suffering from eating disorders is increasing. There is a wide range of healthy body shapes, one of which suits you! Eating disorders can be potentially dangerous. They include: • anorexia nervosa, a disease in which sufferers unrealistically perceive that they need to lose weight and diet to the point of starving themselves to death

• bulimia, which involves binge eating followed by purging (removing recently eaten food by vomiting or using laxatives) • compulsive eating, whereby a person eats huge amounts even when not hungry. People who are more than 25 per cent overweight are described as obese. Obesity can be caused by a number of factors, including overeating and lack of exercise. These conditions may be effectively treated by seeking medical advice.

UNIT

4 .1

UNIT

4.1 16 List some factors that might affect the amount of energy your body uses.

Eating disorders 17 Describe an eating disorder. 18 Compare compulsive eating with obesity.

Think 19 Explain why most teenagers are always hungry and want to eat more often then adults. 20 Explain whether dietary requirements are different for females and males.

[ Questions ]

Checkpoint Food 1 Explain why humans need food. 2 State two substances that contain little or no nutrients, yet are essential for good health.

Fibre 3 Define the term ‘dietary fibre’. 4 Identify two foods that are rich in fibre.

Nutrients 5 Outline why each of the five types of nutrients are required, giving two examples of foods that contain each nutrient. 6 Recall the names of: a five different vitamins. b two vitamins found in bananas c two minerals found in peanuts. 7 Contrast a trace element with a major element. 8 Identify two vitamins and two minerals found in liver. 9 List the names of some foods that contain a number of vitamins. 10 State the name and symptoms of two diseases that may be caused by a lack of a nutrient.

A balanced diet 11 Outline what is meant by a ‘balanced diet’. 12 State two examples of a ‘food serving’.

Energy 13 Explain whether you would be hungrier with high or low blood glucose levels. 14 Outline one of the purposes of a sample menu. 15 Explain what is meant by the term ‘expending energy’.

21 Describe the effect pregnancy would have on a woman’s energy requirements. 22 List the following in order of energy used, starting with the lowest: cleaning, writing, dancing, sleeping, jogging. 23 Calculate how much energy an adult would use: a jogging for 30 minutes b completing a written assignment over 3 hours. 24 Account for the use of energy while sleeping. 25 Explain why the energy requirements listed in the table on page 83 (Average daily energy requirements) are only approximate. 26 Predict what happens if energy intake is less than the energy used over a period of time.

Analyse 27 Construct a simplified sketch of the CSIRO 12345+ food pyramid. 28 Use the table of food contents on pages 83 and 84 to: a construct a day’s menu containing mainly healthy foods. Add up the amount of energy and each nutrient in this menu. b construct a day’s menu containing largely junk food. Once again add up the amount of energy and each nutrient. c compare your answers (eg using a graph) for a and b and comment on the difference in energy supplied.

Skills 29 Construct a pie graph (eg using the percentage pie graph circle on a Mathomat template) showing the composition of the following foods: a meat: 13 per cent fat, 18 per cent protein, 69 per cent water and other substances b potato: 2 per cent protein, 21 per cent carbohydrate, 77 per cent water and other substances >>

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Food

c baked beans: 0.5 per cent fat, 5 per cent protein, 7 per cent fibre, 10.5 per cent carbohydrate, 77 per cent water and other substances. 30 Construct a column graph showing the approximate daily energy requirements for 13-year-olds. 31 The energy requirements of people change throughout life. Outline what you expect the changes to be between the ages of:

a 10 and 17 b 25 and 50 c 50 and 80. 32 It is recommended that a good diet should contain 55– 60 per cent of its energy as carbohydrate and less than 30 per cent of its energy as fat. Calculate how much energy you need to obtain from each source.

[ Extension ] Investigate

Create

1 a Keep a diary of the food you eat over a week and use a table of food composition from a library or other source to calculate the amount of energy and selected nutrients you consumed each day.

4 Compose a song or poem promoting a healthy diet. 5 Construct a poster showing Nutrition Australia’s Healthy Eating Pyramid.

Surf b Compare and contrast your diet with that suggested by recommended dietary allowances in food composition tables. 2 Compare and contrast the amounts of energy, carbohydrate, protein, fat, sugar and dietary fibre in various breakfast cereals.

6 Research the causes and treatment of eating disorders by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button. Summarise your findings in a creative way such as a poster or Powerpoint presentation.

3 Collect three samples (eg photos from magazines, video clips) showing how the media portray an ‘ideal’ body shape for men or women. Contrast this with magazine pictures showing other body types.

UNIT

4 .1

[ Practical activities ] Basic food tests

Prac 1 Unit 4.1

1

Aim To test for the presence of starch, glucose, lipid and protein in food eye dropper

Equipment

Starch, iodine solution, a white tile, glucose solution, Testape, watch-glass, margarine, vegetable oil, brown paper, protein solution, Albustix paper, vitamin C solution, DCPIP solution, test tube, eye dropper, spatula

Method Study the reaction in each of the following (use clean equipment for each one):

86

Fig 4.1.5

starch solution

iodine solution

white tile

UNIT

4.1 Fig 4.1.8

Fig 4.1.6 4

2

Albustix paper

Testape

protein solution

glucose solution

Fig 4.1.7 3

Fig 4.1.9 5

cooking oil

rub fat into paper vitamim C solution

Add drop by drop until a colour change appears or stop after 20 drops. brown paper

DCPIP solution

Testing various foods Prac 2 Unit 4.1

Aim To test various foods and determine the nutrients present

Describe how you could test a food for the presence of: 1 starch

Equipment

2 glucose

Samples of various foods (such as apple, cheese, milk, egg white, butter, a lolly, flour, meat, orange juice, lemon, potato, biscuit, bread), white tile, Testape, watch-glass, brown paper, Albustix paper, DCPIP solution, test tube, mortar and pestle for grinding up foods, spatula

3 lipids

Method 1 Obtain a sample of a food and divide it into five smaller samples. Test one of the samples for starch, one for glucose, one for lipids, one for protein and one for vitamin C, using the techniques outlined in the previous practical activity. Use clean equipment for each test. If necessary, grind the sample and make a food and water mixture ready to test. 2 Choose another food and, using clean equipment, repeat step 1.

4 protein 5 vitamin C.

Questions 1 Construct a table to show what nutrients each food sample contained. 2 A ‘negative’ test result for a particular nutrient does not necessarily mean that the nutrient was not present in that food. Explain why. 3 Assess which food/s contained the most nutrients. 4 Design an experiment to compare the concentration of vitamin C in particular foods.

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Food

Energy in a peanut Prac 3 Unit 4.1

Aim To determine the chemical potential energy

3 Measure the temperature of the water in the test tube.

stored in a peanut

4 Light the peanut and allow it to burn so it can heat the water in the test tube.

Equipment

Peanut, cork, pin, test tube, heat-proof mat, retort stand, bosshead and clamp, thermometer, electronic balance

5 When the peanut is completely burnt, measure the temperature of the water again.

Method

Questions

1 Use the electronic balance to measure the mass of a single peanut.

1 Calculate the rise in temperature of the water in the test tube.

2 Assemble the apparatus as shown in Figure 4.1.10.

2 It takes 42 joules of energy to raise the temperature of 10 mL of water by 1°C. Multiply your answer to question 1 by 42. The answer tells you how many joules of energy were transferred from the peanut to the water. Calculate this value.

bosshead and clamp

test tube

3 ‘The peanut actually had more energy than was calculated in question 2.’ Assess whether this statement is accurate. 4 Use your results to calculate how much energy is in a gram of peanuts. 10 mL water

retort stand

pin peanut cork

heat-proof mat

Fig 4.1.10

88

5 Specify how this experiment could be made more accurate.

UNIT

context

4.2 Sweet, salty or sour—we all love the taste of good food! Digestion begins in the mouth, where we taste all our food as we grind it up until it’s ready to swallow. Although the essential process of digestion starts off

in an enjoyable way, what happens to the food after swallowing is much less attractive. In this unit you will follow food on a journey through the digestive system.

incisors canine

Introducing digestion

molars (for grinding) pre-molars (for grinding) canine (for biting) incisors (for cutting)

Fig 4.2.1

Different types of teeth help with different tasks.

enamel crown (above gum)

When we eat, our face muscles go to work, moving our jaws so that our teeth cut and grind Animal teeth food to make it easier to digest. Sharks have up to 12 000 At around the age of 18, we teeth, organised in multiple generally have all our 32 adult rows ready to move lost ace teeth, with 16 in each jaw. There forward to repl ones. A hippopotamus has are several types of teeth, each 40 teeth, while the narwhal type suited to a particular job, has only one, in the form ing trud pro as is shown in Figure 4.2.1. n of a long hor

molars

dentine gum pulp cavity

neck

Teeth

pre-molars

tough fibres

root (embedded in bone)

Digestion is the process in which nutrients and energy are extracted from the food we eat. It occurs in a six to seven metre tube called the alimentary canal, digestive tract or sometimes simply the gut, which runs from the mouth to the anus where waste is expelled. Along the way, food is broken down into smaller, simpler substances that are able to pass into the bloodstream and travel to various parts of our body where they can dissolve in the water within the cells. It takes food about 24 hours to pass through the entire length of the alimentary canal. There are two main types of digestion: • mechanical digestion, which occurs in the mouth when food is physically broken down or mashed into smaller pieces • chemical digestion, which occurs at various stages along the alimentary canal, when special chemicals called enzymes chemically break down food.

cement nerve blood vessels jaw bone

from its forehead.

Fig 4.2.2

The structure of a tooth

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Digestion Tooth decay Tooth decay is caused by plaque—a thin film of food, saliva and bacteria that builds up on the teeth. The bacteria transform sugar into acid that seeps into the enamel and cause weak spots. If untreated, these weak spots may turn into a tooth cavity that requires cleaning and filling. Regular flossing and brushing with toothpaste after each meal drastically reduce the chances of tooth decay.

The digestive system Elephant teeth Did you know that an elephant’s tusks are actually teeth? The elephant also has giant back teeth up to 30 centimetres long and weighing 3.5 kilograms, which are used for grinding food.

The digestive system consists of the digestive tract together with several attached enzymeproducing organs. The main functions of each part of the digestive system, together with the time taken for food to pass through each section, are explained on pages 92 and 93. The digestive system produces an amazing eight litres of digestive juices per day, as is shown in Figure 4.2.4.

cavity in crown cavity becomes bigger

decay of enamel spreads into dentine decay has destroyed fibres which hold tooth to jaw bone

decay between gum and tooth

abscess on root

Fig 4.2.3

The progression of tooth decay The amount of digestive juices produced by the body in a day

If allowed to spread, decay may enter the pulp where the nerves are. Bacteria from the cavity can cause a painful infection (a toothache), and may require root canal treatment. This involves removing the pulp and disinfecting the pulp chamber, then filling with a rubber-like material to prevent bacteria re-entering the tooth.

Fluoride Scientific research has shown that fluoride helps prevent tooth decay by protecting the enamel and helping repair or rebuild the enamel. Our water supply and toothpaste contain fluoride. There has been some debate about fluoridation of water supplies, but it is now generally accepted that the benefits of a large reduction in tooth decay justify the process.

90

bile

0.8 L

saliva

1.0 L

pancreas

1.3 L

stomach

2.3 L

small intestine

2.6 L Total: 8L

Fig 4.2.4

UNIT

4.2

mouth

salivary gland

tongue oesophagus epiglottis trachea air to lungs

diaphragm

liver

stomach

gall bladder pancreas bile duct

duodenum small intestine ileum

caecum large intestine

appendix anal sphincter muscles

rectum

anus

The human digestive system

Fig 4.2.5

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Digestion

Beaumont’s window On 6 June 1822, a French Canadian soldier named Alexis St Martin was shot in the stomach. His wound was dressed and healed, but left an open hole that led to the inside of his stomach. St Martin m allowed United States army surgeon Willia ual unus this of tage advan Beaumont to take situation by studying digestion of food d. suspended through the hole by a silk threa Beaumont was able to study digestion times and stomach contractions and also identified hydrochloric acid in gastric juice.

Digestion job profile Mouth (1 minute) Digestion begins in the mouth. Food is ground into smaller particles by the teeth, mixed with saliva and made into a smooth lump called a bolus. Saliva contains water, mucus and the enzyme amylase, which begins breaking down the very large molecules of starch into much smaller glucose molecules. The water and mucus help make the bolus smooth so it moves more easily when swallowed.

Oesophagus (pronounced O-SOFF-A-GUS) (3 seconds) The oesophagus, or gullet, is a 25 centimetre tube connecting the mouth to the stomach. A bolus is moved down the oesophagus by wave-like contractions and expansions of muscles called peristalsis (imagine squeezing a marble through a section of rubber tube that is normally slightly narrower than the marble). Peristalsis pushes the bolus so hard that we can swallow food and liquids even when lying flat or upside down. Peristalsis occurs all along the digestive tract. The trachea (or windpipe) branches off the oesophagus and leads to the lungs. When food is swallowed, the top of the windpipe extends slightly, and a flap called the epiglottis folds over to cover its entrance. This stops food from ‘going down the wrong way’.

circular muscles contracted

The stomach is a J-shaped organ that has a capacity of about two litres. Muscles in the stomach churn food, helping it mix with gastric juice. This contains the enzyme pepsin, which helps break down large protein molecules and fats. Hydrochloric acid in the stomach helps the enzyme and kills harmful bacteria. A mucus lining protects the stomach from the enzymes and acid (it stops the stomach from digesting itself!). The entrance and exit of the stomach are controlled by rings of muscles called sphincters. A sphincter at the top of the stomach ensures acid and other stomach contents do not rise into the Gurgling stomach oesophagus. The one at the bottom Those sometimes protects the next part of the digestive embarrassing tract from acid and allows some (but normal) stomach partly digested, semi-liquid food noises have a technical (called chyme) to squirt out every name—borborygmos. minute or so. Next time your stomach gurgles, you might try getting some sympathy by saying ‘Excuse me, but my borborygmos is particularly severe today’.

circular muscles relaxed

food mass

Fig 4.2.6

Stomach (2 to 4 hours)

92

oesophagus

Food is kept moving through the oesophagus and other parts of the alimentary canal by peristalsis—the contraction and relaxation of circular muscles

Pancreas The pancreas is not part of the alimentary canal, but rather a 15 centimetre multipurpose ‘side attachment’. It produces pancreatic juice that contains: • more enzymes that help digest carbohydrates, fats and proteins • a chemical (insulin) that controls the amount of sugar in the bloodstream and how cells use energy. Diabetes is a condition in which the pancreas does not produce enough insulin. People with diabetes must carefully monitor blood sugar levels and the sugar content of the foods they eat. • an alkali (a liquid which neutralises the acidic stomach chyme).

Gall bladder The gall bladder, a small muscular sac about eight centimetres long, stores bile produced by the liver. It can hold about 50 millilitres of bile.

UNIT

4.2 Liver power The liver is so powerful that 90 per cent of it could be removed and survival would still be possible.

Liver An entire chapter could be written about the liver—it is a living ‘chemical factory’ and is involved in over 500 chemical processes. At 1.5 kilograms, the liver is the largest internal organ. It consists of two parts or lobes and has an extensive blood supply, which gives it a rich red-brown colour. The functions of the liver include: • the conversion of glucose (an end-product of digestion that can be used by body cells) into glycogen. Glycogen can be stored in the liver and muscles, and converted back into glucose when needed by the body. • the storage of vitamins and minerals, including iron (needed for the production of red blood cells in bone marrow) • the production of a blood-clotting chemical • the break-down (detoxification) of poisons such as alcohol • the production of around 700–1000 millilitres per day of bile, a green liquid which helps break down It takes time! fats into smaller particles that are then more easily The liver can break down broken down further by enzymes only about 10 grams of • the production of heat—the hundreds of jobs alcohol or one standard performed by the liver generate heat, which is drink per hour. Many transferred around the body by the blood. drivers who were not aware

Duodenum The duodenum is really the start of the small intestine. About ten centimetres along its length, two small tubes come together (one from the pancreas and one from the liver/gall bladder) to allow chemicals, such as bile, and enzymes to enter the small intestine.

of this have been caught by police for being over the blood alcohol limit the day after consuming alcohol.

Large intestine (10 hours to several days) The large intestine is about 1.5 metres long and six to seven centimetres wide, and is made up of five parts—the caecum, appendix, colon, rectum and anus. It is not the longest or the widest part of the digestive system but it is the bulkiest. Undigested ‘waste’ material passes into Intestinal area the large intestine, where water and a few remaining minerals are absorbed. If the inner surface of a typical human Stools (lumps of faeces) form, to be intestinal tract were expelled later from the body via the flattened out, it anus. About one-third of faeces is made would cover an area up from intestinal bacteria. Although equal to that of a these bacteria helped break down fibre tennis court! (and so reduce the amount of faeces) they also contribute to its smell.

colon

caecum

rectum

appendix

Small intestine (1 to 4 hours) With a length of four to six metres, the small intestine is the longest part of the digestive tract. It is called ‘small’ because of its narrow width of about three or four centimetres. Like the stomach, it contains muscles that churn food, and produces enzymes that continue the digestion of carbohydrates, proteins and lipids. By the time it gets to the small intestine food is broken down enough to be able to pass through the walls of the small intestine and into the villi bloodstream. The walls of the small intestine are lined with tiny bumps called villi. The villi increase small the surface area of the intestine walls, so more nutrients may pass through as digested food moves villi through. Villi contain tiny blood vessels, which carry glucose and minerals away to various parts of the body, as well as lymph Villi provide increased surface area Fig 4.2.7 vessels, which carry through which digested food can be away digested fat.

anus

Fig 4.2.8

Faeces formation in the large intestine undigested food

mineral salts and gut lining bacteria

60% water

equal parts

Fig 4.2.9

The composition of faeces

Prac 1 p. 96

Prac 2 p. 97

absorbed into the bloodstream.

Worksheet 4.2 The human digestive system

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Digestion How much gas?

Digestive gases

The average amount of flatus a person produces per day is about 1500 millilitres, in bursts of 30–150 millilitres —enough to inflate a party balloon!

When we eat, we also swallow some air. Some of this air is released from our bodies when we burp. Some oxygen and nitrogen in the air that we breathe in is absorbed into the bloodstream during digestion, and eventually passes into our lungs to be expelled when we breathe out. Bacteria in our intestines feed on undigested food, breaking it down to produce useful vitamins, as well as gases such as sulfur dioxide (better known as rotten egg gas) and methane. Acid in the stomach produces hydrogen gas, which has no odour. Luckily, sphincters stop these gases moving upwards (otherwise burps could produce bursts of very smelly or even explosive breath). Instead, they are released through the anus when we pass wind. Gas released this way is called flatus. Gas in the intestinal tract is called flatulence. Despite its bad publicity, The baked bean effect passing wind is a sign of a properly Baked beans are an ideal functioning digestive system and is a food for the bacteria that by-product of a healthy diet. the of moisten the lining intestines, causing food and gas to move more quickly, before much gas can be absorbed into the bloodstream. This results in more gas that must be released as flatus through the anus.

What happens next?

One of the main products of digestion is glucose. Glucose reaches body cells via the bloodstream, where it provides energy to cells. Cells take in glucose and oxygen, and release carbon dioxide and water as waste products, producing energy in the process. The liver converts glucose to a substance called glycogen, which is made of several glucose molecules joined together. Glycogen is stored in the liver and in muscle cells, where it may be converted back to glucose when energy is needed for movement. Since the liver and muscles can store only so much glucose as glycogen, the excess is transported to various sites around the body, where it is stored as body fat.

94

effect of this increased speed is that the large intestine has very little time to remove water from digested food. The body is at a greater risk of dehydration and waste has a higher water content. Medical research has shown that water intake should be increased to counter the lack of water absorbed when suffering from diarrhoea. Consult a doctor for the appropriate types of fluid to drink.

Heartburn Sometimes certain foods or eating too quickly can result in excess acid being produced in the stomach. This acid may occasionally rise into the oesophagus (eg when burping), causing a burning sensation. Antacid medicines and tablets partly neutralise stomach acid to relieve symptoms. You should seek medical advice if heartburn persists, as damage to the oesophagus may result from regular attacks. Another cause of heartburn may be stomach sphincters not working correctly to seal the stomach.

Vomiting Infections, extreme pain or stress can result in messages from the stomach wall being sent to the brain, triggering reverse peristalsis—contractions which force food up and out of the stomach and mouth in the direction opposite to the usual direction. Vomit usually consists of partly digested food mixed with bile, acid and enzymes and has an unpleasant taste and smell. Babies who begin to choke on milk or food may use a vomiting reflex action to clear blockages.

Stomach ulcers

Digestive disorders

If the mucus lining of the stomach becomes damaged, a sore or ulcer may result. After years of research, Australian scientist Barry Marshall announced in 1983 that many stomach ulcers were caused by the bacterium Helicobacter and not by what was previously thought to be the main cause, stress. They therefore could be treated with antibiotics. This was a major breakthrough, which revolutionised the treatment of stomach ulcers. Stress may, however, weaken the immune system, reducing the body’s defence against the ulcer-causing bacteria.

Diarrhoea

Appendicitis

One way the body gets rid of unwanted bacteria in the digestive tract is to move matter through much more quickly, to be expelled through the anus. A side

The appendix may become inflamed (eg due to a blockage or ulcers), causing severe pain and symptoms from nausea to vomiting and loss of appetite. When

this occurs the appendix is removed in an operation called an appendectomy. It was thought that the appendix had no function in humans, but recent discoveries indicate that it may be involved in the development of the immune system in babies and young children.

UNIT

4 .2

Poo transplants A Sydney doctor once treated over 60 patients who suffered irritable bowel syndrome by recolonising their bowels with ‘good’ bacteria. This was done by giving them a ‘poo transplant’, using faeces from family members not affected by the syndrome.

UNIT

4.2 Liver disease The liver may be damaged by excessive alcohol consumption or by diseases such as hepatitis. Alcohol damage may initially involve a build-up of fat among liver cells, and may lead to a condition called cirrhosis, in which areas of scar tissue form, reducing the ability of the liver to function properly. Eventually, liver failure may result.

[ Questions ]

Checkpoint Teeth

12 Describe how harmful bacteria are killed in the stomach. 13 Define the term ‘chyme’. 14 Recall three jobs performed by the liver.

1 List the mains types of teeth, and what specialist function each has.

Digestive gases

2 List the following in order, starting from the outside of the tooth: blood vessels, enamel, dentine, pulp cavity.

15 Identify three gases that may be present in the digestive system.

3 Explain whether plaque is the same as tooth decay.

16 Describe why bacteria are needed in order to produce digestive gases.

4 Describe how tooth decay can be prevented.

The digestive system 5 List the parts of the digestive system in order from start to finish. Put brackets around those parts that are ‘side attachments’. 6 Identify the part of the digestive system which: a is the longest b food stays in for the longest period of time c is like a cement mixer d contains the caecum e contains the ileum. 7 Identify the part of the digestive system in which each of the following occurs. a Poisons are broken down. b Water is absorbed. c Starch starts to be broken down. d Chyme is produced. e Bile is produced. f Peristalsis begins. g Insulin is produced. h Nutrients pass into the bloodstream. 8 Outline why the large intestine is shorter than the small intestine. 9 Outline why food does not go down ‘the wrong way’ (into the windpipe) when we eat. 10 Outline why sphincters are necessary. 11 Describe the function of enzymes.

What happens next? 17 List some final products of digestion. 18 Outline why it is important for animals to be able to store fat.

Digestive disorders 19 State the function of vomiting and diarrhoea. 20 Identify the organ of the digestive system which may enlarge due to excessive alcohol. 21 State what the production of hard, dry faeces suggests about: a the amount of water being absorbed from the faeces b the speed at which faeces moves through the large intestine.

Think 22 Account for the green colour of vomit. 23 Is heartburn really a condition of the heart? Justify your answer. 24 Explain how chewing food for longer saves digestive time in the long run. 25 Account for the fact that whereas the gall bladder can store only 50 millilitres of bile, a total of 700 millilitres of bile is produced each day. 26 Clarify what is meant by ‘reverse peristalsis’. 27 Explain why it is important that food is broken down into such small particles. >>

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Digestion

28 Explain what would happen if the small intestine was smooth, rather than covered with villi. 29 Explain why all digestive gases do not emerge as burps.

Create 30 Sections of the large intestine are sometimes named as the ascending colon, descending colon and transverse (meaning ‘across’) colon. Construct a diagram of the large intestine, labelling where you think these sections are. 31 Construct a mnemonic to help you remember how to spell ‘diarrhoea’.

3 Research the names and effects of some digestive enzymes and summarise your information in a table form. Enzymes investigated should include proteases, which break down proteins, lipases, which break down fats and amylases, which break down carbohydrates. 4 Design an experiment to investigate the effect of acid on calcium carbonate in teeth and bones. For example, test samples of bone (eg chicken bones) by placing them in various solutions and leaving them overnight or longer. Solutions to try include cola, lemonade, vinegar and water. DYO

[ Extension ]

Creative writing Trip of a lifetime

Investigate

Scientists have developed a mini camera pill containing a miniature video camera, light source and radio transmitter which patients can swallow to provide doctors with information about the alimentary canal. The ‘pill’ measures 11 millimetres by 30 millimetres, and may eliminate the need for tubes to be inserted into the body to obtain a diagnosis. Imagine you are part of the medical team receiving video pictures and sound from the pill which has been swallowed by a patient. Describe the information sent back by the pill as it travels through the patient’s body over a period of 24 hours.

1 Research the digestive systems of other animals (eg worms, sheep, cows) and compare and contrast them with that of humans. 2 Research other digestive disorders. Possible topics include tapeworms, salmonella, listeriosis, dysentery, typhoid, cholera, hernias, gallstones, Crohn’s disease, irritable bowel syndrome, cancer, giardia. a Outline the cause, signs, symptoms and treatments/ cures of the disease. b Write a journal of your day as if you had contracted this disease, describing how you feel at different times, what you have to do during the day to cope and how it affects your life.

UNIT

4. 2

[ Practical activities ] A model intestine Aim To investigate how the small intestine works

Prac 1 Unit 4.2

Equipment

2 Tie a knot in one end of each section and rub the other ends to separate them.

Two 500 mL beakers, two 20 cm lengths of dialysis tubing, starch solution, glucose solution, iodine solution, Testape

3 Fill one tube with starch solution, tie the open end and rinse with water. Place this tube in a beaker containing water and iodine solution as shown in Figure 4.2.10.

Method 1 Soak both sections of dialysis tubing in a beaker of water for a few minutes.

96

4 Fill the other tube with glucose solution, tie the open end and rinse with water. Place this tube in a beaker containing water only. Test the water with a piece of Testape.

Fig 4.2.10 (10 drops) iodine and water

UNIT

4.2 5 After 15 minutes, observe beaker A, and test the water in beaker B with Testape. 6 Write down any important observations. glucose solution dialysis tubing

Questions 1 Explain how you know when starch or glucose is present in a solution. 2 Describe the directions in which starch and glucose molecules were able to move and explain why this was the case.

starch solution

water

3 Compare dialysis tubing with the small intestine.

Fig 4.2.11

Enzyme action Aim To observe the action of enzymes on food Prac 2 Unit 4.2

Equipment Plain unsalted cracker biscuit, crushed junket tablet (rennin) in solution, three test tubes, test tube rack, three 500 mL beakers, heat-proof mat, tripod, gauze mat, Bunsen burner, thermometer

Method Part A Biscuit munching A plain cracker biscuit is a good source of starch. 1 Chew a piece of plain dry biscuit for several minutes without swallowing. 2 Note any change to the taste of the chewed biscuit.

cold

38°C

80°C

(use thermometer to check temperature)

Part B Curdling milk Rennin is an enzyme that occurs in our stomachs, In this experiment it is obtained from a junket tablet. 1 Half-fill three test tubes with cold milk. Place one in an empty beaker.

Questions 1 Describe the taste detected after chewing the cracker for several minutes.

2 Place another of the test tubes of milk in hot water and allow it to reach about 38°C.

2 Account for the change in taste of the cracker.

3 Heat a third test tube of milk in a beaker of water until the temperature reaches about 80°C.

3 Recall the name of the substance in your mouth that contains the enzyme that breaks down starch.

4 Add a third of your rennin solution to each test tube and observe.

4 Account for the temperature at which the enzyme rennin worked best. 5 Describe an advantage of curdling milk in our stomachs.

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UNIT

context

4.3 What am I? You have about 5.5 litres of me and you would die without enough of me. I can be red or blue. I fight diseases and keep your toes warm. I deliver food to, and remove waste from, anywhere in your body. I do this through a network of highways 150 000 kilometres long. I get pushed around by an amazing pump and I am a chemical cocktail like no other. What am I? I am blood!

What is blood? Blood carries water, oxygen and the nutrients obtained from digestion to cells around the body. It also removes carbon dioxide and waste material from those cells and maintains our body temperature. The average human body contains about 5.5 litres of blood made up of red and white blood cells, platelets and plasma.

Red blood cells

plasma

white blood cells and platelets

red blood cells

Fig 4.3.1

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Red blood cells are made in bone marrow. They have no nucleus, allowing them to carry more of a

Blood cells and platelets. Shown are red blood cells (red), white blood cells (yellow) and platelets (pink).

Fig 4.3.2

substance called haemoglobin. Haemoglobin attracts and carries oxygen and contains iron, which gives blood its red colour. Blood containing oxygen is bright red. Blood without oxygen is a much duller red (blue). Red blood cells last for about 100 days. One drop of blood contains about Prac 1 5 million red blood cells! p. 106

Blue bloods Not all creatures have red blood. A lobster has blue-green blood due to the copper chemicals in it. A starfish has clear, watery blood.

Blood reveals the proportion of plasma and red cells if left to settle.

White blood cells White blood cells are bigger than red blood cells, and have a nucleus. Our bodies have far fewer white blood cells that red ones. A drop of blood contains ‘only’ 3000 white cells. White blood cells help rid the body of harmful bacteria and viruses by surrounding and destroying them, or by producing chemicals to kill them.

A white blood cell engulfs a bacterium.

Fig 4.3.3

white blood cell

bacterium nucleus

Platelets Platelets are broken-up blood cells produced in the bone marrow. They have no nucleus, and help trigger formation of fibrin strands, which help blood to clot. Fig 4.3.4

Clotting blood—red blood cells trapped by tiny threads of fibrin (blue)

Antigens are special chemicals involved in fighting microorganisms in the blood. Type A blood contains antigen A, type B blood contains antigen B, type AB blood contains both and type O blood contains neither antigen A nor antigen B. The most common type of blood is type O positive or • Rhesus factor. Rhesus is another type of antigen. Blood that contains the Rhesus antigen is classified as Rhesus positive, or Rh positive. Blood without the Rhesus antigen is classified as Rhesus negative. For a blood transfusion to be safe, the donor blood must not contain any antigens that are not already in the patient’s blood, otherwise blood cells may clump together and form deadly blockages. For example, type A blood may be donated to a patient with type A or type AB blood, but not to a patient with type O blood. The Rhesus factors must also match.

O (49%)

Blood donation People weighing over 50 kilograms may donate up to half a litre of their blood at a time to a blood bank for possible lifesaving uses later on. Some people donate for the purpose of building up their own reserves in the event of an accident or surgery.

Plasma Plasma is a clear, yellow liquid in which red and white cells and platelets are suspended. Plasma is 90 per cent water. The rest is dissolved food, waste products and body chemicals called hormones. Plasma helps regulate temperature by transferring heat around the body.

Blood types There are several ‘varieties’ of human blood. For a blood transfusion to be successful, blood must be matched between the donor and the recipient. Blood can be classified by either: • blood type. Blood contains, at most, one of two types of antigen (antigen A or antigen B).

UNIT

4.3

AB (3%) A (38%)

Fig 4.3.5

B (10%)

Percentages of each blood type in the Australian population

The heart Place your right fist on the centre of your chest and let it hang there. Your Super pump fist now gives the approximate size The heart is really a and position of your heart. The heart super pump—it could fill a pumps blood around the body, beating petrol tanker with about 6000 litres of blood in at around 90–120 beats per minute one day! for children and 70 for adults, though super-fit athletes may have heart rates below 30. Nerve impulses generated within the heart trigger each beat. The heart is made of a strong type of muscle called cardiac muscle and on average pumps about 4.5 litres of blood every minute in adults, and up to 14 litres when beating more rapidly during exercise or stress.

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Blood and circulation Animal hearts An earthworm has 10 hearts, which are really just bulges in the main blood vessels, arranged in pairs down the side of its body. The human heart is really two pumps joined together that do separate jobs. Fig 4.3.6

An elephant’s heart weighs as much as eight people and beats at a rate of around 20 beats per minute, while a mouse’s heart weighs just a few grams and beats at 500 beats per minute!

An X-ray of a healthy human heart showing its shape and main blood vessels

vena cava (from the head) to head aorta to right (main pulmonary artery lung artery) (to lungs) to left lung left atrium

right atrium

semi-lunar valves

pulmonary veins (from lungs) bicuspid valve

vena cava (vein from the body)

left ventricle

tricuspid valve right ventricle septum

thicker wall than other side of heart

Key oxygenated blood

direction of blood flow

Fig 4.3.7

One pump sends blood to the lungs to pick up oxygen. The other receives the oxygen-carrying blood and pumps it to the head and around the body. Blood that is rich in oxygen is said to be oxygenated, while blood that has had most of its oxygen removed is deoxygenated. Both types of blood are red, but oxygenated blood is a brighter red. To show the difference in diagrams, blue is used for deoxygenated blood and red for oxygenated blood. The main parts of the heart are illustrated in Figure 4.3.7. It may appear that the left and right sides are labelled wrongly, but they are correct—imagine the diagram cut out and pasted onto your chest. Notice that each half of the heart, or each pump, has two main sections or chambers: the atrium, where

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deoxygenated blood

A cross-section of the human heart

blood enters, and the ventricle, where blood is pumped out of the heart. Special valves stop blood flowing or leaking back the wrong way. The walls of the ventricle are thicker than those of the atrium, as they must withstand the greater pressure associated with blood being pumped out at high pressure for another circuit around the body.

Animal hearts Fish have hearts with only two chambers. Reptiles and frogs have three—two atria and one ventricle.

Worksheet 4.3 The heart

Blood vessels

Prac 2 p. 106

The adult body contains over 150 000 kilometres of blood vessels, which are tubes in which blood is carried around the body. There are three types of blood vessels: arteries, capillaries and veins.

Arteries Arteries carry blood away from the heart to the organs, such as the kidneys and liver, and to tissues, such as the skin and muscles. Arteries have thick elastic walls to withstand the greater pressure this requires.

Cross-section of an artery artery

Fig 4.3.8 outer layer (tough fibres)

thick middle layer (muscle and elastic fibres)

lining (one layer of cells)

UNIT

4.3 Capillaries lie close to body cells and allow nutrients and oxygen to pass out and then into nearby cells. Waste products from cells pass back into capillaries to be carried away. Capillaries are the most numerous type of blood vessel one layer and service virtually of cells every tissue.

capillary

Sneaky malaria The malaria virus invades red blood cells and changes the outer surface so the cells stick to the artery wall. By doing so, the virus avoids travelling through the spleen, where it would be destroyed.

If an artery is cut, the high pressure may cause the blood to spurt and blood loss can be very rapid. A regular surge, or ‘pulse’, can be felt at several pressure points around the body. Here blood passes into arteries Prac 3 close to bones. p. 107

Red eye Flash photography often results in photographs of people with red eyes due to light reflecting from blood-filled capillaries at the back of the eye.

Fig 4.3.10

Blood flow in a capillary

Capillary

Fig 4.3.11

neck

armpit inside of elbow groin

wrist

body cells capillary behind knee cell waste ankle

oxygen

nutrients red blood cell

Fig 4.3.9

Pulse pressure points

Fig 4.3.12

Flow of materials in and out of a capillary

Capillaries

Veins

The arteries divide and connect with smaller tubes which eventually connect with fine tubes called capillaries, which are only one cell thick.

Capillaries then join with wider tubes called veins, which allow blood to return to the heart, ready to be pumped to the lungs for another load of oxygen.

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Blood and circulation

vein outer layer (tough fibres) lining (one layer of cells)

Because it is at the end of a ‘circuit’, blood in veins is at low pressure. Valves in veins stop blood flowing back the wrong way.

main vein from head

pulmonary artery (to lungs)

Bruises Bruises are caused by blood leakage from ruptured (broken) blood vessels. A bruise Vein showing a Fig 4.3.13 gradually fades from one-way valve purple to yellow to nothing as the haemoglobin is broken down and the leaked blood is eventually cleared away. valve flaps

thin middle layer (muscle and elastic fibres)

Blood pressure You may have heard people discuss their blood pressure. High blood pressure or hypertension may be caused by stress, and increases the risk of heart attack. When blood pressure is measured, two readings are taken. One is taken when the heart contracts (called systolic blood pressure), the other when the heart relaxes (called diastolic blood pressure). A typical pair of readings for adults is around ‘120 over 80’ (systolic = 120 and diastolic = 80) on the most common scale.

First aid If a wound is so severe that clotting is not occurring quickly, blood loss may be reduced by: • applying immediate pressure to the wound • raising the wound above heart level or as high as is practical • applying a pressure bandage. When calling an ambulance (phone 000 in Australia), inform the operator of the injured person’s blood type if known.

The circulatory system The heart, arteries, veins and capillaries all combine to form the circulatory system, illustrated in Figure 4.3.14, which transports oxygen, carbon dioxide, digested food, chemicals and heat around the body.

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main artery (aorta)

right atrium right ventricle

pulmonary vein (from lungs)

main vein from body lungs

artery to liver

liver

gut

vein from gut to liver

kidney

A schematic diagram of the circulatory system

Fig 4.3.14

Worksheet 4.4 The human circulatory system Worksheet 4.5 Blood flow rates

Coronary heart disease and heart attack Coronary arteries branch off the aorta and supply the heart muscle itself with blood. These can become narrow due to a build-up of fat and a chemical called cholesterol that is transported in the blood. If the narrowing reduces blood flow enough, it may lead

to a condition known as angina (insufficient supply of oxygen and glucose to the heart), the symptoms of which include pressure-like chest pain. Angina may also be triggered by exertion or emotional stress. When a coronary artery becomes blocked, the region of heart muscle it supplies dies—this is called a heart attack. The severity of a heart attack depends on the size of the area affected and the condition of the other arteries. If it is discovered that a person has a dangerously narrowed artery, the risk of a heart attack may be reduced by various medical procedures. A healthy artery and a narrowed artery

Fig 4.3.15

healthy artery

• The artery can be widened by inflating a special balloon in the affected area. • A special titanium alloy ‘sleeve’ (called a stent) can be inserted to keep the artery walls apart. • The blockage can be destroyed with a laser beam. • The blockage can be bypassed by connecting a section of vein (taken from the leg) to the artery, on each side of the blockage, creating an alternative pathway.

UNIT

4.3

Heart technology Heart valves For the heart to function normally, all four valves must operate properly. A heart valve may become defective and not allow enough blood to flow when open, or allow blood to leak back the wrong way when shut, and may be heard by a doctor as a heart murmur. Faulty valves can be replaced by artificial valves or valves taken from a deceased human donor or a pig. Since artificial valves tend to cause blood clots, anticlotting drugs have been developed to overcome the problem. Fig 4.3.17

Two types of artificial heart valves Caged-ball valve

cholesterol

narrowed artery

closed

open Tilting disc valve

closed

open

Pacemakers blocked artery

Fig 4.3.16

damaged heart muscle

The shaded region shows the area of the heart damaged due to lack of blood supply.

The heartbeat originates from special pacemaker cells at the top of the heart in the wall of the right atrium. These cells produce electrical impulses that spread to the atria and ventricles to cause the contractions which pump our blood. The electrical impulses can be shown as an electrocardiogram—ECG—on a special detector.

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Blood and circulation Fig 4.3.18

Electrocardiograms

ventricles contract

normal

atria contract

fibrillation (life-threatening)

1 second

Heart disease, stress and medication can cause the heart to beat too slowly, too fast or erratically. An irregular heart beat may be treated by implanting an artificial pacemaker, which sends its own impulses to make the heart beat properly. Canadian John Hopps, an electrical engineer, made the world’s first cardiac pacemaker in 1950 after Prac 4 extensive research in the 1940s. p. 107

UNIT

4.3

[ Questions ]

Checkpoint What is blood? 1 List five things carried by blood. 2 Construct a diagram of a red blood cell. 3 Outline the purpose of a white blood cell. 4 State the name of the part of blood that helps clotting. 5 Define the term ‘plasma’. 6 Recall the name of a gas that is carried by red blood cells.

