tnpsc - science text book 6th standard

1

M1\F:\Modern\Book\NewPC-T1.pmd

We live in the world, called theplanet Earth. We can see the trees,rivers, mountains, animals, deserts andoceans on the Earth.

We see the Sun in the day timebut not during the night. We see thenew moon and full moon. We can seethe stars. If you see the surface of theEarth, where you are living, it will bea flat. Actually, Earth is not flat. It isin spherical shape like a ball.Astronauts travelling in spaceshipshad seen the Earth from largedistances. They took photographs ofthe Earth from space (Fig. 1.1).Photographs taken by the astronautsfrom spaceships clearly show that theEarth is spherical in shape.

1. Our Earth

Fig. 1.2a Solar system

Fig. 1.2b The Sunand the planetsFig. 1.1 The Earth from space

Are you at rest? Is the Earth atrest? No, it is moving continuouslyin space around the Sun. But we donot feel this motion. This is, becauseeverything around us is moving alongwith the Earth.

2


1.1 Solar system

The Sun and all the bodiesrevolving around the Sun is calledSolar system. Our solar system ismade up of nine planets, moons,asteroids and comets (Figs. 1.2a and1.2b). All are revolving around the Sun.The planets are Mercury, Venus, Earth,Mars (Fig. 1.3), Jupitor, Saturn,Uranus, Neptune and Pluto. Sun aloneemits light. All other bodies includingmoon reflect that light.

Sun. The biggest planets are Jupitor(Fig. 1.5) and Saturn (Fig. 1.6). Thefarthest planet is Pluto.

The broken piece of a planetrevolving around the sun is calledasteroid. A comet is made up of solidmatter combined with gases (Fig. 1.7).It has a tail. It is also revolving aroundthe Sun.

The head of the solar system isthe Sun, which is a star. Like the starSun, billions (100 crore) of stars are

A smaller body revolves arounda planet is called moon. Moons areavailable for all planets except forMercury and Venus. Our Earth hasone moon.

Fig. 1.5 Jupitor

Fig. 1.3 Mars

Mercury (Fig. 1.4) is the smallestplanet and the nearest planet to the

Fig. 1.6 Saturn

Fig. 1.4 Mercury

3


available. Billions of stars form agalaxy. Our galaxy is called milkyway. Billions of galaxies form thisuniverse.

When you look up at the stars,does it sometimes seem to you thatyou can trace out squars, letters andother familiar figures? The group ofstars forming a particular shape iscalled constellation (Fig. 1.8). Orion,Taurus and Ursa Major are some ofthe constellations.

1.2 Day and Night

The light from the Sun lights uponly one side of the Earth and all theplaces on that side are having day-time. The sunlight will not reach theother side of the Earth, there it isnight-time. Night turns into day andday into night because the Earth isrotating about an axis passing throughthe north and south geographicalpoles. It takes 24 hours to completeone rotation. On the night side of theEarth, the light comes only from theluminous stars and the moon(Fig. 1.9).

Fig. 1.7 Comet

Fig. 1.8 Constellations

1.3 The Earth and the seasons

We know that the Earth rotatesabout its own axis and also revolvesaround the Sun. If the axis of rotationof the Earth were at right angles tothe direction of the Sun’s light, thelength of the day would always equalto the length of the night. The Sunwould rise due East and set due West(Fig. 1.10).

Fig. 1.9 Formation of day and night

4


Fig. 1.11 shows the path of theSun as it would appear from a pointon the Earth. In fact, this happens onlyon two days in each year March 21st

and September 21st. In the summer,the days are longer than the nights.The Sun rises North of due East andsets North of due West. And in thewinter, the nights are longer than thedays the Sun rises at South of dueEast and sets at South of due west.This is because, the axis of rotationis not at 90o to the direction of theSun’s light.

As the Earth revolves around theSun, its axis of rotation is as shownin the Fig. 1.12

Fig. 1.13 shows what happenswhen the Earth is at A in Fig. 1.12For a person in the northernhemisphere, the days are longer thanthe nights. It is summer.

Fig. 1.13 Summer

Fig. 1.14 shows what happenswhen the Earth is at C in Fig. 1.12For a person in the northernhemisphere the nights are longer thandays. It is winter.

Fig. 1.14 Winter

In positions B and D in Fig. 1.12the Sun’s light is at right angles tothe axis of rotation.

1.4 Full moon and New moon

Moon is the natural satellite ofthe Earth. Moon is not a luminousbody; it gives out no light of its own.We can see it, because it reflects lightfrom the sun. It rotates about its ownaxis and also revolves around theEarth. For both motions, the time issame, 29.5 days. We can see only oneside of the moon. The other sidecannot be seen (Fig. 1.15).

Fig. 1.10 Rotation of the Earth

Fig. 1.11 Path of the Sun

Fig. 1.12Revolutionof Earth

5


As the moon revolves around theEarth and if both the Sun and themoon are in same part of the sky, wecannot see the moon. It is because,that the reflected light from the moondoes not come to us. Now, that moonis called New moon (Fig. 1.16a).

During the motion of the moon,if both the Sun and the moon are in theopposite part of the sky, we can seethe moon. It is because, the reflectedlight from the moon comes to us. Nowthat moon is called Full moon(Fig. 1.16b).

1.5 The structure of the Earth

So far as we know, the Earth isthe only planet in which life exists.No proof for life has been found inany other planet. Our Earth is amedium - sized planet. The presenceof atmosphere, water, rich variety ofanimals and plants makes our Earthunique from other planets. Seen fromspace, Earth can look mostly coveredby ocean and clouds. Land coversonly one quarter of the surface.

If the Earth is compared with thefootball, the highest land likeHimalayas could be represented as thecoat of paint on the ball. Imagine howbig our Earth is? Table 1.1 gives fewmore details of our Earth.

Mountains, deserts, oceans,rivers and land are available on thesurface of the Earth. What about itsinside? Is it solid like a cricket ballor hollow like a foot ball?

The interior of the Earth can bebroadly divided into three differentlayers. These layers are known ascrust, mantle and core (Fig. 1.17).

Fig. 1.15 Motion of the moon

Fig. 1.16a Full moon and New moon

Fig. 1.16b Full moon and New moon

6


6 kilometres thick under the oceans.The crust contains materials likewater, rocks and soil. Limestone,common salt, coal, petroleum, metalslike iron, copper, aluminium and goldare the different types of mineralsfound in the Earth’s crust.

The mantle

The layer in between the crustand outer core is called the mantle.Its thickness is nearly 2900Kilometres. The mantle is made upof hot rocks. The temperature andpressure is more than in the crust. Themantle layer is in semi-molten state.

Table 1.1 Details about Earth

Age : about 4,55,00,00,000 years

(4,550 million years)

Mass : about 6,000 million million tonnes.

Diameter : From pole to pole through the centre12,714 Km; Across the equator throughthe centre 12,756 Km.

Distance from the Sun : 14,96,00,000 Kilometres (1,496 lakh Km)

Circumference : round the poles 40,000 Km; round theEquator 40,076 Km

Area of water : 71 percent of the surface (about 362million square Km)

Area of land : 29 percent of the surface (about 148million square Km)

Average depth of ocean : 3,795 metres below sea level.

The crust

The crust is the Earth’s solidouter layer. It is upto 30 Kilometresthick under the mountains, but only

Fig. 1.17 Inside the Earth

7


The core

The core is divided into two partsas (i) outer core and (ii) inner core.

(i) Outer core

It lies in between the mantle andthe inner core. It is 2240 kilometresthick. This outer core is made mainlyof metals. It is under enormouspressure and so hot. The metals arein molten state. Four-fifth of the outercore may be iron and nickel. The restone-fifth is probably silicon.

(ii) Inner core

The inner core is a solid ball. Itis about 2440 kilometres thick. Likethe outer core, it is also made up ofiron and nickel. The temperature isabout 3700oC.

1.6 Atmosphere

The air that surrounds the Earthis called atmosphere. It extends upfor hundreds of kilometres. Theatmosphere consists of gases like

Plants need carbon dioxide forpreparing their food. About 78 percentof air is nitrogen about 21 percent isoxygen and the remaining one percentconsists other gases (Fig. 1.18).

99% of the air is found upto aheight of about 30 kilometres. Thislayer of atmosphere is known astroposphere. This is the layer nearestto the earth.

At 30 to 50 kilometres aboveEarth’s suface, a layer of hot air at atemperature of 42oC is available. Thehotness is due to the absorption ofheat from the Sun by the ozone layer.

Ozone is the special form ofoxygen. This ozone layer protects usfrom the most harmful Ultraviolet raysof the Sun. Without ozone, we couldnot stand the Sun’s light. Hence, wehave to preserve the ozone layer.

As we go higher and higher, theair becomes thinner. This is whymountaineers carry oxygen cylinderswith them.

The oxygen in the atmospherehelps in burning. The nitrogen in theair keeps the burning under control.The atmosphere allows only a part oflight and heat from the Sun to reachthe surface of the Earth. The suitabletemperature of the Earth is only dueto the presence of atmosphere. Thishelps in the existence of life on Earth.Water vapour in the air makessurrounding as cool.

nitrogen, oxygen, argon, neon, helium,krypton, xenon, water vapour, carbondioxide and sulphur dioxide. Humanbeings and animals need oxygen.

Fig. 1.18 Gases present in air

8


Activity 1.1

Fix a small size candle at thecentre of a trough. Fill it with water.Candle should not be submerged inwater. Now, light the candle. Then,place a glass tumbler upside downsuch that it must cover the lightedcandle. What happens?

The candle needs oxygen toburn. The air available in the tumblerhas oxygen. With this oxygen thecandle burns. After sometime, thecandle blows out. This is because, theentire oxygen has been used up. Nomore oxygen is available. You can see

Ocean currents are like rivers ofwater flowing through the ocean.They are warmer or colder than waterthrough which they pass.

Various kinds of plants andanimals (fish, shark, whale) are livingin the ocean. There is a soft; Oozymud covering the floor of the oceandown to a depth of 3657 metres.

Many useful materials are in theocean. Most important among themare the common salt and iodine.

Tides occur in the ocean. Whatare tides? Tides are the regularmovement of the water caused by thegravitational pull of the moon.

1.8 Water

Water is the most commonsubstance found on Earth. Water isessential for all living things.

In some parts of the world thereis only just enough water for peopleto survive. Each year the farmers waitanxiously for the rain to supply waterfor their crops. In a bad year, there isnot enough rain and plants, animalsand humans die.

All living things contain water.Water melan plant has 97 percentwater. About half the mass of a treeis water. About two-third of your massis water.

the rising of water in the tumbler tofill the place of oxygen (Fig. 1.19).This shows the presence of oxygenin air.

1.7 Oceans

More than two-thirds of theEarth’s surface is covered with water.Most of the water is available in theoceans and seas. Near the north andsouth poles, the oceans are in the formof ice.

Fig. 1.19 Presence of oxygen

9


conversion of water into vapour iscalled evaporation.

Heated by the Sun, water on thesurface of lakes, rivers and oceansevaporates and become water vapourin the atmosphere. It joins with thewater vapour released from the leavesof plants and forms clouds. When theclouds are lifted by upward motionof air, they cool. This can make thewater vapour to condense into tinywater droplets. Often they freeze intotiny ice crystals and start to fall. Theyare too heavy for the air to keep themup. They reach ground as snow ormelted as rain after melting.

Some of the water runs along thesurface in rivers. The rest sinks intothe ground. But again it will be back

Fig. 1.20 Water Cycle

Many minerals found in the soilget dissolved in water. These mineralsare useful for plants in preparing theirfood. Water transports substancesthrough a plant, carrying mineralsfrom the soil to the stem and leaves.Oxygen dissolved in water is used formarine life.

Blood in your body, which ismainly water, carries minerals to allthe cells. The blood in your lungsdissolves the gases into the air andcarries them round your body. Wasteproducts are removed away throughwater.

Everyday you lose some waterin urine and whenever you breath out.the water you lose must be replacedby eating and drinking.

The water cycle

Atmosphere plays an importantrole in the water cycle. During thesummer, the water is not found in thelake. Where did the water go? A partinto the ground. Rest? Water changesinto water vapour. The process of

10


to the sea. This process of circulationof water to water vapour then cloudsand again rain is called water cycle(Fig. 1.20).

The water you drink today mayhave been drunk by someonethousands of years ago!

1.9 Soil

Did you know that nearly all thesoil that exists in the world was oncerock? Nature has been crumbling therock into tiny fragments called soil.This is done in many ways. Thefrequent change in heat and cold,cracks off surfaces of rock. Blow ofwind converts rocks into sand.Glaciers scrape rock surfaces. Wavesbeating against a shore converts rocksinto smaller and smaller pieces.

The soil in which plants grow isa complex substance which containsmineral salts, decayed organicmaterials and decayed livingorganisms. The value of the soildepends on its power to supply plantfood, air and water to the root ofplants.

Water rises in soil just as waterrises in a sponge. The rising of thiswater keeps the plants growing.

Soil is the shelter to a number ofinsects, reptiles and other animals.

1.10 Conditions essential for life

We do know that for life to exist,certain conditions must be present.

There must be a righttemperature. All living things mustremain with certain limits oftemperature.

Another condition is water. Allliving things require water. Light isessential for green plants. Animalsneed a source of food. They cannotexist in places where the food is notavailable. Plants use carbon-di-oxidepresent in the air and sunlight inpreparing their food.

We cannot live withoutbreathing. Human beings and animalsneed oxygen. We get oxygen from theair. Animals living in water like thefish get the oxygen from water

Fig. 1.21 Animals in water

(Fig. 1.21). The oxygen is dissolvedin water.

Hence, for plants carbon di oxideand for animals oxygen are essential

11


requirements. So atmosphere musthave oxygen and carbon-di-oxide.

Water, atmosphere with oxygenand carbon dioxide, suitabletemperature and food are available

only in our Earth. Hence, life existsonly on the Earth. In the other planetsthe above said things are notavailable. So life is not possible inother planets.

SELF EVALUATION

(For the examination, teachers are instructed to frame their own questionsfrom the text matter and activities)

1. In the solar system ___________ emits light its own.

2. The process of conversion of water into vapour is called ___________.

3. Choose the correct answer.

(i) The nearest planet to the Sun is

(a) Pluto (b) Earth (c) Mercury (d) Venus

(ii) The time taken by the moon to complete one revolution around theEarth is

(a) 365¼ days (b) 29.5 days (c) 24 hours (d) 24 days

4. Name the farthest planet to the Sun.

5. How many planets are in the solar system?

6. Write the name of the planets.

7. Day and night changes alternately in the Earth. Give the reason.

8. What is the time taken by the Earth to complete one rotation?

9. If the day is longer than night, then is it summer or winter?

10. If the night is longer than day, then is it summer or winter?

11. Is our Earth like a solid cricket ball or hollow foot ball?

12. What are three layers of Earth?

13. What is called atmosphere?

14. Give the composition of air.

15. What is the use of Ozone layer?

16. Which gas is essential for burning?

17. Name the useful important materials available in the ocean.

12


18. What are tides?

19. What is called water cycle?

20. How is soil formed?

21. State the requirements that are essential for the existence of life on Earth.

22. In which layer of the Earth do you expect to find petroleum?

23. If you breathe out over a glass plate, why the glass plate appears mistyfor some time?

24. What happens to water when wet clothes dry?

25. List out the uses of soil.

26. From where do the fish get oxygen?

Make a visit to the nearby planetorium andobservatory station. List out the events observed.

13


Measurement is necessary ineveryday life. If we go to the textileshop to purchase the cloth forstitching shirt, we do not ask the sellerto give one cloth. If we go to thevegetable shop, we do not ask to givea little amount of potato. If we go tothe provision store, we do not ask togive a little amount of sugar. What isthe journey time of the bus from yourvillage to town?

In the textile shop, we ask for1 metre cloth and the seller measuresit using a scale. In the vegetable shop,we ask for 1/2 kilogram or 1 kilogrampotato and the seller measures it usinga balance. In the provision store, weask for 1 kilogram or 2 kilogramssugar and the seller measures it usinga balance. The journey time of thebus is 30 minutes.

In the above cases, we measurethe quantities like length, mass andtime using a metre scale, a balanceand the time watch. Hence measuringquantities with units like metre,kilogram and hour or minute plays animportant role in our daily life.

What is the size of your sciencebook? At what distance your school

is located from your house? Howmuch milk do you want? What is thearea of your class room? What is yourmass? What is the time taken by youto complete 100 metre running race?

Measurements are necessary toanswer such questions. Withoutmeasurement we cannot make acorrect judgement. A guess or a roughestimate may give a wrong answer.

Science is concerned withfinding out about the world, Whythings happen? How things work?Early scientists, the ancient Greeksrelied almost entirely on their senses.They were good at observing and atsuggesting explanations of what theysaw, but without doing experiments.For example, Aristotle believed thatheavy objects fall faster than lighterobjects. But we know it is wrong.

Measurements have helpedscientists and engineers to understandmotion, how aeroplanes fly, howsatellites behave, how machines work.Measurements make it easier todescribe observations. Carefulmeasurement is an important work ofany scientist.

2. Measurement

14


What is measurement?

See the blackboard in your classroom. What is its length? Let youranswer be 2 metres. Here 2 is thenumber and metre is the unit of length.2 is the unknown quantity and metreis the known fixed quantity. That isthe length of the blackboard is twotimes the length of the fixed quantitymetre called unit.

What is your mass? Let youranswer be 30 kilograms. Here 30 isthe number and kilogram is the unitof mass. 30 is the unknown quantity

and kilogram is the known fixedquantity. That is, your mass is 30times the mass of the fixed quantity,kilogram, called unit. Thus, everymeasurement consists of a number anda unit.

The comparison of an unknownquantity with some known fixedquantity of the same kind is calledmeasurement. The known fixedquantity is called unit.

2.1 Need of standard units

To measure anything, we need aunit of the quantity. Different units

Fig. 2.1 Parts of human body as measuring devices

15


can be used for this purpose. Longago, the lengths are measured withthe units derived from some parts ofthe human body. For example, widthof four fingers, handspan, a cubit, apace or a footstep and yard (Fig. 2.1).But these units were not reliablebecause the lengths of body parts aredifferent for different people.

For example, your teachermeasures the length of the classroomin cubits. Let the answer be 15 cubits.If you measure the same length, theanswer may be 20 cubits. For the samelength of class room, two differentanswers are given, if we use the unitcubit. Hence, cubit cannot be astandard one.

Each measurement must meanthe samething to every one. Therefore,everyone must use the common unitsof measurement called standard unitslike metre, kilogram and second.

