01-547053 Interdependence Layout 1 20/9/16 4:13 PM Page 2 … Science Book-5.pdf · 2020-04-30 · Prepare lists of what animals eat: ‘these animals eat insects’, ‘these animals

INTERDEPENDENCE AND ADAPTATION

Living things depend upon each otherAlthough all living things need food, plants are the only living things that canmake their own food. To do this, they use water, carbon dioxide and sunlight.Inside a plant’s leaves is a green substance called chlorophyll. It is chlorophyllwhich traps the energy from sunlight and uses it to turn carbon dioxide andwater into sugar and other carbohydrates, which are a plant’s food. Thecarbohydrates are a store of energy that has come from sunlight. This processof making food using energy from the Sun is called photosynthesis.

Most leaves are large and flat so that they can absorb as much sunlight aspossible. They also have a network of veins in them. These carry water andmineral salts from the roots into the leaves.The veins also carry the sugar and othercarbohydrates away to other parts of theplant where they are needed.

Producers and consumersBecause green plants are the only living things that can make their own foodthey are called producers. Grass is a producer, so is a rice plant, an oaktree, a fern or a seaweed. Animals do not make their own food. Instead theyuse, or consume, food stored in other living things. A chicken is a consumerin that it feeds on corn. You are a consumer. Sometimes you eat producersdirectly, as when you eat rice, potatoes or lettuce, but often you eatproducers indirectly, as when you eat a chicken that has fed on corn, ordrink milk that came from a cow that had fed on grass. A few animals, suchas humans and brown bears, eat both plants and animals. They are calledomnivores. An omnivore can be either a primary consumer or a secondaryconsumer, depending on what it is eating at any one time.

Food chainsThe way in which the animals and plants in a habitat rely on each other canbe shown by food chains. A food chain shows the way energy flows througha habitat. Food chains usually start with a producer, a green plant, becausethat is where energy (from the Sun) enters the food chain. The producer isthen eaten by a consumer (an animal) which may then be eaten by a

How a plant makes its food.

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sunlight

light energyfrom air

carbon dioxide

water

mineral salts

oxygen

Sun

released intothe air

chlorophyll(green)

from the soil, toall parts of theplant

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Unit

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01-547053_Interdependence_Layout 1 20/9/16 4:13 PM Page 2

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Name a living thing that eachof the organisms below mightdepend on:a) grassb) cowc) ducklingd) beee) tigerf) shark

a) Why do you think thatsecondary consumers or predators need goodeyesight and a keen senseof smell?

b) What do you think wouldhappen to all the plants andherbivores in an area if all the secondaryconsumers or predatorswere killed?

What do you think wouldhappen if the plants at thebeginning of a food chain were sprayed with apoisonous chemical?

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3Divide this list of living things into producers,first consumers (herbivores), and secondaryconsumers (carnivores):grass, sheep, fox, lion, cabbage, eagle, mouse, lettuce, turtle, otter, oak tree, tawny owl, thrush, jungle cat, caterpillar,blue whale, seaweed, limpet, shark, slug

How many food chains can you make usingthe plants and animals from this list?

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corn

leaf beetle

owlfield mouseslug

chicken fox

second consumer (another animal).

Food chains are usually made of three, four, or occasionally five organisms. An example of a short food chain is:

corn chicken fox

producer first consumer second consumer or herbivore or carnivoreor prey or predator

Here is a food chain with five organisms:

leaf slug beetle field mouse owl

Poisoned food chainsIn the 1960s, scientists discovered that somechemicals being used to kill insect pests were beingpassed along food chains. Mice and small birds wereeating the chemically treated plants and their seeds.They in turn were preyed upon by hawks, owls andeagles. The chemicals built up in the bodies of thehawks, owls and eagles, with the result that they laideggs with weakened shells. Fewer chicks survivedand this led to a sharp decrease in the numbers ofhawks, owls and eagles. Some of these chemicalpesticides, such as DDT, have now been banned in many countries.

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Food websFood chains on land areusually made of three or fourorganisms. An example ofsuch a food chain is:

grass grasshopper lizard hawk

producer first consumer second consumer third consumer or herbivore or first carnivore or second carnivore or prey or predator or predator

Longer food chains are often found in the sea. These can have six or evenseven links. The food chains in the sea start with microscopic green plantsfloating in the plankton. These are eaten by tiny animals, which are consumedby small fish. The small fish can be eaten by slightly bigger fish, which maybe eaten by something bigger, such as a shark or killer whale.

Carnivores and detritivoresAt the end of many food chains there is a fierce hunting animal—called the topcarnivore. Examples include lions, tigers, and leopards on land, hawks, owlsand eagles in the air, and killer whales and sharks in the sea. Top carnivoreshunt other animals but are not hunted themselves. However, even these fierceanimals do not last for ever, and when they die they are eaten by other livingthings. Their dead bodies may be eaten by scavengers, such as vultures,kites, crows and some hyenas, or their bodies may be decomposed byanother group of organisms called decomposers. These include maggots,worms, grubs, moulds and other fungi, as well as bacteria. Many of thesedecomposers also feed on dead plant materials.

In any habitat there will be several food chains. Think about this simple food chain:

grass deer leopard

In the natural world, very few animals eat just one kind of food. Many otheranimals feed on grass besides deer, and deer feed on other plants besidesgrasses. Other animals feed on deer besides leopards. And, as we have seen,the plants and animals in a food chain may also be consumed by decomposers.These decomposers return the nutrients which made up the dead plants and

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grass grasshopper lizard hawk

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Collect pictures of the different birds andmammals that are scavengers. Use yourpictures to help you to make a book called‘Nature’s dustmen’.

Work with a group of friends and paint a largepicture of a tree and mount it on a wall. Drawpictures of animals and plants which use thatkind of tree in some way. Add these to yourpicture of the tree. Label your pictures.

Prepare lists of what animals eat: ‘theseanimals eat insects’, ‘these animals eatseeds’, ‘these animals eat plant leaves’, andso on. Use these lists to prepare food chainsand food webs.

Try it out

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The world’s largest plant-eater orherbivore is the African elephant.The male elephant grows up to3.2 m tall and weighs about 6tonnes. It can eat up to 150 kgof plant material a day.

Fact alert

Most human beings areomnivores, they eat a widevariety of plant and animalfoods. How many food chainscan you think of in which youare a part? Write them down.Which is the longest foodchain? Can you join some ofthe food chains into a simplefood web?

Write out these food chains inthe correct order:a) cabbage; thrush;caterpillar

b) fish; tiny plants; tinyanimals

c) grass; human; sheepd) frog; dead leaf;earthworm

Here is a food chain which youmight find on the seashore:

How many more seashorefood chains can you think of?

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animals to the soil where they can be reused orrecycled by other living things.

Food websFood chains have many branches and connections.Scientists sometimes link together food chains fromthe same habitat as a food web. In places where life is hard, such as in a desert or the polar regions,there are few kinds of plants and animals and the foodwebs are fairly simple. In tropical rainforests, wherethousands of kinds of plants and animals live side byside, the food webs are extremely complicated withthousands of links and branches.

sun

dead fox

bacteria andfungi

grass

rabbit

fox

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River habitatsWater is never still. It is constantly on themove as it moves between the land and seain the water cycle. Rivers are part of thisvitally important water cycle. Most riversbegin as springs or glaciers in hills ormountains. They then flow down to the sea.At different stages rivers contain differentkinds of wildlife adapted to living there.

The upper partsThe water in the early stages of a river is cold, clear and fast flowing. Oftenthere are waterfalls and rapids. Few plants can survive there because theyare quickly washed away by the power of the water. Apart from some waterinsects that live under the rocks, few animals live in this part of the river,although some fish, such as trout and mountain barbel, may be able to swim against the strong current there.