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An artificial heart pacemaker

Fig 4.3.19

The heart 10 Outline what happens in: a the aorta b the pulmonary vein c a ventricle d an atrium. 11 Contrast an atrium with a ventricle. 12 State the name of the type of muscle that the heart is made of.

Blood vessels 13 Recall the names of the three types of blood vessels. 14 Identify the name of the blood vessel that carries blood at the lowest pressure. 15 Nutrients are absorbed into blood vessels surrounding the intestine. Recount the journey of these nutrients as they travel the circulatory system and end up being absorbed into a cell in the toe.

Coronary heart disease and heart attack

7 State which type of blood cell has a nucleus.

16 Outline what is meant by a heart attack.

8 State whether the following are true or false. a There are three antigens. b Blood may be Rh positive or Rh negative. c Blood type AB contains both A and B antigens. d Blood having no Rhesus antigen is called Rh negative.

Heart technology

9 Propose one advantage of blood being red.

19 Explain why arteries spurt when cut, but veins don’t.

17 Identify two types of heart implant.

Think 18 Explain why some people donate their own private supply of blood.

20 Account for the fact that there are two blood pressure readings.

26 Describe why the body reacts by increasing the heart rate when you get a fright.

21 Identify the parts labelled a to i in Figure 4.3.20.

27 Explain why the left ventricle has thicker walls than the right ventricle. 28 Calculate how much blood an adult heart would pump in: a a day b a week c a year d a lifetime.

Fig 4.3.20

b main _____ from head

a pulmonary _________ (to lungs)

UNIT

4.3

Analyse c main ______ (aorta)

29 Copy and complete the table below to identify which blood types may be donated to which patients. Donor’s blood

d pulmonary _________ (from lungs)

Patient’s blood

A

B

AB

A

Yes

No

Yes

B AB

e main ________ from body

O

Yes

O

f

[ Extension ]

g

h

Investigate Research some heart or blood disorders. Possibilities include leukaemia, haemophilia, angina and heart attack. Summarise your information as a web page that would inform people who have these diseases about their condition.

i

22 Explain why the heart beats faster when you are running. 23 Explain how you might minimise the chance of a heart attack. 24 Explain how paramedics sometimes restart a heart. 25 Outline why athletes are often required to have blood tests at sporting events.

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Blood and circulation

UNIT

4.3

[ Practical activities ] Blood cells under a microscope

Prac 1 Unit 4.3

Aim To examine a prepared slide of a blood sample Equipment

A pre-prepared microscope slide containing a blood sample, microscope and lamp

Method 1 Place the slide on the microscope stage, and adjust the microscope so it is just above the slide. 2 Adjust the microscope mirror and lamp so that the slide is illuminated.

3 Adjust the focus while looking through the microscope until a clear image is obtained. Remember: always move the microscope up and away from the slide. 4 Sketch the field of view using the lowest magnification. Include the magnification in your sketch. 5 Repeat using higher magnifications.

Questions 1 Describe in words what you observed. 2 Construct diagrams of what you observed.

Heart dissection Aim To dissect a heart and examine its structure Prac 2 Unit 4.3

Equipment A sheep or bullock’s heart, disposable gloves, dissection board, scissors and scalpel

Method 1 Obtain a sheep’s heart and sketch it before any cuts are made. 2 Cut a 2 cm thick disc from the ‘pointed end’ of the heart as shown in Figure 4.3.21. 3 Continue cutting layers from the heart until the heart is fully divided into 2 cm ‘layers’. 4 Sketch a selection of layers into your workbook.

Questions 1 Describe the heart you dissected. 2 Explain any differences in the thickness of the outer wall. 3 State how many chambers were observed. 4 Your heart may already have been sliced open before you dissected it. Explain why.

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Fig 4.3.21

UNIT

4.3 Heart rate Prac 3 Unit 4.3

Aim To examine the effect of activity on heart rate Equipment A watch or timer, graph paper or graphing software

Method 1 Find your resting pulse rate (pulses per minute), while standing, by counting the number of pulses in 15 seconds and multiplying the result by 4. Do this three or more times and average your results. Write down your average resting pulse rate. 2 Repeat step 1 while: a lying down b sitting. 3 Gently jog or run on the spot for 3 minutes (don’t overdo it!). Stop and immediately measure your pulse rate. 4 Keep resting and each minute measure your pulse rate until it doesn’t get any lower. Record all your results in a table like the one below.

Time after end of jog (minutes)

0

1

2

3

Fig 4.3.22

4

5

How to measure pulse rate

6

7

8

9

Pulse rate (per minute)

Questions 1 Construct a bar graph of your results for steps 1 and 2 above.

3 State how long your pulse rate took to return to normal.

2 Construct a line graph for the results in your table for steps 3 and 4.

5 Account for any differences in results.

4 Compare your results with those of classmates.

History of heart research Prac 4 Unit 4.3

Aim To research and present in a database the historical background to our understanding of blood and circulation

Equipment

You will also find useful web links by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button.

Access to the Internet, electronic database

2 Prepare a table using headings such as Date, Scientist, Discovery, Importance etc.

Method

3 Present this to your teacher for feedback.

1 Search the Internet for a historical account of the discoveries about the circulatory system and blood. When searching the Internet use phrases, such as ‘history of blood circulation’.

4 If required, redesign using your teacher’s comments. 5 Record the historical data and present in an electronic database that can be used to sort information.

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UNIT

context

4. 4 When you hear the terms ‘body waste’ and ‘excretion’, you probably think of the solid waste—faeces, which exit from the anus when we go to the toilet. As well as solid waste, however, we get rid of liquid and

gaseous waste, although we get rid of them in different ways. If your body fails to get rid of these different wastes you will become very ill.

The kidneys—our filtration plants Introducing excretion A build-up of any waste in the body can be harmful. Excretion is the removal of waste from the body. Even right now, as you read this book, you are excreting waste! You are breathing out, removing the carbon dioxide from your lungs and bloodstream. Along with water, carbon dioxide is a waste product from the respiration happening in your cells.

Kidneys are red-brown, bean-shaped organs about the size of a fist, which filter an amazing 1.3 litres of blood every minute. This is about a quarter of the blood pumped by your heart! To find your kidneys, allow your arms to dangle straight down by your sides. Your kidneys are located at about elbow level, towards the back of your abdomen.

A wee bit of information

Demonstration The limewater test Your teacher may demonstrate that carbon dioxide is excreted when we breathe out by blowing bubbles through limewater, which turns milky in the presence of this gas. Your teacher may also show how the air we breathe in contains less carbon dioxide than the air we breathe out, by using a fish tank bubbler.

Although camels only occasionally need to drink water, they drink in large quantities when they do. One way they conserve water between drinks is to produce sticky urine with the consistency of honey. roo rat is able to kanga The extract all the water it needs from the food it eats, and does not need to drink water. As a result, wastes in its urine are super-concentrated.

A waste product that is harmful if allowed to build up is urea, produced by the liver after protein has been digested. Protein is needed for growth and repair, but excess protein is broken down into simpler substances, the main one being urea. Urea passes into the bloodstream where it travels to the kidneys to be filtered out with excess water and other waste products in the blood.

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The location of your kidneys

Fig 4.4.1

Each kidney contains over a million tiny filtration units called nephrons. About one millilitre of blood per litre is filtered out as waste liquid, or urine. Urine is produced at the rate of a drop per minute, or one to two litres per day. Urine consists of about 95 per cent water and 5 per cent urea, as well as small amounts of salts and other substances such as bile, which gives urine its yellow colour.

Water loss

UNIT

4.4 Kidney stones

Sometimes concentrated substances in urine may crystallise into small, solid particles called kidney stones within the kidneys, ureters or bladder. Kidney stones can cause extreme pain. Often kidney stones will pass out of the body, though in some cases surgical procedures, based on the properties of sound, are used. They are: • ultrasound—stones are broken up and removed by the direct application of ultrasound waves • Extracorporeal Shock-Wave Lithotripsy (ESWL)— stones are shattered and are passed out of the body in the urine. No surgery is required in either method. One way to reduce the risk of kidney stones is to drink at least a litre of water every day.

About 47 per cent of a human’s water output is in urine, 31 per cent in sweat, 16 per cent is breathed out and 6 per cent is in faeces.

Kidney failure Fig 4.4.2

X-ray showing kidneys (purple, top left and right) and two ureters leading down to the bladder (yellow, lower centre)

diaphragm

kidney kidney cortex

kidney vein

kidney artery

We can lose the function of a single kidney and still continue a normal life with one healthy kidney, but if both kidneys fail, the situation is life-threatening due to the build up of poisonous wastes in the blood. In this case, options for survival include a kidney transplant or dialysis. A transplant is most likely to be successful if a close relative donates a kidney. Dialysis is the filtering of blood by a machine, and must be performed regularly (usually three times per week for about eight hours).

kidney pelvis

A dialysis machine removes waste from blood.

Fig 4.4.4

renal artery

ureter

bladder

renal vein

ring muscle

urethra

The urinary system

Fig 4.4.3

Urine travels down 20 centimetre long tubes called ureters to a muscular storage bag—the bladder, which has a maximum capacity of about one litre. However, when the bladder contains about 300 millilitres of urine, nerve sensors in its walls send messages to the brain that result in the urge to urinate—that is, allow urine to drain from the bladder out of the body through the urethra. Worksheet 4.6 The urinary system

Prac 1 p. 110

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Excretion: getting rid of wastes Excretion;

UNIT

4 .4

[ Questions ]

10 Compare the amount of urine that an average-sized bladder can hold with the amount of urine that makes you feel an urge to urinate.

Checkpoint

11 Explain why movement of a kidney stone can cause extreme pain.

Introducing excretion 1 Define the term ‘excretion’.

12 Explain why drinking lots of water should reduce the risk of a kidney stone.

The kidneys—our filtration plants

13 If someone donates a kidney to someone with kidney failure, both are left with one healthy kidney. Explain how both people can live normal lives.

2 Outline how the following wastes are produced: a carbon dioxide b water c urea. 3 Explain how waste products get to the lungs and kidneys.

Skills

4 State how much blood kidneys can filter in an hour. 5 Recall how many nephrons are in a kidney.

14 Construct a graph that shows the composition of urine.

Think

4 .4 [ Practical activity ]

6 Construct a diagram showing the approximate location of your kidneys.

Body parts circulatory kidneys ureters bladder urethra

UNIT

7 Identify the body part that matches each function. Functions filter blood allow urine to reach storage area tube which allows urine to leave the body urine storage transports wastes and nutrients

Kidney dissection Aim To dissect a kidney and observe its structure Prac 1 Unit 4.4

Equipment Newspaper, a sheep or bullock kidney, dissecting board, scalpel, disposable gloves

Method

8 Explain why people urinate more in cold weather.

1 Try to find the ureter in the middle of the kidney, and cut lengthwise as shown in Figure 4.4.5.

9 A urine sample can tell a doctor quite detailed information about your health. Explain why.

2 Sketch the inner structure of the kidney. Fig 4.4.5

[ Extension ]

1 Cut the kidney lengthwise

Create 1 Construct a crossword about the kidneys and test it on another member of your class. Your crossword should include at least 12 words. 2 Separate the two halves

Investigate 2 Research in more detail how a kidney works. Include the function of a Bowman’s capsule. Create a cartoon strip or series of diagrams to show what happens as blood is filtered by the kidneys.

Action 3 Design an experiment to investigate the effects of various foods on urine. Some suggested foods are red beetroot and asparagus.

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Questions 1 Explain the purpose of fat around the kidney. DYO

2 Compare the sheep’s kidney with a human kidney.

UNIT

context

4. 5 You can’t hold your breath for too long when you dive under water. Your body will tell you that it needs more air in your lungs. The air is needed to supply oxygen that is transported around the body by your circulatory system. The cells in your body need this oxygen for respiration.

The human respiratory system You have seen in Unit 4.3 that blood in the circulatory system carries nutrients and oxygen to cells, and waste products such as carbon dioxide away from cells. Where does the blood get the oxygen from, and where does it take the carbon dioxide to? This is the job of the respiratory system, which consists of the lungs and associated structures. You breathe between 12 and 24 times per minute, for the most part unconsciously. This rate can vary with age, physical activity and your mood. Each breath exchanges about 500 millilitres of air. The maximum amount of air you can breathe out (exhale) after taking a deep breath (inhale) is called the vital capacity of your lungs. It is normally around 4500 millilitres, but may be as high as 6500 millilitres in a welltrained athlete. The composition of inhaled and exhaled air varies, because gases are Prac 1 exchanged between the lungs and your p. 117 bloodstream.

Percentage composition of inhaled and exhaled air Inhaled air

Exhaled air

Nitrogen

79.0

79.5

Oxygen

21.0

14.0

Carbon dioxide Water vapour

0.04

5.6

Varies with location

Fully saturated

Respiration produces carbon dioxide. A respiratory system is needed to provide oxygen to, and remove carbon dioxide from, these cells.

nasal cavity epiglottis pharynx larynx (voice box) oesophagus trachea (windpipe)

bronchus intercostal muscles

lung rib

alveoli

diaphragm

Fig 4.5.1

rib

The human respiratory system

Although air can sometimes enter the respiratory system through the mouth, most inhaled air enters via the nose. Here it is filtered, warmed and moistened. Nostril hairs filter out larger particles, and tiny hairlike cilia on the inside of the nose trap fine particles. The nose is lined with mucus glands that produce sticky mucus to trap dust particles. The mucus and trapped particles move to the back of your nose and into the pharynx. We swallow around 600 millilitres of this mucus per day without usually being aware of it. From the pharynx, air enters the trachea (windpipe), a thin-walled tube with about the same

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Respiratory systems diameter as a garden hose. At the top, the epiglottis, a flap of tissue, stops food entering the trachea. The larynx (voice box) also helps stop food entering. Coughing and sneezing are both reflexes to further protect the trachea. The trachea branches into two main bronchi, which branch successively into smaller and smaller tubes. At the end of the smallest of these tubes (bronchioles), air enters clusters of sacs, the alveoli. Gas exchange in and out of the blood takes place here. The entire system of tubes is lined with cilia, which beat upwards to send foreign material back to the pharynx to be coughed out or swallowed.

The respiratory tree, alveoli and blood vessels

trachea

Smoking Tobacco smoke immediately inhibits the action of the cilia that remove mucus and foreign material. When fluid and foreign material accumulate, infection is more likely to occur. Tobacco smoke also damages the surface of the lungs where gas exchange takes place, leading to shortness of breath. Scientific research has shown that smoking increases the risk of lung cancer and heart attack later in life.

Fig 4.5.3

bronchus

bronchiole

bronchiole

alveolus

The respiratory tree—the trunk is the trachea (top, centre) that branches into the bronchi. Smaller branches (bronchioles) end in the alveoli.

Fig 4.5.2

Alveoli are sacs with walls only one cell thick. There are around 500 million of these in your lungs, with a total surface of about 80 square metres. Each alveolus lies close to the wall of a capillary. These are also one cell thick, so there is only a short distance for gases to travel between the lungs and the bloodstream. The network of capillaries in the lung is so large that at any one time 20 per cent of the total blood volume is in the lungs.

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to heart

from heart

alveolus

capillary

Inside the alveoli, oxygen moves across through the thin walls of the tiny capillaries and into the blood. Once in the blood, oxygen is carried by red blood cells in a special carrier called haemoglobin. Haemoglobin allows much more oxygen to be carried in blood than if it was simply dissolved. At the same time dissolved waste gas—carbon dioxide—comes out of the capillaries back into the alveoli, ready to be breathed out. This gas exchange is shown in Figure 4.5.4. Fig 4.5.4

UNIT

4.5 Bubbles in the blood During deep sea diving the increased pressure causes nitrogen to dissolve in the blood. If the diver returns too quickly to the surface, the reduced pressure causes the gases to form bubbles in the blood. This is similar to the way bubbles form when you take the lid off a soft drink bottle. The bubbles rupture tissues, block blood vessels and cause extreme pains in the joints, known as the ‘bends’. The condition is relieved by returning the diver to high pressure and slowly lowering the pressure. This allows the formation of small bubbles that can be removed by the lungs.

Gas exchange in the alveolus

exhaled air

inhaled air LUNGS exchange of gases CO2

O2

CIRCULATORY SYSTEM CO2

O2 CELLS

CO2

O2

respiration

Movement of respiratory gases

air forced out

air flows in

from the heart

Fig 4.5.5

ribs move up and out

capillary

ribs move down and in

red blood cells oxygen enters red blood cells

wall of the alveolus

lungs expand

air out

diaphragm contracts and is flattened

s i o n of o x y g e n

on

dio xid e

d iff u

d

o iff u s i

f no

ca

rb

moist lining

Breathing in

Fig 4.5.6 carbon dioxide leaves the blood

lungs return to normal intercostal muscles relax

intercostal muscles contract

air in

to the heart

Replacement of the air is the result of breathing. Breathing is a physical process and is clearly different from respiration, which is a chemical reaction. Normally, you breathe without thinking about it, but you can alter the rate and depth of breathing with conscious effort. Take a deep breath. Notice that your ribs move up and out. This occurs due to the action of muscles in the chest (the intercostals) and the diaphragm. The diaphragm is the sheet of muscular tissue that separates the chest from the abdomen.

diaphragm relaxes and is dome shaped Breathing out

Breathing movements

The larger space in the chest causes a pressure decrease, so air rushes into your lungs. Now breathe out. Air is forced out as the chest returns to its normal size.

Prac 2 p. 117

Worksheet 4.7 Asthma

Other respiratory systems The successful exchange or movement of gases in and out of the blood in the lungs in humans depends on several factors: • a high surface area for the exchange • a thin, moist surface for efficient exchange

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Respiratory systems • a system of transporting gases to and from cells • a means of protecting the exchange surface from damage and dehydration.

How do other animals meet these needs?

Human skin also ‘breathes’ but accounts for only 0.06 per cent of our total gas exchange between air and blood. Insects use a different system. They do not have lungs or blood vessels, but use a system of airfilled tubes for gas exchange.

Simple single-celled (unicellular) organisms can exchange gases directly with their watery surroundings through their cell walls or membranes. Many aquatic animals use gills. Flattened, worm-like animals often use their body surface for exchange. Most true air-breathers have lungs but some, like the frog, use their skin for additional gas exchange.

air sacs

trachea

openings opening CO2

O2

O2 moves in trachea

hearts

O2 CO2

branches of blood vessels

blood vessels CO2 moves out

Fig 4.5.8

Insects use a system of air-filled tubes to exchange gases.

Worksheet 4.8 Other respiratory systems

Fig 4.5.7

An earthworm exchanges gases through its skin.

UNIT

4 .5

[ Questions ]

Checkpoint The human respiratory system 1 Identify the structure that relates to each function. Structures trachea epiglottis nose cilia alveolus

Functions filters, warms and humidifies air removes foreign particles from the lungs the site of gas exchange carries air to and from the lungs prevents food from entering the trachea

2 a Recall two structures which prevent food from entering the trachea. b Describe what happens if some food finds its way into the trachea.

114

3 Recall the name of the special structures that give the lungs their very large internal surface area. 4 a Identify the part of the blood that contains haemoglobin. b Outline the function of haemoglobin.

Other respiratory systems 5 Single-celled animals exchange gases directly with their surroundings. Explain why it is necessary for larger animals to have a respiratory system. 6 Identify the structure that is suited to the organism. Structures skin and lungs/bloodstream gills/bloodstream moist body surface/bloodstream lungs/bloodstream body surface/no circulatory system air-filled tubes/no bloodstream

Organisms insect lizard fish earthworm frog single-celled amoeba

UNIT

4.5 Think 7 Outline what happens to each of the following when you breathe in: a diaphragm (contracts or relaxes?) b chest cavity (enlarges or becomes smaller?) c ribs (raised or lowered?) d intercostal muscles (contract or relax?) e pressure in the chest cavity (increases or decreases?).

a b

e

8 Explain why it is important that lungs have a large internal surface area.

c

9 Describe three features needed for effective gas exchange. 10 For each of the following gases, assess whether the proportion of the gas in exhaled air is greater than, less than or about the same as the proportion in inhaled air: a nitrogen b oxygen c carbon dioxide d water vapour.

d

h f

g

11 Explain why is it better to breathe through your nose than through your mouth. Fig 4.5.9 12 A diagram of the human respiratory system is shown in Figure 4.5.9. Identify each of the structures labelled a to h on the diagram using the following list of terms: diaphragm, larynx, epiglottis, nasal cavity, trachea, bronchus, intercostals, alveolus. 13 A diagram of part of the human respiratory system is shown in Figure 4.5.10. a b c d

X

Identify structure X. Outline the function of structure X. Identify structure Y. Outline the function of structure Y. Y

Fig 4.5.10

>>

115

>>>

Respiratory systems

Fig 4.5.11

14 The apparatus shown in Figure 4.5.11 is sometimes used as a model to show what happens when you breathe. a Identify the apparatus that best fits with the body part it represents: Apparatus plastic tube balloons bell jar rubber floor

bell jar

Body parts chest trachea diaphragm lungs

balloons deflate

balloons inflate

b Explain why the balloons inflate when the floor is pulled down. c Contrast this model with the way you breathe.

rubber floor is pulled downward

rubber floor resumes this position under atmospheric pressure

Analyse 15 Figure 4.5.12 shows a diagram of an alveolus and a capillary. a Identify which gas diffuses in the direction of A to B. b Recall what the gas joins onto when it enters a red blood cell. c Discuss whether it is better to have the gas joined to a substance in the blood, or simply dissolved in the blood.

blood from heart

red blood cell

B A

[ Extension ] Investigate 1 Whales, dolphins and seals can dive for long periods under water without coming up for air. a Research the special features marine mammals have that enable them to spend long periods under water without breathing. b Summarise your information in a table. c Propose a design for the ultimate diving mammal that can stay under water for extended periods of time. 2 The pressure of oxygen in the air decreases with increasing altitude. At 3000 metres above sea level, most people begin to experience ‘altitude sickness’. a Research what this is, and find out how highly trained mountain climbers can reach heights over 6000 metres without experiencing this sickness. b Summarise your information as a training manual that would prepare climbers for a high-altitude trip. 3 Construct a detailed report on the respiratory system of a fish, a frog or a bird.

blood to heart

Fig 4.5.12

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UNIT

4 .5

UNIT

4.5 [ Practical activities ] Inhaled and exhaled air Prac 1 Unit 4.5

Aim To investigate the gases that are in inhaled and exhaled air Equipment Flasks and glassware as shown in Figure 4.5.13, limewater

Method 1 Set up the apparatus as shown in Figure 4.5.13. Be sure to check that your set up exactly matches the diagram. Note that only one of the tubes connected to the mouthpiece extends below the level of the limewater. 2 Inhale and exhale continuously for several minutes without removing your lips from the mouthpiece. 3 Record any changes in the colour of the limewater in flasks A and B.

mouthpiece rubber tubing

4 Use a disposable straw as the mouthpiece if the equipment is to be used by more than person.

Questions 1 Explain any changes in flask A. 2 Explain any changes in flask B.

Exercise and breathing flask A (limewater)

Fig 4.5.13

flask B (limewater)

Prac 2 Unit 4.5

Comparing inhaled and exhaled air DYO

Design an experiment to investigate the effect of exercise on the production of carbon dioxide. An indicator such as alkaline bromothymol blue may be used to test for carbon dioxide. This indicator solution is normally pale blue, but turns yellow in the presence of carbon dioxide. You might time how long it takes to change the colour of the indicator before and after exercise.

117

Science focus: Spare parts Prescribed focus area: Current issues, research and developments in science Our bodies are very complicated and sometimes things go wrong or stop working. It is now possible, however, to deal with some major medical problems by removing a faulty body part and inserting a replacement. This is called a transplant. Unfortunately the number of patients needing transplants is far greater than the supply of organs from human donors. To overcome this problem scientists are researching and developing new technologies and materials they can use. This means that replacement body parts can now come from sources other than humans. Maybe in the future fixing a body will be more like buying spare parts for your car.

Rejection of spare parts The immune system helps to protect us from disease and removes foreign objects that get inside our bodies. In order for the spare parts to be implanted into a body they must not be attacked by the immune system of the person. This can be done by having the spare part made of materials that the immune system does

not respond to, or by making the parts so similar to the actual person’s cells that the immune system does not reject them. Regular doses of drugs are required for organ transplant patients to stop their bodies attacking the implanted organs.

Allotransplants Allotransplants are ‘human to human’ transplants and involve taking an organ from one person and placing it into another’s body. Organ transplants are now generally very successful but rely on a supply of suitable organs. Patients need to use drugs to stop the organ being rejected. Hearts, lungs, kidneys, livers and the pancreas have successfully been transplanted from donors who have died. Their organ donations have enabled very ill patients to recover.

Xenotransplants Xenotransplants are transplants from animals to humans. These techniques are still being developed and there are many hurdles to overcome. They usually

Bio reactors in space NASA researchers have invented a ‘bioreactor’. This device grows living cells in space. It has been found that organs and cells grow much better in a weightless environment than they do on the Earth’s surface, where gravity affects them.

Heart transplants have a high rate of success.

118

Fig SF 4.1

involve the use of animals such as pigs or sheep to grow new organs for humans. Special pigs and sheep are bred and have their cells changed to be more like human cells. This means that the human body will be less likely to attack the implanted organ. Xenotransplant causes concern for some in the community. Many people have strong views about whether organs from other animals should be put into humans, and many believe that it is wrong to kill animals for their organs. There is also a fear that viruses could be transferred between animals and humans, causing new diseases.

Organ farming This is an exciting area of research that involves growing cells outside a living human. It is often called tissue culturing. One successful example is the growing of skin for burns patients. An advantage of this technique is that the skin can be grown from the patient’s own cells, which means it is not rejected by the body.

This ear was grown on the back of a mouse using a scaffold.

Fig SF 4.3

have come from the person’s body they would not be rejected. This is an area of great Hear, hear! scientific research. For was developed in The cochlear implant e more about stem cells wid rld wo a e om Australia and has bec ple with peo ny ma see Science Focus 1, ws allo It success. particularly page 108. hearing impairments, is r for the first time. Th children, to hea microprocessor, bionic ear involves a connections and s sor sen , electronics cochlear the o int which are attached hearing for ne agi Im . ear er inn inside the rs of silence! the first time after yea

Fig SF 4.2

This artificially grown human skin is ready for transplant onto a burns patient.

Other techniques involve growing whole new organs. This requires a scaffold for the cells to grow onto. One of the early successes was the growing of a human ear on the back of a mouse. The cells used to grow new organs may be able to come from stem cells. Stem cells are special cells found in our bodies, and in embryos, that have the potential to grow into many different types of specialised cells. Cells could be taken from the body, grown into a new organ using a scaffold, and the organ placed back into the body. Because the cells

Fig SF 4.4

The cochlear implant was developed in Australia. The external part shown includes the microphone and transmitter.

119

Fig SF 4.5

Artificial body parts

Titanium plate in skull Lens implanted in the eye replaces a damaged lens

Hearing implants such as the cochlear implant Alloy jaw prothesis

Speech valve to replace larynx Pacemaker controls heart rate

Shoulder joint

Artificial transplants There are many new materials that can replace parts of the body. Even whole organs have been developed, such as the artificial heart. Because of the design of these materials they are not rejected by the body and last a very long time.

Artificial heart valves control blood flow A whole artificial heart is now available Elbow joint Myoelectric arm, controlled by computer. This arm detects movement in the remaining arm muscle and uses this information to open and close the hand

Blood vessel graft. A special tubing is sewn into the artery and cells grow over it making it part of the body Wrist joint Finger joint

Artificial hip made of cobalt and chromium

Plastic cup inserted into pelvis fits the ball of the new joint

Knee joint

Stainless steel pins in bones

120

Artificial leg with hinged knee joint. Complicated joints controlled by computer allow the leg to be adjusted to the wearer so that it acts like a real leg, allowing normal activity

[ Student activities ] 1 Research the following organs commonly transplanted from human to human and complete the table.

Organ

Body system

Role of organ in human

Possible problems/causes leading to need for replacement

Heart Circulatory Lungs Kidney Liver Pancreas

2 Research xenotransplants and produce a leaflet explaining in simple terms the issues involved in xenotransplantation. Your aim is to allow those who read it to have an understanding of: a what xenotransplants are b what potential benefits there may be to society c what potential problems and concerns are involved. 3 a Find out which materials can be used to make artificial body parts for humans by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4 and clicking on the destinations button. b Construct a poster that outlines some of the materials and how they are used. 4 a Create a simple survey of about eight questions designed to investigate people’s opinions about allotransplants, xenotransplants, tissue culture techniques and artificial body parts. Your survey should give a very short description of each of the techniques. You may include questions that focus on: i which technique the respondents might consider the best to use ii how the respondents would rate each technique in terms of where money should be spent on research in the future iii whether the respondents think that any of the techniques should NOT be used and why

iv whether the respondents would accept a transplant from an animal if their life depended on it. b Summarise your results and produce a report evaluating people’s general opinions on this topic. 5 Write a short story, song, poem or rap to describe your understanding of the use of spare parts in humans. 6 Investigate the history of heart transplants or artificial hearts and learn about the work of Dr Victor Chang or heart transplant recipient Fiona Coote. Use your information to role-play an interview with each person to teach others about heart replacements.

121

>>> Chapter review [ Summary questions ] 1 Identify the nutrient that matches each description. Descriptions High in energy. Our main source of energy. Converted to glucose during digestion. Required in small amounts for good health. Provides bulk to move waste through intestines. Required for growth. Not a nutrient, but required for chemical reactions in the body. Chemically simple, required for good health, not for energy. 2 Identify the vitamin deficiency leading to the following diseases: a beriberi b rickets c scurvy d pellagra. 3 List three: a trace elements b major elements. 4 State the name of the eating disorder involving binge eating followed by purging. 5 Recall the number of teeth an adult normally has.

Nutrients Carbohydrates Water Protein Lipids Fibre Vitamins Minerals

Fig 4.6.1 m

a

n

b o c

p d q

6 Define what is meant by the term ‘dentine’. 7 Explain the difference between a normal tooth cavity filling and root canal treatment.

e

8 Identify each part of the body system shown in Figure 4.6.1.

f

r

g

h

i

j

s

k l

122

t

9 Identify the description that matches each part of the digestive system. Parts of digestive system Oesophagus Gall bladder Small intestine Large intestine Duodenum Mouth Liver Stomach Pancreas

Descriptions Connects mouth to stomach. Digestion begins here. Like a cement-mixer for food and gastric juices. Produces enzymes including insulin. The body’s chemical factory. Stores bile. Start of small intestine. Where most absorption of nutrients occurs. Where water is absorbed. 13 Describe the function of platelets.

10 Label the following diagram.

14 Contrast angina with a heart attack. 15 Identify the substance that commonly clogs arteries. 16 Define the term ‘ECG’.

a

17 Recall what an artificial heart valve is commonly made from.

b c

d

m

l e k f g j i

h

Fig 4.6.2 11 Identify two enzymes and state where each may be found. 12 Identify the correct percentage of red blood cells normally found in blood: A less than 5 per cent B a little under 50 per cent C a little over 50 per cent D about 95 per cent.

[ Thinking questions ] 18 Modify the following statements by rewriting so that they are all correct. a We excrete when we breathe out. b Water and carbon dioxide are waste products of cells. c Your kidneys are about the size of your eyeballs. d Kidneys filter about half the blood pumped by the heart in the same time. e Urine travels down tubes called urethras to the bladder, which has a capacity of about five litres. f Drinking at least a litre of water each day increases the risk of kidney stones. g It is possible to live normally with only one kidney. 19 Compare the energy contained in fats with that in carbohydrates. 20 Contrast a sphincter with peristalsis. 21 Recall which digestive disorder might involve: a damage to the stomach lining b inflammation of a small offshoot of the large intestine c scar tissue forming in the liver. 22 Compare and contrast starch with glycogen.

>> 123

>>> 23 Identify the description which matches the blood vessel. Blood vessels vein artery capillary

[ Interpreting questions ] 25 Modify the following paragraph by rewriting it to include the correct terms:

Descriptions high pressure fine tubes near cells return blood to heart

To breathe in, the diaphragm (contracts/relaxes) and the intercostal muscles (contract/relax). This causes the ribs to move (upwards/downwards) and (outwards/ inwards). These movements (increase/decrease) the size of the chest cavity, causing the pressure to (increase/ decrease). Air then (flows in/is pushed out).

24 Identify the functions described in a to f that match structures i to vi in Figure 4.6.3: a b c d e f

filters, warms and humidifies air contracts and flattens during inspiration the site of gas exchange carries air to and from the lungs prevents food from entering the trachea passage of air through this creates sounds.

26 a The gills of a fish, the skin of an earthworm and the lungs of a bird have many features in common. Outline three of them. b Explain how each feature improves gas exchange. 27 The appropriate daily intakes of calcium, iron, sodium and protein for a Year 8 student are shown below. Identify the appropriate value for each substance.

Fig 4.6.3

2000 mg, 14 mg, 60 g, 1100 mg 28 Contrast the energy requirements of adolescent males and females. 29 State whether a person with B positive blood would be allowed to donate blood to a patient with: a b c d

i ii

A positive blood AB positive blood O positive blood B negative blood. Worksheet 4.9 Body systems crossword

vi

Worksheet 4.10 Sci-words iii

iv

v

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5

Electricity Key focus area:

>>> The applications and uses of science

identify situations in which static electricity occurs describe situations in which static electricity is useful and situations in which it is a nuisance describe what happens when charges are brought close to other charges

Outcomes

describe how objects can become charged

4.3, 4.6.3, 4.6.8, 5.6.3

By the end of this chapter you should be able to:

draw circuit diagrams for simple circuits construct simple series and parallel circuits identify where series and parallel circuits are commonly used identify where energy in a circuit comes from, and where it is used describe what is meant by ‘current’, ‘voltage’ and ‘resistance’, using analogies.

when you rub your shoes on carpet?

3 What causes lightning? 4 What is inside a battery? 5 What is AC and DC and what’s the difference anyway?

6 ‘It takes a lot of electricity to electrocute you.’ True or false?

7 What devices in the home help to protect us against electrocution?

Pre quiz

1 What is electricity? 2 Why do you sometimes get ‘zapped’

>>>

UNIT

context

5.1 Have you ever been ‘shocked’ after touching someone who has just slid down a plastic slide, or noticed a crackling sensation after you have removed your jumper over your head? These phenomena are caused by electricity—or more specifically, static electricity. So what exactly is electricity?

Are you positive (or negative or neutral)? Most objects are neutral—that is, they have no overall electric charge. Objects can become charged, however, if they rub against other objects or materials. To understand how this happens, you need to look at what is happening to the atoms. You will recall from Chapter 2 that everything is made of atoms. Atoms contain positively charged protons, negatively charged electrons and neutral neutrons. Atoms always contain an equal number of protons and electrons, and are said to be neutral. Electrons are found in the outer parts of atoms and may be moved by rubbing different materials together.

This means that they might jump from one surface to another if two are rubbed together. This causes one of the objects to have more electrons than protons, and the other to have fewer electrons than protons. When this occurs, the objects are said to be charged. It is important to remember that it is only the electrons that can move. An object that contains fewer electrons than protons is said to be positively charged. This object would have lost electrons to another material. An object that contains more electrons than protons is said to be negatively charged. This object would have gained electrons from the other material. We use the term charge to refer to either a single proton or electron, or a group of protons or electrons. In the diagrams that follow, a + or – symbol represents many millions of individual protons or electrons respectively. Fig 5.1.2

a neutral object

area of jumper becomes negatively charged

a positively charged object

a negatively charged object

Scientists have found that a: • positively charged object and a negatively charged object will attract each other

pen becomes positively charged

Negative charges (electrons) may be rubbed off a plastic pen and onto a woollen jumper, leaving the pen positively charged.

126

Fig 5.1.1

Opposite charges attract.

Fig 5.1.3

• positively charged object will repel other positively charged objects Like charges repel.

Fig 5.1.4

• negatively charged object will repel other negatively charged objects.

cannot move as they are tightly held in the nucleus of the atoms and so are left at the top of the paper. These positive charges in the paper are attracted to the negative pen and so the paper sticks. After the pen and paper have been in contact for a short time, the charges spread out over both, leaving both with the same (negative) charge. They now repel each other and the paper falls off. Charges such as those on either side of the paper are called induced charges, as, in this case, they were created or ‘induced’ by Prac 2 the charges on the pen. p. 132 Fig 5.1.6

UNIT

5 .1

A neutral object can be attracted to a charged object because of induced charges.

+ + + + + + + + + ++ + +

charged pen neutral paper

Fig 5.1.5

The attraction and repulsion forces referred to above are called electrostatic forces. Prac 1 p. 131 The attraction between opposite charges keeps the negative electrons orbiting the positive nucleus in atoms. You are now in a position to answer the question ‘What is electricity?’ It is really just a collection of charges. Static electricity is a collection of charges that remain stationary for some time, though eventually so-called static electricity will move as it dissipates or leaks into the air.

+ + + + + + + + + + + + +

Like charges repel.

– + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – +

neutral paper

– – – – – – – – – – – – – – – – – – – + + + + + + + + + + + + + + + + + + +

The Van de Graaff generator A device known as a Van de Graaff generator produces a large build-up of charge on its metal dome. This can be used to demonstrate static electricity effects, some of which are really hair-raising.

No charge, but still attracted? If you briskly rub a plastic pen on a woollen jumper you will probably find it can attract small pieces of paper. The pen is charged (so is the jumper you rubbed it on). The paper, however, has no charge and therefore shouldn’t be attracted to the pen. So, what’s happening? The words ‘no charge’ can be misleading—what is really meant is that there are equal numbers of positive and negative charges, or that there is no overall charge. When a negatively charged pen approaches neutral paper, negative charges in the paper are repelled and retreat as far away as they can. This means they move to the bottom side of the paper. The positive charges

Fig 5.1.7

A Van de Graaff generator uses a belt to transfer negative charges to its metal dome.

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Static electricity

Photocopiers

––

– – –

– – – – – – – – – – – – – –– – –– – – – – – – – – – – – – – – – – –– – – – – – – – – – – – – – – – –

Negative charges accumulated on the head and hair repel each other and so spread out.

Fig 5.1.8

Good and bad static electricity Carpet static Static electricity often ‘zaps’ you after you have walked on a carpet. Walking rubs your shoes against the carpet sometimes, causing a build-up of charge on your body. Rubber soles may prevent charge leaving via your feet, so that when you touch another object, all that excess charge may jump into the object. This causes a spark and gives you a small electric shock. Charge tends to concentrate on sharp corners and spreads out more over flatter surfaces, so one way of avoiding a shock when touching an object that has built up charge is to first touch it with an open palm instead of a finger. This spreads the movement of charge and avoids a spark.

128

Movement of water droplets and air molecules can cause charges to build up within storm clouds. If the build-up is large enough, charges may flow suddenly from one part of a cloud to another, or to a separate cloud, or even to the ground. The sudden movement of charges causes the surrounding air to become superheated and expand rapidly. The temperatures can be as high as 30 000°C. This expansion causes shock waves to travel through the air, which we hear as thunder.

+ + + + + + + + + ++ + + +++ + + +

+ + – – + – – – + –+ – + + – + + + –

–

–

– –

– – –– – – – – – – – – – – –– – – – – – – – –

– – –

During refuelling, an aircraft needs to be protected from the effects of static electricity. Friction between the air and the body of the aircraft creates a large charge on the outside of the aircraft and a charge jumping from the aircraft to the fuel hose during refuelling would cause a disastrous explosion. To prevent this, a wire is first connected between the aircraft and the ground, allowing any excess charge to safely leave the aircraft.

In 1987, a lightning strike felled eleven soccer players. In 1970, ten European tourists sheltering under a tree were hit by a shock wave caused by the air surrounding a strike becoming super-heated and rapidly expanding. They emerged naked, but otherwise unhurt!

When electrostatic attraction is strong enough, large amounts of negative charges may move in the form of lightning.

Fig 5.1.9

Aircraft refuelling

Unusual strikes!

