Integrated Science Notes

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INTEGRATED SCIENCE NOTES.docx SCIENCE IN AGRICULTURE 1.PLANT NUTRITION • • • •

Green plants are the only living organisms able to manufacture their own food. They are called food producers of the world. Animals rely on green plants to make food that produces energy. Plants make food in the form of carbohydrates molecules i.e. sugar and starches.

PHOTOSYNTHESIS Photo-means light Synthesis- means make/build up. • It whereby green plants manufacturer their own food using carbon dioxide, water and light as a source of energy. • Green plants are the producers of food and oxygen. • Plants convert light energy into potential chemical energy. • Photosynthesis can be defined as the process by which green plants use light energy to combine carbon dioxide and water into carbohydrates, releasing oxygen as a by-product. • This can be summarized by an equation as follows: Carbon dioxide + water

light Chlorophyll

carbohydrates + oxygen

Experiment : Testing a leaf for starch.

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Method; 1. Place the leaves in boiling water to stop chemical reactions. 2. Boil the leaf in alcohol in water bathto remove chlorophyll. 3. Place the brittle leaves in warm water for few seconds to soften the leaves. 4. Spread the leaves on a white tile and flood the leaves with iodine solution. 5. Record the colour change of iodine. RESULTS. A blue black colour denotes the presence of starch. Conclusion. Green plants make starch during photosynthesis. Experiment : To show that carbon dioxide is necessary for photosynthesis. Materials: two potted plants Method : 1. De-starch the leaf. 2. Cover the plants in a polythene bags for two days, keeping them in a lighted place. 3. Insert an inverted lid containing soda lime or calcium carbonate on the surface of the pot for plant A. This absorbs carbon dioxide. 4. Cover the plant again and leave plant B untreated and keep the plants for 2-3 days. 5. Perform the starch test. 6. Record the results.

Experiment : To show that light is necessary for photosynthesis. Materials:one potted plant,aluminium foil,or cardboard, sellotape, paper clips, starch testing kit.

METHOD 1. Destarch the potted plant by placing it in darkness for at least 24 hours. 2. Take a small piece of aluminium foil or cardboard and cut simple shape out on its middle and cover leaf on the plant with the foil, ensuring the cut out side is uppermost. 3. Leave the plant in sunlight for 4-6 hours. 4. Remove the leaf covered by the foil and test it for starch. 2

Results . The covered part remains brown and the uncovered part turns blue black.

Experiment : To show that chlorophyll is necessary for photosynthesis

: MATERIALS Variegated leaf, starch testing kit.

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Method: 1. Starch is difficult to remove chlorophyll from a leaf without killing it so a leaf which contains chlorophyll only in patches is used. 2. Test the variegated leaf for starch. Results. The green part turns blue black showing the presence of starch yet the white part remains brown. PRODUCTS OF PHOTOSYNTHESIS •

• • • •

Green plants manufacture starch or sugar . Oxygen is also formed during the process. It passes out of the leaves by diffusion into surrounding air through the microscopic pores or holes called stomata which are found on the lower surface of the leaf. These allow the entry of carbon dioxide as well as the exit of oxygen. Carbohydrates molecules formed are transported to other parts of the plant. This is call translocation. Starch is stored in leaves for a source of energy at night or in special storage organs.

EXPERIMENT; What gas is released during photosynthesis? Materials. Water weed, glass beaker, funnel, test tube, and splint.

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Method; 1. Pour water into a deep glass beaker. 2. Place the water weed in the water and invert a short stemmed funnel over it, making sure that the stem of the funnel is completely submerged in the water. 3. Fill a test tube with water and invert it over the stem of the funnel under water. 4. Place the apparatus in sunlight for 2-4 hours. Observations. Gas collects in the test tube. Remove the test tube by lifting it upwards sob that the gas remains in it. Test the gas in the test tube with a glowing splint. RESULTS;The splint burst in to a flame.

FACTORS THAT AFFECT THE RATE OF PHOTOSYNTHESIS. A plant without one of necessary factors cannot photosynthesize. The speed of photosynthesis varies to the amount of each factor present. • The process of photosynthesis would be affected by : - (a) Light intensity (b) Temperature variations (c) Carbon dioxide concentration NB: The rate of photosynthesis can be estimated by measuring one of the products (oxygen and carbohydrates).

Leaves and photosynthesis •

The leaves are the main organs for photosynthesis. Their structure is related or adopted for this process.

Cross section through a leaf.

• • • •

Cuticle layer:- It is a waxy layer on top of epidermis. It is a waterproof and therefore reduces the loss of water from the leaves and also prevents entry of pathogens. Palisade layer/mesophyll- : main organ of food production. The cells contain a lot of chloroplast. Spongy layer :- have got a lot of air spaces and is important for gaseous exchange. Vascular bundle-: contains the xylem and phloem vessels. -Xylem vessels-carries water required for photosynthesis. -Phloem vessels- carry away soluble food to other parts of the plant.

ADAPTATIONS OF THE LEAF FOR PHOTOSYNTHESIS • • • •

Large surface area to trap light. Thin leaf to allow light through and a short diffusion for carbon dioxide. Presents of stomata on the underneath of the leaf to allow gaseous exchange. Spongy layer which creates air spaces to allow carbon dioxide to enter through. 4

• •

Chlorophyll to attract or trap sunlight. Venation (veins) to carry water into the leaf and soluble food out of the leaf.

MINERAL NUTRITION • Plants require mineral salts from their environment. These are absorbed as ions in solution. • Each mineral element has a specific function in the plant. Uses of mineral elements and their deficiency disease MINERAL ELEMENT USES DEFICIENCY DISEASES Nitrogen (N) • Protein formation • Stunted growth • Good leaf growth • Yellowish of leaves(chlorosis) Phosphorus (P) • Producing energy carriers • Purple leaf colour • Good root growth • Stunted roots Potassium (K) • Flower and fruit formation • Yellow/brown leaf margins • For respiration and • Early death of fruits and photosynthesis flowers • For osmosis and ionic balance

2.PLANT PESTAND DISEASES •

Pests are organisms (plant/animal) which are harmful to plant or animal or which affects their activities.

Types of plant pests and diseases. •

•

•

•

Tissue eating pests: Affects the plant by biting and chewing plant roots, stem and leaves. They have got jaws which leaves holes , gaps and cut edges e.g. locusts, caterpillars, snail, beetles etc. Sap-sucking pests Affects the plant by sucking the juices. They have got a needle like mouth which piece through the plant tissue to suck the sap. They cause spots on leaves and stem resulting in wilting and premature drop e.g. aphids and red spider. Bacterial wilt diseases Affects the plant by blocking the xylem vessels of plants so that water and mineral salts cannot be transported e.g. bacterial wilt of tomatoes . Can be controlled by improving drainage and using good seed and rotating crops. Fungal rust diseases Parasite fungi cause white and brown particles on leaves preventing the plant from photosynthesis. Controlled by using resistant varieties.

METHODS OF CONTROLLING PESTS We have 3 methods of controlling pests. • Chemical control 5

•

•

Chemicals are used to control pests. These chemicals are known as pesticides/insecticides and fungicides. Cultural /natural methods Is when one practices crop rotation to destroy life cycle of pests which favour to feed on one crop. Also early planting, burning plant residues, weeding to prevent build up of pests. ] Biological control method This is when pests are used to feed on other pests on a natural enermy e.g. using other animals e.g. hens to feed on snails, aphids, caterpillar etc.

Comparing control methods Chemical methods Advantages • It is a quick method • It is specific

Disadvantages • It is expensive • Kill or damage other animals • Affect normal food chains • Potentially dangerous

Cultural methods Advantages • It is cheap • It is safe • It is readily available Biological methods Advantages • It is cheap

Disadvantages • It is slow • Needs to be repeated often

Disadvantages • Other animals may end up destroying the plant

Safe use of chemicals • • •

All pesticides are dangerous and should be used with precautions. Pesticides are graded depending on how dangerous or poisonous they are . Use pesticides with caution

Very Poison

Very Dangerous poison

Purple Extremely poisonous

Poison

Dangerous poison

Red Amber very dangerous poisonous

notes • Read all instructions carefully. • Wear protective clothing • Always clean up after use. 6

Green use with caution

Caution

• •

Store in locked places out of reach of children. Bury empty containers.

3.ANIMAL NUTRITION To grow , have energy , be healthy and productive , the food eaten must be changed into chemically simpler substances before the body can use it. The simpler substance are soluble and can be absorbed by the blood for use all over the body.

Digestion It is the process of food breakdown from complex to simpler substances that can be absorbed into the blood stream. This is done physically or chemically. The human alimentary canal

1. Mouth – food enters the mouth (ingestion) where it is chewed and mixed with saliva. Starch is digested in the mouth by action of enzyme called salivary amylase. The tongue rolls food into balls and pushes the food down. 2. Gullet/oesophagus – when food is pushed, it is forced to move slowly through this passage to the stomach. This process is called peristalsis (contraction and relaxation of muscles). 3. Stomach – food is kept here for up to 5 hours and chemical digestion takes place. Food is chewed into chime by action of stomach juices. 4. Small intestines – food enters the small intestines from the stomach. This is where digestion is completed. The gall bladder produces bile to digest proteins and other carbohydrates. The ileum joins the large intestines 5. Large intestines /colon – this is for absorption of water which enables wastes (faeces) to pass out via the rectum to the anus where egestion takes place.

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Summary of digestion Place Mouth Stomach Small Intestines Small Intestines

Organ producing Salivary glands Stomach walls Liver (gallbladder) Pancreas

Enzyme Salivary amylase Stomach juices Bile Pancreatic juices

Large Intestines

-

-

Food digested Starch Proteins Make fat drop Proteins, fats other carbohydrates Water absorbed

Digestive system of a cow (ruminant) Cattle are ruminants. They have four stomach parts including the rumen. Alimentary canal of a cow

-When feeding, cows graze and swallow the food without chewing. The food enters the rumen which contains bacteria which makes it possible for these animals to digest cellulose. Later the animal will then pass the food to the rectum and forms lumps. The food is then chewed again as cud. Food is then regurgitated by reverse peristalsis action of chewing. Finally, it passes through omasum sac to the obamasum (stomach) where gastric juices are produced. These contain chemical enzymes to digest proteins. After digestion has been completed, food is moved along the ileum and is absorbed into blood stream. NB: Cows are different from humans because they chew the cud.

Alimentary canal of a rabbit Rabbits are herbivores, but they are not ruminants. They have big front incisor teeth suited for biting off pieces of plant material.

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Plants are chewed and mixed with saliva containing enzymes that help to breakdown starches into simple sugars. After swallowing the food passes down the oesophagus to the stomach where digestion like that of human occurs. Cellulose that passes through the ileum is broken down by special bacteria in the caecum which enhance the process. Residue is passed out of the anus as soft.

Mechanical digestion     

Is the physical breakdown of food in the alimentary canal. It starts in the mouth by the action of teeth. In the stomach, food is squeezed, churned and mixed with gastric juices. Involuntarily muscles in the stomach bring this automatic action about. Peristaltic movements in alimentary canal (successive squeezing movements in the walls of the alimentary canal) Anti-peristalsis in ruminants allows the cow to chew and this is physical. The strong contraction of the rectal muscles helps to expel the undigested matter.

Chemical digestion 

Is the breakdown of food into smaller soluble molecules so that they can be observed into the blood stream. Enzymes bring about chemical digestion.  Enzymes are produced either in the walls of the gut or in glands. They are catalysts which speed up chemical digestion. NB: In the caecum (of rabbits) and rumen (of cattle) the bacteria secretes cellulose that changes cellulose to glucose.

Absorption 

  

Soluble food molecules are the end products of digestion. This happens mainly in the small intestines or ileum. Water and alcohol can be observed directly through the walls of the stomach. The ileum is very long in most mammals and its inner wall with its foldsand villi greatly increase the surface area available for absorption. The walls of villi are one cell thick and this enables simple food molecules to pass through. Inside each villus are capillaries with blood which collect and carry food molecules from the small intestines. Glucose and amino acids are absorbed by diffusion from an area of their high concentration in the ileum to one of their low concentration in the villus. 9

 

Inorganic salts, vitamins and water are also absorbed through the villi in the ileum Fatty acids and glycerol pass into the blood stream via the lacteal ducts of the villi and the lymphatic system.

The role of the liver 

Glucose, amino acids and fatty acids are carried to the liver in the blood via a system of capillaries and veins to the large herpatic portal vein. This connects theblood system surrounding the ileum to the liver. NB: The principal area for the absorption of nutrients is the ileum/small intestines.

Assimilation    

It looks at the fate of the products of digestion that have been absorbed into the body of an animal The carbohydrates and amino acids are taken to the liver through the hepatic portal vein Glucose is stored in the liver or in muscles as glycogen or fats Excess amino acids are taken back to the liver where they are de-animated to remove nitrogen which is made into area. The urea is then taken to the kidneys where it is removed as urine.

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4.Growth and development  



Farm animals that are reared for economic reasons are fed on food types that can be measured e.g. poultry, pigs etc. If the animals can be measured to find out their increase in mass, it should be possible to determine the amount of food that is fed to animal before it gains a unit mass. The animal converts the food into its own flesh. This is called conversion efficiency. Conversion efficiency of live animals can be obtained from growth curves made by plotting graphs of live weight against time. The graph curves are used for other things such as determining the most opportune time when animals kept for meat should be slaughtered.

NB: Conversion efficiency = mass gained by animal per month

x 100 %

Mass of food fed to animal per month Generally animal growth curves are S – shaped, that is they are sigmoid in shape, as shown in the diagram below.

Growth is slow soon after birth and it quickly speeds up. This period of rapid growth is called “grandperiod” of growth .The graph then slows down as the animal reaches maturity. It is most convenient to slaughter your animal for meat just before maturity age but after the start of breeding period.

Balanced rations 



Refers to types of food (s) the animal like to feed on. These supply enough of all the essential nutrients in their right amounts. Balanced rations will always contain carbohydrates,fats,proteins, vitamins and mineral salts. However animals do have special needs at different times of their lives e.g. young animals need extra proteins for growth , pregnant animals will need a lot of amino acids , calcium , iron and carbohydrates for the developing young ones. Animals being fed for slaughter will not require more protein. They require more fats and carbohydrates.

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Types of rations i.

ii.

Production ration– refers to the extra food which an animal needs per day to enable it to produce something such as milk,eggs, wool etc.This is related to the amount the animal is producing. Maintenance ration – refers to the amount of food supplied to an animal in a day to keep the animal in a healthy state without loss of weight. Maintenance rations are often related to the size and mass of the animal.

Malnutrition _-Means incorrect feeding. Animal’sdiet must contain enough of all the essential nutrients. If these are not supplied in correct amounts, the animal develops signs and symptoms of some disease.

5.Animal parasites and diseases  

    

In any situation where large numbers of the same kind of animals are kept , diseases can spread very quickly In livestock, diseases are caused by another organism living in or on the host animal. This organism is called pathogen.Pathogens include parasites and micro organisms like viruses and bacteria. Pathogens destroy the tissues of the host animal and use its food. Some diseases are spread or carried by another animal called a vector e.g. Tsetse flies are vectors that spread sleeping sickness among cattle. A parasite is an organism that livesin or on another living thing and gets food from it. It does not necessarily cause disease e.g. fleas,ticks, lice etc.These lives outside the host. A tapeworm lives inside the intestines and use some of the host animal’s food.The host become weak and thin. Flukes are small flat worms which infect the liver. These are treated by dosing the animals. Also rotational grazing reduces infection by flukes. Ticks cause several diseases in cattle such as heart water and red water. These attach themselves to the skin and suck blood.

Common livestock diseases and their control Diseases Foot and mouth (cattle and goats)

Cause Virus

Anthrax ( cattle and Bacterium goats)

Symptoms Fever, much production of saliva , weight loss reduced milk, blisters in mouth,possible death,loss of appetite , dullness Fever, loss of appetite , blood in watery feaces, blood in noses and mouth of dead animals, blown up stomach , death in 24 hours 12

Control -No cure -Kill diseased animal -Isolation -Regular vaccine -Notify authorities -Antibiotics -Burn and burry dead animals -Notify the authorities

How parasites and diseases are controlled     

Dipping Dosing Quarantine Destruction of infected animals Notifying the authorities

6.REPRODUCTION IN PLANTS Most plants reproduce sexually. This means that they produce male and female sex cells which join at fertilization to form seeds. Flowers are the reproduction organs of flowering plants. There are two main types of flowers. These are:a. Insect pollinated flowers They rely on insects for cross pollination. In the event of this failing, some flowers have mechanism for self pollination. Their petals are brightly coloured and produces nectar and scent to attract insects. NB: The ovary develops to a fruit and ovules develop into seeds. b)Wind pollinated flowers Sometimes the anthers (with pollen) are in one flower and the stigma in another flower on the same plant. This occurs in maize plant, pumpkins etc. The male flower iscollectively known as the tasseland the female flowers are grouped together in a cob. Insect and wind pollinated flowers

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Pollination Is the transfer of pollen grains from anther to stigma. a)Self pollination ---Occurs when pollen grains are transferred from the anther to the stigma of the same flower. b)Cross pollination ----Occurs when pollen grains are transferred from the anther of one plant to the stigma of the flower of another plant. This is done by air currents, small animals and birds or insects.

Adaptation of flowers for pollination or characteristics of flowers. INSECT POLLINATED FLOWERS Flowers are large in appearance and petals are brightly colored. A scent is present A source of food is provided by pollen and nectar Larger pollen grains, thick walled. Sticky and spiky to adhere to the bodies of insects. Anthers and stigma are positioned to brush against visiting insects.

WIND POLLINATED FLOWERS Flowers are small in size and are not brightly colored. No scent No food. No nectar or nectarines. Pollen grains are very tiny smooth walled and light in mass. Pollens are produced invery large quantities. Pollens are easily blown away Anthers are large and loosely attached to thin filaments. Filaments hang outside the flower and move easily in the wind.

Fertilization    

Is the union of the nuclei of male and female sex cells to form a zygote. Fertilization occurs when male and female gametes fuse together. The pollen tube grow towards an ovule and opens into it. The male gamete passes into the ovule where the female gamete or egg cell is present. The nucleus of the male gamete and that of the ovule fuse together to form a zygote. Each ovule must be fertilized by a separate pollen grain.

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Fertilisation in plants



The fertilized zygote develops and forms the embryo of the seed. The ovary develops into the fruit and remainder of the ovule develops into the surrounding parts of the seed. NB: After fertilization ovules develop into seeds, inside the ovary. Ovary ripens into a fruit petals, stamens and pistils usually drop off but sepals may remain.

Seed dispersal 

Dispersal of seeds ensures that the plants offspring do not crowd out the space occupied by the parent plants.

Types of seeds dispersal    

Self dispersal Animal dispersal Wind dispersal Water dispersal

Germination  

Is the beginning of growth in a plant. The seeds which have been released by the plant fall on the ground and some of them will germinate.

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Structure of seeds This can be looked at from two points of view i.e. the external and the internal structure.

Bean Seed

1. Radicle – is the one of the embryo which develops into the root system. 2. Plumule – is the other end of the embryo which develops into the shoot, stem and leaves of the plant. The two cotyledons of the bean seed contains stored food that is mainly starch but also contains valuable proteins. 3. Cotyledon – are modified leaves with food reserves making up part of the embryo in a seed.

Maize seed   

This is a monocotyledon. The cotyledon contains very little food. Bulk of the food is stored as starch in the endosperm. Endosperm – is the main storage area of food in a seed.

Conditions necessary for germination 1. Oxygen– needed for respiration 2. Water – for enzyme action 3. Temperature – of about 250c

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Experiment.- demonstrating the effects of temperature on germination.

\ Experiment; water is necessary for germination

Percentage germination Germination success is usually measured in terms of percentage germination Percentage germination =

No. of seeds germination x 100 %

No. of seeds planted

Vegetative reproduction in plants   

Is also called propagation or reproduction without seeds. It is the production of new plants by methods other than seed formation. This is a non-sexual form of reproduction. Only one parent is involved to produce other plants by use of stem buds with or without leaves or roots.

Methods of vegetative reproduction 1. Natural vegetative reproduction  Some plants develop specialized structuresthat can be used as organs of nature vegetative reproduction.  Shoots develop from these structures and grow till they develop their own adventurous root system and later become independent parent plant.

Examples are:a. Rhizomes –is an underground stem that grows parallel to the ground and develop shoots from buds at nodes on underground stems e.g. sweet potatoes, grass etc. b. Tubers- are underground stems that are swollen with food e.g. 17

(i) (ii)

Stem tubers – these are the swollen ends of stem structures that develop shoots which grow horizontally at first and grow down into the soil heaped around the plant e.g. potatoes. Root tubers

2. Artificial vegetative propagation 1.-Buds -can be induced to produce new plants from cuttings by layering and bud grafting e.g. sugar cane , cassava etc. 2.Cuttings -are small parts of plants. These are cut off and used for producing other plants.

Advantages of vegetative reproduction 1. Plants are identical to the parent plant 2. grow quickly as soon as conditions are favourable. 3. Good chances of survival due to availability of stored food. 4. Maturing more quickly than seed planted at the same time. 5. Don’t rely upon pollination, fertilization and seed dispersal. Disadvantages 1. 2. 3. 4.

No variety (not showing any genetic variation for parent plant). Vulnerable to the same pests and diseases as parent plant. Cannot reproduce in large numbers as in seeds. Cannot be dispersed away from the parent plant thereby causing overcrowding

7.Inheritance Variation   

It means differences between organisms with reference to a specific characteristic. Individual of the same species may look similar to one another but often show variation in many aspects of their appearance e.g. range in height, from very tall to very short. Plants of the same species or kind can vary greatly in appearance, productivity and drought resistance etc.

Factors that cause variations 1. Genetic factors – these are due to in-built mechanism and they are genetic and heritable. These variations result when new mixtures of genes occur during sexual reproduction. 18

2. Environmental factors – there are due to environmental differences of organisms. They are nonheritable or cannot be passed from one generation to the other.

Forms/types of variation 1. Discontinuous /genetic variation.  This shows clear cut differences with no intermediates between the individuals that there have characteristics.  Discontinuous variation is genetically determined. It is not usually affected by environment. Examples includes colour of maize, tongue rolling, blood group, sex etc. 2. Continuous/environmental variation  Shows a gradual range of differences between organisms and is due to interactions between the environment and the gene make up of an organism. E.g. (i) a person may have the genes required for tallness but if they are malnourished they may not grow to their potential full height.  Examples includeSize of leaves, height, weight, number of seeds in pods etc.

Selection   

Is a process of perpetuating desirable organisms, while undesirable ones die out of a population? The fact that variations either small or marked do occur and can be passed on to offspring provides a mechanism for a species population to change. Plants that are better able to resist certain diseases and to tolerate drought may be produced. They will have been selected for by nature to survive better in unfavourable conditions.

Types of selection 1. Natural selection  Used to describe the effect of the environment on the survival of organisms. Organisms that are better adapted to any changes in the environment will survive and pass on their genetic make up to the next generation.  Natural selection arises because:a. Organisms produce large numbers of offspring that show variations b. Many offspring die and only some offspring survive to breed. c. These individuals who do reach their reproductive potential are usually stronger, more resistant to diseases etc and it is these characteristics that they pass on in their genes to their offspring.  Natural selection is therefore a result of a sequence of events which involve a large number of off springs being produced and these show differences, only the fittest survive. 2. Artificial selection  Man influence breeding of plants and animals by choosing the parent stock, keeping seed from the best.

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Applications of artificial selection 



Artificial selection has now become more complex. It can involve the transfer of a selection of a gene into another organism of different species in the processes of genetic engineering. For example genes for resistance to disease can be identified in plant species and transferred into the cells of different plant species so that they also develop resistance to diseases. Other examples of genetic engineering include genes for tolerance to drought, high yields of fruit, high yields of milk and meat etc.

Breeding    a. 

It is the production of off springs. It is practiced in Zimbabwe mostly in cattle and maize production. There are two types of breeding considered. Cross /out breeding Is the mating of two different but pure strains of organisms with a view to combining the good qualities of the organisms.  Animals of different breeds that have good qualities are sometimes cross-bred to obtain the best from both breeds. Advantages 1. Desirable characteristic are produced. The cattle will be worth more money and provide good breeding stock for future generation. 2. Improvement of genetically controlled characteristics 3. Improved quality 4. Increased productivity.

Disadvantages 1. Appearance of undesirable characteristics or lethal genes. 2. Predominance of the same variety with no new characteristics appearing and therefore loss of variety. 3. Takes tins because of need for through research. 4. Requires a lot of materials and finance resources for its success.

b. Inbreeding / line breeding  It is the mating of closely related animals. Advantages -Good qualities of an organism are maintained from one generation to the next. Disadvantages   

It is less productive Variation is reduced Undesirable characteristics increase 20

 

Natural selection is reduced Adaptation to the environment is also reduced.

8.TRANSPORT IN ANIMALS Transport system 

Animals require a system to carry simple food molecules, oxygen, water other nutrients and also unwanted substances which should be removed from body cells.  The blood provides a fluid carrying medium which makes up a circulatory system. In mammals, the system is facilitated by a pump (the heart) to create the force to push these substances through tubes or blood vessels. The circulatory system  

It consists of the heart and blood vessels and these valves to make sure that there is a one way flow. Mammals have got a double circulation or pump action. The double action keeps the blood high enough to force the blood through the vessels.

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The heart

  

The heart consists of muscles which contrast continuously throughout a mammal’s life. It works automatically. The heart has 4 chambers two atria and two ventricles. These contracts to push blood out of the heart into the major blood vessels.

The right ventricle (a) Pulmonary Artery: carries deoxygenated blood from the heart to the lungs. (b) Vena Cava :- a large vein returning blood from the body to the right atrium of the heart (deoxygenated blood) (c) Right Artrium:-thin walled chamber that receives the deoxygenated blood from the body tissues. (d) Tricuspid valve-: these are three flaps to prevent back flow of blood. (e) Herpatic artery/vein-: carries glucose to the heart.

The left ventricle (a) Aorta :- the main artery from the heart to the body. It carries oxygenated blood to the rest of the body. (b) Pulmonary vein: -carries oxygenated blood from the lungs to the heart. (c) Left atrium:- upper chamber of the heart receiving blood from veins.  Blood entering the left side of the heart carries oxygen from the lungs. 22

 NB.

Blood entering the right side comes from the body and is then pumped to the lungs to absorb more oxygen. 1) Blood on the left side of the heart is oxygenated and that on the right side is de-oxygenated. 2) Muscular walls of the left ventricle are much thicker than those on the right because the blood has to reach all parts of the body. Other main blood vessels in the body Hepatic Artery Carries oxygenated blood to the liver Hepatic Portal Vein Carries de-oxygenated blood and products of digestion from the small intestines. Hepatic Vein Carries de-oxygenated blood from the liver.

THE BLOOD -Blood is a fluid tissue made up of plasma, red and white blood cells and platelets. -Blood constitutes about 5-10% of the body mass and normal blood has a pH of 7.4 Components of blood (i)

(ii)

(iii)

(iv)

Plasma: is the main liquid part of blood consisting of about 90% water and 1% dissolved substances. It contains dissolved nutrients, water, waste materials, salts, dissolved gases, blood proteins, antibodies, antitoxins and hormones. The main function of plasma is to carry blood cells. It is the main transport medium. Red blood cells These are small disc like cells with no nuclei. They carry oxygen and they contain the red pigment (haemoglobin) that in turn contains iron.

White blood cells They have a nucleus and are irregular in shape. They can change shape. They are the defence force of the body. They are mobilized when bacteria attack and they engulf the bacteria. The main function of the white blood cells is to fight against infection not only by ingestion but also by producing antibodies and antitoxins to fight the agents of infection. Blood platelets: are small oval shaped cells which are made in the narrow of long bones. They have no nucleus. Platelets help to form blood clots at the site of a wound where capillaries or other blood vessels are cut or damaged. Structures of Red blood cells,whiteblood cells and blood platletes

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Functions of blood 1. To carry oxygen from the lungs to all body cells. To release oxygen to all body cells. 2. To kill off invading germs by ingestion, producing antibodies and antitoxins and neutralizing harmful chemicals. 3. To cause blood clotting at wounds site. 4. Transportation of oxygen, carbon dioxide, waste urea and digested food. 5. Homeostasis. Distribution of heart and temperature control throughout the body. 6. Distribution of hormones (chemicals which affect the rate of vital process in the body). They are carried by blood plasma.

BLOOD VESSELS There are three types which combine to form a network reaching all parts of the body. These are:1. Arteries: these are large vessels which carry oxygenated blood away from the heart. Blood in arteries is under pressure and moves rapidly. To withstand pressure, they are thick walled and muscular. 2. Veins : these are vessels carrying deoxygenated blood to the heart. NB: Only pulmonary vein carries oxygenated blood. The blood in the veins is less pressured hence the walls are thinner and less muscular. Veins have got valves in them to stop the back flow of blood. 3. Capillaries : are microscopic vessels forming a network linking the arterioles to the venuoles. They penetrate between cells in all the body tissues. They are only one cell thick.

Comparing Arteries, veins and capillaries

9.GASEOUS EXCHANGE AND RESPIRATION 24

The respiratory system is responsible for gaseous exchange and breathing so that oxygen can be taken into the body and carbon dioxide released from the body. The oxygen is taken into the cells so that glucose can be broken down to release energy (respiration)

The respiratory system -It consists of a pair of lungs and other organs inside the head and chest -The system is responsible for getting air into and out of the lungs.

Human respiratory system 

  

During inhaling, the intercostals muscles contract lifting the ribs. The volume of the chest cavity increases and pressure inside cavity increases inside cavity is reduced. When breathed in air enters the nasal passages. It is warmed, moistened by mucus and filtered by tiny hairs. It then moves down into the larynx or voice box. The air passes down through the trachea or windpipe which branches into two smaller tubes called bronchi. These are lined with tiny hairs and much to trap germs and other particles in the air. The bronchi branches into smaller and smaller tubes called bronchioles until the tubes end at microscopic air sacs (alveoli) which absorb oxygen. NB.While the air is in the lungs, its composition changes. This is where gaseous exchange takes place.

EXPERIMENT -Differences between inhaled and exhaledc air

GASEOUS EXCHANGE

25

-Each time we take a breath the air which enters the lungs is changed slightly. While the air is in the lungs, gaseous exchange takes place in the alveoli  The air which enters the lungs is different in several ways from exhaled air. Exhaled air contains less oxygen and more carbon dioxide. The air also gets warmer and moister. Gaseous exchange in the alveoli

  

The alveoli have blood capillaries around them for gas exchange. Oxygen diffuses from alveoli into the blood and carbon dioxide diffuses from blood into the alveoli. Inhaled air contains more oxygen, less water vapour and less carbon dioxide than exhaled air.

Respiration   

It is the release of energy by the breakdown of glucose in the presence of oxygen. Oxygen is needed to burn food to release energy. The food is a fuel and the energy in food is released slowly inside cells. Respiration can be represented by a word equation as follow -:

Glucose + oxygen

carbon dioxide + heat energy + water vapour

26



Glucose and oxygen are delivered to body cells by the blood. Here the food is broken down to release its energy. At the same time, water and carbon dioxide are released as wastes. All living organisms respire. Experiment: DoPlants and animals respire?

10.Transport in plants   

  

Inorder for plants to live, they need a constant supply of water. In flowering plants, water is absorbed from the soil by the roots. Plants need substances from the environment such as oxygen, water and carbon dioxide. These substances do not enter the plant over its whole surface. A transport system is also needed to simple sugars in solution to be taken from the leaves to other parts of the plant. Within the roots, stems stem branches, petioles and leaves there are vascular bundles which are made up of vessels. The vessels carry water, dissolved salts and food solutions. These vascular bundles are built-up of microscopic tubes. Water is absorbed mostly by the root hairs. These are thin walled, finger like outgrowths from the epidermal cells into surrounding soil particles. They are constantly placed as roots grow longer and root tips push their way between soil particles. Water enters the root hair by osmosis as below.

How water is absorbed by root hairs

Structure of vascular bundles 

Vascular bundles consist of two types of vessels which are: 27

(i) (ii)

The xylem vessels that conducts waste and mineral salts solution up to the stem to the leaves. The phloem vessels that conduct simple sugar solutions from the leaves and other photosynthetic areas down the stem to the roots and others storage areas.

Cross section of a stem and root of a dicotyledon

-In mature stems, xylem vessels develop into thickened woody walls. The original cell content of the xylem tubes die and disappears leaving hollow tubes. NB-In cross section, the young stem of a flowering plant would show vascular bundles arranged outwards the outside of the stem.

Water uptake    

A continuous stream of water appears to rise from roots to the stem and then into leaves and out into atmosphere. The water is under pressure as it pushes up wards due to the sap in the root hair cells which swells and causes cell pressure. This pressure causes the water with its mineral salts to move into adjoining cells till it gets to the xylem vessels. The same root pressure caused by more and more water molecules entering the xylem vessels from the root cells behind forces the liquid up the stem.

Movement of water into and out of plant structures 

Water molecules in soil move from areas of high concentration to areas of lower concentration. These movements are caused by diffusion.  Diffusion : this is a slow movement of molecules down a concentration gradient from high concentration to low concentration until there is equal distribution of molecules. Molecules will continue to move randomly in all directions even after the distribution.  Osmosis : is the process by which water molecules pass from a region of their high concentration through a semi-permeable membrane.  Plants do not absorb any solution into their cells. Certain solutions are allowed to pass across cell membrane whilst others are not. Experiment: Demonstrating osmosis using visking tubing and using a potato

28



Plasmolysis : if plants cells are immersed in water, water enters the cells by osmosis. As the cells swell, they become turgid or firm. This turgidity helps support the plant tissues and structures. On the other hand, plant cells are put into a more concentrated solution; the cells lose water and become flaccid or soft. The cytoplasm moves away from the cellulose cell wall. This is called plasmolysis. Experiment; Turgid and Flaccid potatoes



Evaporation : molecules also move in and out of plant structures by evaporation. Plant cells in roots, leaves and stems are surrounded by moisture. When air surrounding these is dry, water molecules pass as water vapour from areas of high concentration to those of lower concentration in the atmosphere.



TRANSPIRATATION -Is the process by which plants lose water as water vapour to the air. Most of this loss is through the leaves but transpiration also takes place through the stem and flowers.

Mechanism of transpiration 

Water passes through the xylem vessels to the leaves from here it passes into leaf cells where a little ofit is used for photosynthesis. Pressure in cells forces excess water outwards through cell wall. 29





Osmosis and diffusion both play a part in this. The transpiration stream is one of the forces responsible for water with dissolved mineral salts passing from the soil into the roots and up to all parts of the plant. The transpiration stream does not control the amount of mineral salts that passes into the roots.