Water shrimps, crayfish and insects live further down the river. They providefood for fish, including mahseer, carp and trout. The fish in turn are food forbirds such as kingfishers and herons, as well as for mammals like the otter.

Middle stageAs the river enters the middle stage the land changes; it becomes flatter and the water flows more slowly. The river contains muddy, slightly warmerwater, which winds its way along. Plants can grow in the bed of the river andat its edges. Many species of insects live there, as do fish such as perch andpalla. Swans, moorhens and coots may feed on the water plants and animals,while deer live on the river banks and feed on the plants growing there.

The final stageAs rivers meet the sea, the surroundingland becomes flat. Heavy rain or snow may cause flooding. The mouth of the

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The stages in the life of a river.

The black-tailed godwit feeds in the shallow waters of an estuary. It uses its long beak to probe for tinyanimals in the muddy water.

rain and snow

fast-flowingtributaries

waterfall

meanders

salt marsh

estuary

sea


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The world’s largest living reptile isthe saltwater or estuarinecrocodile which is found in partsof southern Asia, includingPakistan, as well as in NorthernAustralia. It can grow up to 7.6 mlong and weighs almost 2 tonnes.

Fact alert

Write down all the reasons youcan think of why a fish canmove easily through water.Find out as much as you canabout the fish found in rivers.

Make a list of all the riverplants and animals you canthink of. Here are a few to getyou started: otter, trout, swan,dragonfly, reed. How manyfood chains can you makeusing the plants and animalsfrom your list?

Write down all the ways inwhich rivers cana) help people, and b) hinder people.

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Work with a group of friends and make a largeoverhead plan of your local river. Collectpictures or drawings of the different sectionsand stick them on your plan. Show how theriver is used and the different types of plantsand animals that can be found in the waterand on the river banks.

Collect pictures and cuttings from newspapersand magazines describing the pollution ofrivers and the effects pollution has on peopleand wildlife. Make a book using the materialsyou have collected.

Often in low-lying areas, rivers arestraightened and made deeper. Find out whythis is done, even where ships do not use theriver. What effect does this straightening anddeepening have on wildlife?

Try it out

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river may widen out into a stretch of open watercalled an estuary. It is in an estuary that the freshwater of the river meets the salty water of the sea.In sheltered estuaries some of the mud and sandcarried by the river builds up to form salt marshes,which quickly become home to plants and animals.A few fish, such as flounders, mullet, carp andcatfish, can withstand the mixture of fresh and saltwater. Huge flocks of ducks, geese and wading birdsfeed on the thousands of small animals—shellfish,worms and shrimps—that live in the mud and feedon the decaying plant and animal matter it contains.

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A river estuarywith saltmarshes. Only a few species ofplants are ableto survive in themixture of saltand fresh waterin an estuary.


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Life in a forestA forest is not just a collection of trees growing together. It includes many otherplants, growing in layers. They may include shrubs, herbaceous plants, ferns,mosses and fungi. A forest is also home to many different animals which obtainfood, shelter and safety from enemies there.

Forest treesA forest may contain deciduous trees, evergreen trees, or both. Deciduous treeslose their leaves in autumn and grow new ones the following spring. They includethe oak, almond, shisham, mango, peepal and banyan. Although evergreen treesappear to keep their leaves all the year round, they really lose a few at a time,instead of all at once. They include pine, yew, fir, deodar and spruce.

The shrub and herb layersBeneath the tree layer is a shrub layer. This consists of shrubs and small trees.Underneath the shrub layer is a layer of herbaceous plants and ferns. This iscalled the herb layer. Many of the herbaceous plants grow and flower in thespringtime. This is because sunlight can only reach them before the deciduoustrees have developed their new leaves. When the trees above do open theirleaves, these smaller plants then die back and survive on stored food until thefollowing spring. On the forest floor there is often a layer of mosses, liverwortand lichens. These simple plants can make do with very little light. In fact theyprefer damp, shady places.

In a forest of evergreen trees there are few shrubs and herbs growing beneath thetrees. This is because less light can reach the ground and the soil is less fertile.

Fungi feed and grow on fallen logsand rotten branches in a forest.

The layers of growth in a deciduous forestand some of the animals that live there.

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Choose a tree that you knowwell or one which grows nearyour school. Use referencebooks to find out what kinds ofanimals feed on that tree.Write a food chain for yourchosen tree. For each of theliving things in your food chain,say whether it is a producer, afirst consumer or a secondconsumer.

If forests on hillsides are cutdown, the rivers in the valleysbelow often flood. Why do youthink this is?

To help them to survive in theirhabitats, living things havedeveloped special features tosuit the place where they live.Think about the followingforest animals and how theyare suited to their habitat:deer, squirrel, woodpecker,woodlouse, owl, fox.

What would happen to theseanimals if the forest wherethey lived was cleared to makeway for a new road?

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The forest floorThe rotting logs and dead leaves on theforest floor are home to many smalleranimals such as beetles, woodlice,springtails, millipedes, centipedes andspiders. These animals need to stay cool,dark and damp so that they do not dry outand die. Fungi feed and grow on the fallen logs andbranches and soften them as the wood rots away.Insects and their larvae can then start to burrow intothe rotting wood.

Woodland animalsThe tree layer is the habitat of many small insect-eating birds, such as tits and warblers. These feedon the insects and their caterpillars that eat the treeleaves. Woodpeckers have special beaks andtongues that enable them to feed on the insects andtheir larvae that live in rotting tree trunks andbranches. Owls and hawks may sleep and nest inthe taller trees but hunt for their prey in all parts ofthe forest and its surroundings.

DecayWhen leaves fall from a tree or other plant in aforest, they lie on the ground and are wetted by the rain. Gradually they rot or decay into the soil.Animals such as woodlice, millipedes andearthworms also eat pieces of the dead leaves. The decomposers, bacteria and fungi, break up theleaves, slowly changing them into mineral salts inthe soil which other plants can use. When the trunk,branches and twigs of the tree fall, these too decayand form mineral salts.

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Part of a forestfood web.

fly

blue tit

greenfly

thrush

lettuce

sparrowhawk

rosegrass grain

dormouse

owl

slugrabbit chaffinch

fox


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How soil is formedAlmost everywhere on land there is soil. Sometimes there is a lot of soil, butin rocky places there is often very little soil. Some soils grow many plants.We say such a good soil is fertile. Other soils are poor and few plants willgrow in them. These soils are said to be infertile.

Valuable soilSoil is very valuable to us. The plants we eat grow in soil, so do the cotton andflax plants which provide us with some of our clothing. The trees which give uswood for fuel, our timber and paper grow in the soil. Our meat, milk, wool andleather come from animals which feed on plants that grow in the soil. Withoutsoil we would have nothing to eat or read, nothing to write on, and little towear. Nor would we have any of the things which are made from timber.

The importance of humusMosses and lichens can often be seen growing onpieces of rock. When these simple plants die,bacteria and moulds and other fungi grow onthem. The dead plants decay and break up intolittle pieces. The decayed pieces of plant makefood for other plants and also for some smallanimals. Soon the rock has a lot of black pieces ofdecayed plants and animals in it. This blacksubstance is called humus. When there is a lot ofhumus mixed in with the tiny pieces, or grains, ofrock, then a soil has been formed.

These pine trees have been planted so thatthey can be used for timber or to make paper.

The soils on which broad-leaved trees aregrowing are very fertile.

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Lichens growing on a rock.

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In your own words, describehow soil is formed.

Over much of the Earth, rocksare covered by a thin layer of soil. Can you think of someplaces where the rocks areuncovered so that you can see them? Make a list of these places.