– –

Hospital patients are given anaesthetic gases (by a specialist called an anaesthetist) to render them unconscious during operations. Some of these gases are explosive. A spark caused by static electricity build-up could have awful consequences for those in the operating theatre. To avoid this, the floor of the theatre is made ‘antistatic’ by using a conducting floor covering that will ‘quietly’ leak away any charge.

Thunder and lightning

–

Anaesthetic and antistatic

Photocopiers use static electricity to produce images. A cylindrical drum is positively charged, and an image of the original page is projected onto it. Light areas of the image destroy the charge, while black regions leave the charge intact. A fine, negatively charged powder (called toner) drops onto the drum and sticks to the positive areas. The drum then rolls its powder image onto paper, which is then heated to melt the toner permanently onto it. Some people use the term ‘photostat’ to refer to a photocopy made this way. Can you suggest how the word ‘photostat’ came to be?

–

– – – – –

+ + –

–

– –

+ + + + + + + + + – – – – –

+ +

+ –

+

– +

– +

– + – +

– + – +

Strike me down!

s every second. The Earth is hit by about 100 lightning strike tips: safety Here are a few you are travelling, as electricity tends • Shelter in a building or the family car if are outside and your clothes are wet, you If t. objec an of de outsi to flow on the r to flow through the clothes, prefe will nt this may be a good thing, as curre away from water such as the Keep hit. get you if body, your gh rather than throu are on or in water. you if ble possi as surf or lakes—get to shore as soon t outside, crouch down with your feet • Avoid open spaces, but if you are caugh knees. Current flows from high close together and place your hands on your your feet together reduces the ng keepi so ones, charge concentrations to low at each foot. chances of a different charge concentration been many cases of people injured • Do not use the telephone—there have travelled through phone cables to has s strike ing when electricity from lightn the telephone earpiece. wire fences and railway tracks, or • Keep clear of any metal objects, such as fishing rods or golf clubs. ellas, umbr as such ones even tall non-metal on end or your skin tingles you are in a • If you are outside and your hair stands rop to the ground immediately. er—d dang in lightning strike zone. You are

UNIT

5 .1 gravitational field, a charge is surrounded by an electric field. The direction of an electric field is the direction a small positive charge would move if it was free to do so. This means the electric field comes out from a positive charge and in towards a negative charge. Larger charges have stronger electric fields. Once again, the further away you go, the weaker the field becomes. Combinations of charges can produce very Prac 3 p. 132 complex fields, as shown in Figure 5.1.11. Fig 5.1.11

Electric field lines—positive and negative charges

+

–

Fields Scientists use the term gravitational field to describe the invisible force-field that causes objects on Earth to fall downwards, or more scientifically, towards the centre of the Earth.

+

+

car panel (negatively charged)

paint spray gun

Fig 5.1.10

Electric paint

Earth’s gravitational field exerts a force on all objects, towards its centre.

All objects have a gravitational field, but it is usually only noticeable when the object is very large, for example a planet or a star. The direction of a gravitational Electric animals field of a planet is the direction Animals such as sharks, an object would move if dropped. echidnas and platypuses The gravitational field is stronger s field can detect the electric of cles mus the in for heavier planets, and decreases produced other animals. How might a the further away from the planet shark use this ability? you get. Just as a planet has a

paint droplets (positively charged) follow electric field lines

Fig 5.1.12

Electrostatic charging of paint and metal panel helps ensure an even coat.

Worksheet 5.1 Zapping car doors

Paint spray guns used in car factories are kept positively charged, while the car body being sprayed is negatively charged. This creates an electric field between the gun and the car. Paint is charged as it leaves the gun, and fine droplets follow the electric field lines to be deposited evenly onto the car body.

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>>>

Static electricity

UNIT

5 .1

[ Questions ]

Checkpoint

14 List two examples (other than those mentioned in the previous question) of how electric charge may be produced.

Are you positive (or negative or neutral)? 1 State the charge and sign for: a an electron b a proton.

15 Cleaning and polishing a mirror might actually make it more dusty. Explain how. 16 Explain why a Van de Graaff generator makes a person’s hair stand on end, and why it is even more dramatic if the person stands on a rubber mat.

2 Outline what can you say about the number of protons and electrons on: a a neutral object b a positively charged object c a negatively charged object.

17 A spark is more likely to jump to your finger than your forehead when you approach a charged Van de Graaff generator. Explain why.

3 Clarify the term ‘electrostatic forces’.

18 If you tear a polythene shopping bag and try to put the pieces in the bin, they may stick to your fingers. Explain why.

No charge, but still attracted? 4 Define what is meant by an ‘induced charge’. 5 Construct a diagram to show how a neutral object and charged object can attract each other. 6 Clarify the term ‘static’ in static electricity. 7 Describe how charge is built up in a Van de Graaff generator.

Good and bad static electricity 8 Identify two uses for static electricity. 9 Identify two situations in which static electricity is a nuisance.

Fields 10 Define the term ‘field’. 11 Explain what is meant by the direction of an electric field.

19 Explain why static electricity demonstrations work better on warm, dry days. 20 Examine the following statements and modify any that are incorrect. a A positively charged object contains only positive charges. b A neutral object contains no charges. c Induction is the ‘coaxing’ of charges in a neutral object to move to different positions within the object. d An object may become charged only by rubbing electrons off it. e Lightning is caused when a build-up of charge within a cloud jumps from the cloud to earth. 21 Compare an electric field with a magnetic field.

Think 12 Using the terms ‘attract’, ‘repel’ and ‘no force’, choose a term that describes each charge in the table below. Positive charge

Negative charge

Analyse

Neutral charge

22 Use + and – signs in Figure 5.1.13 to demonstrate the position of various concentrations of charge.

Positive charge Negative charge – – – – – – – –

Neutral charge

metal sphere

13 In some industries, paint is positively charged before being sprayed onto negatively charged panels. a Explain why this method would get the paint to spread out nicely. b Explain why the paint is given an opposite charge to the metal panel.

130

Fig 5.1.13 23 Figure 5.1.14 shows one type of Van de Graaf generator. Account for the charge transfer to the dome.

One type of Van de Graaf generator

UNIT

5 .1 Fig 5.1.14 a pulley wheel metal brush metal dome

–

b

– – – – –– +

outside casing

++ + +

– – – – – – – –

rubber belt felt pad

2 Design a new device or machine that uses static electricity, for example a static dust collector or an electrostatic train.

Skills 24 If a balloon is rubbed with wool, it will often stick to a wall. Demonstrate how this happens using a diagram. 25 Construct diagrams to show the electric field near the charges in Figure 5.1.15.

[ Extension ] Create 1 Construct a cartoon that teaches people how to avoid lightning strikes in a storm.

5 .1 UNIT

Fig 5.1.15

Surf 3 Complete the activities below by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 3 and clicking on the destinations button. a Construct a poster illustrating an example of a lightning rod and how it works. b i There is a story about Benjamin Franklin flying a kite with a key attached in the middle of a thunderstorm. Research more about this story. ii Summarise the information you found about the true story of Benjamin Franklin’s experiment in the form of a newspaper article.

[ Practical activities ] Positives and negatives

Fig 5.1.16 secure with Blu-Tack

Aim To investigate static electricity Prac 1 Unit 5.1

Equipment 2 perspex (acetate) and 2 polythene rods or strips, 2 dry woollen cloths, watch-glass, Blu-Tack or plasticine

Method 1 Charge one perspex rod by rubbing it with a dry cloth and place it on a watch-glass as shown. Quickly charge the other perspex rod and bring it near the one on the watch-glass. Note the direction of any movement.

>> 131

>>>

Static electricity

2 Repeat step 1 for the polythene rods but use the other cloth. 3 Now study the effect of a charged perspex rod on a charged polythene rod, using the same cloths that were rubbed on each previously.

Making an electroscope Prac 3 Unit 5.1

Aim To make an electroscope and test for the presence of an electrostatic charge

Equipment

Questions 1 Explain which combinations produced attraction, and which produced repulsion. 2 The charge produced on the perspex rod was positive. Use this information to predict the charge produced on: a the polythene rod b the cloth when rubbed on perspex c the cloth when rubbed on polythene.

Glass jar, aluminium foil, thick wire, card, tape, various rods (eg glass, polythene, ebonite) and cloths (eg wool, cotton, synthetic)

Method 1 Using Figure 5.1.17 as a guide, design and construct a device called an electroscope to detect an electric field. Fig 5.1.17

3 Account for the use of a new cloth used with the polythene rod in step 2.

Static magic

ball of foil

Aim To electrostatically charge a balloon and Prac 2 Unit 5.1

cardboard

a pen

Equipment

glass jar

A balloon, plastic pen wire

Method 1 Inflate a balloon and rub it on your jumper for a minute or so.

foil strip

2 Hold the balloon on a smooth wall and let go. 3 Rub a pen on your jumper. 4 Hold the pen near (but not in) a thin stream of running water.

Questions

2 Use the electroscope to compare the electric fields produced by various combinations of rods and cloths.

1 Explain in words what happened in each case.

3 Record your results in a table.

2 Construct diagrams to support your explanations in Question 1.

DYO

1 Explain how the electroscope works. Use a diagram to support your answer.

Extension A balloon becomes negatively charged when it is rubbed on a jumper. Devise a way of finding whether the charge produced on a rubbed pen is positive or negative.

132

Questions

2 Identify which rod and cloth produced the largest electric field. DYO

3 Propose a use for an electroscope in an everyday situation.

UNIT

context

5. 2 Imagine life without electricity! Most of the appliances we use rely on electricity to function. Television, computers, DVD players, toasters, calculators all have one thing in common—they need electricity moving through them to work.

conductor/ lead

cell

globe

battery

closed switch

fixed resistor

open switch

variable resistor

A

ammeter

leads connected

V

voltmeter

leads crossing

A simple circuit Moving electricity is actually moving charges. The path along which these charges flow is called a circuit, and electricity will flow only if there is a complete circuit for it to go around. The four basic parts of a simple circuit are: • an energy source, such as a battery • a conductor (wires) for the electricity to flow through • something to use up the electrical energy such as a globe or motor • a switch to turn the current on and off. Figure 5.2.1 shows a simple circuit to operate a light globe. To save time describing circuits, symbols are used to form a circuit diagram. A circuit diagram shows the parts or components of a circuit, what each is connected to and the order in which they are connected.

Common symbols used to draw circuits

Fig 5.2.2

Worksheet 5.2 Electrical symbols and circuits

Fig 5.2.1

A simple circuit and its equivalent circuit diagram

circuit

circuit diagram

cell 1.5 V

1.5 V cell

+ –

switch

connecting wire

globe

133

>>>

Current

+

– – –

+ +

moving electron –

– + + –

–

– +

+

+

+ –

–

– –

+ +

current direction of ‘conventional current’ electron direction

The coulomb A coulomb is a ‘packet’ of 6 250 000 000 000 000 000 electron-sized charges. A current of one ampere means that one coulomb of charge passes by each second.

134

0.6

0.8

1.5 V cell 1.0

PS AM

+ A

–

5A

–

1A

1 2

0

VOLT

– 15V V <Measuring current 3V and voltage.>< was Sci 2 fig 6.2.3 p145>

3

+

0.4

Fig 5.2.3

A current made up of moving electrons

fixed positive nucleus

Voltage is a measure of the amount of energy available to push charges around a circuit, and the unit of measurement is a volt (V). Voltage is supplied by electric cells and household power points. Using the water analogy, voltage is like the pressure from the pump that pushes the water through the pipes. To measure the voltage, or energy transferred between two points of a circuit, probes from a voltmeter are connected so it ‘piggybacks’ across the section. You can think of an ammeter as counting every charge that passes through it, and a voltmeter as sampling how much energy is used between two points in the circuit.

S

The term electric current is used to describe moving electric charges. In circuits such as that shown in Figure 5.2.1, these charges are electrons. A large current involves more electrons passing through a circuit each second than a small current does. Current is measured in a unit called an ampere (A or ‘amp’ for short). A milliamp (mA) is equal to one-thousandth of an ampere and is used to measure extremely small currents. Most parts of circuits are made from metals. If you could magnify a metal enough, you would see a network of fixed positive atomic nuclei surrounded by a ‘sea’ of loose negative electrons. It is these electrons that flow in most circuits. Because early scientists wrongly thought that electricity flowed from the positive terminal of a voltage source to its negative terminal, we are stuck with the convention of labelling current direction as the way imaginary positive charges flow. Scientists refer to it as conventional current. The electrons actually move in the opposite direction to conventional current.

Voltage

0.2

The simple circuit shown contains flowing electric current, a voltage source, a switch, conductors and a resistance.

0

Moving electricity

The flow of electric current is similar to the flow of water, but differs in one important aspect: water will flow out of a cut pipe, but electric current will not usually flow out of the end of a cut wire. To measure the flow of current, an instrument called an ammeter is placed in the path of the current to be measured. This involves ‘breaking’ the circuit and inserting the ammeter.

Fig 5.2.4

How to connect an ammeter and a voltmeter

Cells and batteries Electricity typically comes from a power point in the home, or from Living batteries cells or batteries. The human body is full of Power points should be small voltage generators which are used to send treated with extreme care—the mes sages via nerve cells. 240 volts they supply can be The electric eel is able to deadly, so always ensure the generate up to 600 volts, switch is off before connecting or which it uses to stun small fish. disconnecting appliances. Technically, a cell is a single unit and a battery a group of cells, but people tend to use both words to describe a single unit. A typical small cell, such as an AA battery, provides 1.5 volts, while a car battery supplies 12 volts. Think of a cell as a charge pump or an electrical energy supplier.

A diagram of a wet cell is shown in Figure 5.2.5. A wet cell consists of two different metal plates placed in an acid. The zinc plate begins to dissolve in the acid in a chemical reaction, which releases electrons. If a circuit is made that joins the two plates, the electrons flow to the copper plate, lighting the globe as they travel through it.

a chemical reaction generates charge that will flow when the cell is connected to a circuit. There are several types of dry cell. Often several cells are connected as shown in Figure 5.2.7 to provide greater electrical energy or voltage.

UNIT

5.2

Fig 5.2.5

A wet cell

1.5 V

electron flow copper plate

zinc plate

Fig 5.2.7

1.5 V

1.5 V

Cells joined together to provide a higher voltage (4.5 volts)

A photovoltaic cell or solar cell is made of two layers of a substance called a semiconductor. When sunlight strikes the top layer, electrons are given

acid

A car battery is a collection of wet cells. The wet substance is sulfuric acid and the plates or electrodes are made of lead and lead oxide. When a car is running, chemical reactions in the battery are reversed, and help recharge the battery. Eventually, build-up of chemicals on the Prac 1 electrodes prevents recharging and the p. 139 battery ‘dies’. A dry cell is not completely dry, but contains a chemical paste instead of a liquid. As in a wet cell,

+

Fig 5.2.8

Sunlight falling on a photovoltaic cell forces electrons from one layer to the other, causing an electric current.

brass cap

carbon rod manganese dioxide and carbon zinc case

ammonium chloride jelly

outer steel jacket –

The internal structure of a typical dry cell. Zinccarbon cells are cheap; alkaline-manganese are longer lasting but more expensive; lithium cells are compact, light and long-lasting. A nickel-cadmium (nicad for short) cell may be recharged using current from a power point to reverse the chemical reactions within the cell.

Fig 5.2.6

Fig 5.2.9

A solar-powered vehicle

135

>>>

Moving electricity energy to move from one layer to the other, creating an electric current. Several cells are used to make a solar panel.

Conductors and insulators A conductor is a substance that allows current to flow through it easily. Metals are good conductors of electricity. Copper wire is a low-cost and widely available conductor commonly used in electric circuits around the house, in factories and in cars. Aluminium is more expensive but is used where copper would be too heavy, for example for highvoltage transmission lines that need to be strung between distant pylons. Materials that do not normally allow current to pass through them are called insulators. Plastic and rubber are two very Prac 2 p. 140 effective insulators.

copper wire conductor

plastic insulation

Fig 5.2.10

Electrical cable consists of both insulating and conducting materials.

More on circuits

A typical light globe

Fig 5.2.11

soda glass

argon and nitrogen gases

thin tungsten filament

contacts

bayonet fitting

A globe is an example of resistance—something that restricts the flow of charge and ‘robs’ moving charges of energy. Resistance converts electrical energy into heat and light energy. Devices such as electric kettles, toasters, irons and electric hotplates are all simple electric circuits that contain a resistance wire made from the metal nichrome. Nichrome has much greater resistance than the copper wire used in the rest of the circuit, and so it heats up when a current passes through it. Nichrome is ideal as it doesn’t react with oxygen or become brittle when heated till Prac 3 red-hot. p. 140

For current to flow, there must be a complete circuit made of conducting material, and a voltage source such as a battery.

The pump The voltage source acts as a pump and creates an electric field that pushes charges around the circuit, just as a water pump creates pressure that pushes water through pipes.

to power point

The resistance Electrons have much more difficulty getting through the thin tungsten filament of a light globe than they do getting through the much thicker and highly conductive copper wire. The electrons give up a lot of energy trying to get through the filament, this energy being turned into heat and light.

136

wires contained in power cord heating element

The heating element in an electric jug is part of a simple series circuit.

Fig 5.2.12

The electric circuit in Figure 5.2.13 may be compared to a water pump arrangement.

Fig 5.2.14 1.5 V cell

pipe (connecting wire)

+

UNIT

5.2 water pump (voltage)

–

w

w r flo ate rent) ur

(c

electron flow tap (switch)

water wheel (resistance)

A simple circuit with a switch in the ON position

UNIT

5.2

Fig 5.2.13

[ Questions ]

Checkpoint A simple circuit 1 Recall the components needed to get an electric current flowing. 2 List ten devices that use electricity in the home.

Current and voltage 3 Define the following terms: a current b voltage. 4 Recall the device used to measure: a current b voltage.

Cells and batteries

More on circuits 11 In a light globe, oxygen is replaced by other gases, rather than simply removed. Outline why. 12 Identify which part of a circuit causes electrons to lose most of their energy.

Think 13 Outline why copper is used in circuits to connect components and tungsten is not. 14 Copy and complete the following table to demonstrate analogies between electricity and water: Current electricity

Water

charge

water particles

current

5 List five objects that use dry cells. 6 Describe what produces the charges that provide current in a cell. 7 State which type of cell would be best suited to a heart pacemaker. 8 Outline why car batteries are so heavy.

pump connecting wire globe tap

9 Outline why a car battery ‘goes flat’ if the car is not used often.

Conductors and insulators 10 Define the terms ‘conductor’ and ‘insulator’ using examples.

15 Explain why electricians use screwdrivers with plastic or rubber handles. 16 Distinguish between a cell and a battery.

>>

137

>>>

Moving electricity

17 Propose a voltage for each of the following: a torch cell b household power point c car battery.

[ Extension ] Investigate

Skills 18 Construct a table of examples of good conductors and good insulators. 19 Construct a diagram of a dry cell. 20 Construct a circuit symbol for: a a cell b a globe c a switch.

Analyse 21 Evaluate which of the circuits in Figure 5.2.15 are equivalent.

1 Research one of the following scientists by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button. Summarise your information in the form of a newspaper article announcing the scientist’s discovery to the public. a Research the invention of the light globe and other inventions by Thomas Edison. b Research Luigi Galvani’s contribution to the study of electricity. c Alessandro Volta made the first battery, known as Volta’s pile. Research how Volta’s pile worked.

Action 2 Design an alarm that activates when someone stands on a mat near your bedroom doorway.

DYO

3 Design a test to compare the lasting power of different brands of batteries. A

B

4 Investigate electroplating and how it works. Design and conduct an experiment to electroplate a key. 5 Compare cells made using various fruits (see Prac 1 on page 139).

C

D

6 Construct one of the games in Figures 5.2.16 and 5.2.17. Once you get the game working, try adding a buzzer to the circuit, connected in parallel (see Unit 5.3).

Fig 5.2.15 22 An electric eel has cells in its body that can produce a fraction of a volt each. Explain how an electric eel can produce up to 600 volts to kill or stun its prey. cell

wire coathanger

switch screw wooden board

Fig 5.2.16

138

UNIT

5.2 Fig 5.2.17

metal paper fastener

Creative writing Invention/discovery

Inventor/discoverer

Life without cells and batteries Discovered the structure of DNA

Karl Benz

Penicillin

Robert Hooke

Modern light microscope

Francis Crick and James Watson

Dynamite

Howard Florey

Petrol-driven car

Alfred Nobel

An unexpected blast of powerful solar radiation has deactivated all cells and batteries on Earth. It will be several weeks until more cells can be manufactured. How will life be different without cells and batteries? What modifications will be needed to allow equipment to continue to function? Describe how humans cope with this unexpected inconvenience.

5V

1.

cardboard

b increasing the distance between the copper and zinc plates c squeezing the lemon.

Extension

exposed wire probe

5 Combine with another group and attempt to use two lemons to produce a larger current reading.

denotes connecting wires underneath cardboard

Questions 1 Some chemical cells require acid. Explain where the acid comes from in this experiment and what sort of acid is involved.

UNIT

5. 2

[ Practical activities ] A lemon cell Aim To construct a battery using a lemon

Prac 1 Unit 5.2

2 Discuss the validity of your predictions in step 4 above. 3 Explain why the current increased or decreased in each case. 4 In step 5, lemons were linked together to produce a larger current. Was this is a cell or a battery? Justify your answer.

Equipment A galvanometer or microammeter (for detecting small currents), copper and zinc plates (or a galvanised nail and uninsulated copper wire), a lemon, 2 connecting wires

Fig 5.2.18 copper

zinc microammeter or galvanometer

Method 1 Squeeze the lemon without breaking the skin to ‘juice it up’ inside.

lemon

20

150 30

50

4 Predict and then investigate the effect of:

100

mA

250 mA

250

mA

10

40

3 Connect to the current measuring meter, ensuring the copper is connected to the positive terminal of the meter.

50 0

0

0

20

2 Insert the plates (or substitute items) into the lemon.

50 m

A

a pushing the copper and zinc plates further into the lemon

139

>>>

Moving electricity

Fig 5.2.19

Conductors and insulators Prac 2 Unit 5.2

Aim To test various materials and classify them as conductors or insulators

1.5 V cell

+

Equipment

–

A 1.5 volt cell, a 2.5 volt mounted globe, 3 connecting wires, various materials such as a nail, coin, plastic, glass, wood, cloth, metal pieces, paper, rubber, steel wool

material being tested

Method 2.5 V globe

Assemble the circuit shown in Figure 5.2.19, and test whether each material conducts well or not.

Questions 1 Classify the materials used as conductors or insulators. 3 Rubber is normally classified as an insulator, but will conduct electricity if an extreme voltage is connected across it. Justify the use of the term ‘insulator’ for rubber.

2 If the light globe does not light up explain whether this means the material is definitely an insulator.

A mini water heater Prac 3 Unit 5.2

Aim To construct a mini water heater and observe the heating effect while varying the voltage

AC

DC

VOLTS

Equipment

Nichrome wire (20 cm), power pack capable of supplying 12 volts, 250 mL beaker, thermometer, stopwatch or clock, connecting wires

power pack

Method water

1 Copy the table below into your workbook. 2 Connect the apparatus as shown in Figure 5.2.20. Leave the power pack off.

coil of nichrome wire

3 Take the temperature before any heating takes place. 4 Set the voltage knob on 6 volts. As you turn the power pack on, start the timer.

Fig 5.2.20

Questions

5 Record the temperature of the water every minute for 10 minutes.

1 Explain where most of the energy supplied by the power pack is being transferred to.

6 Predict what would happen if you were to increase the voltage to 12 volts. Write down your prediction.

2 Construct a line graph showing the temperature variation over the 10 minutes.

7 Repeat the above steps but increase the voltage to 12 volts to test your prediction.

Time (min) Temperature (°C)

140

0

1

2

3

4

5

6

7

8

9

10

3 Predict what the temperature would have done if the water was heated another 10 minutes. 4 Would the temperature keep rising if the water was heated for a much longer time? Justify your answer.

UNIT

context

5. 3 Circuits are connected up in different ways depending on how we want lights or other appliances to operate. Imagine if we had to turn on the dishwasher, washing machine and all the other appliances around the house just to get the TV working! Or if we

switched the bedroom light on and all the other lights in the house got dimmer. Some circuits will do exactly this: we need to pick the right type of circuit to do what we want it to do.

4A

6V

Circuits

2A

6V

Series circuits

2A

6V

If two globes are arranged one after the other, in a line with the battery, then the globes are said to be in series. This is shown in Figure 5.3.1. The voltage supplied is shared between globes in series, but the current that passes through each is the same. Each globe glows more dimly than a circuit containing just one globe. If either globe in the series circuit is removed or ‘blows’, the circuit is broken, and neither globe will light up. Fig 5.3.1

A series circuit

1A

6V

6V

no current

bulb goes out 1A 3V

1A 3V

bulb removed

2A 4A

current divides

Fig 5.3.2

2A

Prac 1 p. 145

6V 2A

6V

no current

A parallel circuit

Worksheet 5.3 Electric current at the footy

More complex circuits A circuit may be a combination of both series and parallel sections, and contain switches to control current flow, like the one in Figure 5.3.3. As a general rule, current divides so that most current goes the easy way. If switch 1 (S1) is opened, no current flows anywhere. If switch 2 (S2) is opened, 3A current flows only through 6V S1 3V 3V the branch containing the 1 A single globe. S2 6V S3

3A

2A

most current takes easier route

Parallel circuits The circuit in Figure 5.3.2 shows two globes in parallel—that is, in separate branches between the same points. The voltage is the same for each globe in parallel, but the current from the cell is shared between each branch. Each globe glows with equal brightness. If either globe in this circuit is removed or ‘blows’, the other globe will stay alight, as there is still a circuit through which current may flow.

Prac 2 p. 146

This circuit has two globes in series in one branch of a parallel circuit.

Fig 5.3.3

Christmas-tree lights Christmas-tree lights come in two types—series and parallel. A series arrangement of 20 lights would share the 240 volts from the power point, giving each globe 12 volts. Globes come in different sizes (often 6 and 12 volts). For this circuit 12 volt globes should be used.

141

>>>

Using electricity

Fig 5.3.4

Christmas lights in series—if one globe blows, they all go out. mains power

power supply

current

One disadvantage of this arrangement is that if one globe ‘blows’, they all go out. This makes it very difficult to find the failed globe. Other types of Christmas-tree lights may be powered by a low-voltage source. A transformer changes the 240 volts from the power point to 12 volts. The globes are then connected in parallel, with every globe operating at 12 volts. The advantage is that if one globe blows all the others continue to operate.

Fig 5.3.5

Household circuits The mains electricity wiring in your house is just one big parallel circuit. Can you imagine what would happen if it was a series circuit? Power points within the home allow extra parallel branches to be connected, where each branch gets the same 240 volts. The diagram in Figure 5.3.6 shows a simplified version of household wiring. Unlike a battery, where current flows one way (known as direct current, or DC), power stations supply a house with current that is pulled forwards

142

One of the many large parallel circuits in a house

and backwards many times every second. This is known as alternating current, or AC. Electricity is supplied as AC because it is easier to generate and transmit than DC. Worksheet 5.4 Electricity costs Worksheet 5.5 Saving power

Electrical safety

power supply

Christmas lights in parallel—if one globe blows, the others keep working.

Fig 5.2.6

Electric shock or even electrocution (death by electricity) may occur if current finds a path through your body (usually to the earth). A tiny current can cause death by damaging tissues and interfering with electrical signals driving the heart. For this reason, electricians wear rubber-soled shoes and use tools with insulated handles. Never handle a plug without turning off the power point, and never interfere with circuits connected to mains power. If you do come across someone who has had an electric shock, first turn off the power, using the main switch at the fuse box if necessary. If this is not possible, do not touch the person directly, or you will be given a shock too. Sometimes, insulators such as a plastic rope or garden hose can be used to move them away from the source of electrocution. Then assistance and appropriate first aid can be given. Whatever happens, ring 000. A device called a safety switch or residual current detector (RCD) may be connected to the household power supply to reduce the risk of electric shock. An RCD compares the current entering a home with that leaving via the correct circuit.

If there is a difference caused by some current ‘leaking out’ (eg through a person’s body), it switches off the main power switch within a few thousandths of a second. Serious electric shock is prevented.

UNIT

5.3

UNIT

5 .3 loose wire touches metal case

[ Questions ]

Checkpoint current travels through body to earth

Circuits 1 Explain how series and parallel circuits are connected. 2 Identify correct answers for the missing words. In a series circuit, the ________ is shared between the components, but the ________ is the same. In a parallel circuit, the ________ is shared between the branches, but the ________ is the same for each branch.

Christmas tree lights 3 One globe ‘blows’ in a set of Christmas tree lights. Predict its effect if the lights are wired in: a parallel b series.

Household circuits 4 State whether the following statements are true of false. a Household wiring is like a big parallel circuit with many branches. b Current supplied to households goes in one direction only. c A large current is required to cause damage to your body.

Electrical safety 5 Use Figure 5.3.7 to outline how you can reduce the risk of electric shock.

A

Analyse

B

6 In Figure 5.3.8, identical globes and cells are used. Identify the circuit or circuits in which the globes glow: a brightest b most dimly.

Electric shock occurs when current finds a path through the body.

7 Examine the circuit in Figure 5.3.9 and state which other globes would go out if: a globe A blows b globe B blows c globe C blows d globe D blows e globe E blows.

Fig 5.3.7

Fig 5.3.9

E A

B

C D

8 Copy the circuit in Figure 5.3.9 and modify it to show: a a switch that turns all globes on and off b an ammeter that measures the current through globe A c a voltmeter that measures the current through globe E. 9 The circuit diagram for a light at the bottom of a stairway is shown in Figure 5.3.10.

X switch 2 Y

switch 1 A 240 V AC

C

Fig 5.3.8

Fig 5.3.10

B

>> 143

>>>

Using electricity

Copy and complete the following table in your workbook in order to summarise the operation of the circuit. Switch 1 at position

Switch 2 at position

Light

A

X

ON

B

X

A

Y

B

Y

13 The diagrams in Figure 5.3.14 represent three safety switches. The numbers represent currents. Select the diagram in which the safety switch would shut off the main power.

A

0A

10 Identify the correct answer from the list below. The current that flows through point A in Fig 5.3.11 is: A the same as the Fig 5.3.11 current that flows through point B B half the size of the current through point B B C twice the size of the current through G A point B D three times the size of the current through point B. 11 State which fraction of the cell voltage is used by globe G in Figure 5.3.11. 12 Predict what the effect would be if a connecting wire was placed between points A and B to cause a short circuit in Figure 5.3.12 and Figure 5.3.13.

B

0A

10 A

C

10 A

10 A

9.999 A

Fig 5.3.14

Skills 14 Use circuit symbols to construct a circuit with a cell and: a three globes in series b four globes in parallel c two globes in series with three globes in parallel. 15 Construct a diagram showing the circuit in question 14c and insert a single switch which controls the current in: a the entire circuit b one of the globes in parallel. 16 Greg notices that if one globe on his Christmas tree blows, four of its neighbours go out, but the other 45 stay lit. Construct a likely circuit diagram for Greg’s christmas-tree lights.

A

globe 4

globe 1 B globe 2

globe 3

[ Extension ] Action

Fig 5.3.12 Fig 5.3.13

1 Construct a working model of the two-way light switch circuit described in Figure 5.3.10.

DYO

2 Construct a circuit to simulate traffic lights. globe 1 A

B

globe 2

144

3 Use circuit simulation software (eg Crocodile Clips) to construct circuits. Try to predict the current and voltage for various parts of each circuit you construct, then ‘switch on’ and check your predictions.

UNIT

5 .3 Fig 5.3.15

Project 2A A

A model household circuit Construct a model of a household electricity circuit using a low voltage supplied by a cell or battery. Include a main switch, lighting and a power point.

12 V

___ V

___ A A

V ___ A A

Creative writing

A ___ A

Globe trotting

V

Imagine you are an electron who travels with several friends around a circuit containing two light globes in series followed by two globes in parallel as shown in Figure 5.3.15. Write an account of what you experience as you and your friends complete a circuit. Consider things such as: • How do you get your energy?

UNIT

5. 3

[ Practical activities ] Series and parallel circuits

Prac 1 Unit 5.3

___ V

• How do you lose energy? • Was your movement restricted at any stage? • What happens to your friends? Where were they as you were travelling? • What happens to you all if the switch is suddenly opened?

+ –

Aim To construct a series and parallel circuit

1.5 V cell

Equipment

Two 2.5 volt globes, 4 connecting wires (eg with alligator clip ends), 2 connection posts (eg nails in wooden blocks), 1.5 volt dry cell

connection post

connection post

Method 1 Connect and observe the brightness of a single globe in the circuit shown in Figure 5.3.16. 2 Modify the circuit by inserting an extra globe in series as shown in Figure 5.3.17 and note the brightness of each globe. What is the effect of removing a globe? Does it depend on which globe you remove?

A parallel circuit

1.5 V cell

1.5 V cell

+

+

–

–

2.5 V globe

Fig 5.3.16

Fig 5.3.17

A series circuit

Fig 5.3.18

3 Assemble the parallel circuit in Figure 5.3.18 and again compare the brightness of the globes. Again, what is the effect of removing a globe? Does it depend on which globe you remove?

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Using electricity

Questions 1 Contrast the brightness of globes in series with that of a single globe.

3 Predict the effect of removing a globe when they are: a in series b in parallel.

2 Contrast the brightness of globes in parallel with that of a single globe.

4 Predict the circuit in which the cell will go flat most quickly.

Connecting ammeters and voltmeters Fig 5.3.19

Equipment

Two 2.5 volt globes, 6 connecting wires (eg with alligator clip ends), 1.5 volt dry cell, ammeter, voltmeter

3

2

0

1.5 V

4

0.6 0.8

PS AM

0.2

1

0.4

5 1.0

+

0

Prac 2 Unit 5.3

Aim To measure the voltage and current in series and parallel circuits

–

Method

A

1 Assemble the circuit in Figure 5.3.19 and record the current and voltage measurements. 2 Copy each of the circuit diagrams in Figure 5.3.20 into your workbook.

5

10 1

0

15

2

3

0

3 Use an ammeter to record the current where indicated by ammeter symbols.

LTS VO

V

Note: The red or positive ammeter terminal connects to the ‘side’ of the circuit closest to the positive of the cell or battery. Record your current readings on your diagrams. 4 Use a voltmeter to measure the voltage where indicated by voltmeter symbols in Figure 5.3.21. Note: The red or positive voltmeter terminal connects to the ‘side’ of the circuit closest to the positive of the cell or battery.

1.5 V A

A

A A

Fig 5.3.20

2 Describe the voltages around the: a series circuit b parallel circuit.

Left: a series circuit; right: a parallel circuit

V 1.5 V

1.5 V

V

V

Fig 5.3.21

146

A

A

Questions 1 Describe the current at various points around the: a series circuit b parallel circuit.

1.5 V A

V

V

V

Left: a series circuit; right: a parallel circuit

V

Science focus: Solar challenge Prescribed focus area: The applications and uses of science Electricity was first supplied by batteries and only used for scientific experiments. New ways to produce electricity were gradually developed, and more and more electrical devices were invented. Many of the activities in our everyday life now rely on the use of electrical energy. We produce huge amounts of electricity to meet society’s needs.

We rely on electricity for many daily activities.

Fig SF 5.1

Plants are nature’s solar cells. They take the sun’s energy and turn it into a type of energy that is more useful, producing very little pollution.

Fig SF 5.2

Why solar cells?

Unfortunately we often produce this electricity in ways that cause pollution and have harmful effects on the environment. These include burning coal, oil or gas to turn the chemical energy into electrical energy. When supplies of fuel such as coal run low we will need new ways to produce electricity. These will also need to be less polluting. All life on Earth gets its energy from the sunlight that is trapped by plants during photosynthesis. Given this, many scientists have directed their attention to developing solar cells. Solar cells take the energy in sunlight and convert it into electrical energy.

The original materials used to manufacture solar cells were not very good at turning the energy from sunlight into electrical energy. They were also quite expensive to make. Time and money continue to be spent on research and development of solar cells that will enable us to: • provide a reliable source of electricity that can be used in space or hostile environments • provide electricity to remote communities that are too far from power grids • replace noisy, polluting diesel generators in office buildings, holiday venues and isolated research stations with a more environmentally friendly, non-polluting source of electricity • provide small, portable power sources to reduce the need for batteries, for example in calculators • provide a totally renewable and sustainable source of electrical energy to overcome a reliance on fossil fuels and help to reduce global warming.

147

Some current uses for solar cells

Fig SF 5.3

How do solar cells work? Solar cells (or photovoltaic cells) are made of semiconductors. Semi-conductors are special materials such as silicon that are used in computers. They are called semiconductors because they are not very good at conducting electricity compared with metals. However, they are much better at conducting electricity than insulators. A solar cell is made of two layers of semi-conductor. Each layer is made of silicon but small amounts of phosphorus are added to one layer, and boron is added to the other layer to make them conduct a bit better. When light hits the join between the layers its energy knocks electrons off the atoms. These electrons are then free to move or flow. When a circuit is connected to the top and bottom metal conductors of the solar cell the electrons flow out of the top metal conductor and around the circuit. The energy of these moving electrons can be used to make an appliance work. More electrons are released, and more electricity generated, if more sunlight hits the cell.

The Solar Challenge The Solar Challenge is an annual 3000-kilometre race from Darwin to Adelaide. The challenge is to design and build a car capable of crossing Australia powered only by sunlight. To build a solar car requires many great minds and expertise from different areas of science, including physics, electrochemistry, engineering, mathematics

148

Conducting grid of metal to collect electrons

Electron flow out of top of cell, through the circuit and back to bottom of cell

Sunlight

Layer of silicon with boron added Layer of silicon with phosphorus added

Join between layers

–

–

Electrons move to conducting grid on upper surface Light knocks electrons off atoms where the layers join

How a solar cell works

Fig SF 5.4

and psychology. The Solar Challenge has grown over the years and attracts competitors from many countries. Competitors include nearly 100 of the world’s top universities, companies such as Honda and organisations such as the Australian Aurora team. The competition is open to anyone whose vehicle

A solar car As much of the car as possible is covered with solar panels

Fig SF 5.5

Hatch on the cockpit Carbon fibre frame is very strong and lightweight.

The shape or aerodynamics are tested in a wind tunnel

Solar power is changed to electricity by the solar cells

Solar cells can follow the sun to maximise collection of solar energy

Storage batteries Materials such as carbon fibre and teflonare used to build a strong body

Normal accelerator pedal to control speed

A computer controls how electricity is used or stored

Solar energy is stored in batteries or can go directly to motors on wheels

meets the basic requirements. Some of the entries are constructed on very low budgets, and some secondary schools enter the competition. The Solar Challenge is an adventure for people seeking to apply scientific knowledge to solar technology. It promotes a smarter, greener world, an awareness of environmental issues and the development of the best solar technology for the future.

It also provides an opportunity for young minds to develop their potential. Maybe you could give it a go? The vehicles are all powered by panels of solar cells. These provide electricity directly to motors that run the wheels or to storage batteries for use when light levels drop. Many entries use the most advanced technology and specially developed materials in their designs to make lightweight, strong and fast cars.

a A low-budget but successful entry. b The most successful solar car team is based in Australia and called Aurora. c The high-tech Dutch Nuna team car crosses the finish line in Adelaide.

a

b

Fig SF 5.6

c

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>>> Chapter review

[ Student activities ] Learn more about the Solar Challenge and solar cars in general by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5 and clicking on the destinations button. The information on these links may help with the following activities. 1 Outline the energy changes that take place when using a solar cell to run a solar car. 2 Summarise the features that are designed to increase the efficiency of solar cars, explaining why each feature is important. 3 a Investigate solar cells further and make a list of the advantages and disadvantages in using solar power. b Research an answer to the following question: Considering solar cells produce electricity from sunlight, why doesn’t everybody use solar cells to produce the electricity they want? c Evaluate solar cells as an energy source for the future. 4 Propose some reasons why companies and universities invest so much money in their entry for the Solar Challenge. 5 Imagine that by the year 2030 solar cells have become so efficient and cheap that they are used to supply all societies’ electricity. Produce an art work to demonstrate what it would be like to live at this time. 6 In a team, design your own a solar car. Try to make it as energy efficient and innovative as possible. Remember, you want to win the challenge!