2.2 S I Units

People in the world useddifferent unit system like FPS system,(Foot, Pound, Second), CGS system(Centimetre, Gram, Second) and MKSsystem (Metre, Kilogram, Second). forthe sake of uniformity, scientists allover the world have accepted a systemof units called SI system. SI is theabbreviation of “The systemInternational D’ units”. In the SIsystem

(i) the unit of length is metre

(ii) the unit of mass is kilogram

(iii) the unit of time is second

2.3 Conventions to be followed inwriting the units in SI system

(a) The symbols for units should bewritten with a small letter

Symbol for metre is m

symbol for kilogram is kg

symbol for second is s

(b) While writing the unit which isnamed after a scientist it shouldalways be written with a smallletter.

The unit of force is newton

The unit of work is joule.

(c) While writing the symbol for unitwhich is named after a scientist,it should always be a capitalletter

The unit of force is N

The unit of work is J

(d) The symbols for units should notbe written in plural, but whenwritten in words, plurals areused.

Symbol for 30 kilograms is30 Kg (It should not be writtenas 30 Kgs)

Symbol for 2 metres is 2 m (Itshould not be written as 2 ms)

Symbol for 10 newtons force is10 N (It should not be as 10 Ns)

16


(e) There should be no fullstop atthe end of a symbol for units.

Symbol for metre is m (Itshould not be as m.)

Symbol for second is s (Itshould not be as s.)

2.4 Multiples and submultiples ofunits

What is the distance betweenyour school and your home? Let theanswer be 2 Km. Eventhough thedistance, that is length is measuredby the unit metre, we do not use 2000metres. It is convenient for us toexpress the distance in kilometre (1kilometer = 1000 metres). What is thelength of your pencil? Let the answerbe 15 cm. Eventhough the length ismeasured in metre, it is convenientfor us to express in centimetre (1metre = 100 cm). What is thethickness of the coin? Let the answerbe 2 mm. Eventhough the length ismeasured in metre, it is convenientfor us to express in millimetre

(1 metre = 1000 mm). Hence greaterdistances are expressed in kilometresand smaller distances are expressedin centimetres and in millimetres. Thatis, in multiples and submultiples ofmetre.

The farmers use to sell the paddyin terms of quintol (1 quintol = 100kg). The sugarcane carried by a lorryis measured in terms of metric ton(1 ton = 10 quintols). If you go to thejewellary shop, you can see that thejewels are measured in terms of gramsand milligrams (1000 grams = 1 kg ;1000 milligram = 1 gram).

Hence the mass is also expressedconveniently in terms of ton, andquintol, gram and milligram, whichare respectively the multiples andsubmultiples of kilogram.

Table 2.1 shows the multiples oflength and mass. Table 2.2 shows thesubmultiples of length and mass.Table 2.3 gives the prefixes used inSI units. Table 2.4 gives the multiplesof time.

Table 2.1 Multiples of length and mass

Length

1 centimetre (cm) = 10 millimetre (101 mm)

1 decimetre (dm) = 10 centimetre = 100 mm ( 102 mm)

1 metre (m) = 100 centimetre (102 cm)

1 metre (m) = 1000 millimetre (103 mm)

1 kilometre (km) = 1000 metre (103 m)

17


Mass

1 gram (g) = 1000 milligram (103mg)

1 kilogram (kg) = 1000 gram (103 g)

1 kilogram (kg) = 1000000 milligram (106mg)

1 quintol = 100 kilogram (102 kg)

1 metric ton = 1000 kilogram (103 kg)

Table 2.2. Submultiples of length and mass

1 mm = 110 cm = 1

110

= 10-1cm

1 cm = 1100 m = 2

110

= 10-2 m

1 m = 11000 km = 3

110

= 10-3 km

1 mg = 11000 g = 3

110

= 10-3 g

1 g = 11000 kg = 3

110

= 10-3 kg

Table 2.3 Prefixes used in SI units

Name Abbreviation Submultiples

deci d 110 = 10-1

centi c 1100 = 10-2

milli m 11000 = 10-3

micro μ 11000000 = 10-6

(pronounced as mu)

kilo K 1000 = 103

mega M 1000000 = 106

18


Table 2.4 Multiples of time

1 minute = 60 seconds

1 hour = 60 minutes

1 day = 24 hours

1 year = 365¼ days

1 century = 100 years

1 millenium = 1000 years

2.5 Measurement of length

Length is the distance betweentwo points in straight line or in curvedline. To measure the length we use ametre scale or a measuring tape. Inthese devices, the two successivedivisions are separated by amillimetre.

To measure anything, we haveto use the scale carefully. Otherwise,the measurements may not beaccurate. The important precautionsare :

(i) The edge or corner of a scaleis usually worn out. In some scales,the ends may be broken. Hence, zeromark may not be seen. In such cases,you should use any other mark of thescale say 1 cm (Fig 2.2). Then youhave to subtract this mark from thereading at other end.

For example, in Fig 2.3 thereading at one end is 1 cm and at theother end is 6.6 cm. Therefore, thelength of the object is 6.6–1=5.6 cm.

(ii) You should keep the scale incontact with the object along its lengthas shown in the Fig. 2.4 and not as inthe Fig. 2.5.

(iii) For making accuratemeasurements you should keep youreye exactly, vertically above thereading as shown in the Fig. 2.6.Position of eye A is correct. Positionof eye B and C are wrong. Thereading corresponding to B and C willgive parallox error.

Fig. 2.3 Correctmeasurement

Fig. 2.2 Wrongmeasurement

Fig. 2.4 Correctmeasurement

Fig. 2.5 Wrongmeasurement

Fig. 2.6Parallox error

B A C

19


We can measure the length of acurved line using a thread (Fig 2.7)and a divider from the geometry box(Fig 2.8).

Fig 2.7 Usingthread

Fig 2.8 Using divider

the coins must besimilar (25 paisecoins). Measure theheight of 10 coinsusing a metre scale. Inwhat way this readingis useful in measuringthe thickness of onecoin? It is simple. Ifyou divide the value by10 it gives thethickness of one coin.

Activity 2.1

How to measure the thicknessof a coin? Arrange 10 coins one aboveanother as shown in the Fig. 2.9. All

Now arrange the same 25 paisecoins, but this time use 20 coins. Canyou confirm the thickness of one coin?

Activity 2.2

You can measure the thicknessof a paper in this science text book asaccurately as you can. How is itpossible? Take your text book. Bypressing it, measure the total thicknessof the book using a scale. Divide thatvalue by the total number of papers inthe book. You can get the thicknessof a paper.

Activity 2.3

List out the distances

PlaceDistance (km)

From To

Chennai Delhi ...........................

Chennai Mumbai ...........................

Chennai Kolkotha ...........................

Chennai Bangalore ...........................

Chennai Trivandrum ...........................

Chennai Hyderabad ...........................

Chennai Pondicherry ...........................

Coimbatore Chennai ...........................

Trichy Chennai ...........................

Tirunelveli Chennai ...........................

Salem Chennai ...........................

2.6 Measurement of area

The classroom is smaller than theplayground. What exactly are wetrying to compare? We compare thesurface of the class room and theplayground. That is about the area.

Fig 2.9 Thicknessof a coin

20


Area is the measure of a surface of anobject.

2.6.1 Area of regular surface

(i) To find the area of a square,(Fig 2.10) you multiply the side (length)by the side (length).

Area of a square = a × a

Fig. 2.10

(ii) To find the area of arectangle you multiply the length bythe breadth (Fig 2.11).

Area of a rectangle = l × b

Fig. 2.11

The area of smaller objects canbe expressed in the unit of mm2 orcm2. The area of bigger objects canbe expressed in the unit of m2 or km2.

2.6.2 Area of a graph

10 millimetres in 1 centimetre, therewill be 10 millimetres along each side.Each little square in the graph is1 square millimetre. How many littlesquares are there? It follows that100 mm2 = 1 cm2

2.6.3 Measuring area of irregularsurface

Keep the irregular surface overthe graph sheet (Fig 2.13). Mark theboundary of the surface in the graphusing pencil. Remove the object.Count the number of little squareswithin the boundary. Do not count thesquare, if it is less than half. Youknow, that each little square is 1 mm2.Hence you can calculate the total areaby multiplying number of squareswith 1 mm2.

Like this, you can measure thearea of a leaf also.

Fig. 2.13

2.7 Measurement of volume

Your geometry box occupiesmore space than a match box. Thespace occupied by a football is morethan a cricket ball. The space occupiedby an object is called volume. Anobject like a match box or book or

a

a

b

l

Fig. 2.12 represents a biggersquare of a graph. As there are

Fig 2.12

21


brick is known as cuboid. The volumeof cuboid is calculated if you knowits length, breadth and height.

Volume of cuboid = length ×breadth × height.

Fig. 2.14

As in the Fig 2.14, if the lengthof a cuboid is a metre, breadth is bmetre and height is c metre. Then itsvolume is

V = a metre × b metre × c metre

V = abc metre3 = abc m3

The unit of volume is m3

Activity 2.4

Find out the volume of theobjects in the table 2.5.

2.7.1 Volume of liquids

Liquids such as milk, edible oil,lubricating oil, petrol, kerosene andmedicines are measured by theirvolume. The volume of liquid isexpressed in litre (L). How much isone litre? Let us find out.

You might have seen a one litrepack of milk or one litre pack ofedible oil or one litre water bottle.Take a glass vessel of length 10 cm,breath 10 cm and height 10 cm. whatis its volume? It is 10 × 10 × 10 =1000 cm3. Pour any one of the liquidmentioned above into the vessel. Youcan see, that the vessel is completelyfilled by the liquid. Hence one litremilk can occupy a space of 1000 cm3.

Therefore, 1 litre = 1000 cm3.We call this cm3 as cubic centimetre,simply cc.

∴ 1 litre = 1000 cc.

You must have seen some of thevessels used for measuring volume ofliquids as shown in the Fig. 2.15. We

Table 2.5 Volume of regular objects

S.No. object length breadth height volume

1. Brick ..........(cm) ..........(cm) ..........(cm) ..........(cm3)

2. Geometry box ..........(cm) ..........(cm) ..........(cm) ..........(cm3)

3. Science book ..........(cm) ..........(cm) ..........(cm) ..........(cm3)

4. Class room ..........(m) ..........(m) ..........(m) ..........(m3)

5. Almirah ..........(m) ..........(m) ..........(m) ..........(m3)

22


are using such vessels to measure thevolume of milk, kerosene, lubricatingoil, edible oil and medicines.

2.7.2 Measurement of volume ofliquids

It is easy to find out the volumeof a solid rectangular block, but whatcan we do about liquids? They do nothave a definite length, breadth andheight, but take the shape of thecontainer in which they are poured.

Pour the liquid, whose volumeyou want to know, into a container asshown in the Fig 2.16. Measure theinternal length, breadth and height.Multiply all three together and youhave the volume of liquid.

2.7.3 Measurement of volume ofirregular solids

It is easy to calculate the volumeof a regular shaped solids. But manysolids are irregular, for example, astone. How to find its volume?

One way to find the volume of astone is shown in the Fig. 2.17. Pourwater into a measuring cylinder, sothat it is about half full and read thevolume. Then put the stone into thewater. The water level will rise. Readthe new volume. The differencebetween the two readings gives thevolume of the stone.

Fig. 2.17 Volume of Solid

2.8 Measurement of mass

You must have experienced thata brick is heavier than a sponge ofsame size. It is because the quantityof matter in brick is more than that ofsponge. The quantity which measuresthe amount of matter in an object iscalled mass and it is measured inkilograms (kg). Mass and weight are

Fig. 2.15 Measuring devices

Fig. 2.16 Volume of liquid

23


not same. It is unfortunate that peopleuse the word weight when they meanmass. You might have seen a packetof sugar marked as “net weight 500g”. It is wrong. It has to be marked as“net mass 500 g”. Mass is thequantity of matter inside the body.Weight is the pull of gravity on theobject. Weight of a given object isvariable from place to place andplanet to planet. Let us discuss, furtherabout this idea in the chapter 'forceand motion.'

Mass of an object is measuredby comparing it with a standard mass.It is commonly measured with thehelp of a beam balance. Fig 2.18shows the type of a beam balance.Shopkeepers use many types ofbalances for weighing vegetables andprovisions.

Fig. 2.18 Beam balance

In the provision stores, we cansee the balance as shown in the Fig2.18. In the jewellory shops, tomeasure the mass of jewels we areusing the electronic balance (Fig2.19). To measure the accurate mass

of an object, we use the physicalbalance as shown in the Fig 2.20. Youcan see it in your school physicslaboratory.

2.9 Measurement of time

We measure the time with thehelp of clocks and watches. Long ago,people did not have clocks. They usedvarious events that occurred at regularintervals to count time intervals. Onesuch event was occurrence of day andnight. Our Earth rotates about its ownaxis and it takes a time of 24 hours tocomplete one rotation, we call it asone day. The Earth also revolvesaround the Sun; it takes 365¼ daysto complete one revolution, we call itas one year. The moon revolvesaround the Earth and it takes 29.5days to complete one revolution. The

Fig. 2.19 Electronic balance

Fig. 2.20 Physical balance

24


time interval between two rising Sunis 1 day and the time interval betweentwo full moons is 29.5 days.

2.9.1 Sundial

An early device for measuringtime was the sundial (Fig 2.21). Asimple sundial is made of a horizontalcircular board with a triangular plateof metal fixed vertically on it. Theplate is fixed along North-Southdirection. The shadow of the platefalls on the board. The edge of theshadow falls at different angles atdifferent times of the day. The positionof the shadow was used to note thetime of the day. It cannot be used aftersunset.

Fig. 2.21 Sundial

Around 3500B.C.Sumerian people,living in what isnow Iraq, madethe first shadowclock as shown inthe Fig. 2.22.

2.9.2 Sand Clock

Another earlydevice for measuringtime was the sandclock. In a sand clock,sand flows from oneglass container to otherthrough a small holeconnecting them asshown in the Fig. 2.23.In a fixed interval of time, one hour,the entire sand in the top containerflows down to the container at thebottom.

2.9.3 Water Clock

In earlier days, around 500 B.C.people also used water clock. A canof water helps to measure time. Makea tiny hole at the bottom of the can.The can is filled with water and placedat certain height (Fig 2.24). The waterflows out and collected in another can.Everytime you fill the can, it will takethe same time to empty.

Fig. 2.22 Sundial

Fig. 2.23 SandClock

Fig. 2.24WaterClock

25


Stop Clock Stop WatchFig. 2.27

2.9.4 Pendulum clock

In 1581, a seventeen year oldItalian boy made a remarkableobservation about the hanging lightin the church, swinging back andforth. Each swing always took thesame length of time. That is, the timeinterval is fixed. Later, the boy, whosename was Galileo Galilei became oneof the greatest scientists. He used thisprinciple to measure time and made apendulum clock. In this type of clock,a pendulum makes oscillations. Themovement of the pendulum isconnected with the movement ofsecond, minute and hour hands of theclock.

2.9.5 Simple pendulum

Tie a solid ball (metal) with ahook to a thread and hang it as shownin the Fig 2.25. Now, pull the ball toone side and leave it to go. It willcome to its original position andcontinue to move to the other side. Itwill stop and start its return journey.This back and forth motion is calledoscillation. The time taken by thependulum to complete one oscillationis fixed. In a pendulum clock

(Fig 2.26) the time is measured bymaking use of the time taken by thependulum for each oscillation.

Nowadays, to measure the shorttime intervals accurately, stop clocksand stop watches are used (Fig 2.27).

See the clock in the Fig 2.28.That clock does not have hour, minuteand second hands. These clocksdisplay time directly in digits called asdigital clocks.

In the modern clocks mostaccurate one is atomic clock. Basedon the time interval of an energychange in a caesium atom second issecond.

Fig. 2.25 SimplePendulum

Fig. 2.26 WallClock

Fig. 2.28Digitalwatches

26


SELF EVALUATION



(i) The SI unit of length is(a) cubit (b) metre (c) handspan (d) pace

(ii) The unit of force is(a) Newton (b) Joule (c) newton (d) joule

2. The SI unit of mass is _____________________

3. The SI unit of time is _______________________

4. The measuring instrument used by a tailor to make the measurement is________________________

5. The principle of pendulum clock was first discovered by _______________

6. Which event is considered in a pendulum clock to measure the timeinterval?

7. Name the unit of length, which you would like to use while expressing thedistance between Chennai and Madurai.

8. How many Kilograms are there in one metric ton?

9. Name the unit of length, which should be used to express the thicknessof a paper.

10. What is the circumference of a one rupee coin? (use a thread)

11. What is meant by volume of an object?

12. State the unit in which volume of liquids is expressed.

13. How many millilitres are there in one litre?

14. What is mass?

15. Name the two types of clocks used in earlier days.

16. Draw the diagrams of the vessels used to measure the volume of liquids.

17. What kind of watch is used to measure the time in 100 metre race?

18. Why a cubit or handspan cannot be used as a standard unit of length?

19. Arrange the following in the decreasing order.

Kilometre, millimetre, centimetre, metre.

27


20. The value of one division of a measuring cylinder is one ml. Water ispoured into it, so that its level is at 50th division. When a stone is put inthe cylinder, the level of water rises to 75th division. What is the volume ofthe stone?

21. Identify the mistake and correct it.

a) Length of the book is 25 cms

b) Prema takes 30 seconds to cover a distance of 100 m.

22. State True or False

a) Hand span is a standard unit for measuring length.

b) The SI unit of mass is gram.

c) Length of a curved line can be measured using a thread.

d) the unit of volume is m2.

e) The time interval of oscillations of a pendulum is fixed.

23. What is the area of a rectangular field 200 m long by 60 m wide?

24. What is the volume of a block of metal 6 cm long, 5 cm wide and 4cmhigh?

25. What is the volume of the metal cube with side 5 cm?

26. Name the balance used in science laboratory.

27. State two examples for periodic motion.

28. What is the necessity of standard units in measurement?

29. What are the conventions used in writing the unit and their symbols of SIsystem?

30. State two precautions, which should be taken while using a metre scale.

31. How will you measure the thickness of a coin?

32. How will you measure the volume of a stone?

33. The milkman gives you a half litre pack milk. How will you verify thevolume of milk?

34. Find out the area of your science book?

35. Find out the volume of your science book.

36. Estimate the area of the blackboard in your class room in square metres.

37. Estimate the floor area of your class room in square metres.

38. Estimate the volume of your class room in cubic metre.

28


3. Nature of matterWe see many living and non-

living matter around us in this Earth.You will study about living things inChapter-8. In this chapter you aregoing to learn about non-living matter.

In our day-to-day life we see anduse many non-living things like stone,sand, table, iron rod, water, milk, airetc. So learning about these things isquite necessary.

3.1 Matter

Lift an empty iron bucket andfeel its weight. Fill it with dry sandand lift it again. You feel it heaviernow. Don't you? From this youunderstand that sand has mass(Fig. 3.1a). Now try to add moreamount of sand into the bucket. Thesand begins to fall out. The bucketcannot hold any more amount of sandas it is already full. The sand hasoccupied the entire space. From thisyou understand that sand occupiesspace.