The soil on the tops of hills isoften very shallow. On the lowerslopes the soil is much deeper.Why do you think this is?

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Collect samples of soil or sand from thedifferent places you visit. Keep your samplesin small bottles. Label the bottles saying whereand when you collected the soil or sand.

Will mung bean seeds grow without soil? Trygrowing them on wet cotton wool, wet papertowels and other materials. When would themung bean seedlings definitely need soil?

If you wished to make a garden on the side ofa hill, how would you stop the soil beingwashed away? Draw a picture showing whatyour garden would look like and how youwould plant it.

Try it out

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Precious soilA fertile soil may take thousands of years to form, yet every year muchgood soil is covered with buildings, concrete and roads. We shall have to begin to take much more care of the soil we have left if we are tocontinue to obtain our food and all the other things that come from it.

Safety: Always wash your hands thoroughly after you have touched soil or, better still, wear gloves while you are handling soil.

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soil

flowering plantslichensmosses

How soil isformed.

Although a lichen looks like asingle plant it is really a fungusand an alga (a relative of theseaweeds) living together.

Fact alert

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Different types of soilAs we have seen, soils are small pieces of rock mixed with humus. Thereare many kinds of soil. The type of soil depends on the kind of rockunderneath and the climate of the area. The colour of the soil depends on how much humus there is in it, what minerals it contains, and how much the rain has washed minerals out of the soil.

Almost all plants need soil to grow in, but different plants prefer different kinds of soil.

Wet and dry soilsSome soils are formed where the ground is alwayswet. These are not very fertile. Because the groundis so wet, there is not enough air for plant roots tobreathe properly. We call such wet places wherefew plants can grow bogs, swamps or marshes.Sandy soils, such as those in some deserts, arevery dry and they are not very fertile either.

Sandy soilsSandy soils are made of grains of rock that are just big enough to see. You can feel the little grains when you rub the soil between your fingers. A sandy soil is easy to dig and there is plenty of air in it for plant roots tobreathe. When it rains, water runs through sandy soil quickly. In dryweather the plants growing on sandy soil may not haveenough water; then they wilt and die.

Clay soilsSome other soils are made from pieces of rock so tinythat you cannot see them. If you rub a piece of clay soilbetween your fingers it feels slippery like soap. You canpress it between your fingers into a ball. The pieces of rockare so tiny that there is little air in the soil for plant roots to breathe. Digging clay soil is very hard work, particularlywhen it is wet. Water does not pass through a clay soil very

Very wet soils are not very fertile. These mangrove trees have breathing roots that grow above the soil.

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Dry, sandy soils are not very fertile.

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One square metre of fertile soilmay contain over 1000 milliontiny animals.

Fact alert

If a farmer sows 100 kilogramsof wheat seeds, he may laterharvest several thousandkilograms of new wheat seedsand straw. Can you explainwhere this extra amount ofnew material has come from?

Some soils are made of smallstones, called gravel. Fromwhat you know about soils,what properties do you think a gravely soil would have?

Describe in your own wordswhy few plants grow in desert areas.

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Which is more fertile, the soil near the surfaceof the ground or the soil from about 30centimetres down. Plan an experiment tocompare samples of the soil from the twoplaces. What equipment and materials will youuse? How will you make sure your experimentis fair? What measurements will you make? Tryout your experiment to see whether it works.

Find out all you can about earthworms and whythey are good for the soil.

Try it out

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easily, so a spadeful of clay soil is very heavy.When the weather is dry, big cracks may form inclay soil and plant roots near these cracks oftenwilt and die.

Loam soilsThe best kind of soil is called loam. It has as muchclay as sand in it. It also contains a lot of humus.Loam is quite easy to dig and it does not dry outvery quickly in hot weather. Plants grow well inloam soil and it is home to many kinds of plantsand animals. The most fertile loam soils are foundunder grassland and under the forests of broad-leaved trees such as oak. These soils have takenthousands of years to form and they contain largeamounts of humus.

Water runseasily througha sandy soil.

Water does notrun easily througha clay soil.

The most fertile soil is a loam soil.It grows good crops.

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Animal groupsThere are animals and plants living almost everywhere. About 1,500,000different species, or kinds of animals have been named, and more than400,000 species of plants. Scientists believe there are many more speciesof plants and animals that have not yet been discovered.

ClassificationThere are so many kinds of animals and plants that no one could everstudy all of them. For this reason, scientists sort living things into groups.This sorting process is called classification. Knowing about one animal orplant in a group helps you to know more about the others. Each groupcontains animals or plants that are similar in important ways. If you have apet cat, for example, you know a lot about the other cats in the world. Youknow that cats have hair or fur. They have sharp teeth with which they eatmeat or fish, they have long whiskers and they feed their young on milk.

AnimalsAnimals are made up of many cells that form specialized tissues, organsand systems. Animals live by eating food that has been made by plants, orwhich comes from animals that have themselves eaten plants. Most animalshave to move around to find food and escape from danger. Although someanimals spend the whole of their lives in one place, but even these animalscan move at least some parts of their bodies.

Since there are so many different kinds of animal, scientists put them intogroups. The two biggest groups are based on something you cannoteasily see—a backbone. Many animals have a skeleton of bone, like ourown skeleton, with a backbone inside their body. Horses, cows, mice,birds, snakes, frogs and fish all have a backbone made up of severalsmaller bones called vertebrae. An animal with a backbone is called avertebrate. There are about 50,000 species of vertebrates. They are inturn divided up into five large groups called mammals, birds, reptiles,amphibians and fishes.

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151

AN

IMA

L K

ING

DO

M

vertebrates crustaceans

insects

wingless

winged

winged

winged

winged

ticks

worms

scorpion

spider

arachnids

invertebrates

mam

mals

reptiles

amphibians

shark

shark

bony fish

lizards

tuataras

tortoisecrocodilians

jawless fish

fish

birds

flying birds

elephant

hoofed mam

mals

odd toed

even toed

humanprimates

egg laying

pouched

flying

marine mam

mals se

al

dolphin

rodents

rabbit

flesh eating

tiger

fox

monkey

flightless birds

newts

salamanders

frog

How the animal kingdom

isdivided into smaller groups.


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VertebratesThese are the main features of thedifferent groups of vertebrates:

Mammals have hair or fur on theirbodies, are warm-blooded and feedtheir young on milk, e.g. human,elephant, rat, mouse, tiger. Mammalsalso look after their young until they areold enough to fend for themselves.

Birds have two legs and two wings andtheir bodies are covered with feathers.They have beaks but no teeth. Birds arewarm-blooded and lay eggs with hardshells from which the young birdshatch, e.g. crane, eagle, sparrow,parrot, gull, penguin.

Reptiles have bodies covered with scales, are cold-blooded and most layeggs protected by tough, leathery shells, e.g. crocodile, alligator, snake,lizard, tortoise, turtle.

Amphibians have a thin, damp skin; their young breathe with gills whilethe adults have lungs, e.g. frog, toad, newt, salamander.

Fish have a body covered with scales, live in water, swim with fins and arecold-blooded. Most fish lay eggs, e.g. shark, catfish, carp, sardine, trout,eel, seahorse, perch.

InvertebratesThe other big group of animals is the invertebrates. Amazingly, about 97 percent of all animal species are invertebrates. These are animals like crabs,lobsters, jellyfish, butterflies, moths, slugs, snails, woodlice and spiders.Some of them have a shell or tough skin on the outside. This is called anexternal skeleton. But these animals do not have a skeleton and backboneinside their bodies. Other invertebrates, such as jellyfish, sea anemones andearthworms, do not have a skeleton at all. The invertebrate group in turn is

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Vertebrates come inall shapes and sizes.

horse

frog

rat

tiger

turtle

lizarddolphin

bat

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octopus

squid

slug

Use reference books or the Internet to find thenames of five warm-blooded animals and fivecold-blooded animals. What are the mostcommon cold-blooded and warm-bloodedvertebrates in your country?

Find a picture of a cat and a dog. Look at thepictures carefully and think about what youknow about cats and dogs. How many wayscan you find in which cats and dogs aresimilar? How many differences can you find?Make a table of your findings.

Collect pictures of as many animals as youcan, vertebrates and invertebrates. How manyways can you find of grouping the animals?

Try it out

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There are wide differences in structure andbehaviour even within one group of animals.Cuttlefish, octopuses and squid belong tothe same group as slugs and snails.

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Think about each of theseliving things. Write them out astwo lists, one containing plantsand the other animals.grass, seaweed, earthworm,jellyfish, oak tree, goldfish,horse, housefly, daisy, pinetree, moss, dragonfly,snake, lettuce, fern, mouse,eagle, woodlouse,dandelion

Can you now divide yourcolumn of plants into smallergroups and your column ofanimals into smaller groups?

Make a list of all the insectsyou can think of. How manyways can you find of dividingthese animals into smallergroups or sets?

Read the following notes.Name the group of animalsthat is being described ineach.a) Warm blooded; feathers;lay eggs with hard shells.

b) No legs or backbone,body made up of manysimilar segments.

c) Have hair or fur; feedtheir young on milk;warm blooded.

d) Six legs; no backbone.e) Fins; cold-blooded; scalyskin; live in water.

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divided into smaller groups such as the insects,crustaceans (crabs, lobsters and shrimps), worms,arachnids (spiders and scorpions), and so on.

cuttlefishsnail


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Plant groupsPlants are the only living things that can make their own food. They do thisby the process called photosynthesis. During photosynthesis they use theenergy of sunlight to change simple substances such as carbon dioxideand water into food. Oxygen is a waste product of photosynthesis. Likeanimals, plants grow, reproduce and respire, but unlike animals, plantscannot move from place to place, although they can move when they grow.Because plants do not have nerves, they react slowly to changes in theirsurroundings.

Plant groupsScientists sort plants into two main groups. In one group are the plants youare probably most familiar with—the plants that produce seeds. Mostplants, including daisies, sunflowers, tulips and rice plants and othergrasses, produce their seeds in flowers. There is another, smaller, group of plants which produce their seeds in cones. They are often calledconifers and they include pine, spruce, fir, deodar and yew trees.

There are about 550 species of conifers in the world.The plant kingdom.

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PLANT KINGDOM

seed plants seedless plants

ferns

cone-bearing plantsflowering plants

monocots

grasses lilies orchids palms

dicots

heath family asterids buttercups legumes mustards rose family

carrot familymaple family birch familyoaks true rose walnut fruits

mossesalgae


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You can see where spores are made ifyou look at the underside of the leaf orfrond of a fern.

The largest living thing on Earthis a giant sequoia tree inCalifornia in the United States. It is 84 metres tall and about 31 metres around its trunk.

Fact alert

Describe how you think ascientist would decide whethera new living thing he or shehad discovered was a plant oran animal.

How many plant names canyou think of? Make an ABC of plant names. Choose a fewof the plants you have namedand find out more about them.

How many ways can you think of in which we dependupon plants?

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Choose two different plants and make factcards about them. Draw pictures on each ofyour cards and write down all the informationyou can find about your chosen plants.

Make a collection of leaves. Press thembetween sheets of newspaper for a few daysand then mount them on sheets of card. Labelyour leaves.

Make three-dimensional models of somedifferent plants using clay, Plasticine or scrapmaterials.

Try it out

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Flowerless plantsPlants in the second big group produce newplants from tiny dust-like spores. The sporesare made and released in their thousands.Among these plants are the ferns, mosses,liverworts, and algae or seaweeds.

Ferns usually live in damp places on land.They have leaves, or fronds, that are made upof many small leaflets. Ferns form spores onthe underside of their leaves.

Mosses and liverworts are simple, greenplants that live in moist places on land.Liverworts have a ribbon-like or leafy shape.Mosses have leaf-like scales. Both mosses and liverworts reproduce with spores.

Algae live wherever there is water, light andmineral salts. The smallest algae are tiny,single-celled plants which can be seen onlywith a microscope. The largest algae are theseaweeds that live in salty sea water. All of the algae reproduce with spores.

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Introducing keysScientists use keys to sort animals and plants into groups by examiningtheir characteristics. They also use keys to identify plants or animals theyare meeting for the first time.

What is a key?

A key uses differences between a collection of plants or animals to splitthem into smaller and smaller groups. A key consists of a series ofquestions, each with two possible answers. Each question asks about oneimportant characteristic of the plant or animal. The answers lead you to thenext question and eventually to the name of the unknown plant or animal.

Before we see how keys can be used to identify plants and animals, let us look at a key that is used to sort people. A group of seven children in Class 6 decided to make a key so that their new teacher, Mr Kamran,could tell them apart.

When the children were making this key for Mr Kamran to use, why didthey choose the colour of their hair and eyes? Why didn’t they use thedifferent clothes they were wearing?

Types of keyThere are two kinds of key. Branching keys are most useful when there areonly a few things to be identified. The key above is a branching key,although some people call it a sorting key. Numbered keys are usuallymost useful when there are large numbers of plants, animals or otherthings to be sorted.

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7 children

boys girls

blonde hair brown hair brown hair

brown eyesbrown eyes light browneyes

blonde hair

grey eyesblue eyesgrey eyes

How could you tell these children apart?

dark browneyes

EJAZADIL SARAMOHSINYASIR YASMIN NIDA


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In your own words, say what akey is and what it is used for.

Use the key to the sevenchildren in Mr Kamran’s classto answer these questions.a) Which girl has brown hairand brown eyes?

b) Why do we need toknow the colour ofEjaz’s eyes?

c) Which boy has blondehair and grey eyes?

d) Which girls have brown eyes?

e) Which girl has brown hairand grey eyes?

Why do you think that a keycan sometimes be more useful than a picture book inhelping you to identify plantsand animals?

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Make a branching key to identify these fivekinds of big cats:tiger; lion; cheetah; common leopard;jaguar

Begin by asking a question which has theanswer ‘yes’ or ‘no’ for each animal. To startyou off, you could ask the question ‘Does ithave patterned fur?’

Now write out your key again as a numbered key.

Look again at the key to the children in MrKamran’s class, then make a branching ornumbered key to identify a group of five or sixof your friends. Are there any features you canuse to separate them other than their hair oreye colour?

Make a list of all the animals you can think ofwhich live in our homes. Can you make a keyto separate five of them?

Try it out

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Here is a simple numbered key to sort fiveeveryday objects—a wooden ruler, a pencil, awooden pencil box, a plastic pen and a rubber. Ofcourse, when you use this key you have to pretendthat you have never seen these five objects before!

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1 Made at least partly of woodNo wood at all

see 3see 2

2 Made of plastic with a metalpoint at one endNo metal present—rathersoft to the touch

PEN

RUBBER

3 Shape rectangular with amoving lidShape rectangular with nomoving parts

PENCIL BOX

see 4

4 Shape rectangular with inkgraduations along itCylindrical shape with ablack point at one end

RULER

PENCIL


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Using keysUsing a keyWe have seen how keys work using people and everyday objects of the kindyou might find in your classroom. Now let us see how keys can be used toidentify plants or animals. To begin with, here is a simple branching key toseparate six common tree leaves:

Here is the same key set out as a numbered key:

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1 Divided into separate leafletsNot divided into separate leaflets

see 3see 2

2 Fewer than 5 leafletsMore than 5 leaflets

LABURNUMACACIA

3 Smooth outlineIrregular outline

EUCALYPTUSsee 4

4 With toothed edgesLobed edges

MULBERRYsee 5

5 With 4 lobesWith more than 4 lobes

TULIP TREEOAK

Tree Leaves

divided intoseparate leaflets

not divided intoseparate leaflets

fewer than5 leaflets

more than5 leaflets

irregularoutline

lobededges

4 lobeslaburnum

tulip tree

acacia

eucalyptus

oak

mulberry

smoothoutline

toothededges

more than4 lobes


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If you were making a key toseparate some animals, whatsort of features would you lookfor? Explain why you wouldchoose those features.

Write out the numbered keysof vertebrate and invertebrateanimals (above), this time asbranching keys.

Make a key to separate thefollowing animals: goldfish,horse, toad, sparrow, lizard,cow, eel, snake.

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Animal keysHere is a simple numbered key (right) toseparate the five groups of vertebrate animals.

This numbered key below will help you toidentify the main groups of invertebrateanimals to be found in the garden or schoolgrounds:

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1 Animals with soft bodies andno legsAnimals with hard bodiesand legs

see 2

see 4

2 Long bodies divided into ringsor segmentsBodies not divided into ringsor segments

EARTHWORMS

see 3

3 Four tentacles with external(outside) shellFour tentacles with no externalshell

SNAILS

SLUGS

4 Body with more than fourteenpairs of legsBody with fewer than fourteenpairs of legs

see 5

see 6

5 Body flattened, with two legsper segment Body flattened, with four legsper segment

CENTIPEDEMILLIPEDE

6 Seven pairs of legs, body greyor steely blue Fewer than seven pairs of legs

WOODLOUSE

see 7

7 Four pairs of legs Three pairs of legs and a bodyin three parts

see 8INSECTS

8 Body divided into two partsBody not divided, legsextremely long and hair-like

SPIDERSHARVESTMEN

1 Does it have fins?No fins

FISHsee 2

2 Does it have feathers?No feathers

BIRDSsee 4

3 Does it have hair or fur?No hair or fur

MAMMALSsee 4

4 Dry scaly skin?Moist, smooth skin?

REPTILESAMPHIBIANS

snail

spider

slug

Insects

woodlouse

millipede

harvestmen

centipede earthworm


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24

ASSESSMENT

1

Answer these questions:i) Which of the following can make its own food?a) chicken b) shark c) cabbage

ii) Which of the following cannot make its own food?a) grass b) cow c) wheat

iii) Which of the examples below does not show the correct order for a food chain?a) grass cow human b) chicken wheat cowc) wheat chicken human

iv) Which of the following animals are herbivores?a) deer b) wolf c) rabbit d) eagle e) sheep

v) Which of the following animals are carnivores?a) sheep b) horse c) lion d) otter e) leopard

Jamal wants to find out which soil is best for planting his seeds. Histeacher said that the best soil is one that does not need watering toooften but which also has plenty of air in it for the plant roots to breathe.

Jamal took three pots and filled each one with a different soil. He pouredon some water and timed how long it took for the water to just start to runout of the hole at the bottom of the pot.a) Which soil would be best for Jamal’s seeds?

b) Why do you think this?c) Write down two things Jamal must do to make sure his experimentis fair.

d) How do plants get their nutrients (goodness) from the soil?e) How could Jamal find out how much air there is in samples of each

of the three kinds of soil?

Keys

Joanne found three small animals in her garden. She used this key to findout what they were:

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Type of soil Time for water to pass through

Sand 41 seconds

Clay 4 minutes 20 seconds

Garden soil 2 minutes

1 Does the animal have wings? Yes—see 2No—see 3

2 Is its abdomen long and thin? Yes—It is a dragonflyNo—It is a wasp

3 Does the animal have more than eight legs? Yes—It is a woodlouseNo—It is a spider


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251

Here are pictures of the three animals Joanne found. Write their namesunderneath the pictures.

Jake and Katie are investigating some animals. They sort the animals bythese characteristics:

a)Name one animal that would be in groups A, D and F.b) Name one animal that would be in groups B and E.c) Name two animals that would be in groups A and C.d) The frog is an amphibian. What is one characteristic of an amphibian?e) Which three of these groups would a human being be in?

Here is a food chain that you might find in the sea. Plankton is the tinyplants and animals that float in the sea.

Plankton Sardine Mackerel Grouper Humana) Name the producer in this food chain.b) Name the first or primary consumer in this food chain.c) Name the secondary consumer in this food chain.d) What would happen to the populations of sardines and mackerel if

humans hunted and caught large numbers of groupers? Say why.e) What would happen to the population of sardines if the numbers of

plankton increased dramatically?f) Some species of whale feed almost entirely on plankton. Whatwould happen to the number of whales if humans hunted and killedlarge numbers of groupers?

4

5

a) ……………. b …………… c) .…………

Wing

Abdomen

A =Vertebrate

B =Invertebrate

C = Layseggs

D = Givesbirth to liveyoung

E = Cold-blooded

F = Warm-blooded


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CHANGING CIRCUITS

Producing electricityElectricity is a useful form of energy. It can easily be changed to other forms of energy, such as heat or light, and it can be moved from place to place alongwires and cables. Electricity is used to power manydevices, from refrigerators and kettles to computersand televisions. It also provides light and heat in ourhomes, schools, shops and factories.

Power stationsMost of the electricity we use every day comes from a power station. Power stations work in different ways.However, in most of them the electricity is produced usingmagnets. In a power station huge generators are turned to produce electricity. Each generator consists of anenormous magnet surrounded by coils of copper wire. Whenthe magnet is turned very fast it produces electricity.

Most power stations burn a fuel such as coal, oil or gas, or use a radioactive material such as uranium, to produceheat. This heat is used to make water boil. The steam that is produced rushes through pipes to a large wheel fitted with blades, rather like a propeller. This wheel is called a turbine. As the steamrushes past the blades of the turbine, it makes the turbine spin rapidly, up to30,000 times every minute. As the turbine spins, it turns a generator whichproduces electricity.

From the turbines the steam is piped to giant cooling towers, where it turnsback into water. The hot water returns to the boiler where it is boiled again,so saving both fuel and water.

It is difficult to store electricity. Because of this, it must be made as and whenit is needed. In cold weather and at busy times of the day, most powerstations have many turbines and generators working to produce electricity.

The National GridThe cables from power stations are linked up all over the country to form onebig supply system. This is called the National Grid. A power station produces

This power station uses gas tohelp produce the steam that drivesthe machines.

How a power stationproduces electricity.

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generator

rotatingmagnet

water

turbine

Unit

2

02-547053_Changing Circuits_Layout 1 20/9/16 4:52 PM Page 26

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The National Grid brings electricity to most people’s homes.

What are cables?

Why are the pylons on whichelectricity cables are hungvery tall?

Make a list of the ways inwhich a large shop or officemay use electricity.

How many ways can you thinkof in which electricity is usedto cool objects or people?

Name three materials that areelectrical insulators.

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Make an exhibition in your classroom of thingsthat are worked by electricity. Ask your friendsto help you.

Try it out

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electricity at 25,000 volts, but it is sent across theNational Grid at between 110,000 and 500,000volts. Special devices called transformers areused to change the voltage of the electricity.

From the transformer the electricity is taken across the country on overhead cables made of aluminium, because this metal is a goodconductor of electricity. These cables are carriedon tall steel towers called pylons. The cables are hung on porcelain holders because porcelainis a good insulator and stops the electricity from escaping down the pylons to the ground.

On the outskirts of towns and cities moretransformers change the voltage of the electricity,first to 33,000 volts and then to 11,000 volts.Factories take their electricity at these voltages.Near houses, more transformers reduce the voltage to 230 volts and underground cables take the electricity to homes, shops and schools.

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A small transformer near a village.

cables

pylons

The cables on anelectricity pylon aremade of aluminium.


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CHANGING CIRCUITS

Other ways of generating electricityThere are other ways of producing electricity besides using coal, oil, gas or nuclear fuels. Supplies of coal, oil and gas could run out in less than 100 years, and these fuels pollute the air, producing acid rain and adding toglobal warming. Nuclear power stations can also cause dangerous pollution ifradioactive material accidentally leaks out, and the radioactive waste isdangerous and difficult to dispose of. There are other, cleaner ways ofproducing electricity, which will not run out. They are said to be renewable.

HydroelectricityThe power of running water can be used to spin turbines and generators tomake electricity. This kind of power station is called a hydroelectric powerstation. Sometimes pipes lead water from a fast-flowing river on a hillside ormountain into the power station. Other hydroelectric power stations are builtinside a dam. The dam holds back most of the water, so allowing a steadyflow even at dry times. The water that is allowed to pass through the dam isunder great pressure and turns the turbines and generators on its way.

In France and Canada there are power stations which use the energy of themoving water of the tides. As the tide comes in or goes out of the mouth of ariver, the moving water turns the turbines and generators that produceelectricity. In a few places there are small power stations that use the wavesof the sea to drive generators.

Wind energyPeople have been using the energy of thewind for hundreds of years to grind corn, pumpwater or drive machinery. In recent yearsspecial wind-driven machines called wind

This power station uses the energy of movingwater in the tides to turn the generators.

These turbines use the energy of the wind toproduce electricity.

Coal-fired power stations pollute the air.

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This power station burns mainly chickenmanure and straw.

What are the advantages anddisadvantages of obtainingelectricity from cells andbatteries? What are theadvantages anddisadvantages of using mainselectricity? Make a table tocompare the two sources ofelectricity.

Write down what you think arethe advantages anddisadvantages of hydroelectricpower stations, solar powerstations, wind turbines andtidal power stations as ways of producing electricity. Make a table of your results.

Why is electricity carried byunderground cables in townsand cities?

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Mains electricity can be dangerous. Designand make a poster to warn people of thedangers of working or playing near electricitypylons or sub-stations.

Make a list of all the electrical appliances inyour home or school. Draw a table with fourcolumns, headed ‘Light’, ‘Heat’, ‘Movement’and ‘Sound’. Sort out the various electricalappliances into the correct column of thetable. Some appliances, like a light bulb, willappear in more than one column.

Try it out

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turbines have been developed. As the blades of thesewind turbines turn in the wind, they drive generatorsthat produce electricity.

Energy from the sun and from rocksSome calculators have solar cells which changesunlight into electricity. Most solar power stations use similar, but much larger, solar cells to produceelectricity. In a number of countries, including Iceland,Italy, New Zealand and the United States, there arehot rocks not too far below the surface of the Earth.Sometimes water can be pumped down to these hotrocks where it is heated. Sometimes there are hotsprings which shoot steam or hot water into the air. In places, the steam or hot water from underground isused to drive the generators that produce electricity.

Electricity from waste materialsIn a few places in the world there are power stationsthat burn the rubbish from our homes, schools, shopsand factories as a fuel. In eastern England there arepower stations that burn mainly chicken manure orstraw to heat the water that drives the generators. Ofcourse, these power stations can also pollute the air.

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CHANGING CIRCUITS

Cells, batteries and electrical circuitsWe use batteries for torches, radios, cameras, mobile telephones andbattery-operated toys. Batteries are small and easy to carry around. A battery uses chemicals to produce electricity. The battery turns chemical energy into electrical energy.

Simple cells and batteriesThe proper name for a single battery like the one in thepicture is an electric cell. When the cell is joined up in a circuit and the switch is on, the chemicals in the cellproduce an electric current. As the electricity is taken from the cell, the chemicals are slowly used up. Usually,when the cell cannot make electricity any more, it must be disposed of. However, some cells and batteries, such as those in cars and many digital cameras, can be recharged so that they go on working much longer.

A cell provides an electrical force that pushes electricityaround the circuit. The strength of this electrical force ismeasured in units called volts. Most electrical cells producean electrical force of one and a half volts (1.5V). A batteryis really two or more cells joined together. If two or more cells are joined together in series, they make a battery. Two cells joined in a battery produce three volts, while a nine-volt battery, like the one in the picture, consists of six cells joined together.

CircuitsTo make electricity come out of a cell, you need to give it a path, such as awire to move along. For anything that uses electricity to work, it has to bepart of an electrical circuit. You already know that you can connect a bulband a cell so that the bulb lights. When this happens you have made anelectrical circuit. The circuit is a loop with no beginning and no end.

Electricity moves, or flows, around the whole circuit. It can only move inone direction, and it flows through the wires, the bulb and the cell. Thearrows show the way it flows. You cannot see the electricity in a circuit likethis, you can see only what it does. When electricity flows it makes the

How six 1.5 volt cells are joined to make a 9-volt battery.

Inside a single cell ofthe kind used in a torch.

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6 cells

inside a 9 V battery

metal cap (+ terminal)

plastic jacket

chemical paste

zinc case

carbon rod


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What do we call it whenelectricity flows from a cell or battery, through a bulb andback to the cell or battery?

In your own words describehow a simple switch works.

Imagine you have made asimple circuit using a battery, a switch, three wires and abulb. The bulb doesn’t light up. Describe four things thatmight be wrong.

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3How many ways can you find to light a torchbulb? You are only allowed a torch bulb andcell or battery, a pair of metal scissors, and a strip of kitchen foil or tinfoil.

Can you design a circuit with a switch that will warn you when someone steps on thedoormat? Try out your circuit to see whether it works.

Try it out

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bulb light. The cell is needed to make electricity flowaround the circuit. This takes energy, which has been stored in the cell. In the bulb this electricalenergy is changed to heat and light.

SwitchesThis bulb (top left) will not light, because there is agap in the circuit. Electricity cannot flow across the gap and the bulb does not light. There would be a complete circuit if the gap in it were closed up.

We do not use electrical devices all the time. They can be turned on and off.Switches control the flow of electricity. A switch is a way of opening and closinga gap in a circuit. Using a switch is easier and safer than touching two wirestogether or pulling them apart.

In an electric light circuit, you may connect a switch on either side of the bulb. Ifelectricity flows through the bulb it must also flow through the switch. Electricityflows through the bulb only when the switch is ‘on’ and the gap in the circuit is closed. When the switch is ‘off’, there is a gap in the circuit and the electricity cannot flow.

Safety: Batteries are safe to touch because they have a low voltage, but mains electricity is dangerous and can kill you.

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A simple circuit with a switch in the ‘on’position.

How a switch works to open and closea gap in a circuit.


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CHANGING CIRCUITS

Circuit diagramsScientists draw special kinds of diagrams to show how electrical circuits are connected up. Instead of pictures of the parts of the circuit they usesymbols. This saves time and it means that you do not have to be good at drawing to show someone how to make a circuit.

Here are some of the symbols that scientists use:

When you draw a circuit you do not need to show the connecting wiresaccurately. The length, thickness or shape of the wires does not matter.What is important is how they are connected up, and straight lines lookneater than wiggly ones!

Here is a drawing of a simple circuit with a bulb, cell and switch.

TerminalsA cell or battery has two ends, called terminals. Electricity can only movein one direction and it flows from the negative (–) terminal to the positive(+) terminal of the cell or battery. The electricity can only flow from thenegative terminal to the positive terminal if these are joined by an electricalconductor, such as a wire or some other piece of metal. On a circuitdiagram the long vertical line on the symbol is the positive (+) terminal andthe shorter vertical line is the negative (–) terminal. When two or more cellsare connected together you can link the individual cell symbols together, asshown in the chart above.

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switch ‘off’, switch ‘on’,

wirecell

2 cells

bulb motor bell buzzerswitch off

switch on

cell cell

bulbbulb


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In your own words, describewhat is meant by ‘terminals’,where they are found and howelectricity passes through them.

Draw a circuit diagram,showing a circuit with one cell,wires, an open switch and abuzzer.

Draw a circuit diagramshowing a circuit with twocells, wires, an open switchand an electric motor.

Draw a diagram of a circuitwith a cell wired in with twobulbs. There is a switchbetween the cell and one of the bulbs.

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4

Examine a torch carefully. Draw a circuitdiagram to show how the torch works.

Design a set of model traffic lights. Rememberthe lights work in order, starting with red at thetop, then red and amber, then green. Whenthe lights are going back from green to red,they go to amber and then red. Make a list ofthe materials you need. If you are able toobtain the materials, make your model. Doesit work?

Use the Internet and reference books to find out all you can about Michael Faraday,who is associated with the discovery ofelectricity. Write a newspaper article aboutMichael Faraday.

Try it out

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Circuit diagram rulesWhen you draw circuit diagrams remember thesesimple rules:

l Electricity has to travel from the negativeterminal of the cell or battery and back to the positive terminal for the circuit to work.

l No electricity will flow if there is a gap in the circuit.

l There has to be a component, such as a bulb,buzzer or motor in the circuit.

l With some components, it matters which way round the component is connected in the circuit.

331

The two terminals of a cell.

positiveterminal

negativeterminal

+

–


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CHANGING CIRCUITS

Brighter and dimmerIt is possible to light several bulbs with one cell and there are two ways ofdoing this. The picture on the right shows one arrangement of the circuit.This is called a series circuit. The bulbs are placed one after the other, likethe beads in a necklace. In this circuit, electricity flows through each of thebulbs before returning to the positive terminal of the cell.

The more bulbs you add to a seriescircuit like this, the dimmer each bulb will be. You might expect the bulbnearest the cell or battery to be brighterthan the others. It is not, and this isbecause the bulbs are sharing theelectricity that comes from the cell orbattery. Many series circuits are used in televisions and computers, but seriescircuits have one big disadvantage. If there is a break anywhere in the circuit, as for example, when one of the bulbs blows, then the whole circuit is broken.

Parallel circuitsThere is another way of lighting severalbulbs with one cell or battery so that ifone bulb fails, the others stay alight. Thiskind of circuit is called a parallel circuitbecause each simple circuit is parallel to another. The bulbs are brighter thanthey would be if they were connected in series because the electric currentdivides equally between each of the circuits. If you unscrew one bulb in a parallel circuit the others will stay alight. This is because each has itsown separate circuit to the cell or battery. The electric lights in your home or school are connected in a parallel circuit like this.

Extra cellsSometimes three or more cells are used in a circuit. Like bulbs, cells can beconnected in different ways. Usually they are connected in series. Either a

If you unscrew one of the bulbs in a series circuit like this, the others will go out.

If you unscrew one of these bulbs the otherswill stay alight.

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How the cells in a torch are connectedin series.

In your own words, describetwo ways in which you wouldmake an electric motor in acircuit run slower.

Look carefully at an electricalplug. Why are the pins of theplug made of metal while theouter case is made of plastic?

In your own words, explainwhat the word resistancemeans.

1

2

3Test the brightness of torch bulbs of differentvoltages with the same cell or battery.

Compare how long different makes of thesame size torch cell or battery will last. Howwill you make your test fair?

Try it out

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wire connects the bottom of one cell to the top ofthe next or, as in the torch in the picture, the cellsactually touch each other.

Two cells connected in series will light a bulbmore brightly than just one cell. Adding more cellsin series makes the bulb light even brighter. Doingthis may make the bulb burn out more quickly.The tiny wire inside the bulb will glow so brightlythat it melts and breaks the circuit. Bulbs aremade for a certain number of cells. If they areconnected to more cells than they are made for,they quickly burn out.

Longer wiresYou can also change the amount of electricityflowing through a circuit by adding longer wires to it. With ordinary wire in fairly short lengths, theeffect is hardly noticeable. But if you use a specialtype of wire called resistance wire, the bulbbecomes dimmer the longer the pieces of wire you put in the circuit. Long thin wires allow lesselectricity to flow through them than short thickwires made of the same material. How muchelectricity flows also depends on what the wiresare made of. More electric current will flowthrough a copper wire than through an iron wire ofthe same size. The amount by which a wire or anyother object cuts down the electricity flowingthrough it is called its resistance.

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CHANGING CIRCUITS

Using electricityEvery day in our homes and schools we turn electricity into other kinds of energy. We turn electrical energy into light and heat in light bulbs andelectric heaters. We turn electricity into sound energy in telephones,doorbells, burglar alarms and radios. Electric motors turn electrical energyinto movement energy. Electricity is very easy to control, and very quick—it is there at the flick of a switch.

Light bulbsWhenever electricity flows it heats up the material it flowsthrough. If you look at any electric light bulb you will seethat the filament that glows is a very thin coiled wire. Thiswire has a high resistance to electricity. When electricity flows through the filament, it becomes so hot that it glowsand gives out light. The bulb is filled with a special gas,called argon, that stops the filament from burning away too quickly.

Electric heatersThe part of an electric heater which turns electrical energy into heat energy is a long piece of thin wire made of a metalcalled nichrome. This wire has a high resistance to electricityand it is wound round a rod made of an insulator such asfireclay. When electricity flows through the nichrome wire,the wire gets very hot. A shiny metal reflector radiates theheat into the room. The wire used in the cable leading to the electric heater is made of thick copper; because it has a low resistance to electricity it does not get hot.

Electric ovens, fan heaters, hair dryers, irons and electric kettles all haveheating elements which work in a similar way to those in an electric heater.

Electric motorsThere are electric motors in some toys and in most clocks and watches.Many household machines, including washing machines, dishwashers,vacuum cleaners, food mixers and refrigerators have electric motors. Largeelectric motors work electric trains, trams and lifts.

A light bulb and a torch bulb.

All of these devices rely onthe fact that a wire can gethot when electricity passesthrough it.

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case actsas negativeterminal.

filament

gas-filledglass bulb

glassbulb

positiveterminal


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In your own words, say what afuse is and what it does. Whyis it important to have a fuse ina circuit?

How many ways can you thinkof in which electricity helps usto travel from place to place?

Describe in your own wordswhy a wire with a torn cover is dangerous?

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Look around the kitchen and other parts of yourhome. Make a list of all the appliances that havean electric motor in them.

Draw a picture of a light bulb, or copy the pictureof a light bulb on the page opposite. Label yourpicture. Against each part say whether it is anelectrical conductor or an insulator.

Try it out

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An electric motor uses both electricity and magnetism.It contains a coil of wire and a bent permanent magneton a spindle. When electricity flows through the coil,the coil becomes an electromagnet with north andsouth poles. The north pole of the coil starts off nearthe north pole of the permanent magnet. The polesrepel (push) each other, which makes the permanentmagnet and the spindle start to rotate. To keep up therotation, a device called a commutator reverses theelectric current every half-turn. This ensures that unlikepoles of the coil and the permanent magnet are alwaysnext to each other, ready to repel each other.

FusesSometimes the heat given out by an electric current is dangerous. If there is a fault in an electrical machineor its wiring, more electricity might flow than is safe.This can start a fire. Delicate electrical machines, suchas computers, can also be damaged. To stop thesethings happening, there are fuses near the meterwhere electric cables come into a building. There arealso fuses in electrical plugs.

A fuse is a thin wire in an electrical circuit. If the rightamount of electricity is flowing round the circuit, itpasses through the fuse without difficulty. But becausethe fuse has a low melting point, if too much electricityflows, the fuse heats up quickly and melts. It makes agap in the circuit, which stops the electricity flowing.

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These are just a few of the machinesthat use an electric motor.

The fuse inside an electric plug.


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CHANGING CIRCUITS

Electricity and the environmentAlthough some ways of producing electricity have less impact than others, theyall affect the environment in some way or the other. In fact, the production ofelectricity is one of the biggest causes of damage to the environment.

Power stationsMost of our electricity comes from power stations that burn coal, oil or gas.Obtaining these fuels causes damage to the environment and when theyare burned, these fuels produce several gases, one of which is carbondioxide. This gas collects in the air and acts like a blanket around theEarth, keeping it warmer. If this global warming continues, more places willbecome deserts and the Polar ice caps and glaciers will start to melt. Thenthe sea will flood over low land near the coast and there could be moreand more examples of extreme weather.

Carbon dioxide and other gases from power stations are also making the clouds slightly acid. Clouds travel hundreds or even thousands ofkilometres before they drop their load of acid rain, hail or snow. This thendamages lakes, rivers, trees, crops and buildings, as well as human health.

Nuclear power stationsHuge quantities of rock have to be mined to obtain the uranium to make thefuel for nuclear power stations. While nuclear power stations do not pollutethe air, there is always the risk of an accident releasing radioactivity intothe environment. Nuclear power stations use huge quantities of water forcooling, and the waste material remains dangerous for thousands of years.

Power stations, like this coal-burning one,pollute the air and add to global warming.

Nuclear power stations do not pollute the airbut there is always the risk that an accidentwill release dangerous radioactivity.

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Unlike vehicles powered bypetrol or diesel oil, electric carsand other vehicles do notpollute the air. Why are therenot more electric vehicles on our roads? What are theadvantages and disadvantagesof electric vehicles?

In your own words, say whyrecycling or reusing objectsand materials is good for theenvironment.

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Even the methods of producing electricity using renewable sources such as the wind, water, solar energy and fuels can have their disadvantages,as the chart below shows.

The main renewable energy supplies

Even though we need electricity for so many things, we still waste a lot of it. By saving electricity and other forms of energy we are not only savingmoney, we are also helping to save the environment from further damage.Here are some things you can do:

l Turn off the TV and lights when you leave a room.l Do not leave TVs and computers on ‘standby’. This wastes a lot of electricity.

l Close the curtains and blinds at night when it is cold to keep the heat in.

l Save energy by wearing an extra jumper and turning down any form of heating that uses electricity.

l Open the door to a fridge or freezer as little as possible. When warm air gets in, extra electricity is needed to cool it down again.

l Only boil the amount of water you actually need to make a cup of hot drink.

l Long-life electric light bulbs last up to eight times longer and use less electricity.

l Reuse or recycle as many objects and materialsas you can.

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Energy source Where available Advantages Disadvantages

Wind High or windy places Safe, no polluting gases;produce electricity cheaply

Only work when wind blowing;noisy; can spoil scenery andkill migrating birds

Sun Sunny areas Safe and no polluting gases Only work when sun shining;expensive to build

Hydro-electric Fast-flowing rivers Safe and no polluting gases;can produce cheapelectricity all the time

Expensive to build; take up alot of land; affect fish andother water life

Geothermal Only where hot rockscome near to theEarth’s surface

Safe and no polluting gases;can produce cheap heat andelectricity all the time

Require a lot of land, often inbeautiful places


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CHANGING CIRCUITS

Using electricity safelyElectricity is a great help to us in giving us light and heat, keeping our foodcool and fresh, and providing various ways of learning and entertainingourselves. But electricity can also be dangerous. If you touch a bare wireconnected to the mains, it can give you an electric shock, burn you or evenkill you. Always follow these safety rules:

Never leave a television set plugged in overnight.

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Never plug an electric heater into a light socket.

Never touch electrical switches, plugsor sockets with wet hands.

Never fly a kite or use a fishing rod near tooverhead power cables. Even if your rod orline does not touch the wires, electricity mayjump the gap.


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Ask an adult to show you where the electricitymeter and fuses for your home or school are.

Carry out a survey of electrical safety in yourclassroom. Are any sockets too near a tap orsink? Do any of the electrical cables havefrayed covers? Are any electrical deviceswithin easy reach of very young children?Discuss with your friends what should bedone about your findings.

Use a word processor or desktop publishingpackage to print electrical safety instructionsfor display around your classroom and school.

Try it out

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Why is it dangerous to touch anything which works by electricity if your hands are wet?

What would you do if youfound an electricity cable that had been blown down in a storm?

In your own words, explainwhy it would be dangerous tobalance a television set on theside of the bath while youwere watching it.

Why do you think that theswitches in most bathroomswork by pulling a cord?

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Never overload a socket.

Never put electricalwires under a rug orcarpet where theycould be rubbed orstretched.

Make sure thesocket is switchedoff before youplug anything in it.

Never use an electrical device thathas a worn cable or where you cansee any part of a bare wire.

Never connect wires toa socket without a plug.


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ASSESSMENT

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Copy out the following sentences and complete them using these words:hydroelectric, nuclear, wires, pylons, power station, energy, fuse,insulators, generator, cables, filament, conductors, chemical.a) Electricity is one kind of ________.b) The electricity we use in our homes, shops, schools and factories is

produced in a __________.c) The energy of fast-flowing rivers is sometimes used to produceelectricity in a __________ power station.

d) The machine which turns in a power station to produce electricity iscalled a _________.

e) A ________ power station uses the energy from a small piece ofmetal called uranium.

f) Electricity is moved from place to place along ____________.g) ________ are the tall towers which support wires.h) Materials which allow electricity to pass through them are called

________ of electricity.i) A ________ contains a thin piece of wire which melts easily.j) The thin piece of wire inside an electric light bulb is called the_________.

k) A torch battery produces electricity from ________ energy.l) Wires which have protective covers on them are called _________.m) Materials which do not allow electricity to pass through them are

called ____________.

The picture shows a cutaway diagram of a torch.a) The diagram is labelled using letters of the alphabet. Say what each

of these letters stands for, using the words from the list below.batteries, switch, reflector, spring, bulb, glass

b) Why is the reflector made of shiny metal?c) Can you explain why the bulb usually lights when the switch ispushed forward?

d) When the torch shown above was switched ‘on’, the bulb did notlight. Can you suggest THREE reasons for this?


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3 Here is an electric circuit with a gap in it.Which of the following objects would make the bulb light up if they wereplaced across the gap in the circuit?

i) iron nailii) bar of soap iii) steel paperclipiv) piece of paper v) plastic potvi) gold ringvii) copper coin viii) piece of wood ix) rubber x) stone

We use symbols to represent the parts in a circuit diagram.Copy and complete the following sentences by writing the word ordrawing the symbol.a) is the symbol for a ……………….

b) is the symbol for a ……………

c) is the symbol for a ………………d) This is the symbol for a switch ............... .e) This is the symbol for an electric motor ............... .

The picture below shows six circuits. Look at each of the circuits carefully.

a) Which of the bulbs will light up? Explain your answers.b) Explain why the filament in a bulb lights up.c) What will happen if more batteries than the bulb was intended forare placed in a circuit?


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01-547053 Interdependence Layout 1 20/9/16 4:13 PM Page 2 … Science Book-5.pdf · 2020-04-30 · Prepare lists of what animals eat: ‘these animals eat insects’, ‘these animals