[ Summary questions ] 1 State whether the following statements are true or false. a Like charges attract each other. b A charged object may attract a neutral one. c An electron is a small negative charge. d Charge tends to concentrate on sharp corners. e Lightning can occur only when charge flows from a cloud to the ground. 2 Copy each of the following statements and apply the correct word from the brackets. a Current is the flow of (electric/magnetic) charges. b Current is measured in (volts/amperes). c (A conductor/an insulator) does not allow charge to flow through it. d Most (plastics/metals) are good conductors. e (Voltage/current) is a measure of the energy available to push charges around a circuit. f A (wet/dry) cell contains a chemical paste and electrodes to produce free electrons. g It is usually (positive/negative) charges that flow in a circuit. 3 State whether the following statements are true or false. a A circuit contains a single globe glowing normally. It is possible to add 10 more globes to the circuit so that each glows just as brightly as the single globe did. b Voltage is shared in a series circuit. c Current always divides equally when it reaches several parallel branches in a circuit. d Current is measured with an ampmeter. e The least energy is used in the resistance sections in a circuit. f A set of Christmas-tree lights is connected in series. If one globe blows, all will go out. 4 Contrast a cell with a battery. 5 Outline how a safety switch works. 6 Use Figure 5.2.12 to describe how the element in an electric jug heats the water. 7 Outline the purpose of a fuse in an electric circuit.

150

[ Thinking questions ] 8 Explain how wearing rubber-soled shoes helps to protect electricians.

18 Use Figure 5.4.2 to construct a circuit diagram.

9 Identify which two surfaces rub together to produce charge in each of the following situations: a You brush your hair and generate a spark. b A car moves along a road and becomes charged. c You rip off the thin plastic that seals the lid of a container, only to find that it sticks to your fingers. d The hair on your arm is attracted to the surface of a plastic chair.

1.5 V cell

– +

10 Explain why on some cars there is a rubber strip containing metal dangling from the rear of the car and touching the road surface. 11 Contrast a household power supply with a battery or cell. 12 Contrast static electricity with current. Fig 5.4.2

[ Interpreting questions ]

Fig 5.4.3

13 Draw a series of diagrams to explain the stages involved in producing a photocopy of a black square drawn on a white sheet of paper. 14 Draw a diagram of a basic light globe, labelling the main parts. 15 Examine Figure 5.4.1 and identify which diagram best illustrates: a a neutral object b a positively charged object c a negatively charged object. Fig 5.4.1

++ ++ + ++

+ ++ +– – +

–+ –– – ++– –

–+ –+ –+ – +

A

B

C

D

19 Copy Figure 5.4.3 and identify devices used to measure the energy used by globe G and the current that passes through it.

G

20 In Figure 5.4.4 a positive charge is being pulled in the direction shown by another charge. Identify which arrow gives the direction of the electric field acting on the charge.

––– –– – – –– – E

F

D

+

A

16 Draw diagrams to demonstrate the appropriate symbols for the following circuit components: a b c d

open switch globe cell conducting wire.

17 Use appropriate symbols to draw a simple circuit that could turn a globe on and off.

C

B

Fig 5.4.4 Worksheet 5.6 Electricity crossword Worksheet 5.7 Sci-words

151

Ecology Key focus area:

>>> The implications of science for

4.4, 4.10, 5.10

Outcomes

society and the environment

By the end of this chapter you should be able to: write the ecosystem ‘address’ for plants and animals list the effects of bushfire, flood and drought on Australian environments describe how adaptations of animals and plants give them better chances of survival identify living and non-living factors in the environment describe how plants and animals interact in an ecosystem describe how biodiversity assists survival construct food chains and energy chains

Pre quiz

describe how humans have affected the environment.

1 Why don’t plants grow on the deep ocean floor?

2 What tree has its roots above the ground? 3 How do sharks clean their teeth? 4 What do spiders and mushrooms have in common?

5 What is living around you right now, what once lived and what is not living and never was?

6 The Australian desert is so dry and inhospitable that no plants or animals are able to live there. True or false?

7 How can bushfires sometimes be a good thing for an ecosystem?

>>>

6

3.1 UNIT

UNIT

context

6.1 Humans are animals that live in the environment. Like all other organisms, we take from the environment what we need to survive: food and water, shelter and a breeding mate. It is important to understand the way we live and how we

Ecosystems When we talk about an ecosystem, we are referring to the living organisms that inhabit a specific region, how they interact with each other, and the effects on them of the non-living environment around them. Ecology is the study of an ecosystem, the interactions and organisms within it, and the interactions of organisms with the non-living environment. The term living organisms includes all of the plants and animals that live or visit the region. Together they make up the community of the ecosystem. Each organism is also present in certain numbers, or in other words there is a population of organisms. Scientists study these populations to see what factors cause the population to increase or decrease.

fit into the environment. It is just as important for us to understand how other organisms fit in and to understand how we influence their health and survival.

The non-living (abiotic) environment includes physical factors such as rainfall, temperature, wind, sunlight, rocks, soil and water. As you can see, an ecosystem, can be quite a complicated thing!

Biospheres Just as you have an address, so too can we give an address to the organisms that live in a specific area. The biosphere is the broadest category in the address. It refers to that part of the Earth (including its atmosphere) in which living organisms can be found. The Earth biosphere is then divided into a second level of biogeographical regions. For example, Australia and North America are biogeographical regions. Each region has its own unique plant and animal life. These interact with each other, and depend on the unique physical conditions that are present there.

Biomes

Fig 6.1.1

A population of magpie geese.

The biome is the third level of an organism’s address, and refers to areas that have similar climatic conditions; that is, similar soil types, rainfall, temperature and so on. Grasslands, deserts, the tropics, subtropics and the arctic are examples of different biomes. Scientists have observed that organisms living in the same type of biome have similar features, regardless of whether they are in the same biogeographical region. The Simpson Desert, for example,

Biosphere 2 Biosphere 2 is a humanmade structure covering 1.3 hectares near Oracle, Arizona, USA. Four men and four women lived with more than 3800 other plant and animal species within the 200 000 cubic metre structure for two years in order to study plant–animal–human interactions. The outcome? Failure! It appears that there is a lot more to an ecosystem than was ever imagined.

Migration Some animals can move from one biome to another. Salmon begin their lives in a freshwater river biome and then move to a saltwater ocean biome to mature. When they are ready to reproduce, they migrate back to their original freshwater home to lay their eggs. Once the eggs are laid, the adult salmon die, their bodies providing food for the fingerlings (baby salmon).

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Ecosystems

World distribution map of the locations of different biomes

Fig 6.1.2

Equatorial and tropical rainforests Tropical monsoon forests Mediterranean shrub woodlands Temperate forests (evergreen and deciduous) Cold temperate coniferous forests Tropical savanna grasslands Temperate grasslands Deserts and semi-desert Tundra

High mountains

could be the individual sand dunes, the clay pans between them, or a tussock of grass or scraggly tree growing on them. A tropical biome will have vastly different habitats from a desert biome, such as the moist, protected areas at ground level, the very top of the leaf canopy—and everything in between!

Fig 6.1.3

Herds of camels were introduced to Australia and can be found grazing on the tough grasses of the Simpson Desert. They are able to thrive in the Australian desert biome which has a similar climate to the desert biome of their home countries in the Middle East.

is a desert biome in the Australian biogeographical region. The plants and animals found there show many characteristics similar to those found in other desert biomes around the world.

154

Fig 6.1.4

A clay pan habitat in the Simpson Desert. Although it looks dry and lifeless, it is the habitat for a number of living things.

Habitats

Microhabitats

Within each biome are different habitats, the fourth level of an organism’s address. This term defines an even more specific area. In a desert biome the habitats

You may think that we can’t get any more specific than saying an organism lives on the ground in a tropical rainforest or on a sandy dune in the desert.

Think again! In every habitat A different world there are areas where conditions The introduction of the vary from the rest of the habitat. cane toad to control the In a tropical rainforest, some sugar cane beetle has proved spectacularly organisms may live between unsuccessful. Why? the roots of the trees, others Because cane toads live on under the bark and others in the ground, and the beetles the dirt itself. On a desert sand live at the top of the cane t! Living in a different plan dune, a few centimetres below microhabitat can be like the surface beneath a clump living in a different world. of spinifex, you may find a tiny marsupial called a kowari sleeping quite happily in its own microhabitat! The microhabitat is the last and most specific part of an organism’s ‘address’. The microhabitat may also be known as the niche. Fig 6.1.5

The kowari is a small, alert and tenacious little marsupial found in central Australia.

The non-living environment includes the soil type of the dunes, the rainfall and the temperature of the desert. Everything in the ecosystem is connected in some way.

UNIT

6.1 Australia’s ecosystem Australia is the most arid inhabited continent on Earth. It has unique ecosystems with unique communities living in them. Part of this uniqueness comes from these ecosystems being exposed to various human-made and natural events. The three main events affecting Australia’s ecosystems are: • flood • bushfire • drought. Although these events can devastate much of an ecosystem, they can also have some positive outcomes. Floods can deposit fertile new soil for plants to grow in and fire can trigger the germination of new plants. The effects of these events may be felt for many years, resulting in changes within the ecosystem.

Flood

The ‘address’ of the kowari in Figure 6.1.5 could be written as: • Australia (its biosphere) • Central Australia (its biogeographical region) • Stony deserts (its biome). At night the kowari hunts in the sand dunes and clay pans for food such as plants, small birds, marsupial mice and lizards. These areas are its habitat. During the extreme heat of the day, the kowari returns to its burrow, a few centimetres below the surface. This is its microhabitat. The kowari’s community includes: • the plants that the kowari uses for shelter or food • the plants that provide shelter to, or are eaten by, animals that are then eaten by the kowari • the animals that the kowari eats • the other kowaris in the area.

Flooding can cover extremely large areas of Australia, affecting many varied ecosystems. The flooding of Lake Eyre in 1973–74 covered an area of more than 390 000 square kilometres (this is equivalent to about half the area of New South Wales!), filling the normally dry lake bed to a depth of 10 metres. After the initial quick devastation, floods can have positive ecological effects, such as: • replenishment of ground and soil water • increased breeding of water-dependent species such as fish and pelicans, and therefore an increase in numbers • regeneration of long-living and slow-reproducing trees in arid biomes.

Flooding can devastate the natural ecosystem as well as planted crops and property.

Fig 6.1.6

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Ecosystems Bushfire For millions of years, lightning Burnt out strikes have sparked bushfires It may appear from the news in Australia. Many native that most bushfires are deliberately lit. Although plants and animals have arson is a major cause of fire, developed specialised ways lightning is just as much to to survive fire and respond blame. In Victoria over the last 20 years, 26 per cent of quickly to its impact, such as bushfires were caused by the following. lightning and 25 per cent by • Some native plant species arson. A further 16 per cent were caused by ‘escapes’ from need fire to release controlled burning on farms, the seeds they need to 10 per cent from campfires, regenerate. Others will 7 per cent from dropped cigarettes, 3 per cent from die and never regenerate. machinery sparks, 2 per cent The type of bush that from escapes from controlled regenerates after fire will burning in bushland and depend on what plant 12 per cent from unknown or other causes. Some species were there before Aboriginal tribes deliberately and how hot the fire was. set fire to the bush. This • Highly mobile animals reduces tree cover and produces more grazing such as birds, kangaroos pasture for kangaroos, which and wallabies may be can then be hunted for food. able to move out of the way of an approaching fire to safer refuges. Slower wombats and echidnas may survive the fire by sheltering in

burrows or logs while fire passes overhead. Reptiles and amphibians also take refuge underground. Despite this, many animals die and populations initially drop. • Bushfire releases nutrients into the soil that allow plants to recover and seeds to grow quickly. Fire removes vegetation and exposes the soil to wind and water, making it very susceptible to erosion. Worksheet 6.1 Bushfire intensity

Drought Although floods and bushfire bring rapid changes to ecosystems, drought ‘creeps up’ over a number of years when rainfall is less than normal. The effects, however, can be devastating, particularly to humans and their farms. Droughts can have an impact on huge areas of land, affecting many more ecosystems than fire or flood. The ecosystems most prone to drought often have a low capacity to respond, and widespread death and famine is the result for the organisms in the ecosystem. Drought can also degrade the land and affect the way land is used in the future. Definitions of drought vary widely. In the United Kingdom, 14 days without rain is considered a drought! In Australia, a drought Prac 1 is ‘official’ when rainfall over a year is in the p. 158 lowest 10 per cent ever recorded.

Drought kills many living organisms and degrades vast areas of land.

Fig 6.1.7

156

Fire has both negative and positive effects on the environment.

Fig 6.1.8

UNIT

6 .1

[ Questions ]

Checkpoint Ecosystems 1 Identify terms for each of the following: a all of the plants and animals in a region b physical factors such as rainfall, light etc c many organisms living together.

Biospheres 2 Copy each of the following statements and modify any that are incorrect. a Ecology is the study of organisms and their non-living environment. b The small details about where an organism lives are called its biosphere. c The primary or biggest level of an organism's biosphere is its biographical region. 3 State an example of a biogeographical region in Australia.

Biomes 4 Outline the relationship between a biome, a biogeographical region and a biosphere. 5 List four different types of biomes.

Habitat 6 Use an example to demonstrate what is meant by a ‘habitat’. 7 Use Figures 6.1.3 and 6.1.4 to outline some features of the habitats that might be found in desert environments. 8 List two features of the habitat of a tropical biome.

Microhabitat 9 In the desert, living things may not share the same environment. Explain how microhabitats can vary.

UNIT

6.1 Think 16 Classify the following as living (L) or non-living (NL) components of the environment: a a seed d a tumbleweed b dried flowers e the hair in a hairbrush. c the bark on a tree 17 Modify the words in italics to make the following statements correct. a The term ‘biosphere’ refers to that part of the earth (except its atmosphere) in which living organisms can be found. b The term ‘biome’ refers to areas that have different climatic conditions. c The term ‘habitat’ is used to describe a less specific area than the term ‘biome’. d An example of a desert microhabitat would be the Simpson Desert. 18 Use the following list as a guide to identify where you live (your address). The first level is done for you. Biosphere Biogeographical region Biome Habitat Microhabitat

Planet Earth (your country) (your city) (your street) (your house or apartment number)

19 Copy each of the following statements and modify any that are incorrect. a ‘Ecosystem’ refers to the plants that live in a specific area. b The plants and animals in each biogeographical region are unique. c Animals that live in a grassland biome in different biogeographical regions are unlikely to show any similarities. d The island of Tasmania is considered a microhabitat.

Australia’s ecosystem

20 Use an example to list the following in order from smallest (most specific) to largest (least specific): microhabitat, biome, biosphere, habitat, biogeographical region.

11 List the three main events that affect Australia’s ecosystems.

21 Propose a reason for organisms living in the same type of biome having similar characteristics.

12 Drought can be considered the worst of the natural hazards. Outline some consequences of drought.

22 Explain how animals such as the kowari survive the hot dust storms that often whip across the desert.

13 Propose one benefit and one disadvantage of flooding.

23 Copy the following table into your workbook and match the terms on the left with the correct terms on the right.

10 Describe how a microhabitat fits into an organism’s ‘address’.

14 Fire can assist plant species to survive. Outline how this is possible. 15 Construct a pie chart showing the causes of bushfires in Victoria in the last 20 years.

Carnarvon Gorge, Queensland The upstream side Earth Carnarvon River

biosphere habitat of a river rock temperate biome microhabitat

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Ecosystems

Analyse 24 Year 8 students at two high schools, Class A in Broken Hill and Class N in Newcastle, were asked to record the amount of rainfall that fell from 1 May to 1 October. Class A recorded less than 90 mm of rain, and Class N recorded 300 mm of rain. Assess whether the vegetation around Broken Hill and Newcastle would be the same or different and justify your answer. 25 Not all water environments are the same. Consider the saltwater oceans, freshwater rivers or lakes, dams or the family fish tank. Contrast these three water environments.

[ Extension ] Investigate 1 Research the Carnarvon Gorge, Queensland. a Construct a map of Australia, indicating where the gorge is located. b Describe or illustrate the plants and animals that live in the gorge. c Describe the features of the gorge that make it possible for lichens and moss to exist there. 2 Examine your own backyard or school ground to identify: a what plants and animals live there b what their water requirements are c what types of soil they live in. d how the plants there interact with each other.

UNIT

6 .1

27 People who keep fish must be careful to keep the water in their fish tank fresh. To do this, they replace about 70 per cent of the water every few weeks. Justify why 70 per cent of the water is replaced and not the whole lot.

Action 3 Design a way of making your own mini-biome in an aquarium. Model it after something that interests you, using the materials you would normally find in that particular biome. a Explain why your mini-biome is a ‘closed system’. b Propose some problems that might be encountered. c Explain whether a closed system accurately represents a biome.

Creative writing A day in the life of … Imagine you are a kowari (or some other animal of your choice). Write a short story about your activities over the last 24 hours. Include in your story a description of your home, what you have eaten during this time and perhaps an adventure or two that you have had this day.

[ Practical activity ] Cut and paste Aim To compare the different levels of an

Prac 1 Unit 6.1

26 When adult salmon have laid their eggs, they die. This is essential if the ‘fingerlings’ are to survive. Propose a reason for this.

ecosystem

Method Place the diagrams in order from biosphere to niche. You may choose to photocopy the diagrams to cut and paste, or simply redraw the diagrams in the correct order. Fig 6.1.9

158

UNIT

context

6.2 Organisms are affected by their environment in many ways. Predators might eat them and their young, while non-living factors such as extreme daytime temperatures might mean that they can only be active at night. How are you affected by the living and nonliving things in your environment? How do you survive with all these pressures? You adapt!

Adaptations An organism can live only in an environment that it is suited for: it must have behavioural and physical characteristics that will allow it to survive. These characteristics are called adaptations. Consider the echidna. This mammal has a stocky body and its back and sides are covered in spines. Between the spines is a thick, coarse fur, the amount and colour of which depends on where the echidna lives. The colour of the spines also varies. Each spine can have several bands of colour, providing an effective camouflage from predators. The colour of the fur and the presence and colour of spines are examples of physical adaptations—the echidna was born with these adaptations and has no control over them. When an echidna is being attacked, it will roll into a tight ball. If the ground is soft enough, it will then dig itself in. Only the spines are exposed, making the echidna very unappetising and painful to the attacker! This is an example of a behavioural adaptation. Behavioural adaptations can be instinctive or learnt. For example,

Fig 6.2.1

The echidna—an Australian marsupial perfectly adapted to its environment

fish-eater seed-eaters

honeyeater

scavenger

insect-eater

omnivore

predator

These bird beaks show the physical adaptations of various bird species to the different types of food they eat.

Fig 6.2.2

159

>>>

Physical attributes of an ecosystem on hot days people and animals like to seek shade because it cools them down—in cooler weather they cuddle up. This is instinctive behaviour, something we do automatically. When a seal pup watches its mother chase fish, it learns how to hunt for food. The pup then practises until it is able to feed itself. This is an example of a learnt behaviour. Likewise, a pet dog will learn the noises associated with its feeding time and will respond accordingly.

Effects of the non-living environment

pH

Non-living or abiotic factors influence where an organism can live. They include: Hot night life • temperature In the Australian desert the Biological processes such temperatures can reach 50°C during the day. It’s as digestion, respiration, too hot for most animals to excretion and reproduction do anything and they will take place at an optimum spend their days sleeping temperature range. When in a cool shelter. The desert thus looks deserted. The living things get too hot animals will come out, or too cold, they do not however, in the cool of function properly. the night to feed, play and mate. Some humans have • humidity of the air also learnt that this makes This is the amount of water sense in hot climates: the vapour in the air. The Spanish, Portuguese and Mexicans traditionally have amount of water lost from a ‘siesta’ during the hot an organism into the air afternoons, arising in the depends on the humidity cool evenings. of the air. If the air is very humid (as in tropical biomes) plants and animals will lose very little water. In contrast, desert biomes have very little humidity. Plants and animals that live in these areas have special features to help them retain as much water as possible. • amount of light energy available Light provides green plants with the energy they need to carry out photosynthesis. Light is readily available on land. In a water environment, however, most of the light is reflected at the surface—with only a small percentage (the green and blue colours of the spectrum) penetrating to any depth. This is called the photic zone and is where green plants such as seaweeds and kelp will grow. Plants are Prac 1 not found on the deep, dark ocean floor. p. 164

160

• acidity of the soil and water Plants have a preferred soil acidity in which they like to live, as do organisms that live in water. We measure the acidity Prac 2 using the pH scale. p. 164

1

2

3

stronger acid

4

5

6

7

8

9 10 11 12 13 14

weaker

weaker

Sea lettuce Sea lettuce is able to live much deeper than most plants, because it is more efficient at absorbing light in the blue region of the spectrum than other plants.

neutral

The pH scale: 7 is neutral, below 7 is acidic, above 7 is alkaline (basic).

stronger alkaline

Fig 6.2.3

• salinity of the water surrounding, or available to, the organism Salinity is a measure of the ‘saltiness’ of water. Freshwater and marine organisms experience very different salinity and show marked differences in the way their bodies function.

Fig 6.2.4

The albatross is a bird that lives close to the sea. Birds that live in this type of environment possess special salt glands, which are situated on their heads above their eyes. The glands are connected to the nostrils and remove any excess salt they consume. The salt runs out of the nostrils and down grooves in the side of their beaks, finally dripping off the tips.

• mineral salts and trace elements available Where a plant lives is determined by the nutrients that are available in the soil. • wave and water currents The intertidal area is that area that lies between high and low tides. At low tide it is exposed to the air, while at high tide it is completely submerged. Those organisms that live in this region must be able to live in both conditions. They may also need to develop ways to stop being washed away. Likewise, organisms that live in fast-flowing streams require great strength as they battle against the force of the water. • shelter Shelter gives protection from factors such as predators and the weather and can be found in many places in an ecosystem—under rocks, bark or leaf litter; inside hollow trees, or hollow logs on the ground; and even in underground burrows. Different animals and plants require different types of shelter to survive. • wind and air currents Areas that are heavily buffeted by strong winds can be inhabited only by plants that have strong root systems. The effect of the wind on this pine tree can be clearly seen.

Biotic factors include: • competition Often, animals living in the Mutual benefit same area have the same The giant rafflesia is a food or nesting requirements. parasitic plant that lives on other climbing plants in the This means that the amount forests of South-East Asia. of available food or nesting For most of the time, the materials must be shared. Plants rafflesia is hidden within its compete with each other for host. It makes its presence known, however, by nutrients in the soil and for the producing a flower that can light that is available. be as heavy as 7 kilograms • dispersal and emits the fragrance of rotting meat! This attracts This refers to how an organism the flies necessary for its is scattered throughout an pollination. ecosystem. While animals can move freely by themselves, plants rely on the wind, insects or animals to disperse them. Their seeds are often shaped to help them in this process.

Fig 6.2.5

Fig 6.2.6

Effects of the living environment The living or biotic factors that influence where an organism can live include all of the other plants and animals that it comes into contact with directly, or is influenced by indirectly. Sometimes the relationship is beneficial; at other times it isn’t.

A bee collects pollen and transfers it from one plant to another, assisting the plant in its reproduction.

• predation The term ‘predation’ refers to the act of one animal catching and eating another. Every organism in the ecosystem needs nutrients and many will get them by consuming other inhabitants in the area. Of course they might be eaten too!

161

UNIT

6.2

>>>

Physical attributes of an ecosystem • human intervention Human beings are the most powerful and influential biotic factors on the ecosystem. The effects of humans will be investigated in detail in Unit 6.4.

UNIT

6 .2

Defence ed Many animals have develop them ble ena that tics eris charact e toad to evade predators. The can its on ds glan on pois s contain ion shoulders, a physical adaptat toad The nts. pare its by on passed merable has caused the death of innu numbers of native snakes and s and goannas, as well as pet dog had has toad the ly nate ortu cats. Unf it tle bee e can ar no effect on the sug ! trol con to in t ugh bro was

[ Questions ]

Checkpoint Adaptations 1 Use examples to contrast a behavioural adaptation with a physical adaptation. 2 Use an example to contrast an instinctive with a learnt adaptation.

Effects of the non-living environment 3 Define the term ‘abiotic’. 4 List three abiotic features of the environment.

Effects of the living environment 5 Define the term ‘biotic’. 6 Copy each of the following statements and modify any that are incorrect. a The non-living factors that influence where an organism can live are called biotic factors. b The more saturated with water the air is, the less humid it is. c On land, the percentage of oxygen in the air increases with altitude. d Water that flows quickly has less oxygen than water that is still.

Think 7 Animals tend to curl up when they are cold, and lie sprawled out when they are hot. Justify whether this is a behavioural or a physical adaptation. 8 Camels have nostrils that can be closed. This is an adaptation to the sandy, wind-blown areas that they inhabit. Justify whether this is a behavioural or a physical adaptation.

162

Fig 6.2.7

The predatory crocodile of Northern Australia can grow to lengths of up to six metres.

9 The little penguin (sometimes called the fairy penguin) is a fish-eating bird. Draw the type of beak you would expect it to have and explain whether this is a physical or a behavioural adaptation. 10 African finches and Australian finches have similarly shaped beaks. Australian finches eat a variety of seeds. a Predict the type of food you would expect African finches to eat. b Describe their habitat. 11 Identify whether the following statements are true or false. a The colour of the background on which an organism lives (eg a rock face) is an example of an abiotic factor. b The amount of nutrient in the soil is an abiotic factor. c The parasitic nematode Wuchereria bancrofti is responsible for a condition known as elephantiasis in humans. We can say that the human being is a part of the nematode’s biotic environment. d Koalas and magpies living in the same tree are competitors. 12 Predict some of the abiotic factors that would influence the following organisms: a an orca (killer whale) b a red-back spider c a mushroom on a forest floor d your family pet. 13 Elephants have physically adapted to their environment by having very large, thin ears. Propose which abiotic factor caused this adaptation.

14 Mangroves grow in intertidal areas (areas that are exposed to the air at low tide, but are covered in water at high tide). Predict some abiotic factors that they might have to contend with during the course of a day. 15 Marine mammals and marine fish have many similar characteristics. Identify some of the abiotic factors that affect both of them. 16 List three abiotic factors that affect you. 17 List three biotic factors that affect you. 18 Rivers drain into the sea. Explain why fish living in the sea cannot be found in the rivers.

19 Why do farmers often alternate the growing of legume crops, such as peas or clover, with other crops? Justify your answer.

UNIT

6.2 20 Both desert cacti and alpine pine trees have long, needle-shaped leaves. This is an adaptation to limited water availability. Considering the high snowfall of many alpine regions, propose a reason for pine trees exhibiting such a characteristic. 21 The ‘tree line’ is an imaginary line at a certain altitude on a mountain beyond which no trees are found. Propose a reason for trees not growing beyond this point.

[ Extension ] Investigate 1 Research the life cycle of a frog and present your information as a poster aimed at people visiting a National Park who want to learn more about the wildlife there. On your poster: a describe the biotic and abiotic factors that influence the water phase of the life cycle b describe how these factors change when the frog moves onto a land environment c outline the characteristics that adult frogs display that enable them to move from water to land d explain whether the adult frog is able to leave its watery environment completely.

Action 2 a Record ten habits of a family pet for one week. b Explain whether these habits are instinctive or learnt. 3 Bushwalkers think that keeping the environment free from human interference is essential. Land developers say that it is important to utilise the land we have to provide homes and recreational facilities for people to enjoy. Those in the mining and timber industries insist that the land should be used to provide the raw materials to meet the needs of technological progress. Assess the validity of each claim by conducting a class debate.

Surf 4 Find out more about Australian ecosystems by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6 and clicking on the destinations button.

Why have national parks?

The Royal National Park sou th of Sydney is the second oldest national park in the world. Only Yellowstone National Par k in the USA is older. Nowadays, we think of national parks as a way of protecting fragile ecosystems. In 1886, however, Royal Nationa l Park was thought of as a ‘Metropolitan pleasure ground’ where ‘experienced picnickers cou ld forget the labours and worries of town’ and ‘tak e their leisure and recuperate with intellectual activities such as sketching, photography and botany’.

a Select an Australian ecosystem and outline the abiotic features that exist in this ecosystem. b Outline the biotic features of this ecosystem. c Design a diagram or model of an animal to demonstrate the adaptations to survive perfectly in this environment. d Construct a key outlining the main adaptations of your animal.

Creative writing National parks Comment on the statement ‘Australia should have more national parks’. State whether you agree with this statement, or whether you think we have enough national parks. Explain the role that parks play in the conservation of the ecosystem.

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Physical attributes of an ecosystem

UNIT

6 .2

[ Practical activities ] The effect of an abiotic factor on plant growth

Prac 1 Unit 6.2

Aim To determine the effect of the amount of light on plant growth

Testing for soil acidity around the schoolyard Prac 2 Unit 6.2

Aim To test the acidity of the soil at various locations around the schoolyard

Equipment

Equipment

6 individually potted seedlings (these must be of the same species, at the same stage of development), 2 covers—one should be translucent (allowing a small percentage of light through), the other should be completely opaque (allowing no light through)

3 or 4 test tubes, distilled water, 3 or 4 beakers, glass stirring rod, litmus paper, filter paper (eg coffee filter paper)

Method 1 Set aside two of the seedlings as control plants. Place these in a sunlit position. 2 Place two of the other seedlings under the translucent cover. Place the last two seedlings under the opaque cover. 3 Monitor the plants for at least one week. During this time, each seedling should be watered at the same time with a specific amount of water. (Be careful not to overwater the plants.) 4 Record your findings at the end of the specified time period.

Questions 1 Justify the use of more seedlings than required. 2 Justify why it is important that the seedlings should be of the same species and at the same stage of development. 3 Explain why the two seedlings that were set aside and given sunlight were needed. 4 Design an experiment to investigate other abiotic factors such as the soil type, humidity, water availability and temperature.

Method 1 Collect samples of soil (each enough to fill a large test tube) from three or four different areas around the schoolyard. Label your test tubes as sample 1, sample 2 and so on. You could collect your samples from: a under a pine or eucalypt tree b from the middle of the playing field c near a rubbish bin d by the bicycle racks. 2 Place each sample into a beaker (label your beakers sample 1, sample 2 and so on), and add approximately 100 mL of distilled water. 3 Stir the sample for some time, until everything is well mixed. Allow the sample to settle. 4 Separate the water from the soil using a filter paper. 5 Test the acidity of the water using both red and blue litmus paper. Note: Red litmus paper turns blue in the presence of basic substances. 6 Record the results you obtained in a table. For example: Sample number

pH value

Sample 1

6

Questions 1 Identify a suitable control for this experiment. 2 Explain why distilled water was used rather than tap water. 3 Use the table in Figure 6.2.3 to identify the pH of each sample and explain whether it is acidic or basic. 4 Account for the results you obtained from your samples.

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UNIT

context

6.3 Whatever we eat consists of animal or plant parts. The food we consume contains the energy and nutrients that we require for living. All living things require energy. This energy is used by the organism for growth,

Energy for life Some 150 000 000 kilometres from Earth is the Sun— the source of all energy on Earth. Plants, green algae and a number of microorganisms are able to use light from the Sun to provide the energy they need for life. They do this by converting carbon dioxide and water into food (a simple sugar called glucose) and oxygen. This process is called photosynthesis, and can be written as a simple chemical equation:

→

carbon dioxide + water glucose + oxygen (in the presence of sunlight)

oxygen gas (exits through stomata pores)

sunlight carbon dioxide (through stomata)

sugar (to rest of plant)

Fig 6.3.1

water and nutrients (via roots)

repair and reproduction, and allows the organism to do the things necessary for survival. Considering all the living things on Earth, that is an enormous amount of energy. So where does all this energy come from, and where does it go?

Those organisms that produce their own food are referred to as producers or autotrophs. They are essential because they provide oxygen and food for all the other organisms in the ecosystem.

The flow of nutrients through an ecosystem Not all organisms produce their own food. Those that do not are called consumers or heterotrophs. Animals that eat plants are referred to as primary consumers or herbivores. Often, these animals provide food for other animals. The animals that eat the herbivores are called secondary consumers or carnivores. Those consumers that are able to eat both plants and animals are referred to as omnivores. The interaction between producers, primary consumers and secondary consumers (and sometimes tertiary consumers) is illustrated in Figure 6.3.2. This nutritional sequence is referred to as a food chain. It is called a ‘chain’ because each living organism in the chain is like a ‘link’, and each one depends on the organism that comes before it. In general, food chains rarely have more than six links (called trophic levels). In every ecological community several food chains are interrelated because the organisms that make up those food chains have various food sources. This interaction of food chains is known as a food web.

The process of photosynthesis

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Food chains and food webs: interactions of life The interaction between producers, primary consumers, secondary consumers and tertiary consumers

>>>

Fig 6.3.2

green water plants

Sun

small fish, crustaceans penguin

carnivorous fish

Fig 6.3.4

166

An example of a simple food chain— the arrow is drawn so that it points in the direction in which the food is going. The arrow really means ‘is eaten by’.

Fig 6.3.3

An example of a food web; animals are able to survive adverse conditions if they have more than one source of food.

Fig 6.3.5

A primary consumer—an insect—is eaten by a secondary consumer—a spider.

then their fate is determined by the fate of that plant. If the plant were to be wiped out by disease then the herbivores would be wiped out too. In turn, the carnivores that ate them would be wiped out. If, on the other hand, the herbivores have a variety of plants to choose from, they can probably survive the loss of one particular species. Humans have reduced the biodiversity of many ecosystems by removing the natural vegetation and replacing it with one specific type of plant, for example wheat. As a result, many species are now extinct.

UNIT

6.3

The flow of energy through an ecosystem

Biodiversity Biodiversity refers to the number of different species present in a community. Communities with high biodiversity, where there are many different species of plants and animals living together, survive environmental changes better than communities with low biodiversity, where there are few. There are usually many different sources of food in a community of high biodiversity: there are alternatives if one food source is destroyed. The community is more stable and is able to survive changes in the environment more easily. If the herbivores in a community rely on one particular plant species for all of their food needs,

Energy in an ecosystem moves in one direction only. During photosynthesis, glucose is produced inside the leaves of plants from carbon dioxide and water. The energy for this reaction is provided by the Sun’s light. We can say that light energy from the Sun has been converted into chemical energy inside the plant. Plants use only a small amount (approximately 0.2 per cent) of the Sun’s energy available to them, and at each level of the food chain only about 5 per cent—20 per cent of the energy available is transferred to the next level. For this reason, the number of plants in any ecosystem is greater than the number of herbivores and carnivores that eat them.

seal

fish

small crustaceans plankton

A field of wheat. The biodiversity of an ecosystem is reduced when many species of plants are replaced by a single species, causing the ecosystem to be less stable.

Fig 6.3.6

Fig 6.3.7

At each level of the food chain, energy is lost. The ‘food pyramid’ shows the decrease in numbers from the first level of producers to the final level of consumers.

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Food chains and food webs: interactions of life

>>> Clean teeth

Decomposers: the last link in the food chain

Detritus Fragments of dead organic material present in soil are referred to as detritus. Those organisms that eat or ingest this material are called detritivores. Earthworms and dung beetles are examples of detritivores.

Fig 6.3.8

The term organic matter refers to all matter that comes from living organisms. All of this matter contains the element carbon. Organic matter is recycled within the ecosystem due to the activity of decomposers. This group of organisms breaks down the organic matter in dead bodies of plants and animals and releases the nutrients they contain for plants to use in their growth. Decomposers include bacteria and fungi. In effect, they are nature’s recyclers.

Relationships between organisms

No plant or animal living in a community lives in isolation. This interaction may be by direct contact, especially when predators eat other animals! It can also be indirect as in the case of competition for food. The different types of interaction include: • mutualism (symbiosis) Both organisms benefit by their relationship with each other. An example of mutualism is the relationship between the false clown anemone fish with the anemone. Slime on the fish’s body prevents it being stung and it lives and feeds under the protection of its host. The anemone receives in return scraps of food from the fish, and is cleaned of parasites.

A decomposing apple. Food turns mouldy when attacked by a fungus.

Fig 6.3.10

Dung beetles have recently been introduced into public parks by many urban councils in an effort to reduce the amount of dog faeces.

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It was previously thought that sharks had to keep swimming in order to breathe. Recently, however, scientists have observed sharks resting on the ocean floor, with their mouths open. The reason? They are having their teeth cleaned by lots of little ‘cleaner fish’. Now that’s a trusting relationship!

Fig 6.3.9

A mutual relationship—both organisms gain from the relationship.

• commensalism One species benefits from the interaction while the other species is unaffected. Tropical fish called remora attach themselves to faster fish such as sharks using a sucker-like pad on the top of their heads. The sharks don’t benefit from the remora’s presence, nor are they harmed.

Mutual benefit Sea anemones have been observed to ‘hitch’ a ride on the back of hermit crabs. The hermit crab is camouflaged and protected by the anemone, and the anemone gains mobility! This is an example of a relationship that is mutually beneficial.

• amensalism One species is harmed by the Bubble netting interaction while the other Humpback whales employ the unusual technique of species is unaffected. Cows ‘bubble netting’ to gather and sheep commonly form food. Several whales swim trails as they walk to and below a school of fish and then ascend spirally from feeding areas. They are upwards around the fish, unaffected by the trail, but exhaling air as they go up. the plants they trample are The air forms columns of destroyed. bubbles that surround the fish and keep them in a • competition close-knit group, making As seen in Unit 6.2, different it easier for the whales to animals or plants may fight for feed. This is an example of cooperative hunting. the same food resource, water or nesting material. • exploitation One species benefits from the interaction while the other is harmed. This type of interaction includes: a predation One species kills the other for food, such as a dingo hunting a lizard.

UNIT

6 .3

UNIT

6.3 b herbivory Although herbivores eat plants they rarely eat the whole thing and so do not usually kill them. The size of the plant suffers, of course. Kangaroos grazing on spinifex grass keep it short. c parasitism A parasite is an organism that lives in or on another, called the host. In most cases, the parasitic organism does not kill Parasitoids its host, although it can cause Some parasites kill their host. These are called severe problems. Tapeworms are parasitoids. One parasites that live in the gut of parasitoid is the braconid animals. Unless treated, dogs fly, which lays its eggs and cats often have tapeworms. inside a living cabbage white caterpillar. When the Humans can have parasites too. eggs hatch, the fly grubs Head lice are parasites. eat the caterpillar from the inside out!

Worksheet 6.2 Whodunnit?

[ Questions ]

Checkpoint Energy for life 1 Recall the name of the process represented by the following equation: carbon dioxide + water → glucose + oxygen 2 Use an example to outline the role of producers in a food chain.

The flow of nutrients through an ecosystem 3 State whether the following statements are true or false. a All organisms can produce their own food. b Heterotrophs can produce their own food. c Animals that eat plants are primary producers. d Carnivores eat herbivores. 4 State the maximum number of links that may occur in a food chain. 5 Define what is meant by a ‘food web’.

Biodiversity 6 Use an example to explain how biodiversity can help a community to survive.

8 Account for the fact that the number of plants in an ecosystem is greater than the number of herbivores and carnivores.

Decomposers: the last link in the food chain 9 List two features of organic matter. 10 Explain how organic matter is recycled by decomposers.

Relationships between organisms 11 Use an example to explain the meaning of the following terms: a mutualism b commensalism c amensalism d competition e exploitation. 12 Compare predation, herbivory and parasitism.

Think 13 Do you think the Sun really is the source of all life on Earth? Justify your answer.

The flow of energy through an ecosystem 7 State the name of the simple sugar that acts as food and stores the energy from the Sun in plants.

>> 169

Food chains and food webs: interactions of life

14 Copy the text below into your workbook and draw a line to identify the words in the first column that match the names of the organisms in the second column: autotroph heterotroph omnivore

human being rose bush koala

>>> 18 Cooperative hunting could benefit a carnivore species. Justify this statement. 19 Propose a reason for the fact that two organisms of the same species might require different quantities of food. 20 Explain why food chains rarely have more than six links.

15 Is the term ‘producer’ an accurate description of a green plant? Justify your answer. 16 Identify the correct term (parasitism, mutualism or commensalism) for the following relationships: a the tapeworm Echinococcum granulosus and its dog host b the fungus that causes tinea on a human foot c honey possums feed on the pollen of a number of native banksias, dispersing the pollen as they move from tree to tree. 17 Classify the relationship between a dog and its fleas.

[ Extension ]

Skills 21 Construct a simple food chain in your workbook, using the animals listed and including arrows to indicate which organism is eaten by the other: mouse, owl, snake, grass. 22 Identify the producer and the primary, secondary and tertiary consumers in the food chain in the previous question. 23 Construct a simple food chain for a set of organisms that you might find in your own backyard. 24 A scientist was determining the number of food chains present in several different areas. In area A, he found 10 different food chains. In area B, he found 50 different food chains. In which area would you expect to find the greatest biodiversity? Explain your reasoning.

Investigate 1 Many carnivorous animals employ unique strategies to catch their prey. The angler fish uses a ‘lure’ to entice its prey into striking distance. Other organisms, such as the praying mantis, are the same colour as their surroundings (they are camouflaged). Some, such as the killer whale and the hyena, work in a cooperative group.

a Research one particular organism that uses a unique strategy to catch prey. b Summarise the information in the form of a magazine article of 1000 words with illustrations. 2 Dingoes thrive in many different biomes, including the wet and dry tropics of Queensland, the arid and semi-arid region of Central Australia, the cool coastal mountainous region of south-east Australia and the humid coastal mountains of eastern Australia. The food chain is different for each different biome. a Research the different biomes the dingoes occupy and the food chains they are a part of. b Summarise information in the form of a film documentary or produce a series of food webs for each biome.

Surf 3 Construct and analyse some examples of food webs by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6, and clicking on the destinations button. Fig 6.3.11

170

UNIT

context

6. 4 For thousands of years, most people lived and worked in small villages. Populations were small and the natural resources around them were all they needed to survive. People used simple handmade tools and lived in simple dwellings lit and warmed by fire. Clothes were handmade and food was either hunted or gathered from the local surroundings. The waste produced was easily absorbed back into the environment through the natural cycles.

In the mid-1700s, however, the Industrial Revolution began, and by the mid 1850s many small villages had become industrial towns. Machinemade goods were in demand, and the railway was developed to quickly transport them from place to place. New types of wastes and pollutants were produced in large quantities. Human civilisation, and in turn the environment, had been changed forever.

World population (millions)

12 000 11 000 predicted range

10 000 9000 8000 7000 6000 5000 4000 3000 2000

2050

1750 1800 1850 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

1000

Year

Fig 6.4.1

As the human population increases the demands to produce food, energy and shelter and living requirements increase, resulting in a decrease in area for plant and animal habitation.

Pollution A pollutant is anything that makes the environment unfit or unhealthy for the organisms that live there. Pollutants affect the atmosphere, the land and the water. Some may arise from natural causes such as volcanic eruptions, but they are more commonly the result of human activity.

Shortened life span The average life span of a tree in the countryside is about 150 years. In an average city setting, it is only 32 years, while in the middle of a large city, it is as little as 13 years.

Air pollution Industrial activity releases a constant stream of pollutants into the atmosphere. These include sulfur dioxide, nitrogen dioxide, carbon monoxide, carbon dioxide, hydrogen sulfide, dust and smoke. Motor vehicles release hydrocarbons, lead, nitric oxide and carbon monoxide. In the presence of sunlight, these chemicals react to form a variety of new pollutants such as ozone and Prac 1 nitric acid, and organic compounds such as p. 177 formaldehyde. We often see this as smog.

Enhanced global warming Every day the Sun shines on Earth, delivering large amounts of energy. Much of that energy is absorbed by the plants, rocks, buildings, soil and sea but some of it is released back into the atmosphere as heat. This heat would eventually escape into space if something didn’t stop it. However, certain gases in the atmosphere naturally trap this heat, keeping the atmosphere warm. This is called the greenhouse effect: the atmosphere acts like a giant greenhouse, keeping the temperature just right for life. A collection of gases known as greenhouse gases are released whenever fossil fuels such as coal, gas, petrol and oil are burnt. The main greenhouse gases are carbon dioxide, methane, nitrous oxide, ozone and water vapour. The amount of these gases

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Effects of human civilisation on the ecosystem

some of the energy is reflected off atmosphere radiated energy from below energy from Sun

power stations: source of extra carbon dioxide

exhausts from motor vehicles add to the carbon dioxide in atmosphere

heat trapped by carbon dioxide in atmosphere

burning of fossil fuels (coal, oil, etc.) also adds excess carbon dioxide to atmosphere

heat

heat radiated from land

heat radiated off sea felling of trees which would ‘lock up’ carbon dioxide

Fig 6.4.2

Heat is trapped between the blanket of greenhouse gases (carbon dioxide, water vapour, methane, nitrous oxide and ozone) and the Earth’s surface, causing a global increase in temperature.

in the atmosphere has increased dramatically, and with increased industrialisation has caused more heat to be trapped. This is called Turning up the heat the enhanced greenhouse effect ns The United Natio and leads to global warming. Over scientific advisory panel, the Intergovernmental the last 100 years the average Panel on Climate Change, atmospheric temperature has has forecast a rise in global risen 0.6°C, causing the sea level temperature of between 0.8°C and 3.5°C by the to rise by several centimetres. If year 2100 if no action is greenhouse gases continue to be taken to cut the production released into the atmosphere, we of greenhouse gases. can expect further increases in both temperature and sea levels. Flooding of coastal regions could become common, destroying many ecosystems and their inhabitants. On a human scale, cities, valuable farmland and some island nations could disappear too. Global warming is investigated in more detail Prac 2 in Science Focus 1 and 4. p. 178

Water pollution The waterways and oceans of the world have become polluted from a variety of sources. These include:

172

• sewage Sewage contains contaminants such as soap, detergents and other cleaning agents from washing machines, dishwashers and bathing facilities, as well as human wastes from toilets. • agricultural run-off Fertilisers add large quantities of nitrogen and phosphorus to the ecosystem. These find their way into both run-off water and groundwater, eventually ending up in the rivers, bays and oceans. • sediment pollution Clearing the land for housing developments and farming causes large-scale erosion. Soil particles are washed into the waterways, causing silting. • salinisation The removal of trees in order to plant crops and the use of irrigation on farms have resulted in a rise in groundwater level. As the water table rises, it brings with it dissolved salts from the rock surfaces. This increases the salinity of the groundwater, making it unusable by many plant species.

UNIT

6. 4 sulfur dioxide becomes sulfuric acid droplets in clouds

pollutants fall as acidic rain, killing forests

Fig 6.4.3

noxious fumes and poisonous gas from vehicles, power generation and heavy industry released to atmosphere

A deadly mixture is produced when poisonous gases and vehicle exhaust fumes combine in the atmosphere with oxygen and water vapour. These poisons are carried back to the Earth as ‘acid rain’, killing lakes, forests and the organisms that live there.

• inorganic chemicals Industry releases inorganic compounds directly into waterways, or into the soil where they are then carried by groundwater into the waterways. Chemicals released into the atmosphere are absorbed by rain droplets and fall to Earth as acid rain.

water vapour exits leaf via stomata (pores)

water vapour

Soil pollution Soil pollution is more commonly referred to as soil degradation. Over 65 per cent Bigger desert The Sahara Desert in Mali of soil degradation is caused by has increased in size by overgrazing and deforestation. more than 650 square • overgrazing kilometres in the last This is the degradation of 20 years. Can you suggest why? land caused by allowing more animals to graze in an area than the area can sustain. • deforestation This is the large-scale removal of trees to allow for more grazing land. Trees act like giant straws, sucking the water out of the ground and releasing it back into the atmosphere through their leaves in a process called transpiration. This keeps the underground water table at a lower level. When trees are removed, the water level rises, bringing

leaf roots take in water soil

top of ground water (the ‘watertable’)

ground water non-porous rock

Trees suck the water out of the ground, releasing it back into the atmosphere through their leaves in a process called transpiration.

Fig 6.4.4

with it dissolved salts. Remaining trees and plants will die if this ‘salty’ water gets near the surface. Removal of plant life makes the soil vulnerable to the effects of wind and rain. Uncontrolled erosion results, and the land is devastated. About 10 per cent of the Earth’s surface has been reduced to desert (called desertification) and a further 25 per cent has been placed at risk, including a very large proportion of the Australian continent.

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Effects of human civilisation on the ecosystem

Fig 6.4.5

The native bilbies that once inhabited this area are no longer able to do so due to overgrazing by introduced sheep.

Worksheet 6.3 A load of garbage

Introduced species What do the pig, rabbit, European carp, fox, prickly pear and tamarisk tree all have in common? They were all brought to Australia by the early settlers and are now causing huge problems for our native plants and animals. Introduced species are often referred to as exotic species. Pigs, brought by the sailors on the First Fleet, were allowed to freely look for food. Many of them ran off, and Aussie extinctions soon there were great numbers of wild Due to the destruction pigs throughout much of Queensland of their habitat and the and New South Wales. Feral pigs introduction of predators such as foxes and cats, dig up large areas of land, damaging two-thirds of the native native plants and destroying the animals in central Australia nct. habitats of many ground-nesting are now exti birds and native mammals.

>>> Early introductions European carp were first The early English settlers introduced into New South Wales introduced rabbits and foxes so that they could continue and Victorian fish farms in the their tradition of hunting. 1870s. Some escaped into the The prickly pear cactus is waterways, however, and by 1976 now spreading at a rate of had managed to inhabit creeks and about 0.5 million hectares per year. How many house rivers as far north as Queensland. blocks is this? Carp feed by taking in Cane toads were introduced mouthfuls of the muddy river to Gordonville, Queensland, bottom, then spitting them out. in 1935. They are a major threat to native wildlife and The dirt and the small organisms have recently reached the it contains are then suspended outskirts of Kakadu National in the water, where the carp can Park in the Northern Territory. catch and eat them. This method of feeding causes great damage to water plants, whose shallow root systems are made unstable because of the removal of the mud. Worksheet 6.4 Rabbit advance

Endangered species Much of Australia’s unique wildlife and plant life is becoming endangered. This means that unless active steps are taken, these plants and animals are in danger of extinction. Species that are now no longer living on our planet are said to be extinct. Factors that threaten our native wildlife include: • predation by introduced species such as foxes and cats • competition with introduced species like sheep and cattle • the destruction of their habitats when cities, farms, roads, mines and dams are built. The following table gives some examples of animals and plants that are endangered or extinct.

Thought to be extinct

Broad-faced potoroo (last sighted 1875)

Desert-rat kangaroo (1935)

Gastric-brooding frog (1985)

Endangered possums

Leadbeater’s possum

Little pygmy possum

Mountain pygmy possum

Other endangered land marsupials

Hairy-nosed wombat

Several species of wallabies

Several species of potoroos

Endangered marine mammals

Blue whale

Southern right whale

Several dolphin species and some seals

Endangered birds

Night parrot

Helmeted honeyeater

Red tailed cockatoo

Other endangered animals

Southern corroboree frog

Western swamp tortoise

Grey nurse shark

Endangered plants

Box iron bark eucalypt

Hairy quandong

Canberra daisy

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UNIT

6. 4 Frogs—a good sign

Case study The hairy-nosed wombat The northern hairy-nosed wombat is found only in 300 hectares of sandy countryside in the Epping Forest National Park, central Queensland. There are probably fewer than 120 left. Cattle-grazing, land clearing and the introduction of species such as the rabbit and the dingo (introduced by the Aboriginal people), have devastated their numbers. To make the situation worse, the northern hairynosed wombat is very slow to reproduce: they have only one offspring every year and the baby takes one year to wean and three years to reach sexual maturity. To help this wombat species survive, different strategies have been suggested. • Split the colony into several groups. This will prevent the whole population from being destroyed if a fatal disease should threaten them. • Monitor the population carefully. Scientists either watch the animals directly, or use methods such as satellite tracking and helicopter spotting. • Assist during births. It is hoped that this will prevent unnecessary deaths during the birth. • Release the offspring into suitable and protected habitats, where introduced species have been removed. Captive breeding programs in zoos provide another source of wombats that might eventually be placed back into the wild.

Frogs are considered to be ‘environmental indicators’. They are usually the first to be The Easter bilby affected by pollutants in the In recent years, efforts have habitat because they breathe been made to increase public awareness of the through their skin and spend plight of the greater bilby much of their life in water. and the lesser bilby (of Among those that have been which only a few hundred declared extinct is the gastricare left) by releasing lates in the shape of choco brooding frog, which was bilbies at Easter time. last seen in 1985. This small, dull-coloured amphibian was only found in the Blackall and Conondale ranges in south-east Queensland. This frog was unusual in that after fertilisation the female ate the eggs, regurgitating them when they Ulcer cure? How was it that the young had fully developed into young frogs!

Fig 6.4.7

The extinct gastric-brooding frog—logging and gold prospecting have destroyed this amphibian’s habitat.

tadpoles of the gastricbrooding frog were not digested by their mother’s gastric juices? Scientists were hoping that, when they found the answer to this question, they could help people suffering from ulcers. Unfortunately, this frog was declared extinct in 2000, and the answers to this question will never be known.

Take two toads with meals Fig 6.4.6

The northern hairy-nosed wombat is an endangered species.

As destructive as the cane toad is to our Australian environment, it does have one redeeming feature: Chinese medicine ries manufacturers have been using it for centu r. cance and ses disea ular to treat cardiovasc

175

Effects of human civilisation on the ecosystem Conservation Conservation is aimed at keeping alive all the plants and animals that live together in a specific habitat, usually by keeping the habitat undisturbed and free of human interaction. Both short- and long-term conservation actions are often required to maintain the biodiversity of a particular habitat. For example, consider the impact of an oil spill. Conservationists work hard in the short term to remove the oil from any ocean-going mammals, turtles and birds that may be affected. Steps are taken to restrict the oil from spreading further, and skimmer booms are used to remove the oil from the surface of the water. In the long term, legal action is often taken to change the laws regarding the transportation of oil, in the hope that future spills will be avoided.

>>> When we work to conserve one species in an ecosystem, we are helping to conserve all of the other species in that ecosystem because of their interactions with each other.

Why conserve? Humans rely on the living organisms around them. Plants provide us with the oxygen we need, as well as being food for us to eat. They are also food for the animals we eat. Plants and fungi provide the ingredients for many of the pharmaceutical drugs we use when we are ill. It is estimated that of the 400 000 to 500 000 different species of known plants on the Earth, only 10 per cent have been investigated for their chemical components. Who knows what future cures are to be found in the plants and animals we are destroying today? Worksheet 6.5 Threatened plants

6 Identify five sources of water pollution. 7 Outline the two main causes of soil degradation.

Introduced species 8 Use an example to outline a problem for the Australian environment caused by an introduced species.

Endangered species 9 List three factors that have put many species of Australia’s unique wildlife in danger of extinction. Oil spills cause a great deal of destruction to the natural environment.

UNIT

6.4

176

Fig 6.4.8

[ Questions ]

Checkpoint Pollution

Conservation 10 Explain the term ‘conservation’, describing how helping one species in a community helps the others. 11 List three reasons why it is important for human beings to conserve the plants and animals in their environment.

Think

2 Define the term ‘pollution’.

12 Propose reasons for the life span of a tree in the country being longer than the life span of the same species of tree in the city.

3 List three common air pollutants found in today’s industrialised cities.

13 Use an example to explain how overgrazing and deforestation cause soil degradation.

4 Some pollutants become even more deadly in the presence of sunlight. List three products of the combination of air pollutants with sunlight.

14 Which introduced species has proven to be the most damaging and the hardest to control? Justify your answer.

5 Identify the environmental threat caused by greenhouse gases.

15 Explain why a community is more resilient when it is more diverse.

1 Outline the effects of the Industrial Revolution.

16 Use an example to demonstrate how advances in human technology have affected the environment. 17 Describe the short-term and long-term measures that may be taken to stop an oil spill from spreading. 18 Contrast an endangered species with an extinct species. 19 Frogs are considered to be ‘environmental indicators’. Justify this statement.

20 Describe ways of reducing the effects of global warming.

Skills 21 Use a diagram to demonstrate the greenhouse effect. 22 Use the graph in Figure 6.4.1 to predict three effects on the environment of the population increase expected by the year 2050.

[ Extension ] Investigate 1 Research one animal and/or plant that is currently endangered. Summarise your findings, addressing the following issues: a what the term ‘endangered’ means b what has caused this animal and/or plant to become endangered c the numbers left in their natural environment now d what steps are being taken to increase their numbers e what the expected outcome is. 2 Research a habitat that is endangered and produce a brochure for visitors to the habitat. Choose from: a disappearing rainforests b endangered coral reefs c increasing salinity on farmlands d disappearing wetlands. 3 a Explain what is meant by a ‘captive breeding’ program. b Discuss the importance of zoos and captive breeding programs for many species. c Write a letter to the editor of a newspaper to explain your views on captive breeding.

UNIT

6.4

Class debate Separate the class into two groups: • Group A—those that think advances in technology should be allowed to continue in an uncontrolled fashion, with human needs and wants being more important than the health of the environment • Group B—those that think more stringent controls should be put into place to protect the environment, to the extent where technology takes a backseat role to the environment Students should have the opportunity to collect articles (newspapers, periodicals, Internet sources) to support their views.

Creative writing You are a lawyer who has been asked to prosecute a company that has been caught in the act of releasing thousands of litres of poisonous waste into a local creek. Your task is to speak out on behalf of the environment and the future of the creek. Discuss the effects of the dumping of this waste, and explain why the company should clean up the mess.

[ Practical activities ] A climate in a beaker Aim To make a mini-climate in a bowl

Prac 1 Unit 6.4

UNIT

6. 4

Equipment A large glass bowl, jar or beaker, some aluminium foil, ice cubes, some paper tapers, matches

Method 1 Place half a cup of water in the beaker, swirl it around to wet the sides of the beaker and then tip it out. 2 Drop a lighted taper into the base of the beaker. Cover the open top with the aluminium foil and make an indentation. Place the ice cubes in the depression you have made.

>>

177

>>>

Effects of human civilisation on the ecosystem

Fig 6.4.9

3 Record what happens as the air temperature inside the beaker falls due to the layer of cold air immediately under the foil. When the smoke particles and the moisture in the air get trapped together near the surface, they form smog. The smog cannot escape from the beaker, and as it cools it falls back toward the base.

Using a beaker to illustrate how smog forms in cities blocks of ice

aluminium foil

cold air forms beneath foil

Questions

beaker

1 Propose a reason why smog occurs more in those cities that have rivers running through them.

thermometer

2 Smog forms more in winter than in summer. Explain why.

smog forms in this region smouldering paper taper at base

Simulating global warming Prac 2 Unit 6.4

3 The inside of the beaker was wet first. Explain why. 4 Draw conclusions about the accuracy of this re-creation of city smog and a climate.

Cut a hole the width of 2 microscope slides. Cover with 2 microscope slides and stick into place.

Aim To observe the effect of an invisible ‘blanket’ on heat escape from a system

Equipment 2 small fruit juice cartons (‘poppers’), 2 thermometers, 1 pair of scissors, at least 4 microscope slides, sticky tape

Cut a hole the width of 2 microscope slides. Leave open to the air.

popper A

Method 70

70

°C

80

straw hole

90 0

10

place thermometer in straw hole

°C

5 Record the temperature inside each of the poppers every 5 minutes.

0

4 Place the poppers and the thermometers on a sunny window sill.

10

3 Allow about 5 minutes for the temperature inside the poppers to stabilise. Record the temperature inside both poppers.

90

2 Place two microscope slides over the hole of one of the poppers, and stick it into place using the sticky tape, effectively sealing it. Place the thermometers through the straw holes on each of the poppers. Seal around them with sticky tape to prevent heat escaping.

popper B

80

1 Cut a square hole in the large flat side of each of the poppers. The hole should be just smaller than the width of two microscope slides.

An illustration of global warming using two ‘poppers’

Fig 6.4.10

Questions 1 Predict the outcome of the experiment. 2 Describe what happened to the temperature inside the popper that had the microscope slides covering the hole. 3 Contrast your results with what is happening to the Earth.

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Science focus: The right balance—a human problem Prescribed focus area: The implications of science for society and the environment Before the arrival of the First Fleet, Australia was inhabited by Aboriginal people for more than forty thousand years. They lived mainly near the coast but were spread across the entire continent. There was a strong spiritual aspect to the life of Aboriginal people that was closely tied to the land and animals in the area in which they lived. This is shown through corroboree and Aboriginal art in which animals are represented. The Aboriginal people used their own ecological practices to become caretakers of the land.

Environmental impacts before white settlement Evidence suggests that the Aboriginal people were in tune with the natural systems. They used different seasonal food sources and any waste produced was biodegradable, being broken down and returned to the natural cycles. The hunter-gatherer lifestyle of the Aboriginal people depended upon the natural environment to supply all their needs. This is why they developed a strong spiritual association with the

a

Fig SF 6.1

Fig SF 6.2

With their hunter-gatherer lifestyle, Aboriginal people had many food sources in the Australian bush and produced biodegradable wastes.

b

a Aboriginal people dance like their animal totems.

b Animals appear in Aboriginal art in many forms.

179

land, and an understanding of its natural resources. They practised ecology in order to maintain the resources on which they depended and their lifestyle was sustainable. Aboriginal people practised burning the land, often called firestick farming. This burning cleared undergrowth, flushed out animals for hunting, and encouraged new plant growth. Regular burning resulted in some of the ancient rainforests being reduced in size, and more open eucalypt forests developing.

Fig SF 6.3

The early settlers saw the Australian landscape, animals and plants as strange. They took a long time to get used to the Australian environment.

Fig SF 6.4

Firestick farming had many benefits for the Aboriginal people.

The early settlers: a struggle to survive When the first white settlers arrived in Australia they found a much wider range of habitats than they were used to. The plants and animals were very different and considered peculiar or strange. In the first decades the settlers struggled to make the land produce enough food to support the growing population. This meant that settlers were forced to rely on supplies arriving from England. The land was generally described as ‘harsh and unforgiving’. Farming techniques from England were not very successful, with soil losing fertility after only a few harvests. Those who made their way into the bush found some areas with more

180

The settlers cleared the land, built homes and stayed in one place planting large crops of English plants—a very different way of life from that of the Aboriginal people.

Fig SF 6.5

fertile soil, but fresh water and food were hard to find for the settlers. Most early exploration was by boat, close to the coast, so that travelling through the bush could be reduced. In contrast, the Aboriginal people used the same land to supply all their needs.

Comparing attitudes Feature

White settlers

Local Aboriginal people

The landscape

Rugged and picturesque with much of it difficult to travel around. Needed to be cleared to allow for grazing of animals and growing of crops. The natural resources available from the land were there to be found and used.

Their spiritual link to all that had happened and all that was to happen in the future. It provided all their needs as they moved easily through the land, travelling from food source to food source as the seasons changed.

The plants

Mostly rubbish with some that could be used for timber, few suitable to eat. Some useful timber varieties were discovered as clearing and exploration of waterways were undertaken.

A source of food, useful materials, shelter, a home for animals. The Aboriginal people had long used burning the bush as a strategy to keep the undergrowth down to allow easy movement, and to encourage new plant growth.

The animals

Wild and strange, none to domesticate and not many to eat. Fish could provide food near the coast.

A vital component to be nurtured and respected, a supply of food. Associated with dreaming. Each tribe had their own spiritual association with one of the animals found in their area.

Property

Because Terra nullius (Latin for ‘uninhabited land’) had been declared by the British Government, the land could be claimed by free settlers and provided to freed convicts. Originally settlers were given land wherever they chose. All they needed to do was to clear the land to begin their farm.

Each location had a spiritual importance to the people who lived there. Aboriginal people moved about but on their death their bones were buried in their traditional land. There were sacred sites, meeting places and locations where food sources were found. The individual tribes used their own land but resources were shared between tribes. The land was owned by the tribe as a whole and did not belong to any individual.

Land use

The trees and plants needed to be removed providing as much land for grazing or growing of crops. Traditional farming techniques from Britain were employed. Minerals and natural resources were sought so they could be exploited.

There were spiritual links to the land and its animals and plants. Aboriginals tried to maintain the land and encourage new plant growth through burning, that in turn provided conditions where the populations of animals might increase and become available for food. Sacred areas were set aside where hunting was not allowed. These areas were often breeding grounds for animals that were used as food. These areas protected animals from extinction.

The Blue Mountains and Great Dividing Range

An impassable barrier preventing access to the interior of the continent and new land to farm.

An area of abundant water and food with long followed paths to allow contact with the tribes who lived in inland New South Wales.

From then till now The Aboriginal people managed to coexist with the land successfully for well over forty thousand years. After approximately 200 years of white settlement, however, modern Australians face many problems that have arisen from the exploitation of the environment. The Australian population has grown significantly and continues to grow. This and many other factors have had an impact on the Australian landscape, its plants and animals. These factors include modern farming practices, land clearing, introduced animals

and plants, and the production of new nonbiodegradable waste and pollution. Modern land use and land management practices are far more suited to Australia. Food production is generally more efficient, but still relies on nutrients in the soil being replaced. Land clearing (habitat loss), farming and competition, or predation, by introduced species has led to the extinction of many native animals and plants. Australia holds the world record for the highest recorded number of species which have become extinct.

181

Fig SF 6.6

What does each illustration suggest about effects on the Australian environment?

The future really comes down to the values and attitudes of the Australian people. Some still view the land in the same way as the early settlers—as a resource for humans to use or exploit. Others in the community have taken a view more closely resembling that of the Aboriginal people, viewing the land as something to be respected and conserved. We will have to find the right balance. What sort of relationship do you have with the land?

182

Fig SF 6.7

[ Student activities ] 1 After white settlement, the bush, which had been fairly open and easy for the settlers to ride horses through, started to become overgrown, making it more difficult to move through. a Outline possible reasons for the bush around Sydney becoming overgrown. Did it have anything to do with the Aboriginal people? b Firestick farming was a common practice of the Aboriginal people. Discuss the benefits of this technique. c Summarise the ways in which the Aboriginal people used the land. d Outline the problems that settlers encountered in trying to make Australia home. e Propose reasons for the settlers having such problems coming to terms with the land. f Compare and contrast the white settler and Aboriginal relationships with the land. 2 Many farming practices used by early settlers and even used today are not very good for the land. Research a problem caused by farming, such as salinity, erosion, land clearing, or soil infertility and answer the following questions. a Describe the cause of the problem. b Identify the parts of Australia where the problem exists. c Describe the effects of the problem on the land, native animals and plants. d Outline what is currently being done to help to overcome the problem. e Evaluate whether this problem can and will be fixed, giving an indication of how long this may take.

3 Many introduced animal species brought by white settlers have moved into the bush to become feral animals. Research one animal such as the fox, rabbit, camel or pig that has gone feral and produce a poster to demonstrate the effects this animal has had on the environment. 4 Supply of fresh water is a big issues for modern society. The needs of a growing population must be balanced against the costs and the impact on the environment. Research this area and complete the following activities. a Outline why it is difficult to supply enough fresh water to all who need it. b Compare any water restrictions that exist in Sydney with those in a country area. c Propose some ways that enough fresh water may be supplied in the future. d Present an advertisement to help promote better water use. e As a class or group, develop a plan for managing our fresh water supply for the future. Present your plan to the local council or water board, or as a community display. 5 Investigate further the Aboriginal relationship with the land by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 6, and clicking on the destinations button. Use the information you find to produce either a creative story or an artwork to illustrate the traditional relationship of Aboriginal people with the land. Your work should contrast this with the type of relationship people in modern societies have with the land.

183

>>> Chapter review [ Summary questions ] 1 List three abiotic and three biotic factors that affect you. 2 State whether temperature is a biotic factor or an abiotic factor. 3 a State the name given to animals that catch and eat other animals. b Describe the physical adaptations that help such animals to survive. 4 Define the term ‘pollutant’. 5 Explain the concept of biodiversity. 6 State whether the following statements are true or false. a All living things require energy. b The carbon dioxide used by autotrophs is obtained through the soil. c Chlorophyll is the green pigment found in the leaves of plants. d Humans are examples of omnivores. e The number of different plants in an ecosystem is referred to as biodiversity. 7 Agricultural fertilisers can damage the environment. Recall the two main elements of agricultural fertilisers. 8 Identify two major causes of increased salinity of waterways. 9 Define the term ‘desertification’.

19 In the zoo environment, not all the animals are fed the same amount of food. Do you think this is reasonable? Justify your response. 20 The greater bilby lives in the desert area of Central Australia. It has an omnivorous diet (it eats both plant and animal matter). Do you think this provides the bilby with an ecological advantage compared to other animals that eat only plants or only animals? Justify your response. 21 Feral pigs dig up native plants over large areas of land. Affected areas soon show erosion damage, making it unusable. Explain how this happens. 22 Outline how communities of high biodiversity withstand changes to the environment better than those of low biodiversity. 23 The ghost orchid lives in the beech and oak woods of Europe. It contains no chlorophyll and is a pale pink in colour. A fungus has been found growing on its roots. If the fungus is removed, the orchid soon dies. Describe the role of the fungus.

[ Interpreting questions ] 24 Look at the following address and identify the word in the brackets that correctly describes that part of the address.

10 Scientists can help a small population of an endangered species to survive. List four steps that can be taken to do this.

15 Elizabeth Street (biosphere, biome, habitat, microhabitat)

11 Explain why it is important that human beings try to maintain and conserve the environments in which they live.

Australia (biosphere, biogeographical region, biome)

12 Define the terms ‘abiotic factor’ and ‘biotic factor’.

[ Thinking questions ]

Broken Hill (biogeographical region, biome, habitat) New South Wales (biosphere, biogeographical region, biome) Earth (biosphere, biogeographical region, biome) 25 Examine Figure 6.1.2 and: a describe what you notice about those biomes that lie along the equator b predict whether plant life in these areas would be similar.

13 Choose examples of pollutants in the schoolyard to demonstrate the consequences of pollution.

26 Discuss the following statement: ‘The more specialised the habitat, the more vulnerable the species is to any change’.

14 Some people buy worms to add to their soil. Describe the role worms play in the ecosystem.

27 Refer to Figure 6.3.7 to explain why the number of producers is greater than the number of consumers in a food pyramid.

15 The leaves of the water lily float on the surface of the water. Outline the advantage that lilies gain by keeping their leaves above the water, rather than submerged.

184

18 Use an example to demonstrate a behaviour used to catch prey.

28 Use the food web illustrations in Figure 6.3.4 to construct three food chains.

16 Deepwater algae contain red pigments that absorb only the blue wavelengths of light. Explain how this is an advantage.

Worksheet 6.7 Ecology crossword

17 Explain why plants on the forest floor have more chlorophyll in their leaves than plants in more open aspects.

Worksheet 6.8 Sci-words

>>>

7

Plant systems Key focus area:

>>> The nature and practice of science

describe how material is transported around a plant identify what is needed for photosynthesis and respiration to occur in plants

Outcomes

explain why plants are essential to all life on earth

4.2, 4.8.1, 4.8.4

By the end of this chapter you should be able to:

identify what photosynthesis and respiration produce for the plant describe how leaves have special designs to increase photosynthesis explain how plants reduce water loss describe specialised cells that help plants stay healthy.

caves?

2 Very few plants grow at the bottom of deep water. Why?

3 Why are leaves usually green? 4 Why do some trees change colour in autumn?

5 How can you tell the age of a tree that has been cut down?

6 Why do cactus have spikes? 7 Why do plants droop when they haven’t been watered?

Pre quiz

1 Do plants grow in pitch-black

>>>

UNIT

context

7.1 Plants are essential to our lives. They are the producers that make the food that humans and all other organisms depend upon. We also use plant materials for other purposes. Wood is used in building and for

Introducing photosynthesis When exposed to sunlight, the leaves of plants convert carbon dioxide from the air and water from their surroundings into glucose and oxygen. They do this by using a special green chemical called chlorophyll. The process is called photosynthesis. This glucose produced is ‘food’ for plants and is transported around the plant in special pathways.

Sun carbon dioxide (from air)

making paper; flowers are used for decoration, and in making scents and some drugs and medicines; and cotton is used in clothing. Where would we be without plants?

roots carry water and minerals such as phosphorus, potassium, nitrogen, sulfur, calcium, iron Cunning cactus and magnesium from the soil. Cactus plants have needles Xylem tubes are made of dead for leaves. These have little space for the stomata cells strengthened with a woody through which water is substance. Unlike an animal, lost. This adaptation allows a plant does not have a heart the cactus to survive in desert conditions. to pump liquid through its tubes—instead, pressure in the roots pushes water upwards. Evaporation through tiny holes in the leaves (called stomata) further assists the flow by sucking water upwards.

light energy

Fig 7.1.2 chlorophyll in cells glucose + oxygen

Water and glucose flow through a plant.

water (from soil) glucose made by photosynthesis

to all parts of the plant

water evaporates out of stomata

released into the air

Water needs to be transported into a leaf for photosynthesis to happen. The glucose produced also needs to be transported out.

Fig 7.1.1

water travels through xylem vessels

Plant pathways In plants there are two types of transport tubes, which start in the roots and travel up the stem to the leaves. The roots anchor the plant and absorb water and nutrients from the soil. The xylem tubes in the

186

water enters root hairs

Phloem tubes are made from living cells. Their function is to transport the food (glucose) that is produced by photosynthesis in the leaves to the stem and roots. Some plants store glucose directly for use when required (eg to produce new buds in spring). Glucose is stored in the leaves of the lettuce, the stem of the celery plant and the tuber of the carrot plant. In other plants the food is stored in the form of starch, such as in the potato—which explains why potatoes are not as sweet as carrots and other vegetables. Ripening bananas A green banana contains Xylem and phloem tubes are starch. As it ripens, this grouped together in vascular starch changes into bundles, separated by a layer of glucose, with the result cambium cells. Cambium cells are that the banana becomes sweeter. able to become either new xylem or new phloem cells as required.

Fig 7.1.5

Fig 7.1.3

Root hairs increase the surface area through which water is absorbed into a plant.

UNIT

7.1

Cross-section of a stem, showing vascular bundles

cambium

phloem

cell magnified guard cells

underside of leaf

stoma in open position

cell magnified

straight guard cells

wilted leaf

Demonstration Geranium shoots

closed stoma

Stomata (singular: stoma) control the flow of oxygen and water vapour out of a leaf, and also control carbon dioxide intake. Prac 1 p. 190

vascular bundle

xylem

Fig 7.1.4

Ringbark one geranium shoot. Cover the ringbarking with Vaseline to prevent drying and place the shoot in a container of water. Place a similar, non-ringbarked shoot in another container of water. Leave them for two weeks and observe any root growth. Root growth requires food that is produced in the leaves. What can you conclude about food pathways in geranium shoots?

187

>>>

Plant transport systems Firm or floppy

Fig 7.1.7

The soft parts of plants are supported by water in its cells. The plant will be upright and its cells firm (turgid) if enough water is present. The plant’s stem and leaves may droop and become flaccid if the water content in the cells falls.

Wood Trees are just big plants and so they too contain xylem and phloem cells. Vascular bundles in the stem eventually link up to form a vascular cylinder. Phloem cells stay in the outer layer

Aboriginal expertise in plants has been known for many years. Many Australian plants supply bush medicines. Bitter Bark is used to prepare a tonic which reduces blood pressure and is a tranquilliser. Many plants and some types of honey can be used on sores and wounds, as they provide natural antibiotics to help in healing. A native daisy is used to treat toothache, as it contains a local anaesthetic. Over half the world’s supply of two drugs, hyoscine (a muscle relaxant) and scopolamine (for treatment of motion sickness), come from an Australian native tree which was used by Aborigines as an emu and fish poison.

Formation of a growth ring in a tree

vascular bundle

A

B cambium joins up

Fig 7.1.6

C

xylem phloem

phloem

Growth rings in a mature tree

Native cures

cambium D

xylem many annual rings

vascular cylinder formed

of a tree, just under the bark. These phloem cells are the pathways for nutrients to reach all parts of a tree Ringbarking removes a layer of phloem cells and will quickly kill a tree. Each year a new layer of xylem cells is produced, and the inner layers of old xylem cells combine with other plant substances to form wood. A cut crosssection of a tree trunk can reveal these yearly rings of growth. Worksheet 7.1 Water movement in trees

UNIT

7.1

[ Questions]

Checkpoint Introducing photosynthesis 1 Outline what is needed for photosynthesis and what is produced. 2 Figure 7.1.1 shows the function of the leaf in photosynthesis. Outline ways in which the leaf assists in photosynthesis.

188

Plant pathways 3 State whether the following statements are true or false. a Water is conducted up and down the plant stem through the xylem. b Water is transported around the plant in the phloem. c Xylem and phloem are grouped together in the cambium. d Dead xylem and phloem cells turn into cambium.

4 Identify which tubes in plants carry: a nutrients b water and minerals. 5 Explain how water moves through a plant.

Firm or floppy 6 Outline what happens to a plant when it is ‘flaccid’. 7 Describe what is required for plants to remain ‘turgid’.

Wood 8 Ringbarking a tree may kill it. Explain why this occurs. 9 Identify which cells turn into wood.

Think 10 Plants contain a large amount of carbon. Identify where this carbon comes from. 11 A rabbit nibbles the base of a small tree. Identify the plant tubes that are most at risk. 12 Flowers are usually placed in water in a vase to keep them looking good. Explain how this stops them going flaccid.

13 The flat surface of most leaves faces the Sun. Propose a reason for this plant behaviour.

UNIT

7.1 14 Eucalyptus leaves droop, their flat surfaces being vertical. Explain how this adaptation would help eucalypts survive in a hot climate. 15 The leaves from a plant are removed. Assess how this will affect it. 16 Cactus plants often have needle-like leaves. Propose a reason for this adaptation.

Analyse 17 Use Figure 7.1.1 to construct a word equation for photosynthesis. 18 Growth rings are produced because trees grow at different rates during a year, producing different patterns within the tree. Evaluate the age of the tree trunk shown in Figure 7.1.7. 19 Account for the presence of a large network of root hairs on plants like those shown in Figure 7.1.3.

[ Extension ] Investigate 1 Research information about the manufacturing of paper from wood. Construct a poster that shows a diagram of each step in the process and a brief description.

Action 2 Place some radish seeds on moist cotton wool and observe the roots that develop over a few days. Contrast observations made with those predicted by pulling a plant out of the ground.

Surf 3 a Investigate more about the structure of trees and wood by connecting to the Science Focus 2 Companion Website at www.pearsoned.co.au/schools, selecting chapter 7 and clicking on the destinations button. b Use your information to construct a model representing the structure of trees and wood.

Project Reddest radishes Organise a class competition to see who can grow the largest, reddest, tastiest radish. Choose the type of radish seeds carefully, and work out how you will make sure your radish grows up to become a winner. On judging day award various prizes including the largest, longest, reddest, hottest tasting, crunchiest and heaviest radishes. Growing hints • Care for your plants—water, weed and talk to them! • Find out what type of soil radishes like. • When choosing your seeds read what the packet says. • Leave the plants somewhere warm and sunny. • It may help to add compost or fertiliser to the soil. • Research the conditions that seeds and plants like to grow.

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Plant transport systems

UNIT

7. 1

[ Practical activity ] Water transport in celery

Prac 1 Unit 7.1

Aim To observe a movement of water in the xylem of celery Equipment Celery stick with leaves, 2 beakers, razor blade, dye celery

Method 1 Arrange the apparatus as shown in Figure 7.1.8. 2 Leave it overnight and then observe the celery stalk closely. 3 Cut the celery stick lengthways and across the stalk, and note the presence of any dye. dye

water

Extension DYO

Design a modification to this experiment to test the effect the leaves have on the movement of dye. Fig 7.1.8

Questions 1 Describe the directions in which the dye travelled. 2 Construct diagrams of the horizontal slice and of the vertical slice. In each diagram show where the dye travelled.

190

3 Explain why one half of the celery stalk was left in water with no dye.

UNIT

context

7. 2 Humans and other animals depend on glucose as their source of energy, and on a steady supply of oxygen to burn the glucose. However, animals cannot make their own glucose, and cannot replenish the oxygen in the air. Only plants have this ability. They do it in the process of photosynthesis. Ultimately, all life on Earth depends on photosynthesis, a process by which plants trap and use light energy from the Sun.

plant and the soil. He watered the plant regularly and after five years reweighed the plant and the soil. The mass of the plant had increased by 74.5 kilograms, but the mass of soil had not changed. He concluded that the plant had converted water to wood and leaves. In the 1770s, Joseph Priestley demonstrated the importance of oxygen, and its production by plants. Jan Ingenhousz then showed that light was necessary for this production. Jean Senebier in 1782 found that plants absorb carbon dioxide from the air. In 1804 Nicolas de Saussure showed that water was chemically involved in plant growth. The basic facts of the process of plant growth that we now know as photosynthesis were therefore known by the early 1800s. Although hundreds of scientists have conducted many experiments on different aspects of photosynthesis, the process is still not fully understood. For example, scientists have not yet been able to duplicate photosynthesis outside a living cell.

Photosynthesis—a chemical reaction Photosynthesis (from Greek: photo = light, syn = with, thesis = to make) can be represented by the chemical equation: 6CO2 + carbon dioxide

Fig 7.2.1

The Sun is the source of energy for all living things on Earth.

Photosynthesis The search for the secret of plant growth has a long history. The first careful experiments were conducted around 400 years ago by Jan Baptist van Helmont. He grew a willow tree in a tub after carefully weighing the

6H2O

light energy

water

chlorophyll

C6H12O6 glucose

Prac 1 p. 197

+

6O2 oxygen

This equation gives only a general idea of what happens. The equation indicates that chlorophyll, the green pigment in plants, is necessary for the reaction to occur. However, if carbon dioxide, water and chlorophyll are placed in a test tube in sunlight nothing happens! The explanation is that this ‘single’ reaction is in fact a complex chain of smaller reactions. Photosynthesis is essentially a two-stage process. • Stage one is called the light reaction. In this stage, light energy is trapped and changed into chemical

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Photosynthesis and respiration A big production The scale on which photosynthesis occurs is huge. Each year, approximately 150 billion tonnes of carbon (from carbon dioxide) combine with 25 billion tonnes of hydrogen (from water) to produce 400 billion tonnes of oxygen. Ninety per cent of this production is carried out by singlecelled organisms such as diatoms, and the seaweeds of the ocean.

Fig 7.2.2

Single-celled organisms called diatoms come in a variety of shapes. They are important photosynthetic organisms in the ocean. A litre of seawater may contain as many as 450 000 diatoms.

energy. At the same time enzymes split water into oxygen and hydrogen. Enzymes are protein molecules which act as catalysts. A catalyst is something that speeds up a chemical reaction without being used up in the reaction. Enzymes helps reactions occur faster. • Stage two is the dark reaction, a series of enzymecontrolled reactions in which carbon dioxide and hydrogen from water combine to form glucose. Light energy is not needed in this stage. Energy changes during the two stages of photosynthesis

Fig 7.2.3

solar energy

H2O

O2

LIGHT REACTION energy trapped by chlorophyll energy transfer

192

A chloroplast (green) in a leaf cell. In the centre is a starch granule (blue).

Fig 7.2.4

What happens to the glucose produced during photosynthesis? The plant may use the glucose directly for energy through respiration. However, on a sunny day photosynthesis can occur ten times faster than respiration. The excess glucose must be ‘used’ in other ways. Most is converted to starch for temporary storage in the leaf. At night this starch is reconverted to glucose, a process known as destarching. Glucose may be converted to: • cellulose to build plant cell walls • sugars for transport to various parts of the plant or • substances used for producing plant oils and proteins.

The rate of photosynthesis

DARK REACTION CO2

The key to the process is chloroplasts, which are found within the cells of plants. Chloroplasts contain the green pigment chlorophyll, which acts something like a solar cell, trapping light energy and converting it to another form. Chloroplasts act as ‘factories’ for the production of glucose. One plant leaf contains tens of thousands of cells, Prac 2 each containing 40 to 50 chloroplasts. p. 198

glucose

The rate of photosynthesis depends mainly on the availability of carbon dioxide and light. In general, an increase in either causes an increase in the rate

of photosynthesis. The effect is shown in Figure 7.2.5, a graph of the rate of photosynthesis versus light intensity. The rate rises quickly as light intensity increases, because more energy is available. Once the light energy reaches a certain point, no further rise occurs. At this point, carbon Prac 3 dioxide begins to limit the reaction: carbon p. 199 dioxide levels determine the maximum rate of photosynthesis.

Rate of photosynthesis

another factor like carbon dioxide is limiting the rate

maximum rate rate increases as more light is available

Light intensity

Fig 7.2.5

UNIT

7.2 Case study Respiration research Many scientists have spent many years studying how the body uses the energy stored within food. The first great discoveries were made by French chemist, Antoine Lavoisier, over 200 years ago. Lavoisier is best remembered for giving oxygen its name, and for showing that fire needs oxygen and a fuel. In 1783, Lavoisier and Pierre de Laplace analysed the air inhaled and exhaled by a guinea pig, and measured the heat given off by the animal’s body. Most of the oxygen inhaled disappeared and was replaced by carbon dioxide. The amount replaced was almost the same as the amount of oxygen needed. Charcoal was burnt and released the same amount of heat as the guinea pig had. Lavoisier concluded that the process was ‘a combustion, admittedly very slow, but otherwise exactly similar to that of charcoal’. In other words, the body burns food much like a fire does. Lavoisier then studied human subjects in a series of experiments lasting 10 years.

Effect of light intensity on the rate of photosynthesis

Like most chemical reactions, the rate of photosynthesis increases with increasing temperature. The rate of photosynthesis increases up until a temperature of about 30°C, then decreases. At these higher temperatures the enzymes are affected and no longer function correctly.

exhaled air

inhaled air

ice guinea pig

Worksheet 7.2 The effect of temperature on photosynthesis insulating material

Respiration The process by which organisms release energy from food is called respiration. This energy is available to cells for their many activities. These include growth of cells, and transport of substances into and out of cells. Some of the energy released during respiration is given out as heat. For most organisms this process needs oxygen, so it is called aerobic respiration. We can show aerobic Prac 4 Prac 5 p. 199 p. 200 respiration using the chemical equation: C6H12O6 + 6O2 glucose oxygen

→

6CO2 + 6H2O + energy carbon dioxide

water

Lavoisier’s experiment. The guinea pig was surrounded with ice. Heat output was estimated by the amount of melted ice.

Fig 7.2.6

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water

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Photosynthesis and respiration

In other experiments it was shown that a mouse placed in a sealed jar drastically reduced the oxygen content of the air, while increasing the carbon dioxide content. A mouse provided with air, glucose (a type of sugar) and water can function normally for weeks. If another ‘fuel’ (fat, for example) is substituted for glucose, however, the mouse shows signs of weakness. The other fuel is not used as efficiently. Lavoisier’s experiments showed that humans, as well as guinea pigs, produce heat by ‘burning’ food.

Fig 7.2.7

cell. Instead the reaction is gradual and controlled, releasing energy in small amounts. Just how the cell manages this process is still not completely understood. It is known that this ‘single’ reaction occurs as a sequence of at least 30 different reactions arranged in a complicated chain. The keys to all these reactions are those amazing molecules called enzymes. Lock and key Enzymes act as catalysts, Over 700 enzymes have been found in the human speeding up chemical reactions body. The ‘lock and key’ without being used up in the model is one model which reaction. Enzymes are very explains why enzymes are so specific. Enzymes have efficient at speeding up reactions. a particular shape which They can increase reaction speed exactly matches the shape by as much as ten billion times. of reactant molecules. The reactants lock into a That is like taking a minute to do place on the enzymes. This a task which would otherwise interlocking makes reaction take 18 000 years! occur more

Fig 7.2.9

The ‘lock and key’ model that explains enzyme action

reactant molecule breaks

reactant molecule

easily, and therefore at a faster speed. When reaction is complete, the enzyme and product molecules ‘unlock’, leaving the enzyme unaltered.

two product molecules

substance which absorbs carbon dioxide air flow in

air flow out enzyme molecule

limewater (clear solution)

Fig 7.2.8

limewater turns milky, indicating that carbon dioxide has been produced

Fig 7.2.10

Respiration occurs in the cells of all living things. Glucose can also be burned in air: its reaction is rapid and uncontrolled, releasing heat and light. If such a process occurred in cells the heat would destroy the

enzyme unchanged by the reaction

The flow of energy in cells

An experiment to show that carbon dioxide is produced by a mouse energy from glucose

194

enzyme combines with reactant for a short time

energy stores

movement cell growth heat making large molecules transmitting messages transport

How do they put the centre in? Ever wondered how they put the centre in liquid-centred chocolates? An enzyme does the trick. Sucrose (another type of sugar) and flavourings are dissolved in water to create a paste-like solid. An enzyme is also added. The paste is coated with chocolate and kept at a suitable temperature. The enzyme converts the sucrose to two more soluble sugars. These dissolve in the water to form the liquid centre.

Comparing photosynthesis and respiration For almost everything, chloroplasts and photosynthesis are directly or indirectly the basis of life, providing the essential requirements for respiration. The equations for respiration and photosynthesis are the reverse of each other.

UNIT

7.2 Respiration: C6H12O6 + 6O2

→ 6CO2 + 6H2O + energy

Photosynthesis: 6CO2 + 6H2O + sunlight energy → C6H12O6 + 6O2

This is true if we look only at the overall equations. However, we have seen that the two processes are more complex than the equations suggest. They use different steps, different enzymes and occur in different locations. Worksheet 7.3 Photosynthesis and respiration

Comparison of photosynthesis and respiration Photosynthesis

Respiration

Occurrence

Plant cells containing chlorophyll

All living cells

Cell structures used

Chloroplasts

Mitochondria

Reactants

Carbon dioxide and water

Glucose (or other fuel) and oxygen

Products

Glucose and oxygen

Carbon dioxide and water

Type of process

A building process leading to increased mass

breakdown process leading to decreased mass

Energy changes

Light energy changed to chemical energy

Chemical energy changed to heat, energy of movement and other forms

Light requirement

Essential—provides energy

Not required

UNIT

7.2

[ Questions] Photosynthesis—a chemical reaction

Checkpoint

3 Explain why chlorophyll is necessary for photosynthesis.

Photosynthesis 1 Several scientists helped discover the basic features of photosynthesis. Identify the correct discovery for each scientist. Scientists Priestley de Saussure Ingenhousz Senebier

Discoveries Light is necessary Oxygen is used Carbon dioxide is used Water is produced

2 State whether the following statements are true or false: a Photosynthesis can be duplicated outside a living cell. b Photosynthesis is completely understood. c Water is involved in photosynthesis. d Photosynthesis occurs during the night.

4 Describe the energy change that occurs during photosynthesis. 5 Photosynthesis is essential for all living things. Explain why. 6 a List the two reactants in photosynthesis. b Identify what else is needed for photosynthesis to occur. c List the two products of photosynthesis.

Respiration 7 Outline the purpose of respiration. 8 List the products of respiration.

Case study—Respiration research 9 Outline the main conclusion of Lavoisier’s experiments. 10 Identify other experiments which have supported Lavoisier’s findings.

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Photosynthesis and respiration

Comparing photosynthesis and respiration 11 Outline how photosynthesis and respiration complement each other by working together. 12 Identify the cell components in which photosynthesis and respiration occur.

Think 13 Photosynthesis does not occur if chlorophyll, water and carbon dioxide are placed in a test tube in sunlight. Explain why it does not occur. 14 Propose two ways in which the glucose formed during photosynthesis may be used by the plant.

17 The graph in Figure 7.2.12 shows the amount of oxygen produced by a plant as light intensity was increased under two different sets of conditions.

leaf

water

Fig 7.2.11

Y Oxygen produced

15 A leaf was picked from a plant that had been kept in the dark for two days. The leaf was placed in water and the apparatus shown in Figure 7.2.11 used to carry out an experiment. The apparatus was placed in sunlight. The sodium hydroxide removed carbon dioxide from the air. After some time the leaf was placed in boiling water, then boiling alcohol, then boiling water again. A few drops of iodine solution were then added to the leaf. a State the name of the substance being tested for with the iodine. b Outline the expected result of the iodine test. c Explain whether this result would be expected. d Explain why it was necessary to keep the plant in the dark for two days.

196

16 Photosynthesis may be thought of as a two-stage process. a Use a simple equation to demonstrate what happens in the first stage. b Use a simple equation to demonstrate what happens in the second stage. c Identify which stage requires light.

Fig 7.2.12

Analyse

solid sodium hydroxide

Skills

X

Light intensity

a Identify the process that produces the oxygen. b Explain why the amount of oxygen increases as the light intensity increases. c Propose two possible changes that could be made to the experiment to produce graph Y. 18 a Increasing the temperature usually increases the rate of photosynthesis. Explain why. b At temperatures above approximately 30ºC, increasing the temperature slows the rate of photosynthesis until it stops altogether. Explain why this occurs. 19 An experiment was conducted using the set-up shown in Figure 7.2.13. The set-up was placed in sunlight. a Recall the name of the gas produced during the experiment. b Describe how you would test to find out the type of gas produced. c Use a chemical equation to demonstrate the production of the gas. d The experiment was repeated for the same length of time, but using a larger mass of plant. Explain how this would this alter the volume of gas produced.

UNIT

7.2 Action test tube

gas collects here

2 a Design a controlled experiment to investigate the effects of fertilisers on plant growth. b Account for observations made in terms of effect on photosynthesis.

DYO

Surf water

water plant

Fig 7.2.13

[ Extension ] Investigate 1 Construct a timeline to demonstrate the main stages in the discovery of photosynthesis. Include major areas of recent research on your timeline.

UNIT

7.2

3 Complete the following activities on the origins of life by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7 and clicking on the destinations button. a Select one or two types of chemosynthetic bacteria. Research the conditions in which they are found and the kinds of chemical reactions they perform. Summarise your information in the form of a brief article for a scientific journal, including diagrams and equations for chemical reactions. b Research information about the first living things on Earth to discover whether they were photosynthetic. Describe some theories of how life on Earth began. Present your information in comic strip style.

[ Practical activities ] A product of photosynthesis

Prac 1 Unit 7.2

Aim To investigate the products of photosynthesis Equipment

light inverted test tube

2 x 600 mL beakers, 2 glass funnels, 2 test tubes, sodium hydrogen carbonate solution (0.5 per cent), 2 pieces of actively growing Elodea (Canadian pond weed), light source, wooden splint, safety goggles

Method 1 Half-fill each beaker with sodium hydrogen carbonate solution. 2 Place a piece of plant in each beaker and cover the plant with a funnel.

sodium hydrogen carbonate solution funnel Elodea

3 Invert a test tube full of water over the stem of each funnel. 4 Place one beaker in the dark, the other in continuous light for several days.

Testing for a product of photosynthesis

Fig 7.2.14

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Photosynthesis and respiration

Questions

5 Describe any changes in appearance that have developed in each set-up. 6 Test any gas collected. To do this, lift the test tube off the funnel without letting the tube leave the water. Quickly insert a glowing wooden splint into the test tube, making sure not to touch the sides of the wet test tube.

1 State the purpose of the sodium hydrogen carbonate solution. 2 Identify any gas given off. 3 Account for any differences in the changes observed for the two procedures in the experiment.

7 Record the results of the gas test.

Green leaves and photosynthesis Prac 2 Unit 7.2

Aim To examine where the products of photosynthesis are stored in leaves

Testing a leaf for starch

WARNING: Ethanol is highly flammable. At no stage should the test tube containing ethanol be placed near any flame.

Fig 7.2.15

test tube boiling ethanol

Equipment Potted plant with variegated leaves, potted plant of the same species with completely green leaves (suitable plant types include Coleus and Geranium), 3 beakers of boiling water (these should ONLY be heated using an electric hot plate), 2 large test tubes containing ethanol or methylated spirits, iodine solution, forceps, scissors, 2 watch-glasses or 2 glass Petri dishes, safety goggles

boiling water

leaf

boiling water

boiling water

Method 1 Cut a leaf from each plant. Cut a small nick in the edge of the variegated leaf so it can be identified later.

leaf

leaf

leaf

iodine solution

2 Sketch two outlines of the variegated leaf side by side. Do the same for the green leaf. 3 Drop both leaves into one beaker of boiling water for a few minutes. This kills the leaf cells so that no further reactions can occur.

8 Dispose of all solutions as instructed by your teacher.

4 Using the forceps, remove the leaves and place one in each test tube of ethanol.

9 On the outlines prepared in step 2, draw and colour in the areas stained blue-black on each leaf.

5 Stand both test tubes in the second beaker of boiling water. The ethanol will start to boil, and green colour will be dissolved from the leaves. After around 10 minutes the leaves should look quite pale.

Questions

6 Using the forceps, remove the leaf from one test tube and dip it into the third beaker of boiling water for a few seconds. This removes the ethanol and softens the leaf. Place the leaf on a watch-glass or Petri dish. Repeat this step for the other leaf. 7 Add iodine solution to each leaf. Allow it to stand for a minute.

198

1 State the name of the substance identified by the blue-black colour obtained with iodine. 2 Explain why the leaves were boiled in ethanol. 3 Describe any relationship between the presence of green in the leaves, and areas that were stained blue-black. 4 Explain why the stained areas of the leaf show where photosynthesis is likely to occur.

Light intensity and photosynthesis Prac 3 Unit 7.2

DYO

Design an experiment to investigate the effect of light intensity on the rate of photosynthesis. The apparatus shown in Figure 7.2.16 should give you some ideas to get started with. Variables that may be changed include distance of light from test tube, power of the light globe and temperature of the water.

UNIT

7.2 thermometer test tube

sodium hydrogen carbonate solution

water plant

light

water bath distance

A product of respiration Prac 4 Unit 7.2

Investigating light intensity and photosynthesis

Fig 7.1.16

Aim To investigate the products of respiration

Equipment

Questions

Flasks and glassware as shown in Figure 7.2.17, filter pump, sodium hydroxide solution, limewater, potted plant, several insects or earthworms

1 Sodium hydroxide absorbs carbon dioxide from the air. Carbon dioxide dissolves in limewater to form a milky solution. Explain the purpose of flasks A and B.

Method

2 Explain the purpose of flask D. 3 Justify the use of the: a plastic bag b black paper.

1 Set up the apparatus as shown in Figure 7.2.17. 2 Slowly draw air through the apparatus by means of the filter pump.

4 Explain any changes observed in the limewater during the experiment.

3 Record any changes in the colour of the limewater in flasks B and D.

Fig 7.2.17

5 a Modify the experiment, using an animal (eg earthworm) in place of the potted plant in flask C. b Compare and contrast the results of the two experiments.

Testing for the products of respiration

air in

to filter pump

black paper covering the jar

plastic bag A sodium hydroxide solution

B limewater

C plant

D limewater

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Photosynthesis and respiration

Energy production in respiration Prac 5 Unit 7.2

Aim To determine the heat energy produced by respiration in plant seeds Equipment

2 wide-mouth thermos flasks, 2 thermometers, cotton wool, germinating pea seeds, boiling water, mild disinfectant

thermometer

thermometer

cotton wool

cotton wool

thermos flask

thermos flask

seeds

boiled seeds

Method 1 Divide the germinating seeds into two equal batches. 2 Place one batch in boiling water to kill the seeds. 3 Soak these killed seeds in the disinfectant. 4 Set up the apparatus as shown in Figure 7.2.18. 5 Record the temperature in each flask. 6 After several hours record the temperature in each flask again.

Questions 1 Explain any observed changes in temperature. 2 Explain the purpose of the flask containing killed seeds. 3 Explain the purpose of the disinfectant.

200

Testing for energy release in respiration

Fig 7.2.18

UNIT

context

7. 3 Carbon dioxide and water are used in photosynthesis, and glucose and oxygen are produced. Plant leaves have special structures to get these chemicals in and out so that photosynthesis can proceed.

Leaf structure Leaves are the main location at which photosynthesis takes place. They have several features that help them do this important job. Leaves are usually broad and flat, allowing maximum exposure to the sunlight. The upper and lower surfaces of the leaf are bound by a one-cell-thick layer called the epidermis. This layer is transparent, allowing light to reach the lower cell layers. The epidermis is covered with a waxy waterproof cuticle. This layer reduces water loss from the leaf and protects it from both freezing in cold

Light needs to reach the cells in a leaf, and the arrangement of cells ensures that they all get enough light to work efficiently.

weather and invasion by fungi and bacteria. It does not, however, allow gases to pass through it. Gases enter the leaf through small openings called stomata. These are usually located on the underside of the leaf, in the lower epidermis. The size of these openings is regulated by special cells called guard cells. These change shape to allow the stomata to be open or closed. When closed, water is not lost from the leaf. This is crucial in times of low water supply. However, it also means that gases cannot enter and exit the leaf, so photosynthesis stops, or at least slows Prac 1 p. 205 considerably. The structure of a leaf

Fig 7.3.1

cuticle upper epidermal cells

palisade cells

xylem cells

phloem cells air space

mesophyll cells stomate cuticle lower epidermal cells

guard cells

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Leaves

visible in the bright colours of autumn leaves. Prior to losing leaves the plant breaks down chlorophyll and stores some of its components, leaving the red, orange or yellow accessory pigments behind. Plants in water face special problems because water absorbs light. Most aquatic plants are therefore found in the surface layers where light is more available. Some seaweeds (algae) have additional pigments that allow them to absorb more light. Red light is strongly absorbed by water, so in the surface layers we find green algae that use this red light. Brown algae, found in shallow waters, absorb blue, green and yellow light. Red algae, found at deeper levels, absorb mainly blue and green light. Worksheet 7.4 Leaves

Fig 7.3.3 Fig 7.3.2

The numerous vertical palisade cells can be seen containing chloroplasts. The vascular bundles are shown in blue and stomata are seen on the lower surface.

There are two main layers of cells within the leaf. • The upper layer contains the palisade cells, which are tightly packed and contain large numbers of chloroplasts (small spheres). A large amount of photosynthesis occurs here. • The lower mesophyll cells are more loosely packed and give this part of the leaf a spongy appearance. Loose packing allows large spaces for gases to move back and forth between the cells and the air in these spaces. Water is supplied to the leaf by xylem cells. Phloem cells carry glucose and other ‘food’ substances away from the leaf.

Leaf pigments The chlorophyll in leaves absorbs sunlight, but not all colours are equally absorbed. The leaves look green because they reflect green light. Red and blue light are most strongly absorbed by land plants, with some yellow and orange also being absorbed. Some plants contain other pigments such as yellow xanthophylls and orange carotenes. These accessory pigments are

202

Green chlorophyll is not the only pigment in plants. Other pigments often only become obvious in autumn.

UNIT

7.3 Aboriginal plant classification and use

Aboriginal plant classification is based mainly on use. There are two main groups: • maranhu (food) • mirritjin (chemicals). The first and largest main group, maranhu, has two separate divisions: • ngatha—vegetable foods and honey • gonyil—meat foods and eggs. Ngatha is then further divided into: • ngatha—all root foods, nuts and the growth centres of palms • borum—fruit • guku—honey. Any plant considered unsuitable to eat may be referred to as nhangining, which simply means ‘useless food’. The name of the second main group, mirritjin, has developed from the English word ‘medicine’. Within this group there are a number of sub-categories that relate to the type of medicinal or chemical properties involved. These include: • dyes Dyes are made from roots of many plants and are used to colour the fibres of baskets and mats. The two main dyes are red, which come from bulbous Mulubirtdi roots, and yellow, from the Corkwood tree roots (Gumurduk). • glues and resins The sap from the Grass tree is used as a resin, generally to secure prongs and points to fishing spears, and fish hooks to lines. The sap can be removed from the base of the leaves by beating them. It is sometimes found as a hardened knob on the northern side of a tree, where it has seeped out due to the heat of the Sun. • poisons The bark and leaves of various plants were used as ‘fish poisons’ to stun fish in waterholes, making them float to the surface and easy to catch. Some examples are Acacia (wattle) species rich in tannin, which is the active agent.

• medicines Some plants yield medicines for many purposes. Common hop bush is an important medicinal plant among Aboriginal people. The leaves are chewed for toothache and used as a dressing for stonefish and stingray wounds. Soaked in water the leaves are used as a sponge to relieve fever. A liquid made from soaking the roots is used for open cuts and sores. The crushed leaves of Clematis (Headache vine) can be used to relieve headaches.

The fruits, nuts and seeds from plants are used as food and medicine by Aboriginal people.

Fig 7.3.4

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Leaves

UNIT

7.3

[ Questions] Think

Checkpoint Leaf structure 1 State whether the following statements are true or false. a Plant leaves are the main site of photosynthesis. b The epidermis is at the centre of a leaf. c Small openings in a leaf are called stomata. d Guard cells keep stomata closed. 2 Identify the function that best matches each structure. Structures epidermis cuticle stomata guard cells mesophyll cells palisade cells xylem cells

Functions control the size of openings in the leaf specialised water-conducting cells waxy, waterproof covering of the leaf loosely packed cells with air spaces between them outer layer of cells of the leaf allow gases to enter and exit the leaf tightly packed cells containing large numbers of chloroplasts

3 Identify the plant tissue in which photosynthesis occurs. 4 a Recall the name of the structures through which water exits a leaf. b Outline how plants prevent excessive loss of water on hot days. 5 a Outline how each of the raw materials for photosynthesis enters the leaf. b Describe how each of the products of photosynthesis leave the leaf.

Leaf pigments 6 a Identify the colour of light not absorbed by chlorophyll. b Explain how we know this colour is not absorbed. c Identify the colours of light most strongly absorbed by chlorophyll.

10 Mesophyll tissue contains loosely packed cells. Explain why. 11 Leaves are generally broad and flat. Explain how this assists photosynthesis. 12 The leaves of most plants have a waxy cuticle covering their outer surface. Outline: a advantages of this cuticle b one disadvantage of this cuticle. 13 Explain why some algae have light-trapping pigments in addition to chlorophyll.

Skills 14 The diagram in Figure 7.3.5 shows a section through a plant leaf exposed to sunlight. Identify the correct terms from the list below in order to label the diagram. chloroplast, epidermal cell, stomata, cuticle, air space, xylem vessel, palisade cell, mesophyll cell 15 Refer to the leaf shown in Figure 7.3.5. a Identify the section (X or Y) of the leaf in which most sugar is likely to be produced in a given period of time. b Over a day, one gas moves in the direction of the arrow. Identify which gas it is and explain your answer.

c

f

b

g

X

e Y

h

7 Recall the names of two pigments other than chlorophyll found in some plants. 8 Explain why red, yellow and orange are typical colours of ‘autumn leaves’.

a d

9 Water is able to absorb light. Outline two adaptations to overcome this. Fig 7.3.5

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UNIT

7.3 [ Extension ] Investigate 1 The opening and closing of leaf stomata are carefully controlled. Research information about the opening and closing of leaf stomata and: a use a diagram to describe how the opening and closing of leaf stomata are controlled

UNIT

7.3

b use diagrams to contrast the structure of leaves from a desert plant with that of leaves from a rainforest plant c account for any differences in structure. 2 a Research why, how and when different trees lose their leaves. b Explain how this loss of leaves affects plant growth.

[ Practical activity ] Stomata and chloroplasts

Prac 1 Unit 7.3

Aim To examine stomata and chloroplasts in leaves Equipment

Compound microscope, microscope slides and cover slips, dropper, tweezers, razor blade, stain such as methylene blue or iodine, leaves from various plants such as rhubarb and agapanthus, elodea (a water plant)

Method Part A—Stomata 1 Set up the microscope. 2 Peel the lower epidermis (outer layer) from the bottom of a leaf. Using tweezers may help. 3 Place the epidermis flat on the microscope slide. 4 Add a drop of water and carefully lower the cover slip on top. Be careful not to trap any air bubbles under the slip.

Part B—Chloroplasts 1 Take a leaf of elodea. 2 Use a razor blade to cut a very thin slice off the leaf. Your teacher may do this for you. 3 Place the leaf slice on a microscope slide and add a drop of water and a cover slip. 4 View the slide under the microscope. Identify and draw the cells containing green chloroplasts.

Questions 1 Outline the purpose of stomata. 2 Stomata are mainly found on the underside of leaves. Explain why. 3 Outline the function of a guard cell. 4 Describe the role of chloroplasts.

5 Add a drop of stain at one edge of the cover slip and hold a piece of paper towel at the opposite edge to draw the stain under the cover slip and across the leaf sample. 6 View the slide under the microscope, identify and draw the stomata. 7 Try looking at the stomata of other plant leaves in the same way. 8 Choose another leaf and try to find stomata on the upper epidermis.

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>>> Chapter review [ Summary questions ] 1 Copy and modify the following statement to correctly describe photosynthesis. Photosynthesis is the process by which plants make their own food, using energy from glucose and chlorophyll to convert carbon dioxide and sunlight into oxygen and water. 2 Identify which part of a plant provides: a pressure to push nutrients up the stalk or trunk b support to prevent a plant collapsing too easily. 3 List some substances stored by a plant. 4 a The process of photosynthesis can be represented by an equation. Use an equation to demonstrate the process of photosynthesis. b Clarify the importance of photosynthesis to living things.

13 Construct a table to compare photosynthesis and respiration. Your table should include reactants, products, conditions and energy changes. 14 Explain why autumn leaves are so colourful. 15 Outline an experiment that can be conducted to demonstrate that leaves contain starch. 16 Contrast the stomata of leaves found on tropical plants with those in desert regions. 17 Compare and contrast photosynthesis and respiration.

[ Interpreting questions ] 18 Identify the parts described in a to g that match structures i to vii labelled on the diagram of a leaf shown in Figure 7.4.1.

5 Recall which cells result in growth rings in a tree. 6 a List three factors which affect the rate of photosynthesis. b Explain how each of these factors affects the rate.

i

ii

7 Outline two uses of the glucose produced by plants during photosynthesis.

iii

8 A student incorrectly wrote that ‘plants photosynthesise during the day and respire at night’. Modify the sentence to make it correct.

iv

9 a The glucose produced during photosynthesis may be stored by the plant for later use. State the form of storage of the glucose. b State the form of storage of excess glucose in plants.

v

vi

[ Thinking questions ]

vii

Fig 7.4.1

10 Compare and contrast xylem and phloem tissue. 11 Plants trap light energy to enable glucose to be made from carbon dioxide and water. A small number of bacteria produce glucose by other processes. Describe one such process. 12 The chemical equation for photosynthesis is the reverse of that for respiration. Propose two reasons why it is not correct to say that photosynthesis is simply the reverse of respiration.

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a b c d e f g

Controls the size of openings in the leaf. Specialised water-conducting cells. Waxy, waterproof covering of the leaf. Loosely packed cells with air spaces between them. Outer layer of cells of the leaf. Allow gases to enter and exit the leaf. Tightly packed cells containing large numbers of chloroplasts.

19 An experiment was conducted using the flasks shown in Figure 7.4.2. All flasks contained water, were at the same temperature and were in sunlight. After two hours the carbon dioxide and oxygen levels in each flask were measured.

A

B

C

D

rubber stopper

a Identify the flask or flasks in which photosynthesis would occur. b Identify the flask or flasks in which respiration would occur. c Predict which flask would have the highest carbon dioxide level after the two hours. d Predict which flask would have the highest oxygen level after the two hours. 20 An experiment was conducted using three potted plants. Each plant was exposed to continuous light of the same intensity but different colours. Plants and colours used were: plant A—green light; plant B—yellow light; plant C—red light. a List three factors which must be kept constant for all plants in this experiment. b Identify the plant (A to C) that would produce the most glucose in a given time.

plastic plant

plastic plant and fish

pond weed and fish

pond weed

Worksheet 7.5 Plants crossword Worksheet 7.6 Sci-words

Fig 7.4.2

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>>>

Astronomy Key focus area:

>>> Current issues, research and

4.5, 4.9.2, 4.12

Outcomes

developments in science

By the end of this chapter you should be able to: list the main types of rocks in space and identify which are a risk to the Earth convert distances into light years identify some of the individual stars and constellations in the night sky be able to read a sky map identify the location of Earth and its solar system in the universe contrast the four types of galaxies

Pre quiz

explain the importance of remote sensing in our understanding of the Earth and its solar system.

1 What is a shooting star? 2 Does Earth have craters like the Moon?

3 What space rocks pose a threat to Earth?

4 Are there stars in the sky in daylight? 5 How can we use the stars to find which direction is south?

6 Name the twelve signs of the zodiac. 7 What is the Milky Way? 8 What does GPS stand for?

8

3.1 UNIT

UNIT

context

8.1 Astronomy is the study of all the objects that are in space and everything that happens there. Look up at night and you will see the predictable planets and stars. If you’re lucky you might also glimpse some fast-moving and rarer objects such as comets, meteors, ‘shooting or falling stars’ and asteroids.

Asteroids Asteroids are irregularly shaped rocky objects left over from the formation of the solar system. They are also known as ‘minor planets’. Billions of asteroids orbit the Sun in a 345 million kilometre wide asteroid belt located between Mars and Jupiter. Sometimes one may stray closer to Earth, as asteroid 2004 FH did on the 18th March 2004. It missed Earth by a mere 43 000 kilometres, or just over a tenth of the distance to the Moon. Being approximately 30 metres Trojan asteroids in size, 2004 FH was too small The so-called Trojan to cause widespread damage if asteroids orbit the Sun in two groups in the same it had hit the Earth. Asteroids as Jupiter, with one orbit range in diameter from one metre group ahead and one to many hundreds of kilometres. behind the gas giant. The largest, Ceres, was the first

Fig 8.1.2

An artist’s impression of the NEAR spacecraft orbiting the asteroid Eros before landing

Landing on an asteriod

to be discovered (in 1801) and has On 12 February 2001, the NEAR spacecraft a diameter of about 930 kilometres. successfully landed on Scientists estimate that an asteroid one Eros, a 33-kilometre long kilometre or more in diameter striking and 13-kilometre wide asteroid. The spacecraft the Earth would be catastrophic, had been orbiting Eros causing firestorms, earthquakes and for a year and scientists tsunamis. A gigantic dust cloud decided to try landing it, would envelope the planet and as it was almost out of fuel and had collected more last for several months or possibly data than planned. years, blocking the Sun, cooling the atmosphere and wiping out many forms of life. Currently, the most popular theory about the extinction of the dinosaurs involves just such an asteroid, the crater of which has been discovered off the coast of the Yucatan Peninsula in Mexico. Worksheet 8.1 Discovering the asteroid belt

Meteors

Fig 8.1.1

The asteroid Ida is 56 kilometres long and has its own moon, Dactyl, which is 1.6 kilometres across.

Watch a clear night sky for about 20 minutes and you’ll probably see a sudden streak of light commonly known as a ‘shooting star’ or ‘falling star’. Despite these names, what you see is not a star at all, but a meteoroid burning up as it enters the Earth’s atmosphere. A burning meteoroid is called a meteor.

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>>>

Food A stony-iron meteorite

Annual meteor showers

Fig 8.1.3

Meteoroid mop-up

Aussie craters Australia has one of the biggest impact craters so far discovered. The impact occurred 590 million years ago when a four-kilometre-wide rocky meteorite, travelling at 90 000 kilometres per hour, hit an area in north-western South Australia. It caused a crater about 100 kilometres in diameter and up to four kilometres deep. Rocks from the explosion have been found three hundred kilometres away. The crater has been eroded over time and is now filled with water, forming Lake Acraman. The Henbury crater field in the Northern Territory consists of several craters spread over an area of one square kilometre, and is thought to have been made by a single meteorite exploding before it hit the ground.

Occasionally larger chunks of space rock make it to the ground without completely burning up. These are known as meteorites. Meteors travel at speeds of 35 to 95 kilometres per second, and sometimes several appear at once in what is called a meteor shower. A meteor shower occurs when the Earth passes through a region of space containing a cloud of dust particles associated with a comet. Meteors in a meteor shower appear to come from one point, called the radiant. Meteor showers are named after the constellation in which the radiant is located.

The Earth’s atmosphere acts as a sweeper of meteoroids, collecting about one million kilograms of meteoroids each day!

Prac 1 p. 213

Meteor shower

Main date

Quadrantids

3–4 January

Eta Aquarids

4–6 May

Delta Aquarids

29 July – 6 August

Persids

12 August

Orionids

21 October

Geminids

13–14 December

Comets Comets orbit the Sun in a much longer and narrower orbit than the planets. Comets originate from an area called the Oort cloud. This cloud is beyond Pluto and contains many billions of comets. A comet is a small irregularly shaped mass made of ice mixed with a large amount of dust, frozen carbon dioxide and organic matter. Most comets appear unexpectedly, never to be seen again, though some, like the famous Halley’s Comet, appear regularly. Halley’s Comet appears every 76 years, and last appeared in 1986. Most comets have orbits taking thousands to millions of years: comet Hale–Bopp, last seen in 1997, takes more than 4000 years to complete its orbit. A comet can be a spectacular sight as it nears the Sun. Its frozen nucleus begins to evaporate, releasing

Fig 8.1.5

Comet Hale–Bopp showing its gas tail (blue) and dust tail (white)

gas tail

dust coma

Fig 8.1.4

210

This crater in Arizona, USA, is 275 metres deep and 1.26 kilometres in diameter. The meteorite that caused it was around 60 metres in diameter and had a mass of more than 10 000 tonnes.

dust particles and gas to form a coma (head) and two tails. The two tails can reach up to 100 million kilometres in length and are produced by the solar wind (a stream of particles from the Sun), which affects the dust and gas slightly differently. Because the tails are formed by the solar wind Prac 2 they always point away p. 213 from the Sun. Fig 8.1.6

Comet impact on Jupiter The comet named Shoemaker–Levy 9 was discovered in 1993 orbiting Jupiter after being captured by the planet’s strong gravity. The comet broke up and eventually crashed into Jupiter in 1994, producing bright flashes in its atmosphere and leaving huge clouds. Jupiter may well have done the Earth a huge favour!

As a comet approaches the Sun, it develops two tails, which always point away from the Sun.

Sun

UNIT

8 .1

UNIT

8.1 Global killer As with asteroids, a comet collision has the potential to devastate the Earth. Comets, however, are the greater threat, as they originate in the outer reaches of the solar system and are coated with a dark outer layer that makes them difficult to observe until they near the Sun. One proposal to safeguard us against a life-threatening impact involves remote sensing satellites (called sentries) and ‘soldier’ spacecraft armed with nuclear explosives and an Earth-based control centre. Blowing up an asteroid or a comet would be too dangerous, however, since many smaller pieces from the explosion would still strike Earth. Instead, the idea would be to deflect the threatening comet by exploding a nuclear device near it. In order to deflect a global killer one kilometre in diameter, the explosion would need to occur when the object was still a year away from us. Obviously, early detection is essential. An artist’s impression of a rocket nearing an asteroid in an attempt to divert it away from Earth

Fig 8.1.7

[ Questions ]

Checkpoint Asteroids 1 State another name for an asteroid. 2 Recall where asteroids are found in the solar system. 3 a Identify the size range of asteroids. b State the size of an asteroid that would threaten Earth. 4 List three possible consequences of a large asteroid entering Earth’s atmosphere.

Meteors 5 State whether the following statements are true or false. a A shooting star forms when a streak of light travels across the sky. b A meteoroid is a burning meteor. c Meteorites burn on impact with the earth.

6 Define the term ‘meteor shower’. 7 Outline how meteor showers are named.

>> 211

Types of mixtures

Comets 8 Copy the following statement and identify the correct words to fill the spaces. A comet is a snowball made of ______ mixed with a large amount of dust, frozen _________ _______ and ___________ matter. Comets are a few ______ in diameter and orbit the _______. 9 State whether the following statements are true or false. a Most comets are seen regularly every few years. b A comet has two tails. c A comet’s tail appears only when it nears the Sun. d A comet’s tail may be millions of kilometres long. 10 Recall the year in which Halley’s Comet is due to appear again.

Global killer

>>> Analyse 22 Trace the main parts of the photo in Figure 8.1.4 and identify the radiant. 23 a Contrast the size of the meteor crater in Figure 8.1.4 with the size of the meteor that caused it. b Propose a possible fate for the meteorite.

Skills 24 a State how close the asteroid named 2004 FH came to Earth. b Contrast this distance with the distance between the Earth and the Moon (384 000 kilometres).

[ Extension ]

11 Explain what is meant by a ‘global killer’. 12 Outline one suggestion for avoiding destruction due to a ‘global killer’.

Think 13 Copy the following statements and modify any that are incorrect. a Astronomy is the study of the solar system. b A shooting star is not really a star. c Meteors and meteorites are both meteoroids. d All meteorites hit the ground. e Meteors may be caused by comets. 14 Identify the common characteristic in the names of all meteor showers. 15 Contrast the effects of a large and a small asteroid hitting Earth. 16 Account for the fact that Ceres was the first asteroid to be discovered. 17 Predict what would happen to Jupiter if it sped up, or slowed down, in its orbit around the Sun. 18 The dust in a comet’s tail is affected more by the Sun’s gravity than the gas in the tail. Explain how this may cause a comet to have two tails. 19 Explain how Jupiter helps to protect the Earth from impacts. 20 New meteorites are often found in Antarctica. Propose a reason for this. 21 An asteroid named Psyche is composed almost entirely of nickel and iron, like the core of the Earth. Propose a possible origin of Psyche.

212

Investigate 1 Research how Jupiter came to have a great red spot, stripes and strange swirls. Explain whether Jupiter’s surface changes over time or always stays the same.

Action 2 Organise an excursion to an observatory to investigate how astronomy is performed.

Surf Find out more about the following events in astronomy by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. 3 Research comets such as Hale–Bopp, Borrelly and Encke, and construct a short information card on each. 4 Meteorites from Mars hit the news in 1997. a Explain what was found in the meteorites. b Explain what caused the excitement to die down. c Evaluate the evidence you have collected about whether or not there is life on Mars. 5 a Construct a map of the world showing the sites of some major meteor craters. b Evaluate the link between the extinction of the dinosaurs and impact craters. c Assess your research. Is it likely that an impact from space caused the dinosaurs to become extinct? d Summarise your findings on a poster.

Creative writing

UNIT

8.1 Save the Earth! You are a leading astronomer and you calculate that a major asteroid impact with Earth is likely in the next 20 years. What can you do to protect the Earth and to provide sufficient warning for a course of action?

UNIT

8 .1

How will you convince politicians who are reluctant to believe you and unwilling to fund your proposal? How can you muster support for your plan? How can you convince the sceptics?

[ Practical activities ] Crater formation

Prac 1 Unit 8.1

Aim To simulate crater formation on planets and moons Equipment

Flour, chocolate icing sugar, aluminium tray, metre rule, 3 different sized rocks (about 1 cm up to 7 cm), access to electronic scales

Method 1 Record the mass and dimension of the rocks. 2 Place a 4 cm layer of flour into a tray and then sieve a fine layer of chocolate icing sugar. This will simulate an outer layer of rock. To assist in cleaning up, place the tray onto sheets of newspaper.

Teacher demonstration: making a comet Prac 2 Unit 8.1

Aim To make a model of a comet Equipment

Dry ice, water, dirt, Worcestershire sauce, ammonia, spray bottle, plastic bag, leather gardening gloves, plastic mixing bowl SAFETY: Dry ice is at a temperature of –80°C and if it comes into contact with your skin can cause severe burns. Only handle with gloves and in a well-ventilated area.

Method

3 Drop each rock from a constant height of 50 centimetres and record the diameter of the crater. Draw a diagram of the crater formed. Show all features.

1 Place water and dirt into the mixing bowl and stir. Add a small amount (10 mL) of ammonia and Worcestershire sauce.

4 Repeat step 3, dropping the rocks from one metre.

2 Wear leather gloves for the remainder of the demonstration.

5 Compare these craters to the one shown in Figure 8.1.4.

3 Place the dry ice into a plastic bag and crush.

Questions 1 a Outline any problems you encountered as you tried to measure the craters. b Explain how you overcame these difficulties. 2 Describe how your craters varied. 3 Did the same rock produce the same size crater every time? Explain your answer. 4 The above experiment assumes that all objects hit planets vertically. This may not occur very often. Design an experiment to assess the effect of an impact at an angle.

4 Add the crushed dry ice to the material in the mixing bowl. Stir vigorously. 5 Continue stirring until the mixture is almost solid. 6 Squeeze the mixture into a ball shape. Spray a fine mist of water onto the outside to add a fine ice layer. 7 Watch the comet over the next two hours. 8 Remind students not to touch the comet

Questions 1 Record observations of the comet as it melts. 2 Describe the change in shape of the comet over time.

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UNIT

context

8. 2 Over a thousand stars may be visible on a clear night in the country. In the city, this number will be greatly reduced due to light pollution, or glare from artificial lighting. In daylight there are over a thousand stars in the sky too. We only see one, however —the nearest star to us, called the Sun, which is so bright it makes it impossible to see the others. People have looked to the stars for

Light years Alpha Centauri is situated about 42 trillion kilometres (42 000 000 000 000 kilometres) Twinkle twinkle from Earth. To avoid using Twinkle, twinkle, little star, such long numbers when How I wonder what you are! describing distances in space, Up above the world so high, astronomers talk about light Like a diamond in the sky. Jane Taylor (circa 1806) years instead. The A light year is the distance le. Stars appear to twink density of air affects how light travels in a year. Light light is bent as it passes travels at 300 000 kilometres through our atmosphere. every second or 9.45 trillion of air of When patches kilometres (9 450 000 000 000 different density come between a star and our eyes, kilometres) in a year. This can we see different rays of light be thought of as the natural from come that appear to speed limit of the universe. slightly different parts of the star. The constant movement To calculate the distance of air in the atmosphere of Alpha Centauri from Earth means that stars seem to in light years, we divide the twinkle. distance by the speed of light to get 4.3 light years. This also means that it takes 4.3 years for the light from Alpha Centauri to reach us here on Earth. Only eight stars are within 10 light years of Earth. Pluto is the planet furthest from the Sun in our solar system—a mere 0.0006 light years or 5.5 light hours away.

214

guidance throughout history. The stars have allowed sailors to navigate the globe, provided us with information about the seasons and allowed astrologers to think they could predict the future. Whatever your interest, the stars can be fascinating to study!

A celestial street directory The word ‘celestial’ means ‘of the sky’. Astronomers have a way to locate celestial objects such as stars and planets. They imagine the sky and its stars to be on an invisible globe with the Earth at the centre. Although we nowadays know this is not true, people thought this was actually the case only five hundred years ago. This way of thinking, however, provides an easy way of describing the position of objects in the sky. This imaginary globe is called the celestial sphere. Because the Earth rotates from west to east, the celestial sphere appears to rotate the opposite way, so stars rise in the east and set in the west. We use latitude and longitude to describe a position on the Earth’s surface. Lines of latitude run around the Earth’s surface from east to west, while lines of longitude run north to south. On the celestial sphere, we use similar measurements: right ascension (RA) and declination (DEC). These are explained on the diagram in Figure 8.2.1. Sometimes a line called the ecliptic is marked on the celestial sphere. This is the line followed by the Sun as it moves across the sky, and makes an angle of 23.5° to the celestial equator. The stars that are visible depend on your position on Earth and which part of the celestial sphere you are under. For example, the southern hemisphere sky (eg the sky in Australia) appears very different to that in the northern hemisphere (eg in North America).

90°

Hadar). Some of the Australian Aboriginal tribes call the two pointers ‘The Two Men that once were Lions’, while others call them the twins that created the world. The Southern Cross is the smallest constellation and is very close to the 10 times larger Centaurus constellation. Although there are many constellations, the Sun appears to move through only 12 of them in one year. These are the constellations of the zodiac. The word zodiac comes from the Greek word meaning ‘wheel of life’.

60°

The celestial sphere

12h

rig ht 14h

celestial equator

6h N

8h

10h

4h

2h

24h 0°

a s c e n sio 16h

n

S 18h

22h

20h

star

d e c l i n a ti o n

30°

-30°

-60° South Celestial Pole

Fig 8.2.1

UNIT

North Celestial Pole

8.2

-90°

Right ascension is measured in hours, and describes how far around the celestial equator a star is. Declination is the angle (in degrees) we then move (north = +, south = –) to locate a star. The star in the diagram has RA = 22 hours and DEC = –30°.

Alpha Centauri

Hadar

The two pointers, Alpha Centauri and Hadar, form part of the Centaurus constellation. A centaur is a mythical creature— half-man, half-horse.

Time lapse photography produces ‘star trails’. At the centre of the stars’ movements is the South Celestial Pole.

Fig 8.2.3

Fig 8.2.2

Constellations Five thousand years ago there were no streetlights and no pollution to ‘hide’ the stars and no TV to entertain you at night. Instead, some people of the early civilisations watched the heavens, identifying and naming various star groupings or constellations. To aid their memory they imagined that they saw likenesses to mythical beings, animals and monsters, and named the groups after them. The most observed constellation in the southern skies is the Southern Cross (Crux Australis) and its two pointers (Alpha Centauri and

Fig 8.2.4

Crux Australis—the four bright stars are just right of centre.

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The night sky

Locating the South Celestial Pole

extended by about Imagine the long axis of the Southern Cross This gives the n. show tion four times its length in the direc As a check, Pole. tial Celes South the of on locati e approximat ld intersect shou ers point the g the line that bisects that joinin is directly South Pole. tial Celes South the at line the first underneath the South Celestial Pole.

Southern Cross

4x

x

South Celestial Pole

Pointers

Worksheet 8.2 Constellations Locating the South Celestial Pole using the Southern Cross (Crux Australis)

Fig 8.2.5

Career profile Astronomer Astronomers study planets, galaxies and other objects in the universe. An astronomer can be involved in: • observing objects in space, from Earth and via orbiting satellites, using a wide range of telescopes • designing and attaching special equipment to telescopes or spacecraft • recording, analysing and comparing results and observations using electronic and computer systems • developing theories and making predictions to explain observations • attempting to understand the nature and origin of the universe • using computers to produce star maps, catalogues and tables of measurements for use in navigation, and surveying. A good astronomer will have: • imagination and patience • an inquiring mind • an interest in and good skills in maths, computing and physics • good oral and written communication skills • good team skills • a willingness to work at night.

Sky map A sky map shows the entire sky as viewed from a given location at a specified date and time. Sky maps are used to locate stars and other objects in the sky, just like a world map is used to locate countries, states and cities.

216

Fig 8.2.6

Astronomer using an optical telescope

The sky map in Figure 8.2.7 is for September. You may locate one for the current month on the Internet. Excellent software programs for viewing the sky at any time from any location are available as shareware from several Internet sites—search using the keywords CyberSky, SkyGlobe or Sky maps.

Note the star magnitudes in the corner of the map. The lower the number, the brighter the star and the larger the dot symbol on the map. The pointer farthest from the Southern Cross has a magnitude of 0, while Fig 8.2.7

brighter stars may have magnitudes of –0.5 to –1.0. The faintest visible stars to the naked eye have a magnitude of +6.

UNIT

8.2 Prac 1 p. 219

To use a sky map, hold it so the direction you are facing is at the bottom. The centre of the map is the point directly overhead.

Southern hemisphere sky map

September Early Sept, 8pm Late Sept, 7pm

Symbols Galaxy Double star Variable star Diffuse nebula Planetary nebula Open star cluster Globular star cluster Star magnitudes -1 0 1 2 3 4

217

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The night sky

UNIT

8. 2

[ Questions ]

Checkpoint Light years 1 Recall the names of the two closest stars to Earth. 2 The nearest star to Earth is a vast distance away. State this distance in kilometres. 3 Define the term ‘light year’. 4 Recall the distance in kilometres that light is able to travel in a year.

A celestial street directory 5 Define the term ‘celestial’. 6 The celestial sphere is a useful model of the sky. Use examples to explain why this model is useful. 7 Explain why the stars appear to rotate. 8 Some celestial sphere models have an ecliptic. Explain the purpose of the ecliptic.

Constellations 9 Use an example to clarify what is meant by a constellation. 10 Recall another name for the Southern Cross.

Think 11 From the list below identify the objects mostly visible in the night sky: a planets b orbiting artificial satellites c suns d galaxies. 12 Explain why we cannot see all the stars on the celestial sphere from Australia. 13 Identify the following constellation by completing each name in your workbook. a Scor___ b Triangulum ______ c Peg___ d Her____. 14 Identify a constellation near: a Centaurus b Grus.

Skills 16 Calculate how long would it take to reach Alpha Centauri travelling at the speed of: a a bicycle (10 kilometres per hour) b a car on the highway (100 kilometres per hour) c a passenger jet (1000 kilometres per hour) d an orbiting space shuttle (30 000 kilometres per hour). 17 Achernar is one of the brightest stars in the sky and is 1400 trillion kilometres from Earth. Calculate how many light years this is. 18 State the names of two bright stars on the sky map. 19 Identify the symbol used on the sky map for: a a galaxy b a diffuse (fuzzy) nebula. 20 List the following star magnitudes in order from dimmest to brightest: 0, –1, +2, –0.5 21 The Southern Cross and the pointers can be used to find the South Celestial Pole. Explain how this is done. 22 A light year is the distance travelled by light in a year. If the speed of sound is 330 metres per second, calculate what distance could be called a ‘sound year’.

[ Extension ] Investigate 1 Research in order to list bright stars that could be identified in the night sky. Include their distance from Earth. 2 Construct a poster to demonstrate the finer details of a particular constellation such as Orion or Triangulum Australe. 3 Construct a poster to explain what is meant by the ‘zodiac’.

Surf Analyse 15 Trace the celestial sphere on page 217 and identify the approximate position of a star having right ascension 12 hours and declination 45°.

218

4 Find out about sky maps by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button.

Obtain a sky map or planisphere (a device for locating stars at various times of the year). Construct a diagram to demonstrate the stars or constellations you can name using the planisphere. Hint: Use a torch covered with red cellophane to view your star map at night.

Creative writing

UNIT

8.2 Your constellation Using a new type of telescope, you discover a constellation, which you are given the right to name. Sketch your constellation, showing lines joining stars that form part of a picture based on the name you choose. Name the individual stars in the constellation (names should involve letters of the Greek alphabet) and describe the brightness of each star.

Method 1 Double-click the SkyGlobe.exe file to begin SkyGlobe. 2 Set the location to the major city nearest you (eg Sydney) by typing L and selecting a location (you may need to first select ‘More locations’). 3 Use the mouse (move to an edge of the screen) or arrow keys to change the view. 4 Type S to obtain a southerly view.

Fig 8.2.8

A planisphere

UNIT

8.2 [ Practical activity ] Exploring the stars Aim To use a sky map to locate stars and Prac 1 Unit 8.2

5 Position the cursor over a star to find its name. Note some of the brightest stars’ names. Also take note of some constellations and where they appear. 6 Type M or H to advance the view by a minute or hour respectively. Type Shift M or Shift H to go back. Try repeatedly pressing M or H (or Shift M or Shift H). 7 Type Z to zoom in, or Shift Z to zoom out. 8 Investigate the other commands shown at the top left of screen. 9 Another shareware program is CyberSky. Search for the program and compare the two.

Questions

constellations

1 List some of the brightest stars.

Equipment

2 List some constellations that are visible at the current time of year.

The program SkyGlobe (available as shareware— enter SkyGlobe in an Internet search engine to find a download site) installed on a computer running Windows

3 Identify the direction that the stars appear to move when you advance the minute or hour 4 Describe another interesting SkyGlobe command.

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UNIT

context

8. 3 On dark, clear nights we can see a faint band of light studded with many stars stretching across the sky. This is the Milky Way, the galaxy in which we live. The Kaurna, an Aboriginal group from South Australia, called the Milky Way ‘Wodliparri’, a watercourse curving through ‘Womma’, the celestial plains.

Galaxies A galaxy is an enormous collection of gas, dust and stars spinning in space, held together by gravitational forces. In 1926 Edmund Hubble classified the numerous galaxies according to their shape, designating a letter to each of the four main types: • E—an elliptical galaxy that is round or oval with no arms • S—a spiral galaxy, because it reminded Hubble of a pinwheel • BS—a barred spiral galaxy that looked similar a spiral but with a solid bar across the middle • Irr—an irregular galaxy appearing as a random collection of stars with no obvious order. Types E, S and BS are shown in Figure 8.3.1

E

S

Our home galaxy— the Milky Way Our Sun is just one of over 100 billion stars in our galaxy, the Milky In 1784, Charles Messier Way. If we could see the Milky Way compiled a list of fuzzyfrom the outside, it would appear as looking celestial objects, , ters a spiral galaxy, 100 000 light years in including star clus nebulae and galaxies. He diameter, with several arms. It also assigned M numbers to has a bright central bulge, 10 000 these objects, many of y. toda d light years thick. Our solar system which are still use sits out near the end of one of the spiral arms about 30 000 light years from the centre. Along the spiral arms of the Milky Way are open clusters containing a few hundred stars, and surrounding the outer regions are more dense

Messier objects

220

BS

Three of the main types of galaxies

Fig 8.3.1

groups called globular clusters, consisting of up to a million stars. Omega Centauri is a globular cluster that can be seen with the naked eye—it looks like a fuzzy, bright star.

8.3

Core

telescopes, which collect visible light using large mirrors, and radio telescopes, which collect radio waves. Both provide valuable information about the size, composition and movement of stars and galaxies. Our knowledge about the universe has been greatly increased by the placement of telescopes into space, for example the Hubble Space Telescope (HST). The Earth’s atmosphere absorbs and distorts light rays from

The Sun

100 000 light years

Fig 8.3.2

UNIT

Globular clusters

A side view of the Milky Way

Active galaxies

Career profile

An active galaxy is one that exhibits unusual activity in its centre, such as a quasar or a radio galaxy. A quasar is a galaxy whose centre is so bright that it obscures the outer regions. It is as though a quasar has at its centre a black hole that causes gas and dust to spiral around it, heating up as they near the centre. Some of this matter escapes in jets along the axis of the black hole. A radio galaxy gives off energy in the form of radio waves from clouds of matter that have been blasted to either side of the galaxy.

Telescopes

Astronaut An astronaut can be involved in: • commanding space missions • working while on a mission, performing experiments, repairs or other tasks • piloting the space shuttle (or vehicle) through ascent, on-orbit, re-entry and landing phases of flight • planning, testing, training and preparing for space missions.

Prac 1 p. 224

We see some objects in the universe because they emit waves of visible light. However, many objects, such as neutron stars and pulsars, give out their energy as non-visible types of light waves, including infra-red and radio waves. Only visible light and radio waves make it to Earth. Hence there are two main types of large Earth-based telescopes—optical The Australian telescope compact array near Narrabri, New South Wales, detects radio waves from objects such as pulsars, and is equivalent to one incredibly large telescope.

Fig 8.3.3

Fig 8.3.4

Astronauts carry out mirror repairs on the Hubble Space Telescope (HST) from the space shuttle Endeavor.

A good astronaut will be able to: • work with a large team of people • maintain physical fitness and health in preparation for missions • perform experiments and tasks in difficult environments • be a good leader and be able to make decisions under pressure.

221

>>>

Way and other galaxies The Milky way

Hubble trouble! Shortly after the Hubble Space Telescope was launched in 1990, scientists feared it would become a billion dollar dud, as an error in its mirror, one-fiftieth of the width of a huma n hair, caused blurred images. In 1993 the space shuttle Endeavor undertook a mission to fit a series of small corrective mirrors. The missi on was successful, and now Hubble produces breathtaking, crystal-clear astronomical imag es.

Comparison images of galaxy M100 before and after the Hubble Space Telescope mirror repairs

a

b

c

d

Fig 8.3.6

222

Fig 8.3.5

space and obscures the view from the ground for astronomers. A telescope stationed in outer space is entirely above the atmosphere and receives images of much greater brightness, clarity, and detail than do ground-based telescopes with comparable optics.

All these pictures were taken by the Hubble Space Telescope. a The Carina nebula shows many new stars forming in enormous gas clouds. b The Eskimo nebula looks like a face surrounded by a furry parka when viewed from Earth-based telescopes. The Hubble shows much more detail. c This spiral galaxy shows older yellow stars in the centre. The arms are more blue due to the ongoing formation of young blue stars. Interstellar dust is seen as dark patches in the arms. d This image of Mars is considered the ‘best ever’.

UNIT

8.3 Bigger and bigger The Milky Way galaxy is part of a group of more than 30 galaxies called ‘the Local Group’. Only one of these, the Andromeda galaxy, is bigger than the Milky Way. The Local Group in turn is part of the ‘Local Supercluster’. Superclusters combine to form part of the Universe.

Put simply, the Universe includes planets, stars, galaxies—everything! Worksheet 8.3 Parts of a galaxy

Fig 8.3.7

Earth/Moon

Solar System

Oort cloud surrounding Solar System

Nearest stars

Milky Way galaxy

The Local Group of galaxies

Local Supercluster

Universe

UNIT

8 .3

[ Questions ]

Checkpoint Galaxies

5 Describe the shape of the Milky Way galaxy when viewed from the side. 6 Describe where Earth is located in the Milky Way galaxy.

Active galaxies

1 Define the term ‘galaxy’.

7 State the distinguishing feature of an active galaxy.

2 List the main types of galaxies.

8 List two examples of active galaxies.

3 Identify the following galaxy types: a a galaxy whose centre is very bright b a galaxy that emits radio waves.

Our home galaxy—the Milky Way 4 Copy the following statements and modify any that are incorrect. a The Milky Way galaxy is a cluster galaxy. b The Milky Way galaxy contains less than 100 billion stars. c Earth is located in the centre of the Milky Way galaxy. d Omega Centauri is a globular cluster that cannot be seen with the naked eye.

Telescopes 9 State the name of a telescope that: a is Earth-based and uses mirrors b is in space, uses a large mirror and uses solar power c detects radio waves on Earth. 10 The Hubble Space Telescope has expanded our knowledge of the Universe. Outline three ways it has achieved this.

Bigger and bigger 11 Outline how the Milky Way relates to the ‘local group’. 12 State the main components of the Universe.

>> 223

>>>

The Milky Way and other galaxies

13 Propose a reason for telescopes often being built on the top of mountains. 14 Contrast a space satellite with an Earth-based one. 15 A telescope on Earth can create brighter images than those seen with the human eye. Explain how this is possible. 16 When we view a distant galaxy, we are actually looking back in time. Explain how.

Analyse 17 Use the following pictures of the Universe to identify the galaxy type. a

b

c

d

[ Extension ] Investigate 1 Describe some of the major Earth-based telescopes. 2 a Research the main purpose of the Parkes radio telescope in New South Wales. b Outline what type of research is performed by this telescope. c Describe some of the major achievements that have been made by this telescope. d Present your information as a tourist information brochure for people who visit the Parkes telescope. 3 Research the work of Edwin Hubble and recount the story of his life. Include: a personal details, such as date of birth, country of origin, etc. b his education, type of work performed and major achievements c important events in his life.

8.3 [ Practical activity ] UNIT

Think

Globular clusters Aim To locate globular clusters on a sky map Prac 1 Unit 8.3

Equipment The program SkyGlobe (available as shareware—enter SkyGlobe in an Internet search engine to find a download site) installed on a computer that runs Windows

Method

Skills 18 Construct a diagram of the Milky Way Galaxy when viewed: a from above b from the side. 19 Another type of galaxy that has no regular shape is called an ‘irregular galaxy’. Construct a diagram of what this might look like.

224

1 Double-click the SkyGlobe.exe file to begin SkyGlobe. 2 Set the location to the city nearest you by typing L and selecting a location (you may need to first select ‘More locations’). 3 Find one of the following globular clusters by typing F, then selecting ‘Messiers’. 4 Describe the position of each globular cluster, and the constellation it is part of: globular clusters M2, M3, M4, M5, M15.

UNIT

8. 4 asynchronous orbit

context

polar orbit

What do the Moon, the International Space Station and Halley’s Comet have in common? Answer: they are all satellites that orbit a much larger object. In this unit, you will look at artificial satellites—satellites put in orbit around Earth by humans. These satellites may be specialised for different uses, including sending and receiving communication and navigation signals, watching the weather, surveying the land surface and studying space. These satellites provide a lot of information that we nowadays take for granted.

36 000 km

geostationary orbit

Fig 8.4.1

Types of orbit. The scale here is exaggerated for the sake of clarity.

Satellite orbits

Communications satellites

Satellites may be placed into several different types of orbits, Science fiction depending on their function. becomes fact The three main orbits are: The first person to suggest • geostationary orbits the use of satellites for Satellites in this orbit take communication was science fiction writer Arthur 24 hours to revolve around C Clarke, author of the Earth and are always book The Sentinel, which above the same point on was the inspiration for what the Earth’s surface. Most many regard as the greatest ‘sci-fi’ film of all time: communications satellites 2001—A Space Odyssey. are in geostationary orbits. • asynchronous orbits Observation satellites are placed into this orbit. They move in the same rotational direction as the Earth but more quickly, so they pass over different parts of the Earth’s surface. • polar orbit Satellites in this orbit move in a path at right angles to the rotation of the Earth, ensuring complete coverage of the planet Prac 1 over time as it rotates under them. p. 230

Communications satellites can relay information such as telephone calls, television signals and Internet data. An Earth station containing an antenna receives and sends this information to a communications satellite such as Intelsat 5. Intelsat satellites operate from geostationary orbits, 35 900 kilometres above the Earth. The Intelsat 5 communications satellite

Fig 8.4.2

225

>>>

Satellites and remote sensing The satellite then ‘cleans up’ and boosts the signal, which can be distorted and weakened when travelling through the atmosphere. The satellite then relays the boosted signal to another Earth station at a distant location, which may in turn send information via the telephone system or other land-based system. Though information travels at the speed of light, the large distances involved contribute to a delay of up to half a second in conversations via satellite. Satellite footprints

Overlapping satellite footprints

The area on Earth reached by a single satellite is called its footprint. Many communications systems involve fleets of satellites to provide wider coverage, produced by overlapping footprints.

Fig 8.4.3

Remote sensing satellites Many different sensors are now mounted onto satellites, allowing scientists to research and monitor the Earth’s features without going to space themselves or waiting for photographs taken on space missions. This is called remote sensing and is now commonly used for studying and monitoring: • weather patterns • the temperature of the earth and oceans • the shape of the land surface • the seafloor by penetrating the oceans and ice • natural phenomena such as bushfires and volcanoes • vegetation and crop types in farming and forestry • the ozone hole • the movement of animals and pests • pollution, algal blooms and oil spills in lakes and the oceans • the activities of other countries (spying or espionage). Nowadays, remote sensing is also commonly used for navigation. The information obtained from all these sensors is used for weather forecasting, scientific research and military purposes.

How remote sensing works

Fig 8.4.4

Remote sensing techniques

A satellite in orbit has sensors that scan the earth’s surface measuring the amount of light reflected.

One sensor records only the amount of red light reflected.

226

Light and other forms of energy such as radio activity and heat are reflected from the surface of the Earth and can be analysed to reveal a great deal about what is happening. Remote sensing can be used to take ‘normal’ photographs, but special images can also be produced by using special sensors and computers. These images One sensor records often have false colour only the amount of

One sensor records only the amount of blue light reflected.

63 09 20 73 15 11 01 11

52 08 22 44 11 06 05 18

35 16 31 23 16 01 02 18

83 43 45 86 10 02 07 11

27 44 27 87 46 05 01 10

55 66 55 75 68 46 29 93

22 45 23 84 64 53 23 78

green light reflected.

81 62 81 82 76 42 57 81

The information is recorded as numbers.

20 63 73 11 15 09 08 01

The data collected is sent to an antenna on earth.

22 52 44 15 18 08 06 05

31 35 23 18 16 16 01 02

88 88 89 11 10 43 02 07

27 27 87 10 46 44 05 01

55 55 75 72 68 54 46 29

23 23 84 78 75 45 55 19

81 81 82 81 76 62 42 23

Computers are used to process the data. The data about the amount of blue, green and red light reflected off the earth’s surface is put together to make a satellite image.

A satellite photograph of a cyclone

Fig 8.4.5

This remotely sensed computer-generated image of the Earth is based on satellite data. It shows water (blue) bare land (brown) and vegetation (green). The shape of the ocean floor is shown by different shades of blue.

Fig 8.4.7

UNIT

8. 4

severe storms. Unfortunately, some phenomena such as tornadoes form so quickly that remote sensing is still too slow to give much warning.

Navigation The Global Positioning System, or GPS, is probably the best example of a navigation satellite system. GPS consists of 24 satellites, each having the mass of a small car, spread among six different orbits 20 000 kilometres above the Earth. The GPS satellites contain solar panels for power, and atomic clocks. Tracking stations on Earth send information about each satellite’s position to a master control centre, which in turn sends information to the satellites, so that the satellites ‘know’ their position relative to the Earth. A GPS receiver on Earth can receive signals from at least four GPS satellites and use them to calculate your position on Earth.

A satellite image showing bushfires around Sydney, 2003–04

Fig 8.4.6

added to various parts to make information clearer. Examples are ‘heat photos’ that record the infra-red radiation emitted or reflected from the Earth’s surface. Figure 8.4.4 outlines how remote sensing works.

Weather Weather or meteorology satellites are found in both geostationary and polar orbits. They record images and measure temperature, pressure and humidity using specialised sensors. Combined with data collected on Earth, they help forecasters with their predictions and can provide better advance warning of many life-threatening phenomena such as cyclones or

Fig 8.4.8

Twenty-four Navstar satellites in different orbital planes provide global coverage for the GPS.

227

Satellites and remote sensing

Career profile Geoscience technician Geoscience technicians assist scientists in finding and developing mineral and fuel resources hidden in the earth. They also look after the practical tasks involved in servicing a remote field operation. Geoscience technicians can be involved in: • undertaking geophysical surveys • using GPS to establish ore deposit locations • operating geophysical instruments to complete surveys which outline hidden rock features. This may involve measuring magnetism or gravity • collecting, recording and transporting samples of rock, soil, drill cuttings and water • analysing information collected from a range of sources and carrying out computer processing of the data • using digital technology to produce geological and geophysical maps • surveying the Earth’s surface and rocks using satellite remote sensing.

Fig 8.4.9

>>> Some GPS receivers contain electronic maps on which they display your position. Many bushwalkers now use hand-held GPS receivers instead of maps, and luxury car makers now commonly include dashmounted GPS receivers as a standard feature. Worksheet 8.4 Global positioning

Remote sensing spacecraft Exploration of the planets is one of the major achievements of science. The solar system is huge, and sending remote sensing spacecraft to explore it is far easier and cost-effective than sending humans. Remote sensing spacecraft can be smaller; there is no need to provide food, air or accommodation; and the spacecraft do not need to return to Earth. Huge amounts of information have already been gathered using remote sensing techniques. Observations of the bodies of our solar system are commonly done with orbiting spacecraft, flyby, probe and lander missions. Most of the instruments that survey the Earth have been adapted for the exploration of the surfaces and atmospheres of the other planets NASA’s twin robot geologists, Spirit and Opportunity, landed on Mars in 2004. They were equipped with a state-of-the-art sensors and tools designed to collect information about the Martian environment. They include panoramic cameras, spectrometers, magnets, a microscope and a rock abrasion tool.

A geoscience technician finding his location using a hand-held GPS receiver

A good geoscience technician will be able to: • participate in scientific activities and use high-tech instruments • prepare accurate records and reports • work as part of a team • have an interest in rocks, fossils and minerals • stay physically fit • work in remote locations. The Mars rovers are robots that act as remote sensors. Information collected is sent back to Earth via satellites that orbit Mars.

228

Fig 8.4.10

UNIT

8. 4 Think 12 A satellite dish used for TV or entertainment always points in the same direction. Identify the type of satellite from which it receives its signals. 13 Describe the advantages of using a geostationary satellite for communication. 14 Imagine an Ariane rocket delivering a satellite into orbit. Outline what happens to each of the following when they are no longer needed after the launch: a solid fuel booster rockets b main stage rocket. 15 Explain why are there 24 satellites in the GPS system when only four are needed to pinpoint a position on Earth.

Fig 8.4.11

This image was taken by the Spirit rover and shows the extended arm of the robot holding scientific instruments. The flower-shaped marks on the rock were made by the rock abrasion tool for analysis of the rock contents.

UNIT

8. 4

[ Questions ]

Checkpoint Satellite orbits 1 List three naturally occurring satellites of the Sun. 2 Identify three types of satellite orbits around Earth and construct a diagram of each.

Communication satellites 3 List three types of information relayed by communication satellites. 4 Outline the usefulness of Intelsat 5 to communication.

Remote sensing satellites

16 Predict what would happen to a satellite orbiting the Earth if the Earth’s atmosphere suddenly extended beyond its orbit. 17 Solar panels are more effective on satellites than on Earth. Explain why. 18 Satellites rotate so that their transmitters always face the same point on the Earth’s surface. Discuss the reasons for this.

satellite

Skills 19 The diagram opposite shows the footprint of a single satellite. Copy the diagram and explain how, by adding two more satellites, the entire Earth may be covered by footprints from a three-satellite system.

Earth

Fig 8.4.12

5 Clarify the purpose of remote sensors. 6 False colour is added to some satellite images. Explain why. 7 Outline the information gathered by: a a weather satellite b an Earth resource satellite. 8 State two possible uses of a hand-held GPS receiver.

Remote sensing spacecraft 9 Outline the main task of remote sensing spacecraft. 10 List the equipment on Spirit and Opportunity. 11 Explain why remote sensing spacecraft are being used to explore the solar system rather than humans.

[ Extension ] Investigate 1 Research the names and functions of several current satellites. Include one or more Australian satellites (eg Optus Sat, ARIES-1, FedSat 1). 2 Research the Star Wars program proposed by former US president Ronald Reagan, and now being reconsidered by the current government in the United States. >>

229

Satellites and remote sensing

a Outline the aims of the project. b Describe any current scientific research into the Star Wars project. c Assess the advantages and disadvantages of Star Wars. d Evaluate the attitudes of some governments to the Star Wars project (eg why does Russia object to it?). e Assess Star Wars and present your own opinion as to whether it should be completed. f Negotiate with your teacher on how your information could be presented.

Action 3 Construct a crossword to summarise remote sensing and its uses.

UNIT

8. 4

>>> Surf 4 Complete the following activities by connecting to the Science Focus 2 Companion Website at www.peasoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. a Research more about Spirit and Opportunity, and their work in collecting information on Mars. Imagine you are an education officer from NASA. Construct a Powerpoint presentation or website to summarise information for people wanting to know more about these two Mars rovers. Your website should be concise and clear, containing no more than 10 pages. Start your research using the NASA website. b Construct a model of a remote sensing space probe or satellite. You will find many examples on the Internet. Search the NASA site for ‘models’ or ‘model’.

[ Practical activity ] Fig 8.4.13

Satellite speed

Earth (imaginary)

Aim To investigate the relationship between Prac 1 Unit 8.4

satellite speed and orbit radius

Equipment

A smooth hollow tube (eg the body of a pen), cotton or thin string (50 cm), 4 small rubber stoppers with holes, stopwatch, scissors

satellite

Method 1 Construct the apparatus shown below. 2 Spin the top stopper (the ‘satellite’) so it orbits at a steady speed about 15 cm from the top end of the tube (the ‘Earth’). Adjust the speed of orbit until the orbital radius remains steady at about 15 cm. Once you have achieved a steady orbit, find the time taken for 10 revolutions. 3 Reduce the force of ‘gravity’ by cutting off one of the lower stoppers. 4 Orbit the ‘satellite’ once more at a steady speed, but at a distance of 20 cm from the ‘Earth’. Again, find the time taken for 10 revolutions.

230

gravity force

Ensure rubber stopper is not hard up against tube (always leave a gap here).

Questions 1 A satellite is placed in a steady orbit around the Earth. Explain the effect of its distance from the Earth on its speed in orbit.

5 Reduce the force of ‘gravity’ even more by cutting off another stopper, and orbit the ‘satellite’ steadily at a distance of 25 cm from ‘Earth’.

2 Predict what may happen to a satellite in a steady orbit if it suddenly: a speeds up b slows down.

6 Try spinning the ‘satellite’ slower or faster than that required for a steady orbit. Note what happens.

3 Explain why you needed to increase the radius of orbit when each stopper was removed.

Chapter review [ Summary questions ] 1 Outline the features of an asteroid. 2 Explain how a ‘meteor shower’ is named.

[ Interpreting questions ] 23 Copy the diagram of the comet (Figure 8.5.1) into your workbook and add the two tails.

3 Recall three distinguishing features of a comet.

Fig 8.5.1

4 Outline how a comet can pose a threat to Earth. 5 Alpha Centauri is about 42 trillion kilometres from Earth. Recall the name of the unit of measurement used in astronomy to avoid having to deal with such large numbers. 6 The right ascension and declination are two measurements used on the celestial sphere. Outline the meanings of these terms.

Sun

7 Outline the origin of the constellations of the zodiac. 8 Outline four types of work carried out by astronomers. 9 List four different types of galaxies.

11 Telescopes can be used to collect information from outer space. Identify two types of radiation that can be detected on Earth. 12 Satellites can be placed into three different types of orbits. Identify these orbits. 13 Outline four uses for remote satellites. 14 The Global Positioning System is used for navigation. Outline its main advantage.

24 Identify the right ascension and declination of the star labelled S in Figure 8.5.2.

North Celestial Pole

16 Identify the type of space rock that is: a a dirty snowball that orbits the Sun b a burning piece of dust or rock c an irregularly shaped rocky object also known as a minor planet.

60

The celestial sphere

star S

[ Thinking questions ] 15 Describe what Spirit and Opportunity are and what they have done.

90

8h

10h 12h

right asce 14h

celestial equator

6h N

4h

20 Explain what type of celestial objects are known as ‘star nurseries’.

2h

24h 0

nsion

16h

S 18h

22h

20h

-30

-60

17 Contrast a meteor with a meteorite. 18 a Contrast the number of stars visible on a clear night in the country with the number visible in the city. b Propose reasons for any differences. 19 The north star is almost directly above the North Celestial Pole on the celestial sphere. Describe what observers in the northern hemisphere would notice about its position over time.

30

declination

10 Recall the type of galaxy that has a black hole near its centre.

-90

South Celestial Pole

Fig 8.5.2 25 Identify the type of constellations that are close to the ecliptic on the star map on page 217. 26 Construct a diagram of: a a spiral galaxy b a barred spiral galaxy

c an elliptical galaxy.

21 Contrast a pulsar with a quasar.

Worksheet 8.5 Astronomy crossword

22 From the following list, identify the satellites: the Moon, the International Space Station, Mars, Halley’s Comet.

Worksheet 8.6 Sci-words

231

Team research project 4.2, 4.13, 4.15, 4.16, 4.17, 4.18, 4.19, 4.20, 4.21, 4.22.2

Outcomes

Key focus area

>>> The nature and practice of science By the end of this chapter you should be able to: investigate a problem using the scientific method design an experiment to perform a ‘fair test’ use equipment in a safe manner work as part of a team and identify different types of team roles that people may perform gather information from first-hand and second-hand sources analyse, present and evaluate information and data draw conclusions based on the information and data write up an experimental report to present the findings of an investigation

Pre quiz

solve problems creatively as they arise.

1 What are the advantages of working in a group instead of on your own?

2 In the photo is a team of surgeons performing an operation. Why do you think surgeons work in a team?

3 Some questions have no simple answer. Write down an example of one.

4 A report should have an aim and a hypothesis. But what is the difference between them?

5 List what should be included in the report of an experiment.

>>>

9

UNIT

context

9.1 Teamwork is an important part of life. We see it every day on the football field, on the netball court, in operating theatres and in scientific research. Sometimes the members of research teams are spread across different continents, each member doing different parts of the same scientific project. This requires a cooperation between team members. Working together requires the sharing of ideas and resources and can lead to better results. For research to be effective team members need to understand their role in finding a solution to the problem being investigated.

Team skills In this chapter you and your team members are required to make decisions about planning, performing and assessing a science investigation. This will give you the opportunity to practise or ‘do science’ and understand its nature. The project will allow you to apply and develop important skills. Everyone has something that they are very good at. Some in your class will be excellent at mathematics, some at drawing and some at writing. Some will be able to talk to anyone, others will quietly work by themselves. We are all different, but by working as a team these special skills will be shared with other team members, making the whole team stronger. This also means each person will teach others in the team their special skills. Some of the skills that you may use and develop include: • using creativity to solve questions • using logical reasoning and creativity to find solutions to questions • constructing and testing hypotheses • applying scientific processes when testing your ideas • deciding on what each member of the team does • setting realistic time lines for an investigation

Fig 9.1.1

Scientists generally do not work alone. They are involved as part of a team all working on the same problem.

• working safely as a team • maintaining a project workbook outlining the investigation • monitoring the progress of your group against the timeline • asking for assistance from various people • evaluating how well the team worked to complete the task • evaluating how each member contributed to the team.

The role of team members Each member brings different personal strengths to a team. Identified below are five different types of team roles. When choosing members for your team be sure to get together with people who have different strengths. You may be very good at one of these roles, but you are probably able to do more than one of these roles at a time.

233

Teamwork and topics • Explorers/creators They look for better ways to do things and use their imagination to create new ideas. They often solve difficult problems and invent things in unusual ways. This means that they are often thinking one or more steps ahead of where the research is at that very moment. Because an explorers/creators look at the big picture they may miss some of the detail. The organiser (described below) needs to work closely with the creator to catch these missed details. • Scientists They provide explanations for how things work. They like to experiment and try different ideas. They are good at using equipment, analysing information for patterns and accuracy, and making models to explain things. • Researchers They provide information from many sources. They enjoy the hunt for new ideas and learning about new things and are often good communicators who can share information with others in the team. • Leaders They keep the team together and working productively and cooperatively. They match tasks to suitable people and make sure the job is started and completed. Leaders should set clear goals that can be achieved, and motivate people to keep going. They should monitor progress and keep track of timelines. They should be good listeners, who look after people’s personal welfare. • Organisers They like organisation and planning. They are hard workers who like to gets things done. They maintain an accurate record of all experimental data, the successes and the failures. The organisers identify the correct procedures and try to keep all others Eureka! working towards the t weigh the that idea s’ Archimede goal. The organisers of an object is equal to the weight of the liquid it displaced was encourage smooth supposedly found when he stepped running of the team. into his bath. Excited, Archimedes ran naked into the street shouting ‘Eureka!’, meaning ‘I’ve got it!’. Sometimes a discovery comes at the weirdest time.

234

?

Explorers/creators

Scientists

Researchers

Organise Create Research Explain Leaders

? ? Organisers

Fig 9.1.2

Choosing an investigation Selecting an investigation is a very important part of your project. The investigation should challenge you to learn something new. It should not be too simple or too hard. In the following pages you will read about an investigation performed by a group of students. This should help you to develop and perform your own investigation. The class was given the opportunity to choose a problem to solve from a list of suggestions. You can also choose your investigation from this list (see below). The Eggsperts team with their final project

Fig 9.1.3

• Does exercise affect heart rate and blood pressure? • Are some brands of antiseptic soaps better at killing bacteria than others? • Does reaction time increase with age? • Is the performance of batteries affected by the age of the battery? • Is the life of batteries related to their cost? • Do some nuts contain more energy than others? • Is a worm farm better at recycling food scraps than a compost bin? • What type of material is best for making a warm jumper? • Does the length and brand of sticky tape affect its strength? • Does the types of soil affect the growth of geranium cuttings? • Is the effectiveness of heating dependent on the position in a microwave oven? • Which brand of washing powder is the most effective cleaner? • Do the seeds of some species of plant grow faster than others? • Which brand of glue sticks works the best?

There are many investigations that you could do, but you will need to negotiate with your teacher if you wish to select a problem that is not listed below. If you are choosing a problem for your project that is not in the list, make sure that: • it can be solved experimentally • it is safe and does not pose a danger to people or the environment Accidental science • you can get the required materials A chemist called Sapper • it can be finished in the agreed accidentally broke a mercury thermometer by time. doing what every scientist After a great deal of discussion should not do: he was and brainstorming, each team in the using it to stir a beaker containing a mixture of class chose the same project: ‘How naphthalene and sulfuric can you protect a raw egg from acid! Another member from breaking when it is dropped from a his team, Karl Neumann, found that the mercury height of five metres?’. started a reaction, forming At this stage the teams began to a chemical that could then record their ideas and progress in a be converted to the dye project workbook. This was a diary indigo. This was the first time the dye had been of everything that was done. produced. Further research The team you are going to follow found that mercury consisted of five students—Kali, acted as a catalyst in the formation of indigo. Amelia, Michael, Lee and Mia. They named their team ‘The Eggsperts’.

UNIT

9 .1

• Do gel pens last longer than normal ballpoint ink pens? • How can you protect a raw egg from breaking when it is dropped from a height of five metres? • How long do different types of rubbish take to break down in a compost bin? • How much sugar will dissolve in water at different temperatures? • How does the amount of light affect the growth of plants? • Is the colour of a hair dye really what is shown on the packet? • What is the best way to keep lemonade from going flat? • Does the shape or orientation of button holes affect their strength? • Which soft drink has the most bubbles or the most sugar? • What is the strength of a lolly snake? • How can we assess the water quality of the local creek? • How much air pollution is around the school? • What does the wind speed do to temperature?

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Teamwork and topics The question selected is described as open-ended because there are many possible solutions and it cannot be answered with a simple answer such as true/false or yes/no. A good research project is one that is open-ended. Use Worksheet 9.1 to get started in developing ideas for your investigation.

I’m afraid you’ve got … In February 2003 a deadly respiratory illness known as SARS was reported in Asia, North America, and Europe. SARS stands for Severe Acute Respiratory Syndrome. Initially it was called Acute Respiratory Syndrome Epidemic but that acronym was considered not very scientific.

Choosing an investigation 8 a Explain what an open-ended problem or question is. b Write a question that is open-ended. 9 Write a question that can be answered only with: a yes or no b true or false c a number d a colour. 10 Propose a name for the question type described in question 9a. 11 Identify three additional problems that could be investigated by your team.

Worksheet 9.1 Getting started

UNIT

9 .1

Think

[ Questions ]

Checkpoint Team skills 1 Identify three everyday occupations that rely on teamwork. 2 State whether the following statements are true or false: a Scientists rarely share ideas. b Team members do not learn anything from each other. c Different team members will usually have different skills. 3 List three skills that you think are important for a team member to develop, and explain why each is important.

The role of team members 4 Refer to the five different types of team roles on page 234. Identify which main role you feel you will play in a team and why you are suited to that role. 5 If you were to identify your secondary role, what would it be? 6 Explain what a team would be like if everyone took on the same role, such as that of leader or researcher? 7 Read the Science focus—Eureka! on page 234. What role would you think Archimedes would play in your team? Justify your answer.

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12 Identify two skills from the list on page 233 that you are already good at. 13 Identify two skills from the list on page 233 that you are not so good at, and may be able to develop while doing your project. 14 Read ‘Science focus—Accidental science’ and identify the role that Sapper played in the team. 15 Choose two friends or family members and outline which team role or roles they are best at. 16 Compare an open-ended question or problem with a closed question or problem.

[ Extension ] Surf Complete the activities below by connecting to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9, and clicking on the destinations button. a Choose one of the accidental chemical discoveries from this unit or another you can identify, and research it further on the Internet. Summarise your findings in some inventive way. b Find out more about different team roles and compare your findings to the information about team roles presented in this chapter.

UNIT

context

9. 2 At some stage we have all asked questions about what’s going on around us. Some things that happen might be very puzzling, but can be explained, such as why green balloons can be blown bigger than red

Asking questions An investigation usually begins with a scientific question. To answer the question you will have to ask a number of further questions. The problem chosen by the Eggsperts was ‘How can you protect a raw egg from breaking when it is dropped from a height of five metres?’ After a brainstorming session organised by Kali, the team asked the following extra questions. 1 2 3 4 5

balloons Others, such as why dead cockroaches are always on their backs, remain a mystery. How do you find answers to such questions? You need to think, research, and plan before you undertake actual experimental testing.

Have a look at the list of Egg drop websites identified in this research and their summaries by going to the Science Focus 2 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9 and clicking on the destinations button.

What causes an egg to break? Is an egg stronger vertically or horizontally? Is the size of egg important? Is the type and amount of protection material important? Do we need to slow down the speed of the fall?

The team didn’t know the answers to any of these questions, but decided to run experiments to find the answers.

To answer questions such as these in your investigation you may need to learn more about what you want to investigate. You will probably need to conduct some research. This may involve a search of the Internet, asking parents and teachers, contacting organisations or going to the library. Record where you get your information in your project workbook since you will need to include your sources in your final report. Mia was a good ‘researcher’, and the Eggsperts team assigned her the task of researching any similar projects on the Internet. Mia used the following search phrases: • dropping eggs • egg dropping devices • stopping eggs breaking when they fall. She presented her findings to the team as a list of websites and a summary of the sites. All members agreed to view the sites before deciding on the initial steps in designing the experiments.

Fig 9.2.1

Researching on the Internet is a good way to collect information.

After reviewing the Internet research, the Eggsperts added extra questions to the initial five to help them form their hypothesis for investigation. 6 7 8 9

Does the material the egg lands on affect whether or not it breaks? Is there a difference in strength between older eggs and newer eggs? Do some materials offer better protection than others? Does the outside container affect the result?

With these questions in mind, the team realised that there were lots of different factors that could be tested by experiments.

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Planning your investigation Identifying variables Factors that can change in an experiment are called variables. Changing variables can change the results of an experiment. Usually there are a number of variables that will affect the results of any experiment. After compiling their list of questions, the Eggsperts identified the following variables for their experiment: • types of packaging material • amount of packaging material

• • • • •

size of egg what the egg lands on the speed the egg falls at the way the egg is wrapped the height the egg is dropped from.

These variables became useful in designing the aim and hypothesis for the experiment.

Tips for surfing the net Research is an important part of any science project. The Internet can be a useful way to collect information. It is very important to be able to analyse the websites and web pages for accuracy, bias and reliability. To help you ‘surf’ with success, ask yourself the following series of questions.

1

Who wrote the information?

Check the website address or URL. It can tell you a great deal about the source of the information. Elements of the address to check include: a personal name (name, ~, %, ‘users’, ‘people’, ‘members’) This means the site was put together by an individual person, and no publisher or organisation was involved. Information from this site should be treated with care. Try to confirm that the information provided is correct by verifying it on other sites. b information about the server and domain. Information is more likely to be accurate if it comes from a government or a relevant organisation. Note that: .edu refers to an education establishment .org refers to a non-profit organisation .net refers to a public network .gov refers to government resources .au indicates that Australia is the country of origin; for example just gov indicates a US site .com refers to a company or commercial publisher.

238

For example: The address boardofstudies.nsw.edu.au tells you that the name of the organisation is Board of Studies (boardofstudies), the state is New South Wales (.nsw), it’s an educational site (.edu) and its country of origin is Australia (.au). You need to weigh up the information very carefully. Do you think a business would necessarily give a balanced point of view? Could the website http://www.theherbalist-shop.com be relied on for a complete set of facts about herbal medicine?

2 Why was the website page created? Has the website been created to inform, give facts or data, explain, persuade, sell or present someone’s point of view? The address can assist you in coming to your answer. For example, would you get an unbiased view about wood chipping from http://www.chipstop.forests.org.au?

3 How old is the information? It is important to know the age of the information in scientific research. You should also know whether the website is updated regularly. Look on the home page for this information. Note: Search using both Australian and American spelling. For example, searching for ‘centre of gravity’ and ‘center of gravity’ will produce different results. Here are some general differences between Australian and American spellings:

Australian ending

Australian spelling

American ending

American spelling

–our

colour, flavour

–or

color, flavor

–ise

summarise, recognise

–ize

summarize, recognize

–re

centre, metre

–er

center, meter

The aim and hypothesis

Designing an experiment

Once the team members have gathered information through research and have identified the variables, they are ready to construct an aim. The aim outlines what the team wants to investigate.

When designing an experiment you must remember to run a fair test. Careful planning is required to make sure only one variable is changed at a time. All others variables must be kept constant. If you change more than one at a time you will not know which variable is causing the result. Variables can be classified into three groups: • independent variable: the variable that is changed • dependent variable: the variable that is being measured • controlled variables: the variables that are kept the same throughout an experiment. The results obtained depend upon what you change. Therefore what you measure or record is called the dependent variable. Like any experiment, an investigation needs a step-by-step list of instructions called an experimental procedure (or method). This should be detailed enough so that other students or scientists could do your experiment without needing any more information from your team. The procedure should include: • a title • an aim • a hypothesis • a list of variables • a list of equipment that you will need • a step-by-step outline of what to do.

Kali thought that the amount of packaging around the egg would have the most effect on the survival of the egg, while Lee thought that the speed at which the egg falls would be most important. After some debate Kali’s idea was chosen be investigated. Mia’s Internet research showed that bubble wrap was an excellent packaging material. The team decided to control the type of packing material by using only bubble wrap. The team’s aim became: To find out how much bubble wrap will stop an egg breaking when it is dropped from a height of five metres.

Notice that this aim is related to the questions that were asked in the research. A hypothesis was then developed. Remember that a hypothesis is a prediction or ‘educated guess’ about what you may find in an experiment. A hypothesis is something that can be tested by an experiment. The team’s hypothesis became: That three layers of bubble wrap will stop an egg breaking when it is dropped from a height of five metres.

Fig 9.2.2

A dog of a mission! Not all investigations go to plan. The $100 million spacecraft Beagle 2 certainly did not! Beagle 2 was sent to Mars by the United Kingdom’s space agency and is thought to have crashed onto the surface of Mars on Christmas Day 2003. A recheck of the data showed that the Martian atmosphere was thinner than the team had thought. This means the parachutes probably opened too late and the craft did not slow down enough for a soft landing, the impact probably smashing Beagle into bits.

An artist’s impression of Beagle 2 entering the Martian atmosphere

UNIT

9.2

When you write the steps make sure you: • specify the one variable that you are going to change • specify how you are going to change it and by how much • specify how you are going to control all the other variables • include diagrams, drawings or photographs • specify how you are going to measure the changes • specify how you are going to record the changes. A results table is useful here. Your experimental method should be repeated a number of times so that a more accurate conclusion can be made. This is called replicating an experiment. If you are collecting numerical data, do it more than once so that an average can be calculated. This is more accurate than just a once-off, giving reproducible results.

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Planning your investigation The Eggsperts started their experiment by writing the following experimental procedure into their project workbook. Title: Bubble rap by the Eggsperts Date: Thursday 17 June 2004 Team members: Kali, Amelia, Michael, Lee and Mia Aim: To find out how much bubble wrap will stop an egg breaking when it is dropped from a height of five metres. Hypothesis: That three layers of bubble wrap will stop an egg breaking when it is dropped from a height of five metres. Variables:

Experiment Independent variable 1

Amount of packaging material

Dependent variable

Controlled variables

Survival of egg

Type of packaging material, egg size, what the egg lands on, speed the egg falls at, the way the egg is wrapped, distance egg falls

Equipment: Eggs, layers of bubble wrap (10 cm square), Polystyrene foam outer container, tape measure, masking tape, plastic bag, twist tie

Egg

240

Method: Preparation 1 Measure a height of five metres where the egg can be safely dropped. Test 1: No wrap 1 Place an egg in a plastic bag and seal it with a twist tie. This is to reduce mess. 2 Secure the wrapped egg in the polystyrene foam outer container. 3 Release the egg from a height of five metres. Let it drop under gravity— do not throw it. 4 Record results. including filling out a data chart with observations, taking a picture and writing all the conditions of the experiment. 5 Repeat four more times. Test 2: With bubble wrap 1 Place a new egg in a plastic bag and seal it with a twist tie. 2 Wrap egg in one layer of bubble wrap. 3 Secure the wrapped egg in the polystyrene foam outer container. 4 Drop the wrapped egg as it was before. Repeat four more times. 5 Repeat the procedure over and over, each time with a new layer of bubble wrap around the egg. 6 Add more and more bubble wrap until the egg no longer breaks.

UNIT

9.2 The aim and hypothesis 5 Outline what a hypothesis is. 6 Contrast a hypothesis with an aim.

Designing an experiment 7 Outline the three types of variables. 8 State how many variables should change in an experiment. Justify your answer. 9 List the elements, or sections, of an experimental procedure. 10 Explain why you should repeat an experiment a number of times.

Think 11 Examine the following website addresses and state whether they have reliable scientific information or not. Justify your answers in each case. a www.abc.net.au/quantum b www.eskimo.com/~billbembers c www.science.uniserve.edu.au/school/forensic.html d www.csiro.au/helix e www.greens.net.au/boycottwoodchipping f www.greenhouse.gov.au/ The eggsperts’ first attempt using one layer of bubble wrap shows their design for protecting the egg.

Fig 9.2.4

Use Worksheet 9.2 to help you plan your experiment. Worksheet 9.2 Planning your experiment

UNIT

9.2

[ Questions ]

Checkpoint Asking questions 1 State whether the following are true or false. a Asking questions is the last part of planning an investigation. b Research can include asking parents and teachers. 2 Explain why it is important to do some initial research about your topic. 3 Identify two questions you should ask about information you find on the Internet.

Identifying variables 4 Define the term ‘variable’.

12 You find two websites that present conflicting information. Explain what other information could help you determine which is more accurate.

Analyse 13 Examine the procedure designed by the Eggsperts. a Identify whether they have controlled all the variables in their experimental design. b Evaluate the design of this procedure. c Describe how the procedure could be improved.

Skills 14 Propose an aim for the following experiments. a A scientist placed various types of plastic in direct sunlight for two months. The scientist came back every week and observed the plastics. b Bean seedlings were planted, and each seedling had equal amounts of different brand fertiliser added. The growth of the seedlings was recorded for three weeks. c Charlotte plays tennis all around the world and has to deal with many different weather conditions. Charlotte thinks that the height a ball bounces is related to the temperature of the ball. She conducts an experiment to test her ideas.

>> 241

Planning your investigation

d Mark wants to go away for the weekend, but his dog Bingo has to stay home. Mark wants to leave a bowl out, but is worried that the water will evaporate very quickly, leaving Bingo thirsty. Mark designs a test with different-shaped bowls and measures how much water evaporates from each over three days. 15 For each of the experiments in question 14 identify: a the independent variable b the dependent variable c controlled variables. 16 Construct a hypothesis for each of the following experiments. a Nic wanted to find out which fuel contained the most energy—methylated spirits or alcohol (ethanol). He designed a fair test using a thermometer and beakers of water. b Lisa has been asked to try out three different types of battery to work out which one is the best value for money. The cost of a pack of four batteries is: Energex $4.99, Bio Battery $5.80 and Longplay $5.20. Lisa designed a fair test for each battery and carried it out using a torch. c Anthony was about to build a model of the Sydney Harbour Bridge using icy-pole sticks. He wanted to find out which glue would be best to use. He chose three popular brands, StickUp, UGlue and Fast Paste, and designed a fair test to work out which one to use for his model.

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>>> 17 You have been asked to design an experiment to test the effect that different amounts of fertiliser have on plant growth. You have the following equipment available: tomato plants, pots of soil, water, ruler, measuring cylinder, fertiliser. a Construct an aim for this experiment. b Construct a hypothesis. c Identify the independent and dependent variables. d List the variable(s) that would need to be controlled. e Outline any observations would you make. f Outline any measurements you would make. g List the steps in this experiment. h Construct a table to record your results 18 Investigate an experimental procedure for two of the hypotheses you have written for question 16.

UNIT

context

9. 3 Carrying out the experiment is a fun and rewarding part of research. You get to see whether or not your experimental design works. It is also the time when you will prove or disprove your hypothesis. Careful planning,

Getting it done! To carry out your experiment you should follow all of your planned steps carefully. Remember the importance of recording all observations and measurements. Measurements or data can include how long something is, the time for a reaction to occur, the amount of chemical used, or the time it takes. Results or data that are numerical (with numbers) are called quantitative as they usually measure amounts or quantities. If you are having trouble working out how to make accurate measurements, revise Unit 1.3 on page 15. If you are not making any measurements, you are probably using your senses to observe what is happening. Observations that are written down as a description or recorded as a picture or diagram are called qualitative. Good scientists will also record any problems they have with their investigation and will use this information to analyse how well their experiment worked. If results are not repeatable there may be

observing and measuring are required in order to make sure your results are reliable. Are you ready to have a go? Penicillin Part 1 experimental errors affecting the results, or the design may not be a fair test. If an experiment is unsuccessful, the hypothesis, variables and procedure should be reviewed to see if the experimental design could be improved.

This photo of Fleming’s original agar plate experiment shows the large white mould at the bottom. There are fewer and smaller bacterial colonies around the penicillin mould.

Alexander Fleming was growing cultures of bacteria on agar plates. He noticed one day that one of the plates had been contaminated by a mould. He looked at the plate closely and saw that the mould had killed the bacteria! Fleming did not understand what he had discovered but he recorded his results anyway. The mould was found to be penicillin, or common bread mould.

Fig 9.3.2

< new AW Corbis SC004977>

a

Fig 9.3.1

b

a This team concluded that the outer packing material needed to be softer as their egg did not survive. They redesigned their experiment and retested their new design. b This team succeeded by moulding the packing material to the exact shape of the egg.

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Testing and evaluation Lee designed a table for the Eggsperts to record all their observations.

Three layers of bubble wrap Observations (dependent variable)

No bubble wrap

Egg number

Broken

Cracked

Observations (dependent variable) 1

✓

2

✓

✓

3

✓

2

✓

4

✓

3

✓

5

✓

4

✓

Total

5

✓

Total

5

Egg number

Broken

1

Notes

Cracked

Not broken

Notes 0

0

Broken

1

✓

Cracked

2

✓

3

✓

Notes

Not broken

✓ ✓

5 Total

2

3

0

Egg number 3 was cracked but OK but was broken when it was removed from the polystyrene foam package.

Two layers of bubble wrap Observations (dependent variable) Egg number

Broken

1

✓

Cracked

Not broken

2

✓

3

✓ ✓

4 5

✓

6

✓

Total Notes

0

5

Polystyrene foam package was too small for three layers of bubble wrap. Fine cracks in eggs 4 and 5.

Think about it!

Observations (dependent variable) Egg number

4

0

Yuk … big mess!

One layer of bubble wrap

244

Not broken

1

1

4

The bubble wrap used for egg 1 had already been used and had some popped bubbles. A sixth egg was tested and egg 1 was ignored.

Once you have collected your results it is time to analyse them. Penicillin Part 2 You will need to consider: Ernst Chain was • any trends or patterns that occur researching old articles in your results and came across Fleming’s paper on what • whether you need to calculate had happened with the averages bacteria and mould. Luckily • how to present your data or Fleming had recorded observations to show any his results! In 1938 the Oxford University team of patterns or trends. This is where Howard Florey, Ernst Chain a graph may be useful (to revise and Norman Heatley took analysing and presenting results Fleming’s original work further. The team repeated see Unit 1.4 on page 22) the original experiment • how accurate your results were. to check the results. They Think about whether your then grew more mould and injected it into live results were replicated in each mice that had bacterial trial. infections. Amazingly, the • any errors or mistakes that may mice were cured! The team have affected your results (to then investigated methods for growing and purifying revise the difference between enough mould to make it mistakes and errors see Unit a useable drug. Penicillin 1.3 on page 15) is now a widely used antibiotic. • any difficulties or problems your team had in doing the experiment • how your experiment could be improved to get better results • whether you need to repeat your experiment to get better results.

This information is often presented under a Discussion heading. The Eggsperts wrote the following discussion. Discussion

5

There were ‘very’ fine cracks in two of the drops with three layers of bubble wrap. We thought that these fine cracks could have been because of the design of the polystyrene foam package. The packaging was too small to properly wrap the egg with three layers around it. If we had more time we would redesign the experiment to make more room for the three layers of bubble wrap.

4

In conclusion

The number of eggs broken is shown on each test on the graph below.

Number of eggs

Broken

Cracked

Not broken

3

2

1

0 1

2

3

Number of layers of bubble wrap

The graph shows that with no bubble wrap all of the eggs broke. As the number of layers of bubble wrap was increased the number of eggs breaking got smaller, but the number of eggs that cracked got larger. With two layers only one egg cracked, and at three layers no eggs had cracks or were broken. We made this graph using Excel. We think our results are accurate because we dropped each layer of wrap five times to make sure the result was correct. We controlled the other variables well by using new eggs and new bubble wrap for each drop, and had the same person drop the eggs in the same way.

9.3 UNIT

A mistake gave us a problem in test 3. Egg number 1 was wrapped in bubble wrap that had been used in another drop. We decided not to use this result and added another egg drop in its place using new bubble wrap.

[ Questions ]

UNIT

9.3

To sum up your findings you should write a conclusion. A conclusion is simply a summary of the results of your experiment. It should be short and must address the aim and hypothesis. A good conclusion will state: • whether your team’s hypothesis was proven or disproven. Use any trends you saw in the results section to answer your original questions. • what data or observations showed your hypothesis to be wrong/right. If they affect your results and are very important you may also include: • any experimental errors or mistakes that affected your results • any other important things that your team learnt. The Eggsperts’ conclusion is shown below: Conclusion Our experiment showed that our hypothesis was correct. We found that three layers of bubble wrap stopped a raw egg from breaking when it was dropped from five metres. We found that none of the five eggs protected by three layers of bubble wrap were broken.

Finally, do not forget to include a list of any resources (sometimes called a bibliography) used during your research.

Checkpoint Getting it done! 1 Distinguish between qualitative and quantitative data. 2 Identify three different types of measurements that you might take in a typical science experiment. 3 Identify three types of observations you might make. 4 Outline what you would do if your results were not repeatable and your test did not seem fair.

5 As well as recording observations and measurements, describe what else should be recorded as you perform an experiment. 6 Choose the correct answer. Data or observations that you record are directly related to the: A dependent variable B independent variable C controlled variables.

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Testing and evaluation

Think about it!

Results

Time taken to dissolve (seconds)

7 List four considerations when analysing your results. 8 State the title given to the analysis section in a report.

In conclusion

10

White sugar

22

9 Outline what should be included in a good conclusion.

Brown sugar

24

10 After a conclusion there is a final section to include in a report. Identify what this section is.

Sugar cube

55

Think 11 Distinguish between an experimental error and a mistake. 12 Identify three types of graphs that may be useful for presenting data. 13 Explain whether it matters if your hypothesis is proved incorrect.

Analyse 14 Examine the Eggsperts’ discussion and answer the following questions. a Did the Eggsperts cover all of the points that should be in a discussion? If not, identify those they omitted. b Is there anything else that you would add to their discussion after looking at the Eggsperts’ results? c Evaluate their discussion. Is it a good one? Justify your answer. 15 Examine the Eggsperts’ conclusion and answer the following questions. a Did the Eggsperts cover all of the points that should be in a conclusion? If not, identify those they omitted. b Look at the Eggsperts’ results and discussion. Is there anything else that you would add to their conclusion? c Draw your own conclusion from the Eggsperts’ experiment.

3 Stir until no more sugar crystals can be seen and stop timing. a Looking at these results, can you be sure that brown sugar dissolves faster than white sugar? Justify your answer. b Can you be sure that icing sugar dissolves faster than a sugar cube? Justify your answer. c If you look at the method, can you be sure that equal amounts of sugar or water will be used in each test? Justify your answer. d Propose a better way to measure the amount of sugar and water used. e Outline two other problems with the design of this experiment. f Design this experiment again so that it would be a fair test. 17 A group of students performed an experiment to work out how the size of a square parachute would affect the time taken for an egg to fall from 5 metres. The results are shown in the table below. Copy the table into your workbook and answer the questions that follow.

Skills 16 A group of students were using the following method to find out how fast different types of sugar dissolved in boiling water. Equipment cups, water, kettle, teaspoons, icing sugar, white sugar, brown sugar, sugar cubes, stopwatch Method 1 Place boiling water in different cups. 2 Add one teaspoon of sugar and start stopwatch.

246

Icing sugar

Parachute size (cm)

a Calculate the area for each parachute tested. b Calculate the average time for each different size parachute. c Construct a line graph of the results, plotting the area of the parachutes against the average time. d Describe any trends or patterns that you see in the results. e Draw a conclusion for this experiment.

Area of parachute (cm2)

Time taken for egg to fall (seconds) Test 1 Test 2 Test 3 Average time

0

0.5

0.6

0.5

15 x 15

2.6

2.4

2.5

25 x 25

4.8

4.4

4.6

35 x 35

6.7

6.4

6.5

45 x 45

8.5

8.4

8.4

Chapter review [ Summary questions] 1 Match the team role with the description. Explorer/creator

Likes organisation and planning and is a hard worker who likes to get things done.

Scientist

Provides explanation on how things work and is good at using equipment.

Researcher Leader

Organiser

Keeps the team together, and makes sure goals are met. Provides information from many sources and is a good communicator. Uses imagination to create new ideas and looks for better ways to do things.

2 State whether the following statements are true or false. a The problem you choose should be able to be investigated using experiments. b The problem for investigation should be able to be answered by a simple yes or no. c An investigation usually has a scientific question to be answered. d The best websites for correct and unbiased information are personal sites. e The date that an Internet site was written is of no importance. f .gov in a URL indicates that it’s a government site. g Only use Australian spellings when typing your search phrases. h A hypothesis is a prediction or ‘educated guess’. i Quantitative data are usually measure amounts or quantities. 3 Explain what must be done to control variables in an experiment. 4 List in order the headings used for an experimental report. 5 Outline four examples of qualitative observations that might be made in an experiment. 6 Outline four examples of quantitative observations that might be made in an experiment.

7 Identify three things to include in an analysis of experimental results. 8 Outline two features of a good conclusion.

[ Thinking questions ] 9 Explain the relationship between the independent and dependent variables in an experiment. 10 Classify the following problems as either open-ended or closed questions. a Can you blow up green balloons to a larger size that red ones? b Is the average height of boys in your class greater than the height of girls? c Which type of material is best for making a warm hat? d What is the best colour for making road signs so that they can be seen easily during the day? e Is the price of a can of Coke less than that of a 600-millilitre bottle of Coke? f How does the amount of salt in water change the temperature it freezes at? 11 A scientist placed plants in direct sunlight, in the shade and in a dark cupboard. He returned each day to observe the plants. a Propose an aim for his experiment. b Propose a hypothesis for his experiment.

[ Interpreting questions ] 12 Joanne and Marty wanted to find out which hat is best for keeping their heads warm when they go to a school skiing trip. They set up an experiment where bottles of hot water were placed inside different hats and the temperatures recorded over a period of time. a Propose an aim for the experiment. b Identify the independent and dependent variables. c List all of the other variables in the test that could affect the temperature of the bottles. d Explain how you could control the variables to produce a fair test. e Explain how Joanne and Marty will judge which hat is the best.

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247

>>> red cellophane

blue cellophane

green cellophane 250

bean seedling (5 cm tall at start)

measuring cylinder

200

150

100

pot

50

20

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15 cm

ruler

water

Fig 9.4.1

13 Kim and Lize designed an experiment to test the effect of coloured light on the growth of plants. They set up the experiment shown in Figure 9.4.1. a Identify the independent variable. b Identify the dependent variable. c List the controlled variables. d Propose a hypothesis for this experiment.

14 The Eggsperts team decided to modify their project, using helium balloons to slow the speed that the egg falls at. They were trying to reduce the amount of bubble wrap needed to protect the egg. a Identify the independent variable. b Identify the dependent variable. c List the controlled variables. d Propose a hypothesis for this experiment. e Design a procedure for testing this hypothesis.

Kim and Lize got the following results:

Colour of light

Worksheet 9.3 Team research project crossword

Height of plant (cm) Day 1

Day 2

Day 4

Day 6

Day 8

Day 10

Red

5

6.5

8.6

10.5

12.8

14.7

Green

5

6

6.5

6.5

6.5

6.5

Blue

5

6.6

8.2

9.4

11.0

12.4

e Construct a line graph to show these results. You will need three lines on the one graph. f Describe any patterns and trends that you see in the results. g Use these results to draw a conclusion for the experiment. h Could you rely on these results, or believe this conclusion? Justify your answer. i Evaluate the experiment to decide if it is a fair test. j Propose any improvements to the experiment.

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Worksheet 9.4 Sci-words

abiotic environment, 153 abiotic factors, 160 Aboriginal land use, 179–180 plant classification, 203 plant uses, 203 firestick farming, 180 AC, 142 adaptations, 159 behavioural, 159 physical, 159 aerobic respiration, 193 AIDS, 60 aim, 8, 239 air pollution, 171 alimentary canal, 89 alternating current (AC), 142 alveoli, 112 amensalism, 169 ammeter, 134 amoeba, 66 ampere, 134 analysis, 244 angina, 103 anorexia nervosa, 84 antibiotics, 64, 67 antigen, 99 appendicitis, 94 appendix, 94 arteries, 100 asteroid belt, 209 asteroids, 209 asthma, 113 astronaut, 221 astronomer, 216 astronomy, 208 atomic number, 48 atoms, 32 history, 46 atrium, 100 Australia’s ecosystem, 155 autotrophs, 165 average, 16 bacillus, 58 bacteria, 58 reproduction, 64 shapes, 58 balanced diet, 82 batteries, 134

behavioural adaptations, 159 bibliography, 22, 245 bile, 90 binary fission, 64 biodiversity, 167 biome, 153 biosphere, 153 biotic factors, 161 bladder, 109 blood, 98 deoxygenated, 100 oxygenated, 100 pressure, 102 types, 99 vessels, 100–102 body systems, 89–124 circulatory, 98–107, 113 digestive, 89–97 excretory, 108–110 respiratory, 111–115 urinary, 109 Bohr, Niels, 46 breathing, 113 bronchi, 112 bronchioles, 112 bruises, 102 budding, 66 bulimia, 85 bushfire, 156 cambium, 187 capillaries, 101 carbohydrates, 79 careers, astronaut, 221 astronomer, 216 geoscience technician, 228 carnivores, 165 carpet static, 128 catalysts, 41, 194 celestial sphere, 214 cell, 134 cellulose, 192 Ceres, 209 Chadwick, James, 46 change, 38 charge, 126 negative 126

positive, 126 cheese, 71 chemical change, 39 chemical reactions, 39 chlorophyll, 186, 191, 192 chloroplasts, 192 cholesterol, 102 Christmas tree lights, 141 circuits electric, 133 household, 142 parallel, 141 simple, 133 series, 141 circulatory system, 102 cocci, 58 coma, 211 comets, 210 Hale–Bopp, 210 Halley’s, 210 commensalism, 168 communication satellites, 225 community, 153 competition, 169 compounds, 33 compulsive eating, 85 conclusion, 22, 245 conductor, 136 conservation, 176 constellations, 215 consumers, 165 controlled variables, 239 conventional current, 134 coronary arteries, 102 cryptosporidium, 59–60 Crux Australis, 215–216 current, 134 alternating, 142 direct, 142 electric, 134 cuticle, 201 Dalton, John, 46 dark reaction, 192 daughter cell, 64 DC, 142 decomposer, 168 decomposition, 70 deoxygenated blood, 100

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Index dependent variables, 239 dialysis, 109 diaphragm, 113 diarrhoea, 94 diastolic pressure, 102 diet, 82 digestion, 89 digestive gases, 94 digestive tract, 89 direct current (DC), 142 discussion, 22, 245 drought, 156 dry cell, 135 duodenum, 93 eating disorders, 84 ECG, 103 eclipitic, 214 ecology, 153 ecosystem, 153 electric circuit,133 current, 134 field, 129 symbols, 133 electrical safety, 142 electricity, 133 static, 126 electrocardiogram (ECG), 103 electron shells, 48 electrons, 47 electrostatic forces, 127 elements, 30 symbols, 31 endangered species, 174 energy, 83 energy in food, 83 enhanced global warming, 171 enhanced greenhouse effect, 172 environment, 153 enzymes, 41, 194 epidermis, 201 epiglottis, 112 Eros, 209 errors, 15 instrument, 15 parallax, 15 reading, 15 euglena, 59 excretion, 108 exotic species, 174 experimental design, 239 experiments, 3, 12 exploitation, 169 extrapolation, 23

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faeces, 93 fermentation, 72 fibre, 79 fibrin, 99 fields, 129 firestick farming, 180 flagella, 58 Fleming, Alexander, 71 flood, 155 fluoride, 90 food, 79 chain, 165–166 nutrients, 79 poisoning, 70 preserving, 73 pyramid, 167 web, 165–166 formite, 56 formulas, 34 frogs, 175 fungi, 59 reproduction, 65 galaxies, 220 gall bladder, 92 geoscience technician, 228 Global Positioning System (GPS), 227 global warming, 171–172 glycogen, 94 GPS, 227 graphs, 22–24 drawing, 22–23 gravitational field, 129 greenhouse effect, 171 enhanced, 172 greenhouse gases, 171 guard cells, 201 gut, 89 habitat, 154 haemoglobin, 98, 113 hairy-nosed wombat, 175 Hale–Bopp comet, 210 Halley’s comet, 210 heart, 99 valves, 103 hepatitis, 95 herbivores, 165 herbivory, 169 heterotrophs, 165 host cell, 67 household circuits, 142 Hubble, Edmund, 220 Hubble Space Telescope, 221

hypertension, 102 hyphae, 65 hypothesis, 8, 12, 239 independent variables, 239 induced charges, 127 inferences, 7 insulator, 136 Internet, surfing, 238 intestine, 93 introduced species, 174, 181 investigations, 3, 235 kidney stones, 109 kidneys, 108 large intestine, 93 larynx, 112 lattice, 33 laws, 14 leaves, 201–202 Lenard, Philip, 51 light reaction, 191–192 light year, 214 lightning, 128 lipids, 79 liver, 93 lungs, 111 Mars rover, 228 mass number, 48 mean, 16 measurements, 16 metals, 32 meteor, 209 meteor shower, 210 meteorite, 210 meteoroid, 209 meteorology, 227 method, 22 metric units, 23, 57 prefixes, 23–24, 57 microbes, 56 microbiologist, 56 microhabitat, 154 microorganisms, 56 microscope, 57 electron, 57 light, 57 Milky Way, 220 minerals, 81 mistakes, 15 mixtures, 34 model, 12 molecules, 33

nanotechnology, 47 nanotubes, 47 nephrons, 108 neutrons, 47 non-metals, 32 nucleus, 47 number, atomic, 48 mass, 48 nutrients, 79 observations, 7 oesophagus, 92 omnivores, 165 Oort cloud, 210 oxygenated blood, 100 pacemaker, 103 pancreas, 92 parallel circuits, 141 paramecium, 66 parasitism, 169 parent cell, 64 penicillin, 72 pharynx, 111 phloem, 187 photosynthesis, 165, 186, 191, 195 photosynthesis rate, 192–193 photovoltaic cell, 135 physical adaptations, 159 physical change, 38 planisphere, 219 plasma, 99 platelets, 99 pollution, 171 population, 153 predation, 169 prefixes, 23 Priestley, Joseph, 191 producers, 165 project workbook, 235 proteins, 80 protists, 59 reproduction, 66 protons, 47 pseudopod, 59 qualitative observations, 7, 243 quantitative observations, 7, 243 quasar, 221 questions, 237

radiant, 210 reaction rates, 40 reactions, 39 red blood cells, 98 remote sensing, 226 replicating, 239 report, 22 reproduction, bacteria, 64 fungi, 65 protist, 66 research, 7–9, 237 resistance, 136 respiration, 72, 111, 193, 195 respiratory system, 111 rhesus factor, 99 roots, 186 Rutherford, Ernest, 46 satellite orbits, 225 satellites, 225 science careers, astronaut, 221 astronomer, 216 geoscience technician, 228 scientific method, 12–14 semiconductor, 148 series circuits, 141 skills, 3, 233 sky map, 216–217 small intestine, 93 soil pollution, 173 solar cells, 147 solar challenge, 148 solar energy, 147 South Celestial Pole, 215–216 Southern Cross, 215 species, 167 endangered, 174 introduced, 174, 181 spirilla, 58 sporangium, 65 spores, 65 starch, 192 static electricity, 126 stem cells, 119 stomach ulcers, 94 stomach, 92 stomata, 186–187, 201 systolic pressure, 102

telescopes, 221 optical, 221 radio, 221 Hubble Space Telescope, 221–222 Thomson, John Joseph, 46 thunder, 128 tissue culture, 119 tooth decay, 90 toxins, 70 trachea, 111 transpiration, 173 transplants, 118, 120

INDEX

mould, 59 mouth, 92 mushroom, 59 mutate, 67 mutualism, 168

units, metric, 23 prefixes, 23–24 urea, 108 ureters, 109 urethra, 109 urine, 108 vaccinations, 67 Van de Graaff generator, 127 variables, 8 controlled, 239 dependent, 239 independent, 239 vascular bundles, 187 veins, 101 ventricle, 100 viruses, 60 vitamins, 80 volt, 134 voltage, 134 voltmeter, 134 vomiting, 94 water, 79 water pollution, 172 wet cell, 135 white blood cells, 98 wood, 188 word equations, 40 xylem, 186 yeast, 59 yogurt, 70 zodiac, 215

team research project, 232 team, roles, 233–234 skills, 233 teeth, 89

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