Fig. 3.1a Sand has mass and it occupies space

The space occupied by matter iscalled as volume.

Lift an empty iron bucket andfeel its weight. Fill it with water andlift it again. You feel it heavier now.Don't you? From this you understandthat water has mass (Fig. 3.1b). Nowpour more amount of water into thebucket. Water overflows. The bucketcannot hold any more amount of wateras it is already full. Water hasoccupied the entire space. From thisyou understand that water occupiesspace.

Fig. 3.1b Water has mass and it occupies space

Take a deflated ball and keep iton the left pan of a balance. Add somesand on the right pan gradually tillthe pointer comes to zero. Now takethe ball and inflate it with air. Placeit again on the left pan. Now you cansee the pointer moving to the left side.Add more amount of sand to the rightpan till the pointer again comes tozero (Fig. 3.1c). From this youunderstand that 'air has mass'.

Sand

Water

29


Now allow the air to get out ofthe ball. What happens? Ball shrinksin size. Doesn't it? From this youunderstand that air occupies space.

Fig. 3.1c Air has mass and it occupies space

We conclude from the aboveactivities that matter (substance) likesand, water and air have mass andcan occupy space.

'Anything that has mass andoccupies space is called matter'.

Feelings like sorrow, happinessand pain have no mass and cannotoccupy space. So these are notconsidered as matter.

Activity 3.1

Fill half of a glass trough withwater. Take a glass tumbler and plungeit into the water as shown in the Fig.3.2(a). What happens? Water does notenter the glass tumbler beyond a level.

Now tilt the tumbler slowly to aslanting position. You can see the airbubbles coming out of the tumbler and

water entering inside (Fig 3.2b).

From this you understand thatair occupies space.

What is matter made up of?

Matter is made up of very tinyuniform fundamental particles. Theseparticles cannot be seen with our eyes.The particles are held together by anattractive force.

The nature of the fundamentalparticles and the strength of theattractive forces among them varyfrom one substance to another.

These fundamental particles maybe atoms, molecules or ions.

3.2 States of Matter

The physical state of a matterdepends upon the distance and thestrength of the attractive force betweenthe fundamental particles.

Solid

Book, chair, pen, stone, sand andice are in the solid state.

The particles in a solid arepacked very closely to each other andare held together by strong attractiveforces (Fig. 3.3).

Fig. 3.3 Particles in a solid

Air Air Bubbles

Water

Stone

(a) Fig. 3.2 Air occupies space (b)

30


Liquid

Milk, water and fuels like petroland diesel are in the liquid state. Theparticles in a liquid are not very closeto each other. The distance betweenthem is greater when compared to asolid (Fig. 3.4). The attractive forcebetween them is also weaker.

Fig. 3.4 Particles in a liquid

Gas

The air we breathe is a gaseoussubstance. The fundamental particlesin a gas are held together by weakforces of attraction. The distancebetween them is also greater than thatin a liquid (Fig. 3.5).

Fig. 3.5 Particles in a gas

3.2.1 The shape and volume of solids

Place a stone on a table as shownin Fig. 3.6. The stone has a definiteshape and volume. Now place thestone on the floor. It has the samevolume and shape. Place it in a glasstumbler. Now also you do not find

any change in volume or shape of thestone.

Fig. 3.6. Shape and volume of asolid does not change

Solids have definite shape andvolume. When the temperatureremains constant, they do not changetheir shape or volume.

3.2.2 The shape and volume ofliquids

Fill a 100 ml beaker with water.Observe the shape of water. It has theshape of the beaker. Transfer thiswater into a 100 ml conical flask. Nowthe water gets the shape of the conicalflask (Fig. 3.7). But the volume of

Fig. 3.7. Shape of a liquid changesbut volume does not change

water remains the same in both thecontainers.

Liquids like water and oil havedefinite volume. But they do nothave definite shape. They get theshape of the containers in which theyare kept. Since the force of attractionbetween the particles in a liquid isweaker, they are capable of moving.So they can change their shape.

Water

Air

Stone

Water

31


3.2.3 The shape and volume of gases

Blow air into two balloons ofdifferent shapes. The two inflatedballoons differ in shape. The air insidethe two balloons get the shape of theballoons (Fig. 3.8a).

Fig. 3.8a Change in shape of air (gas)

Fill a 200ml jar with 100g ofbrown nitrogen peroxide gas. The gasjar appears brown all over. Thevolume of the gas is 200 ml. Fill thesame amount of 100 gms of nitrogenperoxide in a 300 ml jar. Now alsoyou can see the gas jar appearingbrown all over. Now the volume ofthe gas is 300 ml. (See Fig. 3.8b)

Fig. 3.8b Change in volume of a gas

You can understand from theabove activity that gases do not have

a definite shape and volume. Theyget the shape and volume of thecontainers in which they are kept.

3.3 Properties of Matter

3.3.1 Rigidity and Flexibility ofmatter

Touch and feel a wooden or ironchair you sit. You feel it hard andrigid. Solids contain particles whichare closely packed. The particles havestrong forces of attraction betweenthem. So they are rigid and have highdensity.

How do you feel when you touchwater or when the gentle breezetouches you? You feel them softer.The reason is that the particles in aliquid and gas are comparatively farapart. They are held together by weakforces of attraction. So the liquids andgases are highly flexible, soft andhave lesser density than solids.Density of gases is less than that ofliquids.

3.3.2 Fluidity of matter

Place a table on an unevensurface. Does it move on its own? No.It does not move towards lower level.Since the particles in a solid arebonded strongly, they do not separateeasily and move. Solids do not showthe property of fluidity.

Pour some water on an unevensurface. You can see the water runningfrom higher level to a lower level(Fig. 3.9) Since the particles of a

200ml

300ml

32


liquid are not very close to each otherthey show weaker forces of attraction.So they can move easily. Liquidsshow the property of fluidity. Waterflows from mountains down intorivers due to this property.

Fig. 3.9. Fluidity of liquid

Prick an inflated balloon with apin. The air inside the balloon comesout with a force and noise (Fig. 3.10).What is the reason?

Fig. 3.10 Fluidity of gas

The particles in a gas are farapart from each other and are heldtogether by very weak forces ofattraction. So they move very easily.Gases have the property of fludity.i.e. moving spontaneously from aregion of high pressure to a region oflow pressure.

3.3.3 Solubility of matter

Solubility of solids

Add a spoon of sugar to waterin a cup and stir. What happens? SeeFig. 3.11.

The sugar disappears bycompletely mixing with water. Solidslike sugar and salt dissolve in water.

Sugar - SoluteWater - SolventSugar + water → Sugar solution

The forces of attraction betweenthe sugar particles are removed bywater particles. So the sugar particlesseparate and mix with water.

Place an iron ball in a beakercontaining water and stir it. What doyou observe? Iron ball does notdissolve in water. See Fig. 3.11. Fromthis you understand that some solidsare soluble and some solids areinsoluble in water.

Fig. 3.11 Solubility of solids in water

Solubility of liquids

Add a small quantity of ethylalcohol to water. What happens?Alcohol completely mixes with water.Alcohol is completely soluble inwater.

Activity 3.2

Fill, half of a beaker with water.Add a few drops of coconut oil andstir well. You will understand that oildoes not mix with water. Oil isinsoluble in water.

Sugar

WaterWaterIronball

33


Solubility of gases

How do aquatic living thingsbreathe? Oxygen present in the air issoluble in water. So they breathe theoxygen dissolved in water. The marineplants take the carbon-di-oxidedissolved in sea-water for thephotosynthesis. The soda water, wedrink, is containing dissolved carbon-di-oxide gas.

Generally gases are soluble inwater but certain gases like hydrogenand nitrogen are insoluble in water.

Note : The substances which areinsoluble in water may be soluble insome other solvents.

Paints are insoluble in water. Butthey are soluble in kerosene.

Activity 3.3

Take three test tubes in a stand.Pour some water in each. Add a smallquantity of sand in the first test tube,salt in the second test tube and starchpowder in the third one and shakethem. What do you observe? Sanddoes not dissolve in water. Saltcompletely dissolves. Starch powderis partially soluble.

3.3.4 Change in volume of matterdue to pressure

When pressure is applied oversolids, the volume does not decrease.

Activity 3.4

Compress a piece of iron with awooden log. Do you observe anychange in volume? The volume ofiron piece does not change.

When pressure is applied overliquids their volume does notdecrease.

Activity 3.5

Fill a syringe with water andclose the open end with a cork. Placethat end on a table and press the pistonof the syringe downwards. Thevolume of the water does notdecrease.

When pressure is applied overgases, their volume decreaseconsiderably. Since the distancebetween the particles of a gas is more,they come closer when pressure isapplied.

Activity 3.6

Pull up the piston of a syringe.Air is sucked in. Close the open endwith a cork. Keep the closed end ona table and press the pistondownwards. What happens?

The piston moves easily as theair in the syringe gets compressed.

3.3.5 Change of State of matter

Matter changes its state whenheated or cooled.

34


Change of state due to heat

(i) Solid → liquid

Take out some ice cubes from arefrigerator. Place them in a cup andheat it. Solid ice melts into liquidwater. See Fig. 3.12.

The transformation of a solidmatter into liquid when heated iscalled melting.

The ice-deposits in theHimalayas melt due to heat of the Sunand flow as Ganga and Brhamaputrarivers.

(ii) Liquid → Gas

Heat some amount of water in acup. Water boils and vapours of water(steam) come out. See Fig. 3.12.

The transformation of a liquidinto vapour by heating is calledevaporation. The sea waterevaporates due to Sun light and formsclouds in the sky.

Fig. 3.12 Change of state of matter due to heat

(iii) Solid → Gas

Heat a small piece of camphorin a dish. It does not melt into a liquid.But it evaporates into vapour.

Certain solids when heated, areconverted to vapour state withoutpassing through the liquid state. Thisis called sublimation.

Substances like naphthalene,benzoic acid, iodine and ammoniumchloride have the property ofsublimation.

Activity 3.7

Cut a candle into small piecesand take them in a dish. Heat it. Whathappens? Stop heating and observethe change.

Change of state due to cooling

(i) Gas → Liquid

We enjoy when it rains. How dowe get the rain from the sky? Thewater vapour in the cloud gets cooledand forms tiny particles of water.These water particles unite and formwater drops which fall as rain. SeeFig. 3.13.

Fig. 3.13 Cloud condenses into rain

The change of state from vapourinto liquid by cooling is calledcondensation.

Ice(solid)

Water(Liquid)

Steam(gas)

heatheat

35


Activity 3.8

Take some ice cubes in astainless steel tumbler. Observe theouter surface of the tumbler aftersometime. What do you see? Whatdo you understand?

Water drops get collected on theouter surface of the tumbler. This isdue to the condensation of watervapour present in the atmospheric air.

(ii) Liquid → Solid

Have you visited the placeswhere ice (snow) deposits duringwinter on trees and mountains? Oryou must have seen such deposits ofice in the television pictures. How doesthe ice get deposited on themountains?

Water gets cooled due to severecold climate at high altitude andconverted to ice. These ice particlesdeposit over the mountains and treesduring winter (Fig. 3.14).

The transformation of a liquidinto solid due to cooling is calledfreezing.

Fig. 3.14 Snowy Mountain

Activity 3.9Keep a cup of water in the

freezer of a refrigerator and observethe change of state. Visit an ice factoryand see how ice creams are made.

The following representationgives you a clear understanding ofchange of states of matter.

heat heatmelting evaporation

Solid Liquid Gascool cool

freezing condensation

heatSublimation

3.4 Diffusibility of Matter

The spontaneous mixing up ofparticles of a matter with paricles ofanother matter is called diffusion.

Diffusion of a gas in a gas

When you return from school inthe evening, you must have smelt thenice odour of your mother's spicytiffin. How are you able to get thesmell of the food being prepared inthe kitchen while you are at theentrance of your house? See Fig. 3.15

Fig. 3.15 Diffusion of vapour of foodsubstance in air

The vapours of the cooked foodcome out. The forces of attractionbetween the particles in a gas orvapour is very weak. So the particlesseparate and mix with the particles of

> >< <

>

36


air. When you breathe that air mixedwith vapours of cooked food you feelthe smell of the food.

Activity 3.10

Keep a lighted agarbathi at onecorner of a room. You will feel thepleasant odour of the agarbathi all overthat room. This happens due to thediffusion of the vapours of agarbathiin air.

Diffusion of a liquid in a liquid

Pour a drop of blue ink into abeaker of water. What happens? Theparticles of ink diffuse through theparticles of water and the whole waterin the beaker turns blue. Liquidsdiffuse slower than gases.

Diffusion of solids in liquid

Drop a small piece of potassiumpermanganate carefully into a beakerof water. You can see the pink colourof the crystal slowly diffusing throughthe water as the crystal dissolves. Theattractive force between the particlesof potassium permanganate isremoved by the particles of water. Sothe potassium permanganate particlesget diffused in water.

Note : Since the particles of asolid have strong forces of attraction,diffusion of a solid in another soliddoes not take place naturally.

3.5 Attraction towards a magnet

Certain ores of iron (magnetite)have been known to possess theproperty of attracting iron and settingalong a definite direction. Thismaterial, capable of leading in theproper direction is called as loadstone.

3.5.1 Artificial magnets

When pieces of iron are rubbed withthe loadstone (natural magnet) they acquirethe property of attraction and theyare called artificial magnets.

A magnet has two poles namelyNorth pole and South pole. Poles areat the end of the magnet where thepower of attraction is more. Like poles(N-N and S-S) repel each other.Unlike poles attract each other (N-Sand S-N).

A magnet attracts iron, nickeland cobalt. Magnets have no effecton wood, glass, aluminium, water,paper and plastic. These are knownas non-magnetic substances.

We are using the magnets incranes to lift a heavy load (See Fig.3.16). To remove any iron particlefrom the eyes, magnets are used.Impurities of iron could be removedfrom other metals using magnets.Magnets are available in electric bell,electric fan, telephone and electricmotors. We are using the magnets indoors, window catchers, door closersof almirahs and in beds.

37


Fig. 3.16 Crane

3.6 Conductors of heat

You might have seen the boiler,different pans, milk cooker, pressurecooker and other utensils in thekitchen that are used for cooking.These vessels are made of metals andalso provided with handles made upof wood or some other non-metallicmaterial like plastic.

Why are the vessels providedwith wooden or plastic handles?

Take a vessel. Fill it with hotwater. Put the two spoons in it. Oneis made of metal like aluminium orstainless steel and the other is madeof wood or plastic. After some time,touch the two spoons by your left andright hand. Which one is hotter? Themetal spoon is hotter than woodenspoon. Why? Metals quickly conductheat. So, metals are good conductorsof heat. In metals, heat flowsfrom one end to another quickly. SeeFig. 3.17.

Fig. 3.17 Conduction of heat

In the materials like wood andplastic, heat flows from one end toanother very slowly. Wood, paper,cloth and plastic are bad conductorsof heat.

The metal mercury, which is aliquid, is a good conductor of heat.So, we are using the mercury inthermometers. Gases are poorconductors of heat.

3.7 Conductors of electricity

All of us use electricity forlighting our houses and school. Whenwe switch on the light or fan or motor,electric current flows through thefilament of the bulb or through thecoil. Wires or cables carry the electriccurrent.

Have you seen the electric cable?Take a piece of unused cable or wire.Cut and open the outer coloured layer(insulating material). Inside, you finda number of thin metal wires (copperaluminium). These metal wires carrythe current. Metals are goodconductors of electricity.

The outer coloured layer will notcarry the current. This insulatingmaterial, paper, dry cloth and rubberare bad conductors of electricity andare called insulators.

Pure water is a bad conductor ofelectricity. However, water (what weare using) containing dissolved saltsconducts electricity. It is not advisableto touch the water in which electric

Woodenspoon

Metal spoon

Hot water

38


current flows. It is advisible to alwayswear rubber chappals (insulators) andto keep the hands dry while operatingelectrical appliances. Thus, weconclude that matter can be classifiedas conductors of electricity andinsulators.

Activity 3.11

Take a torch with cells. Switchit on. Take a paper, a dry cloth, arubber sheet and an aluminium foil.Place them one by one in betweenthe bulb and cell and check whetherthe torch lights up in each case. Thetorch does not light up with paper,dry cloth and rubber. But it lights upwith the aluminium foil. Soaluminium conducts electric current.That is why electric wires are made

up of metals. Metals are goodconductors of electricity.

3.8 Transparency

We cannot see through a paper,a metal sheet, a wall and wood. Allthese are opaque materials. Lightcannot pass through them.

We can see through a glass. Soglass is a transparent material. We cansee the fish in clean water. So cleanwater is also a transparent material.We are surrounded by air, and objectsare always seen. So air is alsotransparent material. We mayconclude that the materials whichallow the light to pass through themare called as transparent and thosewhich do not allow the light are calledas opaque.

SELF EVALUATION


1. Which of the following does not change its shape at the room temperature?

a) Cool drink b) Carbondioxide c) Milk d) Cricket bat

2. With regard to petrol which of the following is true?

a) It has a definite shape and mass

b) It has definite mass but does not occupy space

c) It has the shape of the container. It has definite volume and mass.

d) It occupies space but does not have the property of fluidity.

3. During which process the volume of matter increases largely?

a) Freezing b) Melting

c) Evaporation d) Condensation

39


4. You can feel the bad smell of the garbage at a distance. From this youcan understand that gases have the property of _________

5. The reason for the rigidity of solid is the __________ is strong betweenthe particles in a solid.

6. When a matter is in the ___________ state the particles in it show minimumforce of attraction.

7. When a matter is in the _____________ state, the particles do not move.

8. The formation of rain drops from clouds is due to ___________

9. When a perfume bottle is opened ___________ process takes place.

10. In thermometers, the liquid mercury is used. Since it is a ___________

11. Materials which do not allow the light are called __________

12. If you take equal volumes of water and sand, which will have more weight?

13. How are you able to detect the leakage from a gas cylinder?

14. Does the force of attraction between the particles increase or decreasewhen a liquid substance is converted into a solid?

15. Mention two solids that are insoluble in water.

16. Solids are rigid. But the liquids and gases are not rigid. What is thereason?

17. Liquids flow from higher to a lower level. What do you understand fromthis?

18. What is evaporation? Give an example.

19. What is matter?

20. Prove by an experiment that air has weight.

21. Give an example to understand the gaseous diffussion.

22. By an experiment how can you prove that volume of a gas can be reducedby applying pressure.

23. How do aquatic plants respire?

24. Cooking vessels are provided with wooden handles. Why?

25. When you add a drop of ink to water what will happen?

40


It is very essential that the foodwe eat, the air we breathe, the waterwe drink and the different substanceswe use in our day-to-day life are pure.As the environmental pollution ismore nowadays, we must remove thepollutants and the unwantedcomponents from them. Let us studyabout the different methods adoptedin our daily life and laboratories toseparate and purify the substances.

4.1 Pure substances and mixturesSubstances which contain

particles of the same type or singletype are called pure substances.

Pure substances have thefollowing characters.

Definite composition bynature.

Definite physical propertiessuch as melting point, boiling pointand density.

Homogeneous nature.

eg. (i) Elements like gold, silver,hydrogen and oxygen.

(ii) Compounds like coppersulphate or blue vitriol, water andsugar.

A mixture contains two or morepure substances which can beseparated by easy physical methods.

eg. (i) Mixture of iron fillingsand sand (ii) Milk is a mixture ofliquid fat, carbohydrate, protein,dissolved salts and water.

4.2 Need for the separation ofmixtures

We have to separate thecomponents of a mixture in order to

(i) Remove the unwantedcomponents.

(ii) Remove the components that areharmful for our health.

(iii) Get pure substances.

4. Separation of substances

Table 4.1 Shows the differences between pure substances and mixturesTable 4.1

No. Pure substances Mixtures

(i) The components of a puresubstance are of the same type

(ii) Pure substances are homogeneousin nature. Particles are uniformthroughout the substance.

The components of a mixture are oftwo or more types.

Mixtures are heterogeneous innature. They contain particles ofdifferent types.

41


Activity 4.1

Take some crystals of commonsalt in a glass container. Add water toit and stir well. Salt dissolves in water.Carefully observe the bottom of thecontainer. You can see a deposit offine sand. The salt crystals that areobtained from sea water containparticles of sand which do notdissolve in water. So these sandparticles settle at the bottom of thecontainer. What will happen if we addthe salt crystals directly to our foodwhile cooking? Sand particles willmix with our food and affect ourhealth. So, while using crystals of saltfor cooking it is better to use thesolution of salt in water.

4.3 Methods of separating insolublesolid impurities from solidsubstances

There are several methods ofseparating the insoluble solidimpurities from solid substances.

4.3.1 Hand picking

Hand picking is the simplestpurification method. Grains like rice,

Fig 4.1 Hand picking

wheat and pulses contain smallpebbles or stones. We can easily pickthem and separate. If the size, colourand shape of the components aredifferent, it is easy to separate themby hand picking (Fig. 4.1).

4.3.2 Winnowing

Fig. 4.2. Winnowing

In a mixture of solids, if impurityis of light weight, this method is

No. Pure substances Mixtures

(iii) Pure substances have definitephysical properties.

eg. : Water has the freezing pointof 0oC, boiling point of 100oC anddensity 1 g/cc

Mixtures do not have definitephysical properties. They havedifferent physical propertiesdepending upon the componentspresent in it.

husks of grain(Chaff)

Grain

42


followed. This method is useful toremove the husk from grains like rice,wheat and ragi. Farmers drop themixture of grains and husk slowlyfrom a height when the wind blows.Heavier grains fall directly on theground as a heap. Husk being lighterare carried away by wind and fall asanother heap separately (Fig. 4.2).

4.3.3 Sieving

Fig. 4.3 Sieving

If the components of a mixtureare of different sizes, they can beseparated by sieving method using asieve. With the help of a sieve, brokenparticles of grains can be separatedfrom its flour. During sieving, fineflour passes through the holes of thesieve while bigger particles remain inthe sieve (Fig. 4.3).

Activity 4.2

By using sieves of different sizedholes remove husk from wheat flour,and broken pieces of rice from rice.You can also remove worms or smallinsects from sooji or rava and purifyit with the help of a sieve.

4.3.4 Sedimentation and Decantation

When the components of amixture differ in densities they can

be separated by sedimentation anddecantation. The insoluble solids inwater or lighter and heaviercomponents of a mixture, can beseparated by this method (Fig. 4.4).

Fig. 4.4. Sedimentation and Decantation

Sedimentation : The mixturecontaining solid and liquid compon-ents is allowed to stand for sometime.The heavier particles settle at thebottom of the liquid. The process ofsettling down of insoluble particlesin a suspension is called sedimen-tation.

Decantation : The process oftransferring the clear liquid standingabove the sediment carefully intoanother container using a glass rod iscalled decantation.

You know that peanut burfis aremade by mixing the nuts with jaggeryextract. When jaggery is mixed withhot water and allowed to stand forsometime the sand particles mixedwith it settle at the bottom. This isseparated by carefully decanting theclear jaggery liquid. You must haveobserved this at your home.

43


Activity 4.3

Take some muddy water in aglass beaker. Allow the water to standfor sometime without disturbing. Finesand particles settle at the bottom.This is called sedimentation. Clearwater stands above the sand. Transferthis clear water into another vesselwith the help of a glass rod as shownin the Fig. 4.4. Sand remains in thebeaker.

4.3.5 Magnetic separation

If one of the components of amixture has the property of beingattracted by the magnet, then it canbe removed by using a magnet. Thismethod is called magnetic separation.

The iron particles mixed withsand or sooji can be separated easilyby a magnet. When the magnet ispassed through the mixture, fineparticles of iron get attracted by themagnet and stick to it. This can beremoved later (Fig. 4.5).

Fig. 4.5 Magnetic separation

Activity 4.4

Insert a bar magnet through aheap of sand. Take it out. Again insert.Repeat it several times. You can seesmall particles of iron sticking to themagnet near the poles.

4.3.6 Filtration

The process of separatingparticles of different sizes which areinsoluble in a liquid by using a filteris called filtration.

Water, containing insolubleimpurities is filtered by using a thincotton cloth or filter paper. Whenlarge quantities of substances are tobe filtered, cotton, glass wool,charcoal or sand layers are used.

Fig. 4.6 Method of using the filter paper and Filtration

cone

funnel with filterpaper cone

filtrate

Activity 4.5

conein a

funnel

44


In the laboratories we use filterpaper for filtration. Filter paper is inthe round form. Fold the circular filterpaper first into a half circular shape.Then fold it again into a quarter circle.Arrange it in the form of a cone (SeeFig. 4.6). Place the cone shaped filterpaper into a glass funnel and fix it ina stand. Place a flask below the stemof the funnel. Pour the water mixedwith sand into the filter paper fittedin the funnel. Water passes throughthe filter paper and gets collected inthe flask below. It is called thefiltrate. The sand remains in the filterpaper. It is called the residue.

4.3.7 Evaporation

Liquids containing solubleimpurities can be purified by a processcalled evaporation. By this method weget crystals of common salt from seawater.

The process by which a liquid isconverted into vapour by heating iscalled evaporation.

Let us know how we get thecrystals of common salt from seawater. Sea water is passed on to theprepared land surface. It is called saltpan. See Fig. 4.7. The sea waterevaporates by heat of the Sun. Thesalt remains in the land.

Activity 4.6

Take some salt solution in acontainer. Place the container on thewire gauze placed on a tripod stand.Heat the container strongly. When thewater evaporates salt is deposited inthe container See Fig. 4.8.

Fig. 4.8. Evaporation

4.3.8 Crystallisation

Substances like alum and coppersulphate have definite geometricalshape. These are called `crystals'. Toprepare crystals and to separate themfrom the impurities 'crystallisation'method is used.

The process of obtaining purecrystals by cooling hot concentratedsolution of a substance is called`crystallisation'.

Fig. 4.7. Salt pan

45


Activity 4.7

Copper sulphate is soluble inwater. Dissolve some copper sulphatecrystals in water taken in a beaker.Dissolve as much as possible to get asaturated solution. Filter this solutionand collect the filtrate in a china dish.See Fig. 4.9.

Fig. 4.9. Crystallisation

Place the china dish on a tripodstand fitted with a wire gauze. Heatthe dish. You can see a crust formingon the upper layer of the solution.Cool the china dish and drain theliquid below. You can see the purecrystals depositing in the dish. Thesecrystals can be dried using a filterpaper.

4.3.9 Sublimation

One more method followed forpurifying solid substances is`sublimation'.

Some solid substances whenheated are converted into gaseousstate without melting into a liquid.

When the vapours are cooled, theycondense back to solid state. Thisprocess is called `sublimation'.Substances like iodine, naphthaleneand ammonium chloride have thisproperty. So these substances arepurified by this method.

Activity 4.8

Take a mixture of ammoniumchloride and sodium chloride in achina dish. Cover the dish by aninverted funnel. Plug the opening inthe stem of the funnel with cotton.Thisprevents the exit of ammoniumchloride vapours. Place the china dishon a wire gauze placed over a tripodstand. Heat the mixture well.Ammonium chloride vapours riseabove and deposit on the cooler sideof the funnel. Sodium chlorideremains in the dish since it does notundergo the process of sublimation.See Fig. 4.10.

Fig. 4.10. Sublimation

AmmoniumChloride

AmmoniumChloride&SodiumChloride

46


SELF EVALUATION


1. The suitable method used to separate lighter particles from heavier onesin a mixture(a) Sieving (b) Winnowing(c) Crystallisation (d) Filtration

2. Identify the mixture in the following(a) oxygen (b) milk(c) gold (d) silver

3. When your mother makes tea from tea leaves, by which method does sheget pure tea decoction?(a) Filtration (b) Hand picking(c) Crystallisation (d) Evaporation

4. Substances with the same type of particles throughout are called____________.

5. The sand from muddy water is separated by _____________ .

6. The substance that is retained in the filter paper during filtration is called___________.

7. ______________ method is adopted for purifying alum.

8. What is the need for the separation of a mixture.

9. How is a mixture separated by winnowing?

10. For what type of mixtures sieving is needed for separation?

11. Can you use the method of magnetic separation to separate all mixtures?Give reason for your answer.

12. Explain the method of using a filter paper.

13. How is salt obtained from salt pans?

14. Mention the nature of `crystals'.

15. How will you separate the mixture of camphor and salt?

16. Write any two methods of separating lighter solid impurities from solidmixtures.

17. Explain the method of magnetic separation.

18. How is a suspension purified by the method of filtration?

19. Explain a method to separate a mixture of iodine and charcoal.

47


5. Changes around usIn our daily life, we observe

many changes around us. Everythingin this universe undergoes a change.These changes may be observed byus at school, home, play ground orgarden. For example sudden changein weather, flowering of plants,melting of ice, ripening of fruits,drying of clothes, milk changing intocurd. cooking of food, rusting of iron,bursting of fire - crackers etc. are thecommon changes that occur in day-to-day life.

The changes can bring aboutdifferent kinds of alterations in thethings around us. Some of thealterations brought about arepermanent in nature and hence cannotbe reversed. However, somealterations are brought about inposition, shape, size or state of thethings. These alterations are temporaryin nature and hence can be reversed.

Classification of changes :

(i) Slow and fast changes(ii) Reversible and irreversible

changes(iii) Desirable and undesirable

changes(iv) Periodic and non-periodic

changes

(v) Physical and chemical changes.

5.1 Slow and fast changes

Slow changes

The change that takes place overa long period of time, like hours, days,months or years is called a slowchange.

eg.

(i) Evaporation of water from lakesand rivers.

(ii) Curdling of Milk.

(iii) Growth of a baby into an adult(Fig. 5.1).

(iv) Rusting of iron in air

Fig. 5.1 Growth of a babyinto an adult

Fast changes

These changes occur withinseconds or minutes.

48


eg.

(i) Burning of match-stick (Fig. 5.2)

(ii) When an electric bulb isswitched on, it glows instantaneously.

(iii) A piece of cloth dipped inkerosene burns vigorously whenignited.

(iv) Burning of a paper.

Fig. 5.2 Burning of match-stick

Activity 5.1Take a green leaf and allow it to

get dried.Take a dry leaf and burn it.Which is a slow change here?

Activity 5.2

Take two China dishes. Placesome water in one dish and petrol inthe other.

Keep the two dishes in sunlight.Observe which is a slow change andwhich is a fast change?

5.2 Reversible and irreversiblechanges

Reversible change

The change in which the productcan be converted back into its original

form (reactant) is called reversiblechange. i.e. the change can bereversed.

eg.

(i) Water changes into ice oncooling. Ice on being warmedonce again becomes water.

(ii) An electric bulb has a metallicfilament. When electricity isswitched on, the filament in thebulb glows. When electricity isswitched off, the filament returnsto its original state.

(iii) When air is blown into a balloonit inflates. But it shrinks to itsnormal position when air isremoved (Fig. 5.3).

Balloon with air Balloon without air

Fig. 5.3

Irreversible change

The change in which the productcannot be converted back into itsoriginal form (reactant) is calledirreversible change. ie. the changecannot be reversed.

eg.

(i) When a candle is burnt, carbon-di-oxide and water are produced.But from these products thecandle cannot be obtained back.

49


(ii) When wood is burnt ash is leftbehind. You cannot get back thewood from the ash (Fig. 5.4).

(iii) An old man cannot becomeyoung again.

(iv) When a paper is burnt, it changesinto ash and smoke. Paper cannotbe obtained from ash and smoke.

Fig. 5.4 Burning of wood

5.3 Periodic and non-periodicchanges

Periodic changes

The changes which occur againand again at regular intervals of timeare called Periodic changes

eg.

(i) Phases of moon is a periodicchange (Fig. 5.5).

(ii) Change of seasons

(iii) Heart beat

(iv) Position of a moving swing orthe Pendulum of a clock

Non-periodic changesThe changes which do not repeat

themselves at regular intervals of time,are called non-periodic changes.

eg.

(i) Earth quake

(ii) Falling of ripened fruits from atree

(iii) Train accident

(iv) Landslides

(v) Volcano (Fig. 5.6)

Fig. 5.6 Volcano

Full moon New moon Full moonFig. 5.5 Phases of moon

Differences between periodic and non-periodic changes are given in Table 5.1

Table 5.1

S.No. Periodic Non-periodic

(i) They occur again and again at regular They do not repeat themselves.intervals of time.

(ii) They can be predicted (seasons) They can not be predicted (earth quakes)

50


5.4 Desirable and undesirablechanges

Desirable changes

Useful changes are known asdesirable changes

eg.

(i) Curdling of milk

(ii) Fuel is burnt while cooking

(iii) Dead plants turn into manure

(iv) Melting of snow on themountains in summer

Undesirable changes

The changes which are not usefulare called undesirable changes.

eg.

(i) Spoiling of food stuff.

(ii) Breaking of a glass tumbler

(iii) Burning of a house

(iv) Rusting of iron

5.5 Physical and chemical changes

Add two tea spoons of sugar intowater and stir it well. It dissolves andforms a clear solution.

Take two teaspoons of sugar ina china dish and heat it strongly. Sugarturns into a black powder (charcoal)with the liberation of steam.

Do you know the main differencebetween the above two processes.

In the first case, sugar can beregenerated from the solution by

evaporation of water. It is a physicalchange.

In the second case, sugar(reactant) cannot be obtained from theproducts charcoal and steam. It is achemical change.

5.6 Characteristics of physical andchemical changes

Physical change

A physical change is a temporarychange during which no newsubstance is formed.

Characteristics

(i) No new substance is formedduring a physical change.

(ii) It is temporary in nature.

(iii) It can be reversed easily byremoving the factors that causedthe change.

(iv) There may be some changes inthe physical properties of thesubstances such as colour, smell,state etc.

(v) The chemical composition of thesubstance remains unchanged.

eg.

(i) Switching of an electric heater

(ii) Dissolving sugar in water

(iii) Boiling of water, so as to formsteam

(iv) Glowing of an electric bulb

51


Activity 5.3

What happens when you put asmall ice cube into your mouth?

It melts into water. The heat fromthe mouth makes the ice melt.

Chemical change

A chemical change is apermanent change in which entirelynew substances are formed withdifferent properties.

Characteristics

(i) It is a permanent change

(ii) It is irreversible

(iii) New substances are formed

(iv) Energy in the form of heat orlight is either absorbed orreleased.

(v) The chemical composition of thenew substance differs from thatof the initial substance.

eg.

(i) Burning of candle

(ii) Ripening of fruits

(iii) Silver articles turning black

(iv) Fermentation of sugarcane juice,fruit juice etc.

(v) Cooking of food

Activity 5.4

Take few moist iron fillings.Keep them exposed to air. After a fewdays you will notice that the ironfillings are coated with brown rust.

Unlike iron, this rust is notattracted by a magnet. You cannotget back the iron from this rust. Hencerusting is a chemical change.

Activity 5.5

Take a small piece of paper andburn it. We get ash from the paper.From the ash we cannot make thepaper again. So this is a chemicalchange.

5.6.1 Dissolution

When a small amount of sugar isadded to water in a beaker and stirredwell, a clear solution is got. Here sugaris called solute and water is calledsolvent.

Dissolution is a process in whicha solute is dissolved in a solvent toget a solution.

Dissolution is a physical changeas the solute can be regenerated fromthe salt by evaporation.

Activity 5.6

To show that dissolution ofcommon salt in water is a physicalchange.

Take a beaker and fill half of itwith water. Add common salt to itand stir well. Now a clear solution isformed i.e. The salt is completelydissolved in water (Fig. 5.7). Nowheat the solution strongly. Water getsevaporated leaving behind the salt.From this you understand thatdissolution is a physical change.

52


Fig. 5.7 Dissolution of salt in water

5.6.2 Evaporation

Take some water in a containerand heat it. What do you observe?Water goes into its vapour state assteam.

The process in which a substancechanges from liquid state to gaseousstate on heating is called evaporation.

Evaporation is a physical changeas the vapour gives back the substancein a liquid state on cooling.

Activity 5.7

To prove that evaporation is aphysical change.

Take water in a container andheat it strongly. Water gets evaporatedas steam. Show a stainless steel plateover the beaker (Fig. 5.8). Watervapour (steam) condenses into waterdroplets at the bottom of the plate.From this you understand thatevaporation is a physical change.

Fig. 5.8 Evaporation

5.6.3 Boiling

Evaporation of liquids takes placeat all temperatures. But boiling takesplace only at a particular temperaturewhich is called the boiling point of thesubstance.

Boiling point of a liquid is definedas the temp. at which the vapourpressure of the liquid is equal to theatmospheric pressure.

eg. Boiling point of water is 100oC.

Boiling of a liquid is a physicalchange as its vapour can be convertedinto the liquid on cooling (Fig. 5.9).

Fig. 5.9 Boiling

Steam

Water

53


5.6.4 Condensation

If the vapour obtained whileevaporating a liquid is cooled, thevapour changes back to liquid. Thisprocess is called condensation. Steamon cooling forms water. Water onheating gives back steam. Hencecondensation is a physical change.

CoolSteam Water

Heat

eg.

When the water vapour presentin the clouds gets cooled, conden-sation occurs which results in rain.

Activity 5.8

During winter, go to the gardenin the early morning and have a lookat the grasses and plants. You can seeon them the dew drops formed due tothe condensation of water vapour inair.

5.6.5 Freezing

When a liquid is cooled below avery low temperature. It changes intosolid state. This process is calledfreezing and that temperature is calledthe freezing point.

Freezing is a physical change as

the solid on melting gives back the

liquid (Fig. 5.10).

Activity 5.9

Place a metal cup full of water,

in the deep freezer of the refrigerator.

After an hour, take it out. What do

you observe?

You can see the solid ice formed

due to freezing. Now heat the cup.

Ice melts to form water.

5.6.6 Melting

When a solid substance is heated

above a particular temperature it

changes into liquid state. This process

is called melting. That particular

temperature is called the melting point.

Melting point and freezingpoint of a substance are one andthe same.

Melting is a physical change as

the solid can be regenerated by

cooling the liquid.

Activity 5.10

Cut a candle into pieces and put

them in a container. Heat the

container. What happens? The wax

melts into a liquid. Now cool the

container. What happens? Solid wax

is regenerated.

><

cool

Water Ice

Fig. 5.10 Freezing

54


5.6.7 Sublimation

Some solids on heating, changedirectly into the vapour form withoutpassing into liquid form. This processis called sublimation. On cooling thevapour, we get back the solid. Henceit is a physical change.

Iodine, naphthalene andammonium chloride are examples ofsubstances that sublime.

Activity 5.11

Take iodine in a china dish andcover it with a perforated filter paper.Invert a funnel over the china dish.Close the tip of the funnel with acotton plug to prevent the vapours ofiodine from escaping. Place the chinadish on a wire gauze placed over atripod stand. Heat the china dish.Iodine sublimes and is deposited onthe cooler sides of the funnel. Iodinecan be scraped from the sides of thefunnel (Fig. 5.11).

Fig 5.11 Sublimation

5.6.8 Rusting of iron

When an iron lock is exposed tomoist air for several days, the iron on

its surface is converted into Iron oxide(rust). See Fig. 5.12. This process iscalled rusting. The rust cannot beeasily converted back into iron. Ironand Iron oxide (rust) have differentchemical properties. So rusting is achemical change.

Fig.5.12 Rusting of iron

5.6.9 Burning of fuel

When substances like fire wood,kerosene and petrol are burnt, heatenergy is liberated. Such substancesare called fuels. When a fuel is burnt,it produces new substances likecarbon-di-oxide, water and heatenergy. But from these substances thefuel cannot be regenerated. Henceburning of fuel is a chemical change.

Carbon-di-oxide producedduring the combustion of fuel, mixeswith atmospheric air. Carbon-di-oxidereflects the radiation from the Earthand increases the temperature of theEarth. When the temperature of Earthincreases, ice in the polar region meltsand the sea level increases. This maycause serious flood problems. Toreduce the amount of carbondioxidein atmosphere we should plant andgrow more trees.

55


5.6.10 Curdling of MilkTake luke warm milk in a cup

and pour some buttermilk into it. After4 – 5 hours you could see theformation of curd from the milk. Milkand curd are different substances withdifferent chemical properties. Curdcannot be converted into milk. Henceit is a chemical change.5.6.11 Fermentation

A solution of glucose in waterremains unchanged indefinitely. Ifhowever to this solution some yeastis added, after sometime the wholeliquid begins to froth and looks likeboiling. On testing it is found thatglucose has been converted into ethylalcohol and the boiling appearance isdue to the brisk evolution of carbon-di-oxide during the reaction.

Glucose Yeast ethyl alcohol +carbon-di-oxide

This chemical change is a fer-mentation process. Fermentation is aprocess by which a complex organicsubstance is broken into simplerorganic substances by the action ofyeast. Carbon-di-oixde is liberated asa bye product.

When a dough containing riceand black dal is kept for 10 hours, itferments in the presence of yeast. It issuitable to make soft iddli and dosai.5.7 Changes involve energy5.7.1 Exothermic changes

The changes during whichenergy is released in the form of heat

are called exothermic changes.

eg.

(i) Burning of fuels such as petrol,wood, kerosene etc.

(ii) Lighting of a match-stick.

(iii) Dissolution of sodium hydroxidein water.

Activity 5.12

Take a paper and light it. Whathappens? The paper burns andproduces heat.

5.7.2 Endothermic changes

The changes during whichenergy is absorbed in the form of heatare called endothermic changes.eg.(i) melting of ice

(ii) Evaporation of sea water. (Fig.5.13)

(iii) Decomposition of Baking Sodaon heating

Fig. 5.13Evaporation of

sea water

Activity 5.13Take Ice cubes in a vessel and

heat it.What happens?Ice absorbs heat and turns into

liquid water.

>

56


SELF EVALUATION


1. Which one of the following is not a chemical change?

(a) Souring of milk (b) Digestion of food

(c) Corrosion of metals (d) Drying of wet clothes

2. Which of the following is a periodic change?

(a) Blowing of wind

(b) Evaporation and condensation of water

(c) Growth of animals

(d) rotation of the earth

3. In a physical change

(a) The molecules of the substances do not change

(b) The molecules of the substances change

(c) Atoms forming the molecules undergo change

(d) New substances are formed

4. Classify the following as physical or chemical changes

(a) The explosion of a craker (b) Dissolving sugar in water

(c) Burning of a candle (d) Freezing of water

5. Cooking of food can be classified as ___________ change.

6. Evaporation of water is a __________ change.

7. Changes that repeat at regular intervels of time are called _____________

8. An Earthquake is a _________________ change.

9. Formation of day and night is ______________ change.

10. Exothermic reactions involve ________________ of heat.

11. Ripening of fruits is a ____________ change.

12. What is a fast change? Give an example.

13. What is an irreversible change? Give an example.

57


14. What is a non-periodic change? Give an example.

15. Define a chemical change.

16. What is a desirable change? Give an example.

17. What are exothermic reactions? Give an example.

18. What is meant by fermentation? Give an example.

19. What is rusting?

20. Is curdling of milk a chemical change? Why?

21. Mention the characteristics of chemical changes.

22. Evaporation is a physical change. Justify.

23. How will you prove that condensation is a physical change?

24. Freezing is a physical change. Prove it.

25. Why is rusting of iron a chemical change?

26. What is the effect of carbon-di-oxide liberated by the burning of fuels?

58


Things are available around us.They are at rest or moving. Forexample books, chairs, buildings,pictures hanging on wall and trees arefound at rest. Moving bicycle, movingcar, moving bus, kicked football andflying bird are found moving.Eventhough you are sitting at oneplace, the blood is circulating throughthe blood vessels in your body, yourlungs are expanding and contracting,and your heart is beating. All movingthings are said to be in motion.

6. Force and Motion

6.1 Rest and Motion

See a car or a bicycle parkedoutside a building. Is it really at rest?Afterall it is resting on the Earth. Weknow that the Earth is moving on itsown axis and also around the Sun.Since the building is also resting onthe Earth, so the car or bicycle is atrest relative to the building.

Consider you are travelling in amoving bus. If you see the trees onthe side of the road, they seem to

Fig. 6.1 Moving and Stationary objects

59


move in opposite direction. Actuallythey are at rest. If the bus is at restthen the trees are also at rest. If thebus moves, then the trees are movingin opposite direction. Hence, rest andmotion are relative to each other.

A football player is alwayschanging his position during thegame. See the flying bird as shown inFig 6.1. Since, it is changing itsposition time to time it is called asmotion. Hence change in position ofa body is called motion. If a bodydoes not change its position it is calledat rest. A body is said to be in motionwhen it changes its position.

Activity 6.1

Look at the objects around you.Identify which are in motion? Whichare at rest?

S.No. Object Motion / Rest

1.

2.

3.

6.2 Types of motion

Recall the motion of a car or buson a straight road, march-past by thestudents on a sports day, falling of acoconut, motion of the striker incarrom board, motion of second's

Fig. 6.2a Linear motion

Fig. 6.2b Linear motion Fig. 6.2c Linear motion

60


Fig. 6.2e Oscillatory motion

hand of a clock, motion of the bladesof an electric fan, motion of the wheelin the bicycle, motion of the top,motion of the pendulum in the clock,motion of the swing, motion of theacrobat in circus, motion of the Eartharound the Sun and motion of themoon around the Earth.

Can you differentiate the motionsin the above examples? If the objectis moving along the straight path, itis called linear motion (Figs. 6.2a,6.2b and 6.2c). If the object is movingin circular path it is called circularmotion or rotational motion (Fig6.2d). If the motion is to and fro abouta fixed point it is called oscillatorymotion (Fig 6.2e). If the motion isrepeated in regular intervals of timeit is called periodic motion. If themotion is repeated but the interval oftime is not equal, it is called non-periodic motion.

Activity 6.2

List out a few examples ofmotion. Identify the different types ofmotion.

6.3 Motion along a straight line

We know the different kinds ofmotion. The simplest and common ofall these motions is the motion alonga straight line.

6.3.1 Distance and Displacement

Fig. 6.3 Distance and Displacement

Consider your house is at theposition A and your school is at theposition B as shown in Fig 6.3. Youand your brother are starting to theschool. You are walking from A to Bdirectly by covering 1000 m. Yourbrother goes to his friend's house atC and then comes to the school bycovering 1100 m. The distance walkedby you is 1000 m and the distancecovered by your brother is 1100 m.

The actual length of the path thatbody travels is called distance. Notethat the distance travelled will bedifferent for different paths betweenA and B.

Fig. 6.2d Circular motion

200 m900 m

1000 mA B

CE

N

61


The shortest distance betweenthe two positions is calleddisplacement. The distance in aparticular direction is calleddisplacement.

In the above example, thedistance is either 1000 m or 1100 m.In both cases the displacement is1000 m towards East direction.

6.3.2 Speed

Recall your speed of walkingwhile going to the school. Your schoolis at 1000 m (1 km) distance fromyour house. You are walking slowlyand reach the school in 20 minutes.Your brother walks fast and reach theschool in 10 minutes. What does itmean? You are covering the distancein more time and your brother coversthe same distance in less time. Henceyour speed is less and your brother'sspeed is more.

The distance travelled by a bodyin unit time (1 second) is called speed.

speed =

6.3.3 Velocity

The speed in a particulardirection is called velocity. That isthe velocity is defined as the rate ofchange of displacement.

Velocity =

Both speed and velocity are

measured by or

6.3.4 Uniform and non uniformmotion

When the speed of an objectmoving along a straight line remainssame, its motion is called uniformmotion.

The following observations weretaken when the motion of a bodytravelling with uniform speed wasstudied.

Time (second) 0 1 2 3 4 5

Distance (metre) 0 5 10 15 20 25

It is possible to study the motionof a body by using graphs (Fig. 6.4).In such graphs, the time is plotted onthe X-axis and the distance is plottedon Y-axis.

Y-axis

X-axis

Fig 6.4 Graphical representationof Uniform motion

When a body travels withuniform speed its graph will be astraight line passing through theorigin.

distancetime

displacement

time

ms

metresecond

25

20

15

10

5

0

1 2 3 4 5

TIME

DIS

TAN

CE

62


When the speed of a body doesnot remain same, the motion is callednon-uniform motion.

6.4 Force

We are always pushing or pulling.We have a special name for a push orpull ; we call it as force. Forces areeverywhere around us and a fewexamples are shown in drawings

(Fig. 6.5). Look at each picture andthink about what forces are acting.

How do we recognise a force? Ifyou put a football in the middle of afield, it will remain there withoutmoving until a force is applied to it.The force may be caused by the windblowing it or by someone kicking it,or by someone picking it up. In eachcase force causes motion.

Fig. 6.5 Forces around us

63


6.4.1 Effects of force

(i) Force causes motion

When you kick a stationary ball,it moves in the direction of the force.When it is picked up, it moves in thedirection of the upward force. If afootball hits a wall, it will bounce offit. If it hits the wall at an angle, itwill bounce off at an angle ; the forceof the wall has deflected the motion.The direction of the force is veryimportant.

A force can also decrease themotion or stop it. A moving footballcan be stopped by the force exertedwhen it hits a player. A parachuteattached to a jet plane when it islanding causes a force to be exertedon it and this slows it down. We canrecognise a force as something whichchanges motion.

Hence, a force is a push or pullwhich changes the motion of an objectby speeding it up or slowing it downor changing its direction of motion.

(ii) Force changes the shape and size

Take an empty water bottle.Observe the shape of it. Squeez it byapplying force. What happens to theshape? The shape has been changedfrom cylindrical to irregular.

You must have observedkneeding of wheatflour to makepoori ; while making poori we first

take some dough and rool it betweenthe palms to make it spherical. Thenwe change the shape of rooled doughinto a poori with the help of a rooler.

In both these situations changein shape or size or both of the objecttakes place due to the force appliedon them. The figure 6.6 shows somecommon examples of change in sizeand shape of objects on theapplication of force.

Fig. 6.6 Force changes the shape

6.4.2 Unit of force

The unit of force is expressed interms of the force of gravity. That isthe force applied by the Earth onevery object. If you hold 1 kilogramweight in your hand, the forceexperienced by you is due to thegravity of the Earth. This force isnearly ten times the unit of force,which is known as newton. The unitof force called newton after Sir Issac

64


Newton, a great scientist. The abbre-viation for 1 newton is 1 N. Here 1 Nis just about the weight of a 100 grammass of any object in your hand.

6.4.3 Types of forces

We have learnt that a push orpull is known as force. In daily life,we push or pull many things. Whilelifting things we pull them. We haveseen elephants lifting heavy logs ofwood. We also see animals likebullocks, horses and camels pullingcarts (Fig 6.7). In these cases, themuscles of human being and animalsapply forces. Such force is calledmuscular force.

Fig. 6.7 Muscular force

We have seen that forces changethe motion of a body. If we roll a ballon the cement floor and another ballon the polished floor, in the secondcase the ball moves fast and longdistance than in the first case. Ithappens because of frictional forces.Friction arises when surfaces of twoobjects are in contact.

Probably the most common forceis the force of friction. Friction has

some strange properties. It cannotmove a body, it can only oppose themotion and the size of the force canvary automatically.

If a body is in motion and thereis frictional force acting on it, it canbe brought to rest by that force. Ifthere is no force on it, the movingbody will go on for ever.

When forces act on a movingbody its motion will be changed. Butif the forces are in equilibrium, themotion is not changed. For examplelet us consider the motion of anaeroplane as shown in Fig. 6.8. If theforward thrust (force) due to theengine of an aeroplane is equal to thebackward force due to air resistance(friction) the forces are in equilibriumand the aeroplane moves at a constantspeed. If they were not in equilibrium,the aeroplane would speed up or slowdown depends on which force wasgreater.

Fig. 6.8 Motion of an aeroplane

We usually think of friction asnuisance ; we apply oil in machinesto reduce it. But most of the time it isessential to us. Think how difficult it

65


is walking on a slippery surface. Inwalking, there has to be a forwardforce due to friction and it is this forcewhich moves us forward. If there wereno friction, there could not be anyforward force and we could not walk.

Muscular force and frictionalforces act on the bodies in contact.There are some forces which act onthe bodies which are not in contact.We are all aware of the gravitationalforce pulling everything towards thecentre of the Earth. It is thisgravitational force which causes amango to fall from a tree or a brick tofall to the floor when we let go of it(Figs. 6.9a and 6.9b). It is this gravita-tional force between a body and theEarth which we call the weight of thebody.

It was Sir Isaac Newton who firstrealised that there is a force ofattraction between two bodies. It isusually a very small force, but if oneof the masses is the Earth then theforce is very much greater and we areall aware of it.

The Earth is revolving around theSun and the moon is revolving aroundthe Earth (Figs. 6.10a and 6.10b).These are also due to gravitationalforce.

Since the mass of the moon ismuch smaller than that of the Earth,the gravitational force on objects isless on the moon. This means that the

Fig. 6.9a Falling brick

Fig. 6.9b Falling Mango

Fig. 6.10a Motion of the Earth around the Sun

Fig. 6.10b Motion of the moon around the Earth

66


Fig. 6.11 Magnetic Attraction

attractive (pull) sometimes they arerepulsive (push).

Activity 6.3Take a small magnet and find out

what things are attracted to it(Fig. 6.11). Pieces of paper? A paperclip? A piece of cloth? A plasticcomb? A screwdriver? A piece ofwood? The metal end of a hammer?Sticks in a match box? Pins? Coins?Bottle caps? What sort of thingsattracted to it?

weight of a given body will be less onthe moon than it is on the Earth. Theweight of anything on the moon isabout one sixth of its weight on theEarth.

Like gravitational forces thereare other forces which act betweenobjects that are not in contact.Magnetic forces can be felt byholding the ends of two magnetstogether. Sometimes the forces are

Activity 6.4

Sprinkle some iron fillings on apiece of paper. Try picking up the ironfillings with the magnet. Are thefillings attracted to both ends of themagnet? They should be like thedrawing shown in the Fig. 6.12. Thetwo ends are called the poles of themagnet.

Fig. 6.12 Magnetic Poles

67


Activity 6.5

Hang up the magnet by a cottonthread so that it hangs freely. When ithas come to rest, you may notice thatthe magnet is lying approximately ina North - South direction. A freelysuspended magnet always comes torest like this.

The pole at the end which pointstowards the north is called North -seeking pole or for short, a Northpole; the other pole, the South -seeking pole or for short, a South pole.This is an important property of amagnet and it is used as a compass. Ina simple compass, a small magnet isbalanced on a sharp point (Fig. 6.13)

Activity 6.6

Bring two magnets end to endnear each other. What do you observe?You might find that they attract eachother or repel each other, that is goaway from each other.

You can come to the conclusionthat North pole attracts South pole,

South pole attracts North pole ; Southpole repels South pole. This pull orpush exerted by magnets is known asmagnetic forces.

You might have seen the magneticdoors in almirahs and refrigerator.They stick due to magnetic force. Thisforce is used in separating waste ironobjects from the garbage dumb andto lift the objects in the crane (Fig6.14).

Fig. 6.14 Magnetic attraction

Like magnetic force, there isanother force which acts between theobjects which are not in contact.

Activity 6.7

Blow up two rubber balloons.Attach a long thread to each and hangthem up from a horizontal thread asshown in the Fig. 6.15.

Fig. 6.13 Magnetic Compass

68


Fig. 6.15 Balloons

Rub one of the balloons withyour sleeve. Then rub the otherballoon similarly. What happens whenthe balloons come near to each other?What happens when you put yoursleeve near either of the balloon? Theyare repelled away from each other inthe first case and attracted towardseach other in the second case.

Activity 6.8

Blow up a balloon and rub it ona carpet. Then put the balloon againstthe wall of a room or touch the ceilingwith it (Fig. 6.16). Does it stay therewhen you let go?

Fig. 6.16 Balloon stick on the wall

Activity 6.9

Rub a ballloon on a carpetand hold it near to a jet of water

(Fig. 6.17). Does the jet of water bendtowards the balloon?

Fig. 6.17 Jet of water

Activity 6.10

Comb your dry hair (Fig. 6.18a)or rub the comb on a woollen cloth.Hold the comb over some small piecesof paper on a table (Fig. 6.18b). Doesthe pieces of paper move towards thecomb?

Fig. 6.18a Fig. 6.18b

Attraction of paper pieces

These are all strange effects. Thisattraction or repulsion what we callpull and push is due to the electricforces. The electric forces arise due

69


to the two electric charges namelypositive and negative charges. Let ushave a detailed discussion of thesecharges in the next year, 7th standard.

6.5 Pressure

In the previous section, you havelearned about forces. You know thatit matters in what direction they areapplied and where they are applied.In this section, you will learn that theeffect of force can also depend on thearea over which the force is applied.Here are few examples for you tothink and discuss.

(i) If you push a drawing pinagainst a very hard surface, how doespushing the pin in Fig. 6.19a differfrom pushing as in Fig. 6.19b usingthe same push in each case?

(a) (b)Fig. 6.19 Pushing the pin

(ii) It is more painful to standbarefooted on small gravels than it isto stand barefooted on a smooth floor.Why?

(iii) Farm tractors have wheelswith large, wide tyres (Fig. 6.20).Why?

The outcome of the discussionsis the fact that effect of a force ismore when the area of contact issmaller.

To push on the point of adrawing pin is painful. To supportyour weight on a small area of contactis painful. It is similar in the case ofgravel also.

Tractors with small narrow tyreswill sink more easily into soft ground.Can you think of other examples,which show that the effect of a forceis less when the area of contact islarge?

You must have observed cuttingof a wood. It is very easy to cut itwith an axe of sharp edge. But it isnot possible to cut with blunt edge.In the first case the force is appliedover a smaller area, hence the effectis more. In the second case the sameforce is applied over a larger area,hence the effect is less.

The ratio of the force and thearea on which it acts is known aspressure. In other words pressure isequal to force per unit area.

Pressure =Forcearea

Fig. 6.20 Tyres of Tractor

70


In SI units the force is measuredin newton (N) and area is measured insquare meter (m2). Thus the unit ofpressure is N/m2. This unit is alsocalled as pascal (pa) after Pascal, ascientist.

6.5.1 Pressure of liquids

Connect a small and largesyringe together as shown in theFig. 6.21. Fill it with water. Thereshould be no air in the system.

Fig. 6.21

Hold the small syringe. Whilepushing the water from the largesyringe into it, feel the forces. Thenpush the water from the small syringeinto the larger one. Again feel theforces. You will find the forcesdifferent because of different areasinvolved.

In the above experiment it isnoticed that liquids also exert apressure.

Activity 6.11

a) Take a tin can and make holesin it with a round nail. It is better tokeep a block of wood inside the canwhile making the holes. Put the holesat different places round the can but

at the same level. Take care to makethe holes of the same size. Fill the canwith water and watch how the watercomes out (Fig. 6.22a).

Fig. 6.22a

b) Take another can and makeequal holes, one near the bottom, onenear the top and one in the middle.Fill the can with water and watch howthe water flows out through theseholes (Fig. 6.22b).

Fig. 6.22b

c) Take a third can and make itinto an irregular shape. Make holesin three or four different places. Fillit with water and watch what happensthis time (Fig. 6.22c).

Fig. 6.22c

SmallSpringe

LargeSpringe

71


This experiment shows that thepressure is greater at the bottom thanat the top because water comes outfaster where the pressure is greater.You will also notice that the watercomes out at right angles to thesurface. It does not continue in thatdirection because gravity acts on thejet and it falls towards Earth, but italways starts at right-angles to thesurface.

Water pressure is very importantwhen building a dam or the wall of areservoir. Engineers build dams withthe wall thicker at the bottom than atthe top (Fig. 6.23). Why?

Fig. 6.23 Dam

The pressure exerted by liquidsincreases with increasing depth. Inother words, the pressure decreasesas one moves up in the fluid.

Activity 6.12

Take a rubber ball. Put severalholes in it using a pin. Fill the ballwith water. If you squeeze it, wateroozes out with equal forces throughall the holes (Fig. 6.24). From theabove experiment it is a known factthat increase in pressure at a point

within the liquid at rest iscommunicated equally to every otherpoint within it. This principle is knownas Pascal’s law.

Fig. 6.24 Verification of Pascal's law

A liquid seeks its own level.

It is often said that water alwaysfinds its own level. What does itmean? And what is the cause of it?

Two glass tubes should be heldvertically and joined at the bottom byrubber or polythene tubing. Put a clipin the middle so that water cannotflow from one side to the other(Fig. 6.25a). Put some coloured waterin the left hand tube so that it is nearlyfull and less coloured water in theright hand tube.

Fig. 6.25a

We know that the pressuredepends on the depth of the water. Itis greater at A than at B.

72


As a result, when the clipsopened, water will flow from A to B.It will continue to flow until thepressures are same, in other wordsuntil the water levels are the same.The shape of the tubes does not makeany difference as shown in the teapot(Fig. 6.25b) or the odd - shaped glasscontainer (Fig. 6.25c).

Fig. 6.25

Spirit level

The spirit level is used for testingthe horizontality of a surface. Itconsists of a closed glass tube bentinto an arc of a circle and filled witha liquid such as alcohol, leaving asmall air bubble inside as shown inthe Fig. 6.26. This tube is mountedwithin a metal case provided with aplane bottom.

Fig. 6.26 Spirit level

The instrument is so constructedthat when it is placed on anyhorizontal surface, the air bubbleremains at the top of the tube. If it isplaced at any surface and if the airbubble is not at the top position, thesurface is not horizontal and suitableadjustments should be made.

6.5.2 Pressure of gases

Gases also exert a pressure. Ifyou put your finger over the outlet ofa bicycle pump and push the handle,you will feel the force produced bypressure. If you blow up a balloonwith a small hole into, the air willcome out of the hole.

Atmospheric pressure

The atmospheric air also exertsthe pressure. We are so used to thispressure. We do not usually notice it.

Fig. 6.27 Collapsing can

Take a rectangular can withairtight cap as shown in the Fig. 6.27.Put a little water in the bottom of thecan and boil it vigorously with thetop open. The water vapour will drivemuch of the air out of the can. Thenclose the top. Allow the can to cooldown. What happens to the can? Thewater vapour inside will condenseback to liquid.

The pressure inside will be muchless than the atmospheric pressureoutside and the can will collapse. (Donot use the can with petrol or anyother inflammable liquid).

73


Activity 6.13

A tumbler is filled with water anda piece of paper is put on the top. Itis important that there are no airbubbles in the water. With your handholding the paper on the tumbler, turnit over and remove your hand. Whydoes the water stay in the glass?(Fig. 6.28)

Fig. 6.28

Activity 6.14

A sheet of newspaper is placedover a thin piece of wood on a tableas shown in the Fig. 6.29. If a smallsteady force is applied to the end ofthe wood, what happens? If you givea sudden sharp blow to the wood,what happens? Explain the difference.

Fig. 6.29

Activity 6.15

A drinking straw is filled withliquid. Place a finger over both ends

and hold the straw vertically. Whenyou take your finger off the bottom,the liquid stays in the tube. Why isthis?

6.5.3 Measuring pressure

Manometer is the useful devicefor measuring pressure difference.This is a U-shaped tube of glass orclear plastic partially filled withliquid. If the tube is open at both endsthe level of the liquid will be the sameon both sides. The pressure of theatmosphere is of course pressingdown on the liquid surfaces. Since itis same on both sides the level arethe same (Fig. 6.30a).

Fig. 6.30a Fig. 6.30b

Attach a rubber tube at one sideof the tube and blow the air. Henceyou are raising the pressure on oneside. Now the levels of liquid will bedifferent as shown in the Fig. 6.30b.

When the liquid is at rest, thepressure at A will be the same as thepressure at B. The pressure at B willbe equal to the sum of the pressure ofthe atmosphere and the pressure dueto the column of liquid ‘h’. The excessof pressure is ‘h’ of centimetre ofliquid.

74


6.5.4 Liquid pressure detector

Take a small funnel of innerdiameter 8 cm. Cover its mouth tightlywith a stretched membrane (balloonrubber). Connect the funnel to theother end of the rubber tube with themanometer (Fig 6.31).

Push the funnel into a widemouthed can containing water. Whathappens to the water level in the tubeas you lower the funnel into water.You will see that difference betweenthe levels in the arms of themanometer goes on increasing. Thisshows that pressure in liquidsincreases with depth.

6.5.5 Bourdon gauge

Fig. 6.32a

Fig. 6.32b

Bourdon gauge is the deviceused to measure the pressure. You are

Fig. 6.31

Curved Tube

75


familiar with the toy shown in Fig.6.32a. The harder you blow (greaterpressure) the more it uncurls. TheBourdon gauge works on the sameprinciple. The greater the pressureapplied, the more the curved tubeinside straightens out and this movesa pointer across a scale (Fig. 6.32b).Bourdon gauges are calibrated tomeasure the pressure directlyin N/cm2.

6.5.6 Barometer

The barometer tube is usuallymade of thick glass of strength and itis sealed at one end. Fill it completelywith mercury (Fig. 6.33a). Wearinggloves, a finger is then placed overthe open end of the tube. This end isthen lowered and held below the

surface in a trough of mercury(Fig. 6.33b). Can any air get into thebarometer tube when the finger istaken away? Clearly there is no wayin which it can.

When the finger is removed, themercury level in the tube will fall (Fig.6.33c). The height of the mercury is'h' in the tube. The pressure at B dueto the column of mercury is the sameas the atmospheric pressure at A(Fig. 6.33d).

As no air got into the tube, whatwill there be in the top of the tube atC? It is vacuum.

You can now measure theatmospheric pressure in centimetresof mercury by measuring theheight 'h'.

Fig. 6.33 Barometer

76


What happens to the height if thebarometer tube is inclined at an angle?The level of mercury raises in the tubeas no air is available (Fig. 6.33e). Thelevel of mercury does not depend onthe size of tube (Fig. 6.33f).

Usually the height 'h' of mercuryin the tube is 76 cm. This shows thatthe atmospheric pressure is 76 cm or760 mm of mercury.

This barometer is known asTorricelli barometer used to measurethe atmospheric pressure.

As we go up in the atmospherethe pressure goes on decreasing.People going to places of highattitude, experiences bleeding throughnose. This happens due to drop in theatmospheric pressure outside. As aresult of this, the blood pressurebecomes higher than the atmosphericpressure.

Similarly the pressure goes onincreasing as we go deeper and deeperin the ocean. That is why deep - seadivers wear special suits to managethe pressure.

Activity 6.16

Visit a petrol pump. Observe theinstruments which is used to measurethe pressure in the tyres of vehicles.List out the values of the air pressurein vehicles.

VEHICLEPRESSURE

Front RearWheel Wheel

Scooter

Motor cycle

Car

Lorry / Bus

Fig. 6.33 Barometer

77


SELF EVALUATION


1. The motion of the floating body in water waves is _________.

2. The unit of speed is ____________.

3. The wheel of a bicycle performs __________ motion.

4. When the football player hits the ball, its speed will _________ .

5. When you throw a ball upwards, its speed will __________ .

6. Name the three types of motion.

7. What are the types of motion involved in a moving bicycle?

8. If you are sitting in a moving bus, are you at rest or in motion?

9. Give two examples of periodic motion.

10. An object is hung from a spring, pulled down and left. What type ofmotion does the object perform?

11. What is called speed?

12. Define velocity.

13. Give two examples of objects changing their speed while in motion.

14. What happens to the speed of your bicycle when you pedal faster?

15. What happens to the speed of your bicycle when you apply brakes to it?

16. Give two examples of linear motion.

17. Which type of motion does the foot of a tailor perform while sewing somecloths on sewing machine?

18. A train moves with a speed of 120Km/hr. What is the distance travelled byit in 1 minute?

19. A snail moves a distance of 3 metres in 300 seconds. What is the speedof the snail?

20. Give two examples of rotational motion.

21. The distance between the staff room and your class room in your schoolis 40 metres. If your teacher takes 80 seconds to come to your class, findout his/her speed.

78


22. Identify the types of motion in the following examples.

a) The motion of the top

b) The motion of the pendulum in wall clock.

c) The motion of the wheels of a bullock - cart.

d) The motion of your friend in running race.

23. A body moves 10 metres in 10 seconds. Further it moves 50 metres in50 seconds. Find the speed in both the cases. Is the motion uniform ornon-uniform?

24. _____________ force makes a rolling body stop.

25. To collect the iron dusts from the floor ________ force is used.

26. The unit of force is ____________.

27. The direction of a freely suspended magnet is along ___________ .

28. ___________ force is used by the elephants in lifting heavy logs of wood.

29. What are the effects of forces?

30. Name the types of forces.

31. Which force is responsible for raising our body hair when we try to takeoff a polyester shirt on a dry weather?

32. It is difficult to walk on the highly polished floor. Give the reason.

33. Give two examples of muscular force.


(i) The force involved in the falling leaf from a tree is (a) magnetic force (b) electric force (c) gravitational force (d) muscular force

(ii) The force which is responsible for wearing out of a bicycle tyre is (a) magnetic force (b) electric force (c) gravitational force (d) frictional force

35. Why does the shape of a tooth paste tube change when we squeeze it?

36. Give two examples from your daily life where force changes the shapeof the object.

37. What happens to the spring of a sofa when you sit on it?

38. To stop the bicycle or car, we have to apply the brake. Which force acts?

39. Name the two forces which act on the bodies in contact.

40. What is the necessity of using oil in the machinery parts of a bicycle?

41. The gravitational force on the moon is less than that on the Earth. Why?

42. If your weight is 30kg, what will be your weight on the moon?

79


43. Name any two objects available in your house that are attracted by amagnet.

44. Which pole of a magnet will repel the south pole of another magnet?

45. Which force is used in cranes in the harbour to lift heavy load?

46. Give examples of each of the following.(a) A force exerted on something which starts it moving.(b) A force exerted on something which stops it moving.(c) A frictional force exerted by gas.(d) A gravitational force on a moving body.(e) An electric force.

47. Name the types of forces involved in the following :(a) A magnetic door catcher (b) A person lifting the weight(c) Balloons moving away from each other after they are rubbed against a nylon.

48. Farm tractors have wheels with large, wide tyres. Why?

49. Suggest one reason why football players have studs on their boots.

50. You can carry a suitcase comfortably by the handle. But if you have nohandle and you tie the case with string, why is it very painful carryingthe case with your hand through the string?

51. What is called pressure?

52. What is the unit of pressure?

53. Dams are built with thick walls at the bottom. why?

54. State Pascal’s law.

55. What is the use of spirit level?

56. Name the device used to measure the pressure.

57. A boy has a mass of 50 kg. The gravitational field exerts a force of 10newtons on each kilogram. If the total area of his shoes in contact withthe ground is 100 cm2. What is the pressure exerted on the ground?

58. What is the value of normal atmospheric pressure?

59. Name the device used to measure the atmospheric pressure.

60. People going to places of high altitude experiences bleeding through nose.Why?

61. Deep sea - divers use to wear special suits. Why?

62. Illustrate Pascal’s law with the help of a simple experiment.

63. How will you measure the atmospheric pressure with a barometer?

80


You are certainly familiar withthe word work. We speak about doingwork digging a garden or lifting sacksof rice. We may say we are doingsome hard work, reading a sciencebook. But this everyday use of theword work is a bit vague. In sciencea precise meaning has been given towork.

Work is said to be done if theforce is able to move a body. We areusing the machines to do work. Theability to do the work is called energy.We need energy to do work. Energyexists in different forms. Energy canbe converted from one form intoanother form. This idea of science isvery much useful in the developmentof technology.

7.1 Work

If you lift an object above theground, you do work. If you pull someobject up a hill or take the bucket ofwater from a well, you have donesome work.

In the above cases, you haveapplied some force and the objectmoves. In science, work is said to bedone only if the force moves anobject. If you push the wall, the wall

does not move. Eventhough you areapplying the force, since the wall isnot moving, work is not done.

Suppose you lift a bag of 10 kgrice through 1 metre (Fig. 7.1a).Hence you are doing work. Then lifta bag of 20 Kg rice through 1 metre(Fig. 7.1b). Here also you are doingwork. In the first case you are movingthe bag through a distance of 1magainst the force of gravity 100N. Inthe second case you are moving thebag through the same distance of 1 magainst the force of gravity 200N.Hence the work done in the secondcase is double the work done in thefirst case.

a b cFig. 7.1

If you lift the rice bag of 20Kgthrough a distance of 1/2 metre (Fig.7.1c). the work done is same as thework done in the first case.

Thus there is a relation betweenwork done, force applied and thedistance moved.

7. Work and Energy

81


When the object moves in thedirection of applied force, work doneis the product of force and the distancethrough which it moves.

Work done = Force × distance moved

The work is measured by the unitjoule denoted by J after the scientistJoule. Let us find the work done inthe above cases.

(i) In the first case

Work done =100N x 1m = 100J

(ii) In the second case

Work done =200N x 1m = 200J

(iii) In the third case

Work done =200N × 1/2m = 100J.

7.2 Work and machine

We do various kinds ofwork in our daily life. Lifting an

object, pushing or pulling the object,climbing on a staircase, opening adoor, pulling the bucket of water fromthe well, opening the lid of a milkpowder tin, opening the lid of coco-cola bottle are some of the work doneby us in life. We can perform thesework easily with the help of machines.A machine is a device which makeswork easier to do. Machines havechanged the quality of our life. Amachine can do work only after workhas been done on it.

We use different kinds ofmachines such as electric lift, tractor,bicycle, sewing machine, crane,pulley, a screw driver, a pair ofscissors, opener, nail cutter, nutcracker and crowbar.

Machines like pulley, crowbar, apair of scissors, inclined plane, wedgeare known as simple machines(Fig. 7.2).

Fig. 7.2 Some simple machines

82


Machines like electric lift,tractor, bicycle, sewing-machine andcrane are called as complex machines(Fig. 7.3). Complex machines aremade up of two or more simplemachines.

Fig. 7.3 Complex Machines

7.3 Simple Machines

Simple machines are used toincrease the effect of force or changethe direction of the applied force orboth. There are six kinds of simplemachines. They are (i) the lever,(ii) the inclined plane, (iii) the wedge,(iv) the screw, (v) the wheel and axleand (vi) the pulley (Fig. 7.4).

Fig. 7.4 Six kinds of simple machines

7.3.1 The lever

Look at the Figs. 7.5 (a) and7.5 (b) of the two ways, which one iseasier to shift the object?

In Fig. 7.5a number of personsare required to lift and shift the object.But by using a rod resting on a

support (Fig. 7.5b) one person alonecan do the same work. The crowbaris an example of lever.

Fig. 7.5a Fig. 7.5b

The lever is the simplestmachine. We are familiar of it. It is abar. It is a free to move about a pointon which it rests. The point on whichthe lever is at rest is called fulcrum (F).The body to be shifted is called loador resistance (L). The applied forceis called effort (E).,

Levers are classified into threeclasses namely (a) first class lever, (b)second class lever and (c) third classlever.

(a) First class lever

If the fulcrum is in between theload and effort, it is called first classlever (Fig. 7.6).

Fig. 7.6

The examples of first classlever are tongs, scissors, see-saw(Fig. 7.7).

83


(b) Second class lever

If the load is in between thefulcrum and effort, it is called secondclass lever (Fig. 7.8).

Fig. 7.8

Wheel barrow, nut cracker andopener are the examples of secondclass lever (Fig. 7.9).

Fig. 7.9 Examples of Second class levers

(c) Third class lever

If the effort is in between loadand fulcrum, it is called third classlever (Fig. 7.10).

Fig. 7.11 Examples of third class levers

The examples of third class leverare fishing rod, fire tongs and spade(Fig. 7.11).

Do you want to balance yourfather’s weight?

Fig. 7.7 Examples of First class levers

Fig. 7.10 Fig. 7.12 See-saw

84


You must have played on a see-saw. It is possible for you to balanceyour father or mother, if both of yousit in the right place. How is itpossible? Try this activity in thebullock-cart or in the see-saw avai-lable in the park (Fig. 7.12). Knowthe science of see-saw and understandthe secret of the balancing act.

The above principle of lever isused in weighing machines like steelyard. This is a lever of the first class.Its one arm is much smaller whencompared to the other arm. Thebalance is supported at the fulcrumby means of a hook as shown in Fig.7.13. The unknown load is suspendedat the smaller arm. A movablestandard weights slides over the longarm, which is graduated in kilograms.Hence, a heavy load placed at a verysmall distance is balanced with a smallweight placed at a larger distance. Youcan see such balances on railwayplatforms.

Fig. 7.13 Steel Yard

7.3.2. The inclined plane

To put an object on the back ofa lorry, the object could be lifted(Fig. 7.14a) on or it could be pushed

Fig. 7.14

up with an inclined plank (Fig. 7.14b).In the first case it is very difficult andmore effort is required.

In the second case, the plankenables us to do it more easily andless effort is required. An inclinedplane is a surface reaching from onelevel to a higher level at an angle.

Roads in hilly regions, astaircase, flyovers are examples ofinclined plane.

7.3.3. The screw

A screw is really an inclinedplane wound upon a cylinder. Cut asheet of paper in the form of rightangled triangle, and wind it on to apencil as shown in the Fig. 7.15.

Fig. 7.15 The screw is aninclined plane wound upon a cylinder

The common screw is used forjoining section of wood or inconjunction with a nut, for holding asection of wood or metal in place.

A screw jack isused to lift a car or abus for changingwheels (Fig. 7.16).

Fig. 7.16ScrewJack

85


7.3.4 The wedge

Fig. 7.17a

The wedge is really a doubleinclined plane (Fig. 7.17a). A woodcutter’s wedge, a knife and an axeare the examples of wedge. We haveto move an object up on an inclinedplane but we have to move a wedgethrough the object. For example,during slicing of an apple, the knifeis through the apple. Fig. 7.17b showshow a wedge is used for woodcutting.

7.17b Using a wedge

7.3.5 The wheel and axle

When a wheel is used with anaxle, it is considered as a simplemachine. An axle itself is a kind of a

wheel. Hence, a wheel and axleconsists of two wheels of differentsizes attached together as shown inthe Fig. 7.18a.

The common examples of wheeland axle are windlass (Fig. 7.18b), asteering wheel of a car (Fig. 7.18c)and bicycle pedal (Fig. 7.18d).

7.3.6 Gears

Gear wheels usually have teethon them which mesh with one anotheras shown in the Fig. 7.19a.

Fig. 7.18 Wheel and axle and examples

If you rotate one wheel, otherwheel also rotates. All the teeth havesame size. Wheels of different sizeshave different numbers of teeth. Ifwheel B in the diagram (7.19b) has

Fig.7.19a, & 7.19b Principle of Gears

AB

86


twice as many teeth as wheel A, thenA will turn round completely twice forevery complete turn that A makes.

If you turn the wheel A, energyis transferred to wheel B and itsload.

If the handle is fixed to B, let 10rotations be given to lift an object. Ifthe handle is attached to A, we haveto give 20 rotations to lift the sameobject, but the turning force will besmall.

7.3.7 The Pulley

A simple pulley has a wheel thatrotates around a fixed point calledfulcrum. A rope or a string or a chainpassing over the pulley is used toconnect the load and the force applied(Fig. 7.20a)

Fig. 7.20

A single pulley is a lever of firstclass. If you pull the rope at one end,the weight moves up. Thus, the forceapplied in downward direction ischanged into force in upwarddirection. The pulley is used to changethe direction of the force. You mighthave seen the pulley in the flag poleof your school.

Pulleys are mostly used to liftobjects. A combination of pulleys maybe used to lift a heavy load with asmall force (Fig. 7.20b). You mighthave seen a crane lifting heavy loadswhich are based on the principle ofpulleys.

Archimedes, a famous scientistof ancient times, is said to be theoriginator of lever as a machine.

Thus, the machines are used totransform the energy, to transfer theenergy, to increase the force, toincrease the speed and to change thedirection of force.

7.4 Work and Energy

You might have heard phraseslike feeling energetic or having noenergy. You might have seenadvertisements for food which "giveyou energy." What is meant by thisword energy? You need energy to liftthings, to ride a bicycle, to hammernails. If you play a hard game offootball or Kabadi and if you runabout a lot, then you feel tired andhungry at the end. And you need toeat before you can do much more.

7.4.1 Energy

Work can also be done byengines of various kinds. Bus cancarry people up a hill, cranes can liftmasses, electric motors can pump thewater. Do these engines need a supplyof energy? Yes. A bus engine needs

87


diesel or petrol. An electric motorneeds electric current. In the same waythat human beings need to be fed,engines need to be fed with fuel.Hence, work and energy are related.The ability to do the work is calledenergy.

Energy is stored not only in food,but also in petrol, diesel, wood, coaland gas (Fig. 7.21).

Fig. 7.21 Some sources of energy

7.4.2 Different forms of energy

Energy exists in different forms.One form of energy can be convertedinto another form.

(i) Potential energy

Look at the stone lying on theground (7.22a). Has it got any energy?

Fig. 7.22

Can it do a job of work?

Suppose the stone is picked upand put on the table (Fig. 7.22b). If itfalls from the table to the ground, itis capable of doing work. It couldcertainly burry a peg into the ground(Fig. 7.22c) or it could make a dentin your foot.

Consider the raised stone isattached to a load over a pulley asshown in the Fig. 7.22d. The fallingstone can lift the load

As in the diagram 7.22e. thefalling stone can pull the load. In bothcases, the raised stone is capable ofdoing work. In other words it hasenergy. But, when the stone hasreached the floor, it cannot lift or pullthe load further.

The stone has this energybecause of its position at the top ofthe table. Similarly, water at a heighthas energy; and in falling can do

88


useful work, like turning a wheel.(Fig. 7.23) The turning wheel canrotate the coil. Energy due to positionis called potential energy. It is alsocalled as possible energy and storedenergy.

Fig. 7.23 Falling water turning a wheel

A body can have this storedenergy in various ways. Height is oneway. Here are some other ways. A

(ii) Kinetic energy

Keep a thin wooden plank on thefloor as shown in the Fig. 7.27. Placea brick on the wood. It is unable tobreak it. Now raise up the brick to aheight of 1 metre so that it has gotpotential energy. Then, release thebrick. It falls on to the wood and thistime it does break it.

Fig. 7.24 Compressed spring in a gun

compressed spring in trying to releaseitself can do work (Fig. 7.24). Astretched rubber band can do work in

restoring itself to its original state(Fig. 7.25). Both the compressedspring and the stretched rubber bandhave potential energy. Few moreexamples are shown in the Fig. 7.26.

Fig. 7.25 Stretched rubber

Fig. 7.26

When the brick is falling down,its potential energy becomes less.When it reaches the wood, itspotential energy is left and it breaksthe wood. Therefore it must havesome other kind of energy to do thatwork. This is energy due to its motion,we call it as motion energy or kineticenergy.

A moving cricket ball can knockover the stumps (Fig. 7.28). A movingcar gets lot of damage if it hitssomething (Fig. 7.29).

brick on plank falling brick broken plank

Fig. 7.27

89


Wind, which is air motion, canturn the sails of a windmill (Fig. 7.30).The wind can push the sails of a boat

and move it forward along the surfaceof water (Fig. 7.31). Water in motioncan turn the paddles of a water wheel(Fig. 7.32). All these are able to dothe work because of the energy dueto their movement.

Both the potential energy andkinetic energy are called asmechanical energy.

(iii) Chemical energy

Wood, coal, petrol, diesel and gashave energy stored in them. Thisstored energy is potential energy, butwe call it as chemical energy. Thechemical energy of wood, coal, petrol,diesel and gas can be released byburning them. It is used to do the worklike cooking food, producing light anddriving the machines. In the processof photosynthesis, the green plants

Fig. 7.29 Damaged car after a collision

Fig. 7.28 Knocked stumps

Fig. 7.30 Sailsof a windmillturning inbreeze

Fig. 7.31 Wind moving a sail boat

Fig. 7.32 Flowing water turning a wheel

90


store the energy of the Sun in the formof chemical energy. The food we eathas the chemical energy. Our body cando all the work with this energy.

(iv) Heat energy

If you rub your palms together,due to friction, they become warm.The mechanical energy of your handhas been changed into heat. When youburn the coal or wood heat isproduced. The steam formed due toheat is able to do work. The steamwill rotate the blades of turbine ingenerators to produce electricity(Fig. 7.33).

Fig. 7.33 Steam turbine

(v) Light energy

The hot filament in an electricbulb gives off light. A piece of redhot iron is visible in a dark room.That emits light. Sun is the biggestsource of light energy. Green plantsuse the light energy to prepare theirfood (photosynthesis). Light willaffect a photographic film, so that wecan take a picture with a camera. Light

will change the coloured material tofade. Since, light is used to do work,it is also energy called light energy.

Using solar cell, you can actuallymake light energy to lift a small object(Fig. 7.34). The light from the Sunfalls on the solar cell produceselectricity, which turns a motor. Hencethe object is lifted. Solar cells convertlight energy into electricity. Solar cellsare used in satellites and space stationto produce electricity.

Fig. 7.34 Solar cell

(vi) Sound energy

Sound is also a form of energy.When a body vibrates or oscillates, itproduces sound. When you strike thediaphragm of a miruthangam it startsvibrating and sound is produced. Ifyou pluck the string of violin,it produces sound. If you make theair to vibrate in flute andnadhaswaram, sound is produced. Inthe loudspeaker and telephonereceiver the electrical energy isconverted into sound energy.

91


(vii) Magnetic energy

A magnet has the ability to dothe work by attracting an iron nailfrom a distance. Hence the magnetpossesses the energy called magneticenergy. In the electric call bell, magnetattracts the hammer; the hammerstrikes the gong, hence sound isproduced. In the cranes, magneticenergy is used to lift the objects. Inthe loudspeaker, the magnetic energyis used to reproduce the sound.

(viii) Electrical energy

A torch cell and a car batterycan heat a wire (Fig. 7.35) or light abulb (Fig. 7.36). The chemical energystored in the cell is converted intoelectrical energy. Electrical energy isused to produce heat in a heater.

Electrical energy is used toproduce motion. When you switch ona fan, it starts rotating. Electricalenergy is also used to produce sound,in a call bell or in a horn of a car.Some of you might have seen electrictrains used for moving people andgoods trains (Fig. 7.37).

Fig. 7.35 Electricalenergy can heat a wire

Fig. 7.36 Electricalenergy can light a bulb

Fig. 7.37 Electrical energy moving a train

The fuel, coal burnt, in thethermal power stations produceselectricity.

7.4.3 Energy conversions

Consider three familiarhappenings; the glowing of an electrictorch; the burning candle; the burningof coal.

In the torch light, the bulb givesout light energy. This is obtained fromthe electrical energy. This electricalenergy is given by the cell from thechemical energy stored in it.

Chemical electrical lightenergy energy energy

Cell Bulb

In the burning candle, thechemical energy of the candle isconverted into light energy and heatenergy.

Chemicalenergy light energy

Candle

Heat energy

In the coal fire, in the act ofburning, the coal changes the chemi-cal energy to heat energy.

> > >

>>

>Candle

92


> >

(ii) The coil is made to move by theenergy from the wind in windmill - electric power station.(Fig. 7.38).

(iii) The coil is made to move by theenergy from the coal (Thermal -electric power).

Chemical energy Heat energyCoal

These are all examples ofconversion or transformation ofenergy. Energy is capable oftransformation from one form toanother form. This is known asconservation of energy.

7.4.4. Technological applications

If you press the switch, theelectricity comes. Have you everthought of where the electricity comesfrom? It is produced in many ways. Inan electric torch, it comes from thechemical nature of the cell, but in largescale it is prodced by a machine,called a generator. A generator is theenergy converter, changing the kineticenergy of the coil, moving betweenmagnets into electrical energy. The coilcan be made to move in many waysas mentioned below.

(i) The coil is made to move by theenergy produced by burningdiesel (Diesel generator).

Fig. 7.38 Wind mill

Fig. 7.39 Hydro electric power station

93


SELF EVALUATION


1. What is a machine?

2. The machine which can change the direction of force is ________ .

3. Steel yard is working on the principle of ________ .

4. Choose the correct answer :

(i) The energy possessed by the compressed spring in a gun is

(a) Kinetic energy (b) Heat energy(c) Potential energy (d) Sound energy

(ii) The energy possessed by a torch cell is

(a) Chemical energy (b) Kinetic energy(c) Light energy (d) Magnetic energy

5. What is meant by work in science?

6. In what unit is work measured?

7. What is the work done, measured in joule, when the 10 Kg mass is raisedthrough 10 metres?

8. Name the six classes of simple machine.

9. Give one example for each simple machine.

(iv) The coil is made to move bymoving or falling water availablein Hydro - electric power station(Fig. 7.39).

(v) The coil is made to move by theenergy from the Uranium atom(Atomic - electric power).

In our state, Tamil Nadu, theelectricity is generated at thefollowing places.

There are hydro enerctic powerstations Mettur and Papanasam.

There are thermal power stationsat Neyveli and Tuticorin.

There is a windmill power stationat Aralvaimozhi.

There is an atomic power stationat Kalpakkam. At Koodangulam,atomic power station is underconstruction.

94


10. What is lever?

11. Show the positions of fulcrum, the effort and the load in three classes oflever in the diagram.

12. What is inclined plane?

13. Give two examples of inclined planes.

14. Identify the levers of first, second and third class from the following

(a) Human arm (b) A pair of scissors

(c) Wheel barrow (d) Beam balance

(e) A pair of tongs (f) Crowbar

(g) Lemon squeezors (h) Pliers

(i) Bottle opener (j) Spade

15. What is the use of a single pulley?

16. Why does a person find it easier to get an object on to the lorry using theinclined plane?

17. Draw diagrams of two common levers in everyday use.

18. What is the use of screw jack?

19. What is energy?

20. What is potential energy? Give two examples of bodies that have potentialenergy.

21. What is kinetic energy? Give two examples of bodies that have kineticenergy.

22. Name some devices that change

(a) Electrical energy into Light energy

(b) Electrical energy into Mechanical energy

(c) Electrical energy into Heat energy

(d) Chemical energy into Electrical energy

(e) Sound energy into Electrical energy

(f) Electrical energy into Sound energy

23. When a lathe is used in a metal workshop, there is usually a flow of liquidon to the cutting tool. What is the reason for this?

95


24. Chemical energy from the petrol is necessary to start moving a car fromrest. Some of the chemical energy is transferred to motion energy of thecar, but not all of it. Suggest whatelse the chemical energy turned into.

25. State the energy conversion in the following :

(a) Solar cell

(b) Lighting a match

(c) Call bell

(d) Electric fan

26. State the sources of chemical energy.

27. Name the fuel used in thermal power station.

28. What is known as conservation of energy?

29. Identify the energy possessed by the following :

(a) Compressed air in a balloon.

(b) Cricket ball thrown by a bowler

(c) Moving bus

(d) Wind moving a sail boat

30. Explain the energy conversion in your bicycle dynamo.

31. What are the ways to rotate a coil to produce electricity?

32. Mention the places where electric power is produced.

SCIENCESTANDARD VI

TAMILNADU TEXTBOOK CORPORATIONCOLLEGE ROAD, CHENNAI - 600 006.

Untouchability is a Sin

Untouchability is a Crime

Untouchability is a Inhuman

CHAIR PERSONDrDrDrDrDr. S. . S. . S. . S. . S. GUNASEKARANGUNASEKARANGUNASEKARANGUNASEKARANGUNASEKARAN,,,,, M.Sc., Ph.D.

ReaderPost Graduate and Research Department of Physics

Pachaiyappa's College, Chennai - 600 030.

© Government of T© Government of T© Government of T© Government of T© Government of Tamilnaduamilnaduamilnaduamilnaduamilnadu

First Edition 2003

Wrapper design : M. RAMDOSS

Price Rs.

This book has been printed on 60 GSM paper

REVIEWERSREVIEWERSREVIEWERSREVIEWERSREVIEWERS

N.A. MASILN.A. MASILN.A. MASILN.A. MASILN.A. MASILAMANI, AMANI, AMANI, AMANI, AMANI, M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.HeadmasterGovt. Hindu High School,Rasathupuram, Vellore District - 632 509

B. ILB. ILB. ILB. ILB. ILANGOANGOANGOANGOANGOVVVVVAN, AN, AN, AN, AN, M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.P.G. Assistant in ChemistryKarnataka Sangha Hr. Sec. School,T.Nagar, Chennai - 600 017.

DrDrDrDrDr. . . . . A.J. BENSAM, A.J. BENSAM, A.J. BENSAM, A.J. BENSAM, A.J. BENSAM, M.Sc., Ph.D.M.Sc., Ph.D.M.Sc., Ph.D.M.Sc., Ph.D.M.Sc., Ph.D.HeadmasterGovt. Hr. Sec. School,Savalaperi & P.O. Thoothukudi Dt.

STELLSTELLSTELLSTELLSTELLA PRONE, A PRONE, A PRONE, A PRONE, A PRONE, M.Sc., M.Ed., M.PhilM.Sc., M.Ed., M.PhilM.Sc., M.Ed., M.PhilM.Sc., M.Ed., M.PhilM.Sc., M.Ed., M.Phil.....P.G. Assistant in ZoologyDr. K.K. Nirmala Girls Hr. Sec. School,Ashok Nagar, Chennai - 600 083.

AUTHORSAUTHORSAUTHORSAUTHORSAUTHORS

S. RASARASAN, S. RASARASAN, S. RASARASAN, S. RASARASAN, S. RASARASAN, M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.P.G. Assistant in PhysicsGovt. Hr. Sec. School,Kodambakkam, Chennai - 600 024.

S.S.S.S.S. SEEMAN, SEEMAN, SEEMAN, SEEMAN, SEEMAN, M.Sc., M.A., M.Ed.M.Sc., M.A., M.Ed.M.Sc., M.A., M.Ed.M.Sc., M.A., M.Ed.M.Sc., M.A., M.Ed.B.T. AssistantGovt. Hr. Sec. School,Nellikuppam - 603 108.

G.G.G.G.G. SIVSIVSIVSIVSIVAKAMI, AKAMI, AKAMI, AKAMI, AKAMI, B.Sc., M.Ed.B.Sc., M.Ed.B.Sc., M.Ed.B.Sc., M.Ed.B.Sc., M.Ed.P.G. Assistant in ChemistryGovt. Boys Hr. Sec. School,Nanganallur, Chennai - 600 061.

PPPPP..... VENKAVENKAVENKAVENKAVENKATTTTTAAAAACHALCHALCHALCHALCHALAPAPAPAPAPAAAAATHYTHYTHYTHYTHY, , , , , B.Sc., B.Ed.B.Sc., B.Ed.B.Sc., B.Ed.B.Sc., B.Ed.B.Sc., B.Ed.B.T. AssistantGovt. Girls Hr. Sec. School,Arakonam, Vellore Dt. - 631 003.

A. PARIMMALA. PARIMMALA. PARIMMALA. PARIMMALA. PARIMMALA DEVI, A DEVI, A DEVI, A DEVI, A DEVI, M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.P.G. Assistant in BotanyGovt. Girls Hr. Sec. School,Ashok Nagar, Chennai - 600 083.

PPPPP. GO. GO. GO. GO. GOVINDVINDVINDVINDVINDA RAJAN, A RAJAN, A RAJAN, A RAJAN, A RAJAN, M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.M.Sc., M.Ed.P.G. Assistant in BotanyMunicipal Hr. Sec. School,Cuddalore - 1.

KANNAKI PRABAKARAN,KANNAKI PRABAKARAN,KANNAKI PRABAKARAN,KANNAKI PRABAKARAN,KANNAKI PRABAKARAN, M.Sc., M.Ed., M.Phil. M.Sc., M.Ed., M.Phil. M.Sc., M.Ed., M.Phil. M.Sc., M.Ed., M.Phil. M.Sc., M.Ed., M.Phil.P.G. Assistant in ZoologySri R.K.M.Sarada Vidyalaya Model Girls Hr. Sec. School,T.Nagar, Chennai - 600 017.

M. MARGARETM. MARGARETM. MARGARETM. MARGARETM. MARGARET, , , , , M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.M.Sc., M.Ed., M.Phil.P.G. Assistant in ZoologyGovt. Boys Hr. Sec. School,Chinnasalem, Villupuram Dt.

Typeset by : THE MOTHER COMPUTER GRAPHICST.Nagar, Chennai-17. : 24312209

PrefaceThis Science book has been prepared as a single discipline; that is as an

integrated science. Much effort has been taken in reforming and updating this

text book in Science at the upper primary stage. The following points have been

kept in mind while preparing the subject matter :

Minimum levels of learning principles have been applied.

A fresh look has been given to concepts at this stage.

Importance has been given to develop scientific and technological

values among the learners. Few technological applications have also been

included at this level.

The subject matter has been presented in simple language.

Number of activities have been included in the text. These activities

are simple. They can be carried out at school or at home.

This book introduces the subject in terms of the students' personal

experience. A strong foundation of scientific theory is laid.

Questions are frequently asked in the body of the text and a number

of questions have been given at the end of each chapter.

For the examination purpose, teachers are instructed to frametheir own questions (Fill in the blanks, Choose the correct answer,True/False, Matching, Short answer questions etc.,) from the contentsincluding activities and not to adhere only to questions available forself evaluation.

– Textbook Committee

CONTENTS

CHAPTER PAGE NO.

1 Our Earth ..................................................................................... 1

2 Measurement................................................................................. 13

3 Nature of matter .......................................................................... 28

4 Separation of substances............................................................. 40

5 Changes around us ...................................................................... 47

6 Force and motion ......................................................................... 58

7 Work and energy ......................................................................... 80

8 Characteristic features of life .................................................... 96

9 Biodiversity ................................................................................... 113

10 Structure and functions of the living systems ......................... 129

11 Our Environment ......................................................................... 145

12 Applied Biology ............................................................................ 159

13 Health and Hygiene ..................................................................... 172

M1 \ F \ FINAL-BIO-EN.P65

96

8. Characteristic Features of Life

The branch of science dealingwith living organisms is calledbiology. Biology includes the studyof plants and animals.

Can you differentiate livingthings from non-living things? Thatis not at all difficult. For example,what is the difference betweenyourself and a doll? You can walk,eat, see and do many works. Does adoll perform all these activities?However, the above mentionedcharacteristics of living organismsmay not be seen in all livingorganisms. Because majority of theplants can neither move from oneplace to another nor eat as we do.

Can we consider these plants as onewithout life?

Animals including man dependdirectly or indirectly on plants fortheir food requirements. Plantssynthesise their own food byphotosynthesis. This importantactivity cannot be performed by manand animals in nature.

The plant world is an uniqueworld for the reason that it providesfood for all living organisms. Besidesfood, plants provide us oxygen andmaterials for clothing, shelter,medicines etc. Forests are specificallyvery important for good rainfall.

Fig. 8.1 Man and his environment


97

In our life, eating, growth,metabolism, sensation, locomotion,reproduction etc. are the importantactivities. These activities are notconfined to man alone. They are alsoseen in animals. These are thecharacteristic features of livingorganisms.

8.1 Nutrition

What did you eat this morning?Why do you eat? Do plants eat?

All organisms require food ornutrients for carrying out life activitiessuch as movement, growth,reproduction, etc. As plants preparetheir food with the help of chlorophyllof the leaf by the process ofphotosynthesis (Fig. 8.2), they arecalled producers.

Fig. 8.2 Plants synthesise food by photosynthesis

As chlorophyll pigment is absentin animals, they cannot synthesisefood. Plants, animals, pebbles, soil,

wooden articles, etc. are found aroundus. Among these plants and animalsare living organisms and remainingare non-living things. Food is verymuch necessary for all livingorganisms. Is n’t it?

Activity 8.1

Prepare a list of names of plants,animals and non-living objects foundaround you.

8.1.1 Importance of nutrients

For performing activities such asgrowth, movement, reproduction, etc.organisms obtain energy fromnutrients only. They get these nutrientsby two modes.

(i) Autotrophic mode of nutrition.(Self dependent)

(ii) Heterotrophic mode of nutrition.(depend on other sources)

8.1.2 Autotrophic nutrition

The synthesis of food materialsby the plant themselves constitutesautotrophic nutrition. Algae andother green plants are autotrophs. Asthis ability is not found in otherorganisms, they depend on plantseither directly or indirectly for theirfood requirements. Hence the plantsare called as producers.

The organisms which use plantsonly as food are called herbivores.eg. cow, buffalo and sheep. The

CO2

O2

leaf

<

<


98

organisms that eat the herbivores likesheep, cattle and deer are called ascarnivores. eg. lion, tiger etc. Thosewhich eat both plants and animals arecalled omnivores. eg. man, dog. Ifthe above said herbivore, carnivoreand omnivore are arranged in a series,it is clearly observed that energy flowsfrom plants to other organisms. Thisreveals that the energy level (Fig. 8.3)is stabilised by plants.

Fig.8.3 Energy level - plants are the basis forenergy requirements of other organisms

1. Producer 2. Primary consumer 3. Secondaryconsumer 4. Tertiary consumer 5. Omnivore

8.1.3 Heterotrophic nutrition

Animals, Fungi and majority ofbacteria which obtain their nutritionfrom plants and animals whetherliving or non-living. This mode ofobtaining nutrients from other sourcesis known as heterotrophic mode ofnutrition. This is classified into threetypes.

(i) Holozoic nutrition

The process by which anorganism engulfs plant or animal as awhole is called holozoic nutrition.Certain fungi obtain their nutrition byswallowing bacteria and spores of theother fungi. Among animals, theunicellular organism Amoeba feeds onmicro organisms by swallowing.

(ii) Parasitic nutrition

Certain organisms obtain theirnutrition by way of affecting otherorganisms. In such situation theaffected organism is called host. Thehost becomes a victim of diseases.This is called parasitic mode ofnutrition. For example, malaria feveris caused by a parasite calledPlasmodium. Similarly plants are alsoaffected by parasites.

(iii) Saprophytic nutrition

The mode of obtaining nutrientsfrom decaying organic materials ofplants and animals is known assaprophytic mode of nutrition.Agaricus (mushroom) obtainsnutrition in this method.

Activity 8.2

During rainy season, you canobserve the appearance of mushroomson dead woods. Observe a small partof the fungus through a microscope.You will find minute thread likestructures. Some of these mushrooms

5

4

3

2

1


99

are used as food. At times, in yourhome, you can observe cotton likestructures growing over beans, breadetc. The cotton hlike structures arenothing but the saprophytic fungi.When observe through a microscope,you will see how the body of thefungus is made up of thread likestructures called hyphae.

Activity 8.3

Indicate the mode of nutrition ofthe following organisms.

S.No. Organism Mode of nutrition

1 Fish ...............................

2 Goat ...............................

3 Earthworm ...............................

4 Frog ...............................

5 Elephant ...............................

6 Cockroach ...............................

7 Man ...............................

8 Sparrow ...............................

9 Lizard ...............................

10 Snail ...............................

11 Cat ...............................

12 Hen ...............................

8.1.4 Basic components of food

We have already studied aboutthe importance of food for organisms

for their growth and other activities.The food that we eat containsnutrients such as carbohydrate,protein, fat, water, vitamin, minerals,etc. in proper proportions is knownas balanced food. For proper growthand good health, balanced food isessential.

(i) Carbohydrate

Carbohydrate provides energy.Rice, sugar, sweetpotato, potato,millets and ragi are the rich sourcesof carbohydrates.

(ii) Protein

Proteins are important forgrowth. eg. pulses.

(iii) Fat

It provides energy and the excessamount of energy is stored as a reservein the form of fat. Vegetable oils andbutter contain fat.

(iv) Water

Water is very much essential forall organisms right from the microbesto man and plants. One can live forseveral days without food but notwithout water. Our body is made upof several hundred crores of cells. Theprotoplasm in every cell contains 90%of water. Similarly the body of plantsand animals contain large quantity ofwater.


100

(iv) Vitamins

Vitamins regulate the growth andmetabolism. The vitamins are rich inGreen vegetables, egg, milk etc.

(iv) Minerals

They are involved in biochemicalreactions. The minerals are present ingreen vegetables, wheat, etc.

8.2 Growth

Growth may be defined as thedivision of one cell to two cells, twoto four and four to eight cells andmore and these cells are differentiatedinto organs of the body. Observe thestages of growth that take placeduring the growth of plants and man(Figs. 8.4. and 8.5).

Fig.8.4 Stages in growth anddevelopment of plants

Fig.8.5 Stages in growth and

development of man

Activity 8.4

Observe the growth of plants andanimals like tomato, cucumber, chick,kitten and puppy.

Different types of plants andanimals have different life span(Fig. 8.6). Plants are of various types.They range from unicellular bacteriato gigantic banyan tree that is madeup of innumerable cells. Generally inplants growth occurs due to a kind oftissue called meristematic tissue. Themeristematic tissue is found at the tipsof stem and root and it is responsiblefor the vertical growth of a plant.

The type of growth seen in plantsis of unlimited type ie. plant growscontinuously unlike that of animalsin which growth is limited. After aperiod of time there will not be growthin animals.

8.2.1 Limited and unlimited growth

Unicellular organisms such asbacteria and yeast grow neithercontinuously nor into big size. Thistype of growth is known as limitedgrowth; but you have seen higherplants that develop into trees and growcontinuously. This type of growth iscalled unlimited growth. The growthand development of flowers andleaves are limited one.

The banyan tree develops froma very small seed only. Because ofunlimited growth, the small seeddevelops into a gigantic tree.


101

Activity 8.5

Soak some seeds in water for aspecific time. Take them out and plantin your garden or a pot. Allow themto germinate. After they germinate,observe closely. Record the changesthat occur in the seedlings. Measurethe height of the seedlings every dayand record.

Activity 8.6

Measure and record the heightof a potted plant in centimetres. Countthe number of leaves branches budsand flowers and record their numbersEveryday observe the changes thatoccur in the plant and record. Youwill see an increase in the height of the

plant, appearance of new leaves,branches, buds and flowers.

8.2.2 Factors affecting the growth

Factors that affect or regulate thegrowth of organisms are known asgrowth affecting factors or growthregulators. Several kinds of factors areinvolved in the growth of organisms.Among these, external factors play animportant role. The external factorsinclude biological factors, chemicalfactors and physical factors.

Generally the rate of growth ofplants in summer is restricted and low.One of the reasons for this is theinsufficient availability of water. Herewater is an external factor to controlthe growth of the plants.

8.6 Span of life of plants and animals

1 Week

20 daysFewyears Many

years80-100 years

70-90 years

45-50 years

16-18 years2-3 years

1-4 months

Amaranthus

Shoeflowerplant

Mushroom

Sequoia

3,000 - 4,000 years

House fly

Rat Dog

Ostrich

Elephant

Man

Mango tree


102

Many internal factors are alsoimportant for the growth of organisms.For example, for the uniform growthof plants, growth substances calledhormones are very important. As thesehormones are formed in the plantitself, they are called internal factors.Similarly, in animals and man, severalkinds of growth hormones areproduced for regulating the growth.

8.2.3 Different sizes of animals

Unicellular organisms suchas Amoeba, Euglena andParamaecium are micro organismswhich cannot be seen with the nakedeyes. The body is made up of singlecell. These can be seen only with thehelp of microscopes. But all small andlarge organisms that can be seen withthe naked eyes are multicellularorganisms. Their body is made up ofmany cells. eg. Hydra, fish and man.They are found to be in different sizes

and shapes. Compare an ant to that ofan elephant. Which one of theseanimals is large in size Definitely youknow that it is the elephant. Theanimal which is many times largerthan elephant is blue whale (Fig. 8.7).

Activity 8.7

Arrange the animals given belowaccording to their sizes. House fly,ant, butterfly, sparrow, cow, goat andcamel.

Activity 8.8

Give four examples in the tablegiven below :

S. Unicellular MulticellularNo. organisms organisms

1 .................. ..................

2 .................. ..................

3 .................. ..................

4 .................. ..................

8.3 Metabolism

Metabolism may be defined as agroup of interrelated biochemicalreactions that occur in living cells.

Fig. 8.7

WhaleElephant Man Bird Snake


103

8.3.1 Types of metabolism

Metabolism may be divided into(i) anabolism and (ii) catabolism.

(i) Anabolism

This involves biochemicalreactions resulting in the synthesis oflarger biomolecules from simplemolecules. eg : Photosynthesis

(ii) Catabolism

This involves biochemicalreactions resulting in the breakdownof larger molecules to smaller ones.eg. Digestion.

8.3.2 Photosynthesis

Photosynthesis means synthesisor formation of starch with the helpof light. During photosynthesis, starchis synthesised with the help ofchlorophyll pigment, carbon-di-oxide,water and the light energy of the Sun.Plants alone can carry outphotosynthesis. Without plants, noother organisms in the world can live.Hence it is not an exaggeration to saythat plants support the life of all otherorganisms in this world (Fig. 8.2).

Destruction of plants in theforests is the main reason for poorrainfall. Forests control thetemperature in the biosphere.

Activity 8.9

You can grow different kinds ofplants in and around your house andin the school campus.

8.3.3 Energy content of food

Food is a substance whichprovides energy to the body. The foodconstituents are proteins,carbohydrates, fats, mineral salts,water and vitamins. Energy ismeasured in terms of calories.

One gram carbohydrate yields4.1 calories of energy, 1 gram ofprotein releases 4.0 calories of energyand 1 gram of fat gives 9.3 caloriesof energy.

8.3.4 Bio-chemical nature of lifeactivities

Chemical reactions that aretaking place in a living organisms arecalled bio-chemical activities. Inrespiration, digestion and bloodcirculation bio-chemical activities aretaking place. Digestion is an activityin which the food is digested torelease energy. Respiration involvesintake of oxygen and release ofcarbon-di-oxide. Blood circulationmeans the transport of the nutrientsand oxygen to different parts of thebody and the removal of carbon-di-oxide and other wastes to theexcretary organs through the blood.

In addition to it, metabolicactivities, removal of waste materialsthrough excretary organs, co-ordination activity of nervous systemand activities related to reproductionthat take place in the living cell are


104

examples for bio-chemical nature oflife activities.

8.4 Stimulus and response

The excess secretion of Saliva onseeing delicious food and immediatewithdrawal of feet as soon as you walkon the hot surface are calledresponses. Here food and heat whichcause responnses are known asstimulus.

The cockroach that is very muchactive in darkness, immediately runsaway and hides, when you switch onthe light. In this activity of cockroachyou can infer that the light is stimulusand hiding of cockroach is response.

8.4.1 Types of stimuli

All organisms have the ability ofperception. Organisms respond to thestimuli. The response may beobserved immediately under certainsituations. Sometimes, the responsemay be delayed. The stimulus may benatural or artificial.

(i) Natural stimulus

The flowers of jasmine,Nyctanthes and Morinda blossom atnight time. The lotus flower opens inday time and closes at night. Theenvironmental factor sunlight is actingas a stimulus. Similar to this there areseveral external factors act as stimuli.In telegraphic plant (Desmodiumgyrans) the lateral leaves show

movements up and down during theday time (Fig. 8.8).

Fig. 8.8 Desmodium gyrans

(ii) Artificial stimulus

The response caused in anorganism due to the touching on itssurface is called thigmotropism. Inthe touch-me-not plant (Mimosapudica) when the leaflets are touched,they immediately fold up. After sometime they return to the normalcondition (Fig. 8.9).

Fig. 8.9 Mimosa pudica

Activity 8.10

(i) Touch the leaflets of touch-me-not plant and observe.

(ii) In plants such as green gram andblack gram, the leaves foldduring night time and open inthe day time. Observe thesemovements.


105

8.4.2 Responses of organisms inrelation to the stimuli.

Depending upon the externalfactors such as sunlight, water,temperature and chemical substances,plants show various responses.

(i) Phototropism

The movement of parts of anorganisms towards sunlight is knownas phototropism. Potted plants keptnear the windows, (Fig.8.10) bend andgrow towards the direction of light.

Fig. 8.10 Phototropism

(ii) