Collins - Concise Revision Course For Csec Human And Social Biology.pdf

CONCISE REVISION COURSE

CSEC Human and ®

Social Biology Anne Tindale & Shaun deSouza

CONCISE REVISION COURSE

CSEC Human and ®

Social Biology Anne Tindale & Shaun deSouza

William Collins’ dream of knowledge for all began with the publication of his first book in 1819. A self-educated mill worker, he not only enriched millions of lives, but also founded a flourishing publishing house. Today, staying true to this spirit, Collins books are packed with inspiration, innovation and practical expertise. They place you at the centre of a world of possibility and give you exactly what you need to explore it. Collins. Freedom to teach. Published by Collins An imprint of HarperCollinsPublishers The News Building 1 London Bridge Street London SE1 9GF Browse the complete Collins Caribbean catalogue at www.collins.co.uk/caribbeanschools © HarperCollinsPublishers Limited 2018 Collins Concise Revision Course: CSEC® Human and Social Biology is an independent publication and has not been authorised, sponsored or otherwise approved by CXC®. CSEC® is a registered trademark of the Caribbean Examinations Council (CXC®). All rights reserved under International and Pan-AmericanCopyright Conventions. By payment of the required fees, you have been granted the non-exclusive, non-transferable right to access and read the text of this e-book on screen. No part of this text may reproduced, transmitted, downloaded, decompiled, reverse engineered, or stored in or introduced into any information storage into any retrieval system, in any form or by any means, whether electronic or mechanical, now known or hereafter invented, without the express written permission of HarperCollins. Authors: Anne Tindale and Shaun deSouza Publisher: Dr Elaine Higgleton Commissioning editor: Tom Hardy In-house senior editor: Julianna Dunn Project manager: Alissa McWhinnie, QBS Learning Copy editor: Aidan Gill Proofreader: Rebecca Ramsden Illustrator: Ann Paganuzzi Production controller: Tina Paul Typesetter: QBS Learning Cover designers: Kevin Robbins and Gordon MacGilp Cover photo: Andrii Muzyka/Shutterstock Printed and bound by Grafica Veneta, SpA, Italy Acknowledgments P11:Eric Isselee/Shutterstock, P11:Robert_s/Shutterstock, P11:Tatiana Belova/Shutterstock, P11:Feathercollector/ Shutterstock, P11:Stephen McSweeny/Shutterstock, P11:Vitalii Hulai/Shutterstock, P11:Wim van Egmond/Visuals Unlimited, Inc./Getty Images, P11:Anat Chant/Shutterstock, P11:Matt9122/Shutterstock, P11:Roland Birke/Getty Images, P21:Anne Tindale, P24:Brian A Jackson/Shutterstock, P25:Billion Photos/Shutterstock, P25:Peangdao/ Shutterstock, P25:Alexander Prokopenko/Shutterstock, P25:leonori/Shutterstock, P25:leonori/Shutterstock, P25:JPC-PROD/Shutterstock, P26:BURGER/PHANIE/Alamy Stock Photo, P26:MAURO FERMARIELLO/SCIENCE PHOTO LIBRARY, P46:bioraven/Shutterstock, P49:PROF. P. MOTTA/DEPT. OF ANATOMY/UNIVERSITY LA SAPIENZA, ROME/SCIENCE PHOTO LIBRARY, P80:ARZTSAMUI/Shutterstock, P91:Southern Illinois University/ Science Photo Library, P91:Addyvanich/Shutterstock, P91:Image Point Fr/Shutterstock, P91:Areeya_ann/Shutterstock, P96:Alila Medical Media/Shutterstock, P114:Jian Hongyan/Shutterstock, P120:Alila Medical Media/Shutterstock, P122: elenabsl/Shutterstock, P139:Dima Sidelnikov/Shutterstock, P139:Luis Carlos Jimenez del rio/Shutterstock, P146:BLUR LIFE 1975, P150:National Institutes of Health/Stocktrek Images/Alamy, P157:Christian Weber/Shutterstock, P157:Huguette Roe/Shutterstock. eBook Edition © September 2018 Print book Edition ISBN 9780008273408 eBook Edition ISBN 9780008326296 Version: 2018-08-29

Contents 1

2

3

4

5

The pathway to success v Section A – Living organisms and the environment 1 Living organisms and cells 1 The characteristics of living organisms 1 Cells 1 Movement of substances into and out of cells 6

6

Photosynthesis, food chains 7 and cycles 10

Photosynthesis 10 Food chains 11 Recycling of carbon and nitrogen in nature 13 Section B – Life processes 19 Nutrition 19 The human diet 19 A balanced diet 25 Digestion 27 Teeth and mechanical digestion 28 The chemical digestion of food 30 Absorption 34 Egestion 35 Assimilation 35 The respiratory system 37 Breathing and gaseous exchange 37 Structure of the human respiratory system 37 The mechanism of breathing and gaseous exchange 39 Mouth-to-mouth resuscitation (rescue breathing) 41 The effects of smoking cigarettes 41 Respiration 43 The circulatory system 46 The need for a transport system in the human body 46 The cardiovascular system 46

8

9

Blood Blood vessels The heart Circulation Causes and effects of heart attacks The lymphatic system

46 49 51 52 53 54 The skeletal system 56 The human skeleton 56 Movement 58 Excretion and homeostasis 63 Excretion 63 The kidneys and excretion 63 The skin 65 Homeostasis 67 Coordination and control 71 Some important definitions 71 Coordination by the nervous and endocrine systems 71 The nervous system 71 Voluntary actions 74 Involuntary actions 74 Sense organs 77 The eye 77 Sight defects and their corrections 79 The endocrine system 81 The reproductive system 83 Asexual and sexual reproduction compared 83 The female and male reproductive systems 83 The menstrual cycle 86 Bringing sperm and ova together 87 From fertilisation to birth 87 Prenatal and postnatal care 88 Birth control and family planning 89 Issues related to abortion 92

Contents

iii

10

Section C – Heredity and variation 102 Cell division and variation 102 An introduction to chromosomes and genes 102 Cell division 102 Variation 105

14 Drug use and misuse

108 Monohybrid inheritance 108 The inheritance of sex in humans 111 Sex-linked characteristics 112 Some important genetic terms 113 Genetic engineering 113 Section D – Disease and its impact on humans 119 Health and disease 119 Types of disease 119 Signs and symptoms of disease 119 Asthma 119 Lifestyle-related diseases 121 Infectious diseases (communicable diseases) 124 Vectors and vector-borne infectious diseases 128 The impact of diseases on the human population 132

15

11 Inheritance and genetic engineering

12

13 Hygiene and defences against disease Personal hygiene Controlling the growth of microorganisms Defence against disease

iv

Contents

133 133 134 135

138 Drug dependence 138 Prescription drugs 138 Non-prescription drugs 138 The social effects of drug misuse 141 Section E – The impact of health practices on the environment 144 Pollution and its effects 144 Air pollution 144 Water pollution 145 Methods of controlling pollution 147

16 The cycling and treatment of water 148

The water cycle 148 Water purification 149 The impact of human activities on water supplies 150

17 The treatment and disposal of human waste 152 Sewage disposal Sewage treatment Domestic refuse disposal

Index

152 154 155 161

The pathway to success About this book

This book has been written primarily as a revision course for students studying for the CSEC® Human and Social Biology examination. The facts are presented concisely using a variety of formats which makes them easy to understand and learn. Key words are highlighted in bold type and important definitions which must be learned are written in italics and highlighted in colour. Annotated diagrams and tables have been used wherever possible and the relationship between structure and function is continually emphasised. Questions to help test knowledge and understanding, and to provide practice for the actual examination, are included throughout the book. The following sections provide valuable information on the format of the CSEC® examination, how to revise successfully, successful examination technique and key terms used on examination papers.

The CSEC® Human and Social Biology syllabus and this book

The CSEC® Human and Social Biology syllabus is available online at http://cxc-store.com. You are strongly advised to read through the syllabus carefully since it provides detailed information on the specific objectives of each topic of the course and the format of the CSEC® examination. Each chapter in this book covers a particular topic in the syllabus. • Chapters 1 and 2 cover topics in Section A, Living organisms and the environment • Chapters 3 to 9 cover topics in Section B, Life processes • Chapters 10 and 11 cover topics in Section C, Heredity and variation • Chapters 12 to 14 cover topics in Section D, Disease and its impact on humans • Chapters 15 to 17 cover topics in Section E, The impact of health practices on the environment At the end of each chapter, or section within a chapter, you will find a selection of revision questions. These questions test your knowledge and understanding of the topic covered in the chapter or section. At the end Chapters 2, 9, 11, 14 and 17 you will find a selection of exam-style questions, which also test how you apply the knowledge you have gained and help prepare you to answer the different styles of questions that you will encounter in your CSEC® examination. You will find the answers to all these questions online at www.collins.co.uk/caribbeanschools.

The format of the CSEC® Human and Social Biology examination The examination consists of two papers and your performance is evaluated using the following two profiles: • Knowledge and comprehension • Use of knowledge

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Paper 01 (1 ¼ hours)

Paper 01 consists of 60 multiple choice questions. Each question is worth 1 mark. Four choices of answer are provided for each question of which one is correct. • Make sure you read each question thoroughly; some questions may ask which answer is incorrect. • Some questions may give two or more correct answers and ask which answer is the best; you must consider each answer very carefully before making your choice. • If you do not know the answer, try to work it out by eliminating the incorrect answers. Never leave a question unanswered.

Paper 02 (2 hours)

Paper 02 is divided into Sections A and B, and consists of six compulsory questions. Each question is divided into several parts and is worth 15 marks. The answers are to be written in spaces provided on the paper. These spaces indicate the length of answer required and answers should be restricted to them. Take time to read the entire paper before beginning to answer any of the questions. • Section A consists of four compulsory structured questions whose parts require short answers, usually a word, a sentence or a short paragraph. The questions usually begin with some kind of stimulus material, very often a diagram, which you will be asked questions about. One question will be an investigative/practical-related question, which will provide you with some form of data that you will be expected to answer questions about. The data might be in the form of a table or a graph. If you are given a table, you may be asked to draw a graph using the data and may then be asked questions about the graph. Make sure you know how to draw graphs (see page ix). • Section B consists of two compulsory structured essay questions, each worth 15 marks. These questions require a greater element of essay writing in their answers than those in section A. The marks allocated for the different parts of each question are clearly given. A total of 90 marks is available for Paper 02 and the time allowed is 120 minutes. You should allow between 15 and 20 minutes for each question. This will allow you time to read the paper fully before you begin and time to check over your answers when you have finished.

Successful revision

The following should provide a guide for successful revision. • Begin you revision early. You should start your revision at least two months before the examination and should plan a revision timetable to cover this period. Plan to revise in the evenings when you do not have much homework, at weekends, during the Easter vacation and during study leave. • When you have a full day available for revision, consider the day as three sessions of about three to four hours each, morning, afternoon and evening. Study during two of these sessions only, do something non-academic and relaxing during the third.

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• Read through the topic you plan to learn to make sure you understand it before starting to learn it; understanding is a lot safer than thoughtless learning. • Try to understand and learn one topic in each revision session, more if topics are short and fewer if topics are long. • Revise every topic in the syllabus. Do not pick and choose topics since all questions on your exam paper are compulsory. • Learn the topics in order. When you have learned all topics once, go back to the first topic and begin again. Try to cover each topic several times. • Revise in a quiet location without any form of distraction. • Sit up to revise, preferably at a table. Do not sit in a comfy chair or lie on a bed where you can easily fall asleep. • Obtain copies of past CSEC® Human and Social Biology examination papers and use them to practise answering exam-style questions, starting with the most recent papers. These can be purchased online from the CXC® Store. • You can use a variety of different methods to learn your work. Chose which ones work best for you. Read the topic several times, then close the book and try to write down the main points. Do not try to memorise your work word for word since work learned by heart is not usually understood, and questions test understanding as well as the ability to repeat facts. Summarise the main points of each topic on flash cards and use these to help you study. Draw simple diagrams with annotations, spider diagrams and flow charts to summarise topics in visual ways which are easy to learn. Practise labelling diagrams that you have been given. You may be asked to do this in your exam. Use memory aids such as: – acronyms, e.g. GRIMNER for the seven life processes; growth, reproduction, irritability, movement, nutrition, excretion, reproduction. – mnemonics, e.g. ‘many people support basketball players’ for the five functions of the skeleton; movement, protection, support, breathing, production of blood cells. – associations between words, e.g. tricuspid – right (therefore the bicuspid valve must be on the left side of the heart), arteries – away (therefore veins must take blood towards the heart). Test yourself using the questions throughout this book and others from past CSEC® examination papers.

Successful examination technique

• Read the instructions at the start of each paper very carefully and do precisely what they require. • Read through the entire paper before you begin to answer any of the questions. • Read each question at least twice before beginning your answer to ensure you understand what it asks. • Underline the important words in each question to help you answer precisely what the question is asking. The pathway to success

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• Reread the question when you are part way through your answer to check that you are answering what it asks • Give precise and factual answers. You will not get marks for information which is ‘padded out’ or irrelevant. The number of marks awarded for each answer indicates how long and detailed it should be. • Use correct terminology throughout your answers. • Give any numerical answer the appropriate unit using the proper abbreviation/ symbol e.g. cm3, g, °C. • If a question asks you to give a specific number of points, use bullet points to make each separate point clear. • If you are asked to give similarities and differences, you must make it clear which points you are proposing as similarities and which points as differences. The same applies if you are asked to give advantages and disadvantages. • Watch the time as you work. Know the time available for each question and stick to it. • Check over your answers when you have completed all the questions. • Remain in the examination room until the end of the examination and recheck your answers again if you have time to ensure you have done your very best. Never leave the examination room early.

Some key terms used on examination papers

Account for: provide reasons for the information given. Annotate: add brief notes to the labels of drawings to describe the structure and/or the function of the structures labelled. Compare: give similarities and differences. Contrast: give differences. Construct: draw a graph, histogram, bar chart, pie chart or table using data provided or obtained. Deduce: use data provided or obtained to arrive at a conclusion. Define: state concisely the meaning of a word or term. Describe: provide a detailed account which includes all relevant information. Discuss: provide a balanced argument which considers points both for and against. Distinguish between or among: give differences. Evaluate: determine the significance or worth of the point in question. Explain: give a clear, detailed account which makes given information easy to understand and provides reasons for the information. Give an account of: give a written description which includes all the relevant details.

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Give an illustrated account of: give a written description which includes diagrams referred to in the description. Illustrate: make the answer clearer by including examples or diagrams. Justify: provide adequate grounds for your reasoning. Outline: write an account which includes the main points only. Predict: use information provided to arrive at a likely conclusion or suggest a possible outcome. Relate: show connections between different sets of information or data. State or list: give brief, precise facts without detail. Suggest: put forward an idea. Tabulate: construct a table to show information or data which has been given or obtained.

Drawing graphs

Graphs are used to display numerical data. When drawing a graph: • Plot the manipulated variable on the x-axis (horizontal axis) and the responding variable on the y-axis (vertical axis): The manipulated variable is the factor that is changed by the person carrying out the investigation. It will be given in the left column of the table of data. The responding variable is the factor that is measured by the person carrying out the investigation. It will be given in the right column of the table of data. • Choose appropriate scales which are easy to work with and which use as much of the graph grid as possible and enter the variables along the axes. • Label each axis to indicate the variable that it is showing. To do this, use the column headings in the table of data. • When drawing a line graph, use a small dot surrounded by a small circle to plot each point, plot each point accurately, and join the points with a sharp continuous line. • When drawing a histogram or bar chart, the height of each bar indicates the value of the responding variable. Draw vertical bars of equal width and draw an accurately positioned horizontal line to show the top of each bar. When drawing a histogram ensure that the bars touch each other. When drawing a bar chart ensure that spaces of equal width are left between the y-axis and the first bar, and between each of the other bars. • Give the graph an appropriate title which must include reference to the responding variable and the manipulated variable.

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Section A – Living organisms and the environment 1 Living organisms and cells

All living organisms are made of cells. Cells are so small that they can only be seen with a microscope and not with the naked eye. From the simplest unicellular organisms to the most complex multicellular organisms, living organisms all share certain characteristics.

The characteristics of living organisms

All living organisms share the following seven characteristics: • Nutrition (feeding): the process by which living organisms obtain or make food. Animals take in ready-made food and are called heterotrophs. Plants make their own food by the process of photosynthesis and are called autotrophs. • Respiration: the process by which energy is released from food by all living cells. Aerobic respiration requires oxygen and takes place in most cells. Anaerobic respiration takes place without oxygen in certain cells. • Excretion: the process by which waste and harmful substances, produced by the body’s metabolism, are removed from the body. • Growth: a permanent increase in the size and complexity of an organism. • Irritability (sensitivity): the ability of organisms to detect and respond to changes in their environment or within themselves. • Movement: a change in the position of a whole organism or of parts of an organism. Most animals can move their whole bodies from place to place, known as locomotion. Plants and some animals can only move parts of their bodies. • Reproduction is the process by which living organisms generate new individuals of the same kind as themselves. Sexual reproduction involves the fusion of gametes (sex cells) produced by two parents. Asexual reproduction does not involve the fusion of gametes and requires only one parent.

Cells

The cell is the basic structural and functional unit of all living organisms. A single cell possesses all of the seven characteristics of living organisms. Some organisms are unicellular, being composed of a single cell; others are multicellular, being composed of many cells.

Plant and animal cells

All plant and animal cells contain structures called organelles that are specialised to carry out one or more vital functions, for example the nucleus, mitochondria, endoplasmic reticulum, ribosomes, chloroplasts and vacuoles. Organelles are found within the cytoplasm of the cells and most are surrounded by one or two membranes. The following structures are found in all plant and animal cells: • a cell membrane or plasma membrane • mitochondria (singular mitochondrion) • cytoplasm • endoplasmic reticulum • a nucleus • ribosomes 1 Living organisms and cells

1

In addition to the above, plant cells also possess: • a cell wall • chloroplasts • a large vacuole ribosomes – small circular organelles cell membrane – a partially (differentially) permeable layer composed of protein and lipid around the outside of the cell cytoplasm – a jelly-like substance composed of about 80% water and 20% dissolved substances, especially protein nuclear envelope nucleoplasm chromatin thread nucleolus

nucleus – surrounded by a double membrane. Chromatin threads contain genetic information in the form of DNA rough endoplasmic reticulum – a network of tubules throughout the cytoplasm. Has ribosomes attached smooth endoplasmic reticulum – no ribosomes attached mitochondrion – a rod-shaped organelle with a smooth outer membrane and folded inner membrane. Contains respiratory enzymes vacuoles – small, membrane-bound compartments which may contain water, food, cell secretions or waste products

Figure 1.1 Structure of a generalised animal cell cell wall – a freely permeable wall made of cellulose cell membrane chloroplast – a disc-shaped organelle surrounded by a double membrane. Contains many internal membranes, the green pigment called chlorophyll and photosynthetic enzymes ribosomes mitochondrion vacuole – a large membrane-bound compartment containing cell sap, a solution of sugars, mineral salts, amino acids and waste products rough endoplasmic reticulum nucleus cytoplasm smooth endoplasmic reticulum

Figure 1.2 Structure of a generalised plant cell

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1 Concise Revision Course: Human and Social Biology

Table 1.1 A summary of the functions of the different cell structures Cell structure Function Cell membrane Controls what substances enter and leave the cell. Cytoplasm Supports the organelles. The site of many chemical reactions. Nucleus Controls the characteristics and functioning of the cell. Essential for cell division. Mitochondrion Where respiration occurs to release energy for the cell. Endoplasmic Transports substances throughout the cell. reticulum Ribosome Where proteins are synthesised (produced). Vacuole Stores food, cell secretions or cell waste. Supports plant cells when turgid. Cell wall Supports and protects the plant cell and gives it shape. Chloroplast Where photosynthesis occurs to produce food for the plant. Table 1.2 Plant and animal cells compared Animal cells Do not have a cell wall. Do not have chloroplasts or chlorophyll. When present, the vacuoles are small and scattered throughout the cytoplasm and their contents vary. May contain glycogen granules as a food store. Can have a great variety of shapes.

Plant cells Have a cell wall which is made of cellulose. Usually have chloroplasts which contain chlorophyll. Usually have one large, central vacuole which contains cell sap. May contain starch grains as a food store. Have a regular shape, usually round, square or rectangular.

Microbes

Microbes or microorganisms are extremely small organisms which include viruses, bacteria, protozoa and some fungi. Many microbes are pathogens, i.e. they cause disease (see Chapter 12, page 124). • Viruses lack a cellular structure and they can only reproduce inside other living cells. proteins viral envelope – contains proteins capsid – protein shell enclosing the nucleic acid strands nucleic acid strand

Figure 1.3 Structure of a typical virus particle

1 Living organisms and cells

3

• The cells of bacteria lack a true nucleus and other membranebound organelles. Their DNA exists in a region called the nucleoid, which lacks a nuclear membrane, and also in smaller regions called plasmids.

capsule – slimy outer covering found in some bacteria. Protects the cell cell wall cell membrane nucleoid – a single, long, coiled loop of DNA. Controls all cellular activities cytoplasm plasmid – small, circular piece of DNA flagellum – long, whip-like projection. Aids in movement

Figure 1.4 Structure of a generalised bacterial cell • Most fungi are multicellular, though yeasts are unicellular. Their cells contain true nuclei and other membrane-bound organelles except chloroplasts, and are surrounded by a cell wall made of chitin.

spores – used for reproduction spore case hypha – thread-like branching structure composed of many cells, or a single cell with many nuclei and a central vacuole. Surrounded by a cell wall mycelium – body of the fungus made up of a network of hyphae

Figure 1.5 Structure of a typical fungus

Cell specialisation and organisation in humans

The human body is composed of trillions of cells. These cells are of different types due to them becoming specialised or differentiated to carry out specific functions. This enables humans to carry out all essential life processes as efficiently as possible. Table 1.3 Specialised cells and their functions Cell type Function Epithelial Covers and protects body surfaces. Sperm (spermatozoon) Male gamete; fuses with the female gamete during fertilisation to form a zygote. Egg (ovum) Female gamete; fuses with the male gamete during fertilisation to form a zygote. Nerve (neurone) Transmits impulses throughout the body to control and coordinate the functioning of the body. Muscle Contracts to cause movement of parts of the body.

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cell membrane cytoplasm

tail – for swimming

middle head piece

nucleus basement membrane

acrosome – contains enzymes to dissolve a passage into the ovum

nucleus mitochondria – supply energy for swimming

Figure 1.6 Epithelial cells

Figure 1.7 A sperm cell or spermatozoon

follicle cells – act as protection layer of jelly membrane cytoplasm – contains yolk which supplies nutrients to the newly formed embryo nucleus

dendrites

cell body

Figure 1.8 An egg cell or ovum

motor end plates – pass nerve impulses to a muscle

nucleus

axon – nerve fibre. Carries impulses

myelin sheath – fatty layer. Insulates the axon

Figure 1.9 A motor neurone (nerve cell)

cell membrane

light band nuclei – many in each cell dark band

nucleus

a smooth muscle cells

b skeletal muscle cells (muscle fibres)

Figure 1.10 Muscle cells Cells of the same type that are specialised to carry out a particular function then work together in groups called tissues. Tissues may contain one or, in some cases, more than one type of cell, e.g. epithelial tissue, nerve tissue and muscle tissue. Different tissues are then grouped together to form specialised organs which may perform one or more specific functions, e.g. the stomach is composed of epithelial, connective, muscle and nerve tissues. Organs work together in organ systems to carry out a major function. All organ systems then work together in an organised way to form an organism.

i.e. cells

ssues

organs

Table 1.4 Examples of organ systems Organ system Organs Digestive Stomach, liver, pancreas, intestines Reproductive Ovaries, uterus, testes, penis Respiratory Nose, larynx, trachea, bronchi, lungs Nervous Brain, spinal cord, nerves Circulatory Heart, blood vessels

organ systems

organism

Function Digests and absorbs food. Produces offspring. Exchanges oxygen and carbon dioxide. Detects and responds to stimuli. Transports substances around the body.

1 Living organisms and cells

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Revision questions

1 Explain THREE ways in which a car can be considered similar to a living organism and 2 3 4 5 6 7 8

THREE ways in which it is different from a living organism. What is a cell? Outline the function of EACH of the following cell structures: a a mitochondrion b the endoplasmic reticulum c a chloroplast d ribosomes e the cell membrane What would happen to a cell if its nucleus is removed? Give FOUR differences and THREE similarities between the structure of a typical plant cell and a typical animal cell. What features would enable a scientist to distinguish a bacterial cell from other cells when viewed under the microscope? a Explain the need for cell specialisation in multicellular organisms. b Name THREE different types of cells found in the human body and give the function of EACH. Suggest a definition for EACH of the following: a a tissue b an organ c an organ system

Movement of substances into and out of cells

Substances can move into and out of cells, and from cell to cell by three different processes: • diffusion • osmosis • active transport

Diffusion Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration until the particles are evenly distributed. The particles (molecules or ions) are said to move down a concentration gradient. Particles in gases, liquids and solutions are capable of diffusing. Diffusion is the way cells obtain many of their requirements and get rid of their waste products which, if not removed, would poison them.

The importance of diffusion in living organisms

• Oxygen for use in aerobic respiration moves into cells by diffusion, and carbon dioxide produced in aerobic respiration moves out of cells by diffusion. • Some of the glucose and amino acids produced in digestion are absorbed through the cells in the ileum and capillary walls and into the blood by diffusion. • Carbon dioxide for use in photosynthesis moves into leaves and plant cells by diffusion, and oxygen produced in photosynthesis moves out of plant cells and leaves by diffusion.

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Osmosis

Osmosis is a special form of diffusion. Osmosis is the movement of water molecules through a partially (differentially) permeable membrane from a solution containing a lot of water molecules, e.g. a dilute solution (or water), to a solution containing fewer water molecules, e.g. a concentrated solution. partially (differentially) permeable membrane – has tiny pores which allow only water molecules through sucrose molecule – tries to diffuse through the membrane into the dilute solution but is unable to pass through water molecule – is able to diffuse through the membrane into the concentrated solution dilute solution, e.g. 10% sucrose solution

concentrated solution, e.g. 50% sucrose solution

net movement of water molecules

Figure 1.11 Explanation of osmosis Visking tubing bag – partially (differentially) permeable 40% sucrose solution 10% sucrose solution a Water molecules enter the solution in the bag. The volume of this solution increases and the bag becomes turgid (firm).

Visking tubing bag 10% sucrose solution 40% sucrose solution b Water molecules leave the solution in the bag. The volume of this solution decreases and the bag becomes flaccid (limp).

Figure 1.12 Demonstrating osmosis In any cell, the cell cytoplasm – a solution membrane is partially of about 80% water, 20% dissolved substances water leaves the cytoplasm (differentially) through the cell membrane cell membrane – differentially permeable. There is by osmosis permeable always cytoplasm, a solution of protein and water enters the cytoplasm other substances in through the cell membrane by osmosis water, on the inside of the membrane, and a An animal cell in water or a solution b An animal cell in a solution that is usually a solution on the that is more dilute than its cytoplasm. more concentrated than its cytoplasm. The cell swells and eventually bursts. The cell shrinks. outside. Water molecules, therefore, move into and Figure 1.13 The effect of different solutions on a single animal cell out of cells by osmosis.

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Plant cells are surrounded by a strong, freely permeable cell wall. Because of this they behave differently from animal cells when placed in different solutions. 1 Water enters the cytoplasm and cell sap by osmosis cell membrane – differentially permeable vacuole membrane – differentially permeable

1 Water leaves the cytoplasm and cell sap by osmosis 2 The vacuole and cytoplasm swell and press outwards against the cell wall

a A plant cell in water or a solution that is more dilute than its cytoplasm and cell sap. The cell swells and becomes turgid.

2 The vacuole and cytoplasm shrink and pull the cell membrane away from the cell wall

cell wall – freely permeable

3 Concentrated solution passes through the permeable cell wall b A plant cell in a solution that is more concentrated than its cytoplasm and cell sap. The cell shrinks and becomes flaccid. When the membrane has pulled away from the wall, the cell is said to be plasmolysed.

Figure 1.14 The effect of different solutions on a single plant cell

The importance of osmosis in living organisms

• Water moves into animal cells from blood plasma and body fluids by osmosis. This keeps them hydrated. • Water is absorbed from the intestines into the blood by osmosis. This ensures that the body obtains the water it needs from food and drink consumed. • Water is reabsorbed from the filtrate in the kidney tubules into the blood by osmosis. This prevents the body from losing too much water. • Water moves into plant cells by osmosis. This keeps them turgid, which causes non-woody stems to stand upright and keeps leaves firm. • Water is absorbed from the soil by the root hairs of plants and moves through the cells of roots and leaves by osmosis. This ensures that leaves get a constant supply of water for photosynthesis.

Active transport Active transport is the movement of particles through cell membranes against a concentration gradient using energy released in respiration. During active transport, energy released in respiration in the form of ATP (see page 43) is used to move the particles (molecules or ions) through cell membranes from areas of lower concentration to areas of higher concentration. Active transport allows cells to accumulate high concentrations of important substances, e.g. glucose, amino acids and ions.

The importance of active transport in living organisms

• Some of the glucose and amino acids produced in digestion are absorbed from the ileum into the blood by active transport. • Useful substances are reabsorbed from the filtrate in the kidney tubules into the blood by active transport. • Mineral ions move from the soil into plant roots by active transport.

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Revision questions

9 Distinguish between diffusion and osmosis. 100 Give THREE reasons to support the fact that diffusion is important to living organisms. 11 Explain what happens to an animal cell if it is placed in a solution more dilute than its cytoplasm. 122 You place a plant cell in a solution that is more concentrated than its cell sap and cytoplasm. Draw a labelled diagram to show how the cell would appear when viewed under the microscope after being left for 15 minutes in the solution. 133 Give THREE reasons why osmosis is important to living organisms. 144 Why is the root of a plant unable to absorb mineral ions from the soil if it is given a poison that prevents respiration?

1 Living organisms and cells

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2 Photosynthesis, food chains and cycles

Green plants produce their own food by photosynthesis. All other living organisms depend either directly or indirectly on green plants for their food. This food is passed on from one living organism to the next through food chains.

Photosynthesis

Photosynthesis is the process by which green plants convert carbon dioxide and water into glucose by using energy from sunlight absorbed by chlorophyll in chloroplasts. Oxygen is produced as a by-product. The process can be summarised by the following word equation: carbon dioxide + water

energy from sunlight absorbed by chlorophyll

glucose + oxygen

Photosynthesis occurs in any plant structure that contains chlorophyll, i.e. which is green; however, it mainly occurs in the leaves. Chlorophyll molecules in the chloroplasts of leaf cells absorb the energy from sunlight and use it to convert carbon dioxide, absorbed from the air, and water, absorbed from the soil, into glucose and oxygen.

Fate of the products of photosynthesis

The plant uses the oxygen and glucose produced during photosynthesis for various different functions.

Oxygen

The oxygen is used by the leaf cells in respiration. Excess oxygen diffuses out of the leaves into the air.

Glucose

The glucose can be used in a variety of ways: • It can be used by the leaf cells in respiration to release energy. • It can be converted to starch by the leaf cells and stored. The starch can then be converted back to glucose and used, e.g. during the night. • It can be converted to other useful organic substances by leaf cells, e.g. amino acids and protein, vitamins or chlorophyll. • It can be converted to sucrose and transported to other parts of the plant such as growing parts and storage organs, where it can be converted to: Glucose, and used in respiration to release energy. Starch, and stored in seeds, e.g. wheat and rice; in fruits, e.g. breadfruit; and in tubers, e.g. English (Irish) potato and sweet potato. Amino acids and protein, by the addition of nitrogen from nitrates and sulfur from sulfates obtained from the soil. Protein is then used for growth. Lipids, and stored, mainly in seeds, e.g. peanuts and soya beans.

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Food chains

Energy from sunlight enters living organisms through photosynthesis occurring in green plants, which are also known as producers. This energy is incorporated into the organic food molecules produced by the plants and is passed on to consumers through food chains. A food chain is a diagram showing the flow of food and energy from one organism to the next. A food chain includes: • A producer, i.e. a green plant. • A primary consumer that eats the primary producer. • A secondary consumer that eats the primary consumer. • A tertiary consumer that eats the secondary consumer. • Some food chains may also include a quaternary consumer that eats the tertiary consumer. Consumers can also be classified according to what they consume: • Herbivores consume plants or plant material only, e.g. cows, grasshoppers, snails, slugs, parrot fish, sea urchins. • Carnivores consume animals or animal material only, e.g. lizards, toads, spiders, centipedes, eagles, octopuses, sharks. • Omnivores consume both plants and animals, or plant and animal material, e.g. hummingbirds, crickets, humans and crayfish. Trophic level refers to the position or level that an organism occupies in a food chain. Trophic level

Organism’s status

A terrestrial food chain

A marine food chain

5

quaternary consumer (carnivore)

hawk

tiger shark

4

tertiary consumer (carnivore)

snake

barracuda

3

secondary consumer (carnivore)

lizard

flying fish

2

primary consumer (herbivore)

grasshopper

zooplankton

1

producer (green plant)

grass

phytoplankton

Figure 2.1 Examples of food chains

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Food webs

Any environment usually has more than one producer and most consumers have more than one source of food. Consequently, food chains are interrelated to form food webs.

Dependence of other living organisms on plants

tertiary consumers

heron

secondary consumers primary consumers

carp pond snail

producers

tilapia water flea

pond weed

mosquito larvae

phytoplankton

All other living organisms, including humans, depend both directly and Figure 2.2 An example of a food web from a freshwater lake indirectly on plants for food since plants are the only living organisms capable of producing organic food molecules from simple inorganic molecules, i.e. carbon dioxide and water. When a human eats any food of plant origin, e.g. fruits, vegetables, cereals and nuts, he or she is depending directly on plants. When a human eats any food of animal origin, e.g. meat or fish, he or she is depending indirectly on plants.

Energy transfer in food chains

Not all the energy incorporated into organic food molecules made by green plants during photosynthesis is passed along a food chain, some is used and some is lost at each trophic level. Some of the food produced by plants is used by the plants in respiration. This releases energy that the plants use in life processes. The rest of the food is used by the plants for growth or is stored. When plants are eaten by herbivores, some of the organic matter that contains energy is lost in faeces and some is lost in organic excretory products, e.g. urea. Some is used in respiration during which the stored energy is released and used in life processes, or is lost as heat. The remaining food that contains energy is used to build body tissues or is stored, and is then passed on to the next trophic level when herbivores are consumed. This then continues at each trophic level in a food chain. Organisms that are not consumed eventually die. These dead organisms and the organic matter in faeces and excretory products are decomposed by decomposers, which release the energy during respiration. Energy, therefore, flows from producers to consumers and decomposers in one direction and is not recycled. In general, only about 10% of the energy from one trophic level is transferred to the next level. energy from energy lost the Sun during respiration

energy lost during respiration

energy lost during respiration

energy lost energy lost during respiration during respiration

primary consumption primary consumption secondary consumption tertiary producer consumer consumer consumer 10% 10% 10%

death

faeces and excretory products death

faeces and excretory products death

faeces and excretory products death

decomposers

Figure 2.3 Energy flow through a food chain

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Ecological pyramids

Because there is less energy and biomass (mass of biological matter) at each trophic level in a food chain, fewer organisms can be supported at each level. Energy, biomass and the number of organisms at successive levels can be represented by ecological pyramids. Due to the loss of energy and biomass at each level, food chains rarely exceed four or five trophic levels.

trophic level 5 4 3 2 1

quaternary consumer tertiary consumer secondary consumer primary consumer primary producer

Figure 2.4 Pyramid of energy, biomass or numbers

Recycling of carbon and nitrogen in nature

The different chemical elements which make up the bodies of all living organisms, e.g. carbon and nitrogen, are continually cycled through these living organisms and their physical environment. Unlike the energy from the Sun, these elements are present in nature in finite amounts; therefore, recycling is essential to prevent them from gradually running out. Decomposers are essential for recycling. These are microorganisms, i.e. bacteria and fungi, which feed on dead and waste organic matter causing it to decompose. Decomposers are also known as saprophytes.

The carbon cycle

The cycling of carbon (C) atoms occurs by them being converted into different carbon-containing compounds, including carbon dioxide (CO2) present in the air, and various organic compounds, mainly carbohydrates, proteins and lipids, present in living organisms. • Carbon dioxide is removed from the air and converted to organic compounds by green plants during photosynthesis. • Carbon dioxide is returned to the air by: Respiration occurring in all living organisms including plants, animals and decomposers. Combustion, mainly of fossil fuels such as coal, oil and natural gas, though all materials containing organic compounds release carbon dioxide when burned, e.g. wood and paper. carbon dioxide (CO2) in the air – 0.038% photosynthesis

organic compounds in green plants

respiration

eaten by animals

respiration

combustion

respiration

organic compounds in fossil fuels

organic compounds in animals

death and decomposition

death and decomposition

organic compounds in decomposers

fossilisation fossilisation

Figure 2.5 A simplified carbon cycle 2 Photosynthesis, food chains and cycles

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The nitrogen cycle

Most living organisms are unable to use nitrogen (N2) gas directly. The cycling of nitrogen (N) atoms occurs mainly by them being converted into different nitrogen-containing compounds including proteins present in living organisms, and ammonium (NH4+) compounds, nitrites (NO2−) and nitrates (NO3−) present in the soil. • Nitrogen is removed from the air and converted into ammonium compounds by nitrogen-fixing bacteria in the soil and in the root nodules of legumes, e.g. peas and beans. The legumes use these compounds to make proteins. • Nitrogen is returned to the air by denitrifying bacteria which convert nitrates in the soil to nitrogen. • Nitrate ions in the soil are removed from the soil by plants and used to make protein. This protein is passed on to animals when the plants are eaten. • Nitrate ions are returned to the soil by the decomposition of dead plants and animals by decomposers (saprophytic bacteria and fungi). This decomposition forms ammonium compounds which are then converted into nitrites and nitrates by nitrifying bacteria. nitrogen (N2) in the air – 78%

denitrifying bacteria in the soil

excretion of urea fixation by nitrogen fixing bacteria in root nodules of legumes

animal protein eaten by animals plant protein

in the soil

death and decomposition by decomposers ammonium (NH4+) compounds in the soil death and decomposition by decomposers

absorbed by plants nitrates (N03–) in the soil

nitrifying bacteria in the soil

nitrites (N02–) in the soil nitrifying bacteria in the soil

Figure 2.6 A simplified nitrogen cycle

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Revision questions

1 Define the term ‘photosynthesis’ and give a word equation to summarise the process. 2 Suggest FOUR ways that the plant can make use of the glucose produced 3

4 5 6 7 8 9

in photosynthesis. a What is a food chain? b Some aphids were observed on the tomato plants in a garden and ladybird beetles were seen feeding on the aphids. The ladybirds were, in turn, being eaten by dragonflies which were, themselves, being fed on by toads. Use this information to draw a food chain for the organisms in the garden. From the organisms in item 3 b above, identify: a a carnivore b a herbivore c a producer d a primary consumer e a secondary consumer When Jared eats a barracuda he only gets about 10% of the energy that the barracuda obtained from the flying fish it ate. Explain THREE reasons why so little energy is passed on to Jared. Why is it important that elements such as carbon and nitrogen are recycled in nature? Outline how carbon is recycled in nature. Identify FOUR different types of bacteria responsible for recycling nitrogen in nature. Explain each of the following: a How nitrates in the soil can be returned to the soil after being absorbed by grass growing in a field. b How bacteria can remove nitrogen from the air and return it to the air.

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Exam-style questions – Chapters 1 to 2 Structured questions

1 a) Figure 1 shows a generalised animal cell. W X Y Z

Figure 1 A generalised animal cell i) Name the structures labelled W and X. ii) State ONE function of EACH organelle labelled Y and Z. iii) In what way does the property of structure W differ from the cell wall in a plant cell? b) Figure 2 shows two different specialised cells found in the human body.

Cell A

(2 marks) (2 marks) (2 marks)

Cell B

Figure 2 Specialised cells found in the human body i) Identify cell A. ii) Explain TWO ways in which the structure of cell B makes it suitable for its function. iii) Why is it important that the human body is made of specialised cells? c) i) Anya thinks that a virus is a living organism. Do you agree with her? Give ONE reason for your opinion. ii) Anton and Elijah are playing a game of tennis. Identify and explain TWO characteristics of living organisms that they are displaying.

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Exam-style questions – Chapters 1 to 2

(1 mark) (2 marks) (1 mark) (1 mark) (4 marks) Total 15 marks

2 a) Figure 3 summarises the process of photosynthesis. sunlight energy absorbed by substance C used to convert substance D and water into substance E and oxygen

Figure 3 The process of photosynthesis i) Identify substances C, D and E. (3 marks) ii) Explain TWO ways in which the leaves of plants use substance E. (2 marks) iii) Tasha tells Mia that they both depend directly and indirectly on plants (2 marks) to survive. Provide a suitable explanation to support what Tasha said. b) Table 1 below shows the food sources of several organisms found in the ocean. Table 1 Food sources of some organisms found in the ocean Organism Food source zooplankton phytoplankton shrimp phytoplankton jellyfish zooplankton and shrimp crab shrimp sea turtle crab and jellyfish i) Using only the information contained in Table 1, construct a food web for the (2 marks) organisms. ii) Which organism in the food web would you expect to be present in the (1 mark) LOWEST numbers? iii) Outline the reason for your answer to b) ii) above. (3 marks) c) Ramon and Sean both cut their lawns each week. Ramon leaves his grass cuttings on his lawn, whereas Sean rakes up his cuttings, puts them in bags and throws them out with the rest of his garbage. After many months of doing this, Ramon finds his grass grows faster and looks healthier than Sean’s. (2 marks) Use your knowledge of natural cycles to explain Ramon’s observations. Total 15 marks

Exam-style questions – Chapters 1 to 2

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Structured essay question

3 a) Jacinta set up the apparatus in Figure 4 below and observed that the level of the meniscus in the capillary tube gradually rose up the tube. capillary tube meniscus of the sucrose solution beaker 25% sucrose solution Visking tubing – partially permeable water

Figure 4 Apparatus used to study the movement of particles i) Give an account of why the meniscus gradually rose up the capillary tube. (4 marks) ii) Explain TWO differences between the process occurring in Jacinta’s apparatus and the process of diffusion. At the beginning of your answer, name the process (5 marks) occurring in the apparatus. b) i) Define the term ‘active transport’. (2 marks) ii) By referring to TWO different places in your body where active transport (4 marks) occurs, explain its importance to you. Total 15 marks

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Exam-style questions – Chapters 1 to 2

Section B – Life processes 3 Nutrition

Humans need a variety of nutrients to provide them with energy, to enable them to grow and develop, and to keep them healthy. These nutrients include carbohydrates, proteins, lipids, vitamins and minerals, and they are contained in the food we eat. Nutrition is the process by which living organisms obtain or make food.

The human diet

The food an animal eats is called its diet. The human diet must contain the following: • Carbohydrates, proteins and lipids, also known as macronutrients. These are required in relatively large quantities. • Vitamins and minerals, also known as micronutrients. These are required in relatively small quantities. • Water and dietary fibre (roughage).

Carbohydrates, proteins and lipids Carbohydrates

Carbohydrates include reducing sugars, non-reducing sugars and starch. They are molecules composed of carbon, hydrogen and oxygen atoms. The ratio of hydrogen atoms to oxygen atoms is always 2:1. Based on their chemical structure, carbohydrates can be classified into three groups: monosaccharides, disaccharides and polysaccharides. • Monosaccharides are the simplest carbohydrate molecules, they have the formula C6H12O6. All monosaccharides are reducing sugars (see page 25). • Disaccharides are formed by chemically joining two monosaccharide molecules together; they have the formula C12H22O11. All disaccharides are reducing sugars except sucrose, which is a nonreducing sugar. • Polysaccharides are formed by joining many monosaccharide molecules into straight or branched chains. Polysaccharides include starch, cellulose and glycogen (animal starch). single monosaccharide molecule

monosaccharide molecules

two monosaccharide molecules joined

many monosaccharide molecules joined

disaccharide part of a polysaccharide molecules molecule condensation – joining molecules with the loss of water hydrolysis – splitting molecules by adding water

Figure 3.1 The three types of carbohydrates 3 Nutrition

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Table 3.1 Properties of different carbohydrates Carbohydrate Physical and chemical properties Reducing sugars Have a sweet taste. Soluble in water. React with Benedict’s solution. Non-reducing sugars

Starch

Have a sweet taste. Soluble in water. Do not react with Benedict’s solution. Does not have a sweet taste. Insoluble in water. Reacts with iodine solution.

Examples Glucose (a monosaccharide) Fructose (a monosaccharide) Galactose (a monosaccharide) Maltose (a disaccharide) Lactose (a disaccharide) Sucrose (a disaccharide)

Proteins

Proteins are molecules composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur and phosphorus atoms. These atoms form small molecules known as amino acids. There are 20 different common amino acids. Protein molecules are formed by joining hundreds or thousands of amino acid molecules together in long chains. different amino acids

peptide links

part of a protein molecule

Figure 3.2 Part of a protein molecule Proteins have the following properties: • Their chemical structure can be changed by heat or certain other chemicals, i.e. they can be denatured. • Some are globular in structure and are soluble in water, e.g. haemoglobin and albumen, others are fibrous and are insoluble, e.g. collagen and keratin. • They react with biuret reagent.

Lipids

Lipids are fats and oils. They are molecules composed of carbon, hydrogen and oxygen 3 fatty acid atoms. Their molecules have fewer oxygen molecules atoms than carbohydrate molecules, e.g. a lipid molecule beef fat has the formula C57H110O6. Each lipid molecule is made up of four smaller molecules joined together; three fatty acid molecules and Figure 3.3 A lipid molecule one glycerol molecule. Lipids feel greasy, are insoluble in water and they leave a grease spot on paper.

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1 glycerol molecule

Recognising carbohydrates, proteins and lipids

Tests can be performed in the laboratory to identify carbohydrates, proteins and lipids. Apart from the tests for lipids, the tests are usually carried out on about 2 cm3 of a solution of the test substance in a test tube. Table 3.2 Laboratory tests to identify carbohydrates, proteins and lipids Food substance Test Positive result Reducing sugars Add an equal volume of Benedict’s solution An orange-red precipitate and shake. Heat the mixture. forms. Non-reducing sugars Add a few drops of dilute hydrochloric An orange-red precipitate acid and heat for 1 minute. Add sodium forms. hydrogencarbonate until effervescence stops. Add an equal volume of Benedict’s solution and shake. Heat the mixture. Starch Add a few drops of iodine solution and Solution turns blue-black. shake. Protein – the biuret Add an equal volume of sodium hydroxide Solution turns purple. solution and shake. Add drops of dilute test copper sulfate solution and shake. Or add an equal volume of biuret reagent and shake. Lipid – the emulsion Place 4 cm3 of ethanol in a dry test tube. A milky-white emulsion forms. test Add 1 drop of test substance and shake. Add an equal volume of water and shake. Lipid – the grease Rub a drop of test substance onto A translucent mark (grease spot) absorbent paper. Leave for 10 minutes. spot test remains.

Reducing sugars form an orange-red precipitate with Benedict's solution

Starch turns iodine solution blue-black

Figure 3.4 Laboratory tests to identify reducing sugars and starch 3 Nutrition

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Sources and functions of carbohydrates, proteins and lipids

Carbohydrates, proteins and lipids are organic compounds which supply the body with energy and the materials for growth and repair. Table 3.3 Sources and functions of carbohydrates, proteins and lipids Class Sources Functions Carbohydrates Sugars: fruits, cakes, • To provide energy (16 kJ g−1): energy is easily released when respired. sweets, jams • For storage: glycogen granules are stored in many cells. Starch: yams, potatoes, rice, pasta, bread Fish, lean meat, • To make new cells for growth and to repair damaged Proteins tissues. milk, cheese, eggs, peas, beans, nuts • To make enzymes that catalyse (speed up) reactions in the body. • To make hormones that control various processes in the body. • To make antibodies to fight disease. • To provide energy (17 kJ g−1): used only when stored carbohydrates and lipids have been used up. Butter, vegetable • To make cell membranes of newly formed cells. Lipids oils, margarine, • To provide energy (39 kJ g−1): used after carbohydrates nuts, fatty meats because their metabolism is more complex and takes longer. • For storage: fat is stored under the skin and around organs. • For insulation: fat under the skin acts as an insulator.

Vitamins and minerals

Vitamins are organic compounds and minerals are inorganic substances. They are only required in small amounts by the human body, but they are essential for healthy growth and development. • Vitamins required include: Vitamins A, D, E and K, which are fat soluble. Group B vitamins and vitamin C, which are water soluble. • Minerals required include calcium, iron, phosphorus, iodine, sodium, potassium and fluorine. Table 3.4 Some important vitamins and minerals required by the human body Vitamin/mineral Sources Functions Vitamin A Liver, cod liver oil, yellow and • Helps to keep the skin, cornea and mucous membranes healthy. orange vegetables and fruits, e.g. carrots and pumpkin, green leafy • Helps vision in dim light (night vision). vegetables, e.g. spinach • Strengthens the immune system. Vitamin B1 Whole-grain cereals and bread, • Aids in respiration to produce energy. brown rice, peas, beans, nuts, • Important for the proper functioning of yeast extract, lean pork the nervous system.

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Vitamin/mineral Sources Functions Vitamin C West Indian cherries, citrus fruits, • Keeps tissues healthy, especially the skin and connective tissue. raw green vegetables • Strengthens the immune system. • Helps the body absorb iron in the ileum. Vitamin D Oily fish, eggs, cod liver oil. • Promotes the absorption of calcium and Made in the body by the action of phosphorus in the ileum. sunlight on the skin • Helps build and maintain strong bones and teeth. • Strengthens the immune system. Calcium Dairy products, e.g. milk, cheese • To build and maintain healthy bones and teeth. (Ca) and yoghurt, green vegetables, e.g. broccoli • Helps blood to clot at cuts. Iron Red meat, liver, eggs, beans, nuts, • To make haemoglobin, the red pigment in red blood cells which transports oxygen (Fe) dark green leafy vegetables around the body for use in respiration.

Vitamin and mineral deficiency diseases

A shortage or lack of any of the essential vitamins or minerals in the diet can lead to health problems and certain deficiency diseases. Table 3.5 Some vitamin and mineral deficiency diseases Disease Cause Symptoms Treatment Night Deficiency of • Poor vision in dim light. • Increase the intake of foods rich in vitamin A. blindness vitamin A • Vision adapts slowly between bright and dim conditions. • Take vitamin A supplements. Rickets Deficiency • Soft, weak, painful, deformed • Increase the intake of foods bones, especially limb bones. rich in vitamin D and calcium. (in children) of vitamin D and/or • Bow legs. • Take vitamin D and calcium calcium supplements. • Increase exposure to sunlight. Anaemia Deficiency of • A reduced number of red • Increase the intake of foods blood cells in the blood. rich in iron. iron • Pale complexion. • Take iron supplements. • Tiredness. • Increase the intake of foods rich in vitamin C. • Lack of energy.

Water

Water is essential in the diet since the human body is about 65% water. • Water acts as a solvent to dissolve chemicals in cells so that they can react. • Water acts as a solvent to dissolve substances so that they can be transported around the body, e.g. products of digestion are dissolved in blood plasma. • Water acts as a solvent to dissolve waste substances so that they can be excreted from the body, e.g. urine contains dissolved urea. 3 Nutrition

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• Water acts as a reactant, e.g. in hydrolysis which occurs during digestion of food. • Water acts as a coolant, removing heat from the body when it evaporates from sweat.

Dietary fibre (roughage)

Dietary fibre is food that cannot be digested. It consists mainly of the cellulose of plant cell walls, lignin of plant xylem vessels, husks of brown rice and bran of wholegrain cereals. Fruits, vegetables and grains are excellent sources of dietary fibre. Dietary fibre adds bulk to the food which stimulates peristalsis (see page 34) so that food is kept moving through the digestive system. This helps prevent constipation and reduces the risk of colorectal (bowel) cancer.

Constipation and diarrhoea

Figure 3.5 Fruit and cereals are rich in dietary fibre

Constipation is a condition of the bowels (colon and rectum) in which the faeces are dry and hard, difficult and often painful to pass, and passed infrequently. Diarrhoea is a condition in which faeces are passed frequently and in a liquid form. It is usually a symptom of gastroenteritis (see page 126). Table 3.6 Common causes and effects of constipation and diarrhoea Condition Causes Effects Constipation • Not eating enough dietary fibre. • Bloating. • Not drinking enough water or other fluids. • Abdominal pain. • Not exercising or being inactive. • Haemorrhoids (piles). • A change in diet or daily routine. • Faecal impaction. • Ignoring the urge to defaecate. • Colorectal (bowel) cancer. • Stress, anxiety or depression, and certain medications. Diarrhoea • Being infected with certain viruses, e.g. norovirus. • Dehydration. • Being infected with certain bacteria, • Electrolyte imbalance. e.g. Salmonella, E. coli, Shigella. • Impaired kidney function • Being infected with an intestinal parasite, (kidney failure). e.g. Giardia. • Malnutrition in severe • Conditions such as irritable bowel syndrome, cases. colorectal cancer, coeliac or Crohn’s disease. Food poisoning, i.e. eating contaminated food, is a common way of becoming infected with pathogens that cause diarrhoea. Chances of getting food poisoning can be reduced by practising good food hygiene when preparing food: • Wash hands, utensils and food preparation surfaces regularly. • Wash fruits and vegetables thoroughly before cooking or eating. • Keep uncooked foods, especially meat, poultry and fish, separate from ready-to-eat foods. • Cook food thoroughly, especially meat, poultry and fish. • Defrost frozen food thoroughly and safely, i.e. in a refrigerator, before cooking.

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A balanced diet

ug sem

slam morf doinoA F

r

F

s ti u

Energy requirements

Le

selpa tS

Humans must consume a balanced diet each day. This must contain carbohydrates, proteins, lipids, vitamins, minerals, water and dietary fibre in the correct proportions to supply the body with enough energy for daily activities and the correct materials for growth and development, and to keep the body in a healthy state. A balanced diet should contain a variety of foods selected from each of the six different Caribbean food groups shown in Figure 3.6. Each group contains foods that supply similar nutrients in similar proportions. The size of each sector indicates the relative amount of each group that should be eaten daily.

Fats & O il s

Vegetables

The amount of energy required Figure 3.6 The six Caribbean food groups daily from the diet depends on a person’s age, occupation and gender (sex). In general, daily energy requirements: • Increase as age increases up to adulthood. They then remain fairly constant up to old age when less energy is required daily. • Increase as activity increases, e.g. a manual labourer requires more energy than a person working in an office. • Are higher in males than in females of the same age and occupation. • Increase in a female when she is pregnant or breastfeeding.

Malnutrition Malnutrition occurs when a person’s diet does not contain the right amount of nutrients. Malnutrition can be caused by eating a diet in which certain nutrients are lacking, known as undernutrition, or are in excess, known as overnutrition. Malnutrition can lead to several serious conditions.

Obesity

Obesity is characterised by an excessive accumulation and storage of fat in the body. It is generally caused by the excessive consumption of energy rich foods high in sugar and/or fat, especially animal fat, and a lack of physical activity. Obesity increases a person’s risk of hypertension (high blood pressure), heart disease, stroke, diabetes, osteoarthritis and some cancers (see page 121). 3 Nutrition

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Anorexia

Anorexia is a serious mental health condition where a person keeps his or her body weight as low as possible by eating very little, vomiting, using laxatives and exercising excessively. It mainly affects girls and young women, and can eventually lead to death.

Bulimia

Bulimia is an eating disorder and mental health condition where a person tries to control his or her weight by repeating a cycle of binge eating followed by purging. The person eats large quantities of food very quickly and then induces vomiting or takes laxatives to get rid of the food.

Protein-energy malnutrition (PEM)

Protein-energy malnutrition (PEM) refers to a group of related disorders, including kwashiorkor and marasmus, which are caused by an inadequate protein or energy intake. Both disorders mainly affect young children in developing countries. • Kwashiorkor is caused by a severe shortage of protein in the diet. Its symptoms include loss of muscle mass, failure to grow, oedema (swelling) of the abdomen and legs, changes in skin and hair pigmentation, and fat accumulation in the liver. • Marasmus is caused by a severe shortage of protein and energy rich foods such as carbohydrates in the diet. Its symptoms include low body weight, thin face with sunken eyes, ribs and shoulders clearly visible through the skin, thin arms and legs with very little muscle and fat, dry skin and brittle hair.

Figure 3.7 A child with kwashiorkor

Figure 3.8 A child with marasmus

Body mass index (BMI)

Body mass index can be used as an indicator of body fat. It compares the mass of a person, determined by weighing the person, to his or her height using the following formula: body mass (in kilograms) body mass index (kg per m2) = height (in metres) × height (in metres) Table 3.7 Body mass index for adults Body mass index in kg per m2 18.4 and below 18.5 to 24.9 25.0 to 29.9 30.0 to 39.9 40.0 and above

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Condition Underweight Healthy weight Overweight Obese Severely obese

3 Concise Revision Course: Human and Social Biology

Revision questions

1 Construct a table to give TWO physical properties, TWO sources and TWO functions

of EACH of the following macronutrients in the human diet: starch, proteins, lipids. 2 Distinguish between a reducing sugar and a non-reducing sugar and give a named example of EACH. 3 You are given three solutions labelled X, Y and Z and told that they contain starch, glucose and gelatin (a protein), respectively. Describe THREE laboratory tests you could perform to confirm what you are told about X, Y and Z 4 Classify vitamins based on their solubility in water or fat. 5 Construct a table to give ONE source and the major functions of the following micronutrients: vitamin B1, vitamin C and iron. 6 Identify the cause, symptoms and treatment of EACH of the following: a night blindness b rickets c anaemia 7 Identify THREE reasons why water is important in the diet. 8 Outline the consequences of Annette not consuming enough dietary fibre daily. 9 Food poisoning can result in a person suffering from diarrhoea. Suggest THREE consequences of diarrhoea and THREE ways a person can reduce their chances of food poisoning. 100 What is a balanced diet? 11 a What is malnutrition? b Name THREE serious conditions that can result from malnutrition. 122 a Keenan is 1.5 m tall and weighs 75 kg. Determine his body mass index (BMI). b What can you deduce about Keenan?

Digestion

Digestion is the process by which food is broken down into a form that is useful for body activities, i.e. simple, soluble food molecules. It occurs in the alimentary canal which is a tube, 8 to 9 metres long with muscular walls, running from the mouth to the anus. The alimentary canal and its various associated organs including the liver, gall bladder and pancreas make up the digestive system (see Figure 3.14, page 32). The digestive process involves: • Mechanical digestion during which large pieces of food are broken down into smaller pieces. Mechanical digestion begins in the mouth where food is chewed by the teeth, and it continues in the stomach where contractions of the stomach walls churn the food. • Chemical digestion during which large, usually insoluble food molecules are broken down into small, soluble food molecules by enzymes (see pages 30–32). Chemical digestion begins in the mouth and is completed in the ileum. 3 Nutrition

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Teeth and mechanical digestion The importance of teeth in digestion

When food is chewed or masticated, the teeth break up large pieces of food into smaller pieces. This is important because: • It gives the pieces of food a larger surface area for digestive enzymes to act on, making chemical digestion quicker and easier. • It makes food easier to swallow.

Types of teeth

incisors Humans have four different types of teeth, incisors, canines, premolars and molars, canine or eyetooth and they have two sets of these teeth in their lifetime: premolars or bicuspid • Milk teeth start to appear from about molars 6 months and start falling out from about 6 years old. They consist of 8 incisors, 4 canines and 8 molars. • Permanent teeth replace the 20 lost milk teeth and an additional 12 develop. They Figure 3.9 Teeth of the upper jaw of an adult human consist of 8 incisors, 4 canines, 8 premolars and 12 molars. Table 3.8 The different types of teeth in humans Type Position Shape Functions Incisor At the front of the jaw. Chisel-shaped crown To cut food. with sharp, To bite off pieces of food. root thin edges.

Canine Next to the incisors. (eye tooth) Premolar

Cone-shaped and pointed.

To grip food. To tear off pieces of food.

At the side of the jaw next to the canines.

cuspp To crush and grind food. Have a fairly broad surface root with two pointed cusps. Molar At the back of the jaw next Have a broad To crush and grind food. to the premolars. surface with 4 or 5 pointed cusps. A tooth is divided into two parts; the crown which is the part above the jaw and the root which is the part embedded in the jawbone. The internal structure of all teeth is similar.

Tooth structure

A tooth is divided into two parts; the crown, which is the part above the jaw, and the root, which is the part embedded in the jawbone. The internal structure of all teeth is similar. The crown is covered with enamel and the root with a thin layer of cement and the periodontal membrane. The bulk of the tooth is composed of dentine and the pulp cavity occupies the centre. Nerves and blood vessels run throughout the pulp cavity.

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enamel – non-living. Covers the crown of the tooth. The hardest substance in the body. Resistant to chipping and relatively resistant to decay; however, it can be dissolved by acid produced by bacteria in the mouth dentine – bone-like. Contains channels of living cytoplasm from cells in the pulp cavity

crown

pulp cavity – composed of living cells blood vessels gum jawbone nerves cement – bone-like. Covers the root of the tooth periodontal membrane – contains fibres which are embedded in the cement at one end and the jawbone at the other end

root

Figure 3.10 Internal structure of a canine tooth Table 3.9 Functions of the main parts of a tooth Structure Functions Enamel Protects the tooth against decay. Insulates the tooth against hot and cold foods. Provides a hard surface for chewing. Dentine Forms the bulk of the tooth. Supports the enamel. Protects the pulp. Pulp cavity Blood vessels supply living cells of the tooth with food and oxygen, and remove carbon dioxide and other waste. Nerves are sensitive to pain, hot and cold. Cement Covers the dentine in the root of the tooth. Periodontal Anchors the root of the tooth in the jawbone. Allows slight movement for shock membrane absorption.

Tooth decay (dental caries)

Tooth decay occurs when bacteria, saliva and food particles in the mouth form a sticky layer on teeth and gums called plaque. Bacteria in the plaque feed on sugars in food and make acid, which eats away at teeth.

1 Acid in plaque slowly eats away the hard enamel.

2 Acid eats away 3 The decay continues 4 the softer dentine and the cavity more quickly forming reaches the pulp. a hole or cavity. Bacteria enter the pulp causing infection. enamel

The infection spreads and reaches a root causing an abscess to form.

dentine pulp No toothache

abscess Some toothache

Severe toothache

Agony

Figure 3.11 The process of tooth decay 3 Nutrition

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Causes of tooth decay

Tooth decay is made more likely by: • Eating foods with a high sugar or starch content, and drinking drinks with a high sugar or acid content, e.g. fruit juices. • Poor oral hygiene practices, e.g. not brushing properly, not brushing and flossing regularly, and not visiting the dentist regularly. • Not getting enough fluoride. • Grinding the teeth. • Smoking.

Guidelines for the care of teeth • • • • •

Brush teeth and gums in the proper way, twice a day. Use a fluoride toothpaste and good quality toothbrush when brushing. Use dental floss and an interdental brush once a day. Use an antibacterial mouthwash after brushing and flossing. Avoid eating sugary and starchy foods and drinking sugary drinks, especially between meals and before going to bed. • Visit a dentist regularly for a checkup and cleaning.

The chemical digestion of food

During chemical digestion the large food molecules are broken down into small molecules by hydrolysis. During hydrolysis, the bonds within the large food molecules are broken down by the addition of water molecules. Chemical digestion is catalysed (speeded up) by digestive enzymes (see Table 3.10, page 32).

Enzymes Enzymes are biological catalysts produced by all living cells. They speed up chemical reactions occurring in living organisms without being changed themselves. Enzymes are proteins that living cells produce from amino acids obtained from the diet. Without enzymes, chemical reactions would occur too slowly to maintain life.

Examples

• Amylase catalyses the breakdown of starch into sugars, mainly maltose. It is present in saliva and pancreatic juice. starch amylase maltose • Catalase catalyses the breakdown of hydrogen peroxide into water and oxygen: hydrogen peroxide catalase water + oxygen

Catalase is found in most cells. It prevents the build-up of harmful hydrogen peroxide, which is produced as a by-product of many chemical reactions occurring in cells.

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Properties of enzymes

All enzymes have similar properties: • Enzymes are specific, i.e. each type of enzyme catalyses only one type of reaction. • Enzymes work best at a particular temperature known as the optimum temperature. This is about

37 oC for human enzymes.

as temperature increases, the rate of enzyme activity increases optimum temperature

noitcaer fo etar 0

as temperature increases, the rate of enzyme activity rapidly decreases

10

20 30 40 50 temperature (°C)

60

Figure 3.12 The effect of temperature on the rate of a reaction catalysed by enzymes • High temperatures denature enzymes, i.e. the shape of the enzyme molecules changes so that they are inactivated. Enzymes start to be denatured at about 40 oC to 45 oC. • Enzymes work best at a particular pH known as the optimum pH. This is about pH 7 for most enzymes. as acidity increases, the rate of enzyme activity decreases

optimum pH

noitcaer fo etar

as alkalinity increases, the rate of enzyme activity decreases

0

increasing acidity

7 pH

increasing alkalinity

14

Figure 3.13 The effect of pH on the rate of a reaction catalysed by enzymes • Extremes of acidity or alkalinity denature most enzymes. • The action of enzymes is helped by certain vitamins and minerals, e.g. vitamin B1 helps the action of respiratory enzymes. • The action of enzymes is inhibited by certain poisons, e.g. arsenic and cyanide. 3 Nutrition

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Digestive enzymes

There are three categories of digestive enzymes and several different enzymes may belong to each category (see Tables 3.10 and 3.11). Table 3.10 Categories of digestive enzymes Category of digestive enzyme Food molecules hydrolysed Products of hydrolysis Carbohydrases Polysaccharides and disaccharides Monosaccharides Proteases Proteins Amino acids Lipases Lipids Fatty acids and glycerol

The digestive system and chemical digestion The process of chemical digestion is summarised in Table 3.11.

nasal cavity mouth – digestion of starch begins teeth – used in mechanical digestion tongue salivary glands trachea diaphragm

salivary gland – produces saliva pharynx (throat) epiglottis – closes over the trachea during swallowing oesophagus – transports food to the stomach stomach – produces gastric juice. Digestion of proteins begins

liver – produces bile

pyloric sphincter – a muscle which relaxes periodically to release food from the stomach

gall bladder – stores bile

pancreas – produces pancreatic juice

bile duct pancreatic duct no function in humans

duodenum ileum

caecum appendix

anal sphincter – a muscle which relaxes during egestion anus

small intestine – receives bile and pancreatic juice. Produces intestinal juice. Digestion of starch, maltose, sucrose, lactose, lipids, proteins and peptides is completed. Products of digestion are absorbed

colon – absorbs water and mineral salts rectum – stores faeces for egestion

Figure 3.14 The structures of the human digestive system and their functions

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Table 3.11 A summary of chemical digestion Organ Digestive juice Source Main components Mouth Saliva Salivary • Water and mucus (pH 7–8) glands.

Functions of the components

• Moisten and lubricate the food allowing tasting and easy swallowing. • Salivary • Begins to digest: amylase* starch maltose (a disaccharide) Stomach Gastric juice Cells in the • Hydrochloric • Maintains an optimum pH of 1–2 acid for pepsin and rennin, and kills (pH 1–2) stomach bacteria. wall. • Rennin* • Produced in infants to clot soluble protein in milk so the protein is retained in the stomach. • Pepsin* • Begins to digest: protein peptides (shorter chains of amino acids) Small intestine Bile Cells in • Bile • Excretory products from the pigments, breakdown of haemoglobin in (duodenum (pH 7–8) the liver. It e.g. bilirubin the liver. Have no function in and ileum) is stored digestion. in the gall bladder and • Organic bile • Emulsify lipids, i.e. break large salts lipid droplets into smaller enters the droplets increasing their surface duodenum area for digestion. via the bile duct. Pancreatic Cells in the • Pancreatic • Continues to digest: starch maltose juice pancreas. It amylase* (pH 7–8) enters the • Trypsin* • Continues to digest: duodenum protein peptides via the • Pancreatic • Digests: pancreatic lipase* lipids fatty acids and glycerol duct. Intestinal Cells in the • Maltase* • Digests: maltose glucose juice walls of (pH 7–8) the small • Sucrase* • Digests: intestine. sucrose glucose and fructose • Lactase* • Digests: lactose glucose and galactose • Peptidase* • Digests: (erepsin) peptides amino acids * digestive enzymes

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Movement of food through the alimentary canal

circular muscles – in the walls of the oesophagus and intestines

Food is moved through the oesophagus and the rest of the alimentary canal by a process known as peristalsis.

circular muscles contract behind the bolus, squeezing it along

Absorption

Absorption is the process by which the soluble food molecules, produced in digestion, move into the body fluids and body cells. Absorption occurs in the small intestine and colon.

Absorption in the small intestine

bolus of food circular muscles relax around and in front of the bolus

Figure 3.15 The mechanism of peristalsis

The products of digestion are absorbed through the lining of the small intestine, mainly the ileum, and into the blood capillaries and lacteals (lymph capillaries) in its walls. Substances absorbed include monosaccharides, amino acids, fatty acids, glycerol, vitamins, minerals and water. Water is absorbed by osmosis; the other substances are absorbed by both diffusion and active transport (see pages 6 and 8). The ileum is very long, about 5 m in an adult, and its inner surface has thousands of finger-like projections called villi (singular villus); both features help to give it a very large surface area for absorption. The wall of each villus, known as the epithelium, is only one cell thick and the epithelial cells have tiny projections called microvilli. Each villus has a network of blood capillaries and a lacteal (lymph capillary) inside. microvilli – increase the surface area of each villus for rapid absorption goblet cell – secretes mucus epithelial cell

arteriole from the mesenteric artery

epithelium – one cell thick so food molecules can pass rapidly through into the capillaries and lacteal blood capillaries – form an extensive network to rapidly absorb the products of digestion

lacteal or lymph capillary – leads into a lymphatic vessel and provides a means of absorbing fatty substances

venule to the hepatic portal vein – takes water-soluble substances to the liver lymphatic vessel – takes fatty substances to the blood before it enters the heart

Figure 3.16 Structure of a villus showing its adaptations for absorption • Water-soluble substances, i.e. monosaccharides, amino acids, minerals, vitamins B and C, and some water are absorbed into the blood in the capillaries. • Fatty substances, i.e. fatty acids, glycerol, and vitamins A and D are absorbed into the lymph in the lacteals.

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Absorption in the colon

Any food that is not digested in the small intestine passes into the colon where water and mineral salts are absorbed from it. As this undigested waste moves along the colon to the rectum it becomes progressively more solid as the water is absorbed.

Egestion

Egestion is the process by which undigested food material is removed from the body. The almost solid material entering the rectum is called faeces and consists of undigested dietary fibre, dead bacteria and intestinal cells, mucus and bile pigments. Faeces is stored in the rectum and egested at intervals through the anus when the anal sphincter relaxes. Egestion must not be confused with excretion which is the removal, from the body, of waste and harmful substances produced by the body’s metabolism. Other than the bile pigments, the components of faeces are not produced by the body’s metabolism, so their removal cannot be classed as excretion.

Assimilation

Assimilation is the process by which the body uses the soluble food molecules absorbed after digestion.

Monosaccharides

Monosaccharides are taken by the blood to the liver in the hepatic portal vein and the liver converts any non-glucose monosaccharides to glucose. The glucose then enters the general circulation where: • It is used by all body cells in respiration to release energy. • Excess is condensed to glycogen by cells in the liver and muscles. These cells then store the glycogen, or • Excess is converted to fat by cells in the liver and adipose (fat) tissue found under the skin and around organs. Fat made in adipose tissue is stored, and fat made in the liver is transported by the blood to adipose tissue and stored.

Amino acids

Amino acids are taken by the blood to the liver in the hepatic portal vein. They then enter the general circulation where: • They are used by body cells to make proteins that are used for cell growth and repair. • They are used by body cells to make enzymes. • They are used by cells of endocrine glands to make hormones. • They are used to make antibodies. • Excess are deaminated by the liver because they cannot be stored. The nitrogen-containing amine groups (NH2) are removed from the molecules and converted to urea (CO(NH2)2). The urea enters the blood and is excreted by the kidneys. The remaining parts of the molecules are converted to glucose which is used in respiration, or are converted to glycogen or fat and stored.

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Fatty acids and glycerol

Fatty acids and glycerol are carried by the lymph to the general circulation where: • They are used to make cell membranes of newly forming cells. • They are used by body cells in respiration under some circumstances. • Excess are converted to fat and stored in adipose tissue under the skin and around organs.

Revision questions

133 Describe what happens during: a mechanical digestion b chemical digestion. 144 Why are teeth important in the digestive process? 155 Joyann has FOUR types of teeth in her mouth. Identify these and state the function 16 17 188 199 200

21 222 233

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of EACH. By means of a fully labelled and annotated diagram only, describe the internal structure of a canine tooth. Matthew develops a cavity in one of his teeth. Outline how this cavity formed and suggest FOUR things he should do to prevent cavities forming in his other teeth. What are enzymes? a Outline the effect that temperature has on enzyme activity. b Other than the effect of temperature on enzyme activity, give THREE other properties of enzymes. Sate the function of EACH of the following parts of the digestive system in the digestive process. a the oesophagus b the liver c the colon d the rectum For lunch, Beth consumes a ham sandwich made with two slices of buttered bread and two slices of ham. Describe how this sandwich is digested as it passes through Beth’s digestive system. Explain how the structure of each villus in Beth’s ileum is adapted to absorb the products of the digestion of her meal. What use does the body make of any amino acids produced during digestion?

3 Concise Revision Course: Human and Social Biology

4 The respiratory system

All living organisms need energy to carry out life processes in order to survive. They obtain this energy from food when the food is respired. Humans respire aerobically and their respiratory system is responsible for taking in the oxygen they need to sustain this respiration and to constantly get rid of the carbon dioxide they produce.

Breathing and gaseous exchange

Breathing refers to the movements that cause air to be moved into and out of the lungs. Breathing must not be confused with respiration, which is the process by which energy is released from food by all living cells (see page 43). Gaseous exchange is the process by which oxygen diffuses into the blood and carbon dioxide diffuses out of the blood through a gaseous exchange surface (see below). Humans respire aerobically, meaning that they release energy from food using oxygen. Aerobic respiration produces carbon dioxide as a waste product. Breathing and gaseous exchange are essential because: • They ensure that humans have a continual supply of oxygen to meet the demands of aerobic respiration. • They ensure that the carbon dioxide produced in aerobic respiration is continually removed so that it does not build up and poison cells.

Gaseous exchange surfaces

In many animals, including humans, the surface through which gases are exchanged, known as the gaseous exchange surface, forms part of the respiratory system. These surfaces have several adaptations which make the exchange of gases through them as efficient as possible: • They have a large surface area so that large quantities of gases can be exchanged. • They are very thin so that gases can diffuse through them rapidly. • They have a rich blood supply to quickly transport gases between the surface and the body cells. • They are moist so that gases can dissolve before they diffuse through the surface.

Structure of the human respiratory system

In humans, the gaseous exchange surface is found in the lungs which make up part of the respiratory system. Humans have two lungs composed of thousands of air passages called bronchioles and millions of swollen air sacs called alveoli. Each lung is surrounded by two pleural membranes which have pleural fluid between them. A single bronchus leads into each lung from the trachea. The larynx forms the top part of the trachea and the nasal cavities and the mouth lead into nasal cavity – hollow space lined with the pharynx or throat, which cilia (microscopic hairs) and mucus leads into the larynx. pharynx or throat Each lung receives blood from the heart via a pulmonary artery nose epiglottis – thin flap of cartilage behind and blood is carried back to the upper lip the tongue at the top of the larynx heart via a pulmonary vein. The two lungs are surrounded by larynx or voice box – contains vocal cords teeth the ribs which form the chest cavity or thorax. The ribs have trachea tongue intercostal muscles between and oesophagus a dome-shaped sheet of muscle, the diaphragm, stretches across the floor of the thorax. Figure 4.1 Structure of upper part of the human respiratory system 4 The respiratory system

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larynx trachea – hollow tube with rings of cartilage in its walls. Lined with cilia and mucus

external inercostal muscles between the ribs internal inercostal muscles

left lung left bronchus – hollow tube with rings of cartilage in its walls. Lined with cilia and mucus heart

bronchioles – hollow tubes branching throughout the lung. Lined with moisture pleural cavity – airtight cavity filled with pleural fluid pleural membranes – one surrounds the outside of the lung, one lines the rib cage and diaphragm cut end of a rib

ribs

diaphragm – a muscular sheet

magnified cluster of alveoli at the end of a bronchiole

Figure 4.2 Structure of the human thorax

capillary from the pulmonary artery – carries deoxygenated blood

alveoli – thin-walled. Provide a large surface area for gaseous exchange

capillary to the pulmonary vein – carries oxygenated blood bronchiole network of capillaries – surrounds the alveoli

Figure 4.3 Surface view of a cluster of alveoli showing the blood supply Table 4.1 Summary of the functions of the main parts of the respiratory system Structure Functions Nasal cavities Warm the inhaled air. Mucus traps dust and pathogens in the inhaled air and moistens the air. Cilia move the mucus to the throat to be swallowed. Epiglottis Prevents food from entering the trachea when swallowing. Larynx Vocal cords produce the sounds of speech. Trachea and bronchi Carry air into and out of the lungs. Rings of cartilage in their walls keep them open. Bronchioles Carry air to and from the alveoli. Alveoli Exchange oxygen and carbon dioxide between inhaled air and blood in the capillaries.

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Structure Pleural membranes and pleural fluid Intercostal muscles and diaphragm

Functions Form an airtight cavity between the lungs and the rib-cage and diaphragm so that any changes in volume of the chest cavity causes the volume inside the lungs to change. Pleural fluid also acts as a lubricant during breathing. Contract and relax to change the volume inside the chest cavity and lungs, which causes air to move into and out of the lungs.

The mechanism of breathing and gaseous exchange

Breathing is brought about two sets of muscles, the intercostal muscles and the diaphragm. Table 4.2 The mechanism of breathing Features Inhalation (inspiration) Exhalation (expiration) 4

4

1

3

1 3

2 1

2 3 4

External intercostal muscles Internal intercostal muscles Ribs and sternum Diaphragm muscles Diaphragm Volume inside thorax and lungs Pressure inside thorax and lungs Movement of air

Contract Relax Move upwards and outwards Contract Moves downwards or flattens Increases Decreases Air is drawn into the lungs due to the decrease in pressure

2

Relax Contract Move downwards and inwards Relax Domes upwards Decreases Increases Air is pushed out of the lungs due to the increase in pressure

As the air is drawn in during inhalation it is warmed in the nasal passages, and cleaned and moistened by mucus lining the nasal passages and trachea. The air passes through the bronchi and bronchioles and enters the alveoli where gaseous exchange occurs between the air and the blood in the capillaries. The walls of the alveoli form the gaseous exchange surface. Each alveolus: • Has a pocket shape. A human has two lungs, each containing over 350 million alveoli, giving a very large total surface area of about 90 m2. • Has a very thin wall that is only one cell thick. • Is surrounded by a network of capillaries giving it a rich blood supply. • Is lined with moisture. 4 The respiratory system

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exhaled air − 16% O2, 4.0% CO2 deoxygenated blood − low oxygen content, high carbon dioxide content. Plasma and red blood cells transport carbon dioxide from body cells

inhaled air − 21% O2, 0.04% CO2 oxygenated blood − high oxygen content, low carbon dioxide content. Red blood cells transport oxygen to body cells

carbon dioxide diffuses out of the plasma and red blood cells

oxygen dissolves in moisture lining the alveolus and diffuses into red blood cells

layer of moisture lining the alveolus red blood cell wall of the capillary − one cell thick wall of the alveolus − one cell thick

Figure 4.4 Gaseous exchange in an alveolus

Factors affecting the breathing rate

The normal breathing rate for a healthy adult at rest ranges from 12 to 16 breaths per minute. The medulla of the brain (see page 69) controls the breathing rate by detecting the level of carbon dioxide in the blood and sending impulses to the intercostal muscles and diaphragm. • Any factor that increases the rate of respiration in body cells will cause the level of carbon dioxide in the blood to increase. If carbon dioxide levels increase, breathing rate increases to remove the excess carbon dioxide. Factors that increase breathing rate include: Carrying out exercise. Taking drugs that are stimulants, e.g. caffeine, amphetamines, cocaine. Smoking cigarettes. Suffering from anxiety or fear. Being exposed to certain environmental factors, e.g. being in a confined space or in polluted air. Being at high altitude. Being overweight. • Any factor that decreases the rate of respiration in body cells will cause the level of carbon dioxide in the blood to decrease. If carbon dioxide levels decrease, breathing rate decreases. Factors that decrease breathing rate include: When resting or asleep. Taking drugs that are depressants, e.g. sedatives, sleeping pills, alcohol. Being exposed to certain environmental factors, e.g. being in fresh, unpolluted air.

Vital capacity Vital capacity is the maximum volume of air that can be exhaled from the lungs after inhaling as deeply as possible. Measuring vital capacity can be used to indicate lung function and if a person is suffering from lung disease. Vital capacity depends on age, gender, body size and fitness. It can be increased by regular

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exercise and is decreased by smoking, obesity or respiratory disease. Other volumes and capacities associated with the lungs are shown in Figure 4.5. 6 5

)3md( emulov

4 3

vital capacity tidal volume – volume of air inhaled and exhaled in a single normal breath

total lung capacity – volume of air in the lungs after maximum inhalation

2 residual volume – volume of air remaining in the lungs after forceful exhalation

1 NB 1 dm3 = 1 litre

Figure 4.5 Lung capacities and volumes

Mouth-to-mouth resuscitation (rescue breathing)

Mouth-to-mouth resuscitation is a technique used to supply oxygen to a person who has stopped breathing. The rescuer forces his or her exhaled air, which contains about 16% oxygen, into the victim’s lungs every few seconds, allowing for passive exhalation between. To perform mouth-tomouth resuscitation: • Lie the victim on his or her back. • Gently tilt the victim’s head backwards to open the airways by lifting the chin. • Open the victim’s mouth and remove any debris. • Pinch the victim’s nostrils to close them and breathe in. • Seal your lips over the victim’s open mouth and breathe out into the mouth for 1 second. • If the victim’s chest rises, breathe into the mouth a second time. • Continue rescue breathing by giving one breath every 5 seconds until normal breathing resumes or medical help arrives.

The effects of smoking cigarettes

When smoking cigarettes made from tobacco, smoke containing over 4000 thousand different chemicals including nicotine, tar and carbon monoxide is inhaled into the respiratory system. Cigarette smoking poses serious health risks including the following.

Figure 4.6 Some components of cigarette smoke 41 4 The respiratory system

Nicotine addiction

Nicotine is an addictive substance that causes smokers to continue to smoke and makes it extremely difficult for them to stop. Addicted smokers need enough nicotine during each day to ‘feel normal’.

Reduced oxygen carrying capacity of the blood

Carbon monoxide combines more readily with haemoglobin than oxygen does, which reduces the amount of oxygen carried to body cells. This reduces respiration and the smoker’s ability to exercise. In a pregnant woman it deprives the foetus of oxygen, reducing its growth and development.

Lung damage

Cigarette smoke damages lungs: • It causes mucus production to increase and it paralyses the cilia, which stops them from beating so the mucus is not removed. The person then develops a persistent cough to try and remove the mucus. • It irritates and inflames the walls of the bronchi and bronchioles. This, together with the increased mucus production and paralysis of the cilia, causes the airways to become obstructed, making breathing difficult, and leads to chronic bronchitis. • It causes the walls of the alveoli to become less elastic and the walls between the alveoli to break down, which decreases their surface area. This reduces gaseous exchange, makes exhaling difficult and causes air to remain trapped in the lungs, a condition known as emphysema. The bronchioles often collapse when exhaling, obstructing the airways, making exhaling even harder. Chronic bronchitis healthy

healthy

inflammation and excess mucus

Emphysema alveolar membranes break down

Figure 4.7 Chronic obstructive pulmonary disease (COPD)

Cancer of the mouth, throat, oesophagus or lungs

Some components of tar and many other chemicals in cigarette smoke are carcinogenic. These cause mutations in cells in different regions of the respiratory system. This leads to the development of cancerous tumours which replace normal, healthy tissue in these regions. Note that chronic bronchitis and emphysema are two types of chronic obstructive pulmonary disease or COPD.

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Respiration

Respiration is the process by which energy is released from food by all living cells. Respiration is catalysed by enzymes and occurs slowly in a large number of stages: • Most of the energy released at each stage is used to build energy carrying molecules called adenosine triphosphate or ATP. An ATP molecule is formed by combining some of the energy released with an adenosine diphosphate or ADP molecule and a phosphate group present in the cell. The energy can then be re-released where ever it is needed in the cell by the reverse reaction:

ADP + phosphate + energy   ATP ATP is known as the ‘energy currency’ of cells. Cells earn ATP as a result of energy-producing reacons, and spend it on reacons requiring energy. Energy released by ATP is used by cells:

To manufacture complex, biologically important molecules, e.g. proteins, DNA. For cell growth and repair. For cell division. In active transport to move molecules and ions in and out of the cells through their membranes. For special functions in specialised cells, e.g. contraction of muscle cells, transmission of impulses in nerve cells. • Some of the energy is released as heat and this helps to maintain the body temperature at 37 °C. There are two types of respiration: • aerobic respiration • anaerobic respiration.

Aerobic respiration Aerobic respiration is the process by which energy is released from food by living cells using oxygen. Aerobic respiration occurs in most cells. It uses oxygen and takes place in the mitochondria. It always produces carbon dioxide, water and about 38 ATP molecules per molecule of glucose. enzymes in carbon dioxide + water + energy glucose + oxygen mitochondria

Anaerobic respiration Anaerobic respiration is the process by which energy is released from food by living cells without the use of oxygen. Anaerobic respiration occurs in some cells. It takes place without oxygen in the cytoplasm of the cells. The products of anaerobic respiration vary and it produces considerably less energy per molecule of glucose than aerobic respiration. Yeast cells, certain bacteria and muscle cells are capable of carrying out anaerobic respiration.

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Industrial and domestic uses of anaerobic respiration Making bread and alcoholic beverages

Yeast cells carry out anaerobic respiration known as fermentation. It produces ethanol, carbon dioxide and 2 ATP molecules per molecule of glucose. in ethanol + carbon dioxide + energy glucose enzymes cytoplasm When making bread, the yeast ferments sugars present in dough. The carbon dioxide produced forms bubbles in the dough which cause it to rise. When baked, heat from the oven causes the bubbles to expand, kills the yeast and evaporates the ethanol. When making alcoholic beverages such as beer, wine, rum and other spirits, the yeast ferments sugars present in grains, fruits or molasses. Fermentation stops when the ethanol concentration reaches about 14–16% because it kills yeast cells, so the ethanol content of beer and wine is always below about 16%. Spirits are made by distillation of the fermentation mixture.

Making yoghurt

Certain bacteria, e.g. Lactobacillus, ferment the lactose in milk forming lactic acid. The lactic acid makes the milk proteins curdle, which forms thick yoghurt and gives the yoghurt its sour taste.

Producing biogas

Certain bacteria are used to break down organic matter, e.g. manure and garden waste, anaerobically in an anaerobic digester. This produces biogas which is a mixture of approximately 60% methane (CH4), 40% carbon dioxide and traces of other gases, e.g. hydrogen sulfide (H2S). Biogas can be used as a fuel for cooking, heating and to generate electricity.

Oxygen debt

Muscle cells can carry out anaerobic respiration during strenuous exercise. During strenuous exercise, if oxygen cannot be delivered to the muscle cells quickly enough for the demands of aerobic respiration, the cells begin to respire anaerobically. This produces lactic acid and 2 ATP molecules per molecule of glucose. in lactic acid + energy glucose enzymes cytoplasm Lactic acid builds up in the muscle cells and begins to harm them, causing fatigue and eventually collapse as they stop contracting. The muscle cells are said to have built up an oxygen debt. This debt must be repaid directly after exercise by resting and breathing deeply so that the lactic acid can be removed by respiring it aerobically.

Revision questions

1 What is meant by the term ‘breathing’ and why is breathing important to humans? 2 State the function of EACH of the following structures found in the 3

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respiratory system: a the nasal cavities b the bronchi c the bronchioles Identify the gaseous exchange surface in a human and explain FOUR ways in which the surface is adapted to perform its function efficiently.

4 Concise Revision Course: Human and Social Biology

4 Explain the mechanism by which air is drawn into the lungs. 5 Give FOUR factors that can increase the breathing rate and TWO factors that can

decrease it. 6 a What is meant by the term ‘vital capacity’? b Why is it important to measure a person’s vital capacity? 7 Your friend, Kendra, suddenly collapses and stops breathing. Outline the steps you would take to perform mouth-to-mouth resuscitation on Kendra. 8 a Name the THREE main components of cigarette smoke. b Outline how smoking cigarettes damages the lungs. 9 Distinguish between aerobic and anaerobic respiration and write ONE word equation to summarise EACH process. 100 What is ATP and what is its role in body cells? 111 Ché carried out strenuous exercise for an extended period of time and eventually collapsed and found he had to rest before resuming any exercise. Explain why he collapsed and why he had to rest before he could exercise again.

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5 The circulatory system

Humans need to constantly exchange substances with their environment. They need to take in useful substances and get rid of waste. The circulatory system provides a means of transporting these substances between the surfaces where they are exchanged and the body cells. The circulatory system is composed of the cardiovascular system and the lymphatic system.

The need for a transport system in the human body

The absorption and transport of substances in humans is affected by two factors: • Their surface area to volume ratio. • The limitations of simple diffusion. Humans have a small surface area to volume ratio. Diffusion through their body surface is not adequate to supply all their body cells with their requirements and remove their waste. In addition, most of their body is too far from its surface for substances to move through it by simple diffusion. Humans have, therefore, developed a transport system to carry useful substances from specialised organs that absorb them, e.g. the lungs and ileum, to body cells, and to carry waste substances from body cells to specialised organs that excrete them, e.g. the kidneys and lungs.

Materials transported around the human body

The following materials are transported around the human body: • Useful substances: oxygen, water, digested food (mainly glucose and amino acids), vitamins, minerals, hormones, antibodies and plasma proteins. Heat is also carried. • Waste substances: carbon dioxide and nitrogenous waste, e.g. urea.

The cardiovascular system

The cardiovascular system consists of: • Blood, which serves as the medium to transport substances around the body. • Blood vessels, which are tubes through which the blood flows to and from all parts of the body. • The heart, which pumps the blood through the blood vessels.

Blood

Blood is composed of three types of cells: • red blood cells • white blood cells • platelets These cells are suspended in a fluid called plasma. The cells make up about 45% by volume of the blood and the plasma makes up about 55%.

Figure 5.1 Red blood cells

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Composition of plasma

Plasma is a yellowish fluid composed of about 90% water and 10% dissolved substances. The dissolved substances consist of: • Products of digestion, e.g. glucose, amino acids, vitamins and minerals. • Waste products, e.g. dissolved carbon dioxide and urea. • Hormones, e.g. insulin and thyroxine. • Plasma proteins, e.g. fibrinogen, prothrombin, albumen and antibodies.

Functions of plasma

The main function of plasma is transporting the following: • Products of digestion, from the ileum to the liver and the body cells. • Carbon dioxide, from body cells to the lungs. • Urea, from the liver to the kidneys. • Hormones, from the glands that produce them (endocrine glands) to target organs. • Heat, from the liver and muscles to all parts of the body.

Serum

Serum is plasma without fibrinogen and other factors needed for the blood to clot (see page 48). Serum is the part of the blood that is left over after red and white blood cells, platelets and clotting factors have been removed. serum = plasma – clotting factors

Blood cells

Table 5.1 Structure and functions of blood cells Cell type and structure Formation of cells Functions Red blood cells (erythrocytes) • Formed in the red • Transport oxygen as oxyhaemoglobin from bone marrow found in flat bones, e.g. the the lungs to body cells. cell membrane pelvis, scapula, ribs, • Transport small sternum, cranium and amounts of carbon vertebrae; and in the dioxide from body cells ends of long bones, e.g. the humerus and to the lungs. femur. cytoplasm cy rich in hhaemoglobin, • Broken down mainly an iron-containing iron-co protein in the liver and spleen. • Biconcave discs with a thin centre and relatively large surface area to volume ratio so gases easily diffuse in and out. • Have no nucleus, therefore they only live for about 3 to 4 months. • Contain the red pigment haemoglobin. • Slightly elastic allowing them to squeeze through the narrowest capillaries. 5 The circulatory system

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Cell type and structure Formation of cells Functions White blood cells (leucocytes) Slightly larger than red blood cells and less numerous; approximately 1 white blood cell to 600 red blood cells. There are two main types; 25% are lymphocytes and 75% are phagocytes. • Develop from cells • Produce antibodies to Lymphocytes in the red bone destroy disease-causing marrow and mature bacteria and viruses cell membrane in other organs, e.g. (pathogens). lymph nodes, spleen, • Produce antitoxins large, round nucleus thymus gland. to neutralise toxins non-granular cytoplasm produced by pathogens. • Have a rounded shape. • Have a large, round nucleus that controls the production of antibodies. • Have only a small amount of cytoplasm. • Formed in the red Phagocytes • Engulf and destroy bone marrow. pathogens. cell membrane • Engulf pathogens destroyed by lobed nucleus antibodies. granular cytoplasm • Have a variable shape. • Move by pseudopodia; can move out of capillaries through their walls and engulf pathogens using pseudopodia. • Have a lobed nucleus. Platelets (thrombocytes) cell membrane

• Formed from cells in • Help the blood to clot the red bone marrow. at a cut or wound (see Blood clotting, below).

cytoplasm

• Cell fragments. • Have no nucleus and only live for about 10 days.

Blood clotting

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When the skin is cut and bleeds, the blood quickly clots. The following events occur to form the clot: • Platelets in the blood at the cut become spiky in shape, stick to each other and begin to plug the cut. They also release an enzyme called thrombokinase or thromboplastin. • Thrombokinase, with the help of calcium ions (Ca2+) and vitamin K in the blood, converts the inactive plasma protein, prothrombin, into active thrombin. • Thrombin converts the soluble plasma protein, fibrinogen, into insoluble fibrin which forms fibres. 5 Concise Revision Course: Human and Social Biology

• The fibrin fibres form a network across the cut, which traps blood cells and forms a clot. • The clot dries and develops into a scab. New skin forms below the scab and the scab drops off. Clotting is important because: • The clot prevents further blood loss. • The clot prevents pathogens from entering the body.

Blood groups

Blood can be classified into different blood groups based on chemicals present on the surface of red blood cells Figure 5.2 Red blood cells and platelets known as antigens. There are two grouping systems: • The ABO system, which divides blood into four groups; trapped in a network of fibrin fibres group A, group B, group AB and group O. • The rhesus system, which divides blood into two groups; rhesus positive and rhesus negative.

Blood vessels

There are three main types of blood vessels: • arteries • capillaries • veins artery direction of blood flow

organ arteriole – small artery heart capillary

venule – small vein oxygenated blood deoxygenated blood

vein

Figure 5.3 The relationship between the different blood vessels

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Arteries carry blood away from the heart. On entering an organ, an artery branches into smaller arteries called arterioles which then branch into a network of capillaries which run throughout the organ. Capillaries then join into small veins called venules which join to form a single vein which leads back from the organ towards the heart. Table 5.2 Arteries, capillaries and veins compared Arteries Capillaries Veins Transport blood away from Transport blood throughout Transport blood back towards the heart to body tissues and all body tissues and organs, the heart from body tissues and organs. linking arteries to veins. organs. Blood flows through under high Blood flows through under low Blood flows through under low pressure. pressure. pressure. Blood moves in pulses created Blood flows smoothly. Blood flows smoothly. as the ventricles contract. Blood flows rapidly. Blood flows very slowly. Blood flows slowly. Blood is oxygenated, except in Blood becomes deoxygenated as Blood is deoxygenated, except the pulmonary arteries. it travels through capillaries. in the pulmonary veins. Most lie deep within the body Run throughout all tissues and Many lie close to the body so they are protected. organs. surface. Do not possess valves, except Do not possess valves. Possess valves to prevent the the aorta and pulmonary artery low pressure, slow flowing as they leave the ventricles of blood from flowing backwards. the heart. free-flowing blood – valve open

Have walls composed of three layers. The walls are thick and elastic to withstand the high pressure of the blood. fibrous layer – fairly thick and elastic muscle and elastic layer – thick endothelium – one cell thick lumen – narrow

The walls are composed of a single layer of endothelial cells so substances pass easily between the blood and body cells. They are extremely narrow and branch repeatedly so that all body cells are close to capillaries. endothelial cell lumen – extremely narrow

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back-flowing blood – valve closed

Have walls composed of three layers. The walls are thin because they do not have to withstand high pressure. The lumen is wide so it does not resist the flow of low pressure blood. fibrous layer – thin and elastic muscle and elastic layer – thin endothelium – one cell thick lumen – wide

The heart

The pumping action of the heart maintains a constant circulation of blood around the body. The walls of the heart are composed of cardiac muscle which contracts without nerve impulses, i.e. it is myogenic, and it does not get tired. The heart is divided into four chambers. The two on the right contain deoxygenated blood and are completely separated from the two on the left, which contain oxygenated blood, by the septum. • The top two chambers, called atria, have thin walls and they collect blood entering the heart from the anterior and posterior vena cavae and the pulmonary veins. Their walls are thin because they only have to pump blood a short distance into the ventricles. • The bottom two chambers, called ventricles, have thick walls and they pump blood out of the heart via the pulmonary artery and aorta. Their walls are thick because they have to pump blood longer distances around the body and to the lungs. The wall of the left ventricle is thicker than the wall of the right ventricle because it has to pump blood longer distances (see Figure 5.4). Valves are present between each atrium and ventricle and in the pulmonary artery and aorta as they leave the ventricles to ensure that blood flows through the heart in one direction. pulmonary artery – carries deoxygenated blood to the lungs aorta – carries oxygenated blood to the body

anterior vena cava – carries deoxygenated blood from the head

left atrium – collects oxygenated blood from the lungs pulmonary veins – carry oxygenated blood from the lungs

right atrium – collects deoxygenated blood from the head and body

semi-lunar valves – prevent the backflow of blood into the ventricles when they relax

posterior vena cava – carries deoxygenated blood from the body

bicuspid valve or mitral valve – same function as the tricuspid valve

tricuspid valve – prevents the blood flowing back into the atrium when the ventricle contracts

tendons – prevent the valve turning inside out

right ventricle – pumps deoxygenated blood to the lungs cardiac muscle

left ventricle – thicker walled than the right ventricle to pump oxygenated blood longer distances around the body septum

deoxygenated blood

oxygenated blood

Figure 5.4 Longitudinal section through the human heart showing the function of the parts

The heart’s pacemaker (sinoatrial node)

A group of specialised cells in the wall of the right atrium, called the pacemaker or sinoatrial node, spontaneously produce electrical impulses which travel through the heart muscle causing it to contract about 75 times per minute. This rate can be modified by nerve impulses or the hormone adrenaline, e.g. the rate increases during exercise or when nervous. An artificial pacemaker is a small, battery-operated device that generates electrical impulses to regulate heartbeat. It is implanted under the skin and connected to the heart via tiny wires and may be used if the heartbeat is too slow, too fast or irregular, or if a person has suffered a heart attack (see pages 121–22). 5 The circulatory system

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Cardiac cycle

The atria and ventricles at the two sides of the heart contract and relax together. The contraction of a chamber is called systole and its relaxation is called diastole. One cardiac cycle or heartbeat involves the following: • Diastole – the atria and ventricles relax together, the semi-lunar valves close, the atria fill up with blood from the anterior and posterior vena cavae and pulmonary veins, and the blood flows into the ventricles. This takes 0.4 seconds. • Atrial systole – the atria contract together forcing any remaining blood through the tricuspid and bicuspid valves into the ventricles. This takes 0.1 second. • Ventricular systole – the ventricles contract together, the tricuspid and bicuspid valves close and blood is forced through the semi-lunar valves into the aorta and pulmonary arteries. This takes 0.3 seconds.

Blood pressure Blood pressure is the pressure of circulating blood on the walls of blood vessels. It is usually measured in the large arteries in millimetres of mercury or mm Hg. It is expressed as: blood pressure (mm Hg) = systolic pressure (highest pressure when the heart contracts) diastolic pressure (lowest pressure when the heart relaxes) Ideal blood pressure is between 90/60 mm Hg and 120/80 mm Hg. High blood pressure or hypertension results if a person’s pressure rises to 140/90 mm Hg or above. This can be caused by a variety of factors (see page 122).

Circulation

During one complete circulation around the body, the blood flows through the heart twice, therefore, humans have a double circulation: • In the pulmonary circulation, blood travels from the right ventricle through the pulmonary arteries to the lungs to pick up oxygen and lose carbon dioxide, i.e. it becomes oxygenated. It then travels back via the pulmonary veins to the left atrium. • In the systemic (body) circulation, blood travels from the left ventricle through lungs the aorta to the body where it gives up oxygen to the body cells and picks up carbon dioxide, i.e. it becomes pulmonary artery pulmonary vein deoxygenated. It then travels back via the anterior or posterior vena cava to the right atrium. right atrium left atrium A double circulation is necessary because blood loses pressure when it passes left ventricle right ventricle through the lungs, so it goes back to aorta the heart to be given enough pressure vena cava to reach body organs to supply them with oxygen. As it loses pressure passing through organs, the blood goes back body to the heart again to be given enough deoxygenated blood oxygenated blood pressure to reach the lungs to get rid of waste carbon dioxide and pick up Figure 5.5 Double circulation in the human body more oxygen.

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jugular vein

head

carotid artery

arms anterior vena cava

lungs pulmonary vein

pulmonary artery

aorta posterior vena cava heart hepatic vein

liver

hepatic artery

hepatic portal vein intestines

renal vein

mesenteric artery

kidneys

renal artery

legs deoxygenated blood

oxygenated blood

Figure 5.6 The major blood vessels in the human body

Causes and effects of heart attacks

The main cause of a heart attack or myocardial infarction is atherosclerosis. This occurs when fatty deposits containing cholesterol, known as atheromas, build up on the inside of the walls of the coronary arteries that supply oxygenated blood to the heart muscle. The atheromas cause the lumens of the arteries to narrow, and their walls to harden and become less elastic. A blood clot, known as a coronary thrombosis, may then form in one of the narrow arteries (see Figure 12.2, page 122). This clot can partially or completely block the blood flow through the artery and the section of the heart muscle supplied by the artery cannot get oxygen so starts to die, and a heart attack occurs. The risk of a heart attack is increased if a person has hypertension (high blood pressure) or is exposed to risk factors that can lead to hypertension, including: • Being overweight or obese. • Smoking. • Too much salt or too much fat in the diet. • Consumption of too much alcohol. 5 The circulatory system

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• Lack of physical exercise. • Stress. Symptoms of a heart attack include: • Chest pain or discomfort as the chest feels as if it is being pressed or squeezed. • Upper body pain or discomfort, e.g. in the arms, shoulders, neck, jaw or back. • Shortness of breath. • Feeling weak, lightheaded or dizzy. In some cases the heart stops beating, known as cardiac arrest, and it can result in death.

The lymphatic system

The lymphatic system consists of: • Lymph, which serves as the transporting medium. • Lymph vessels or lymphatic vessels, which are tubes through which lymph flows. Lymph vessels begin inside tissues. They have thin muscular walls, valves to prevent the backflow of low pressure lymph and oval-shaped swellings along their length called lymph nodes or lymph glands. Lymph nodes form clusters in various parts of the body, especially in the neck, armpits and groin. Lymphocytes and phagocytes are numerous in lymph nodes. Lymph is a colourless watery fluid that contains lymphocytes. It is formed in body tissues from tissue fluid which is constantly being formed from plasma. Lymph rejoins the plasma in the subclavian veins from the arms just before they join the anterior vena cava. Lymph flows in one direction from tissues towards the heart and its flow is helped by the contraction of surrounding muscles, especially during exercise. lymph capillary – walls are one cell thick 2

arteriole

3

1

2

lymph vessels

1 3 3 2 2

body cells surrounded by tissue fluid

1

1

venule

blood capillary

1 Plasma containing oxygen and nutrients is forced out of blood capillaries where they branch from arterioles. This forms tissue fluid. Blood cells and plasma proteins remain in the blood. Body cells absorb the oxygen and nutrients from the tissue fluid and give out carbon dioxide and other cellular waste. 2 Some tissue fluid containing carbon dioxide and other waste flows back into the blood capillaries before they join into venules. This reforms plasma. 3 The remaining tissue fluid containing carbon dioxide and other waste flows into lymph capillaries and forms lymph which flows into larger lymphatic vessels.

Figure 5.7 The formation of tissue fluid and lymph

Functions of the lymphatic system Functions of lymph • • • • •

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Lymph removes cellular waste and cell debris from around body cells. Lymph drains excess tissue fluid from tissues, which helps to prevent fluid from building up in them. Lymph helps maintain normal blood volume and pressure. Lymphocytes in lymph defend the body against pathogens. Lymph in the lacteals (lymph capillaries) in the ileum absorbs fatty products of digestion. 5 Concise Revision Course: Human and Social Biology

Functions of lymph nodes

• Lymphocytes and phagocytes in lymph nodes help destroy pathogens in lymph. • Lymph nodes filter dead cells and cancerous cells out of lymph. • Lymph nodes release lymphocytes into lymph during times of infection.

Revision questions

1 a Explain why the human body needs a transport system.

b Name FOUR materials transported around the human body. 2 Explain the relationship between plasma and serum. 3 a By means of TWO labelled and annotated diagrams, give THREE differences between the structure of a red blood cell and a phagocyte. b State the function of EACH of the cells you have drawn in a above. 4 Explain how the loss of blood at a cut is prevented. 5 State THREE differences between the structure of an artery and a vein and provide a reason for EACH difference. 6 Explain: a How blood flow through the heart is maintained in one direction. b Why the wall of the left ventricle of the heart is thicker than the wall of the right ventricle. c How the beating of the heart is controlled. 7 Distinguish between systole and diastole. 8 Explain to Naomi why humans need a double circulation. 9 Draw a simple flow diagram to show the pathway that a red blood cell takes as it journeys from the lungs around the body and back to the lungs. 100 What happens during a heart attack and how is it caused? 11 Explain the relationship between blood plasma, tissue fluid and lymph. 122 Give FOUR functions of the lymphatic system.

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6 The skeletal system

Humans need to be able to move their entire bodies from place to place as well as parts of their bodies. They also need to have a means of supporting and protecting the soft tissues and organs of their bodies. These functions are all carried out by the skeletal system.

The human skeleton

The human skeleton is made of 206 bones, which are held cranium together at joints by ligaments. The skeleton is made from two skull upper jaw clavicle types of connective tissue, bone lower jaw (collar bone) and cartilage. pectoral girdle scapula (shoulder blade) • Bone makes up the bulk of the sternum skeleton. It is composed of rib (breast bone) living cells surrounded by the non-living mineral, calcium humerus vertebral phosphate, together with column forelimb (arm) ulna some collagen (protein) fibres. radius Bone is hard and has blood vessels running throughout. • Cartilage is composed of living carpals cells surrounded mainly by metacarpals collagen fibres. It is more thumb elastic and flexible than bone and does not have blood phalanges vessels running through it. pelvic girdle Cartilage is important because: femur patella It covers the ends of hindlimb tibia (knee cap) (leg) bones at joints where fibula its slipperiness helps to reduce friction and it aids in shock absorption. It forms the skeleton of tarsals certain fleshy appendages, metatarsals e.g. the nose and outer ear, which maintains phalanges their shape. big toe It makes up the intervertebral discs between Figure 6.1 The human skeleton the vertebrae enabling the discs to act as shock absorbers. The skeleton can be divided into the axial skeleton and the appendicular skeleton.

The axial skeleton

The axial skeleton consists of the skull, vertebral column, ribs and sternum: • The skull is made up of the cranium and upper jaw which are fused, and the lower jaw which articulates with the upper jaw. The skull encloses the brain and sense organs of the head.

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• The vertebral column is composed of 33 bones known as vertebrae. The spinal cord runs through the vertebral column. The column supports the body, provides points of attachment for the girdles and many muscles, and protects the spinal cord which runs through it. It also allows some movement. • The ribs are attached to the vertebral column dorsally and the sternum ventrally. They form the rib cage around the heart and lungs, and movement of the ribs is essential for breathing.

The appendicular skeleton

forelimb pectoral girdle

The appendicular skeleton is composed of the pectoral girdle, the pelvic girdle, the arms (forelimbs) and the legs (hindlimbs). • The girdles connect the limbs to the axial skeleton and have broad flat surfaces humerus for the attachment of muscles that move the limbs. The pelvic girdle is fused to the bottom of the vertebral column to provide support for the lower body and to transmit the thrust from the legs to the radius vertebral column which moves the body forwards. ulna • The limbs are composed of long bones carpals – which have joints between to allow for wrist bones metacarpals – easy movement. Being long, the bones hand bones provide a large surface area for the attachment of muscles and permit long phalanges – finger bones strides to be taken. thumb or Both the arms and the legs are built on big toe the same basic pattern known as the pentadactyl limb. Figure 6.2 The pentadactyl limb

hindlimb pelvic girdle ball and socket joint femur

hinge joint tibia fibula tarsals – ankle bones metatarsals – foot bones phalanges – toe bones

articular cartilage – covers the head of the humerus head – ball shaped to articulate with the socket of the scapula at the shoulder shaft – long, hollow and cylindrical. Reduces chances of breakage occurring across the bone

spongy bone – composed of a structural network of bony processes with red bone marrow between. Light, strong and withstands stress in all directions. Red bone marrow produces blood cells compact bone – dense, hard, strong bone. Main function is support

articular cartilage

marrow cavity – contains fatty yellow bone marrow which serves as a fat store

points of articulation with the radius and ulna at the elbow

lower end composed of spongy bone

Figure 6.3 Structure and functions of parts of a typical long bone – the humerus 6 The skeletal system

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Functions of the skeleton

The human skeleton has five main functions: • Movement. The skeleton is jointed and muscles work across these joints to bring about movement. Most movement is brought about by the legs and arms while the vertebral column allows some movement. • Protection for the internal organs. The skull protects the brain and sense organs of the head, i.e. the eyes, ears, nasal cavities and tongue. The vertebral column protects the spinal cord. The rib cage and sternum protect the lungs and heart. • Support for the soft parts of the body. This is mainly carried out by the vertebral column, pelvic girdle and legs. • Breathing. Alternate contractions of the internal and external intercostal muscles between the ribs bring about movements of the rib cage, which cause air to be drawn into the lungs and expelled from the lungs (see page 37). • Production of blood cells. Red blood cells, most white blood cells and platelets are produced in the red bone marrow found in the spongy bone inside flat bones, e.g. the pelvis, scapula, ribs, sternum, cranium and vertebrae, and in the ends of long bones, e.g. the humerus and femur.

Tendons and ligaments

Tendons and ligaments must not be confused: • Tendons attach the ends of muscles to the bones of the skeleton. They are made of tough, fibrous connective tissue. They are strong and non-elastic so that, when a muscle contracts, the force is transmitted directly to the bone, causing the bone to move. • Ligaments attach bones together at joints. They are made of tough, fibrous connective tissue with some elastic tissue. They are strong but elastic so they hold the bones together firmly and prevent dislocation, but can stretch slightly to allow movement at the joints.

Movement

Movement in humans is brought about by skeletal muscles working across joints.

Skeletal muscles

Skeletal muscles consist of bundles of multinucleate muscle fibres which are surrounded by connective tissue. Tendons attach these muscles to the bones of the skeleton. muscle

bundles of muscle fibres muscle fibre nuclei connective tissue surrounds the bundles of muscle fibres

tendon

Figure 6.4 A portion of a skeletal muscle

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Joints A joint is formed where two bones meet. Most joints allow the rigid skeleton to move. There are three types of joints: • Fixed joints or fibrous joints. The bones are joined firmly together by fibrous connective tissue which allows no movement, e.g. the cranium is made of several bones joined by fixed or immovable joints. • Partially movable joints or cartilaginous joints. The bones are separated by cartilage pads which allow slight movement, e.g. the vertebrae are separated by intervertebral discs of cartilage. • Moveable joints or synovial joints. The articulating surfaces of the bones are covered with articular cartilage and synovial fluid fills the joint cavity between the bones. The bones are held together by ligaments. There are two types of moveable joints: Hinge joints are formed when the articulating bone, ends of the bones meet. They allow e.g. humerus or femur movement in one plane (direction) capsule – composed of tough, only. This limited movement provides slightly elastic ligaments. Holds the bones together. Can stretch strength and the joints are capable of to enable movement bearing heavy loads, e.g. the elbow, synovial membrane – lines the knee, finger and toe joints. capsule. Secretes synovial fluid synovial fluid – lubrictes the joint allowing friction-free movement, and prevents damage to the cartilage articular cartilage – reduces friction between the bones, prevents damage to the articulating surfaces and aids in shock absorption articulatory bone e.g. ulna or tibia

Figure 6.5 Structure and functions of the parts of a generalised hinge joint Ball and socket joints are formed where a ball at the end of one bone fits into a socket in the other bone. They allow rotational movement in all planes. The free range of movement provides less support and makes the joints more susceptible to dislocation than a hinge joint, e.g. the shoulder and hip joints.

pelvic (or pectoral) girdle articular cartilage

synovial membrane rane

capsule

synovial fluid

femur (or humerus)

Figure 6.6 Structure of the parts of a ball and socket joint

Movement of a limb

When a muscle contracts it exerts a pull, but it cannot exert a push when it relaxes. Therefore, two muscles, known as an antagonistic pair, are always needed to produce movement at a moveable joint: • The flexor muscle is the muscle that bends the joint when it contracts. • The extensor muscle is the muscle that straightens the joint when it contracts. 6 The skeletal system

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Both muscles are attached by tendons at one of their ends to a bone that does not move and at the other end to a bone that does move. The origin of a muscle is the attachment point of the end of the muscle to a bone that does not move during contraction. The insertion of a muscle is the attachment point of the end of the muscle to the bone that moves during contraction. The origin is usually as far away as possible from the joint and the insertion is usually very close to the joint.

Movement of the elbow joint

The biceps and triceps muscles move the radius and ulna causing the elbow joint to bend or straighten: • The biceps is the flexor muscle. Its origin is on the scapula which does not move, and its insertion is on the radius close to the elbow joint. • The triceps is the extensor muscle. Its origin is on the scapula and top of the humerus which do not move, and its insertion is on the ulna close to the elbow joint. To bend the elbow joint, the biceps contracts and the triceps relaxes. To straighten the elbow joint, the triceps contracts and the biceps relaxes. two origins of the biceps

tendons

scapula

biceps (flexor) – contracts pulling the radius and ulna upwards humerus triceps (extensor) – relaxes

radius ulna

a radius and ulna raised

three origins of the triceps triceps – contracts pulling the radius and ulna downwards

biceps – relaxes insertion of the biceps

insertion of the triceps b radius and ulna lowered

Figure 6.7 Movement of the elbow joint

The effect of exercise on the skeletal system Exercise has many benefits: • It improves muscle tone, which is the unconscious low-level contraction of muscles while they are at rest. Good muscle tone is important because it maintains balance and a good, upright posture, and it keeps muscles in an active state ready for coordinated action. • It increases production of synovial fluid in joints which keeps joints healthy, reduces friction and increases flexibility.

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• It improves the strength and elasticity of ligaments, which increases the range of movement at joints. • It stimulates the growth of muscle tissue, which increases muscle size and strength. • It encourages bone to lay down more mineral matter so bones become denser and stronger, which reduces the risk of fractures and osteoporosis.

Factors which adversely affect the skeletal system Poor posture

Posture refers to the relative position of the different parts of the body. A poor posture strains muscles and causes them to need more energy to keep the body upright, which leads to fatigue and backache. It also changes the curvature of the spine, which leads to back, neck and shoulder pain, puts stress on certain joints and wears down the intervertebral discs in the spine causing a decrease in height. Poor posture also causes major organs to become compressed and to function less efficiently. Compression of the lungs and airways makes breathing less efficient, compression of the digestive system makes it harder to digest food, and compression of blood vessels makes it harder for blood to circulate properly.

Poor foot-wear

Wearing shoes with high heels causes the body weight to shift forwards to the ball of the foot, leading to painful arches and a change in the curvature of the spine, which causes bad posture and can result in lower back pain. High heels also cause calf muscles to shorten and bulge, and place excess pressure on knee and hip joints. Wearing badly fitting shoes, narrow pointed shoes or high heels can lead to corns, bunions, hammer toe or ingrown toenails.

Obesity

Extra weight puts strain on the skeleton, especially the joints. This causes cartilage to wear down and leads to arthritis.

An unbalanced diet

A diet deficient in vitamin D leads to rickets in children (see page 23) and osteomalacia in adults. A diet deficient in calcium leads to rickets in children and osteoporosis in adults. A diet deficient in protein can cause a decrease in bone density and muscle mass.

The importance of locomotion to humans

Many human activities involve locomotion, i.e. movement from one place to another. Locomotion is essential for work and recreation, to find food, to find a partner for reproduction, to escape from danger, to avoid being overcrowded and for exercise to keep the body healthy. Walking on their two hindlimbs means humans can use their forelimbs and hands for other activities, e.g. manipulating tools and writing.

Revision questions

1 a Distinguish between bone and cartilage. 2 3

b State TWO reasons why cartilage is important in the skeleton. By referring to the different parts of the human skeleton, discuss THREE of its functions. Distinguish between a tendon and a ligament. 6 The skeletal system

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4 a What is a joint?

5 6 7 8 9

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b How does movement at a hinge joint differ from movement at a ball and socket joint? c Identify TWO places in the human body where you would find EACH type of joint named in b above. a Why are two muscles needed to bring about movement of a hinge joint? b Explain how muscles of the leg bring about bending and straightening of the knee joint. Name the muscle that bends Jaden’s elbow joint and the muscle that straightens it. What is the difference between the insertion and the origin of a muscle? What is meant by ‘muscle tone’ and why is good muscle tone important? Outline the adverse effects that poor posture and poor foot-wear have on the skeleton.

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7 Excretion and homeostasis

Chemical reactions occurring in the human body constantly produce waste and harmful substances which must be got rid of from the body. It is also essential that the body’s internal environment is kept constant. The mechanisms of homeostasis are responsible for keeping conditions surrounding cells constant.

Excretion

Excretion is the process by which waste and harmful substances, produced by chemical reactions occurring inside body cells, i.e. the body’s metabolism, are removed from the body. Excretion is important because: • It prevents toxic metabolic waste substances from building up in the body and damaging or killing cells. • It helps to keep the environment within the body constant (see page 67). Excretion must not be confused with egestion, which is the removal of undigested dietary fibre and other materials from the body as faeces. This dietary fibre is not produced in the body’s metabolism, so its removal cannot be classed as excretion.

Metabolic waste excreted by humans

Humans produce the following waste substances during metabolism: • Carbon dioxide is produced in respiration. • Water is produced in respiration. • Urea (nitrogenous waste) is produced by the deamination of amino acids in the liver (see page 35). • Bile pigments, e.g. bilirubin, are produced by the breakdown of haemoglobin from red blood cells in the liver. • Heat is produced in general metabolism.

Excretory organs

Humans have several organs that excrete waste products. • The kidneys excrete water, urea and salts as urine. • The lungs excrete carbon dioxide and water vapour during exhalation (see page 39). • The skin excretes water, urea and salts as sweat. It also excretes heat (see page 68). • The liver excretes bile pigments. It also makes urea.

The kidneys and excretion

Humans have two kidneys which form part of the urinary system. The kidneys have two functions: • To excrete metabolic waste, mainly urea, from the body. • To regulate the volume and concentration of blood plasma and body fluids by regulating the amount of water they contain, a process known as osmoregulation (see page 67). Each kidney is divided into three regions, an outer region called the cortex, an inner region called the medulla, and a central hollow region called the pelvis. A renal artery carries blood to each kidney and a renal vein carries blood away. 7 Excretion and homeostasis

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posterior vena cava

aorta

renal artery left kidney

renal vein

ureter – tube carrying urine to the bladder

right kidney

bladder – bag with muscular walls which stores urine sphincter muscle – keeps the bladder closed. Relaxes to allow urine to leave the bladder

urethra – tube which carries urine out of the bladder

Figure 7.1 Structure of the urinary system in a human Each kidney is composed of thousands of kidney tubules or nephrons that produce urine. Each nephron begins with a cup-shaped Bowman’s capsule in the cortex which surrounds an intertwined cluster of capillaries called a glomerulus. After the Bowman’s capsule, each nephron is divided into three sections: • The first convoluted (coiled) tubule in the cortex. • The loop of Henle in the medulla. • The second convoluted (coiled) tubule in the cortex. An arteriole, which nephron Bowman’s capsule – branches from the renal cup-shaped structure artery, leads into each around the glomerulus collecting duct glomerulus. A capillary leads out of each glomerulus – glomerulus and branches cluster of to form a network of renal artery capillaries at capillaries which wrap the end of an renal vein arteriole around each nephron and then join into a venule, pelvis – hollow region which leads into the renal medulla – vein. Nephrons join into inner region collecting ducts in the cortex – cortex and these ducts lead outer region pyramid – inner part of through the medulla and the medulla out into the pelvis. ureter Figure 7.2 A longitudinal section through a kidney showing the position of a nephron

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Urine is produced in the nephrons by two processes: • Ultra-filtration or pressure filtration • Selective reabsorption Bowman’s capsule

first convoluted tubule

second convoluted tubule

A

glomerulus

C

arteriole from the renal artery

B

venule to the renal vein

B

cortex medulla

capillaries B loop of Henle flow of filtrate

C

collecting duct flow of urine

flow of blood

A Ultra-filtration occurs in the glomeruli. The diameter of the capillary entering each glomerulus from an arteriole decreases causing the pressure of the blood to increase. Small molecules are forced from the blood into Bowman’s capsule forming filtrate. Filtrate contains glucose, amino acids, hormones, vitamins, water, salts and urea. Blood cells and large molecules, e.g. plasma proteins, remain in the blood. B Selective reabsorption occurs in the nephrons. Useful substances are reabsorbed from the filtrate back into the blood travelling through the capillaries wrapped around each nephron: Glucose, amino acids, hormones, vitamins, some water and some salts are reabsorbed in the first convoluted tubule. Some water is reabsorbed in the loop of Henle. Some salts and some water are reabsorbed in the second convoluted tubule. Water is reabsorbed by osmosis, the other substances are reabsorbed by diffusion and active transport. C Filtrate containing urea, excess water and excess salts enters the collecting ducts where some water can be reabsorbed from it by osmosis. The filtrate, now called urine, travels down the collecting duct to the ureter and then to the bladder where it is stored.

Figure 7.3 Detailed structure of a nephron showing how urine is formed

Renal dialysis

When nephrons stop functioning properly so that they are unable to remove waste from the blood and regulate the volume and composition of blood plasma and body fluids, kidney failure occurs. Harmful waste, especially urea, builds up in the blood and can reach toxic levels resulting in death. Kidney failure can be treated by a kidney transplant or renal dialysis. During dialysis blood from a vein, usually in the arm, flows through a dialysis machine and is then returned to the body. In the machine, the blood is separated from dialysis fluid by a partially permeable membrane. Waste products, mainly urea, pass from the blood into the dialysis fluid together with excess water and excess salts. In this way, waste from the blood is removed and the volume and composition of the blood plasma and body fluids are regulated. Dialysis must occur at regular intervals; most people require three sessions a week, each lasting four hours.

The skin

The skin is the largest organ in the human body. It is made up of three layers: • The epidermis, which is the outermost layer. • The dermis, which is below the epidermis. • The subcutaneous layer, which is the bottom layer made up mainly of fat cells.

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nerve endings epidermis – three layers

hair hair follicle

sweat pore sebaceous gland

malpighian layer – actively dividing cells that form the other layers of the epidermis and contain melanin, a brown pigment

dermis – connective tissue

sweat duct sweat gland capillary – to the sweat gland arteriole

subcutaneous layer fat cells

cornified layer – dead cells rich in keratin. Layer is waterproof living layer – living cells

venule hair papilla – actively dividing cells form the hair

hair erector muscle

capillary network

Figure 7.4 A section through the human skin showing its structure Table 7.1 Functions of the structures of the skin Structure Function Epidermis Protects the body against pathogens, water loss, the Sun’s harmful ultraviolet rays and harmful chemicals in the environment. Sebaceous glands Secretes sebum, an oily substance, which helps to keep the skin soft, supple and waterproof, and inhibits the growth of bacteria. Nerve endings Detect various stimuli, e.g. touch, pressure, pain, temperature and hair movement. Hairs and hair erector Muscles contract causing hairs to stand upright. This causes ‘goose bumps’ muscles in humans, but traps a layer of air next to the skin which acts as insulation in hairy mammals to prevent heat loss. Arterioles and Help regulate the body temperature (see page 68). capillary networks Sweat glands Produce sweat by absorbing water, urea and salts from the blood passing through them. The sweat passes up the sweat ducts and onto the surface of the skin where the water evaporates and cools the body if it is too hot. Subcutaneous layer Protects the body against heat loss in low environmental temperatures and against damage by acting as ‘padding’.

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Homeostasis

Homeostasis is maintaining a constant internal environment. Conditions surrounding cells must be very carefully controlled; these include the water content or concentration of blood plasma and body fluids, levels of carbon dioxide in the blood, body temperature and blood sugar levels.

Feedback mechanisms and homeostasis

Homeostasis is achieved by using negative feedback mechanisms that involve both the nervous system and hormones. If the level of something in the body changes, receptors in the body detect the change and send messages to the appropriate effectors causing them to respond and return the level to normal, i.e. the effectors exert an opposite or negative effect.

level rises

corrective action taken by appropriate effector(s), i.e. muscles, glands or organs

normal level level drops

level drops normal level

corrective action taken by appropriate effector(s)

level rises

Figure 7.5 The principles of negative feedback mechanisms If the corrective mechanism fails, the level cannot be returned to normal and will continue to increase or decrease. This can result in a person’s health being impaired, e.g. diabetes, and may even cause death.

Osmoregulation

Osmoregulation is the regulation of the water content of blood plasma and body fluids. Their water content must be kept constant to prevent water moving into and out of body cells unnecessarily. • If body fluids contain too much water (become too dilute), water will enter body cells by osmosis. The cells will swell and may burst. Drinking a lot of liquid or sweating very little because of being in cold weather can cause body fluids to become too dilute. • If body fluids contain too little water (become too concentrated), water will leave body cells by osmosis. The cells shrink and the body becomes dehydrated. If too much water leaves cells, metabolic reactions cannot take place and cells die. Not drinking enough, excessive sweating or eating a lot of salty foods can cause body fluids to become too concentrated. The kidneys regulate the water content of body fluids by controlling how much water is reabsorbed into the blood plasma during selective reabsorption. This determines how much water is lost in urine. Control involves: • The hypothalamus of the brain, which detects changes in the concentration of blood plasma. • Antidiuretic hormone (ADH), which is produced by the pituitary gland at the base of the brain in response to messages from the hypothalamus. ADH is carried by the blood to the kidneys where it controls the permeability of the walls of the tubules and collecting ducts to water. 7 Excretion and homeostasis

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pituitary gland – releases very little or no ADH into the blood hypothalamus – detects blood plasma is too dilute

kidneys – tubule and collecting duct walls remain almost impermeable to water. Very little water is reabsorbed from the filtrate. A lot of dilute urine is produced

water content of blood rises

water content of blood drops

water content of blood is normal

water content of blood is normal

water content of blood drops

water content of blood rises

hypothalamus – detects blood plasma is too concentrated

kidneys – ADH makes tubule and collecting duct walls more permeable to water. Most of the water is reabsorbed from the filtrate. Very little concentrated urine is produced pituitary gland – releases ADH into the blood

Figure 7.6 Osmoregulation

Regulation of body temperature Humans must maintain a constant internal body temperature of 37 °C for enzymes to function correctly. Most heat is gained from metabolic processes, mainly respiration, and the blood carries this heat around the body. Heat is lost mainly by conduction, convection and radiation through the skin, and also by evaporation of water during exhaling and sweating. The hypothalamus of the brain detects changes in temperature of the blood and sends messages to appropriate effectors, mainly in the skin.

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• Skin produces sweat. Water evaporates removing heat. • Vasodilation occurs. Arterioles supplying the capillaries in the skin dilate, increasing blood flow through them and heat loss. temperature rises • Respiration slows, especially in liver and muscle cells, above 37 °C decreasing heat production. normal body temperature – 37 °C

temperature drops normal body temperature – 37 °C

• Skin stops producing sweat. temperature drops • Vasoconstruction occurs. temperature below 37 °C rises Arterioles supplying the capillaries in the skin constrict, decreasing blood flow through them and heat loss. • Respiration speeds up, especially in liver and muscle cells, increasing heat production. • Shivering occurs to generate heat.

Figure 7.7 Control of body temperature 7 Concise Revision Course: Human and Social Biology

Note that heat and temperature are not the same: • Heat is the total amount of energy an object contains. It is measured in joules or J. • Temperature is a measure of how hot or how cold an object is. It is measured in degrees Celsius or °C.

Regulation of carbon dioxide levels

Carbon dioxide reacts with water in plasma and forms carbonic acid. As carbon dioxide levels increase the blood becomes more acidic (its pH decreases). Carbon dioxide levels must be controlled to stop the blood from becoming too acidic or too alkaline. Receptors, mainly in the medulla of the brain, detect changes in pH and send messages to the intercostal muscles and diaphragm to adjust the rate and depth of breathing (see page 40).

Regulation of blood sugar (glucose) levels

The normal concentration of glucose is approximately 80 mg per 100 cm3 of blood. The pancreas constantly monitors the level of glucose in the blood and secretes two hormones directly into the blood to keep the level constant: • If the blood glucose level rises, e.g. after a meal rich in carbohydrates, the pancreas secretes insulin. Insulin stimulates body cells to absorb glucose for respiration and the liver cells to convert excess glucose to glycogen, which it stores. • If the blood glucose level falls, e.g. between meals, or during exercise or sleep, the pancreas secretes glucagon. Glucagon stimulates liver cells to convert stored glycogen to glucose, which enters the blood. ettess pancreas secretes insulin into the bblood l od loo od blood glucose level increases normal blood glucose level

absorb sooorrbb body cells ab glucose for res respiration spppirraattiioon liver cells convert glucose to glycogen and store it

blood glucose level decreases normal blood glucose level

blood glucose level decreases pancreas secretes glucagon into the blood

blood glucose level increases liver cells break down stored glycogen into glucose and release it into the blood

Figure 7.8 Control of blood glucose levels Diabetes mellitus occurs when a person is unable to regulate his or her blood glucose levels such that they remain too high (see page 121).

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Revision questions

1 a Define ‘excretion’.

b Explain why egestion is not considered to be excretion. 2 Explain what will happen to an organism if excretion does not occur. 3 Construct a table to show the different excretory organs in the human body and what EACH excretes. 4 Outline how urine is produced in Marissa’s kidneys. 5 A person suffering from kidney failure can be treated using dialysis. Explain why this treatment must occur at regular intervals. 6 State the function of EACH of the following structures of the skin: a the epidermis b the subcutaneous layer c the sebaceous glands 7 a What is meant by the term ‘homeostasis’? b Explain why negative feedback mechanisms are important in homeostasis. 8 a Name the process by which the water content of body fluids is regulated. b Tyler plays tennis all day in the hot sun and drinks very little. What effect will his behaviour have on the quantity and concentration of his urine? Explain your answer. 9 a Distinguish between heat and temperature. b Explain the changes that occur in a person’s skin if their body temperature rises above 37 °C. 100 After a meal rich in carbohydrates, the blood glucose level rises. How does the body function to return the level to normal?

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8 Coordination and control

Humans must constantly monitor their environment and respond appropriately to any changes in this environment to help them survive. To do this, two systems are involved, the nervous system and the endocrine (hormonal) system.

Some important definitions

Stimulus is a change in the internal or external environment of an organism that initiates a response. Response is a change in an organism or part of an organism which is brought about by a stimulus. Receptor is the part of the organism that detects the stimulus. Effector is the part of an organism that responds to the stimulus.

Coordination by the nervous and endocrine systems

Coordination is brought about by receptors detecting stimuli, both internal and external, and passing messages on to the appropriate effectors causing them to respond. In humans, receptors are the sense organs, which contain specialised receptor cells, and effectors are muscles and glands. Two systems are responsible for this coordination, the nervous system and the endocrine (hormonal) system. Table 8.1 Control by the nervous and endocrine systems compared Control by the nervous system Control by the endocrine system Messages are carried as electrical impulses Messages are carried by chemicals (hormones) in along nerves. the blood. Messages are transmitted rapidly. Messages are usually transmitted slowly. Messages are carried to precise places in Messages are carried to generalised regions of the body. the body. Messages have an immediate effect on the body. Messages usually have a slow effect on the body. Messages have a short lasting effect on Messages usually have a long lasting effect on the body. the body.

The nervous system

The human nervous system is composed of neurones or nerve cells and is divided into two parts: • The central nervous system (CNS), which consists of the brain and the spinal cord. • The peripheral nervous system (PNS), which consists of cranial and spinal nerves that connect the central nervous system to all parts of the body. The PNS is divided into the autonomic nervous system and the voluntary or somatic nervous system.

Peripheral nervous system (PNS) cranial nerves

Central nervous system (CNS) brain spinal cord

spinal nerves

Figure 8.1 Organisation of the human nervous system 8 Coordination and control

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The brain

The human brain is an extremely complex organ. It has five main parts, each concerned with different functions. cerebrum – composed of two cerebral hemispheres

hypothalamus pituitary gland medulla oblongata

cerebellum spinal cord

Figure 8.2 The main parts of the human brain as seen in longitudinal section Table 8.2 Functions of the main parts of the brain Part of the brain Functions Cerebrum • Controls conscious thought, problem solving, decision making, planning and emotions. • Responsible for intelligence, memory, learning, speech and language. • Processes visual, auditory and other external information. • Coordinates voluntary actions. Cerebellum • Controls balance and posture. • Coordinates movement. Medulla • Controls automatic, involuntary actions, e.g. heart rate, breathing rate, blood pressure, peristalsis. oblongata Hypothalamus • Regulates body temperature. • Regulates the concentration of body fluids by controlling the release of ADH by the pituitary gland. • Controls reproduction by controlling the release of FSH and LH by the pituitary gland. Pituitary gland • Secretes a variety of hormones, e.g. ADH, GH, FSH, LH (see Table 8.4, page 77).

Neurones Neurones are specialised cells that conduct nerve impulses throughout the nervous system. All neurones have a cell body with thin fibres of cytoplasm extending from it called nerve fibres. Nerve fibres that carry impulses towards the cell body are called dendrites. Nerve fibres that carry impulses away from the cell body are called axons; each neurone has only one axon. There are three types of neurones: • Sensory neurones, which transmit impulses from receptors to the CNS. • Motor neurones, which transmit impulses from the CNS to effectors. • Relay or intermediate neurones, which transmit impulses throughout the CNS. They link sensory and motor neurones.

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receptor

node of Ranvier – constriction in the myelin sheath

myelin sheath – fatty sheath to insulate and protect the nerve fibre and speed up transmission of impulses

synaptic knobs cell body

axon – short

dendrite – long direction of nerve impulse

Figure 8.3 Structure of a sensory neurone effector – a muscle or gland

dendrites myelin sheath

cell body

axon – long

direction of nerve impulse

node of Ranvier

motor end plate

Figure 8.4 Structure of a motor neurone sensory neurone

PNS

CNS

receptor

synapse

relay neurone – does not have a myelin sheath

effector motor neurone

boundary of the CNS

Figure 8.5 The connection between a receptor and an effector Neurones have two major properties: • Irritability. They can convert a stimulus into an electrical (nerve) impulse. • Conductivity. They can transmit nerve impulses to other neurones, muscles or glands.

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Nerves Nerves are cordlike bundles of nerve fibres of neurones surrounded by connective tissue through which impulses pass between the CNS and the rest of the body. Nerves can be classified into three types based on what they are composed of: • Sensory nerves (afferent nerves) are composed of the nerve fibres of sensory neurones only and they carry impulses from receptors to the CNS. • Motor nerves (efferent nerves) are composed of nerve fibres of motor neurones only and they carry impulses from the CNS to effectors. • Mixed nerves are composed of nerve fibres of both sensory and motor neurones and they carry impulses in both directions, from receptors to the CNS and from the CNS to effectors. Nerves can be classified into two types based on where they connect to the CNS: • Cranial nerves connect to the brain. • Spinal nerves connect to the spinal cord.

Synapses

Adjacent neurones do not touch. There are tiny gaps called synapses between the synaptic knobs at the end of one axon and the dendrites or cell body of adjacent neurones. Chemicals known as neurotransmitters are released into the synapses by vesicles (small sacs) in the synaptic knobs. These chemicals cause impulses to be set up in adjacent neurones. This ensures impulses travel in one direction only and allows many neurones to interconnect.

Voluntary actions

A voluntary action is an action that is consciously controlled by the brain. The cerebrum of the brain initiates voluntary actions in one of two ways, both of which involve conscious thought: • It can coordinate incoming information from sensory neurones and initiate an action. • It can spontaneously initiate an action without receiving any incoming information. To initiate the action, impulses are sent from the cerebrum along relay neurones in the brain and spinal cord to motor neurones. These motor neurones then carry these impulses to skeletal muscles (effectors) initiating a conscious response, e.g. talking, writing, running. Voluntary actions: • are learned • are relatively slow • are complex because a variety of different responses can result from one stimulus.

Involuntary actions

An involuntary action is an action that occurs without conscious thought. Involuntary actions: • are not learned • are rapid • are simple because the same response always results from the same stimulus.

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There are two types of involuntary actions: • Actions controlled by the autonomic nervous system. • Reflex actions.

Actions controlled by the autonomic nervous system

The autonomic nervous system is composed of motor nerves only and regulates the functioning of internal organs, e.g. it controls breathing rate, heart rate, digestion, peristalsis and blood pressure. Information from internal receptors passes to the medulla of the brain which sends impulses out along motor neurones in cranial and spinal nerves to the effectors. The autonomic nervous system is important in homeostasis (see page 66).

Reflex actions A reflex action is a rapid, automatic, involuntary response to a stimulus by a muscle or gland. A reflex action is always initiated by an external stimulus. The pathway between receptor and effector is known as a reflex arc. It is simple and involves the following: • A receptor that detects the stimulus. • A sensory neurone that carries the impulse to the central nervous system. • A relay neurone in the central nervous system that carries the impulse to a motor neurone. • A motor neurone that carries the impulse away from the central nervous system. • An effector that responds to the stimulus. Simple reflexes are classified as cranial reflexes or spinal reflexes.

Cranial reflexes

In cranial reflexes, impulses pass through cranial nerves and the brain, e.g. the pupil reflex, blinking, sneezing, coughing and saliva production. 1 Bright light stimulates light sensitive cells of the retina of the eye

eye light rays

2 Impulses travel along a sensory neurone to the brain

iris

boundary of the brain

3 Impulses travel through a relay neurone to a motor neurone in the brain

pupil circular muscles

5 Circular muscles of the iris contract causing the diameter of the pupil to decrease

4 Impulses travel along a motor neurone to the iris of the eye

Figure 8.6 The pupil reflex 8 Coordination and control

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Spinal reflexes

In spinal reflexes, impulses pass through spinal nerves and the spinal cord. Spinal reflexes include the knee jerk reflex which lacks a relay neurone, and the withdrawal reflex in response to pain, e.g. when the finger is pricked, pain receptors are stimulated and the hand is rapidly withdrawn from the source of the pain. neurone – extensor muscle sensory in a spinal nerve stretch receptor 3 knee cap 6

2 1

femur tibia

1 2 3 4 5 6

dorsal root of spinal nerve – composed of sensory fibres

5 motor neurone – in a spinal nerve nerve endings in the extensor muscle spinal nerve – composed of sensory and motor fibres

Stimulus, a tap just below the knee cap. Stretch receptor in the muscle is stimulated. Impulses travel along a sensory neurone into the spinal cord. Impulses travel directly into a motor neurone in the spinal cord. Impulses travel along the motor neurone to the extensor muscle of the leg. The extensor muscle contracts causing the lower leg to rise.

dorsal root ganglion – contains cell bodies of sensory neurones

4

white matter – composed of axons by grey matter – surrounded myelin sheaths ventral root of mainly relay spinal nerve – and composed of motor neurones cell bodies fibres spinal cord

Figure 8.7 The knee jerk reflex showing the structure of the spinal cord

Revision questions

1 Give THREE differences between coordination by the nervous system and

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coordination by the endocrine system. 2 Describe the main divisions of the nervous system. 3 Give ONE function of EACH of the following regions of the brain: a the medulla oblongata b the cerebellum c the cerebrum 4 a Distinguish between a neurone and a nerve. b Name the THREE types of neurones found in the nervous system and indicate the function of EACH. c Identify the TWO major properties of all neurones. 5 What is a synapse and why are synapses important in the nervous system? 6 Distinguish between a voluntary action and an involuntary action and give TWO examples of each. 7 What is the autonomic nervous system and what does it control? 8 What is a reflex action? 9 Jan pricked her finger and immediately withdrew her hand from the source of the pain. Draw a simple flow diagram to show the pathway along which the impulses passed in Jan’s body to bring about her response. 8 Concise Revision Course: Human and Social Biology

Sense organs

Sense organs contain specialised receptor cells that detect changes in the environment, i.e. stimuli. The cells turn these stimuli into electrical impulses which travel along sensory neurones to the CNS. The cerebrum of the brain then interprets these messages as sensations of seeing, hearing, smelling, tasting and touching. Table 8.3 Sense organs in the human body Sense organ Specialised receptor cells Stimuli detected Eyes Rods and cones (photoreceptors) in the retina. Light. Ears Mechanoreceptor cells in the inner ear. Sound waves and the position of the head. Nose Olfactory cells (chemoreceptors) in the top Chemicals in the air. of the nasal cavities. Tongue Taste receptor cells (chemoreceptors) in the Chemicals in food. taste buds. Four tastes are detected; sweet, sour, salty and bitter. Skin Touch receptor cells. Touch and texture. Pressure receptor cells. Pressure. Pain receptor cells. Pain and itching. Temperature receptor cells. Hot and cold.

The eye

The eye detects light that has been reflected from an object and converts it into nerve impulses. The impulses are transmitted along the optic nerve to the brain, which translates them into a precise picture of the object. The eyes are situated in bony sockets of the skull called orbits and have muscles attached to move them. The orbits protect the back of each eye from damage, and the eyelids and eyelashes protect the front from foreign particles. Tears, produced by tear glands above each eye, keep the eyes moist, wash away foreign particles and contain an enzyme that destroys microorganisms. conjunctiva – thin, transparent layer continuous with the lining of the eyelids. Protects the cornea cornea – transparent front part of the sclera. Refracts (bends) light rays onto the retina

ciliary body

vitreous humour – jelly-like fluid. Maintains the shape of the eyeball sclera – tough, white, fibrous coat. Protects the eyeball

aqueous humour – colourless fluid. Maintains the shape of the cornea

choroid – contains blood vessels which supply the retina with food and oxygen, and melanin to prevent reflection of light inside the eye

lens – transparent, elastic, biconvex structure. Makes fine adjustments to focus light rays on the retina

fovea – contains cones only. The most sensitive part of the retina, most light rays are focused here

pupil – hole in the centre of the iris. Allows light to enter the eyeball

retina – contains light-sensitive cells called rods and cones. Where the image forms

iris – coloured disc composed of muscle. Controls the amount of light entering the eye suspensory ligament – attaches the lens to the ciliary body

optic nerve – carries impulses from the retina to the brain ciliary muscle – circular ring of muscle running through the ciliary body. Alters the shape of the lens during accommodation

blind spot – point where the optic nerve leaves the eye. No light-sensitive cells are present

Figure 8.8 Structure and functions of the parts of the human eye, as seen in longitudinal section 8 Coordination and control

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Image formation

In order to see, light rays from an object must be refracted (bent) as they enter the eye so that they form a clear image of the object on the receptor cells of the retina. Being convex in shape, both the cornea and the lens refract the light rays. light rays from the object

3 An image of the object is formed on the retina. This stimulates the light-sensitive cells of the retina. The image is inverted, reversed and smaller than the object

object

1 The cornea refracts the light rays 2 The lens refracts the light rays focusing them onto the retina

4 The optic nerve carries the impulses to the brain. The brain turns the image the correct way up, the correct way round and forms an impression of size, shape, colour and distance away of the object

Figure 8.9 Formation of an image in the eye

Detection of light intensity and colour by the eye

The retina is composed of two types of specialised light-sensitive cells or photoreceptors: • Rods function in low light intensities. They are responsible for detecting the brightness of light and are located around the sides of the retina. Images falling on the rods are seen in shades of black and white only. • Cones function in high light intensities. They are responsible for detecting colour and fine detail, and are mainly located around the back of the retina. The fovea is composed entirely of cones which are packed closely together. There are three types which detect either the red, green or blue wavelengths of light.

Control of the amount of light entering the eye

The size of the pupil controls the amount of light entering the eye. Muscles of the iris control the pupil size. wide pupil – allows as much light as possible to enter the eye

circular muscles relax

radial muscles contract

circular muscles contract

radial muscles relax a dim light

Figure 8.10 Controlling the amount of light entering the eye

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b bright light

narrow pupil – reduces the amount of light entering the eye, preventing damage to the retina

Focusing light onto the retina – accommodation

By changing shape, the lens makes fine adjustments to focus the light rays onto the retina. Changing the shape of the lens to focus light coming from different distances onto the retina is called accommodation and it is brought about by the ciliary muscles in the ciliary body. ciliary muscle relaxes – its circumference increases suspensory ligaments are pulled tight by the ciliary muscle lens is pulled thin by the suspensory ligaments

cornea bends the light rays

thin lens bends the light rays slightly to focus on the retina light rays from the distant point focus on the fovea of the retina

light rays from a distant point

a focusing on a distant object ciliary muscle contracts – its circumference decreases

cornea bends the light rays

suspensory ligaments slacken lens is allowed to spring into a bulged shape

light rays from the near point focus on the fovea of the retina light rays from a near point bulged lens bends the light rays a lot to focus on the retina

b focusing on a near object

Figure 8.11 Accommodation

Sight defects and their corrections Short-sightedness (myopia)

A person with short sight can see near objects clearly, but distant objects are out of focus. Light rays from near objects focus on the retina; light rays from distant objects focus in front of the retina. It is caused by the eyeball being too long from front to back or the lens being too curved (thick). It is corrected by wearing diverging (concave) lenses as spectacles or contact lenses. light rays from a distant point

diverging lens bends light rays outwards before they enter the eye

focus of light rays from the distant point before correction – in front of the retina

focus of light rays from the distant point after correction – on the retina

Figure 8.12 The cause and correction of short sight 8 Coordination and control

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Long-sightedness (hypermetropia)

A person with long sight can see distant objects clearly, but near objects are out of focus. Light rays from distant objects focus on the retina; light rays from near objects focus behind the retina. It is caused by the eyeball being too short from front to back or the lens being too flat (thin). It is corrected by wearing converging (convex) lenses as spectacles or contact lenses. light rays from a near point

converging lens bends light rays inwards before they enter the eye

focus of light rays from the near point before correction – behind the retina focus of light rays from the near point after correction – on the retina

Figure 8.13 The cause and correction of long sight

Old sight (presbyopia)

A person with old sight finds it increasingly difficult to see near objects clearly. It occurs because the lens loses its elasticity as a person ages and the ciliary muscles weaken so that the lens is less able to curve. It is corrected by wearing converging lenses to look at near objects.

Astigmatism

Both near and distant object appear blurry or distorted to a person who has astigmatism. It occurs if the cornea or lens is unevenly curved so not all light rays are equally refracted and not all focus on the retina. It is corrected by wearing unevenly curved lenses that counteract the uneven curvature in the eye.

Glaucoma

Glaucoma is a condition in which the pressure of the fluid within the eye increases due to the flow of aqueous humour from the eye being blocked. If left untreated, the optic nerve becomes damaged and it can lead to blindness. The most common type develops slowly and causes a gradual loss of peripheral (side) vision. Glaucoma is treated with eye drops to reduce fluid production or improve the flow of fluid from the eye, or by laser treatment or surgery to open the drainage channels.

Cataract

A cataract is a cloudy area that forms in the lens. It develops slowly and, as it increases in size, it leads to cloudy or blurred vision, halos forming around lights, colours appearing faded and difficulty seeing in bright light and at night. It is usually caused by ageing and is usually corrected by surgery to remove the clouded lens and to replace it with an artificial lens.

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Figure 8.14 An eye with a cataract 8 Concise Revision Course: Human and Social Biology

The endocrine system

The endocrine system is composed of endocrine glands or ductless glands which secrete hormones directly into the blood.

thyroid gland – in front of the trachea in the neck pancreas – in the loop of the duodenum testis – in the scrotal sac in males

pituitary gland – attached to the hypothalamus on the underside of the brain

adrenal gland – immediately above the kidney ovary – at the end of the fallopian tube in females

Figure 8.15 The position of the main endocrine glands Table 8.4 Hormones of the main endocrine glands and their functions Endocrine gland Hormone(s) Function(s) Pituitary gland Antidiuretic Controls the water content of blood plasma and body hormone (ADH) fluids by controlling water reabsorption in the kidney (see page 63). Growth hormone • In children: stimulates growth by stimulating protein synthesis in cells and bone growth. (GH) • In adults: helps maintain healthy bone and muscle masses. Follicle stimulating • In females: helps regulate the menstrual cycle by stimulating the development and maturation of the hormone (FSH) follicles and ova in the ovaries and stimulating the ovaries to produce oestrogen (see page 86). • In males: helps control production of sperm in the testes. Luteinising hormone • In females: helps regulate the menstrual cycle by stimulating ovulation and the development of the corpus (LH) luteum in the ovaries (see page 86). • In males: stimulates the production of testosterone by the testes. Thyroid gland Thyroxine Controls the rate of metabolism and energy production in cells, and physical growth and mental development, especially in children. Adrenal glands Adrenaline (flight, Released in large amounts when frightened, excited or fright or fight anxious. Speeds up metabolism, mainly respiration, and hormone) increases blood sugar levels, heartbeat, breathing rate and blood supply to muscles, i.e. it triggers the fight-or-flight response and gives the feeling of fear. Pancreas Insulin and glucagon Regulate blood glucose levels (see page 69). 8 Coordination and control

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Endocrine gland Hormone(s) Ovaries Oestrogen (produced by the Graafian follicle)

Placenta during pregnancy Testes

Progesterone (produced by the corpus luteum) Progesterone Testosterone

Function(s) Controls the development of female secondary sexual characteristics at puberty, i.e. development of breasts, pubic and underarm hair, and a broad pelvis. Helps regulate the menstrual cycle by stimulating the uterus lining or endometrium to thicken each month after menstruation (see page 86). Helps regulate the menstrual cycle by maintaining a thick uterus lining after ovulation each month (see page 86). Maintains a thickened uterus lining during pregnancy, which prevents menstruation. Stimulates the growth of milk-producing glands in the breasts during pregnancy. Controls the development of male reproductive organs and secondary sexual characteristics at puberty, i.e. development of a deep voice, facial and body hair, muscles and broad shoulders. Controls sperm production in the testes.

Revision questions

100 Make a list of the different sense organs in the human body and indicate the stimulus 11 122 133 144 155 166

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or stimuli detected by EACH. Construct a table to show the function of EACH of the following parts of the eye: the conjunctiva, the sclera, the pupil, the choroid, the optic nerve and the vitreous humour. Explain how an image is formed in Omari’s eye. Explain how Samara’s eyes adjust when she: a walks from a dimly lit room into the bright sunshine b looks at a book in her hand after watching an aeroplane in the sky. Malik has his eyes tested and is told that he is short sighted. Explain the possible cause of his sight defect and how it can be corrected. What is a cataract and how can it be treated? For EACH of the following endocrine glands, identify where the gland is located in the body, name the hormone it produces and outline the functions of the hormone: a the thyroid gland b the adrenal glands c the testes

8 Concise Revision Course: Human and Social Biology

9 The reproductive system

All living organisms must produce offspring in order for their species to survive. Reproduction is the process by which living organisms generate new individuals of the same kind as themselves. There are two types of reproduction, asexual reproduction and sexual reproduction.

Asexual and sexual reproduction compared Asexual reproduction

Asexual reproduction involves only one parent and offspring are produced by mitosis (see pages 102–3). All offspring produced asexually from one parent are genetically identical, i.e. they do not show variation, and are collectively called a clone. The process is rapid because it does not involve gamete production, finding a mate, fertilisation and embryo development. Asexual reproduction occurs in unicellular organisms, e.g. Amoeba and bacteria, in fungi, in some plants and in a few animals.

Sexual reproduction

Sexual reproduction involves two parents. Gametes, or sex cells, are produced in reproductive organs by meiosis (see pages 103–4). A male and a female gamete fuse during fertilisation to form a single cell called a zygote. The zygote divides by mitosis to form an embryo and ultimately an adult. Offspring produced sexually receive genes from both parents, therefore they possess characteristics of both parents, i.e. they show variation. The process is slow because it involves gamete production, finding a mate, fertilisation and embryo development.

The female and male reproductive systems The female reproductive system

The female gametes are called ova and they are produced in two ovaries which form part of the female reproductive system. fallopian tube or oviduct – narrow tube with muscular walls lined with cilia. Transports ova from the ovary to the uterus. Where fertilisation occurs

ovary – oval-shaped. Produces ova and secretes female sex hormones uterus or womb – pearshaped. Where the foetus grows and develops during pregnancy

cervix – ring of muscle around the neck of the uterus. Keeps the neck closed during pregnancy

uterus lining or endometrium – has a rich blood supply. Where the embryo is implanted uterus wall – thick and muscular. Stretches during pregnancy to accommodate the developing foetus. Contracts during birth vagina – thin-walled, muscular passage from the uterus to the outside. Receives the male penis and where sperm is deposited during intercourse. Stretches to let the baby out during birth

Figure 9.1 Structure and function of the parts of the female reproductive system 9 The reproductive system

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The male reproductive system

The male gametes are called sperm or spermatozoa and they are produced in the testes which form part of the male reproductive system. that secrete fluid seminal vesicle glands which mixes with sperm prostate gland to form semen. The fluid stimulates the sperm to swim

urethra from the bladder vas deferens or sperm duct – muscular tube. Carries sperm to the urethra epididymis – series of coiled tubules. Stores sperm penis – connective tissue with many blood spaces surrounding the urethra. Becomes erect during intercourse to deposit sperm in the vagina

urethra – muscular tube. Carries semen to the outside of the body testis – oval-shaped, composed of many coiled seminiferous tubules. Produces sperm and secretes male sex hormones scrotal sac or scrotum – a sac of skin. Holds the testes at a temperature slightly below 37 °C to enable sperm to develop normally and to survive foreskin – retractable skin. Protects the head of the penis

Figure 9.2 Structure and function of the parts of the male reproductive system

Production and structure of ova and sperm

At birth, each female ovary contains many thousand immature ova. Each is surrounded by a fluidfilled space that forms a primary follicle. Each month between puberty at about 11 to 13 years old, and menopause at about 45 to 50 years old, one immature ovum develops into a mature ovum. About 450 immature ova will mature in a woman’s lifetime. To produce a mature ovum, the immature ovum undergoes meiosis (see pages 103–4). One of the four cells produced develops into a mature ovum which is released during ovulation. 1 Immature ova inside fluid-filled primary follicles

2 An immature ovum undergoes meiosis. One cell matures and the fluid-filled space increases in size forming a Graafian follicle

mature ovum 5 The corpus luteum breaks down 4 The empty Graafian follicle forms a corpus luteum (yellow body)

3 Ovulation – the Graafian follicle bursts, releasing the mature ovum into the oviduct

Figure 9.3 Production of an ovum in an ovary

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Sperm cells are produced continuously from puberty in the seminiferous tubules of the testes. Cells in the tubule walls undergo meiosis and all the cells produced develop into mature sperm. These are stored in the epididymis until ejaculation. Table 9.1 Ova and sperm cells compared Ova Sperm cells Structure layer of follicle cells – act membrane

as protection

layer of jelly

nucleus cytoplasm containing yolk

Production One is produced each month from puberty to menopause. Movement Are moved down an oviduct after ovulation by muscular contractions of the oviduct walls and beating of the cilia. Life span Live for about 24 hours after ovulation.

tail – for swimming

middle piece – contains mitochondria to release energy for swimming nucleus

small amount of cytoplasm

head acrosome – contains enzymes to dissolve a passage into the ovum

Thousands are produced continuously from puberty. Swim actively using their tails when mixed with secretions from the seminal vesicles and prostate gland during ejaculation. Can live for about 2 to 3 days in the female body after ejaculation.

Cancers of the reproductive systems

Cancer is a disease resulting from abnormal cells developing and dividing in an uncontrolled way. These cells replace normal cells and usually produce a tumour (lump). Some of the cells can also metastasise, i.e. spread to other parts of the body. Cancer can be treated by surgery to remove the tumour or the entire organ containing the tumour, radiotherapy or chemotherapy. Cancer can affect various parts of the reproductive systems. Table 9.2 Cancers of the reproductive systems Type of Organ Notes cancer affected Ovarian Ovary Symptoms include abdominal pain and lower back pain. Cervical Cervix Usually caused by the human papilloma virus (HPV) passed on through sexual contact and can be detected by a cervical smear test (Pap smear test). Early stages are free of symptoms. Vaginal bleeding, pain during sexual intercourse and vaginal discharge are symptoms of the later stages. Uterine Uterus The most common symptom is abnormal bleeding from the vagina. Breast Breast A tumour in a breast can be detected by hand or by a mammogram (X-ray). Breast reconstruction often follows surgery when the entire breast is removed. Prostate Prostate A tumour forms in the gland, which starts to block the urethra causing gland frequent but slow urination. It can be diagnosed using a prostate specific antigen (PSA) blood test or a digital rectal examination (DRE). Testicular Testis A tumour in a testis can be detected by hand. Symptoms may include testicular discomfort.

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The menstrual cycle

yravo na ni stneve

This is a cycle of about 28 days comprising two main events: • Ovulation, which is the release of an ovum from an ovary. • Menstruation, which is the loss of the uterus lining from the body. This starts to occur about 14 days after ovulation if fertilisation has not occurred. The cycle is controlled by four hormones which synchronise the production of an ovum with the uterus lining being ready to receive it if fertilised. The start of the cycle is taken from the start of menstruation: • Follicle stimulating hormone (FSH) is secreted by the pituitary gland at the beginning of the cycle. FSH stimulates a Graafian follicle to develop in an ovary and an ovum to mature inside the follicle. FSH stimulates the follicle to produce oestrogen. • Oestrogen is produced by the Graafian follicle mainly during the second week of the cycle. Oestrogen stimulates the uterus lining to thicken and its blood supply to increase after menstruation. Oestrogen causes the pituitary gland to stop secreting FSH and to secrete luteinising hormone (LH). • Luteinising hormone (LH) is secreted by the pituitary gland in the middle of the ovulation corpus luteum cycle. corpus luteum ovum matures inside a Graafian (day 14) develops breaks down follicle A sudden rise in LH causes ovulation to take place. LH stimulates the corpus 1 7 14 21 28 luteum to develop in the time (days) ovary after ovulation and oestrogen secreted progesterone secreted by to secrete progesterone. by Graafian follicle the corpus luteum • Progesterone is produced by the corpus luteum during the third week of the cycle. progesterone Progesterone causes the level oestrogen uterus lining to increase level slightly in thickness and 1 7 14 21 28 remain thick. time (days) If fertilisation does progesterone decrease in progesterone not occur, the corpus causes the uterus causes the uterus lining to oestrogen luteum breaks down stimulates the lining to remain thick begin to break down uterus lining during the fourth week to thicken and reduces secretion me nst of progesterone. The r ua tion decrease in progesterone causes the uterus lining to begin to break down, and the pituitary gland to 1 7 14 21 28 secrete FSH at the end of time (days) the fourth week. Figure 9.4 A summary of the events occurring during the menstrual cycle senomroh nairavo fo level

gninil suretu eht fo ssenkciht

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Bringing sperm and ova together

When a male becomes sexually excited, blood spaces in the penis fill with blood. The penis becomes erect and is placed into the female vagina. Semen, composed of sperm and secretions from the seminal vesicles and prostate gland, is ejaculated into the top of the vagina by muscular contractions of the tubules of the epididymis and sperm ducts. The sperm swim through the cervix and uterus and into the fallopian tubes.

From fertilisation to birth Fertilisation

If an ovum is present in one of the fallopian tubes, one sperm enters, leaving its tail outside. A fertilisation membrane immediately develops around the ovum to prevent other sperm from entering, and the nuclei of the ovum and sperm fuse to form a zygote.

Implantation

The zygote divides repeatedly by mitosis using yolk stored in the original ovum as a source of nourishment. This forms a ball of cells called the embryo, which moves down the oviduct and sinks into the uterus lining, a process called implantation. Food and oxygen diffuse from the mother’s blood into the embryo, and carbon dioxide and waste diffuse back into the mother’s blood.

Pregnancy and development

The cells of the embryo continue to divide and some of the cells develop into the placenta. The placenta is a disc of tissue with finger-like projections called villi which project into the uterus lining and give the placenta a large surface area. Capillaries run throughout the placenta, including inside the villi. The embryo is joined to the placenta by the umbilical cord, which has an umbilical artery and umbilical vein running through it. These connect the capillaries in the embryo with those in the placenta. muscular wall of the uterus

umbilical cord embryo or foetus

placenta – disc-shaped. Provides a large surface area for the exchange of substances between the mother’s and the embryo’s blood. Secretes progesterone, which maintains a thickened uterus lining thickened lining of the uterus with a rich blood supply capillary network throughout the placenta

umbilical vein – carries dissolved food and oxygen to the embryo umbilical artery – carries dissolved carbon dioxide and other waste away from the embryo

food and oxygen diffuse from the mother’s blood in the uterus lining into the embryo’s blood in the placenta. Carbon dioxide and waste diffuse from the embryo’s blood into the mother’s blood

villi – increase the contact area between the placenta and the uterus lining amnion

support and protect the amniotic fluid embryo plug of mucus in the cervix vagina

Figure 9.5 The developing human embryo/foetus in the uterus 9 The reproductive system

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The placenta allows exchange of materials between the mother’s blood and the embryo’s blood, but prevents mixing of the two bloods, which may be of different types (see Figure 9.5, page 87). It also prevents certain unwanted substances entering the embryo’s blood from the mother’s blood, e.g. many bacteria and viruses. The developing embryo is surrounded by a thin, tough membrane called the amnion, which forms a sac containing amniotic fluid. Table 9.3 The development of a human embryo/foetus Time after fertilisation 7 to 10 days 4 weeks

Characteristics

A hollow ball of cells, which is implanted in the uterus lining. The brain, eyes and ears are developing along with the nervous, digestive and respiratory systems. Limb buds are forming and the heart is beginning to beat. 8 weeks The embryo has a distinctly human appearance. All the vital organs have been formed and limbs with fingers and toes are developed. 10 weeks The embryo is now known as a foetus. External genitals are beginning to appear, fingernails and toenails form and the kidneys start to function. 11 to 38 weeks The foetus continues to grow and the organs continue to develop and mature. 38 weeks Birth occurs. Note that the gestation period (pregnancy) is considered to last for 40 weeks or 280 days since it is calculated from the first day of the last menstrual cycle and not from the time of fertilisation.

Birth

The foetus turns so it lies head down. Secretion of progesterone by the placenta is reduced and this stimulates the pituitary gland to secrete the hormone oxytocin. Oxytocin stimulates muscles in the uterus wall to start contracting, i.e. labour begins. The amnion bursts and the contractions strengthen and cause the cervix to gradually dilate. When fully dilated, strong contractions push the baby, head first, through the cervix and vagina. The baby starts to breathe and the umbilical cord is clamped and cut. The placenta is then expelled as the afterbirth by further contractions of the uterus wall.

The effect of pregnancy on the menstrual cycle

If fertilisation takes place, the corpus luteum remains in the ovary and it secretes increasing amounts of progesterone. This causes the uterus lining to increase in thickness and it prevents menstruation. As the placenta develops, it takes over secreting progesterone, which keeps the uterus lining thick and inhibits the development of mature ova in the ovaries and menstruation throughout pregnancy.

Prenatal and postnatal care Prenatal or antenatal care

Prenatal care, or care before birth, is essential to ensure the foetus grows and develops normally and healthily, and that the mother remains healthy throughout her pregnancy. During pregnancy the mother must: • Attend regular prenatal checkups with her doctor or clinic to monitor her health and the development of her baby. • Eat a balanced diet that contains adequate quantities of protein, carbohydrates, vitamins and minerals, especially calcium and iron, to ensure the foetus obtains all the nutrients it needs to grow and develop.

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• Not use drugs of any kind, especially alcohol, cigarettes and illegal drugs, which will harm the developing foetus, and she must protect herself against infectious diseases. • Exercise regularly to maintain fitness. • Prepare her body for the birth by attending prenatal classes, which teach correct exercises and breathing rhythms as well as how to care for her baby after the birth.

Postnatal care

Postnatal care, or care after birth, is essential to ensure the baby grows and develops healthily, and that the mother remains both physically and emotionally healthy. • The newborn baby should be breastfed, if possible for a minimum of 6 months, because: Breast milk contains all the nutrients the baby needs in the correct proportions. Breast milk contains antibodies, which protect the baby against bacterial and viral diseases. Breast milk is sterile so reduces the risk of infection, is at the correct temperature and is available whenever needed. Breastfeeding lowers the baby’s risk of developing asthma, allergies and other non-communicable diseases as it grows older. Breastfeeding creates a strong emotional bond between mother and baby. • The newborn baby must be kept warm and clean, have plenty of interaction with both parents and its surroundings, and be taken for regular checkups with the doctor. As the baby grows it must be vaccinated against infectious diseases, weaned onto semi-solid and solid food, cared for physically and emotionally, and given continual teaching. • The mother must continue to eat a balanced diet, not use drugs of any kind, exercise regularly and be given both physical and emotional support.

Birth control and family planning Methods of birth control (contraception)

A variety of methods are available to prevent pregnancy from occurring. They are designed to prevent fertilisation or to prevent implantation, and they can be natural, barrier, hormonal or surgical. Two methods, abstinence and the condom, also protect against the spread of sexually transmitted infections (STIs), e.g. HIV. When choosing a method, its reliability, availability, side effects and whether both partners are comfortable using it, must be considered. Table 9.4 Methods of birth control Method Abstinence Withdrawal

How the method works Advantages • Refraining from sexual • Completely effective. intercourse. • Protects against sexually transmitted infections. • Penis is withdrawn • No artificial device before ejaculation. needs to be used or pills taken, i.e. it is natural, therefore is acceptable to all religious groups.

Disadvantages • Relies on self-control from both partners. • Very unreliable since some semen is released before ejaculation. • Relies on self-control.

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Method Rhythm method

How the method works Advantages • Intercourse is restricted • No artificial device to times when ova needs to be used should be absent from or pills taken, i.e. it the oviducts. is natural, therefore is acceptable to all religious groups.

Spermicides

• •

Condom

•

• Diaphragm

•

• Intra-uterine • device (IUD or coil) • Contraceptive pill

•

• •

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Disadvantages • Unreliable since the time of ovulation can vary. • Restricts the time when intercourse can occur. • Unsuitable for women with an irregular menstrual cycle. Creams, jellies or foams • Easy to use. • Not reliable if used inserted into the vagina • Readily available. alone, should be used before intercourse. with a condom or diaphragm. Kill sperm. • May cause irritation or an allergic reaction. A latex rubber or • Very reliable if used • May reduce sensitivity polyurethane sheath correctly. so interferes with placed over the erect • Easy to use. enjoyment. penis or into the • Condoms can tear female vagina before • Readily available. allowing sperm to enter intercourse. • Protects against the vagina. sexually transmitted Acts as a barrier to • Latex may cause an prevent sperm entering infections. allergic reaction. the female body. A dome-shaped latex • Fairly reliable if used • Must be left in place rubber disc inserted correctly. for 6 hours after over the cervix before • Not felt, therefore, intercourse, but no intercourse. Should be not interfere with longer than 24 hours. used with a spermicide. does enjoyment. • Latex may cause an Acts as a barrier to allergic reaction. • Easy to use once the prevent sperm entering female is taught. • May slip out of place if the uterus. not fitted properly. A T-shaped plastic • Very reliable. • Must be inserted by a device, usually medical practitioner. Once fitted, no further containing copper or • action • May cause progesterone, inserted exceptisanrequired annual menstruation to be into the uterus by a checkup. heavier, longer or more doctor. painful. • No need to think Prevents sperm further about reaching the ova or contraception. prevents implantation. • Few, if any, side effects. A hormone pill, • Almost totally reliable if • Ceases to be effective if taken daily, which taken daily. one pill is missed. contains oestrogen is lighter, • May cause side effects and progesterone, or • Menstruation shorter and less painful. in some women, progesterone only. especially those who Prevents ovulation. smoke. Makes cervical mucus thicker and more difficult for sperm to swim through.

9 Concise Revision Course: Human and Social Biology

Method Surgical sterilisation (vasectomy in males, tubal ligation in females)

How the method works • The sperm ducts or oviducts are surgically cut and tied off. • Prevents sperm leaving the male body or ova passing down the oviducts.

Advantages Disadvantages • Totally reliable. • Usually irreversible. • No need to think further about contraception. • No artificial device needs to be used or pills taken. Note that one disadvantage of all methods except abstinence and condoms is that they do not protect against sexually transmitted infections.

Condoms

Diaphragm

Intra-uterine device (IUD) Figure 9.6 Methods of birth control

Contraceptive pills

The importance of family planning

Family planning involves making decisions about the number of children in a family and the time between their births. Contraception plays a major role in family planning. Family planning is important because: • If the family is small, parents have more time to spend with each child, so each child receives greater emotional and physical care and a better education from their parents. • It is less expensive to have a small family. 9 The reproductive system

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• It enables parents to decide at what age they wish to have a family, i.e. when they are young or later in life after pursuing their careers. • It decreases health risks to women and maternal deaths caused by unintended pregnancies and unsafe abortions. • It enables women to complete their education before having a family. • It enables women to participate fully in society and advance in the workplace by allowing them to plan when they have a family. From a global perspective, the human population is growing rapidly and predictions are that this will cause shortages of food, water, land and other natural resources, will increase pollution, the destruction of the environment, unemployment and the spread of disease, and will decrease living standards. Family planning can reduce population growth which should help maintain a healthy, productive environment without shortages, and should improve living standards.

Issues related to abortion

Abortion is the termination of a pregnancy. It can occur naturally, known as a spontaneous abortion or miscarriage, or it can be induced.

Spontaneous abortion

A miscarriage can occur for various reasons: • The foetus has a chromosomal abnormality. • The mother has a uterine abnormality so the embryo cannot implant properly in the lining, or she has a weak cervix that cannot hold the foetus in the uterus as it grows. • The mother suffers from certain medical conditions, such as diabetes or thyroid disease, that can make conditions in the uterus difficult for the embryo to survive. • The mother has an immune system disorder causing the foetus not to be accepted by her body. • The mother smokes very heavily, drinks too much alcohol or overdoses on illegal drugs during pregnancy.

Induced abortion

Abortion can be induced by the mother taking an abortion pill containing hormones or undergoing a surgical procedure. Induced abortion is a very controversial topic and is illegal in many parts of the world.

Arguments for the use of induced abortion

The following could be put forward as reasons for carrying out induced abortions: • If the health of the mother or of the foetus is at risk. • If the foetus has a severe genetic abnormality which would adversely affect the quality of life after birth and put a strain on other family members. • If the pregnancy is the result of rape and giving birth to an unwanted child would be a constant reminder to the mother of the traumatic event. • If the parents are unable to support a child or the child was conceived as a result of contraceptive failure or the child is not wanted for other reasons, abortions prevent unwanted children from being brought into the world.

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Arguments against the use of induced abortion

The following could be put forward as reasons against carrying out induced abortions: • They can be used as a form of contraception and lead to irresponsible behaviour. • They can give rise to medical complications, e.g. infection, and can lead to infertility, especially if carried out illegally by unqualified persons (back street abortions). • They can have a serious impact on a woman’s mental state, causing depression and other psychological problems, sometimes years after the abortion. • They are considered to be murder by persons who believe that life begins at conception, and many religions believe that abortion is morally wrong.

Revision questions

1 Distinguish between sexual and asexual reproduction and suggest ONE possible

advantage and ONE possible disadvantage of EACH. 2 By means of a labelled and annotated diagram, indicate the function of EACH of the different parts of the female reproductive system. 3 State the function of EACH of the following parts of the male reproductive system: a the epididymis b the sperm ducts c the prostate gland d the penis 4 a What happens in a person’s body to cause cancer to develop? b Identify TWO parts of the female reproductive system and TWO parts of the male reproductive system where cancer may develop. 5 a What happens during ovulation and menstruation? b Explain the role of oestrogen and progesterone in the menstrual cycle. 6 Outline how ova and sperm are brought together for fertilisation to occur. 7 What role does the placenta play in the development of a human embryo? 8 Outline the steps involved in the birthing process. 9 a Sabrina is 3 months pregnant. Outline some of the steps she should take to ensure the health of her developing baby. b After Sabrina gives birth, she is strongly advised to breastfeed her baby for a minimum of 6 months. Give FOUR reasons to support this advice. 100 Construct a table which explains how EACH of the following methods of birth control prevents pregnancy, and gives ONE advantage and ONE disadvantage of EACH method: the contraceptive pill, surgical sterilisation, the rhythm method and the condom. 11 Suggest THREE reasons why family planning is important. 12 a What is a spontaneous abortion? b Identify THREE possible causes of a spontaneous abortion.

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Exam-style questions – Chapters 3 to 9 Structured questions

1 a) Figure 1 is a diagram of the human digestive system. 1 3

4

2

A

 Figure 1 The human digestive system i) Name the structure labelled 1, and state its function. (2 marks) ii) Nikoli is 7 years old and his mother is beginning to worry that his legs are showing signs of bowing outwards, so she takes him to the doctor and the doctor suggests he might be lacking vitamin D. Identify ONE way Nikoli (1 mark) could increase his intake of vitamin D. iii) Which numbered structure in Figure 1 would vitamin D have an effect on? (1 mark) iv) Explain how increasing his intake of vitamin D would affect the structure (1 mark) identified in a) iii) above and help treat Nikoli’s condition. b) Table 1 gives the body mass index (BMI) of five people. A person with a healthy weight would have a body mass index between 18.5 and 24.9 kg per m2. Table 1 Body mass index of five people Name Body mass index in kg per m2 Akeem 37.9 Zane 5.4 Alex 28.6 Romain 43.0 Mitchell 22.5 i) Which person has the healthiest body mass index? ii) Draw a bar graph to represent the data in Table 1.

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Exam-style questions – Chapters 3 to 9

(1 mark) (3 marks)

2

iii) Which two people in Table 1 are most likely to be suffering from malnutrition? (2 marks) iv) Name a disease that EACH person identified in b) iii) might be suffering from and identify the main factors that could have led to the development of EACH disease (4 marks) named. Total 15 marks a) Distinguish between respiration and breathing. (2 marks) b) Figure 2 shows part of the human respiratory system.

B C

alveoli

Figure 2 Part of the human respiratory system i) Name the structures labelled B and C. (2 marks) ii) Complete the following sentence by filling in the blank spaces: To inhale, the external intercostal muscles and diaphragm muscles causing the ribcage to move upwards and , and the (3 marks) diaphragm to . iii) Identify TWO features of the alveoli that make them efficient in carrying (2 marks) out gaseous exchange. c) A study was carried out into the link between smoking levels and lung cancer. The researchers recorded the number of deaths from lung cancer per 100 000 individuals in the population, and the smoking levels of each person dying. The results for men aged 60 to 69 years are given in Table 2 below. Table 2 Death rates from lung cancer among men aged 60 to 69 years related to smoking levels Death rate per Level of smoking 100 000 population Never smoked 12 234 Smoked 20 cigarettes 30 years per day for: 40 years 487 576 Smoked 40 cigarettes 30 years per day for: 40 years 608 i) Which individuals are most at risk of dying from lung cancer? (1 mark) ii) Give TWO conclusions that the researches could have drawn from the results. (2 marks) Exam-style questions – Chapters 3 to 9

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d) Tamara used to be a very good sprinter; however, she started to smoke heavily and now finds that whenever she tries to run she quickly becomes breathless and at times she even collapses. i) Write a word equation to summarise what causes Tamara to collapse. ii) Other than lung cancer, suggest TWO ways that Tamara’s heavy smoking contributes to her breathlessness.

(1 mark) (2 marks) Total 15 marks

3 a) Figure 3 shows the internal structure of the heart. aorta anterior vena cava Q R

S

Figure 3 The internal structure of the heart i) Identify the parts labelled R and S. ii) What is the function of the structure labelled Q? iii) Complete Table 3 to compare the aorta with the anterior vena cava. Table 3 Differences between the aorta and the anterior vena cava Aorta Anterior vena cava Pressure of blood carried Thickness of the walls

(2 marks) (1 mark)

(2 marks) (2 marks)

iv) Humans have a double circulation. Explain what this means. b) Jerome is rushed to hospital complaining of a tight feeling and pain in his chest and pain in his arms, shoulders and neck. i) What might Jerome be suffering from? (1 mark) ii) Explain what could have led up to Jerome’s current situation. (3 marks) c) Sabrina spends all day sitting working at her computer and by the end of the day she notices that her feet and ankles appear swollen. i) By reference to her lymphatic system, explain why Sabrina’s feet and ankles (3 marks) are swollen. ii) What suggestion would you give to Sabrina to avoid the same thing (1 mark) happening again? Total 15 marks

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Exam-style questions – Chapters 3 to 9

4 a) State TWO functions of the skeleton, other than movement. b) Figure 4 is a diagram of a knee joint.

(2 marks)

F

5

Figure 4 A knee joint i) Name the type of joint shown in Figure 4. (1 mark) ii) Identify F and state its main function. (2 marks) iii) How does movement of the knee joint differ from movement at the hip joint? (2 marks) iv) Jordan is told by his doctor that he needs to have one of his knees replaced. (2 marks) Suggest TWO reasons why this might be necessary. c) Shakira works as a shop assistant and goes to the gym each day after work. i) Explain how Shakira’s elbow joint works as she bends and straightens it (4 marks) repeatedly during her daily workout using dumbbells. ii) Shakira wears high-heeled shoes to work each day. Suggest TWO adverse (2 marks) effects this might have on her body. Total 15 marks a) i) What is meant by the term ‘excretion’? (2 marks) ii) Name ONE excretory organ, other than the kidney, found in the human body (2 marks) and identify ONE substance that it excretes. b) Figure 5 is a diagram of a nephron found in a human kidney. Y H

G Z J

Figure 5 Diagram of a nephron i) Identify the structures labelled G, H and J in Figure 5. ii) Briefly describe the process that takes place in EACH of the structures labelled Y and Z.

(3 marks) (4 marks)

Exam-style questions – Chapters 3 to 9

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6

c) Table 4 shows the composition of Andrew’s urine 1 hour after he drank 2 large glasses of water and again 1 hour after he played a 90-minute game of football in the heat of the day, without drinking. Table 4 Composition of Andrew’s urine in Andrew’s urine % in Andrew’s urine Component % after drinking after playing football Urea 2.0 6.0 Salt 0.3 1.0 Water 95 90 i) Which activity caused Andrew’s urine to have the HIGHEST concentration? (1 mark) ii) Name the hormone secreted by Andrew’s pituitary gland when there is not (1 mark) enough water in his body fluids. iii) Explain how the hormone named in c) ii) above functioned to prevent Andrew losing too much water in his urine when his body fluids became too (2 marks) concentrated. Total 15 marks a) Complete the following sentence: The nervous system can be divided into the nervous system (2 marks) and the nervous system. b) Figure 6 is a diagram of a neurone. K

L

M

Figure 6 A neurone i) Name the parts labelled K and L. (2 marks) ii) State the function of L. (1 mark) iii) How do impulses travel from the structures labelled M to adjacent neurones (1 mark) in the brain? c) Complete Table 5 below, which gives information about three different regions of the brain. Table 5 Functions of three regions of the brain Region of the brain One function Medulla oblongata • • Controls conscious thought Cerebellum

• (3 marks)

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Exam-style questions – Chapters 3 to 9

d) i) Dana’s dress has a hole in it that needs mending, so she cuts a piece of cotton thread and threads her needle. Are her actions voluntary or involuntary? Give ONE reason to (2 marks) support your answer. ii) Dana starts to mend the hole, but accidently pricks her finger causing her to immediately pull her hand away from the needle. Complete Figure 7 below by drawing (3 marks) and labelling THREE neurones involved in bringing about Dana’s action. pain receptors in the skin

spinal cord

biceps muscle in the upper arm

Figure 7 Parts of the nervous system iii) What term is used to describe Dana’s action in d) ii) above?

(1 mark) Total 15 marks

7 a) Figure 8 shows the male and female reproductive systems. III IV I II

Figure 8 Male and female reproductive systems i) Complete Table 6 below by writing the name and ONE function of EACH of the structures labelled I and III Table 6 Name and function of parts of the human reproductive systems Name of structure One function I III ii) Suggest TWO reasons why structures labelled II and IV in Figure 8 may be described as having similar functions. iii) Place arrows on the male reproductive system to show the pathway taken by sperm as it travels out of the male body.

(4 marks) (2 marks) (2 marks)

Exam-style questions – Chapters 3 to 9

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b) Figure 9 shows the number of births to teenage mothers aged 16 and 17 years over five-year periods from 1980 to 2009 in a certain Caribbean territory. 400

16 year olds

350

17 year olds

300 shtrib fo rebmuN

250 200 150 100 50 0

80–84

85–89

90–94

Years

95–99

00–04

05–09

Figure 9 Number of births to mothers aged 16 and 17 years between 1980 and 2009 i) In which five-year period was the total number of births the HIGHEST? (1 mark) ii) Between which two five-year periods was the GREATEST decrease in the (1 mark) number of births recoded? iii) Describe TWO trends shown in Figure 9. (2 marks) iv) It is thought that increased use of contraception among teenagers, particularly condoms, could possibly account for the overall trend in teenage pregnancy numbers in the country. Explain how condoms act as a method of birth control (3 marks) and give ONE advantage and ONE disadvantage of their use. Total 15 marks

Structured essay questions

8 a) Alexa is advised by her doctor that after her baby is born she should feed him on breast

milk for the first 6 months of his life because breast milk is a complete food for babies. i) Why is breast milk considered to be a complete food for babies? (2 marks) ii) Alexa takes her doctor’s advice and breastfeeds her baby, Jay, from birth. Describe how the milk is digested as it passes through Jay’s digestive system. (6 marks) iii) There is a tendency for babies fed on powered milk to gain weight more (2 marks) rapidly than breastfeed babies. Suggest TWO reasons for this. b) Alexa is also told that Jay must develop teeth before he can digest solid foods properly. i) Explain why Jay needs to develop teeth before he can properly digest any (3 marks) solid food in his diet. ii) Why is it important that the enamel of Jay’s teeth is the hardest substance (2 marks) found in his body? Total 15 marks

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Exam-style questions – Chapters 3 to 9

9 a) Define the term ‘homeostasis’ and outline how negative feedback mechanisms

(4 marks) play an important role in homeostasis. b) Jason goes on a hiking expedition into the mountains and loses his way as it begins to get dark. He is forced to spend the night high up in the mountains and begins to get very cold. Explain how his body responds to conserve as (6 marks) much heat as possible. c) On Sports Day Britnee runs a 200 m race. After crossing the finish line she realises that she is breathing much faster and deeper than normal. Explain what (5 marks) is taking place in her body to bring about the changes in her breathing. Total 15 marks 10 a) Give THREE differences between control by the nervous system and control (3 marks) by the endocrine system. b) i) Describe the changes that occur in Aiden’s eyes as he looks up from the (4 marks) smart phone in his hand to watch a bird in the top of a tree. ii) As Aiden gets older, he finds it harder and harder to focus on his smart phone. Suggest the possible cause of Aiden’s difficulty and explain what (4 marks) he must do to correct it. c) Aiden is also found to have developed an underactive pituitary gland. By referring to TWO different hormones produced by Aiden’s pituitary gland, explain how this (4 marks) reduced activity could affect his body. Total 15 marks 11 a) i) Describe the events taking place in Rasheeda’s ovaries and uterus during one (5 marks) complete menstrual cycle. ii) Name TWO hormones, other than those secreted by Rasheeda’s pituitary gland, (4 marks) that control her menstrual cycle and outline the role played by EACH. b) Rasheeda misses her period and decides to go to the doctor because she thinks she might be pregnant. Her doctor confirms her suspicions. Outline the role that the placenta, umbilical cord and amniotic fluid play in the development of (6 marks) Rasheeda’s baby during her pregnancy. Total 15 marks

Exam-style questions – Chapters 3 to 9

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Section C – Heredity and variation 10 Cell division and variation Cells contain all the information they need to control their activities coded as genetic information in their genes. These genes are passed on to new cells during cell division. Living organisms show variation and much of this variation is passed on from one generation to the next via genes.

An introduction to chromosomes and genes Chromosomes

Chromosomes are present in the nuclei of all living cells. Each chromosome is composed of a single deoxyribonucleic acid (DNA) molecule wrapped around proteins called histones. DNA molecules contain genetic information in the form of genes. In any cell that is not dividing, chromosomes exist as long, thin strands known as chromatin threads, which are spread throughout the nucleus. Chromosomes become visible when a cell begins to divide, due to them becoming shorter and thicker. Chromosomes are passed on from one generation to the next in gametes and each species has a distinctive number of chromosomes per body cell; every human cell has 46 chromosomes. The number of chromosomes in each cell is known as the diploid number or 2n number. Chromosomes exist in pairs known as homologous pairs. Every human cell has 23 pairs, one member of each pair being of maternal origin and the other of paternal origin. With the exception of the pair of sex chromosomes, members of each homologous pair are similar in shape, size and genetic composition.

Genes

Genes are specific sections of chromosomal DNA molecules and are the basic units of heredity. Each human body cell has over 30 000 genes and each gene controls a particular characteristic. Genes work by controlling the production of proteins in cells, mainly the production of enzymes. Each gene controls the production of a specific protein. All the cells of one individual contain an identical combination of genes. It is this combination which makes each individual unique since no two individuals, except identical twins or organisms produced asexually, have the same combination of genes. Within any cell some genes are active while others are inactive, e.g. in a nerve cell, genes controlling the activity of the nerve cell are active and genes that would control the activity of a muscle cell are inactive.

Cell division

When a cell divides, chromosomes with their genes are passed on to the cells produced, known as daughter cells. There are two types of cell division: mitosis and meiosis.

Mitosis

Mitosis is the type of cell division that results in the formation of two daughter cells, each with the same number and kind of chromosomes as the parent cell. Mitosis occurs in all body (somatic) cells except in the formation of gametes. During mitosis, two genetically identical cells are formed. Each cell contains the diploid number of chromosomes. All cells produced by mitosis from a single parent cell are collectively called a clone. Mitosis is important because: • It ensures that each daughter cell has the same number and type of chromosomes as the parent cell. • It ensures that each daughter cell has an identical combination of genes. • It is the method by which all cells of a multicellular organism are formed, hence it is essential for growth and to repair damaged tissues. • It is the method by which organisms reproduce asexually, forming offspring that are identical to each other and to the parent. 102 10 Concise Revision Course: Human and Social Biology

nuclear membrane centrioles chromatin threads composed of DNA centromere two chromatids spindle fibres

centromere – attached to the equator of the spindle spindle fibres

chromatids separating

spindle fibres disintegrate chromosomes

new cell membranes form

When the cell is not dividing, the chromosomes are not visible; they exist as long, thin strands called chromatin threads

The chromosomes shorten, thicken, duplicate themselves and become visible; each consists of two identical chromatids joined at the centromere. The centrioles separate forming spindle fibres between them

The nuclear membrane disintegrates and a spindle forms between the centrioles. The chromatid pairs line up around the equator of the spindle

The centromeres split and the spindle fibres pull the chromatids, by their centromeres, to opposite poles of the cell

The chromatids reach the opposite poles and are now called chromosomes. The spindle fibres disintegrate, and the cell constricts at the equator

A nuclear membrane forms around each group of chromosomes. The cell divides forming two, identical daughter cells each with the diploid number of chromosomes. The chromosomes then become long and thin so they are no longer visible

Figure 10.1 The process of mitosis in an animal cell with four chromosomes; two of paternal origin (blue) and two of maternal origin (red)

Meiosis (reduction division)

Meiosis is the type of cell division that results in the formation of four daughter cells, each with half the number of chromosomes as the parent cell. Meiosis occurs only in the reproductive organs during the production of gametes. During meiosis, four genetically non-identical cells are formed. Each cell contains the haploid number or n number of chromosomes, i.e. half the diploid number. 10 Cell division and variation

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Meiosis is important because it ensures that: • Each daughter cell or gamete has the haploid number of chromosomes. The diploid number can then be restored at fertilisation. • Each daughter cell or gamete has a different combination of genes. This leads to variation among offspring (see page 105). two chromosomes of maternal origin centrioles two chromosomes of paternal origin centromere centrioles separating nuclear membrane

crossover point spindle fibres

spindle exchanged segments of crossed over chromatids

bivalents separating

nuclear membrane The chromosomes shorten, thicken and become visible pair of homologous chromosomes forming a bivalent The homologous chromosomes pair forming bivalents. The centrioles separate forming spindle fibres between

Each chromosome duplicates itself forming two chromatids joined by a centromere. Adjacent chromatids cross over each other The nuclear membrane disappears and the bivalents arrange themselves around the equator of the spindle. The chromatids break at the crossover points and rejoin with opposite chromatids thus exchanging genetic material The homologous chromosomes of the bivalents separate and the spindle fibres pull the chromosomes, each composed of two chromatids, to opposite poles of the cell  A nuclear membrane forms around each group of chromosomes. The spindle fibres disintegrate and the centrioles divide. The cell constricts at the equator forming two cells

The centrioles in each cell separate forming two new spindles at right angles to the first spindle

The nuclear membranes disappear. The chromosomes, each composed of two chromatids, line up around the equators of the spindles

chromatids separating The centromeres split, and the spindle fibres pull the chromatids to opposite poles of the cells

The chromatids reach the opposite poles of the cells and are now called chromosomes. The spindle fibres disintegrate. A nuclear membrane forms around each group of chromosomes and each cell divides. Four daughter cells are formed, each with the haploid number of chromosomes whose compositions are different. The chromosomes then become long and thin, so they are no longer visible

Figure 10.2 The process of meiosis in an animal cell with four chromosomes

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immature ovum 2n in an ovary

in the wall of a 2n cell seminiferous tubule in the testis meiosis

meiosis one cell develops n into a mature ovum n

n n

fertilisation

n

n

n

n

sperm cells

2n a zygote mitosis embryo composed 2n 2n an of two cells mitosis an embryo composed of 2n 2n four cells – by mitosis 2n 2n continuing; an adult is eventually formed with all cells containing the 2n number of chromosomes

Figure 10.3 The relationship between mitosis and meiosis

Variation

No two living organisms are exactly alike, not even identical twins. Variation refers to the differences that exist between individuals and it arises from a combination of genetic causes and environmental causes. The observable characteristics of an individual make up the individual’s phenotype, and the composition of genes within the cells of an individual makes up the individual’s genotype. The phenotype of an individual is determined by his or her genotype and the influences of his or her environment: phenotype = genotype + environmental influences

Genetic and environmental causes of variation Genetic variation

Genetic variation is controlled by genes and can be passed on from one generation to the next, i.e. it can be inherited. It arises in several ways: • Meiosis. Every gamete produced by meiosis has a different combination of genes as a result of: Chromatids of homologous chromosomes crossing over and exchanging genes. Chromosomes arranging themselves around the equators of the spindles in totally random ways. • Sexual reproduction. During fertilisation, male and female gametes fuse in completely random ways to create a different combination of genes in each zygote. • Mutations. A mutation is a change in the structure of a single gene, the structure of part of a chromosome containing several genes or in the number of chromosomes in a cell. Mutations cause new characteristics to develop in organisms. Mutations occurring in body cells cannot be inherited, whereas mutations occurring in a gamete or zygote can be inherited. Many mutations are harmful; however, a few produce beneficial characteristics which help the organism survive. Examples of mutations include: Albinism, which is caused by a mutation in a gene controlling the production of melanin. People with albinism produce very little or no melanin in their skin, eyes and hair (see page 108). 10 Cell division and variation

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Down’s syndrome, which occurs when an individual has an extra chromosome 21 in each of their cells because pair 21 fails to separate properly during meiosis and both chromosomes pass into one gamete. Individuals with Down’s syndrome usually have flattened facial features, a short wide neck, small ears, a bulging tongue, slanted eyes, short stocky arms and legs, poor muscle tone and slow learning capabilities. Antibiotic resistance, which can arise in bacteria from a mutation occurring in some bacterial cells that makes them resistant to certain antibiotics. When exposed to these antibiotics, the resistant organisms are more likely to survive and reproduce than the non-resistant ones, passing their resistance on to the next generation.

Environmental variation

Environmental variation is caused by different factors in an organism’s environment. It is not caused by genes and cannot be passed on from one generation to the next. Environmental factors affecting humans include: • The type and quantity of food they eat. • The diseases they suffer from. • The drugs they take. • The climate they are exposed to, especially the amount of sunlight. • Their upbringing and living conditions. • The education they receive. • The amount of exercise they get and their daily activities.

Continuous and discontinuous variation

There are two basic types of variation within a species: continuous variation and discontinuous variation.

Continuous variation

slaudividni fo rebmun

Continuous variation is where characteristics show continuous gradation from one extreme to the other without a break. Most individuals usually fall in the middle of the range with fewer at the two extremes, i.e. the characteristics show a normal distribution. Examples include height, weight, foot size, hand span, hair colour, skin colour and intelligence. Characteristics showing continuous variation are usually controlled by many genes and can be affected by environmental factors.

mean height

height

Figure 10.4 A normal distribution curve showing height Discontinuous variation is where characteristics show clear cut differences with no intermediates. Individuals can be divided into distinct categories. Examples include gender, ABO blood groups, rhesus blood groups and tongue-rolling ability. Characteristics showing discontinuous variation are usually controlled by a single gene and environmental factors have little, if any, influence on them.

Discontinuous variation

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The importance of variation to living organisms

Within any species, individuals with variations that make them best suited to their environment have a better chance of survival than the others. More of these individuals will survive to reproduce and when they do, they pass on the genetic information for their beneficial characteristics to their offspring. This process is known as natural selection. Over time, this enables species to remain well adapted to their environment or to gradually change and improve by becoming better adapted, i.e. it enables species to evolve. For example, some species of bacteria have become resistant to almost all commonly available antibiotics, enabling them to survive when antibiotics are used to treat a bacterial infection.

Revision questions

1 Define the following terms: a mitosis b meiosis 2 Outline the process of mitosis. 3 Give THREE reasons why mitosis is important to living organisms. 4 In what ways does meiosis differ from mitosis? 5 Give TWO reasons why meiosis is important to living organisms. 6 Distinguish between genetic and environmental variation. 7 a What is a mutation? b By reference to albinism and Down’s syndrome, explain how mutations cause

variation. 8 Identify FOUR environmental factors that can cause variation in humans. 9 Outline the differences between continuous and discontinuous variation. 100 Explain why variation is important to living organisms. Support your answer by referring to antibiotic resistance in bacteria.

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11 Inheritance and genetic engineering

The branch of science which seeks to understand how characteristics are passed on from one generation to the next is known as genetics. For over 200 years humans have selected and crossed plants and animals to produce improved varieties due to the mixing of genetic material. Since the structure of DNA was discovered in 1953, gene technology has moved at an ever-increasing pace to improve food production and the production of medicinal drugs.

Monohybrid inheritance

Monohybrid inheritance is the inheritance of a single characteristic. Like chromosomes, genes exist in pairs. One gene of each pair is of maternal origin and one is of paternal origin, and the pairs occupy equivalent positions on homologous chromosomes. A gene controlling a particular characteristic can have different forms known as alleles. Each gene usually has two different alleles.

Example: albinism

People with albinism produce very little or no melanin in their skin, eyes and hair. The gene controlling the production of the pigment melanin has two different alleles which can be represented using letters: • N stimulates melanin production • n fails to stimulate melanin production The allele stimulating melanin production, N, is dominant, i.e. if it is present it shows its effect on the phenotype. The allele for albinism, n, is recessive, i.e. it only has an effect on the phenotype if there is no dominant allele present. Three combinations of these alleles are possible; NN, Nn and nn. If the two alleles are the same, the organism is said to be homozygous. If the two alleles are different, the organism is said to be heterozygous. Heterozygous individuals are carriers because they can pass on a recessive allele. Table 11.1 Possible combinations of the alleles controlling melanin production Genotype How the alleles appear on Phenotype (appearance) (combination of alleles) homologous chromosomes N NN Normal pigmentation of the skin, eyes and hair Homozygous dominant (pure breeding) N N Nn Normal pigmentation of the skin, eyes and hair Heterozygous (carrier) nn Homozygous recessive (pure breeding)

n n n

Albino – very pale skin that does not tan, white or light blond hair and very pale blue eyes

Gametes produced in meiosis contain only one chromosome from each homologous pair. As a result, they contain only one allele from each pair. When fertilisation occurs, chromosomes and the alleles they carry recombine to form pairs in the zygote.

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Results of possible crosses 1 If one parent is homozygous dominant and one is homozygous recessive: Parental phenotypes Parental genotypes (2n)

normal pigmentation NN

Gametes (n)

albino nn

N

N

n

n

Nn

Nn

Nn

Nn

Random fertilisation First filial generation (F1) genotypes First filial generation (F1) phenotypes

normal pigmentation

All the offspring have normal pigmentation

2 If one parent is heterozygous and one is homozygous recessive, showing the use of a Punnett square to predict the outcome of the cross: Parental phenotypes normal pigmentation Nn Parental genotypes Gametes N n gametes

n

n

N

Nn

Nn

n

nn

nn

Random fertilisation F1 genotypes

albino nn n n

Nn

Nn

nn

normal pigmentation F1 phenotypes 50% of the offspring have normal pigmentation 50% of the offspring have albinism

nn albino

3 If both parents are heterozygous, i.e. carriers: Parental phenotypes Parental genotypes Gametes

normal pigmentation Nn

F1 genotypes

n

N

Random fertilisation NN

normal pigmentation Nn n

N

gametes

N

n

N

NN

Nn

n

Nn

nn

Nn

F1 phenotypes normal pigmentation 75% of the offspring have normal pigmentation 25% of the offspring have albinism

Nn

nn albino

Co-dominance

Sometimes neither allele dominates the other, such that the influence of both alleles is visible in the heterozygous individual. These alleles show co-dominance. Examples include sickle cell anaemia and ABO blood groups. 11 Inheritance and genetic engineering

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Sickle cell anaemia

The blood of a person with sickle cell anaemia contains abnormal haemoglobin S instead of normal haemoglobin A. The disease is caused by an abnormal allele. The normal allele HbA stimulates the production of normal haemoglobin A, the abnormal allele HbS stimulates the production of abnormal haemoglobin S. These alleles show co-dominance. Table 11.2 Possible combinations of alleles controlling haemoglobin production Genotype Haemoglobin produced Phenotype HbA HbA Normal. 100% haemoglobin A A S Hb Hb Sickle cell trait. Usually no symptoms. Symptoms of 55–65% haemoglobin A 35–45% haemoglobin S sickle cell anaemia may develop in very low oxygen concentrations, e.g. at high altitude or during extreme physical exercise. People with the trait are resistant to malaria. S S Hb Hb Sickle cell anaemia. Symptoms of sickle cell anaemia 100% haemoglobin S develop which include painful crises, anaemia, increased vulnerability to infections and jaundice. For example, if both parents have sickle cell trait: Parental phenotypes

sickle cell trait

sickle cell trait

Parental genotypes

HbAHbS

HbAHbS

Gametes

HbA

HbAHbA

F1 phenotypes

normal

HbA

HbS

gametes

HbA

HbS

HbA

HbAHbA

HbAHbS

HbS

HbAHbS

HbSHbS

Random fertilisation

F1 genotypes

HbS

HbAHbS

HbAHbS sickle cell trait

25% of the offspring are normal 50% of the offspring have the sickle cell trait 25% of the offspring have sickle cell anaemia

ABO Blood groups

ABO blood groups are controlled by three alleles, IA, IB and IO. • IA and IB are both dominant to IO. • IA and IB are co-dominant, i.e. there is no dominance between them. Only two alleles are present in any cell.

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HbSHbS sickle cell anaemia

Table 11.3 Possible combinations of alleles controlling ABO blood groups Genotype Phenotype IA IA Blood group A IA IO Blood group A B B II Blood group B IB IO Blood group B IA IB Blood group AB O O I I Blood group O For example, if one parent is heterozygous with blood group A and the other is heterozygous with blood group B: Parental phenotypes Parental genotypes Gametes

blood group A I A IO IA IO

blood group B I B IO IB I O

gametes

IB

IO

IA

I A IB

I A IO

IO

I B IO

I O IO

Random fertilisation F1 genotypes F1 phenotypes

I A IB I A IO blood blood group AB group A 25% of the offspring have blood group AB 25% of the offspring have blood group A 25% of the offspring have blood group B 25% of the offspring have blood group O

I B IO blood group B

I O IO blood group O

The inheritance of sex in humans

In each cell, one pair of chromosomes is composed of the sex chromosomes. There are two types, X and Y, and they determine the individual’s sex. Genotype XX is female; genotype XY is male. Only the male can pass on the Y chromosome, consequently the father is the parent who determines the sex of his offspring. Parental phenotypes

female XX

Parental genotypes Gametes

male XY

X

X

X

Y

XX female

XY male

XX female

XY male

Random fertilisation F1 genotypes F1 phenotypes 50% of the offspring are female 50% of the offspring are male

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Sex-linked characteristics

Sex-linked characteristics are characteristics determined by genes carried on the sex-chromosomes that have nothing to do with determining the sex of the offspring. These are known as sex-linked genes. Since chromosome X is longer than chromosome Y, it carries more genes. Males only have one X chromosome and any allele carried on this chromosome only, whether dominant or recessive, will be expressed in the phenotype. Examples of sex-linked characteristics include haemophilia and colour blindness.

Haemophilia

Haemophilia is a sex-linked condition where the blood fails to clot at a cut. The dominant allele, H, causes blood to clot normally; the recessive allele, h, causes haemophilia. These alleles are carried on the X chromosome only. Males are much more likely to be haemophiliacs than females; if the single X chromosome in a male carries the recessive allele he will have the condition, whereas both X chromosomes must carry the recessive allele in a female for her to have the condition. Table 11.4 Possible combinations of alleles controlling blood clotting Genotype Phenotype XH XH Female, normal blood clotting XH Xh Female, normal blood clotting (carrier) Xh Xh Female, haemophiliac H XY Male, normal blood clotting Xh Y Male, haemophiliac

Example

A cross between a female with normal blood clotting who is a carrier, and a male with normal blood clotting. Parental phenotypes Parental genotypes

female, normal clotting XHXh

Gametes

F1 genotypes F1 phenotypes

Xh

XH

Random fertilisation

XHXH

male, normal clotting XHY XH

gametes

XH

Y

XH

XHXH

XHY

Xh

XHXh

XhY

XHY

female, male, normal clotting normal clotting All the female offspring have normal blood clotting 50% of the male offspring have normal blood clotting 50% of the male offspring have haemophilia

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Y

XHXh

XhY

female, normal clotting

male with haemophilia

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Colour blindness

Colour blindness (also known as red–green colour blindness) is a sex-linked condition where the sufferer is unable to distinguish differences between certain colours. The dominant allele, R, allows normal vision and the recessive allele, r, causes colour blindness. These alleles are carried on the X chromosome only, so colour blindness is inherited in the same way as haemophilia.

Some important genetic terms

Chromosome: a thread-like structure composed of deoxyribonucleic acid (DNA) and protein, which contains genetic information in the form of genes. Gene: the basic unit of heredity which is composed of DNA, occupies a fixed position on a chromosome and determines a specific characteristic. Allele: either of a pair (or series) of alternative forms of a gene that occupy the same position on a particular chromosome and that control the same characteristic. Dominant allele: the allele which, if present, produces the same phenotype whether its paired allele is identical or different. Recessive allele: the allele that only shows its effect on the phenotype if its paired allele is identical. Dominant trait: an inherited characteristic that results from the presence of a single dominant allele. It is seen in an individual with one or two dominant alleles. Recessive trait: an inherited characteristic that results from the presence of two recessive alleles. It is only seen in an individual with no dominant allele. Co-dominance: neither allele dominates the other such that the influence of both alleles is visible in the heterozygous individual. Genotype: the combination of alleles present in an organism. Phenotype: the observable characteristics of an organism. Homozygous: having two identical alleles in corresponding positions on a pair of homologous chromosomes. Heterozygous: having two different alleles in corresponding positions on a pair of homologous chromosomes.

Genetic engineering

Genetic engineering or recombinant DNA technology involves changing the traits of one organism by inserting genetic material from a different organism into its DNA. The organism receiving the genetic material is called a transgenic organism or genetically modified organism (GMO). Genetic engineering is used to: • Improve the quality of a food product, e.g. by increasing nutritional value. • Improve yields of livestock and crops, e.g. by increasing size or growth rate, or by making organisms hardier. • Protect agricultural crops against environmental threats, e.g. pathogens, pests, herbicides and low temperatures. • Make organisms produce materials that they do not usually produce, e.g. vaccines and drugs.

Genetic engineering and food production

Genetic engineering is used to improve food production. Some examples follow. 11 Inheritance and genetic engineering

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Golden rice

By inserting two genes into rice plants, one from maize and one from a soil bacterium, the rice grains are stimulated to produce beta-carotene which the body converts to vitamin A. Golden rice should help fight vitamin A deficiency, which is a leading cause of blindness, and often death, of children in many developing countries.

Bovine somatotrophin (BST) hormone

By transferring the gene which controls the production of BST hormone from cattle into bacteria, the bacteria produce the hormone, which is then injected into cattle to increase milk and meat production.

Figure 11.1 Golden rice

Chymosin (rennin)

By transferring the gene which controls the production of chymosin from calf stomach cells into bacteria or fungi, the microorganisms produce chymosin, which is used in cheese production. This has considerably increased the production of cheese worldwide.

Genetic engineering and medical treatment

Genetic engineering is used to produce many drugs used in medical treatment. Some examples follow.

Insulin

By transferring the gene that controls insulin production in humans into bacteria, the bacteria produce human insulin which is used to treat diabetes. bacterium

human pancreas cell plasmid – ring of DNA chromosome with insulin-producing gene in its DNA

plasmid DNA is removed and cut using restriction enzymes

insulin-producing gene is cut out

insulin-producing gene is inserted into the plasmid DNA forming recombinant DNA

recombinant DNA is reintroduced into a bacterium the bacterium multiplies and all the cells produce insulin

insulin is separated and purified

Figure 11.2 Recombinant DNA technology to produce insulin

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Human growth hormone (HGH)

By transferring the gene controlling the production of HGH into bacteria, the bacteria produce the hormone which is used to treat growth disorders in children.

Hepatitis B vaccine

By transferring the gene controlling the production of hepatitis B antigens by the hepatitis B virus into yeast, the yeast produces the antigens, which are used as a vaccine.

Other drugs produced by genetic engineering

• Blood clotting drugs for haemophiliacs. • Follicle stimulating hormone (FSH) used to stimulate the ovaries to release ova in women that are infertile. • Interferons used to treat viral infections and certain cancers. • Anticoagulants used to prevent the development of life-threatening blood clots in heart patients. • Human papilloma virus vaccine.

Possible advantages of genetic engineering

• Yields can be increased by genetic engineering, which should increase the world food supply and reduce food shortages. • The nutritional value of foods can be increased by genetic engineering, which should reduce deficiency diseases worldwide. • The need for chemical pesticides that harm the environment can be reduced by genetically engineering crops to be resistant to pests. • Vaccines produced by genetic engineering are generally safer than vaccines containing live and weakened, or dead pathogens. • Larger quantities of drugs in a safer and purer form can be produced than were previously produced from animal sources, resulting in more people worldwide having ready access to safe, life-saving drugs. • It overcomes ethical concerns of obtaining certain drugs from animals, e.g. insulin used to be obtained from pigs and cows.

Possible disadvantages of genetic engineering

• Plants genetically engineered to be toxic to a pest may also be toxic to useful organisms, e.g. insects which bring about pollination. This could reduce reproduction in crops, reducing food production. • Plants genetically engineered to be resistant to pests and herbicides could create unpredictable environmental issues, e.g. they could lead to the development of pesticide-resistant pests and herbicide resistant ‘superweeds’. • Once a genetically modified organism is released into the environment it cannot be contained or recalled. Any negative effects are irreversible. • The number of allergens in foods could be increased by transferring genes causing allergic reactions between species. • As yet unknown health risks may occur as a result of eating genetically modified plants and animals. • Large companies with funds and technology to develop genetically modified organisms could make large profits at the expense of smaller companies and poorer nations. • Future steps in genetic engineering might allow the genetic makeup of higher organisms, including humans, to be altered, e.g. to produce ‘designer babies’. Difficult moral and ethical issues then arise, e.g. how far should we go in changing our own genes and those of other animals? 115 11 Inheritance and genetic engineering

Revision questions

1 Distinguish between the following pairs of terms: a genotype and phenotype b gene and allele c homozygous and heterozygous 2 PTC is a chemical that tastes bitter to some people and is tasteless to others. The

allele for tasting PTC, T, is dominant. Draw a Punnett square to show how a couple who can both taste PTC could produce a child who is unable to taste PTC. 3 What is the chance that a couple who both have sickle cell trait will have a child who suffers from neither the trait nor sickle cell anaemia? Use a genetic diagram to explain your answer. 4 Is it the mother or the father that determines the sex of their children? Explain your answer by means of a genetic diagram. 5 What are sex-linked characteristics? 6 Colour blindness is caused by an X-linked, recessive allele. Is it possible for a mother with normal vision and a father with colour blindness to have a colour-blind child? Use a Punnett square to explain your answer (XR = normal vision; Xr = colour blindness). 7 What is meant by the term ‘genetic engineering’? 8 Outline TWO ways genetic engineering is being used to improve food production. 9 Outline how genetic engineering can be used to produce insulin to treat diabetes. 10 Discuss THREE possible advantages and THREE possible disadvantages of using genetic engineering.

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Exam-style questions – Chapters 10 to 11 Structured questions

1 a) Distinguish between a chromosome and a gene.

(2 marks)

b) Figure 1 shows a dividing cell.

X

2

Figure 1 A dividing cell i) Name the structure labelled X. (1 mark) ii) Identify the type of cell division that the cell in Figure 1 is undergoing. (1 mark) iii) Give TWO reasons for your answer to b) ii) above. (2 marks) iv) Name ONE place in the human body where the type of cell division shown in (1 mark) Figure 1 would occur. v) How many chromosomes would each daughter cell possess when the cell (1 mark) shown in Figure 1 has finished dividing? vi) Give TWO reasons why this type of cell division is important. (2 marks) c) i) All living organisms show variation. What is meant by the term ‘variation’? (1 mark) ii) Distinguish between continuous variation and discontinuous variation. (2 marks) iii) Explain what happens to cause a person to be born with Down’s syndrome. (2 marks) Total 15 marks Some people can roll the edges of their tongues upwards to form a tube, other people cannot do this. The allele for rolling the tongue is dominant, and tongue-rolling is NOT sex-linked. Selena can roll her tongue whereas her husband, Ario, cannot roll his. Figure 2 below shows the phenotypes of Selena, Ario and their five children. Selena

Ano

Key Male Female Cannot roll tongue Can roll tongue

Figure 2 The inheritance of tongue rolling in Selena and Ario’s family a) i) What is meant by the term ‘dominant allele’? (2 marks) ii) Complete the following Punnett square to show the possible genotypes of Selena and Ario’s children. 117 Exam-style questions – Chapters 10 to 11

Use R to represent the dominant allele for being able to roll the tongue and r to represent the recessive allele for not being able to roll the tongue. gametes

(4 marks)

iii) What is the chance that Selena and Ario’s next child will be unable to roll his (1 mark) or her tongue? iv) What term is used to describe Selena’s genotype? (1 mark) b) i) Identify the type of variation shown in Figure 2. (1 mark) ii) Identify ONE other human characteristic that shows the same type of variation. (1 mark) iii) Tara and Ashlee are identical twins. Explain, using suitable examples, how it is possible for them to have differences in their phenotypes even though they (3 marks) have the same genotypes. iv) Why is it important that living organisms show variation? (2 marks) Total 15 marks

Structured essay question

3 a) i) Haemophilia is caused by an X-linked recessive allele. Use a Punnett square to

determine the genotype of the offspring of a cross between a female carrier of haemophilia and a normal male. Use XHXh to denote the genotype of the female carrier and XHY to denote the (4 marks) genotype of the normal male. ii) State the phenotype of EACH offspring in a) i) above. (4 marks) b) i) Kemar suffers from Type 1 diabetes. Explain how genetic engineering is used to help treat Kemar’s condition. Your answer must include the name of the product produced by genetic engineering and an explanation of how the (5 marks) product is made. ii) Give TWO concerns that people might have about the use of genetic (2 marks) engineering to change the traits of organisms. Total 15 marks

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Exam-style questions – Chapters 10 to 11

Section D – Disease and its impact on humans 12 Health and disease

According to the World Health Organisation (WHO), healthy people are able to function well physically, their minds are free from worry and depression, and they are able to show care and concern for others. Health is a state of complete physical, mental and social wellbeing and not merely the absence of disease and infirmity. A disease is a condition that impairs the normal functioning of part or all of an organism, and leads to a loss of good health.

Types of disease

Diseases may be classified into the following two types: • Communicable (infectious) diseases • Non-communicable diseases

Communicable diseases

Communicable diseases are caused by pathogens (organisms that cause disease) and can be passed from one person to another. They are also known as infectious diseases and include sexually transmitted infections (STIs), air-borne diseases, water-borne diseases, food-borne diseases and vector-borne diseases (see Tables 12.3, 12.4 and 12.5).

Non-communicable diseases

Non-communicable diseases are not caused by pathogens and cannot be passed from one person to another. Many are chronic, i.e. they are long-term medical conditions that often get worse over time. Non-communicable diseases include: • Nutritional deficiency diseases (see page 23). • Degenerative diseases, which are conditions that cause a breakdown of body tissues or organs over time which prevents them from functioning normally, e.g. Alzheimer’s disease, Parkinson’s disease and osteoporosis. • Inherited disorders, which are passed on from one generation to the next via genes, e.g. cystic fibrosis and sickle cell disease. • Lifestyle-related diseases (see page 121).

Signs and symptoms of disease

Diseases are detected by signs and symptoms. • Signs can be detected by someone other than the person affected by the disease, e.g. a rash, high body temperature and low blood pressure. • Symptoms are experienced by the person affected by the disease. They are what the person feels, e.g. pain, fatigue and nausea.

Asthma

Asthma is a non-communicable disease that affects the respiratory system. During an asthma attack, the muscles surrounding the bronchi and bronchioles contract, causing these airways to become narrower. The bronchial lining also becomes inflamed and there is increased mucus secretion. 12 Health and disease

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air trapped in alveoli relaxed smooth muscles

normal airway

tightened smooth muscles

wall inflamed and thickened asthmatic airway asthmatic airway during attack

Figure 12.1 The effects of asthma on the respiratory system

Main causes of asthma

The main causes of asthma include: • a family history of asthma • lung infection • childhood exposure to tobacco • a mother who smoked during pregnancy. Certain substances or conditions trigger an asthma attack. The triggers vary from person to person, and include: • allergens, e.g. pollen, dust mites and animal fur • airborne irritants, e.g. smoke and fumes • respiratory infections • anxiety or stress • sudden temperature changes • exercise.

Primary symptoms of asthma Symptoms of asthma include: • shortness of breath • coughing • wheezing • chest pain.

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Possible treatment of asthma

There is no cure for asthma. However, asthma can be controlled by avoiding exposure to allergens and other asthma triggers. Two types of medication are used to treat asthma: • Quick relief medications – administered using an inhaler to relax the muscles around the airways during an asthma attack. • Long-term control medications – inhaled steroids that are generally taken daily for long-term relief of inflammation of the bronchial tubes.

Lifestyle-related diseases

Lifestyle-related diseases are non-communicable diseases. They are said to be lifestyle-related because certain practices and behaviours, including poor eating habits, smoking and inactivity, contribute to persons developing these diseases. Other factors such as age, gender and inherited traits have an impact. Lifestyle-related diseases include obesity, diabetes mellitus and cardiovascular disease (CVD).

Obesity

When persons consume more food than the body requires, the excess is converted to fat and is stored under the skin and around organs. Obesity is a form of malnutrition in which persons have accumulated so much body fat that it has a negative effect on their health. Obese persons are very overweight, i.e. they have a BMI greater than 30 kg per m2 (see page 26). • Causes: Excess carbohydrate and fat intake, especially animal fats that are rich in saturated fatty acids, and a lack of physical activity. • Signs/symptoms: Breathing difficulties, increased sweating, back and joint pains, inability to cope with physical exercise, chronic fatigue and elevated blood pressure. Persons who are obese are also at increased risk of having other serious health problems, such as type II diabetes, hypertension, stroke and coronary heart disease. • Treatment and prevention: Changing to a low-carbohydrate and low-saturated fat diet, and doing more physical activity (exercise) are important measures used in the prevention and treatment of obesity.

Diabetes mellitus

Diabetes mellitus is a condition in which the blood sugar level is consistently high over a prolonged period. The blood glucose level is so high that the kidneys are unable to reabsorb all of the glucose from the filtrate (see page 69) and some is passed out in the urine. There are two types of diabetes mellitus: • Type I (insulin-dependent diabetes) – This is the less common type of diabetes mellitus, accounting for 5–10% of the total cases of diabetes worldwide. It develops mainly in young children. • Type II (non-insulin-dependent diabetes) – This accounts for 90–95% of diabetes cases worldwide, and is most often seen in adults. Being overweight or obese and having a close relative with Type II diabetes increase a person’s chances of developing the condition.

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Table 12.1 Causes, signs/symptoms, treatment and prevention of diabetes mellitus Type I diabetes Type II diabetes Causes The pancreas does not produce insulin. The pancreas does not produce enough insulin or the body cells do not respond to the insulin. Signs/symptoms • Higher than normal blood glucose level • Excessive thirst • Frequent urination • Glucose present in the urine • Extreme hunger • Unexplained weight loss • Fatigue • Blurred vision • Slow-healing wounds Treatment and • Insulin treatment by means of regular • Oral medication to help lower prevention insulin injections or using an insulin blood glucose levels pump • Weight management • Regular monitoring of blood glucose • A healthy diet low in sugar levels and saturated fats and high in • A healthy diet low in sugar and dietary fibre saturated fats and high in dietary fibre • Regular exercise • Regular exercise • Regular medical checkups • Regular medical checkups

Cardiovascular disease (CVD)

Cardiovascular disease refers to a group of conditions that affects the heart and blood vessels, such as hypertension and coronary heart disease. • Hypertension (high blood pressure) occurs when the blood pressure in the arteries is consistently high (≥140/90 mmHg). Obesity increases the risk of hypertension developing. This is called secondary hypertension, as it results from another medical condition. • Coronary heart disease (CHD) is a condition caused by a build-up of fatty material (plaque) inside coronary arteries. These are arteries that supply oxygenated blood to the heart muscle cells. The process by which plaque is deposited in the lining blood clot of the arteries is called atherosclerosis. The plaque plaque reduces the internal diameter of the coronary buildup arteries and causes the blood pressure in the arteries to increase. A blood clot may then form in one of the blocked narrow arteries. coronary artery dying muscle

Figure 12.2 Atherosclerosis

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Table 12.2 Causes, signs/symptoms, treatment and prevention of cardiovascular disease (CVD) Hypertension Coronary heart disease (CHD) Causes • Being overweight or obese • A diet high in saturated fats • Alcohol use • Lack of exercise • Smoking • Smoking • Stress • Lack of exercise • A diet rich in salt Signs/symptoms • Higher than normal blood pressure • Chest pain (angina) (≥140/90 mmHg) • Heart attack (myocardial • In many cases, there are no warning infarction) signs/symptoms (‘silent killer’) • Heart attack (myocardial infarction) • Stroke Treatment and • Prescription drugs to lower blood • Coronary artery bypass surgery prevention pressure (heart bypass surgery) • Weight management • A daily low-dose aspirin tablet to help prevent blood clot formation • Stress management • Weight management • Reduced alcohol consumption • A diet low in saturated fats and salt • A diet low in saturated fats and salt • Regular exercise • Regular exercise • Stopping smoking • Stopping smoking

The importance of diet and exercise to lifestyle-related diseases

Diet and exercise are important components of the treatment and prevention measures for all of the lifestyle-related diseases discussed above. Eating a healthy, balanced diet ensures that excess carbohydrates and fats, which contribute to these diseases, are not consumed. This limits weight gain and helps in the maintenance of normal heart rate and blood pressure. In particular, the diet should be low in saturated fats and high in dietary fibre supplied by fresh fruits, vegetables and whole grains. Regular, aerobic exercise also limits weight gain, promotes more efficient gaseous exchange, a faster metabolic rate, a lower heart rate and an increase in muscle size and strength. Exercise has the additional benefit of improving mental health, as it helps to reduce depression and anxiety, and boosts self-esteem.

Revision questions

1 Define the terms: a health b disease 2 Using examples, distinguish between the following terms as they relate to disease: a communicable and non-communicable b signs and symptoms 3 Explain how asthma affects the respiratory tract. 4 a Describe FOUR signs/symptoms of obesity. 5 6

b Identify TWO other diseases that may affect persons who are obese. Describe the treatment measures for Type I and Type II diabetes. Discuss the importance of diet and exercise in the prevention and treatment of lifestyle-related diseases. 12 Health and disease

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Infectious diseases (communicable diseases)

Infectious diseases or communicable diseases are caused by pathogens such as viruses, bacteria, protozoans and fungi. These pathogens can be spread directly or indirectly from one person to another in a variety of ways (see Tables 12.3, 12.4 and 12.5). When controlling any of these diseases, the aim is to prevent further development and spread of the disease so that its incidence in the population is gradually reduced. Vaccinating individuals against a disease (see page 136) and treating their symptoms are two important methods that can be used to control infectious diseases. The aim of treating a disease is to relieve the symptoms experienced by the person suffering from the disease and to cure the disease if possible. Table 12.3 Examples of air-borne, water-borne and food-borne infectious diseases Disease Causative agent Method of Signs Symptoms transmission Influenza Virus Air-borne • Cough • Headache droplets from • Shivering • Sore throat the respiratory • Elevated • Muscle system body aches temperature (fever) • Stuffy or runny nose

Bronchitis (acute)

Virus

Air-borne • droplets from the respiratory • system • •

Pneumonia

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Bacterium (most common) – Streptococcus pneumoniae

Bacterial • spores in • air-borne droplets from • the respiratory system

Prevention and control measures • Influenza vaccination • Treat with painkillers, fever reducers, bed rest and antiviral drugs • Avoid overcrowded areas • Good ventilation Cough with • Chest • Treat with bed mucus discomfort rest and lots of fluids to drink Wheezing • Avoid Shortness of overcrowded breath areas Fever • Avoid lung irritants • Good ventilation Cough • Chest pain • Treat with antibiotics Fever • Nausea • Avoid Shortness of • Fatigue overcrowded breath areas

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Disease

Causative agent Method of Signs transmission Tuberculosis Bacterium – Air-borne • Chronic Mycobacterium droplets from cough tuberculosis the respiratory • Blood in system sputum • Fever • Weight loss • Lung tubercles (nodules) Ringworm Fungus – Tinea Spores on • Red patches surfaces, skin, on the body animals

Cholera

Typhoid

Symptoms • Loss of appetite • Fatigue

Prevention and control measures • BCG vaccination • Treat with antibiotics • Avoid overcrowded areas

• Itching

• Treat with fungicide ointments, creams or lotions • Ensure the skin is kept dry • Avoid sources of infection Bacterium – Contaminated • Severe • Stomach • Cholera watery pain vaccination Vibrio cholera water diarrhoea • Muscle • Treat with • Vomiting cramps antibiotics and by drinking • Dark• Thirst rehydration coloured (associated fluids urine with (associated dehydration) • Chlorination of with drinking water dehydration) • Proper disposal of faeces Bacterium – Contaminated • Fever • Stomach • Typhoid Salmonella water and pain vaccination • Rash typhi food with • Diarrhoea • Headache • Treat antibiotics • Loss of appetite • Chlorination of drinking water • Weakness • Wash fruits and vegetables thoroughly

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Disease

Causative agent Method of transmission Gastroenteritis Viruses – e.g. Contaminated rotavirus, water and norovirus food Bacteria – e.g. E. coli

Signs

Prevention and control measures • Diarrhoea • Abdominal • Rotavirus pain vaccination • Vomiting • Fatigue • Treat by • Fever drinking • Nausea rehydration fluids • Chlorination of drinking water • Proper disposal of faeces • Frequent hand washing • Good food hygiene Note that influenza, acute bronchitis and pneumonia are classified as acute respiratory infections. An acute infection is one that comes on rapidly, has distinct symptoms and lasts for a short time. Chronic bronchitis is a long-lasting inflammation of the bronchi and bronchioles that is associated with smoking (see page 42). It is not a communicable disease.

Sexually transmitted infections (STIs)

Symptoms

Sexually transmitted infections (STIs) are passed from one person to another during sexual intercourse. Examples of STIs are gonorrhoea, syphilis, genital herpes and HIV/AIDS. Table 12.4 Examples of sexually transmitted infections Infection Causative agent Method of Signs Symptoms Prevention transmission and control measures Gonorrhoea Bacterium • Unprotected • Pus • Itching • Treat with – Neisseria sexual discharge and antibiotics gonorrhoeae intercourse from the burning • Condom use with an vagina or sensation during sexual infected penis when person urinating intercourse • Blindness • Public • Mother to the in babies education eyes of her infected • No vaccine baby during during exists childbirth childbirth • Sterility Syphilis Bacterium – • Unprotected • Painless • Muscle • Treat with sexual round aches antibiotics Treponema intercourse sores on pallidum of • Condom use with an the genitals • Loss appetite during sexual infected lasting 3 to 6 intercourse person weeks • Public • Mother to • Body rash education foetus across and sores • No vaccine the placenta • Stillbirths exists • Brain damage

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Infection

Causative agent

Method of transmission

Signs

Symptoms

Prevention and control measures Genital Viruses – herpes • Unprotected • Recurrent • Genital • Treat with herpes simplex virus sexual genital itching antiviral type 1 (HSVintercourse blisters and drugs to 1) and herpes with an ulcers reduce simplex virus type infected symptoms 2 (HSV-2) person • Condom use during sexual intercourse • Public education • No cure or vaccine exists AIDS – Virus – human • Unprotected • Rapid weight • Extreme • Treat using acquired immunodeficiency sexual loss tiredness antiretroviral immune virus (HIV) intercourse • Recurring to slow • Headache drugs deficiency with an reproduction fever syndrome infected of the virus • Night sweats person (main • Condom use method in the • Swelling of during sexual Caribbean) lymph glands intercourse • Using • Prolonged • Use sterile infected diarrhoea needles needles and cutting • Skin rash or cutting instruments instruments • Sores around • Test blood for the mouth, • Transfusions HIV prior to anus or of infected transfusion genitals blood • Public • Infected education mother to • No cure or baby during vaccine exists pregnancy and breastfeeding

Mode of action of HIV/AIDS

When the human immunodeficiency virus (HIV) enters the blood, the virus particles bind to certain specialised white blood cells of the immune system known as T lymphocytes. They then enter these cells and begin to make copies of themselves. The new HIV particles burst out of the lymphocytes, destroying them. The new particles go on to attack more lymphocytes and this starts to weaken the body’s immune system. When a person is first infected, flu-like symptoms lasting 1 to 2 weeks may develop 2 to 6 weeks after infection. The person may then remain without symptoms for 10 years or more, but the virus is continuing to weaken their immune system. When the immune system is weakened to a point that it cannot destroy invading pathogens, the person becomes ill and develops AIDS. People with AIDS display signs and symptoms outlined in Table 12.4 and are susceptible to other infections, known as opportunistic infections, such as pneumonia, tuberculosis and some types of cancer, e.g. Kaposi’s sarcoma. 12 Health and disease

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The significance of HIV/AIDS

There is major concern worldwide regarding the spread of HIV/AIDS. HIV was first identified in 1983. At the end of 2016, the WHO estimated that 36.7 million people worldwide were living with HIV and that 35 million people have already died from AIDS. The Caribbean is the second most-affected region in the world after Africa. The spread of HIV/AIDS is very difficult to control for several reasons. • There is currently no vaccine or cure for HIV/AIDS. • The virus has a long incubation period between when it enters the body and when symptoms develop. This can be 10 years or more. During this time, the infected person can pass on the virus without knowing it. • It can be very difficult to convince persons to change their sexual behaviour. • Anti-retroviral drugs are relatively expensive and have to be taken daily for the remainder of the infected person’s life. Side effects are severe in some persons and include fatigue, nausea and vomiting, diarrhoea, headaches and insomnia. • There is still a social stigma associated with HIV/AIDS so persons who have the disease may not disclose this to others or seek medical assistance.

The effects of STIs on a pregnant mother and her foetus

Many STIs can infect the foetus during pregnancy or the baby during birth. Syphilis can pass from mother to foetus across the placenta and can result in stillbirths or premature births and syphilitic babies can develop serious problems with many internal organs. HIV can also pass across the placenta, or from mother to baby during birth or while breastfeeding, causing the baby to become HIV positive. Gonorrhoea can infect the eyes of the baby during birth, leading to eye infections and blindness. Active herpes blisters on the genitals can infect the baby with the virus as it is being born.

Vectors and vector-borne infectious diseases

Vector-borne diseases are infectious (communicable) diseases that are transmitted by a vector. A vector is an organism that carries pathogens in or on its body and transmits the pathogens from one host to another. The vector is not usually harmed by the pathogen. Rats, mosquitoes and houseflies are examples of vectors. Rats transmit leptospirosis; mosquitoes transmit several diseases including malaria, dengue, chikungunya and zika; and houseflies transmit gastroenteritis. Table 12.5 Examples of vector-borne diseases Disease Causative Method of Signs and Treatment Prevention and agent transmission symptoms control measures Malaria Protozoan – Mosquito • High fever • Drugs • Measures to such as control the Plasmodium – Anopheles and sweating quinine and Anopheles • Feeling cold chloroquine mosquito (see and shivering page 131) • Weakness • Antimalarial • Can lead to drugs to protect death against infection • Protect against mosquito bites, e.g. long sleeves, insect repellents, mosquito nets • Public education 128 12 Concise Revision Course: Human and Social Biology

Disease

Causative agent Viruses – DEN-1, DEN-2, DEN-3 and DEN-4

Method of transmission Mosquito – Aedes aegypti

Signs and symptoms Dengue • High fever fever • Severe headache • Severe joint and muscle pains • Skin rash • Bleeding from the nose, gums and beneath the skin (dengue haemorrhagic fever) Leptospirosis Bacterium Rat urine • Headache – Leptospira Urine of • Muscle pains domestic and • High fever farm animals • Nausea and vomiting • Jaundice (yellowing of the skin) • Red eyes • Liver and kidney failure

Treatment

Prevention and control measures • Painkillers • Measures to and fever control the Aedes reducers aegypti mosquito (not aspirin) (see page 131) • Bed rest • Protect against mosquito bites • Increase (see malaria fluid intake above) • Public education

• Antibiotics • Painkillers and fever reducers

• Rodent control (see page 132) • Vaccination of domestic animals • Avoid contact with animal urine, infected animals and contaminated soil and water • Public education

The life cycle of a mosquito

There are four distinct stages in the life cycle of a mosquito: • Egg: The adult female lays eggs in standing water. The eggs float on the surface of the water. • Larva: When eggs hatch, the larvae emerge. Larvae hang from the surface of the water and breathe air through breathing tubes. This is the feeding and growing stage of the mosquito life cycle. The larvae feed on microorganisms and organic matter in the water. • Pupa: The larva develops into a pupa. Pupae live in the water and also breathe air through breathing tubes. This is the non-feeding stage of the mosquito life cycle in which the larval tissue re-organises into adult tissue. • Adult (imago): The adult emerges from the pupa. The adults are able to fly and they feed on nectar and sugars from plants. This is the reproductive stage of the mosquito life cycle. After mating, the female needs a blood meal to mature her eggs before she lays them. This blood is usually taken from a human when the female mosquito flies and feeds in the evenings. During the day, the adults rest in cool, dark places around human residences.

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breathing tube antenna larva

surface of water egg

feeding brushes

breathing tube

compound eye developing limb

adult

pupa

Figure 12.3 The life cycle of a mosquito

The mosquito as a vector

Humans are the primary hosts of the pathogens that are transmitted by mosquitoes. Mosquitoes are the secondary hosts. The pathogens cause disease in the primary hosts, but the secondary hosts are not harmed by them. When a female mosquito bites an infected person, she sucks up blood that contains pathogens. The pathogens pass through the walls of her intestines and move into her salivary glands. When she bites another person, the pathogens are transmitted to that person when she injects saliva into that person’s blood to prevent it from clotting.

The life cycle of a housefly

There are four distinct stages in the life cycle of a housefly: • Egg: The adult female lays eggs in faeces, compost or other decomposing organic material, e.g. the bodies of dead animals. • Larva (maggot): When eggs hatch, the larvae emerge. This is the feeding and growing stage of the housefly life cycle. Maggots feed and grow rapidly and then burrow deep into the organic material they were feeding on. • Pupa: The larva develops into a pupa which has a hard, brown protective covering. This is the nonfeeding stage of the housefly life cycle in which larval tissue re-organises into adult tissue. • Adult (imago): The adult emerges from the pupa. The adults have legs and wings and are able to fly. They feed on decaying organic matter and human food. This is the reproductive stage of the housefly life cycle. After mating, the female lays eggs.

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adult

the adult house fly feeds on human food, faeces or other waste material

pupa

egg eggs are laid in faeces, compost or other decomposing organic matter larvae live in organic matter

larva

Figure 12.4 The life cycle of a housefly

The housefly as a vector

Houseflies transmit several pathogens that cause food poisoning while they are feeding. A housefly feeds using its proboscis (an elongated sucking mouthpart) which it lowers onto its food. Digestive juices are released through the proboscis onto the food to digest it externally. The dissolved food is then sucked up into the fly’s gut. Houseflies collect pathogens on their legs, body and mouth parts when they feed on organic waste and faeces, and also take them into their gut in the food consumed. The flies then transfer these pathogens onto human food while walking on the food and feeding, or they pass them onto the food in faeces or vomit spots.

Methods of controlling vectors

The control of vectors is very important in order to control the spread of diseases transmitted by these vectors. Studying the life cycle of a vector helps in the control of that vector, as this knowledge can be used to determine at which stage or stages control will be easiest, cheapest and most effective.

The control of mosquitoes

Mosquito larvae and pupae can be controlled by: • Draining all areas of standing water. • Adding insecticides to breeding areas to kill the larvae and pupae. • Introducing fish into breeding areas to feed on the larvae and pupae (biological control). • Spraying oil onto the surface of standing water to prevent the larvae and pupae from breathing. Adult mosquitoes can be controlled by: • Spraying with insecticides to kill the adults. • Removing dense vegetation to remove the adult’s protection.

The control of houseflies

Houseflies can be controlled by: • Proper disposal of human and animal waste. • Covering food so that flies cannot land on it. • Spraying adults with insecticides to kill them. • Using fly traps to kill adults. • Treating all sewage.

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The control of rats

Rats can be controlled by: • Using traps and/or bait to kill them. • Introducing cats or other animals that prey on rats (biological control). • Rodent-proofing buildings (exclusion).

The impact of diseases on the human population

Diseases have several socio-economic impacts on the human population including: • Increased demand on health services. • Job losses and loss of earnings for affected people. • Reduced productivity of businesses. • Reduced foreign exchange earnings for the country. • Lowered standards of living. • Shortened life expectancies.

Revision questions

7 Name the causative agent of each of the following diseases: a influenza b ringworm c typhoid d tuberculosis 8 Heavy rain resulted in flooding in a rural community. This was followed by an

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outbreak of cholera. a Identify FOUR signs/ symptoms that will be experienced by affected community members. b Outline the measures that should be taken to prevent further spread of the disease. Describe the causative agent, signs/symptoms and treatment measures of gonorrhoea. There is great concern in the Caribbean regarding the spread of HIV/AIDS. Discuss FOUR reasons for this. Describe TWO ways in which STIs may be passed from a mother to her baby. a What is a vector? b Identify TWO vector-borne diseases and the vector responsible for their transmission. Using a labelled diagram, describe the life cycle of a housefly. Describe control measures for ANY TWO stages in the life cycle of a mosquito. Discuss the impact of diseases on the human population.

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13 Hygiene and defences against disease

The human body is always surrounded by microorganisms, some of which are pathogens. However, there are measures that can be taken in order to reduce the likelihood of these pathogens entering the body and causing disease. The body also has natural defences against pathogens, such as a healthy, functioning immune system.

Personal hygiene

Personal hygiene refers to practices that are carried out by individuals in order to maintain cleanliness and good grooming of the body. Maintaining personal hygiene is important because it helps to: • Ensure good health. • Prevent the spread of infections. • Eliminate body odours. • Prevent dental caries. • Promote social acceptance.

Skin and hair hygiene

When people are active or the air temperature is high, sweat is produced in order to cool the body. Evaporation of the water in sweat leaves salts, urea and dead skin cells on the surface of the skin. Bacteria feed on these substances and produce an unpleasant odour, called body odour (BO). They can also cause infections. In order to reduce body odour and the likelihood of infections, the following measures should be carried out: • Regular washing of the body, especially the armpits, genitalia and between the toes. • Regular washing of the hair. • Drying the skin and hair thoroughly after washing. • Applying a deodorant to clean, dry skin of the armpits. • Changing and washing clothing frequently.

Genital hygiene

Genital hygiene is maintained by: • Thorough cleaning of the genitalia, especially during menstruation in females. • Wiping the female genitalia from front to back to prevent faeces entering the vagina. • Male circumcision (removal of the foreskin) or pulling back the foreskin and washing the area with soap and water.

Hands hygiene

Hands hygiene is maintained by: • Washing hands before preparing and eating meals. • Washing hands after using the toilet. • Keeping fingernails short and clean.

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Dental hygiene

Dental hygiene is outlined in page 30.

Controlling the growth of microorganisms Sterilisation Sterilisation is the complete destruction of all of the microorganisms present in a specified region. Methods of sterilisation include: • Ultra-high temperature treatment (UHT) – This method is used for the sterilisation of liquid food items such as milk, soups, sauces and baby food and can affect the flavour. The food is heated to temperatures higher than 135 °C for 1 to 2 seconds, cooled rapidly and packaged in pre-sterilised containers. • Pasteurisation – This method kills most of the microorganisms in food and drinks while maintaining the quality of the product. It is a commonly used method for sterilising milk. The process involves heating the milk to 72 °C for 15 to 25 seconds and then cooling it very quickly. • Canning – This method is used to protect a wide variety of foods from the action of microorganisms. Containers are filled with the food, covered with lids and placed into a boiling water bath or a steam bath. The heat kills the microorganisms in the food and the lids are sealed onto the containers after removal from the bath, preventing further entry of microorganisms. • Autoclaving – This method is also referred to as steam sterilisation, and involves the use of pressurised steam in an autoclave to kill microorganisms in and on liquids, equipment and instruments such as hospital equipment and surgical instruments. An autoclave is similar to a pressure cooker. Inside the autoclave, the high pressure ensures that high temperatures of above 121 °C are maintained in order to destroy all microorganisms and their spores. • Boiling – This method involves boiling materials to be sterilised, such as surgical instruments, in water at 100 °C for 15 to 30 minutes. It is also used for the purification of drinking water. Boiling kills all bacteria and some spores.

Disinfection Disinfection involves the use of chemicals to reduce the number of microorganisms that are present in a specified region to a level that cannot cause infection. Disinfection can be carried out by using disinfectants or antiseptics: • Disinfectants are chemicals used to destroy microorganisms in or on non-living objects, e.g. in water and on counter tops and floors. Examples of disinfectants are chlorine and ethanol. • Antiseptics are chemicals used to destroy microorganisms on living tissues, e.g. on the surface of the skin and in the mouth. Examples of antiseptics are hydrogen peroxide, rubbing alcohol and iodine. Disinfectants are stronger and more toxic than antiseptics and can be harmful to living tissues. Antiseptics are milder and cause little or no harm to living tissues.

Antibiotics and antifungal agents

Antibiotics are chemicals that are used to kill bacteria or to slow their growth. Many antibiotics are produced by living organisms. The first antibiotic to be discovered was penicillin, which is produced by the Penicillium fungus. Scientists are now able to make synthetic antibiotics to treat or prevent different bacterial infections. Antifungal agents (fungicides) are chemicals that are used in the treatment of fungal infections such as athlete’s foot and ringworm.

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Defence against disease

The immune system protects the body from infections in different ways. Some white blood cells are able to engulf and digest pathogens by the process of phagocytosis. Other white blood cells, called lymphocytes, produce antibodies. An antibody is a specific protein produced by lymphocytes in response to a specific antigen. An antigen is a substance that is recognised as foreign to the body and stimulates lymphocytes to produce antibodies. An antitoxin is an antibody that is produced in response to a specific toxin and that is able to neutralise this toxin. Antigens include toxins and bacterial, different types of antibody – fungal and viral proteins. These proteins each antibody is produced in are usually displayed on the surface of the response to a specific antigen pathogen, as shown in Figure 13.1. When antigens are detected in the body, antigen – a specific the appropriate lymphocytes multiply protein displayed on the surface quickly and produce specific antibodies of the pathogen for these antigens. These antibodies bind to the antigens and cause the pathogens antigen-antibody interaction – the to clump together so that the phagocytes pathogenic specific antibody microorganism can engulf them, or they cause the causes destruction of the pathogen pathogens to disintegrate. Antibodies can also neutralise the toxins produced by Figure 13.1 The antibody–antigen interaction the pathogens.

Types of immunity

Immunity is the body’s temporary or permanent resistance to a disease. Immunity can be innate or acquired: • Innate immunity refers to the Acquired immunity inborn ability of the body to resist disease. It is inherited genetically and is present from Natural Artificial birth. (Antigens or antibodies (Antigens or antibodies are enter the body in a deliberately introduced into the • Acquired immunity refers to the natural way) body to stimulate an immune response or to provide protection) immunity that the body gains over time. It is not present at birth. There are four different Active Passive Active Passive types of acquired immunity. (Antibodies are (Antibodies pass (Antibodies are (Antibodies in

Natural active immunity

made in response to antigens that entered the body naturally)

from mother to the foetus via the placenta or to the baby in breast milk)

made in response to antigens introduced in vaccines)

serum are injected into the body)

Natural active immunity is acquired by a person exposed to Figure 13.2 The types of acquired immunity a pathogenic disease. When the antigen is recognised, the lymphocytes begin to produce the specific antibody. While antibody production is taking place, the person experiences signs and symptoms of disease. When enough antibodies have been produced,

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noitartnecnoc ydobitna

they destroy the pathogens or neutralise the toxins, and the person recovers. The antibodies gradually disappear from the blood and some lymphocytes develop into lymphocyte memory cells that remember the specific antigen. When the same pathogen re-enters first exposure the body, the memory cells recognise to the pathogen the antigen, multiply and produce second exposure antibodies build up slowly. to the pathogen large amounts of the specific antibody This gives the pathogen time rapidly. The antibodies destroy the to cause symptoms of the disease pathogen or neutralise its toxins so antibodies slowly large quantities of quickly that the person does not disappear from the antibodies are made blood after recovery develop any signs or symptoms of the rapidly. The pathogen is destroyed before disease, i.e. the person is immune to symptoms develop the disease. This is known as active immunity because the antibodies are produced by the body of the person time exposed to the pathogen. This type of immunity may provide short-term Figure 13.3 Antibody production during the acquisition of protection, e.g. against the common active immunity cold, or long-term protection, e.g. chicken pox is rarely caught twice.

Natural passive immunity

Natural passive immunity is acquired by the transfer of antibodies from the mother to the foetus or baby. Antibodies are passed from the mother to the foetus across the placenta and from the mother to the baby in breast milk, especially colostrum, the first breast milk formed after birth. This is known as passive immunity because antibodies are produced by another organism’s body. The protection provided is short-term as no memory cells have been produced in the baby’s body, and the antibodies will gradually disappear from the blood.

Artificial active immunity

Artificial active immunity is acquired by the deliberate introduction of a small amount of the weakened or dead pathogen, or the antigen itself into a person’s body. This process is known as vaccination and the preparation that is injected is called a vaccine. The antigen or toxin present in the vaccine does not cause disease, but it stimulates lymphocytes in the person’s body to produce the specific antibody needed. Lymphocyte memory cells also develop and provide protection against future infection by that pathogen. Vaccines that provide long-term protection have been developed for several infectious diseases including tuberculosis, typhoid and polio. Immunisation is the process by which a person is made immune or resistant to an infectious disease. Immunisation is usually carried out by administering a vaccine.

Artificial passive immunity

Artificial passive immunity is acquired when serum containing antibodies or antitoxins produced in the body of another organism is injected into a person’s body for immediate relief of symptoms of infection. The immunity provided is short-term as the antibodies will eventually disappear from the blood. For example, serum containing antibodies against tetanus is used if tetanus is suspected.

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Revision questions

1 Why is it important to maintain personal hygiene? 2 Outline THREE measures used to maintain EACH of the following: a skin and hair hygiene b dental hygiene c hands hygiene 3 Distinguish between the following terms:

4 5 6 7

a sterilisation and disinfection b disinfectant and antiseptic c antibiotic and antifungal agent Describe THREE methods of sterilisation. Define the terms ‘antibody’ and ‘antigen’. Name the cells that produce antibodies and describe how antibodies work to protect the body. Identify and explain the type of immunity that is gained in the situations described: a Kryssie contracted chicken pox when she was a child. She does not get sick several years later when there is another outbreak of chicken pox. b Enrique was injected with a serum after being bitten by a snake. c Shiann got the influenza vaccine before travelling abroad.

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14 Drug use and misuse A drug is any chemical substance that affects the functioning of the body. Some drugs are used to treat medical conditions and to improve health while others are illegal. All drugs can have harmful effects on the body if they are used incorrectly.

Drug dependence

Drug dependence takes place when a person takes a drug over a period of time and needs the drug in order to function. The person is said to be addicted to the drug. Drugs affect the body in different ways. Some drugs affect the physical functioning of parts of the body, and are said to have physiological effects. Some drugs affect the brain and cause changes in mood and behaviour. These are described as psychological effects. Drug dependence can be physical or psychological: • Physical dependence occurs when the body adapts to the drug and the body’s cells cannot function without it. The person will experience withdrawal symptoms if drug use stops suddenly; these are often painful and include tremors, nausea, diarrhoea and body aches. • Psychological dependence occurs when the person feels the constant need for the drug. The drug becomes the central focus of their lives and they feel they cannot function without it. Drug misuse refers to the use of a drug for purposes for which it was not intended or using a drug in excessive quantities.

Prescription drugs

A prescription drug is a drug that legally requires a prescription from a medical practitioner to be dispensed. Some prescription drugs have very strong effects, and persons may develop dependence on these drugs. Prescription drug abuse is an area of growing concern. Examples of prescription drugs that can be abused include: • Sedatives – These are drugs that are used to treat anxiety and insomnia. They slow down body functions, cause the user to feel calm and induce sleep. Examples include sleeping pills and tranquillisers. Sedatives are depressants of the central nervous system. They slow the heart rate, breathing rate and the speed of transmission of nerve signals. Sedative misuse can lead to poor muscular coordination, slurred speech, blurred vision and mental confusion. • Painkillers – These drugs interfere with the transmission of nerve signals and reduce the perception of pain. Examples include paracetamol, aspirin and morphine. They also reduce anxiety and promote muscle relaxation. Some painkillers have similar effects to depressants, slowing the breathing rate, lowering the blood pressure and causing drowsiness. Misuse of painkillers may result in nausea, vomiting, mental confusion, dizziness and fluctuations in the heart rate. • Antibiotics – These are drugs that are used to treat bacterial infections, as they either kill or inhibit the growth of bacteria. Examples include penicillin and streptomycin. Misuse of antibiotics may result in the development of antibiotic-resistant strains of bacteria. Some persons are also allergic to antibiotics, in which case their use can be fatal.

Non-prescription drugs

Some non-prescription drugs are legal and can be obtained over-the-counter at a pharmacy (without a prescription from a medical practitioner). Other non-prescription drugs, e.g. alcohol, may only be used legally by persons who are of a certain age. This age limit differs in different countries. Some non-prescription drugs are illegal, e.g. cocaine and heroin.

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Cocaine

Cocaine is a white powdery substance that is usually inhaled through a tube. It is a highly addictive illegal drug which is a powerful stimulant of the central nervous system. Misuse of cocaine causes increased heart rate, breathing rate, blood pressure and body temperature. These can lead to sudden death by a heart attack or stroke. Cocaine use may also result in weight loss, destruction of the septum of the nose, reduced need for sleep, paranoia, anxiety, depression and, later, schizophrenia and other mental illnesses.

LSD (acid)

LSD, also known as acid, is a very powerful hallucinogenic illegal drug. It is taken as a pill or on blotting paper, and causes the user to go on a ‘trip’ or a state of altered consciousness, during which colours seem more intense and lights seem brighter. The pupils become dilated and the body temperature and blood pressure increase. Users may also become disoriented, anxious and have impaired judgement.

Heroin

Heroin is a highly addictive, illegal narcotic obtained from the opium poppy. It is taken by sniffing or by injections into the limbs or directly into veins. It is a depressant of the central nervous system, which initially reduces stress and anxiety by slowing the heart rate, breathing rate and the speed of transmission of nerve impulses. Dependence is established very quickly and withdrawal symptoms are severe, including diarrhoea, vomiting, muscle pain and cold flashes with goose bumps. Injection of heroin is also associated with the transmission of HIV and other pathogens, as drug users often share unsterilised needles.

Figure 14.1 Heroin and pills can kill

Ecstasy

Ecstasy is a hallucinogenic drug that is taken in tablet form. It causes heightened perception, sexual stimulation and reduced appetite. Ecstasy users experience mood changes and the reduction of inhibitions, which may result in unprotected sexual intercourse. It also causes increased heart rate, blood pressure and body temperature. Heat exhaustion may occur as a result of the elevated body temperature, which could lead to death. Long-term ecstasy use often results in an irregular heartbeat, brain damage and kidney failure. 14 Drug use and misuse

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Marijuana (cannabis)

Marijuana (also known as cannabis, ‘ganja’, ‘herb’ and ‘pot’) is a hallucinogen that is usually smoked. It is the most commonly used illegal drug. Marijuana produces a feeling of wellbeing (a ‘high’) followed by a feeling of despair (a ‘low’). Short-term effects include dilated pupils, red eyes due to dilation of capillaries in the eyes, dizziness, increased appetite, slowed reflexes, increased heart rate and hallucinations. Heavy marijuana use may cause long-term lung and heart problems, mental disorders Figure 14.2 Marijuana leaves are dried, rolled into a cigarette in vulnerable individuals and and smoked reduced fertility in males.

Alcohol

Alcohol is a legal drug that is a depressant of the central nervous system. It slows down the passage of nervous impulses. It is a very commonly used and misused drug which acts on the body quickly, as it is rapidly absorbed into the bloodstream. Persons who are dependent on alcohol are called alcoholics. Alcoholism is considered to be a disease. Misuse of alcohol has short-term and long-term effects on the body.

Short-term effects of alcohol use • • • • • • • • •

Slowed reflexes and reduced muscular coordination. Impaired concentration and judgement. Lack of self-control and aggression. Slurred speech, distorted vision and hearing. Dehydration due to frequent urination. Memory lapses (blackouts). Vomiting. Drowsiness. Loss of consciousness.

Long-term effects of alcohol use • • • • • • • •

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Fatty liver disease and cirrhosis (scarring) of the liver. Increased blood pressure, heart attack and stroke. Cancer of the mouth, throat and oesophagus. Ulcers and other intestinal disorders. Permanent brain damage. Long-term memory loss. Alcohol poisoning. Malnutrition. 14 Concise Revision Course: Human and Social Biology

Alcohol can be passed across the placenta from the mother’s blood into the blood of the foetus. Babies that were exposed to large quantities of alcohol prior to birth may develop foetal alcohol syndrome (FAS), which is characterised by mental retardation.

The social effects of drug misuse

Drug misuse has a devastating impact on individuals, families and communities. Addiction may lead to broken relationships, loss of parents from households, personal neglect and neglect of family members. Higher suicide rates and antisocial behaviour are associated with drug use. Babies born to drug addicts may have developmental problems or they may be addicted to the drug as well. Drug addicts may suffer the negative health effects associated with the misuse of drugs and require treatment and rehabilitation. The cost to society to provide these services is very high. Drug use may also lead to loss of jobs and reduced productivity. This affects families directly and the society as a whole. In the case of Caribbean countries, it may mean reduced foreign exchange earnings. Criminal acts such as murder, burglary and prostitution are often carried out in order for drug addicts to obtain money to buy drugs. Thus, the crime rate tends to be higher in areas where drug misuse is prevalent. There are also more automobile accidents when people drive under the influence of drugs.

Revision questions 1 2 3 4 5 6 7 8 9

What is a drug? Define drug dependence. Distinguish between physical and psychological dependence. What is the function of EACH of the following prescription drugs? a antibiotics b sedatives Describe FIVE effects of cocaine use on the human body. Name TWO hallucinogenic drugs and describe their effects on the human body. Why is alcohol considered a drug? Describe FIVE short-term and FIVE long-term effects of alcohol misuse. Discuss the social effects of drug misuse in your country.

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Exam-style questions – Chapters 12 to14 Structured questions

1 a) i) Define the term ‘non-communicable disease’.

b)

c)

2 a) b)

c)

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(1 mark)

ii) Name TWO non-communicable lifestyle-related diseases that are prevalent (2 marks) in the Caribbean. iii) Explain why diet and exercise are important measures in the prevention (3 marks) and treatment of the diseases named in a) ii) above. Dengue fever is a vector-borne disease that has affected many countries in the Caribbean. i) Name the vector that is responsible for the spread of dengue fever. (1 mark) ii) State TWO signs/symptoms of dengue fever, other than fever. (2 marks) iii) Describe THREE measures that can be taken by community members to (3 marks) control the spread of dengue fever. Scientists recently announced the development of a dengue vaccine. Explain (3 marks) how this vaccine will work to provide immunity to dengue fever. Total 15 marks i) What is meant by the term ‘drug misuse’? (1 mark) ii) Name THREE drugs, other than heroin, which are commonly misused in the (3 marks) Caribbean. A study was carried out in a particular country to assess heroin use within various age groups. Table 1 below shows the results of the study. Table 1 Heroin addicts in various age groups Age group Number of addicts 15–24 475 25–34 1035 35–44 354 45–54 198 55 or older 81 i) Construct a bar graph using the data in Table 1. (3 marks) ii) Compare the number of heroin addicts in the various age groups. (3 marks) iii) Discuss THREE socio-economic implications of the findings of the study (3 marks) for the country. The spread of HIV/AIDS is often associated with drug use. State TWO ways in (2 marks) which HIV/AIDS is transmitted, other than by sharing drug needles. Total 15 marks

Exam-style questions – Chapters 12 to14

Structured essay question

3 a) Sterilisation and disinfection are both methods that are used to prevent harmful

microorganisms from affecting us. i) Describe TWO differences between sterilisation and disinfection. (4 marks) ii) Suggest how sterilisation and disinfection could be used when caring for (2 marks) a patient in a hospital. Provide ONE situation for EACH method. iii) Your classmate, Jordan, suggests that antiseptics are the same as disinfectants. Explain to Jordan that they are different, stating ONE difference between (2 marks) them. b) Your new friend, Jess, has poor hygiene and it is affecting her self-esteem. Advise Jess on measures she should take to maintain good personal hygiene. Include in your answer: • THREE reasons for maintaining good personal hygiene • TWO methods of skin hygiene (7 marks) • TWO methods of dental hygiene Total 15 marks

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Section E – The impact of health practices on the environment 15 Pollution and its effects

Pollution is the unfavourable alteration of the environment by the release of harmful substances or forms of energy into the environment. A pollutant is a harmful substance or form of energy that causes unfavourable changes to the environment. Based on their origin, pollutants can be classified into domestic, agricultural and industrial pollutants. • Domestic pollutants – These are pollutants that are released from homes. They include sewage from the kitchen, the bathroom and the laundry room, as well as food waste. • Agricultural pollutants – These are mainly associated with modern agricultural practices, and include pesticides and fertilisers. • Industrial pollutants – These are pollutants that are released from industry. They include oxides of carbon, oxides of nitrogen, smoke, dust and other particulate matter.

Air pollution

Air pollution results from the release of harmful substances or forms of energy into the atmosphere. Many cities experience air pollution associated with industrial activities, such as energy production in power plants and processing of materials, as well as the operation of numerous motor vehicles in cities. Air pollution in rural areas is often associated with agricultural practices such as land clearance by slash and burn. Table 15.1 Examples of air pollutants and their effects Pollutant Origin Harmful effects Carbon dioxide • Burning fossil fuels in • Builds up in the atmosphere and enhances the industry, motor vehicles greenhouse effect which contributes to global (CO2) warming (see page 145). and power plants • Some is absorbed by oceans and causes ocean acidification. This is a lowering of the pH of ocean water, which harms aquatic organisms. Carbon monoxide • Burning fossil fuels in • Combines with haemoglobin in the blood more industry and motor readily than oxygen. This reduces the amount of (CO) vehicles oxygen being carried to body cells and results in headaches, dizziness, loss of consciousness • Cigarette smoke and death. Sulfur dioxide • Burning fossil fuels in • Combines with water vapour, smoke and other industry and power air pollutants to form smog, which causes (SO2) plants respiratory problems, e.g. asthma, bronchitis and lung disease, and irritates the skin and eyes. • Dissolves in rain water to form acid rain. Acid rain lowers the pH of the soil and bodies of water such as lakes, streams and rivers, and makes them unsuitable for organisms. It also damages plants, harms animals and corrodes buildings.

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Pollutant Origin Oxides of nitrogen • Combustion at high temperatures in industry, motor vehicles and power plants Volatile organic • Vehicle exhaust fumes compounds (VOCs) • Industrial waste Dust and other • Combustion in industry particulate matter • Mining and quarrying • Domestic fires

Harmful effects • Combine with water vapour, smoke and other air pollutants to form smog (see above). • Reduce plant growth. • Dissolve in water to form acid rain (see above). • Combine with water vapour, smoke and other air pollutants to form smog (see above). • Cause respiratory problems, e.g. asthma, bronchitis and lung disease. • Coat leaves, which reduces photosynthesis.

The greenhouse effect and global warming

Greenhouse gases, e.g. carbon dioxide, water vapour and methane (CH4), in the atmosphere allow heat energy from the Sun to pass through them and to warm the Earth. However, they trap much of this heat in the atmosphere by reflecting it back towards the surface of the Earth. The trapped heat also warms the Earth. This is similar to how a greenhouse traps heat, so it is called the greenhouse effect. 2 The Earth reflects some radiation back into space.

Sun

3 Greenhouse gases absorb some radiation and radiate it back to Earth. This also warms the Earth.

1 Radiation from the Sun passes through the Earth’s atmosphere and warms the Earth. Earth

Earth’s atmosphere containing greenhouse gases

Figure 15.1 The greenhouse effect Human activities that release carbon dioxide, such as burning fossil fuels and deforestation, enhance the greenhouse effect and contribute to an increase in the Earth’s temperature over time. This is called global warming. Global warming is also leading to global climate change, which is having several effects on the environment, including: • Melting of polar ice caps and glaciers. • Rising sea levels. • Flooding of low-lying coastal areas. • Changes in global weather patterns. • Extreme weather and severe natural hazards. • Rising sea temperatures. • Wider spread of some infectious diseases.

Water pollution

Water pollution results from the release of harmful substances or forms of energy into a body of water. These pollutants make the water unsuitable for organisms to live in and for human use. 15 Pollution and its effects

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Table 15.2 Examples of water pollutants and their effects Pollutant Origin Harmful effects Suspended solids • Soil erosion, which causes silt • Reduce light penetration, which reduces and soil to wash into bodies of photosynthesis in aquatic plants. water when it rains • Block rivers and lakes. • Domestic and industrial waste Plant nutrients • Chemical fertilisers • Cause eutrophication (see below). (e.g. nitrates and • Sewage • Make water unsuitable for consumption. phosphates) High nitrate levels in water make it • Manure and other farm waste poisonous for babies to drink. • Detergents Organic matter • Sewage • Reduces the amount of oxygen dissolved in water, leading to the death of fish and • Manure and other farm waste other aquatic organisms. • Industrial waste Pesticides • Used in agriculture to control • Can harm beneficial organisms as well as pests, pathogens and weeds harmful ones. • Become higher in concentration up food chains and can harm top consumers. Heavy metal ions • Industrial waste • May be toxic to organisms and kill them directly. (e.g. mercury and lead) • May become higher in concentration up food chains and can harm top consumers. • Damage many body tissues and organs, especially parts of the nervous system. Pathogens • Sewage • May cause various infectious diseases, e.g. typhoid, cholera and dysentery. • Animal manure Heat • Factories and power plants, • May kill organisms directly. which release waste heat into • Makes organisms more susceptible to bodies of water pathogens. • Reduces the amount of oxygen dissolved in water, leading to the death of fish and other aquatic organisms. Radioactive waste • Nuclear power plants • Causes genetic defects (mutations). • Hospital waste • Can lead to death.

Eutrophication

Excess nutrients in water, especially nitrates and phosphates, cause an overgrowth of aquatic plants and algae, which gives the water a green appearance. When the plants and algae die, decomposers in the water break them down. These decomposers are aerobic bacteria, which multiply quickly and use up the dissolved oxygen in the water. This causes other aquatic organisms, e.g. fish, to suffocate and die.

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Figure 15.2 Eutrophication 15 Concise Revision Course: Human and Social Biology

Methods of controlling pollution Controlling air pollution

The following are measures that can be used to reduce the amount of air pollution: • Reduce the use of fossil fuels by using alternative energy sources, e.g. solar and wind energy, which do not cause air pollution. • Pass laws with strict penalties that limit the release of air pollutants by industry, e.g. a Clean Air Act. • Clean gaseous emissions from factories before releasing them into the atmosphere. • Equip motor vehicles with pollution control devices and modify engines to make them more fuel efficient. Burning less fuel means less air pollutants will be released. • Ban smoking or restrict the activity to specific locations. • Put public education programmes in place.

Controlling water pollution

The following are measures that can be used to reduce the amount of water pollution: • Carry out proper treatment of sewage before releasing it into bodies of water. • Compost plant waste, such as vegetable peelings and crop residues. • Use farm waste and waste from the food industry to produce biogas. • Use organic fertilisers instead of inorganic chemical fertilisers. • Use biodegradable detergents. • Use biological control or natural, biodegradable pesticides instead of synthetic pesticides. • Pass laws with strict penalties that limit the release of water pollutants by industry, e.g. a Clean Water Act. • Put public education programmes in place.

Revision questions

1 Define the terms: a pollution b pollutant 2 Several air pollutants are released into the atmosphere when fossil fuels are burned 3 4 5 6 7

in industry. Name THREE such pollutants and outline the harmful effects of EACH. Explain what is meant by the term ‘global warming’. Dawn wants to know why her teacher said that agriculture contributes to water pollution. Explain to her how the overuse of chemical fertilisers and pesticides affects aquatic environments. Identify the sources and outline the harmful effects of the following water pollutants: a suspended solids b organic matter c heavy metal ions List FOUR methods of controlling air pollution. Discuss FOUR methods of controlling water pollution.

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16 The cycling and treatment of water

All living organisms need water for survival and there is a great demand on water resources by the human population for various purposes. Most of the freshwater withdrawn from water bodies is used in agriculture for irrigation and to provide water for farm animals. A large amount of water is also used in industry, as well as for domestic purposes.

The water cycle

The water cycle, also known as the hydrological cycle, shows how water moves on, above and below the surface of the Earth. It also shows the changes of the state of water as it moves. The cycling of water ensures that all living organisms have a continuous supply of water to keep their cells hydrated and to act as a solvent for chemical reactions. Plants also need a steady supply of water for photosynthesis. The water cycle also ensures that aquatic organisms have a constant environment in which to live.

condensation

evaporation

precipitation transpiration

exhalation

surface runoff

infiltration percolation

Figure 16.1 The water cycle The following processes are involved in the water cycle: • Evaporation – Heat from the Sun causes liquid water in bodies of water, e.g. oceans, lakes, ponds, rivers and streams, and in the soil to change into water vapour, which enters the atmosphere. • Transpiration – Heat from the Sun also causes water from plants to be lost to the atmosphere as water vapour. • Respiration – When organisms respire aerobically, water is produced as a by-product and some of this is released into the atmosphere as water vapour when the organisms exhale. • Condensation – As water vapour rises, it cools and becomes water droplets that form clouds. • Precipitation – Water returns to the surface of the Earth in the form of rain, hail or snow. • Surface runoff – Some water flows across the surface of the ground into bodies of water. • Infiltration – Some water moves downwards through the soil. • Percolation – The water then moves through rocks into groundwater and may eventually return to bodies of water.

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Water purification

Water may become polluted in different ways as it moves through the environment, as outlined in Chapter 15. As a result, various forms of purification are required to make water safe for human use. Water that is safe to drink or to use in food preparation is called potable water. The aim of water purification is to ensure that drinking water: • Is safe for human consumption. • Is clear and not discoloured. • Has an acceptable taste. • Has an acceptable smell. In order to achieve this aim, drinking water from rivers, streams and lakes, as well as rainwater collected using gutters, needs thorough treatment. Treatment methods include the small-scale measures often used in the home and large-scale measures that provide water for cities and towns.

Small-scale domestic water purification Filtration

Muslin cloth can be used as a filter to remove suspended material from water. This does not make the water safe for drinking, but it can be used for other domestic purposes, such as bathing and washing clothes. Domestic filters can be attached to taps. Their pore sizes are tiny enough to remove suspended material, including bacteria and protozoa.

Boiling

This is the oldest method and is still satisfactory for purifying water on a small scale. For it to be effective, water must be brought to a ‘rolling boil’ for 10–20 minutes. This kills bacteria, spores, cysts and ova of intestinal parasites. It also removes hardness of water, producing soft water.

Chlorination

Chlorine tablets are very effective for disinfecting small quantities of water. One 500 mg tablet can be used to kill microorganisms in 20 litres of water. Chlorine bleach is also effective for killing microorganisms in water. One teaspoon of bleach should be added to one litre of water.

Large-scale water purification

There are four steps involved in the large-scale purification of water: 1 Screening – Water from rivers, lakes and reservoirs passes through grid screens to remove large floating materials and suspended solids. 2 Sedimentation – The water is then pumped to a settlement tank where fine suspended solid particles coagulate (clump together) and settle. 3 Filtration – The clear water from the settlement tank passes through sand filters containing microorganisms. These microorganisms remove organic matter from the water by feeding on it. 4 Chlorination – The filtered water is treated with chlorine to kill all harmful microorganisms that are still in the water. Fluoride is sometimes added at this stage to reduce tooth decay. The water is then pumped to storage tanks for distribution to consumers.

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river, lake or reservoir screen

pump sedimentation

clean water distributed to homes and factories storage tank pump

chlorination

filtration

Figure 16.2 Large-scale water purification

Testing water for bacteria

The presence of pathogenic coliform bacteria in water can be determined by using agar plates. The agar is a liquid when hot and forms a gel when cooled. It has nutrients in it that will allow bacteria to grow rapidly. Water that is safe for drinking will have no colonies of coliform bacteria. The steps involved in testing water for bacteria are outlined below: 1 Collect a sample of the water to be tested in a sterile container. 2 Pour a small amount of the water onto an agar plate. Cover the plate and tape the lid to ensure it does not come off. 3 Incubate the plate at 35 °C for 24 hours. Figure 16.3 Bacterial colonies on an agar plate 4 Count the number of colonies of bacteria.

The impact of human activities on water supplies

Humans are having a negative impact on water supplies in several ways: • They harvest freshwater for agricultural, industrial and domestic use, and as the human population grows, the demands for freshwater increase. • They carry out deforestation, which reduces the amount of transpiration and precipitation that take place to replenish water sources. • They release different types of waste and harmful substances into bodies of water. By carrying out the above activities, humans: • Reduce the amount of freshwater available for agricultural, industrial and domestic purposes. • Contaminate water sources, leading to a loss of potable water. • Increase the cost of water treatment, as multiple steps have to be used in the purification of heavily contaminated water. 150 16 Concise Revision Course: Human and Social Biology

Harmful effects of contaminated water on human health

Contaminated water is detrimental to human health because it may contain: • Pathogens that cause diseases such as typhoid, cholera and gastroenteritis. • Pesticides that may harm the nervous and endocrine systems. • Heavy metal pollutants, e.g. mercury and lead, that affect many body tissues, especially those of the nervous system, resulting in mental illnesses and brain damage. • Nitrates, which are especially harmful to infants and pregnant women because they reduce the amount of oxygen carried in the blood and can lead to blue baby syndrome. • Radioactive waste that may result in genetic defects and even death.

Revision questions

1 Draw and label a diagram of the water cycle, including the following processes: 2 3 4 5 6

evaporation, transpiration, condensation, respiration and infiltration. Describe TWO simple ways of purifying water in the home. Outline the processes involved in large-scale water purification. Your teacher asks you to outline the steps used to test water for the presence of bacteria. List the steps you would include in your answer. Discuss THREE impacts of human activities on water supplies. Explain, giving at least THREE reasons, why contaminated water is detrimental to humans.

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17 The treatment and disposal of human waste

Human activities produce waste material that must be properly treated and disposed of in order to keep the environment clean and to reduce the spread of disease. Some of this waste is in liquid form with suspended solids known as sewage, and some of the waste is solid waste, also known as refuse or garbage.

Sewage disposal

Sewage consists of human faeces and urine, household wastewater, wastewater from some industries and rainwater.

Improper sewage disposal

Improper sewage disposal takes place when untreated sewage: • is released directly onto the land • is released directly into open water • leaks from cracked sewage pipes. Improper disposal of sewage has a negative effect on human health and the environment: • Untreated sewage is directly responsible for the spread of infectious diseases such as cholera, typhoid and dysentery. • Untreated sewage that is released onto the land promotes the breeding of vectors, such as flies and rats, which transmit diseases. • Untreated sewage that is released into water may float on the surface of the water and reduce the amount of light that is absorbed by aquatic plants. This reduces the amount of photosynthesis taking place in the water and affects aquatic food chains. It may also reduce the amount of oxygen dissolved in the water, leading to the death of aquatic organisms. • Nutrients in untreated sewage may contribute to eutrophication of water bodies (see page 146). • Sewage gives off a foul odour that contaminates the environment.

Proper sewage disposal

Sewage is disposed of properly when it is removed from houses and other buildings through underground pipes or sewers, which take it to sewage treatment plants (see page 152) or into areas that are far enough from homes and water sources so as to not be problematic. Flush toilets and pit latrines are commonly used in the Caribbean to dispose of human faeces and urine.

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Flush toilets water tank water from piped mains supply

valves control water flow into and out of the tank handle water in the tank lid seat

water runs down this pipe and into the bowl when the toilet is flushed water that is flushed into the bowl washes the waste down to the sewers or a septic tank

toilet bowl this bend keeps some water in the toilet, which prevents odours and microorganisms coming up from the sewers

Figure 17.1 A flush toilet Faeces and urine are passed out into the toilet bowl, and water from the tank is used to flush them out of the building and into the sewers. The bend in the toilet keeps some water in the toilet and prevents unpleasant odours and microorganisms from coming up from the sewers. Flush toilets are very effective means of disposing of sewage, however, they generally require a large amount of water. New low-flow toilets are now available which use significantly less water.

Pit latrines Pit latrines are used in areas with fly screen made of galvanised limited water supply or where wire mesh iron roof there is no sewage treatment wire mesh-covered ventilation pipe to allow system in place. They should vent to allow air gases and odours produced circulation during decomposition in be carefully sited and used to the pit to escape into the ensure that water sources are not door atmosphere contaminated and to reduce the lid to keep base made of smooth likelihood of health hazards. The out vectors material for easy cleaning following guideline should be concrete cover cement pit collar prevents followed when siting pit latrines: slab to prevent the side from caving in entry of vectors • They should be dug to at least deep pit to reduce odours three metres (3 m) deep in order drop hole escaping and to allow the to reduce odours coming up pit latrine to be used for a long time at least 3 m from the pit and to ensure that they can be used for a long human waste time before they fill up. porous soil allows liquids to drain from the pit • They should be placed in sandy soil because bacteria in the latrines break down the faeces Figure 17.2 A pit latrine and convert them into liquids. Sandy soil will allow the liquids to drain away. • They should also be placed downhill and far enough away from wells and other sources of drinking water so that they do not contaminate these water sources.

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While the pit latrine is in use, no disinfectants should be added as these will kill bacteria, thereby preventing them from decomposing the faeces. When the pit is full, it should be covered and left for at least six months before the land can be used for another purpose.

Advantages of pit latrines

Pit latrines have been very effective for disposal of sewage in the Caribbean. • They require less water than flush toilets. • They are relatively cheap to construct.

Disadvantages of pit latrines

• They contribute to the risk of water and food contamination. • They can contribute to the spread of infectious diseases. • The rapid growth of the Caribbean population makes it difficult to site pit latrines. There is now limited land space available in appropriate locations. As a result of these disadvantages, pit latrines are due to be phased out throughout the Caribbean and replaced with modern disposal methods and sewage treatment systems.

Sewage treatment

There are two methods that are usually used in the treatment of sewage: • biological filter method • activated sludge method The initial treatment steps for both processes are as follows: 1 Screening – Large objects, e.g. plastic bottles, rags, paper and twigs, are removed from the sewage by using screens. 2 Grit settling – The sewage passes slowly through a grit pit, and the grit and sand settle out. 3 Sedimentation – The sewage flows slowly through sedimentation tanks where the remaining solid material settles and forms sludge. The sludge is removed from the bottom of the tanks and is used to make methane in a sludge digester or to make fertiliser. The liquid from the sedimentation tanks still contains suspended organic matter and is known as effluent. This effluent is then either passed into a biological filter, or into an aeration tank for treatment using the activated sludge method.

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sewage in sewer pipes screen – large objects are removed grit pit – grit and sand settle out sedimentation tank – solid material settles and forms sludge Biological filter method side view of percolating filter sprinkler

effluent in bed of stones covered with a film of microorganisms

effluent out

sludge removal

Activated sludge method side view of aeration tank effluent in mixing paddle

effluent out air bubbles

final settlement tank

compressed air

final settlement tank

water bodies, e.g. a river or the sea

Figure 17.3 Sewage treatment

Biological (percolating) filter method

The effluent is sprayed onto small stones that are covered with a film of aerobic bacteria and protozoa. The microorganisms feed on the organic matter in the effluent, breaking it down. The effluent is then passed to a final settlement tank to allow any remaining solids to settle, after which it is safe for release into bodies of water, e.g. a river or the sea.

Activated sludge method

The effluent is passed into aeration tanks where compressed air is forced through it. Paddles are also used to help with the mixing of air and effluent. This ensures that enough oxygen is present for aerobic bacteria in the tank to decompose the organic matter. The effluent from the tank is then passed to a final settlement tank to allow any remaining solids to settle, after which it is safe for release into bodies of water.

Domestic refuse disposal

Domestic refuse refers to all the unwanted solids that accumulate after use in the home, including organic matter such as waste food and garden waste, and other solid waste such as plastics, paper, glass and other materials. It is important that domestic refuse is disposed of properly. Disposal in landfills, incineration, composting and recycling are some of the main ways to dispose of domestic refuse. Before collection, refuse should be placed into bins with tight-fitting lids to prevent the entry of rats and flies. The refuse should be collected at least once per week, and the bins should be inspected and cleaned regularly. 155 17 The treatment and disposal of human waste

Table 17.1 Evaluation of some of the methods of domestic refuse disposal Method How method Advantages Disadvantages works Landfill (see below) • Once constructed, it is • Requires continuous convenient and relatively easy maintenance to prevent to use to dispose of refuse. leachate and toxic gases entering the environment. • Many different types of waste can be disposed of. • Waste gases can contribute to air pollution and unpleasant • Methane can be used as a fuel odours if allowed to escape. to generate electricity. can contaminate soil • The site can be re-landscaped • Leachate and water sources if allowed to and put to good use once the escape. landfill is full. • Uses up valuable land. • Unsightly when in operation. Incineration Solid • Reduces the volume of solid • Incinerators are relatively waste entering landfills. expensive to build and operate. combustible waste is • High temperatures kill harmful • Energy requirements to burned in pathogens in the waste. operate incinerators are high. incinerators • Heat produced can be used to • Waste gases are produced at very high generate electricity or to heat which can contribute to air temperatures. water and nearby buildings. pollution and cause respiratory problems. • Incinerators do not take up a lot of land. Composting Biodegradable • Reduces the volume of solid • Can be time consuming to waste entering landfills. ‘turn’ the compost daily. waste is broken down • Produces organic fertiliser • Compost heaps can give off by aerobic rich in mineral ions which is unpleasant odours. bacteria in beneficial to soil. • Compost heaps can attract compost heaps • Reduces the demand for pests and vectors of disease. or composters. synthetic chemical fertilisers which can harm soil.

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Figure 17.4 An incinerator

Landfills

Landfills consist of large, deep pits in which compacted solid waste is buried to isolate it from the surrounding environment. Domestic refuse is often disposed of in a landfill. To make a landfill, topsoil is removed and a large, deep pit is dug into the ground. The pit is lined with an impermeable material which forms the bottom liner to prevent liquids from the waste, known a leachate, seeping into the ground and contaminating soil and water. Two sets of pipes are installed, one to help drain off any leachate and carry it to a treatment plant, and the other to remove any waste gases, e.g. methane, which can be used as a fuel to produce electricity. On arrival at the landfill, the refuse is sorted to remove materials that can be recycled. The remaining refuse is then compacted to make it difficult for vectors to penetrate and to reduce its volume so the landfill can be used for a long time. The compacted refuse is then placed into the landfill and is covered with a layer of soil at the end of each day so it is not exposed to the wind and vectors, and to reduce smells.

Figure 17.5 A landfill site 17 The treatment and disposal of human waste

157

Any biodegradable organic material in the refuse is broken down by soil bacteria and fungi. It is during this decomposition that gases such as methane are given off. Any non-biodegradable refuse remains, and when a landfill is full, it is capped to seal it, the topsoil is replaced and vegetation is grown so that the land can be used in a variety of ways, e.g. recreational purposes or building. Landfills are the most cost-effective means of solid waste disposal in the Caribbean. However, finding suitable sites for landfills is becoming difficult.

The impact of solid waste on the environment

If solid waste is not disposed of properly it becomes a threat to the environment: • Toxic chemicals in the waste can leach out and contaminate the soil, aquatic environments and water sources. • Greenhouse gases, e.g. methane and carbon dioxide, can be released into the atmosphere where they contribute to the greenhouse effect (see page 145). • Hydrogen sulfide gas can be released into the air. This gas is extremely toxic, and even low concentrations irritate the eyes and respiratory system. • Plastics can enter waterways and oceans where they are harmful to aquatic organisms. • Refuse attracts rodents, which can spread disease. • Refuse creates an eyesore, which impacts negatively on tourism, especially eco-tourism.

Controlling the volume of solid waste

The volume of solid waste to be disposed of can be controlled by using ‘The Three Rs’ of waste management – reduce, reuse and recycle. Reduce means to cut down on the purchase and use of materials. Manufacturers can reduce the amount of waste to be discarded by using less packaging material. Individuals can also reduce waste by using electronic mail (e-mail) rather than paper mail and carrying shopping bags to the supermarket so that plastic bags are not taken. Reuse means to use again for the same or for a different purpose. Items that can be reused include glass bottles, clothing, old tyres and old newspapers. Recycling involves the separation and reprocessing of a resource into new products. Materials that can be recycled include paper, glass, metals and some plastics. Paper can be repulped and reused to make new paper, glass and metal can be melted and recast, and some plastics can be melted and reformed to make plastic wood, fibres for clothing and other useful materials. Composting recycles organic material into fertilisers. The Three Rs have several advantages: • They allow materials and energy resources to last longer, as they reduce the need for new products to be made. • They reduce the amount of waste to be disposed of in landfills and by incineration. • They reduce the amount of pollution that would result from manufacturing and waste disposal measures. One disadvantage of The Three Rs to consumers is that they must spend additional time separating waste into the different categories for disposal or recycling.

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Biodegradable and non-biodegradable waste

Waste can be classified as biodegradable and non-biodegardable: • Biodegradable waste is waste that can be broken down by microorganisms into harmless materials that can be recycled into the environment, e.g. food waste, paper, garden and farmyard waste, and a few plastics. • Non-biodegradable waste is waste that cannot be broken down by microorganisms, so it remains in the environment, e.g. most plastics, rubber, metal and glass.

Revision questions 1 2 3 4

Name THREE components of sewage. Distinguish between proper and improper sewage disposal practices. Discuss THREE impacts of improper sewage disposal practices. Identify ONE similarity and ONE difference between the biological filter and activated sludge methods of sewage treatment. 5 Outline the function of EACH of the following parts of a pit latrine: a ventilation pipe b lid c cement lining 6 Your neighbour is planning to construct a pit latrine in her yard. Explain to her some factors to consider when siting and constructing the pit latrine. 7 Discuss TWO advantages and TWO disadvantages of the use of pit latrines in the Caribbean. 8 Identify THREE methods of disposal of domestic refuse. 9 Describe a landfill and the operations that take place there. 100 Discuss THREE impacts of solid waste on the environment. 11 Define EACH of the following terms, as it relates to waste management: a reduce b reuse c recycle 122 Distinguish between the terms biodegradable and non-biodegradable materials, giving TWO examples of EACH.

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Exam-style questions – Chapters 15 to 17 Structured questions

1 Community members were advised by the health authorities to avoid polluted floodwater after a tropical storm. a) i) What is meant by the term ‘pollutant’? ii) Name TWO examples of water pollutants. b) i) Describe a test the health authorities could use to determine if the community’s water supply is contaminated with bacteria. ii) Describe ONE small-scale method of water purification that community members would be encouraged to use. c) Outline THREE methods of controlling water pollution. d) Discuss THREE impacts of human activities on water supplies.

2 a) i) Complete the following statement by filling in the blank spaces. Sewage consists of

,

(1 mark) (2 marks) (4 marks) (2 marks) (3 marks) (3 marks) Total 15 marks

and

(3 marks) . ii) Describe ONE improper sewage disposal practice. (1 mark) iii) Explain how the practice described in a (ii) above poses a threat to the health of (3 marks) communities in the Caribbean. b) Your neighbour thinks that pit latrines are inappropriate for sewage disposal. (3 marks) Outline THREE advantages of the use of pit latrines in the Caribbean. c) Biological filter and activated sludge are two methods used in sewage treatment. i) Which stage in the sewage treatment process is done immediately before the (1 mark) biological filter? ii) Compare the treatment of sewage by biological filter and activated sludge (4 marks) methods, giving TWO similarities and TWO differences between them. Total 15 marks

Structured essay question

3 a) Solid waste may be classified as biodegradable or non-biodegradable.

160

i) What is meant by the term ‘biodegradable’? (1 mark) ii) Give ONE example of a biodegradable waste material and ONE example of a (2 marks) non-biodegradable waste material. b) Solid waste is sometimes disposed of in a landfill. i) Describe how a landfill is made. (3 marks) ii) Describe the daily operations at a landfill. (4 marks) c) A small village in your country does not have a garbage collection system in place. You visit the village as a Health Inspector, and notice there is solid waste strewn all over the village. What advice would you give to the villagers about the proper (5 marks) disposal of this solid waste? Total 15 marks Exam-style questions – Chapters 15 to 17

Index

A ABO blood groups, 49, 110–111, 111t abortion defined, 92 induced, 92–93 spontaneous, 92 absorption in colon, 35 defined, 34 in small intestine, 34 acids, 29 amino, 6, 10, 20, 35 fatty, 20, 36 lactic, 44 acquired immunity, 135, 135f active transport, 8, 34 adenosine diphosphate (ADP), 43 adenosine triphosphate (ATP), 43 ADH. see antidiuretic hormone (ADH) adipose (fat) tissue, 35 ADP. see adenosine diphosphate (ADP) aerobic bacteria, 146 aerobic respiration, 1, 37, 43 agricultural pollutants, 144 air pollution, 144–145, 144t–145t controlling, 147 albinism, 105, 108 alcoholic beverages, anaerobic respiration and, 44 alcoholism, 140–141 alimentary canal, 27 movement of food through, 34 allele, 113 alleles, 108, 108t alveoli, 37, 42 gaseous exchange in, 40f walls of, 39 amino acids, 6, 10, 20, 35 amylase, 30 anaerobic respiration, 1, 43 industrial and domestic uses of, 44 anal sphincter, 35 animal cells, 1–2, 2f, 3t anorexia, 26 antagonistic pair, 59 anterior vena cavae, 51 antibiotic resistance, 106 antibiotics, 134, 138 antibodies, 35 antibody, 135

antidiuretic hormone (ADH), 67 antifungal agents, 134 antigen, 135 antigens, 49 antiseptics, 134 antitoxin, 135 anus, 27, 35 aorta, 51 appendicular skeleton, 57, 57f arteries, 49f, 50, 50t coronary, 53 artificial active immunity, 136 artificial pacemaker, 51 artificial passive immunity, 136 asexual reproduction, 1, 83 assimilation, 35–36 asthma, 119–121, 120f causes of, 120 effects on respiratory system, 119, 120f symptoms of, 120 treatment of, 121 astigmatism, 80 atheromas, 53 atherosclerosis, 53, 122, 122f ATP. see adenosine triphosphate (ATP) atria, 51 atrial systole, 52 autoclaving, 134 autonomic nervous system, 71, 75 autotrophs, 1 axial skeleton, 56–57 axons, 72 B bacteria, 4, 4f, 29, 44 aerobic, 146 denitrifying, 14 nitrifying, 14 nitrogen-fixing, 14 balanced diet, 25–26 ball and socket joints, 59, 59f biceps, 60 biconcave discs, 47 biodegradable waste, 159 biogas, 44 birth, 88 birth control, 89 methods, 89t–91t, 91f Biuret test, 21t

Index

161

blood cells, 46, 47t–48t, 58 clotting, 48–49, 53, 122 deoxygenated, 51, 52 groups, 49 oxygenated, 51, 52 plasma, 46–47, 54 blood pressure, 52 blood sugar (glucose) levels, regulation of, 69–70, 69f blood vessels, 49–50, 49f, 50t, 53f teeth, 28 BMI. see body mass index (BMI) body mass index (BMI), 26, 26t, 121 body temperature, regulation of, 69, 69f bones, 56 bovine somatotrophin (BST) hormone, 114 Bowman’s capsule, 64 brain, 72 functions of, 72t involuntary actions, 74–75 nerves, 74 neurones, 72, 73f parts of, 72, 72f reflex actions, 75–76 synapses, 74 voluntary actions, 74 bread making, 44 breathing, 37, 58 cigarette smoking and, 41–42 mechanism of, 39, 39f rate, factors affecting, 40 rescue, 41 bronchioles, 37, 42 bronchus, 37 BST hormone. see bovine somatotrophin (BST) hormone bulimia, 26 C cancerous tumours, 42 cancers, of reproductive systems, 85, 85t canine tooth, 28, 28t, 29f cannabis, 140 canning, 134 capillaries, 34, 49f, 50, 50t carbohydrates, 19, 19f functions of, 22, 22t laboratory tests to identify, 21, 21f, 21t properties of, 20t sources of, 22, 22t types of, 19, 19f

162

Index

carbon (C) atoms, 13 carbon-containing compounds, 13 carbon cycle, 13, 13f carbon dioxide, 6, 37, 44 levels, regulation of, 68 carbon monoxide, 42 cardiac arrest, 54 cardiac cycle, 52 cardiac muscle, 51 cardiovascular disease (CVD), 122, 123t cardiovascular system blood. see blood blood vessels, 49–50, 49f, 50t heart. see heart Caribbean food groups, 25 carnivores, 11 cartilage, 56 cartilaginous joints, 59 catalase, 30 cataract, 80, 80f cell division, 102 meiosis, 103–104, 104f mitosis, 102, 103f cell membrane, 1, 2f, 7, 36 cells animal, 1–2, 2f, 3t bacteria, 4, 4f blood, 46, 47t–48t, 58 defined, 1 egg (ovum), 4t, 5f epithelial, 4t, 5f muscle, 4t, 5f, 44 nerve (neurone), 4t, 5f plant, 1–2, 2f, 3t specialised, 4–5, 4t, 5f sperm (spermatozoon), 4t, 5f yeast, 44 cell sap, 2f cell wall, 2f, 8 central nervous system (CNS), 71. see also brain CHD. see coronary heart disease (CHD) chemical digestion, 27, 30–34 digestive system and, 32f, 33t chitin, 4 chlorination, 149 chlorophyll, 10 chloroplasts, 2f, 10 chromatin threads, 102 chromosomes, 102, 113 sex, 111 chronic obstructive pulmonary disease (COPD), 42, 42f

chymosin, 114 cigarette smoking, 41–42 components of, 41f and lungs, 42 cilia, 42 ciliary muscles, 79 circulation, 52–53, 52f double, 52, 52f pulmonary, 52 systemic (body), 52 circulatory system, 46–55 blood. see blood blood vessels, 49–50, 49f, 50t heart. see heart lymphatic system, 54–55, 54f need for, 46 clone, 83 clotting, blood, 48–49, 53, 122 CNS. see central nervous system (CNS) cocaine, 139 co-dominance, 109, 113 ABO blood groups, 110–111, 111t sickle cell anaemia, 110 colon, absorption in, 35 colour blindness, 113 combustion, 13 communicable/infectious diseases, 119, 124 examples of, 124t–126t sexually transmitted infections, 126–128, 126t–127t vector-borne, 128, 128t–129t cones, 78 constipation, 24, 24t consumers, food chains, 11 contaminated water, 151 continuous variation, 106 contraception. see birth control contraction, 52 coordination, by nervous and endocrine systems, 71–76 COPD. see chronic obstructive pulmonary disease (COPD) coronary arteries, 53 coronary heart disease (CHD), 122 coronary thrombosis, 53 cranial nerves, 74 cranial reflexes, 75 crown, teeth, 28 CVD. see cardiovascular disease (CVD) cytoplasm, 1, 2f, 7

D decomposers, 13, 14 deficiency diseases, 23, 23t degenerative diseases, 119 denature enzymes, 31 dendrites, 72 dental hygiene, 134 dentine, 28 deoxygenated blood, 51, 52 deoxyribonucleic acid (DNA) molecule, 102 dermis, 65, 66f, 66t diabetes mellitus, 70, 121, 122t dialysis, 65 diaphragm, 37, 39 diarrhoea, 24, 24t diastole, 52 diet, 19–24 balanced, 25–26 carbohydrates. see carbohydrates dietary fibre, 24 and lifestyle-related diseases, 123 lipids. see lipids minerals, 22–23, 22–23t proteins. see proteins unbalanced, 61 vitamins, 22–23, 22–23t water, 23–24 dietary fibre, 24 diffusion, 6, 34 digestion chemical, 27, 30–34 defined, 27 mechanical, 27, 28–30 digestive enzymes, 32, 32t digestive system, 27 and chemical digestion, 32f, 33t disaccharides, 19, 19f discontinuous variation, 106 diseases communicable/infectious. see communicable/ infectious diseases defence against, 135–136 defined, 119 degenerative, 119 hygiene as defences against, 133–134 impact on human population, 132 non-communicable. see non-communicable diseases signs/symptoms of, 119 disinfectants, 134 disinfection, 134 domestic pollutants, 144

Index

163

domestic refuse disposal, 155–159, 156t landfills, 157–158 dominant allele, 113 dominant trait, 113 double circulation, 52, 52f Down’s syndrome, 106 drug misuse, 138 social effects of, 141 drugs defined, 138 dependence, 138 misuse, 138 non-prescription. see non-prescription drugs prescription, 138 E ecological pyramids, 13, 13f ecstasy, 140 effector, 71, 73f egestion, 35, 63 egg (ovum), 4t, 5f elbow joint, movement of, 60, 60f emphysema, 42 Emulsion test, 21t enamel, 28 endocrine (hormonal) system, 81, 81f, 81t–82t coordination by, 71–76 energy, 11, 25 transfer in food chains, 12, 12f environmental variation, 106 enzymes, 30, 35, 43. see also proteins denature, 31 digestive, 32, 32t properties of, 31 epidermis, 65, 66f, 66t epithelial cells, 4t, 5f epithelium, 34 erythrocytes. see red blood cells eutrophication, 146, 146f excretion, 1, 35 defined, 63 kidneys and, 63–65 excretory products, 12 exercise, 89 effect on skeletal system, 60–61 and lifestyle-related diseases, 123 exhaled air, 41 extensor muscle, 59 eyelashes, 77 eyelids, 77 eyes, 77 astigmatism, 80

164

Index

cataract, 80, 80f colour detection by, 78 glaucoma, 80 image formation, 78, 78f light detection by, 78 light entering, 78, 78f long-sightedness, 80, 80f old sight, 80 parts, structure and functions of, 77f retina, 78, 79, 79f short-sightedness, 79, 79f F faeces, 35, 154 family planning, importance of, 91–92 fat, 25, 36 fat soluble vitamins, 22 fatty acids, 20, 36 fatty substances, 34 feeding, 1 female reproductive system, 83, 83f fermentation, 44 fertilisation, 87 fibrin fibres, 49 fibrinogen, 47 fibrous connective tissue, 59 filtration, water, 149 fixed/fibrous joints, 59 flexor muscle, 59 flush toilets, 153, 153f follicle stimulating hormone (FSH), 86 food chains, 11, 11f energy transfer in, 12, 12f food poisoning, 24 food production, genetic engineering and, 113–114 food webs, 12, 12f fossil fuels, 13 FSH. see follicle stimulating hormone (FSH) fungi, 4, 4f G gametes, 83, 102, 103, 108 gaseous exchange, 37 in alveolus, 40f mechanism of, 39, 40f gaseous exchange surface, 37 gastroenteritis, 24 genes, 102, 113 gene technology, 108 genetically modified organism (GMO), 113 genetic engineering, 113–115 advantages of, 115

disadvantages of, 115 and food production, 113–114 and medical treatment, 114–115 genetics, 108 genetic variation, 105–106 genital hygiene, 133 genotype, 105, 113 girdles, 57 glands, 81f, 81t–82t glaucoma, 80 global warming, 145 glomerulus, 64 glucagon, 69 glucose, 6, 10, 35 glycerol, 20, 36 glycogen, 69 grease spot test, 21t greenhouse effect, 145, 145f greenhouse gases, 145 growth, 1 H haemophilia, 112 hair hygiene, 133 hands hygiene, 133 health, 119 heart blood pressure, 52 cardiac cycle, 52 chambers, 51 circulation, 52–53, 52f functions of, 51f pacemaker, 51 heart attack, 51 causes and effects of, 53–54 risk factors, 53–54 symptoms of, 54 heartbeat, 52 heat, 69 hepatic portal vein, 35 herbivores, 11 heroin, 139 heterotrophs, 1 heterozygous individuals, 108, 109, 109f, 113 HGH. see human growth hormone (HGH) high blood pressure, 52 hinge joints, 59, 59f histones, 102 HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome) mode of action of, 127 significance of, 128

homeostasis, 63, 67–70 blood sugar (glucose) levels, regulation of, 69–70, 69f body temperature, regulation of, 69, 69f carbon dioxide levels, regulation of, 68 defined, 67 feedback mechanisms and, 67, 67f osmoregulation, 67, 68f homozygous individuals, 108, 109, 109f, 113 hormones, 35 bovine somatotrophin, 114 follicle stimulating, 86 human growth, 115 luteinising, 86 progesterone, 86 housefly control of, 131 life cycle of, 130, 131f as vector, 131 human brain. see brain human diet. see diet human growth hormone (HGH), 115 human papilloma virus (HPV), 85t human skeleton, 56–58, 56f appendicular skeleton, 57, 57f axial skeleton, 56–57 bones, 56 cartilage, 56 ligaments, 58 tendons, 58 humerus, 57f hydrolysis, 30 hygiene, personal, 133–134 hypermetropia, 80, 80f hypertension, 52, 53, 122 hypha, 4f hypothalamus, 67, 69 I immunisation, 136 immunity acquired, 135, 135f artificial active, 136 artificial passive, 136 innate, 135 natural active, 135–136, 136f natural passive, 136 implantation, 87 improper sewage disposal, 152 incisors, 28, 28t induced abortion, 92–93 industrial pollutants, 144

Index

165

inheritance co-dominance. see co-dominance monohybrid, 108 of sex in humans, 111 innate immunity, 135 insulin, 114, 114f intercostal muscles, 37, 39 intermediate neurones, 72 involuntary actions, 74–75 ions mineral, 8 nitrate, 14 irritability, 1 J joints defined, 59 types of, 59 K kidneys, 67 dialysis, 65 and excretion, 63–65 nephrons, 64, 64f kwashiorkor, 26, 26f L lacteals/lymph capillaries, 34 lactic acid, 44 landfills, 157–158 larynx, 37 leucocytes. see white blood cells LH. see luteinising hormone (LH) lifestyle-related diseases diabetes mellitus, 121, 122t diet and, 123 exercise and, 123 obesity, 121 ligaments, 58 limbs, 57 movement of, 59–60 pentadactyl, 57, 57f lipids, 10, 20, 20f functions of, 22, 22t laboratory tests to identify, 21, 21f, 21t sources of, 22, 22t living organisms active transport importance in, 8 characteristics of, 1 dependence on plants, 12 diffusion importance in, 6 osmosis importance in, 8

166

Index

variation in. see variation locomotion, 1, 61 long-sightedness, 80, 80f LSD (acid), 139 lungs, 37, 63 cigarette smoking and, 42 vital capacity, 40–41, 41f luteinising hormone (LH), 86 lymph, 54, 54f functions of, 54 lymphatic system, 54–55, 54f functions of, 54–55 lymph nodes/glands, 54 functions of, 55 lymphocytes, 48t, 54 lymph vessels, 54 M male reproductive systems, 84, 84f malnutrition, 25 maltose, 30 marasmus, 26, 26f marijuana (cannabis), 140 mechanical digestion, 27 teeth and. see teeth meiosis, 103–104, 104f, 105 mitosis and, 105f menstrual cycle, 86, 86f menstruation, 86 microbes/microorganisms bacteria, 4, 4f defined, 3 fungi, 4, 4f growth, controlling, 134 viruses, 3, 3f microvilli, 34 milk teeth, 28 mineral ions, 8 minerals, 22, 22t–23t deficiency diseases, 23, 23t mitochondrion, 2f mitosis, 102, 103f meiosis and, 105f mixed nerves, 74 molars, 28, 28t molecules lipid, 20, 20f protein, 20, 20f monohybrid inheritance, 108 albinism, 108 co-dominance, 109–111 monosaccharides, 19, 19f, 35

mosquitos control of, 131 life cycle of, 129, 130f as vector, 130 motor nerves, 74 motor neurones, 72, 73f mouth, 27, 37 mouth-to-mouth resuscitation, 41 moveable/synovial joints, 59 movement, 1 active transport, 8 diffusion, 6 joints, 59 of limbs, 59–60 osmosis, 7–8, 7–8f skeletal muscles, 58, 58f multicellular, 1 muscles cells, 4t, 5f, 44 ciliary, 79 extensor, 59 flexor, 59 insertion of, 60 intercostal, 37, 39 origin of, 60 skeletal, 58, 58f muscle tone, 60 mutations, 105 mycelium, 4f myocardial infarction. see heart attack myogenic heart, 51 myopia, 79, 79f N nasal cavities, 37 natural active immunity, 135–136, 136f natural passive immunity, 136 nephrons, 64, 64f nerve (neurone), 4t, 5f nerve fibres, 72 nerves, 74 nerves, teeth, 28 nervous system central, 71 coordination by, 71–76 organisation of, 71f peripheral, 71 neurones defined, 72 properties, 73 types of, 72, 73f nicotine, 42

nitrate ions, 14 nitrogen (N) atoms, 14 nitrogen-containing compounds, 14 nitrogen cycle, 14, 14f non-biodegradable waste, 159 non-communicable diseases, 119 asthma, 119–121, 120f lifestyle-related diseases, 121–123 non-prescription drugs, 138 alcohol, 140–141 cocaine, 139 ecstasy, 140 heroin, 139 LSD (acid), 139 marijuana (cannabis), 140 nucleoid, 4, 4f nucleus, 2f nutrients, 19 nutrition, 1, 19–36 absorption, 34–35, 34f assimilation, 35–36 defined, 19 digestion and. see digestion egestion, 35 human diet and. see diet O obesity, 25, 61, 121, 122 oestrogen, 86 old sight, 80 omnivores, 11 optimum pH, 31, 31f optimum temperature, 31, 31f orbits, 77 organelles, 1 organic compounds, 22. see also carbohydrates; lipids; proteins; vitamins organism, 5 organs, 5 excretory, 63 sense, 77, 77t organ systems, 5, 5t osmoregulation, 63, 67, 68f osmosis defined, 7 demonstrating, 7f explanation of, 7f overnutrition, 25 ovulation, 86 ovum, 87 production and structure of, 84–85, 84f oxygen, 6, 10, 37

Index

167

oxygenated blood, 51, 52 oxygen debt, 44 oxytocin, 88 P pacemaker, heart, 51 pain killers, 138 pasteurisation, 134 pathogens, 119, 124 PEM. see protein-energy malnutrition (PEM) pentadactyl limb, 57, 57f periodontal membrane, 28 peripheral nervous system (PNS), 71 peristalsis, 24, 34, 34f permanent teeth, 28 personal hygiene, 133–134 dental hygiene, 134 genital hygiene, 133 hands hygiene, 133 skin and hair hygiene, 133 pH, 68 phagocytes, 48t, 54 pharynx, 37 phenotype, 105, 113 photosynthesis, 1 defined, 10 pit latrines, 153–154, 153f pituitary gland, 67 placenta, 87, 88 plant cells, 1–2, 2f, 3t, 8, 8f plaque, 29 plasma, 46, 54 composition of, 47 functions of, 47 serum, 47 plasmids, 4, 4f platelets (thrombocytes), 46, 48t pleural fluid, 37 pleural membranes, 37 PNS. see peripheral nervous system (PNS) pollutant, 144 pollution, 144 air, 144–145, 144t–145t methods of controlling, 147 water, 145–146, 146t polysaccharides, 19, 19f poor posture, 61 posterior vena cavae, 51 postnatal care, 89 posture, 61 pregnancy, and development, 87–88, 87f, 88t premolars, 28, 28t

168

Index

prenatal care, 88–89 presbyopia, 80 prescription drugs, 138 primary consumer, food chains, 11 producers, food chains, 11 progesterone, 86 proper sewage disposal, 152 flush toilets, 153, 153f pit latrines, 153–154, 153f protein-energy malnutrition (PEM), 26 proteins, 20, 20f, 26, 35. see also enzymes functions of, 22, 22t laboratory tests to identify, 21, 21f, 21t sources of, 22, 22t pulmonary artery, 37, 51 pulmonary circulation, 52 pulmonary vein, 37 pulp cavity, 28 pupil reflex, 75, 75f Q quaternary consumer , food chains, 11 R rats, control of, 131 receptor, 71, 73f recessive allele, 113 recessive trait, 113 recycling, 158 red blood cells, 46, 46f, 47 reduce, 158 reflex actions, 75–76 reflex arc, 75 relaxation, 52 reproduction asexual, 1, 83 defined, 1 sexual, 1, 83, 105 reproductive systems cancers of, 85, 85t female, 83, 83f male, 84, 84f rescue breathing, 41 respiration, 10, 13, 36, 43–44 aerobic, 1, 37, 43 anaerobic, 1, 43–44 defined, 1, 43, 83 respiratory system, 37–44 breathing. see breathing gaseous exchange. see gaseous exchange parts, functions of, 38t–39t structure of, 37, 37f

response , defined, 71 retina, 78, 79, 79f reuse, 158 rhesus system, 49 ribosomes, 2f ribs, 37, 57 rods, 78 root, teeth, 28 rough endoplasmic reticulum, 2f S saprophytes, 13 secondary consumer, food chains, 11 sedatives, 138 selective reabsorption, 65, 65f sense organs, 77, 77t sensitivity, 1 sensory nerves, 74 sensory neurones, 72, 73f septum, 51 serum, 47 sewage disposal, 152–154 improper, 152 proper, 152 sewage treatment, 154–155, 155f sex chromosomes, 111 sex-linked characteristics, 112–113 colour blindness, 113 haemophilia, 112 sexually transmitted infections (STIs), 126–128, 126t–127t sexual reproduction, 1, 83, 105 short-sightedness, 79, 79f sickle cell anaemia, 110 signs, of diseases, 119 sinoatrial node, 51 skeletal muscles, 58, 58f skeletal system effect of exercise on, 60–61 factors adversely affect, 61 functions of, 58 human skeleton, 56–58, 56f skin, 63, 65 functions of, 66t hygiene, 133 structure of, 66f skull, 56 small intestine, absorption in, 34 smooth endoplasmic reticulum, 2f solid waste impact on environment, 158 volume, controlling, 158

somatic nervous system., 71 specialised cells, 4–5, 4t, 5f, 51 sperm (spermatozoon), 4t, 5f, 84, 87 production and structure of, 84–85 spinal nerves, 74 spinal reflexes, 76, 76f spontaneous abortion, 92 spores, 4f starch, 10, 30 sterilisation, 134 stimulus, 71 STIs. see sexually transmitted infections (STIs) stomach, 5 subcutaneous layer, 65, 66f, 66t sugars, 29 symptoms, of diseases, 119 synapses, 74 synovial joints, 59 systemic (body) circulation, 52 systole, 52 T tears, 77 teeth care, guidelines for, 30 importance in digestion, 28 milk, 28 permanent, 28 structure, 28, 29f types of, 28, 28t temperature, 69 tendons, 58, 60 tertiary consumer, food chains, 11 thorax, 37 structure of, 38f “Three Rs” of waste management, 158 thrombin, 48 thrombocytes, 46, 48t thrombokinase, 48 tissue fluid, 54 tissues, 5 tooth decay causes of, 30 process of, 29, 29f trachea, 37 transgenic organism, 113 triceps, 60 trophic level, 11, 11f U UHT. see ultra-high temperature treatment (UHT) ultra-filtration, 65, 65f

Index

169

ultra-high temperature treatment (UHT), 134 unbalanced diet, 61 unicellular, 1 urinary system, 63 structure of, 64f urine, 153 production of, 65, 65f V vacuoles, 2f valves, 51, 54 variation continuous, 106 defined, 105 discontinuous, 106 environmental, 106 genetic, 105–106 importance to living organisms, 107 vector-borne infectious diseases, 128, 128t–129t vectors, 128 housefly, 130–131, 131f methods of controlling, 131–132 mosquitos, 129–130, 130f veins, 49f, 50, 50t ventricles, 51 ventricular systole, 52 venules, 50 vertebral column, 57, 58 villi, 34, 34f viruses, 3, 3f vital capacity, 40–41, 41f vitamins, 22, 22t–23t deficiency diseases, 23, 23t voluntary actions, 74 voluntary nervous system, 71

170

Index

W waste biodegradable, 159 domestic refuse disposal, 155–159, 156t non-biodegradable, 159 sewage disposal, 152–154 substances, 46, 63 water, 8, 23–24 contaminated, effects on human health, 151 cycle, 148, 148f supplies, impact of human activities on, 150–151 water molecules, 7 water pollution, 145–146, 146t controlling, 147 water purification, 149 large-scale, 149, 150f small-scale domestic, 149 testing water for bacteria, 150 water-soluble substances, 34 water soluble vitamins, 22 white blood cells, 46, 48t word equation, photosynthesis, 10 Y yeasts, 4, 44 yoghurt, 44 Z zygote, 87

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CSEC® CONCISE REVISION COURSE

Get ready to succeed in CSEC® Human and Social Biology with this full-colour Concise Revision Course. Written by experienced teachers and authors, this book offers complete course coverage and is packed with illustrations, revision questions and exam practice to ensure that you are fully prepared for the exam. • Full coverage of the CSEC® Human and Social Biology syllabus • Advice on your revision process includes tips on exam technique, explanations of exam command words, and help with organising your revision effectively • Revision questions at the end of each topic to help secure your knowledge and understanding • Exam-style questions at the end of each section provide effective practice for the actual exam • Answers available for free at www.collins.co.uk/caribbeanschools About the authors Anne Tindale is a best-selling author of texts and resources for CSEC® Biology and Chemistry. She has taught science to CSEC® levels with great success for many years and is author of concise revision courses, workbooks and multiple choice practice materials for both CSEC® Biology and Chemistry, all published by Collins. She is currently Head of Science at St Winifred’s School, St Michael, Barbados. Shaun deSouza has 20 years’ experience teaching science subjects at CSEC® and CAPE® levels, producing excellent results. Shaun has been an assistant examiner for CSEC® Human and Social Biology and CAPE® Environmental Science for several years. She currently lectures at the Montego Bay Community College, Jamaica. CSEC® Concise Revision Course range:

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