Effects of environmental factors on transpiration 1. Light :- this increases transpiration by opening the stomata during photosynthesis. The open stomata allow more water vapour to diffuse out and evaporate from the leaf surface. 2. Temperature :- high temperature causes rate of transpiration to increase. Direct sunlight heats the leaves and causes an increase in water evaporation and therefore transpiration. 3. Humidity :- increased humidity reduces the rate of transpiration. This is because the water concentration gradient is stepper when the leaves are surrounded by dry air. Diffusion occurs faster as a result. 4. Air movements:- windy conditions will increase the rate of transpiration by lowering the concentration of moisture in air around the leaves. 5. Surface area:- leaves with large surface areas have got a lot of stomata. This implies that they lose more water vapour than leaves with small surface area. 6. Microhabitants :- plants growing densely together will be exposed to wind and sun. They form a shadow and contain more moisture.

Adaptations of plants to reduce transpiration 1. 2. 3. 4.

Reducing leaf surface area exposed to the atmosphere Increased thickness of the cuticle layer covering the leaf to minimize evaporation Confining stomata to the lower leaf epidermis. Here are less exposed to direct sunlight. The presence of hairs on the leaf surface. These trap the moisture produced by transpiration around the leaf surface. The hairs trap air to reduce transpiration through the stomata.

Wilting   

This occurs when the water lost by transpiration is greater than the water absorbed. In wilting, the cytoplasm in cells withdraws from the cell walls making them. In the absence of the cytoplasm lining the cell wall is no longer semi-permeable but permeable water passes freely through it. Wilting results from excessive water loss by transpiration. It is a feature of hot dry weather.

11.ECOSYSTEMS  

An ecosystem is a self contained system of interdependent organisms and their environment. An ecosystem is driven by energy from the sun which enters from the system via the green plants and later passed on to the animals.

Components of an ecosystem (a) Physical (abiotic) factors 30

-Are present to control the number of organisms in an ecosystem. They influence their reproductive behaviour growth, responses and distribution. Physical components include:- temperature, rainfall, light, wind , slope of land ( water run-off and water distribution), oxygen , carbon dioxide concentration etc. (b) Biological / living / biotic factors -There are two kinds of living things in any ecosystem. The plants that make their own food and the animals that feed on them. The plants are the producers which supply energy to the consumers in the system. -When plants and animals die ,their bodies still contain energy and complex chemicals. These chemicals are broken down and decomposed by micro-organisms, mostly bacteria and fungi. These organisms are called decomposers. NB: 1. The distribution of living components in an ecosystem is influenced by physical components like shelter and food availability. 2.Energy from the sun flows into an ecosystem and is lost in various ways and stages. Biological components include plants, litter, fungi, bacteria and humus etc.

THE SOIL     

The soil is the key component in an ecosystem in which plants and animals interact. Micro-organisms carry out the recycling in it , releasing nutrients into the soil. Plants rely on the soil for food production Soil is a mixture of minerals (inorganic) particles, organic matter, water and air. Organic particles: includes water, litter, earthworms, fungi, bacteria, humus, termites etc. Inorganic particles: includes water, air , mineral salts, rock particles.

Types of soil -Soil particles are broadly grouped as consisting mostly of sand, loam and clay soil. They differ in particle size,appearance,air, water holding capacity, humus content, drainage and absorption of water by capillary action and mineral salt.

Characteristics of sand , clay and loam soils Properties Particle size Appearance Texture Humus content Air spaces Drainage Leaching

Sand Very large Rough Poor Very large Very high Very high

Loam Average Dark Fine High Reasonable Average Low/medium 31

Clay Very tiny Very fine Better LESS Very low Very low

Soil pH Plant growth Infiltration

Soil pH

More acidic Poor High

Less acidic Very good Medium

Alkaline Better Low

-Is the measure of the acidity or alkalinity of soil solutions? This depends on the concentration

of hydrogen ions in the soil solutions. When the concentration is high, the soil is said to be acidic.

Role of biological components in the soil -They improve soil fertility -They improve drainage -They improve aeration -They improve crumb structure 1.Experiment :Comparing water holding capacity and drainage of sand and clay soils.

Method

:

Make sure that everything used is equal.

Observations :

There was more filtrate from sand soil and very little clay soils.

Conclusion

Sand soil drained more retained little water. Clay soil drained less and

:

Retained more water 2.Experiment :Comparing air content of sand and clay

Conclusion

:

Sand soil contains more air than clay soil.

Explanation

:

Water added into each soil sample displaces the air present in it. The 32

more the air spaces, the more the air is displaced and hence the lower the final volume reading. NB: A hand lens was used to examine collected organisms where necessary. Observations :

Worms and insects were collected

Conclusion

Soil contains worms and insects

:

3.Experiment :

showing the presence of micro-organisms in the soil.

Observations : JAR A B

Conclusion

LIME WATER Change from clear to milky Remained clear

BICABONATE INDICATOR Change from red to yellow Remained red

: Living organisms in A produced carbon dioxide, indicating that they respired.

4.Experiment; Extracting micro organisms in the soil

5.Experiment :Determining the amount of organic matter in a soil sample.

33

-After heating over a burner with regular stirring, left to cool and weighed. The soil was re-weighed. Conclusion

:Soil contains organic matter

Natural ecosystems *-In natural ecosystems, there is a close interaction between green plants and animals. Plants are the producers, which are eaten by animals which are the consumers. -There are levels of the consumers and tertiary consumers (carnivores) which eat other animals. The links between producers and consumers are shown by a food chain. Each food chain is driven by energy from the sun and energy is transferred from one link to the next as each link is used by another.

Food chain It is a linear feeding relationship. It is made up if basic components as shown below:Sun – producers– primary consumers - secondary consumers – tertiary consumers (green plants)

(Carnivores)

e.g. Grass – Grasshopper – Lizard – Snake – Eagle 

As organisms die, they are broken down by decomposers. The nutrients trapped in living organisms are finally released back into the soil for use by plants. NB: Decomposers are not usually included as part of a food chain.

Food webs   

Expresses the interdependence and competition for food among organism in an ecosystems These changes with the seasons according to what foods are available. Food webs show feeding interrelationships between plants and animals in an ecosystem. An organism feeds on several organisms and can itself be food for more than one type of organism. Food web

34

Pyramids of numbers / biomas  

The different levels are called trophic levels. Energy decreases at each trophic level through respiration, movement and excretion. Only about 10% of the energy received at each level is passed onto the next level.



The beginning of a food chain may be tree leaves or grass. Just as the number of trees and grass leaves is greater than the numbers of primary consumers supported so is their biomass. NB: Biomass is the amount of living matter i.e. plants and animals

Energy flow in an ecosystem 

Energy is not recycled in an ecosystem. It flows an ecosystem and is lost at each trophic level. It is constantly re-supplied via primary producers that capture energy in the food making process, called photosynthesis.  Energy from the sun is the input that drives the metabolic process that take place in all living things in an ecosystem.  It is passed from plant producers to consumers via complex food webs. This would produce a pyramid of energy with the producers at the base having the greatest energy  Energy is lost in between each level. NB: Energy is lost at each trophic level by the organism’s functions of growing, moving hunting, respiring, reproduction, excreting and responding. Much energy is lost as heat energy to the atmosphere from one trophic level to another.

Decomposition 

Various organisms from soil feeders use dead plants and animals for food. As a result of decomposition, they break down dead organic matter into smaller components and are agents in recycling chemical materials back into the ecosystem. 35

Recycling by Decomposition. Decay

SOIL

PRODUCERS

Die

CONSUMERS

The carbon cycle. Carbon is an element present in all living organisms. Plants take in carbon in the air as carbon dioxide animals take in carbon in their food when they eat plants or other animals. Later carbon dioxide is returned to the air. It is a product of respiration of all organisms including those that cause decay.

Carbon cycle

Green house effect    

Atmospheric carbon dioxide is one of the gases that keep the earth warm by trapping the sun’s energy in the atmosphere. An increase in carbon dioxide level in the atmosphere results in an increase in overall temperature on the earth. This is called the green house effect. This slight increase in temperature, with time causes major changes in world temperature. Warmer global climate means melting of ice caps resulting in flooding of coastal areas, endangering lives.

Nitrogen cycle 



Nitrogen is present in all proteins in plants and animals. Both animals and plants need nitrogen for the formation of proteins. The air contains 79% nitrogen but plants cannot use it as gas. They only use nitrogen as a soluble compound as in ammonium nitrite or nitrates. In artificial ecosystems, farmers improve fertility of soil by adding artificial fertilisers. 36



In natural ecosystems dead plants and animals’ faeces and excretions containing nitrogenous compounds are returned to the ecosystem.

Nitrogen cycle

Artificial ecosystems 

It is a natural ecosystem that has been interfered with and altered by people. It is one reflecting human interference and change e.g. fish pond,garden, orchard etc.  Artificial ecosystems are usually characterized by low species diversity e.g. mono-culture.  The natural balance that allows an ecosystem to be self-sustaining is disrupted in an artificial one. The system maybe forced to produce more than it would naturally.  Crops and animals produced are removed. To maintain self-sustaining artificial ecosystem energy, water and fertility must be supplied.  Seeds which are supposed to be dispersed naturally are introduced from elsewhere, planted in prepared soil close together.  Natural predators and control mechanisms are removed in an artificial system and where monocultivation is practiced; pest numbers build up alarmingly leading to the introduction of outside control. Problems caused by farming practices and limited species diversity in artificial ecosystem (i) (ii) (iii) (iv) (v)

Soil erosion Soil infertility Need for the use of artificial fertilisers Plants and animals pests and diseases built up. Much human and fuel energy and water is spent in maintaining an artificial productivity level which is intended to produce more biomass than a natural ecosystem would.

Ground cover Ground cover takes the form of natural litter, artificially applied mulching and cover of ground by ground level plants and taller trees. Advantages of ground cover   

Increases water holding capacity Decreases evaporation of water from soil Improves humus content 37

    

Improves soil fertility and texture Reduces weed growth and reduces soil composition Adds to the organic matter Helps entry of water into the soil Helps reducing water run-off

Effects of human activity in ecosystems -Agriculture, industrial and social pressures create artificial ecosystems by:(a) (b) (c) (d)

Causing soil erosion Causing desertification Reduced bio-diversity. Pollution which can cause acid rain and global warming or greenhouse effect.

Zimbabwean Savanna soils   

These are characterized by high temperatures, rapid de-nitrification,low fertility and drying out which reduces soil organism activity. Sand soils are rapidly leached and become acidic. Alluvial soils in wide flat valleys have deeper, more fertile and less acidic soils.

Management of marginal land ecosystems 

Where people are using plants and animals, they need to look after the ecosystem since human can have good and bad effects on an ecosystem. This calls for planned management programmes of the soils.

Problems of farming in marginal lands (i) (ii) (iii)

Low fertility – soils lack nutrients Unreliable rainfall pattern – no clearly established pattern of rainfall season. Low rainfall – rainfall per season is very low. Marginal land ecosystems are also found in steep sloping escarpments and mountainous areas with high rainfall and leached soils. These are regions 4 and 5 in Zimbabwe.

Factors affecting marginal land ecosystems (a) Climate : high temperatures , erratic rainfall, periods of drought and low rainfall. (b) Soil : it is sandy and easily leached and do not hold together, humus content is low , soil temperatures are very acidic, littercover is low in marginal areas.

Ways of using marginal lands (i) (ii) (iii)

Limited cropping of drought resistant short season crops Game ranching Cattle ranching with low stock levels

Carrying capacity 38



It is the maximum number of animals which can be sustained by an area of land without damaging it. Plant biomass determines the carrying capacity. The limiting factors are oxygen, food, water, space and shelter.

Effects of exceeding carrying capacity 1. It results in overstocking which in turn causes overgrazing and deterioration of veld. 2. Soil erosion. -Ways of maintaining and controlling animal populations within carrying capacity of a habitat 1. Culling – killing of animals to maintain carrying capacity 2. Destocking – reducing numbers to sustainable levels. 3. Paddocking – keeping animals in paddocks and rotating them accordingly.

SCIENCE IN INDUSTRY 1.NATURE AND BEHAVIOR OF MATTER -

Matter can be defined as anything that exists. Matter exists in three states. A kind of matter or substance can be classified as solid, liquid or gas. Each of these three states of matter has its own distinct properties that characterize it. The nature and behaviour of matter of solid, liquids and gases has been explained in terms of the energy of its particles. This explanation is called the Kinetic Theory of matter.

States of Matter 1. SOLIDS 39

-

Particles are closely packed and held in fixed position by attractive forces. Solids have a definite shape and volume.

2. LIQUIDS - Water is a common example of liquid. It is pouring and takes the shape of the container; therefore liquids have no shape of their own. - Particles in a liquid are free to move relatively to one another but they are not independent of each other. They are still close together and when they flow, they do so together because of attractive forces between them. - Like solids, liquids have definite volume and they are not compressible.

3. -

GASES Gases have no shape of their own. Like liquids, they take the shape of their container. Particles in gas are far apart and are therefore free to move independent of each other. There are no forces of attraction acting between them. This free movement of particles enables gases to diffuse and spread evenly throughout their containers. As a result, gases have no definite volume. Gases are compressible because of the particles which are far apart, so it is possible to compress them and bring ttogether hem closer

-

.

SUMMARY OF PROPERTIES OF SOLIDS, LIQUIDS AND GASES Particles arrangement Movement of particles Force of attraction

SOLIDS Very closely packed

LIQUIDS Closely packed

Vibrate and rotate about a fixed point Strong force at attraction

Relatively free to move and flow Weak force of attraction 40

GASES Far apart Free to move independently No force of attraction

between particles Amount of kinetic energy Rate of diffusion Compressibility Shape Volume

Very little kinetic energy Very slow diffusion Not compressible Rigid. Have a definite shape Have a definite volume

More kinetic energy

High kinetic energy

Slow diffusion Not compressible No shape. Take shape of container Have a definite volume

Rapid diffusion

No volume. Fills up the container

CHANGES OF STATES These changes are caused by gaining or losing heat energy. Heat is added in melting and evaporation and it is removed in condensation, freezing, etc Sublimation

Solid

LL Liquid

meltin gggg

evaporation

GAS

condensation

Solidifying/freezing

Experiment: To show changes of shape and volume when iodine crystals are heated

NB: Iodine gas is very poisonous if inhaled. Heat iodine in well ventilated areas.

STRUCTURE OF ATOMS 41

-

Any substance that exists in made up of particles. These particles are in different materials. John Dalton, in his Atomic Theory (1803) said that every element is made up of its own kind of particles. He called these Atoms

Definition: Atoms are the smallest indivisible particles of an element. Dalton also said:i) All atoms of one element have the same properties. ii) Different atoms combine in small whole numbers to form compounds. iii) During chemical reactions, in which new compounds are formed, atoms are re-arranged. Structure of an Atom

-

Atoms are made up of protons (positive), elements (negative) and neutrons (no charge) They have a nucleus and electron shells. An atom with an equal number of electrons and protons is neutral.

NB: Neutrons and protons are found in the nucleus of an atom and electrons are found in shells outside the nucleus. -

Electrons move around the nucleus in special obits or shells just as the planets of the universe move around the sun.

Elements, mixtures and compounds -

Some substances are made up of the same kind of atoms. Any splitting of such substance will always give the same kind of substance. These substances are called elements.

1.An Element – is a substance which cannot be divided into simpler substance even by chemical means e.g. Hydrogen, carbon, oxygen, magnesium, zinc, etc 2. Mixture -

It consists of different elements, molecules and compounds which are mingled together but not chemically combined. There is no definite ratio of components and each component retains most of its characteristic properties.

NB: Separation of the components of a mixture is a simple physical process. In this case, dissolution, filtration, and evaporation methods are used 42

3. Compounds – consists of two or more elements which are chemically combined. This means different atoms from different elements combine chemically together or react to form these compounds. Therefore, a compound is a pure substance which chemically split will give rise to two or more elements chemically combined. Examples of compounds include:1. 2. 3. -

Magnesium + Oxygen heat magnesium oxide Iron + Sulphur heat iron sulphide Carbon + Oxygen heat carbon dioxide Components of a compound are not easily separated and the properties of a compound do not resemble those of the original elements. When compounds are formed, bonds are made and usually heat energy is given off.

4. Molecules – are the smallest parts of an element or compound that can exists freely on their own. -

Most elements are not found as free atoms in a pure state in nature, but they form molecules because atoms are very reactive and cannot exist freely. For example, in one molecule of water, there are two atoms of hydrogen chemically combined with one atom of oxygen (H2o) Carbon dioxide is a compound of oxygen and carbon. Each molecules contains one atom of carbon and two atoms of oxygen (Co2)

NB: Some elements are made up of molecules e.g. oxygen molecules are made up of two oxygen atoms, hydrogen molecules, are made up of two hydrogen atoms.

DIFFERENCES BETWEEN MIXTURES AND COMPOUNDS MIXTURE The formation is a physical change No new substance formed Can be separated easily by physical means Heat energy is not usually given out

COMPOUND - Formation is a chemical change - A new substance is formed - Cannot be separated by physical means - Heat energy is given out during its formation - Properties are those of the added - New properties are formed substances - They are different from combined substances NB: Chemical reaction is a reaction which involves a chemical change.

2.METALS AND NON-METALS Elements are divided into two groups which are metals and non-metals. 1. Metals

43

-

Are elements that are good conductors of heat and electricity? They have high tensile strength and are lustrous when polished. They combine with oxygen to form a basic oxide. - Metals can be alloyed (mixed with other metals or non-metals to produce a material with even useful properties. - Examples of metals are elements like copper, lead, tin, gold, zinc, iron, etc 2. Non-metals - When an element has no lustre and is a poor conductor of heat or electricity and is neither malleable nor ductile, then it is usually a non-metal. - Examples of a non-metal are carbon, phosphorus, sulphur, oxygen, hydrogen, nitrogen, plastic, wood, rubber, etc. Differences between metals and non metals METALS NON METALS Are lustrous (can be polished) Cannot be polished to give a shiny surface Are ductile (can be pulled into wires) Cannot be pulled to wires Are malleable (can be hammered) Are brittle (can break easily ) Are good conductors of heat and Are insulators electricity Have a high tensile strength Have low melting point

Reactivity of metals -

-

Metals react differently with air, water, acids and other chemicals. Some react with oxygen in the air at ordinary temperatures, others when they are heated in air. Other metals hardly react even at higher temperatures. Those metals that react most vigorously in air produces bright flames and a smaller flame shows decreased reactivity. Metals that react vigorously on heating in air have a high affinity for oxygen. The metals arranged in their order of reactivity with air and water gives the reactivity series.

Metals on top of the series are the most reactive metals as shown on the reactivity series table below.

44

Reactivity Series Table Sodium Calcium Magnesium Aluminium Zinc Iron Lead Copper

Decreasing reactivity with oxygen and water

Reaction of Metals with Dilute Acids

-

When metals react with dilute acids, hydrogen gas is released. Metals that react with cold water react more vigorously with acids. The metals which show a reaction with the acid dissolve and disappear. They form a salt with the acid.

Metal + Acid

Salt + hydrogen

For example Magnesium + hydrochloric acid Magnesium + Sulphuric Acid

magnesium chloride + hydrogen gas magnesium Sulphate + hydrogen gas

Summary of reactions of some metals Metals reaction of metals With Air/Oxygen Calcium Burn readily to form Magnesium oxides Zinc React slowly to form Iron oxides Copper

Very slow oxidation

With Water/Steam React with cold water to give hydrogen gas React with steam to form oxides and hydrogen No reaction

NB: Metals near the top in the reactivity series react with:1) Oxygen in air to form metal oxides 2) Water or steam to form metal oxides and hydrogen 3) Dilute acids to form salts and hydrogen - Metals near the bottom in the reactivity series are unreactive. 45

With Dilute Acids Dissolve to form salts, and give off hydrogen gas

No reaction

Oxidation and reduction (Redox Reactions) Oxidation – is a chemical reaction in which a substance gains oxygen or loses hydrogen. For example, oxidation occurs during combustion/burning of elements e.g. carbon + oxygen carbon dioxide Magnesium + Oxygen magnesium oxide - In the above processes, oxygen is the oxidizing agent. - Oxidation can also be a reaction in which hydrogen is removed. In this case, the oxidizing agent removes hydrogen. For example water is the oxidizing agent in the reaction below:Magnesium + water (steam) magnesium oxide + hydrogen gas Reduction – is the removal of oxygen but can also be the addition of hydrogen. A reducing agent adds hydrogen or removes oxygen. OXIDATION - Addition of oxygen - Removal of hydrogen OXIDIZING AGENT - Adds oxygen Removes hydrogen

-

REDUCTION Removal of oxygen Addition of hydrogen REDUCING AGENT Removes oxygen Adds hydrogen

Reduction of Metal Oxides - Metals cannot be obtained by heating the oxides. - The oxides must be heated with something to remove the oxygen. Oxidation of iron (Rusting) - The oxidation of iron is called rusting. Oxygen is added to the iron and iron objects look unsightly and eventually start to disintegrate. NB: Rusting and combustion are examples of oxidation processes.

3.ACIDS, BASES AND SALTS 1. ACIDS - Are solutions of oxides of non-metals? - Acids have a sour taste. - Acids turns universal indicator to red, orange and yellow. - Acids are corrosive. - Acids react with metals forming a salt and hydrogen gas. - Acids react with bases forming a salt and water (this is called neutralization reaction) - The strength of an acid can be measured on the P.H scale. Strong acid has a low P.H scale e.g. hydrochloric acid. THE P.H SCALE Increased acidity NeutralIncreased alkalinity

46

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 -

It ranges from zero to fourteen (0 – 14) It shows how acidic or alkaline a solution is. Acids have P.H values less than 7 while alkaline have P.H values greater than 7 - If a substance has a P.H of 7, it is neutral e.g. pure water NB: Universal indicator is a mixture of indicators used to determine P.H values 2. BASES – are oxides of metals - Bases are alkalis; P.H value is greater than 7 - They turn red litmus paper to blue. - They turn universal indicator solution to green, blue then purple. - Bases are soapy. - Bases react with acids to form a salt and water. PREPARATION OF BASES - Bases are oxides of metals e.g. magnesium oxide - Oxides of reactive metals are soluble (they dissolve in water to form alkalis called hydroxides) - Some bases are soluble while others are insoluble e.g. iron oxide, copper oxide, etc NB: Acid + Base salt + water 3. SALTS - Is always the product of neutralization reaction? - A salt is a neutral substance formed when:a) Metal reacts with an acid e.g. Zinc + hydrochloric Acid Zinc chloride + hydrogen b) React an acid with carbonate. c) React an acid with insoluble base e.g. Copper oxide + Sulphuric Acid copper sulphate + water d) React an acid and a soluble base (an alkaline) e.g. Sodium hydroxide + hydrochloric acid sodium chloride + water NB: The sodium chloride is then crystallized by heating the solution to a saturation point in order to evaporate water. The saturated sodium chloride solution is then cooled to form crystals of sodium chloride. Sodium hydroxide + hydrochloric Acid

sodium chloride + water

Speed of Reaction -

Chemical reactions occur at different speeds or rates. This same reaction occur very fast while others very slow. Reactions between substances occur when particles collides. The speed of reactions will therefore increase if there are more collisions.

Measuring the Speed of a Chemical Reaction - Speed/rate of a reaction can be measured by: a) Finding out how much of a gaseous product is collected in a given time. (this is possible for chemical reaction in which one of the products is a gas) e.g. magnesium + sulphuric Acid

magnesium sulphate + hydrogen

b) Reactions between a metal and a carbonate 47

e.g. calcium carbonate + hydrochloric acid

calcium chloride + water

Factors effecting rate of reaction 1) Temperature – increases the kinetic energy of the particles. This will cause the particles to collide and the reaction is speeded up. 2) Concentration – increased concentration increases the number of particles present and increases the chances of particles colliding and the reaction is speeded up. 3) Surface Area – a large surface area provides more chance of the particles to collide with each other e.g. powdered calcium carbonate has a greater surface area and will react much faster than lamps of calcium. 4) Catalyst – it is a substance that speeds up chemical reactions but remain chemically unchanged at the end of the reaction. 5) Pressure – when particles are pressurized, they move faster and collide frequently thereby increasing the rate of reaction.

Reversible Reactions -

Is a reaction that occurs in both/either directions. This means that the reactions proceed in both forward and backward directions at the same time. e.g.

Nitrogen + hydrogen

Ammonia (Haber process)

Sulphur dioxide + Oxygen NB: The sign

Sulphur Trioxide means reversible reaction

Speed of a chemical reaction can also be measured by finding the time taken for:a) b) c) d)

a change in colour to occur. for a solid to dissolve. a change in P.H to occur. a change in temperature to occur.

4.EXTRACTION OF METALS The occurrance and extraction of iron 48

-

Iron occurs in the earth as Hematite iron II oxide.In Zimbabwe iron ore is found at Redcliff near Kwekwe and Buchwa near Mberengwa. The main use of iron is to make steel or alloy of iron.

Extraction of iron in the Blast Furnace (at ZISCO) THE BLAST FURNACE At the Top Iron(111) oxide + carbon monoxide

Iron + carbon dioxide

At the middle Carbon dioxide + Carbon

Carbon monoxide

At the bottom Carbon (coke ) + oxygen (from air )

Carbon dioxide (heat)

Molten iron sinks to the bottom of furnace. It is denser than slag.

Raw materials fed in the Blast Furnace 1) Iron ore – is the source of iron. 2) Coke– is a pure form of carbon formed from coal in the absence of air. Coke is used as burning fuel and also carbon (in coke) is the reducing agent which reduces iron oxide to iron. 3) Limestone/calcium carbonate – acts a flux which removes impurities in the iron. Heat in the blast furnace decomposes the limestone (calcium carbonate) to form calcium oxide and carbon dioxide. - Sand (silica/silicon dioxide) silicon IV oxide is an impurity in iron and reacts with calcium oxide forming calcium silicate (slag) - The slag is less dense then the iron so it floats above the iron and can be trapped off as a liquid calcium. Calcium oxide + silica -

calcium silicate

The molten iron hardens to form cast iron which is used to made pots and engine blocks. The molten cast iron is collected in the containers called pigs and is nicknamed “pig iron” Cast iron is brittle because it contains high carbon content (about 4%) The high carbon content of cast iron is reduced in the oxygen lance furnace.

THE OXYGEN LANCE FURNANCE -

Oxygen under pressure is blown into the molten iron where it oxidizes (reacts) with carbon and phosphorus impurities. These leaves as gaseous oxides. Addition of other elements like manganese nickel forms various steel. Steel is an alloy of iron.

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OXYGEN LANCE FURNACE

PROPERTY AND USES OF IRON AND STEEL MATERIAL Cast iron

-

PROPERTIES Is brittle (4% carbon)

Wroght iron

-

Is malleable (0.05%)

Stainless steel

-

Chrome and nickel It resist corrosion and staining 0.25% carbon has iron cast It can be machined and welded Contains carbon tungsten, chrome and manganese

Mild steel Tool steel

-

USES Engine block Pots Chains and decorations

-

Kitchen ware Hospital equipment Bolts

-

Cutting tools Dices

Extraction of Copper -

In Zimbabwe copper is mined in Mhangura, Shackleton, Muriel Mine and Alaska Mines. Copper comes from the ore copper pyrites alternatively called chalcopyrite or as an oxide or sulphide ore. Extraction of copper

The stages are:-

-

1. concentration/flotation Firstly sulphide ores are crushed to small particles. The powdered ore is mixed with oil water mixture by means of powerful jet of air. The copper bearing pyritestends to stick to the oily froth at the top while the waste rock and clay are deposited at the bottom as sediments. The froth is skimmed off, concentrated and thickened.

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2.Roasting -

The concentrate from the flotation plant is transported to the smelting as copper II sulphide and iron II sulphide. The ore is roasted in air to reduce the copper

Copper pyrites + oxygen – Copper sulphide + sulphur dioxide + iron II oxide 3. Smelting /Sintering - The new mixture is sintered by heating with silica which removes the iron II oxide. Iron II oxide + silicon dioxide – iron II silicate -

Copper (I) sulphide left is further heated in a blast of air which creates some copper (I) oxide. 4.Reduction/converter Unchanged copper (I) sulphide and copper (I) dioxide undergo mutual reduction to give copper called blister copper (impure copper).

5.Purification by Electrolysis -

-

Impure copper is moulded into thick sheets. These become positive plates (anode) in an electrolyte cell. The negative electrode (cathode) is a thin sheet of very pure copper. The electrolyte is copper sulphate solution.

When current is passed through this copper, it is transferred from the anode to the cathode. Insoluble impurities from the anode form sludge at the bottom of the cell.

NB: (i) Metals such as gold and silver can be recovered from the sludge. (ii) Briefly the extraction of copper process isConcentration – Roasting – smelting– Reduction processes – electrolysis.

Uses of Copper 51

Making-(a) cooking pots (b) car radiators (c) hot water pipes (d) electricity wires Alloys of copper and their uses Alloy Brass (Copper + Zinc)

Properties of Alloy -High lustre when polished -Resonant and soft

Uses of Alloy Screws, ornaments, hot water pipes, musical instruments,bullet

Bronze (Copper + Tin)

-

-

Nickel – Silver (Copper +Nickel)

Hardness Wear resistance Toughness Lightness Wear resistance

Statues Medals Bells Silver coins

COATING PROCESSES -

Many metals are affected by environmental agents such as water, air, acids and salts. These causes chemical degradation of metals. This is called corrosion or rusting in case of iron or steel. To overcome the disadvantages of rusting of these metals, it is proper to coat these metals with other less reactive metals. This is called electroplating. Coating is done to prevent corrosion/rusting and also for decorative purposes.

Methods of Coating Materials 1) 2) 3) a) b) c) d) 4)

Painting Oiling Electroplating – a current is passed through a solution of metal irons. The object to be plated becomes the cathode. The anode supplies the metals ions. Positive metal ions move to the cathode where they pick up electrons and become atoms that coat the cathode. Examples:Copper plating Nickel plating Chrome plating Tin plating Galvanizing – provides sacrificial protection by galvanizing the iron with zinc.

5.INDUSTRIAL PROCESSES Production of Sulphuric Acid (The Contact Process) -

Sulphuric acid is produced at Zimphos near Harare.

Stage A: iron sulphide/iron pyrites/sulphur is roasted to form sulphur dioxide. 52

Sulphur + Oxygen

Sulphur Dioxide

Stage B: sulphur dioxide is mixed with excess air and passed to a convertor where it is converted to sulphuric acid by contact process. This reaction is reversible. To speed up, a catalyst vanadium (V) oxide is used to speed up reaction. Also pressure of one atmosphere is used. This will yield up to 95%

Sulphur dioxide + Oxygen Catalyst

Sulphur Trioxide + water

450ºC , 1 Atmosphere Stage C: Production of oleum -

Sulphur trioxide is cooled and absorbed into concentrated sulphuric acid to produce oleum. Oleum is a mist of sulphuric acid which is difficult to condense

Sulphur Trioxide + sulphuric acid

oleum

Stage D: oleum is diluted with water or dilute acid to give concentrated sulphuric acid THE CONTACT PROCESS FURNACE SULPHUR

OXYGEN

CONVERTER SULPHUR + OXYGEN SULPHUR DIOXIDE

ABSORPTION SULPHUR DIOXIDE + OXYGEN OVER CATALYST,4500C, 1 Atm

Sulphur Trioxide

DILUTION SULPHUR TRIOXIDE + SULPHURIC ACID

OLEUM + WATER CONCENTRATED SULPHURIC ACID

OLEUM

Uses of Sulphuric Acid -

Making of fertilizers In paints and plastics As an electrolyte in car batteries In extraction of metals Detergents and in paper making As a drying agent because it absorbs water

INDUSTRIAL GASES Electrolysis - is the decomposition of a compound molten or in solution, by electricity. When an electric current is passed through some solutions, chemical changes occur at the electrodes. The cathode is connected to the negative terminal of the battery while the anode is connected to the positive. 53

-

The compound that conducts the electricity is called an electrolyte. It contains ions that carry current through the solution.

Preparation of hydrogen by Electrolysis of water -

Hydrogen can be produced by electrolysis of water. Pure water does not conduct electricity well so potassium hydroxide or sulphuric acid is added to it. Carbon electrodes are used to carry current into and out of the electrolyte. These electrodes do not change during electrolysis. Water is broken down into the elements hydrogen and oxygen. Hydrogen comes off at the cathode (-)while oxygen is collected at the anode (+) Electrolysis of Water

NB: Oxygen is produced at the ratio 1:2 to hydrogen. -

Oxygen is used in the manufacturer of steel. The hydrogen is used in the ammonia synthesis plant at Sable and in the manufacture of margarine.

Preparation of Oxygen and Nitrogen from Liquid Air -Gases are liquidified by lowering temperatures so that they can be separated by fractional distillation. These gases are used for different purposes but not be used as air. They should be separated into different elements.

Fractional Distillation of Liquid Air

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-

Solidified water and carbon dioxide are removed after air is cooled to -78ºC The remaining gases are compressed and cooled. The liquid air is pumped into a distillation column and the temperature allowed to rise. The nitrogen, which has a boiling point of -196ºC is collected from the top of the column because it evaporates first. The oxygen, which has a boiling point of -183ºC remains as a liquid and is removed from the bottom of the column.

The manufacturer of Ammonia (Haber Process) -

Ammonia is manufactured by reacting nitrogen and hydrogen. One volume of nitrogen reacts with three volumes of ammonia. The gas pressure is raised to 200 atm and the temperature to 500ºC. The mixture is passed over an iron catalyst and about 17% of it is converted to ammonia.

NB: The reaction between nitrogen and hydrogen is reversible and exothermic

Nitrogen + Hydrogencatalyst (1)

Ammonia + Heat

(3)

500ºC, 200 Atm -

As ammonia is produced, the pressure of the gases drops. If the gases are compressed (their pressure increased, more ammonia is produced. Lower temperatures, are maintained to obtain a good yield. The temperatures of the reaction is kept as low as possible (about 450ºC) The reaction is slowed when the temperature is lowered and for the reason, an iron catalyst is used to speed up the reaction of ammonia but it does not alter the total amount of ammonia produced.

THE HABER PROCESS

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HYDROGEN (3 )

Reaction Chamber

MIXING OF GASES

IRON CATALYST, 5000C / 200 ATM

NITROGEN (1)

UNREACTED HYDROGEN + NITROGEN

Uses of Industrial Gases GAS Hydrogen

-

SOURCE Electrolysis of water

Oxygen

-

Liquefaction of air Electrolysis of water

Nitrogen

-

Liquefactions of air

Ammonia

-

Haber process

Carbon Dioxide

-

Liquefaction of air Fermentation processes

-

USES Manufacture of ammonia and margarine Cutting and welding metals Steel manufacturer Medical use manufacture of ammonia manufacture of nitric acid as a refrigerant for freezing vegetables in medicine Manufacture of fertilizers As refrigerant In fizzy drinks As a dry ice refrigerant Fire extinguishers

Production of Nitric Acid (catalytic oxidation) -

Some of the ammonia from ammonia synthesis plant is used for making nitric acid. When producing nitric acid, firstly ammonia is oxidized to nitric oxide over a platinum or rhodium catalyst at high temperatures.

Ammonia + Oxygen -

Nitric oxide + Water + Heat

After cooling, the nitric oxide is mixed with excess air and passed slowly over the catalyst. It is oxidized to nitrogen dioxide.

Nitric oxide + OxygenCatalyst Nitrogen dioxide + Heat 9000c

-Nitrogen dioxide and excess air is absorbed into water to form nitric acid. Oxygen (from air) + Nitrogen dioxide + Water Catalytic Oxidation of Nitric Acid 56

Nitric Acid

AMMONIA Reaction chamber Platinum/Rhodium catalyst and 9000c

MIXED AND COMPRESSED

temperature

OXYGEN

oxygen

. water

NO2 . . .

nitric acid

Uses of Nitric Acid   

Manufacture of explosives Manufacture of dyes Manufacture of fertilizers e.g. Ammonia Nitrate

Manufacture of Ammonia Nitrate -

Nitric acid is neutralized by ammonia vapour. Ammonia Nitrate is the salt produced by this neutralized process

Nitric Acid (acid)

+

Ammonia (Base)

Ammonia Nitrate (salt)

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SCIENCE IN ENERGY USES 1.FUELS -A fuel is a substance which can burn to release heat energy. Most fuels are made of compounds which mainly contain atoms of carbon and hydrogen. When a fuel is burnt chemical energy is converted into heat energy. Types of Fuels 1.Solid

Fuels – These includes wood, charcoal, coke and coal.

I) Wood – is plentiful in Zimbabwe. It is very cheap and has low heat energy content. Wood is less efficient and produces a lot of smoke when burning. 11) Charcoal – is a more efficient fuel made by heating wood to very high temperatures in the absence of air. 111) Coal – is a fossil fuel mined at Hwange. Coal has higher carbon content, therefore has a higher heating value. iv) Coke– is a hard, porous residue formed from dry distillation of coal (when coal is burnt in the absence of air)

Dry/Destructive Distillation of Coal/Wood

Uses and Products of Dry Distillation (coking process) BY PRODUCT Coke

REFINING PROCESS Destructive Distillation

Ammonia liquor

Distillation

Benzol Coal Tar

Fractional Distillation to give only liquid products Distillation

Coal Gas

Dry Distillation

USES Fuel (heat energy) Smelting metal ores Make fuel gases e.g. water gas Fertilizers Metal processing industries Solvent for paint, drugs, dyes, plastic, disinfectants, perfumes, insecticides, etc Rood making, termite, proofing in wood, naphthalene Fuel for coke ovens

2.Liquid Fuels 58

– Common liquid fuels are obtained by fractional distillation of petroleum. These includes alcohol, ethanol, petrol, diesel, paraffin, etc

Ethanol – is a liquid fuel that burns with a pale blue flame and leaves no residue. It is made by fermenting plants that have high sugar content. In Zimbabwe, ethanol is produced at the ethanol plant at Triangle. The enzymes in yeast cause the breakdown of the sugars into smaller glucose molecules which is then converted into ethanol by the action of zymase in yeast. Glucose

enzyme zymase

ethanol + carbon dioxide

Fractional Distillation of ethanol

Uses of ethanol -As a solvent for dyes and medicines -As a beverage/drink -In blended fuels e.g. petrol blend -In methylated spirits Uses of Carbon dioxide -Used in fire extinguishers -As dry ice or coolant. -Used in fizzy drinks as a preservative.

3.GaseousFuels – gases are better than solid and liquid fuels in many domestic and industrial uses. They do not cause much pollution and are easy to control by turning a tap. Examples include butane, biogas, coal gas, methane etc.

PRODUCTION OF BIOGAS Biogas is a gas evolved when organic material decomposes. It is a mixture of gases including methane, carbon dioxide and hydrogen sulphide. Biogas is obtained from fermenting manure.

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THE BIOGAS PLANT/BIO-DIGESTER

Uses of Biogas -For cooking -For lighting FERMENTATION – is the breakdown of glucose in the absence of oxygen to produce ethanol and carbon dioxide. FACTORS AFFECTING FERMENTATIONS -Temperature -P.H -Role of yeast -Type of waste -Time

FUEL EFFICIENCY -Fuels are different – they give out different amounts of heat. It is very useful to know which fuel is better than the other. We can do this by measuring the temperature rise of water when it is heated by a known mass of fuel. Experiment: to determine the amount of heat liberated when different liquid fuels burn

Method 1. Record the temperature of 100cm³ of water. 2. Weigh the spirit burner and place the burner under the beaker and heat water. 3. Note the temperature of the water. 4. Re-weigh the lamp to find out how much fuel has been burnt. Record the results. 5. Repeat the experiment with paraffin, ethanol, etc NB: The fuel that liberates more heat using fewer amounts is the most efficient fuel. 60

COMPLETE AND INCOMPLETE COMBUSTION 1.Complete combustion– combustion is complete when a fuel burns in plentiful supply of air producing carbon dioxide and a lot of heat. e.g. Methane + oxygen water + Carbon dioxide + lot of heat NB: In a Bunsen burner, complete combustion occurs when air holes are opened and the burner burns with a blue or non luminous flame which is not soot. 2.Incomplete combustion – occur when a fuel burns in limited supply (insufficient) air producing carbon monoxide (soot) and very little heat energy. In a Bunsen burner, incomplete combustion occur when air holes are closed and the burner burns with a yellowish orange luminous flame which is less hot and soot.

FUEL ENGINES -Fuel engines such as petrol and diesel convert chemical energy into heat energy and then into kinetic energy. Chemical energy Heat energy Kinetic energy

THE FOUR STROKE PETROL ENGINE 1.INTAKE STROKE Piston moves downwards due to the starter motor turning the crankshaft. The volume in the cylinder increases and pressure decreases. The petrol air mixture enters the cylinder through the open inlet valve. The exhaust valve is closed. 2.COMPRESSION STROKE The piston moves upwards compressing the petrol air mixture. Both valves are closed. 3.POWER STROKE A spark jumps across a point in the spark plug exploring or igniting the petrol air mixture. This forces the piston to move downwards while both valves are closed. It is during the power stroke that the chemical energy in the fuel is converted to heat and then to kinetic energy. 4.EXHAUST STROKE The inlet valve is closed while the exhaust valve is opened. The piston moves upwards pushing the exhaust gases out through the exhaust valve.

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THE FOUR STROKE ENGINE

THE CARBURETOR -The carburetor produces a petrol air mixture in its correct proportion -The petrol is cleaned by passing through a petrol filter to prevent blockage of jets. -The air filter removes any dirty from the air that is drawn in

The choke controls the air supply, closing it gives a richer petrol air mixture and makes starting easier. The throttle controlled by the accelerator allows more or less of the petrol air mixture through to the cylinder. If the jets in the carburetor are blocked by dirty, not enough fuel is supplied to the engine making it less efficient.

THE DIESEL ENGINE The four stroke diesel engine operates as the petrol engine with few differences as follows; 1. Diesel engine has no spark plug. 2. Diesel is used instead of petrol. 3. A fuel injector replaces the carburetor. On the intake stroke air is drawn into the cylinder. When the piston moves up during the compression stroke, it compresses the air twice more than in a petrol engine. This compression in a diesel engine causes the air to become very hot. Diesel oil is pumped into the cylinder by the injector pump during the power stroke and it is ignited by the high temperatures of compressed air. The resulting explosion forces the piston downwards. NB: Diesel engines are called compression igniting.

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DIFFENCES BETWEEN PETROL AND DIESEL ENGINES PETROL ENGINE Fuel is petrol Petrol air mixture is introduced into the cylinder during the intake stroke Fuel is ignited by the spark plug. There is half compression of diesel engine Lighter than diesel engine 25 % efficient. A large amount of carbon monoxide is produced

DIESEL ENGINE Fuel is diesel Fuel is injected into the cylinder after air has been compressed in the power stroke. Fuel is ignited by heat produced from the compressed air. There is very high compression Very heavy engines 40 % efficient. There is not much pollution. They are more economic and reliable

2.ELECTROSTATICS -Is the study if static electricity. Electric charge is due to the presence of extra electrons (- ve) or absence of electrons (+ve) charge. If a piece of polythene e.g. rubber or pen is rubbed into your hair or a woolen cloth, it becomes negatively charged and can attract small pieces of paper. Rubbed polythene is therefore said to contain a negative charge. When a glass/Perspex is rubbed in hair or on a woolen cloth, it loses electrons, thus gaining a positive charge. A rubbed Perspex/glass is therefore said to contain a positive charge. When a polythene rod is rubbed, electrons are transferred into it but when a Perspex rod is rubbed, electrons move to it. NB: It is only electrons which move, the protons remain in nucleus.

Like and unlike charges If a polythene rod is brought towards each other after rubbing or if Perspex rod is also brought towards each other, they move away from each other (repel) This is because they have like/similar charges and like charges repel each other. But when a rubbed polythene rod is brought towards a rubbed glass/Perspex, they move towards each other (attraction). This is because they have unlike charges and unlike charges attract each other. The closer the charges, the greater the force of repulsion or attraction.The larger the charges, the greater the forces to. Conductors-are materials that allow electrons to move freely in them. They cannotbe charged except by holding them in an insulating handle to prevent the charge passing through one’s body to the earth e.g. metals and carbon. Insulators -are materials in which electrons are firmly held by their atoms. They can be charged e.g. plastic like polythene and Perspex, nylon, rubber, our thunder clouds, etc .

Lightning -Lighting is the sudden discharge of electrons by a thunder cloud to the earth. Clouds are poor conductors as they are made up of water particles, so they can become positively charged by friction between them. When electrons are discharged to a cloud a flash of lighting is seen as they flow towards the earth. If a conductor e.g. human body happens to be in the way, the electrons trap him to the ground, causing death or serious burns.

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A lightning Conductor Protects tall buildings by providing electrons with an easy path to the ground. Lighting conductors are made of a thick copper plateplaced on outside of a building with a metal plate in the ground and stuck up. The spikes are positively charged so that if a thundercloud is discharged near the conductor, the charge will be attracted towards the spikes and conductors then carries excess electrons to the earth. A lightning conductor

Safety precautions against lighting 1-Never stand under tall objects during thunder storm as they provide a path to the earth for lightning. 2-Disconnect roof top aerials as they provide lightning with a pathway to the earth. 3-Connect lightning conductors to the roofs of all buildings. 4-Avoid standing near fences, metal objects, rocks, hilltop, etc as they carry a positive charge which attract lighting.

CURRENT ELECTRICITY -It is produced when electrons flow from one point to another in a conductor/electrolyte. Symbols for circuit diagrams

CURRENT, VOLTAGE AND RESISTANCE 1.CURRENT Is the flow of electrons through a conductor or ions through an electrolyte. It is measured with an ammeter in Amperes/Amps (A) The ammeter is connected in series anywhere in the circuit.

2.VOLTAGE/POTENTIAL DIFFERENCE 64

Voltage is the electrical pressure which pushes electrons causing current to flow through a circuit. This force is normally provided by cells. The greater the voltage, the larger the current, so voltage and current are directly proportion Voltage is measured with a voltmeter (v) in volts. A voltmeter measures potential difference between two points in a circuit and placed across two points in parallel. A voltmeter in parallel with a lampand with a cell

The flow of current in a circuit Electric current is a flow of negatively charged particles around a circuit. These charged particles are electrons that start at the negative terminal and flow to the positive terminal of the power supply (battery) In electrical circuit diagrams howeverthe conventional flow of current is shown by arrow symbols as if it was going from positive terminal to the negative terminal 3.RESISTANCE– is the force that opposes the flow of an electric current. Circuit components such as thin conductors in bulb filaments resist the flow of an electric current. The units for measuring resistance are called ohms ( ). The relationship between voltage, resistance and current is shown by the formula V=IR If you are given or have measured experimental values of voltage, and current in a circuit, you can see the formula to find the resistance R =V/I hence I = V/R THE OHMS LAW The law says that current passing through a wire is directly proportional to the voltage across its ends provided the temperature in constant. USING MORE RESISTORS The resistance of a circuit can be changed by placing more resistors in series or parallel in a circuit. Resistors in series In series, current only uses one path to flow, so total resistance is the sum of the resistors. i.e. R2 + R3 R1

R2

R3

NB: Resistors in series offer more resistance to current. Resistors in parallel Current has more than one path to flow and one current will flow in the point where there is less resistance.

65

R1 +

RESISTORS IN PARALLEL AND IN SERIES

Total Resistance = Product of Resistors e.g . R1 xR2 x R3 Sum of resistors R1 + R2 + R3

POWER - is the rate of doing work or rate of using energy. Power is measured in watts.

Power = Voltage X current

ELECTRICAL CELLS -Cells convert chemical Electrical energy -Two metal electrodes are dipped in an electrolyte. -During the chemical reaction that take place one electrode loses electrons and one gain electrons therefore a cell has a positive and negative terminal.

1.PRIMARY CELLS Are those cells that cannot be recharge once they become flat. They stop working when the chemical inside them is used up. a)A Simple Cell The simple cell consists of two electrodes of different metals such as copper and zinc in an electrolyte of sulphuric acid. A chemical reaction occurs between zinc.

b)Dry Cell 66

-Simple cells are inconvenient and difficult to move because of the electrolyte solution so they can be charged to make a dry cell. A dry cell produces about 1.5 v and goes flat when chemicals are used up. The negative electrode is zinc and positive electrode (semi-conductor) is carbon. The electrolyte is a paste of ammonium chloride. Around the carbon anode, hydrogen is produced. When the current is turned on, electrons leave the zinc through the external part of the circuit. They perform work in the load i.e. radio/bulb before re-entering the cell through the rod. In the cell the electrons (negative) are mopped up by positive ammonium ions and then splits into the neutral gases hydrogen and ammonia which causes polarization. Note: that the current is generated in expense of the zinc case which corrodes in the process. Deporisation is effected by manganese dioxide.

Dry cell

c)Photovoltaic/Solar Cells -Are solar cells made from silicon a solar conductor. They convert solar energy toelectricalenergy and producing about 0.5 v and 0.03Amps in bright sunlight. NB: For a larger voltage, cells are connected in series. For a larger current they are connected in parallel. Photovoltaic cells are used in rural areas to provide electricity and satellites. Cells in series Several cells may be joined together to give a larger voltage. If cells are connected in series, voltage may be added together to give the total force that moves the electrons around the circuit.

Total voltage = 1.5v+1.5v+1.5v=4.5volts.

NB. Combination of cells is called a battery. Negative terminal of one cell is connected to the possitive terminal of the next cell. cells in parallel. *-Parallel circuits have got many pathways. When cells are connected in parallel all the possitive and negative terminals are joined and they produce current for a longer time but the voltage is the average of the cells ie 1.5 volts.

67

NB. Cells last longer when they are connected in parallel.

2.Secondary cells Are those that can be re-charged once they become flat e.g. lead acid accumulator? a)The lead acid accumulator -It is a storage cell or accumulator which stores the energy which have been actively pumped into it with a suitable battery charge.It consists of six wet cells or accumulators.Those cells are completely covered in electrolyte dilute sulphuric acid.The reaction in this cell is reversible. charging Chemical energy electrical energy. Discharging Lead acid accumulators are storage cells. Electrical charge is passed into the cells and chemically stored. This is done by passing current through the cell in the opposite direction to which it supplies current. In this type of a cell the possitive electrode is dioxide and the negative electrode is the lead. The electrolyte is sulphuric acid. The charging up process converts water and lead sulphate to lead dioxide, metallic lead and sulphuric acid. The normal use of the battery/ discharge converts lead dioxide, metallic lead and sulphuric acid to lead sulphate and water. NB: Charging concentrates the battery while discharging dilutes the battery acid. Charge Water + lead sulphate

lead dioxide + sulphuric acid Discharge

Lead acid accumulator

A lead acid accumulator requiresfrequent charging otherwise it will sulphate i.e.lead sulphate will be deposited in an insoluble form which will impede future charging or use of the battery.

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Care and maintenance of a car battery 1-Battery terminals must be kept clean, greased and tight to prevent corrosion. 2-Avoid total discharge 3-Top up electrolyte with distilled water.

Effects of electric current -An electric current has:1.Heating effect - it is used in irons, stoves, heaters, etc. 2.Lighting effect - it is used for lighting houses. 3.Magnetic effect– it is used to make magnets.

A magnetic field -Is a space around a magnet in which its force can be felt. Magnetic field is made up of magnetic lines of force. Magnetic field for a Bar Magnet

THE ELECTRIC MOTOR -Are devices that convert electrical to kinetic energy?

OPERATION OF AN ELECTRIC MOTOR -An electric current flows through the coil creating a magnetic field around the coil. The magnetic field of the coil carrying electric current interacts with the magnetic field for the permanent magnets forcing the coil to turn in a clockwise direction. Rotation is maintained.

FACTORS AFFECTING THE SPEED OF THE electric motor 1.Size of electric current – increases currents and speed of the motor. 69

2.Strength of magnet – the stronger the magnet, the stronger the magnetic field and the faster the motor/coil will turn. 3.Number of turns of coil – the more the number of turns of coil, the faster the motor moves.

THE GENERATOR -A generator converts kinetic (mechanical) energy to electrical energy. Kinetic energy

electrical energy

-A generator produces direct current (D.C) or alternating current from electro-magnetic induction. The Generator Electro-magnetic induction -If a bar magnet is pushed into a coil to a centre zero galvanometer, an electric current is induced in the coil resulting in the galvanometer pointer deflecting to the right.

When the bar magnet is pulled out of the coil, an electric current is again induced in the coil but this time in an opposite direction. NB: Thus an electric current is induced/produced whenever the magnet lines of force cut across the coil. The greater the rate of cutting of lines of the force, the greater the induced current. The size of induced current depends on -; 1.The strength of the magnet. The stronger the magnet, the more the induced current. 2.The number of turns of coil – The more the number of turns of the coil, the greater the induced current. 3.The rate at which the magnet moves cuts across the coil. The faster the rate of movement, the greater the induced current.

THE GENERATION OF ELECTRICITY AT KARIBA -It uses the flowing water to turn turbines of the generator. Potential energy

Kinetic energy

Electrical energy

THE GENERATION OF ELECTRICITY AY HWANGE Chemical energy

Heat energy

Kinetic 70

Electrical energy

-In a generator, the magnet is stationary and the coil moves as it is turned by steam of water. -Generators can be A.C called alternators or D.C called the dynamo. THE D.C GENERATOR -The D.C generator is similar to the A.C generator except that the slip rings are replaced by commutators. -As the coil rotates, there is a change of contact. -In the vertical position so that carbon remains positive and the other negative. D.C AND A.C GENERATORS

THE A.C GENERATOR -It consists of a rectangular coil of wire that is turned in a magnetic field between the poles of a permanent magnetic field. -The end of the coil is connectedto two slip rings and the current that is induced in the coil is passed into carbon brushes which press against the slip rings. However the direction of the current changes as the coil turns. An alternating current is produced.

Different Between A.C and D.C Generator A.C (alternating current)

D.C (direct current)

Flow to and from Can be stepped up and down by transformers Source:- A.C is produced by A.C generator (alternators)

Flows in one direction Cannot be stepped up and down Source:- is produced by the cell/battery and D.C generator/dynamo

TRANSMISSION OF ELECTRICITY The alternating current (A.C) produced by huge A.C generators at Hwange and Kariba is stepped up by transformers. The electricity is transmitted as alternating current (A.C) of up to 132 KV (132 000 volts) If electricity was transmitted at a low voltage, very thick cables would be required and this would be very expensive. At high voltage much thinner cables are used and it is much cheaper. Substations then transform (step down). The high voltage to 240 volts for domestic use. 71

ELECTRICAL SAFETY Mains electricity can be very dangerous as it electrocute people. The following are basic safety rules that must be followed when using electricity. 1-Make sure your hands are dry when touching an electrical appliance. 2-Keep electrical cables and appliances covered. 3-Switch off at the socket before plugging in and removing an appliance. 4-Check that electrical cables are not in frayed. 5-Use a fuse that has the correct rating for the appliance. 6-Do not overload an electric socket with many appliances. 7-Make sure that the plug is correctly wired. NB--A plug is used to carry electricity current from the mains power circuit to the appliance e.g. Radio, TV, stove, etc THE THREE PIN PLUG

1.The Live wire – has a brown insulation and is connected to the pin marked (L) in the plug. 2.The Neutral wire – has a blue color and is connected to the pin marked (N) in the plug. 3.The Earth wire – has a yellow and green or (green) color and is connected to the pin marked (E) in the plug. This is not present in the two pin plug. THE TWO PIN PLUG Two pin plug have only a live and neutral pins. There is no earth in pin and the appliance is usually double insulated by a plastic casing.

FUSES AND FUSE RATING -A fuse contains a short piece of thin wire that melts when two much current flows. This breaks the circuit so protecting the appliance from overheating. -Each appliance must be connected to a plug containing a fuse of the correct rating. NB*Fuses are available in different sizes.i.e-5 Amps, 10 Amps, 13 Amps, 20 Amps and 25 Amps NB.To calculate the correct fuse rating the formula USED IS :i.e. Current = Power Watts Voltage = Power Voltage Volts

Current

-P ower = I ² R i.e. P = I x R x I -The units for electricity power are to watts (w) or kilowatts (kw) Example: - calculate the current used by 1.A bulb marked 60w and 240v 2.An electric heater marked 3000w and uses voltage of 240v Answers: 72

1.Current= Power = 60 w = 0,25A Voltage 240v 2.Current = Power = 3000w = 12,5 A Voltage 240v

SOLAR ENERGY --Solar radiation consists of 1.Infrared radiation--which warms our body. 2.Light – which enables us to see. 3.Ultraviolet radiation – which converts fat in our bodies into vitamin D. however too much ultraviolet (radiation) light damages the eyes. REFLECTION OF LIGHT Light travels in a straight line called rays Light ray A group of light rays is called a beam of light Beam of light -Mirrors and other shiny surfaces change the direction in which light travels. They reflect light rays.

INVESTIGATING REFLECTION BY PLACE MIRROR -A ray of light falling into the mirror is called the incident ray and the angle it makes with normal line is called the angle of incidence. -The incident at ray light is reflected by the mirror and the angle between reflected ray and the normal line is called the angle of reflection. Reflection by shiny surfaces

LAWS OF REFLECTION 1-The incident ray, the reflected ray and the normal all lie in the same plane. 2-The angle of incidence is equal to angle of reflection (angle i = angle r)

REFLECTION BY CURVED SHINY SURFACE -The reflection of light by parabolic surface mirrors is made use of in the solar dish cooker where all reflected rays are made to meet at one point called the focus. 73

THE SOLAR DISH COOKER Solar radiation falls on the shiny surface of the dish. The curved surface of a dish reflects the radiation to a sharp point called the focus. The pot is then placed at the focus point.

TRANSMISSION OF HEAT -Heat travels in three main ways namely Conduction, convection and radiation. 1.CONDUCTION – is the flow of heat through solids from places of higher temperatures to places of lower temperature. Metals are good conductors of heat while wood, glass, plastic, rubber etc are bad conductors. EXPERIMENT: Heat Conduction in Brass and Wood.

If a rod is passed over a flame many times, the paper scotches over wood but not over brass. This is because the brass conducts away from the upper paper quickly, preventing it from reaching the temperature at which it burns. The wood only conduct the heat slowly.

74

EXPERIMENT : To show that the liquids are very poor conductors of heat.

The water at the top of the test tube boils because the ice at the bottom can melt. Different metals have different thermo- conductivities (different materials conduct heat at different rates.. 2.CONVECTION – is the flow of heat through fluids (liquids or gases) from places of higher temperatures to places of lower temperatures. Convection in liquids Convection in liquids can be demonstrated by dropping a few crystals of potassium permanganate down to a tube to the bottom of a flask of water. When the flask is heated using a small flame, purple streaks of water rises upwards and fall outwards as shown in the diagram below.

These streams of warm moving fluid are called convection currents and they arise because when a fluid (liquid or gas) is heated it becomes less dense than cold fluids so it rises while the cold fluid moves downwards.The direction of convection currents by the burning candles are made visible by smoke from the paper. It is made by smoke it in strong potassium nitrate solution and then drying it. Convection in gases

3.RADIATION– is the flow of heat by means of electro-magnetic waves. It can be transmitted through a vacuum, unlike conduction and convection which require material such as solid and fluid. Solar radiation from the sun is made up of light (ultraviolet and visible) and heat. When radiation falls on an object, it is partly transmitted, partly reflected and absorbed.

Good and Bad Absorbers Some surfaces absorb (heat) radiation between than others as shown below. 75

Good and Bad Emitters of Heat Some surfaces are better emitters of heat than others. Surface that are good absorbers of heat are also bad emitters of heat. Thus dull black surfaces are good emitters of heat while shine surface are bad emitters of heat.

THE SOLAR WATER HEATER

-Is designed to produce warm/hot water it is placed on the roof of a house with the direction where it can receive maximum (radiation) from the sun. the solar water heater can be of thin copper tubes on a metal plate mounted on a good thermal insulator in a metal frame. The tubes and plates are of copper because it is a very good conductor of heat. The tubes and plates are black (painted black) because black is a good absorber of heat. The glass plate and narrow air space reduce heat loss to the atmosphere from the tubes and plate. -They trap solar radiation like a green house. -Heat loss to the roof by conduction is prevented by separating the heating panel from the roof by a layer of polystyrene which is a thermal insulator.

SCIENCE IN STRUCTURES 76

1.Beams :- are supported bars that carry/bear a load. Types of beams 1.simple supported beams -these are supported at both ends or only supported at the middle.. -In a simple beam, the top is under tensional forces while the bottom experiences compression forces. 2.Cantilever beams : one end is built into a fixed or rigid wall e.g. a bookshelf. Cantilever and simple supported beams

Strength of a beam----It depends on: (a) Span ; the longer the span, the weaker the beam becomes (b) Thickness : the thicker the beam , the stronger the beam. (c) Type of material-Materials like bricks, stones, concrete are weaker in tension. This explains why concrete is cast with mild steel rods in it and left to dry forming reinforced concrete.

Forces that affects a beam -When beams are subjected to force, internal forces called stresses are set up and these are:1.Tensile (tensional) stresses: these are forces which try to pull the material apart. Most materials are very strong in tension. . 2.Compressional stresses: are forces trying to compress/squash/crush a material. Concrete stones and metals are very strong in compression. 3.Shearing (twisting) stresses: these are produced by equal and opposite forces not in a line. They cause one part of a material to slide over another.

Strength of materials (i)

(ii)

Stiffness: a stiff material does not bend easily. It is not flexible e.g. steel is stiff as well as strong while stones are stiff but they break under bending forces. Constructions of structures such as bridges require materials that are stiff and strong. Porosity : it measures the extent to which materials absorb water through their surfaces. 77

Earth ware products (baked clay) are porous while plastic like nylon and terylene are non-porous. Loading a beam -When a beam is loaded, the top is under compression while the bottom is in tension. The middle part is the neutral axis (zone) i.e. there are no forces.

-The greater the distance from the neutral zone the greater the tensional or compression forces. -The neutral zone does not play any part in supporting the load. -NB: When loading a cantilever beam (beam with one end supported) the tensional forces are at the top and the bottom experiences compression forces.

Strength mass ratio -To have efficient structure, beams must have low mass, so material close to the neutral axis is removed to leave hollow beams. Hollow beams are lighter, stronger and much cheaper than solid beams. Types of beams

   

Lighter beams have a higher strength to mass ratio therefore their strength to mass ratio increases. However the strength of the beam is not affected. Hollow beams are often used in wood constructions where light weight beams are necessary. They resist shear forces. In I beam the middle part resist shear forces whilst the flanges resist tension and compression. The flanges in T, L, Z and I beams resist tension and compression while the middle part resists shear forces. 78

NB: Tensile strength is the ability of a material to withstand tension/pulling forces. Most hollow beams have a higher tensile strength. Joining beams 1. Metal beams- can be joined by:(a) Pinning methods :- examples of pinning methods includes:Bolt and nut,reverting , screwing (b) Surface contact methods :- examples includes:Welding, brazing, soldering 2. Plastic beams--can be joined by welding and gluing. 3.-Wooden beams- can be joined by the following methods:(a) (b) (c) (d) (e)

Pinning methods Doweling and gluing Screwing Bolting ( Bolt and nut) Nailing (use of nails) or gang nails. Joining materials by surface contact methods

Factors affecting strength of a joint 1-Surface area in conduct 2-Number of pins and nails 3-Position of pins

Building materials used in large structures Materials

Uses

Durability

Wood

Houses, roots, bridges, furniture, fences

Wood is not a fire proof and can be attacked by termites. Can decay in moist conditions

Metal

Bridges

Is strong in tension and compression.

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Stone e.g. granite and marble

Buildings

Concrete mixture of sand cement gravel and water

Bridges Dam walls

Very expensive Very durable Is not liable to corrosion Is heavy to cut to size and very heavy to transport. Long lasting materials. Strong in compression but weak in tension. Can be reinforced by mild steel rods. Cheaper to use than metals.

Trusses    

Are triangular structures used to support the roof of a house, verandas or bridges? They take the shape of triangles because they resist shear better than rectangular beams. Trusses are strong, lighter and have a higher strength to mass ratio than beams. They are also very stable. A truss has members in tension called ties and those in compression called struts . A load is spread through members of struts. There is no weight between trusses to reduce weight of the structure.

. Notes 1.Use of triangles in trusses is for stability and strength. 2. A strut is a beam under compression forces. A tie is a beam under tension forces 3.Ties can be replaced by cables.

2.Bridges -A bridge is used to carry cars, people, buses etc over a river or another road or railway line. -It has a deck on which traffic move and abutment and piers that support the deck. 80

Types of bridges (a) Beam and pier bridge : consist of a beam of reinforced concrete across a river supported at both ends and underneath by piers

a)Suspension bridges The bridge deck (beam) is supported by steel cables. The cables hang from towers or pylons at each end. The cables are in tension and towers are in compression. The greater the load, the greater the tension. A lot of cables are used so as to make the failure of one wire not to be disastrous.

3.Arch bridge   

The bridge deck is supported by an arch either from above or below e.g. Victoria falls, birchenough etc. The arch support the load by converting into downwards force and sideways thrust The arch is made of reinforced concrete or steel which are able to resist compression forces.

81

ARCH BRIDGE

Dams - A dam is a structure designed to hold back water in a reservoir. The dam wall should be shaped so that it can effectively hold back the water. -Usually dams are made of concrete with foundations on a firm ground e.g. rock. Pressure increases with depth, so dams are broader at the base so as to withstand the greater water pressure. A broad base thus increases strength and stability. Types of dams (i)

Concrete Dam e.g. lake Mutirikwi

-These dams are often arch shaped. The arch resists the compression from the water well.  Steel is used to reinforce concrete then embedded in solid rock beneath the foundations to make reinforcement more effective.  A jecking device tensions the rods at the top of the dam.  They are arched (curved shape) to transmit the thrust force of water into the embedment’s.  The arch collect the horizontal forces and turns theminto sideway forces. Concrete dam

82

Earth dams e.g. lake chivero

(ii)   

Not as strong as concrete dams. Have a broader base for stability and strength. Although more material is used in construction. They are cheaper to build than concrete dams

MECHANICAL SYSTEMS 83

4.MACHINES • • •

A machine is a device that makes work easier to do e.g. levers, pulleys, and gears and incline planes. A machine is a device or structure which is designed to move and to apply a force. Machines make work easier by reducing the effort applied and by changing the direction in which effort is applied.

1.levers -Levers are simple machines -It is a bar or string tool used for lifting or moving bearing stiff objects. Levers have got a pivot/fulcrum the end where a load is found and another end where effort is applied e.g wheelbarrows, crowbar, hammer, shovel e.t.c.

• •

Size of effort depends on distance of load and effort from the pivot. The greater the distance of effort from the pivot, the smaller the size of the effort e.g. borehole can be made more efficient by putting a longer handle i.e. increasing the distance of the effort from the pivot.

Mechanical advantage • Is the ratio of the load lifted to the effort applied? Mechanical advantage (MA) = load lifted effort applied e.g. if effort 0f 40N is used to lift 80N of soya beans. Calculate the MA MA = L/E = 80N/40N = 2 (MA) • •

The lever has in this case enable the effort to raise a load twice as large. Thus a lever moved twice the distance of the load.

Velocity Ratio (VR) • Is the ratio of the distance moved by the effort to the distance of the load. VR

= Distance moved by effort( Input ) 84

Distance moved by load

( output )

.Work done Is the amount of force multiplied by the distance moved in the director of force. Work done(joules) = force(newtons) x distance (meters) Efficiency • Is the ability of machine to do work satisfactorily? It can be reduced by friction or the weight of the machine. • Efficiency can be improved by lubricating, using ball bearings or rollers between moving parts to reduce friction. • Light parts should be used to reduce self load. Efficiency

or

=

work output x 100% Work input

or work done by load x 100% work done by effort

load x distance moved by load x 100% effort x distance moved by effort

Inclined planes

2. -An inclined plane is a sloping which is less than a right angle (90°) -It is a machine used to lift heavy loads using a smaller effort but the load move through a great distance. -The smaller the angle of the inclined plane the smaller the effort applied. It is easier to load a lorry by pushing up an inclined plane than lift the load vertically.

M.A

=

load and effort

V.R = length of incline (L) height of incline (E)

NB: The steeper the inclined plane (small angle) the bigger the mechanical advantage and velocity ratio.

3.Pulleys -A pulley is grooved wheel attached to an axle. Two or more pulleys on the same axle is a pulley block. Passing over the pulley is a string which grips the wheel and turns it. -Pulleys are used to lift heavy loads. They change the direction in which the effort is applied. 85

Types of pulleys 1. Single fixed pulley – enables lifting or load by applying a downward force. if there is no friction, it will have a MA and VR of one but because of friction the effort is always slightly bigger than the load. NOTES:1. LOAD = EFFORT

2. M.A = LOAD = EFFORT EFFORT EFFORT 3. V.R = 1 4.

EFFICIENCY = M.A X 100 %

V.R

2.Single movable pulley -The effort applied is two times the load since two parts of ropes supports one load, if there is no friction ,VR and MA would be 2 but in practice is always slightly less due to friction.

M.A = V.R V.R = No. Of movable pulleys x 2= 2

3. Block and tackle • • •

Normally used in crane s, it consists of two blocks each with one or move pulleys mounted on the same axle. Each fixed pulley simply changes the direction in which the effort is applied. Each pulley increases the MA of the system by 2 (provided friction is negligible and light parts are used for the lower block. 86

•

This means the more the pulleys; the easier it is to lift a load. A block and tackle combines fixed and movable pulleys.

NB: In pulleys -Efficiency increase as the load increases. -Efficiency is reduced by friction in strings and weight of movable pulleys. M.A = LOAD

V.R = No. Of movable pulleys x 2 EFFICIENCY = M.A

X 100

V.R

4.Gears -

Are systems of wheels linked directly by teeth (meshed) or by chains? Gears has got teeth (cog wheel) mounted on shafts. When the gear lever is changed, the speed which drive shaft turn is changed. This is because different teeth (cog wheels) make contact and change velocity ratio.

1.

M.A

2.

V.R

=LOAD EFFORT =number of teeth on load Number of teeth on effort

3. EFFICIENCY = V.R

M.AX 100 %

OR M.A X No. Of effort gear x 100 % No. Of teeth on driven gear (load)

NB: The load gear is the driven gear and the effort gear is the driver gear. Energy loses in machines -In many machines, it is possible to obtain velocity ratio but not high value of mechanical advantage due to energy loses caused by friction.

Ways of reducing friction • • •

Lubricating – with oil or grease so that the surfaces can slide more easily over each other. Using rollers or ball bearings so that surfaces roll rather than slide over each other. Using lighter parts for machines because friction increases as the weight of the machine increases. 87

• •

Making surfaces smooth – so that surfaces slide over each other easily. Rough surfaces have more friction.

NB: Friction is useful in brakes, for stopping moving vehicles and for balance e.g. when wearing shoes in a rough surfaces.

5.Pressure in fluids Pressure is force acting over an area. It is the ratio of weight/force to the area supporting it. The bigger the surface area, the smaller the forces or weight each unit area supports.

Pressure area (m2)

=

force (N)

= N/m2 = (Nm2)

Pressure in fluids • •

A fluid/liquid cannot be compressed. Gravity pulls a liquid into a container and the liquid exerts a pressure on the other container.

Principles in pressure in fluids •

Pressure in a liquid at a certain depth acts equally in all directions.

-Pressure increases with depth because of the weight above. in the above diagram pressure at D.E.F is smaller than at A.B.C -Pressure increases with density. A heavier (denser) liquid e.g. mercury exerts more pressure than water of the same volume.

•

Area x height x gravity x density= PRESSURE of LIQUID = Area

hgd

88

h= height of the liquid. g = force of gravity d= density of liquid. -We use a manometer to measure pressure. -It is a U-tube filled with liquid e.g. water or mercury. -When both arms are open to atmosphere pressure, the levels of the liquid is the same.

A manometer

Pressure of gas = atmosphere + (h)

PRESSURE = P +pgh Where p = pressure P=atmospheric pressure P (rho) =density g = gravity h= height difference in pressure level

Pumps 89

-Pumps are used to lift liquids and gases using atmospheric pressure. Types of pumps

1. Lift pump

– Has two valves. One valve is the position, the other near the base of the cylinder. When one valve is open, the other is closed. The pump is primed (filled with water) first before it can be used so as to prevent air leaking past it.

Upstroke -Is when piston moves upwards valve A (in the piston) is closed and pressure in the cylinder fall. -Atmospheric pressure then pushes water up the pipe through valve which is at the bottom which would have open. Water above the piston is forced out of the water spout.

Down stroke -Piston moves downwards. Valve B closed due to pressure of water on it and valve A open allowing water to pas upwards into the cylinder above the piston.

Disadvantages of a lift pump. -Needs priming before use (laborious) -It only delivers water on the upstroke also making it laborious. -Only raise water through height of 9 meters.

Force pump

2.

-They force water to more than 10 metres -They do not need priming before use. Upstroke -Piston moves up, the outlet valve closes. -Pressure in the barrel decreases -Inlet valve opens and water enters the barrel

90

Down stroke - Piston moves down and inlet valve closes - Outlet valve opens forcing water into the reservoir and out at the spout. - Water flows continuously from the spout because of the pressure of air in the reservoir.

3. Blair pump -It is a combination of a force and a lift pump. -It is used in a covered well. -It lifts water to a height of about of 10 meters. -It gives a steady supply of water for small communities. - It has got a handle connected to a piston which moves in a cylinder that is fixed below the water level in a well. -It has two valves which both open only upwards.

Up stroke Piston moves up; atmospheric pressure of water in the well pushes water against valve 1, which opens and water enters the cylinder.

Down stroke Piston moves down, valve 1 closes pressure of water in cylinder forces valve 2 to open and water enters the handle and flows out of the spout.

ADVANTAGES 1. The Blair pump is made of plastic making it light, cheap and easy to assemble, operate and repair. 2. No lubricating oil or grease is used (water is colourless and odourless).

Bicycle pump 91

-Air is compressed in the cylinder by the piston which is fitted with leather or rubber washer to give an air tight fit. When piston is pushed inwards, the air in the cylinder is forced through the rubber valve in the rubber tube. This prevents air from escaping.

] Withdrew piston -Rubber washer move away from the barrel -Air pressure at front of barrel reduces and air moves from the back barrel. Pushing piston -Washer moves back to the walk of the barrel. Air in front is compressed and tyre is forced to open. Air enters the tyre.

Fluid systems Works on the principle that; 92

• •

Liquids transmit equally in all directions Liquids cannot be exposed or compressed.

Examples of fluid systems includes. The siphon – is a tube used to empty liquid from a tank that is not fitted with an outlet. -When outlet Q is open, pressure inside the tube will be greater than outside. -Liquid in the tube will flow out. This reduces the pressure in the tube to air pressure on the surface at P which pushes more liquid. -The tube must be full of water and one end of the tube must be below level of liquid in the tank. -The liquid to be siphoned should be at a higher level than where it is being taken.

-A fountain of water is produced because pressure of water at P is higher than at Q. -The higher pressure causes water to come at the mouth of the tube.

Hydraulic breaks Car breaking system

-Pressure of foot on the brake pedal causes the piston in master cylinder to exert pressure on the brake fluid. -The pressure is passed on equally to the piston in the wheel cylinders -This pressure forces the brake pads against the brake drums. NB: Air bubbles must not be found in the brake fluid as air is compressible and thus reducing the effort of the braking system. The principles used in hydraulic systems are that liquids cannot be compressed and an applied pressure is transmitted.

93

Hydraulic jack These are used to lift cars.

To work the hydraulic jack :These use the facts that-; 1. Liquids cannot be squeezed. 2. Liquids pass on pressure applied to them. • • •

Effort is exerted to push down the small piston. Pressure is transmitted through the liquid and acts on the large piston The large piston is lifted up a small amount, compared with how far the small piston has been moved down. Force is applied at Area B to lift a load at A. The pressure exerted at piston 1 is transmitted equally to the larger piston 2 which is carrying the load. Piston 2 moves up raising the load.

• For example; If a downward force of 20N act on small piston (piston 1) of area 10 cm2. The pressure applied to liquid would be – Pressure = Force =20N = Area 10cm2

2 N/cm2

The pressure is passed through the liquid and acts on the large piston (piston 2) of Area 100cm2. Upward force on piston 2 would be -: PRESSURE = FORCE= 2pa x 100cm2 = 200 N. AREA NB; Thus a load of 200N can be raised by an effort of 20N. NB: In machines such as hydraulic brakes and hydraulic jacks, work input equals work output, ignoring energy losses.

1.M.A

=

LOAD

EFFORT

2. V.R = Ratios of Areas i.e100cm2 (load area) 10cm2(effort area)

94

3. EFFICIENCY = M.A V.R

X 100%

95

SCIENCE IN COMMUNITY 1.HEALTH AND WELL BEING -Health is the physical, mental and social well being or fitness. -It is maintained by 1. Good hygiene 2. Eating balanced diet 3. Regular exercises.

NUTRITION • • •

A person needs a balanced diet to be healthy. A balanced diet is a diet /food that contain all the required nutrients in the right quantities. The required nutrients comprises of :-

*Carbohydrates : for releasing energy. These are found in cereals like maize, wheat, beans, and potatoes *Proteins : for growth and replacement of worn out tissues. These are found in milk meat, eggs / leguminous plants etc. *Fats/oils (lipids): for energy store and warmth. (Insulators). -They have more energy value than carbohydrates but are difficult to digest. These are found in peanut butter, margarine,cheese,pork, milk etc. *Vitamins and mineral salts-For protection against diseases. These are found in green vegetables, fresh fruits etc. They are for vital processes in the body. (Metabolism) *Roughage / dietary fibre -- Are indigestible matter found in fruits, vegetables and cereals along the alimentary canal. They are for normal bowel movement and facilitate peristalsis. * Water - Needed for body chemical activities to transport dissolved substances. Water assists in removal of waste from the body. -It is also a major component of body fluids.

People and energy Nutritional needs are different depending on age, sex, occupation and health status. Example a manual worker like a builder needs more carbohydrates than a secretary like a clerk. Males eat more than women; teenagers eat more than adults because they are more active. Pregnant women need more proteins, vitamins, calcium and iron for the developing baby. Nursing mothers need more energy to provide milk for the baby. There are many advantages for the mother and baby. Main benefits of breast feeding 1 Mother and infant are closer (bonding). 2 Less upset stomachs and crying. 3 Mother can breast feed at work. 4 Breast milk is a perfect diet for babies. 5 Healthier teeth in breast fed babies. 6 Baby’s brain development is optimal. 7 Babies obtain protection from disease (immunity) from breast milk. 8 Breast fed infants are healthier than bottle fed babies.

96

Food and energy To find energy content of food you burn equal amount of different food nutrients e.g. 100g fats , 100g proteins , 100g starch and note the temperature changes in each beaker brings to water.

MALNUTRITION Malnutrition is when the body is not getting the right amounts of food i.e. getting too much or too little food. It can cause problems.Malnutrition causes deficiency disease. A deficiency disease is caused by lack of certain nutrient in the diet. Deficiency diseases Kwashiorkor Rickets Scurvy Anaemia Goitre Night blindness

Caused by lack of Proteins Vitamin D Vitamin C Iron Iodine Vitamin A

*Obesity : too much carbohydrates result in excess fat being stored under skin causing the person to put on weight and becomes obese. *Heart problem: too much fat may block blood vessels.

Food tests NUTRIENT

REAGENT(S)

Starch

Iodine Solution

Simple/reducing a)Benedict’s Solution sugar(glucose) b)Clinistix a)Biuret Test Protein copper sulphate solution and sodium hydroxide solution(equal quantities) b)Albitix

Fats

a)Ethanol/Emulsion Test b) Transparent Test

RESULTS WHEN NUTRIENT PRESENT Brown to blue black

WHEN NUTRIENT IS ABSENT Brown

a) Blue to orange/brick red b) Pink to purple

a) Blue b) pink

a)Blue to purple/violet

a) Blue

b) Green to Dark green

b) Green clear

a) White emulsion b) Transparent Mark

TEETH AND TOOTH DECAY Teeth are used for cutting and chewing food. Causes of dental decay/dental caries Caused by bacteria and plague. Plague- It is a thin layer of food remains on the tooth surface which contains bacteria.

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Stages in Tooth Decay 1. Damage to the enamel results in no pain being felt. 2. Dentine damage results in extreme cold/heat causing a pain sensation. 3. Opening into the pulp results in severe toothache as a result of exposure of the blood capillaries and nerve endings. Tooth extraction is usually recommended at this stage. N.B- Action of bacteria on sugary food remains has been associated with dental decay.

Decaying Teeth

CARING FOR TEETH Regular brushing

eat a balanced diet

Use a tooth brush brush after meal

Caring of brush teethgently for 1-3 minutes

visit the dentist regularly eat fibrous foods brush in circular motion

2.SUBSTANCE USE AND ABUSE 1.Smoking • • • • • • •

Smoke from cigarettes contains tar and a poisonous drug called nicotine. It is addictive Smoke particles irritate lung tissue and reduce diffusion of oxygen in the blood. Tar causes lung cancer and break down the air sacs. A disease called emphysema which reduces blood oxygen. It irritates lining e.g. bronchioles causing bronchitis and a persistent cough. It also contributes to heart diseases ,increased BP Pregnant women who smokes give birth to premature babies/underweight babies’ or miscarry or have still births.

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2.ALCOHOL – is a depressant drug which slows down the nervous reactions of the body and affects judgement. -Reaction time is reduced leading to accidents. -It causes cirrhosis of the liver in which cells’ are damaged. -It is addictive. -Some people develop anti-social behaviour. 3.MANDRAX– a hallucinogen which play trick on brain and alter behaviour of the person taking it. It is addictive and illegal. 4.CANNABIS/MBANJE/MARIJUANA – hallucinogenic and illegal drugs. -Lack of self control. -Can cause blood poison. -Criminal tendencies like violence. -Increases chances of H.I.V infection. NB: These drugs are dangerous and can damage the brain and body muscles. People taking drugs or alcohol may neglect the families, healthy is affected and they lose direction of their life. NB – Hallucinations means seeing, imagining things that are not there. Effects of Inhaling Solvents Eg.glue sniffing. -Hallucinations -Reduced self control -Damage to the nasal passage. - Damage to the muscles and the heart.

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3.FOOD PRESERVATION Is done to destroy micro-organisms like bacteria and fungi or stop their growth. Micro organisms are responsible for food rotting or going bad. Bread left over a week develops moulds due to presence and growth of fungi. - Milk becomes sour due to bacteria that convert milk to lactic acid. - Micro-organisms which decomposes food causing it to become stale and rotten. - Work best in warm, moist conditions with air. - Food should be kept dry to minimise decay. METHODS OF FOOD PRESEVATIONS METHOD ACTION Dehydration All metabolic activity occurs in a liquid medium. Drying of food prevents respiration and causes cells to shrink e.g. fruits, vegetables, meat Caning Tinned foods have a long shelf life. They are heated/cooked and sealed. Micro-organisms are destroyed by heat and also lack of oxygen .Food includes milk,fruits,etc. Salting Slating foods causes the death of organisms that spoil food. smoking Certain wood smokes produce antibacterial and fungicidal compounds. Sugaring Jams are rich in sugar which shrinks the cells and prevents bacterial and fungal growth. Refrigeration Cooling/freezing food prevents growth of bacteria and fungus. Pickling

Some foods are preserved in acids e.g vinegar as micro-organisms cannot survive at low p.H. N.B – Food preservation has the disadvantage of altering the flavour of food.

CONDITIONS NECESSARY FOR FOR GROWTH OF MICRO-ORGANISMS 1. Temperature of 25 - 35 degrees celcius (warmth). 2. Moisture or water. 3. Oxygen

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3.DISEASES -Are caused by microscopic pathogens like viruses, bacteria, fungi and protozoa. -Pathogens are organisms causing diseases. -A vector is that carries the pathogen e.g. mosquitoes, flies, snails, dogs etc

TRANSMISSION OF DISEASES -diseases are transmitted in the following ways: 1. Droplet Infection - transmitted in tiny water droplets e.g influenza, colds, T B etc. 2. By Contact - transmitted by physical contact e.g leprosy, some STDs, tetanus, ring worms etc. 3. Contaminated Water/ Food- such disease are transmitted after eating/drinking contaminated food/water e.g cholera, typhoid, hepatitis etc. 4. Vectors – diseases can be carried by an insect or organisms from one person to another eg malaria, sleeping sickness etc. 1.CHOLERA SIGNS -Loss of water (dehydration) through watery faeces, vomiting, and muscle cramps, fever, weak and quick death (especially children). PREVENTION -Good hygiene, do not use bush toilets, wash food thoroughly, cover the food, cook the food thoroughly and drink treated water. Treatment -Replace fluids by giving salt and sugar solution (ORS) -Give antibiotics that the kill the bacteria. MAKING SALT AND SUGAR SOLUTION -Mix½ tspn of salt to 6 tspn sugar. -Dissolve in750 ml of water. NB - cholera is highly contagious (spreads quickly) especially in crowded areas. 2. MALARIA- is a spread by a female anopheles mosquito. It is caused by protozoa called plasmodium which live in the mosquito. LIFE CYCLE OF THE ANOPHELES MOSQUITO - An adult mosquito passes the plasmodium to a human being through its saliva when it bites the person. -The plasmodium parasite called sporozotes goes to the liver where they multiply as merozoites which enter the red blood cells and multiply causing red blood cells to burst.

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LIFE CYCLE OF PLASMODIUM (MALARIA PARASITE) -Malaria prone areas includes lowveld, Dande, Zambezi Valley and Gokwe.

PREVENTION/CONTROL OF MALARIA 1. Taking prophylactic drugs (preventive drugs) before and after visiting malaria prone areas e.g malaquin, maolanova and coatrymetter,malasone,maloprim,dapsone. 2. Removing stagnant water it offers breaking/breeding area of mosquitoes. 3. Spraying the water or covering with oil to kill lava and pupa, spraying chemicals e.g. D.D.T. 4. Wear long sleeved clothes to prevent mosquito bites. 5. Apply mosquito repellent creams, mosquito nets, preventive drugs e.g. prophylactic. CURE OF MALARIA - Drugs like chloroquine, Fansida and quinine,primaquine phosphate. NB : Malaria has been difficult to control because of plasmodium developing resistance to drugs.

DEFENCESYSTEMS NATURAL BARRIERS AND DEFENCE MECHANISMS -Includes tears for cleaning eyes. -Skin to prevent entry of pathogen. -Mucus/hairs to trap dust and bacteria. -Wax/hairs in ears to prevent entry of pathogens. -Stomach acids that kill bacteria. -Vaginal secretions which kill bacteria. -White blood cells for destroying bacteria. -Blood clotting to prevent blood loss and entry of bacteria. -The body can produce antibodies, chemicals that destroy bacteria.

IMMUNITY - is the ability of the body to resist infection. 1.ACQUIRED IMMUNITY/ACTIVE IMMUNITY -When one suffers from a disease like small pox or measles, they develop immunity. One will not suffer from the disease again. This is because antibodies are produced against the pathogen and they remain active in the blood ready for new attack. 2. NATURAL PASSIVE IMMUNITY -Passed on through the placenta or from mother to child during breast feeding. -Antibodies are transferred from the mother to the child to gain immunity.

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3.ARTIFICIAL IMMUNITY -Antibodies are produced after vaccination. A vaccine containing dead and weakened pathogen of a disease. When they are injected into the body, the body produces antibodies that destroy the weak pathogens.

IMMUNISATION -Is to offer artificial immunity. In Zimbabwe children are vaccinated against the killer diseases such as Polio, Diphtheria, Measles, whooping cough, Tetanus, T.B. Hepatitis B. N.B.B.C.G is a vaccine against T.B. NB: H.IV. Causes a destruction of the immune system (bodies defence system) that is why a person suffers from many diseases. It interferes or destroys the white blood cell that produces antibodies.

4.REPRODCUTION IN HUMAN BEINGS -Reproduction is a characteristic of all living things. -In sexual reproduction, two gametes fuse, the sperm (male sex cell) and the ovum produced by the female reproductive system. -Male and female bodies become sexually mature at puberty when the body undergoes changes in appearance and behaviour. MALE REPRODUCTIVE SYSTEM

Functions of the male reproductive system Structure Function Testes Sperms are made in the testes and stored in the epididymis. Produces male sex hormone, testosterone. Sperm duct Muscular tube through which the sperm travel, from the testes to the urethra in the penis. Penis Either urine or sperm pass out through the penis. Scrotum Bag of skin, outside the body which protects the testes at lower temperature. This encourages sperm production. Urethra For passage of both sperms and urine from the body, separately. Prostate gland Both secret nutrients and enzymes to stimulate the sperm, the fluid from And seminal glands together with sperm is called semen. vesicles

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The female Reproductive System

FUNCTIONS OF THE FEMALE REPRODUCTIVE SYSTEM Structure ovary

Oviduct Uterus Cervix Vagina

Function To release egg cells(ova)during ovulation to secrete hormones called oestrogens.They stimulates the uterus lining to build up. Narrow tube through which egg cells travel to the uterus. Wide muscular tube where the foetus develops. Ring of muscle that closes the neck of the uterus from the vagina. Muscular tube that links the uterus to the outside, and through which a baby is born.

Structure of male and female gametes

A gamete is a special cell (sex cell) that has only half the number of chromosomes of the parent cell. After fertilisation, the full number of chromosomes is restored as two gametes join to form a zygote.

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FERTILISATION This refers to the fusion of the male and female gamete nuclei to form a zygote; it takes place in the oviduct or fallopian tube.

THE MENSTRUAL CYCLE -Describes the changes that occur in a woman`s body during an average 28 day period.

-During menstruation, the extra lining of the uterus breaks down and is passed out through the vagina as flow of blood over a period of 4 – 5 days. -The lining of the uterus builds up again during the next few days. About 10 – 14 days after the day of menstruation, an ovum is released during ovulation and it is at this time that sexual intercourse is likely to result in pregnancy. CAUSES OF INFERTILITY 1. Low sperm count 2. Poor quality of sperm 3. Physical conditions 4. Cancer 5. Damage by sexually transmitted diseases (STDs) 6. Blockage of the oviducts or sperm ducts.

DEVELOPMENT OF THE FOETUS/EMBRYO(PREGNANCY) -After fertilisation,a zygote is formed in the oviduct or fallopian tube. The embryo then implants itself into the lining of the uterus and begins to develop on placenta. At about eight weeks after fertilisation, the embryo begins to develop features such as a heart, head and limbs, at this stage is called fetus(foetus). The normal gestation period is about 40 weeks. 105

THE PLACENTA

FUNCTIONS OF THE PLACENTA,UMBLICAL CORD AND AMNION. 1.Placenta - allows the diffusion of substances such as oxygen, glucose, amino-acids, salts and antibodies from the mother`s blood to the fetus. -Also waste substances like carbon dioxide and urea are excreted together with the mother’s waste substances. NB: The placenta is selectively permeable, not all substances in the mother`s blood pass to the fetus. Alcohol and nicotine do pass through the placenta and may affect development of the fetus. 2.Umbilical Cord – attaches the fetus to the placenta and carries the umbilical artery (carries oxygenated blood) and umbilical vein (carries deoxygenated blood) 3.Amnion fluid - is a fluid filled sac that supports the fetus and protects it from physical knocks and mechanical damage.

METHODS OF CONTRACEPTION There are a number of contraception methods for preventing fertilisation or conception. Some methods are very effective and safe while others are less reliable. Contraceptive

Success

Advantages

Disadvantages

Rhythm method

50 %

*No chemicals

Withdrawal method

50%

*No chemicals added

Abstinence The pill

100 % 99 %

*No chance of pregnancy *Very reliable *Easy to use

Condom

98%

Cap

98%

Intra-urine device (IUD)

99%

*Reliable *Cuts risk of HIV and STDs *Free of medical side effects *Easy to buy and use *Reliable *Virtually free of medical side effects *Very reliable *Does not interfere with spontaneity

*Unreliable *Requires strong will *No protection against HIV or STIs *Unreliable *Difficult timing *Difficult to stick to *may cause nausea, weight gain, swollen breasts in first few months *Can cause depression,headaches,yeast fungal infections *No protection against HIV and STIs *Slight loss of sensation *Interferes with spontaneity

Spermicides

40%

Sterilization

100%

*Simple to use

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*No protection against HIV or STIs *Some women cannot use caps *No protection against HIV or STIs *Can cause heavier menstrual bleeding, pelvic inflammatory disease, urine cramps, backache. *Very unreliable *No protection against HIV and STIs *Can cause allergic irritation *No protection against HIV and STIs *In most cases is irreversible

SEXUALLY TRANSMITED DIESEASES These are caused by micro organisms’ i.e. viruses or bacteria that can not usually survive outside the body. They are transmitted from one person to another when people have sexual intercourse.

Symptoms and effects of some S.T.DS Causative organism signs disease Bacterium chancroid *Sores on penis or

Gonorrhoea

Bacterium

Syphilis

Bacterium

H.I.V/AIDS

Virus

vagina *Swollen glands in groin Male *inflammation of penis *Yellow discharge Female *Pus and discharge *Sore on pennies or vagina (a week after infection) *Spots on skin *Blindness and insanity (longterm) *Skin sores *Weight loss *Persistent cough *Diarrhoea *Swollen glands *Low white blood cell count

symptoms

Treatment/cure

Pain from sores and glands

Antibiotics

*pain during urination *But may be unnoticed

Antibiotics

Mild fever

Antibiotics(if attended to early)

*Pneumonia *No immunity *Fevers *Fatigue

No cure Use of ARVs to prolong life.

These diseases can be controlled by several means as follows; a) b) c) d)

Abstinence from sexual contact. Having a long term sexual relationship with only one person. Using a condom to prevent semen reaching the vagina. Contact tracing. Once a person is diagnosed as having an S.T.D. The sexual partner/partners must be tested and treated as soon as possible in order to limit the spread of the disease to others. Most STDS can be controlled by antibiotics if a person goes on the doctor in the early stages. There is however no known cure for the H.I.V.

4.POPULATION AND DYNAMICS 107

-Population dynamics are the ways in which a population changes in number. -Population is the number of organisms of the same kind living in an area at a particular time,such as a country. -Demography is the study of changes in population. The following factors affect the growth rate of a population. 1. Birth Rate – the number of live births per 1000 people in the population per year Birth Rate = Number of births x 1000 Number of people 2.Death(Mortality) rate - the number of deaths per 1000 people per year. 3.Death Rate =

Number of deaths X 1 000 Number of people

If the death rate is higher than birth rate the population will decrease in total. 4. Infant Mortality - is the number of deaths of babies less than one year old per 1000 babies born that year. This can be a guide to the quality of health services in an area. 6.Migration- is the movement of people into and out of an area. This has not been a major factor affecting population growth. a ) Emigration- people living an area permanently. B )Immigration - people entering an area permanently.

5.Growth Rate - Birth Rate – death rate.

Predictions of population growth and patterns of development 1.

Doubling time is the time takes for a population to double. Doubling Time: 70 Percentage growth ratio

2.

Dependency Ratio is a comparison of the number of children and old people to the number of productive adults. Children are those under 15 years of age and old people are those over 65 years of age.

Dependency Ratio =

Number of elderly people + Number of children Number of people of working age

Human population pyramid: sex and age 108

Effects of population growth on natural resources 1.

Environmental effects e.g. environmental degradation due to soil erosion and desertification resulting from clearing of land for agricultural activities. 2. Social effects include overcrowding resulting in increase of criminal activities and immorality. 3. Educational effects: Too high a population growth can result in over-stretching of educational facilities and lowering of the quality of education. 4. Health effects: Health facilities become over-stretched resulting in manpower shortages, lowering of quality of services and demand for large investment in the sector at the expense of other needs. 5. Poverty: Generally increases with increasing population, especially in the developing countries, resulting in a spiral effect on the general standard of living. -Humans will use up trees for fuel and housing. - Vegetation will be removed and soil erosion will increase. - Humans will keep more livestock in areas which cannot support many animals.

ENVIRONMENTAL HEALTH - Human society produces huge amounts of waste every day. Different societies produce different amount of waste. Most of the refuse produced by the community can be divided into two categories i.e. Bio- degradable and non -biodegradable.

1.Biodegradable refuse - unwanted food either used as pig food or decomposed by fungi and Bacterial. -Paper, cardboard and so on that can be recycled into more paper products.

2.Non-biodegradable refuse -Plastic bottles and other containers. -Polystyrene packaging. -Metal food and drink containers. -Old motor vehicles and other unwanted metal N.B: Refuse and garbage refer to solid waste that accumulates as a result of domestic and industrial activity. - All waste should be cleared and disposed of quickly by one of the following methods. a. Recycling e.g. metal cons, newspapers, glass etc b. Burning c. Burying.

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Importance of minimising Industrial pollution 1.

Effluent pollutes water sources and increases cost of water purification. The mineral ions which pollute the water are harmful to health and bacteria involved in sewage treatment. 2. Smoke contains sulphur dioxide, can result in acid rain, which destroys natural vegetation, crops and later, causes bronchitis and emphysema. Car exhaust fumes contain harmful monoxide and carcinogens. 3. Asbestos dust is common in asbestos mining areas and causes asbestosis and lung cancer.

Sewage Sewage is the name given to human urine and faeces when collected together. It also includes organic waste from kitchen and industrial waste effluent. Human waste in the form of feaces and urine must be disposed off effectively to ensure a healthy community. The waste matter may contain dangerous pathogens. It can be got rid of in different ways.

Methods of sewage disposal a. Pit latrine b. Blair ventilated pit toilet c. Water closet (W.C)

1. Pit Latrine -Consists of a deep hole in the ground into which all human urine and faeces may be deposited. They are best for isolated houses or small villages. They must be built on solid ground permeable to water. There should be no well within 30meters to prevent water contamination. Add water from time to time to improve decay of waste. Keep surface structures clean and fly – free by cleaning with disinfectant. A lid must cover the squat hole to keep out flies and cockroaches so as to prevent spread of diseases.

2. Blair Toilet It is designed for use in rural areas where water supplies may be difficult. It is spiral shape requiring no door but still providing privacy. The vent allows for escape of bad smells making it well ventilated so that flies are not attracted to it. The lining is deeper to prevent seepage/burrowing by rats and other rodents. The flyer screen at the top of the vent pipe traps any flies that will have managed to enter the Blair Toilet. The life span of such a toilet depends in the depth, the amount of water available and the number of users.

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3. Water Closet/Flush Toilet -Is generally used in urban areas where there is large population. -Urban homes have a flush toilet which carries the waste away in water. Toilet bowl is made of material which is easy to clean and is attractive. Without a lid, droplets of water from closet get sprayed all over after and hence the need for washing hands after visiting the toilet.

Processers of sewage Treatment -Sewage treatment is based on the action of bacteria on faeces (decomposition) making the diseases causing bacteria harmless. -In such communities where piped water is available, the sewage from flush toilets can be disposed of by three methods:1.

Cess pits – raw wastes from flush toilets are piped into a large tank underground where the wastes collect. Water seeps out through the walls but eventually the pit fills and has to be empted. Bacterial breakdown the waste.

2.

Septic Tank – These are large, underground, sealed tanks which receive wastes from flush toilets. Bacteria decompose the wastes. The tank requires a sock away outlet for semi-processed fluid. This means that this arrangement requires a large area and is found in low density housing areas. 111

A sewage works The raw sewage from flush toilets is carried by pipe to a sewage treatment plant where the waste matter undergoes physical and biological treatment. The treatment begins with physical separation of solids and grit from the incoming sewage. The solids are removed and the liquids pass to settling tanks. The suspended solids precipitate to form sludge which is later digested by aerobic bacteria. This process generates methane gas. NOTE: Biogas (methane + Co2) is burned in boilers to keep the digesters at optimum temperatures. Sludge is broken down by the bacteria and the solid leftovers are used as farm `compost` or fertiliser. The liquid from the settling tanks is treated by aerobic bacteria which convert any ammonia to nitrates. The effluent cannot be empted into rivers as it causes rapid growth of algae, so many sewage works are being converted to the activated sludge method which process sewage so that the left over from sewage treatment, the effluences, can be passed into rivers without polluting them. The activated sludge method uses bacteria in an oxidation panel to breakdown the sewage completely, reducing the levels of nutrients in the water and making it more suitable for entry into a river into a river system. WATER Humans need clean safe water for their consumption. Safe water means absence of pathogens and disease causing organisms and pollutants from industrial activities which may be poisonous. Methods of purifying water 1. Boiling 2. Filtration 3. Chlorination 1.Filtration

2. Chlorination The water may come from a large dam and be passed through a water purification plant before being piped for domestic/industrial use. The purification plant operates into two ways – physical and chemical. 112

Firstly water pumped into the purification system must be allowed to settle to remove some of the solid particles. A chemical (called flocculent) may be added to speed up this sedimentation process. The water is then filtered through said to remove any remaining solid particles. The water should now be clear but still unsafe to drink. The water is then chlorinated. Chlorine is added to kill any microorganisms such as bacteria. It is passed into a storage reservoir until it is pumped to houses. The water is tested for bacteria at several stages before being passed on to the consumer.

-To prevent contamination of water, the source and therefore avoid water Protecting water supplies borne diseases like cholera, typhoid, dysentery and bilharzia. This explains the importance of sitting of toilet in relation to water source. If the water is obtained from a well, the well should be away and uphill from the living area and latrines. This is to ensure that water which seep into the well from the surrounding area is not contaminated by human wastes. Well should not be placed near rubbish dumps, animal enclosures or any other sources of contamination. Traditional wells can be protected further by improving the structure in the following ways; 1. Using a bucket with a handle and hook to reduce contact with the surface around the top of the well. 2. Building a brick/cement surround with a water run-off channel around the top of the well to carry away spills. 3. Covering the well to prevent rubbish animals from falling into the water and decaying. 4. Lining the well with bricks or cement. 5. Using a Blair pump to raise water from the well.

CHILDREN LEARN AS THEY GROW 113

*IF A CHILD LIVES WITH CRITCISM. HE LEARNS TO CONDEMN. *IF A CHILD LIVES WITH HOSTILITY. HE LEARNS TO FIGHT. *IF A CHILD LIVES WITH RADICULE. HE LEARNS TO BE SHY. *IF A CHILD LIVES WITH SHAME. HE LEARNS TO FEEL GUILTY *IF A CHILD LIVES WITH TOLERTENCE. HE LEARNS TO BE PATIENT. *IF ACHILD LIVES WITH ENCOURAGEMENT. HE LEARN CONFIDENCE. *IF A CHILD LIVES WITH PRAISE HE LEARNS TO APPRECIATE. *IF A CHILD LIVES WITH FAIRNESS HE LEARNS JUSTICE. *IF A CHILD LIVES WITH SECURITY HE LEARNS FAITH. *IF A CHILD LIVES WITH APPROVAL. HE LEARN TO LIKE HIMSELF. *IF A CHILD LIVES WITH ACCEPTANCE AND FRIENDSHIP. HE LEARN TO FIND LOVE IN THE WORLD.

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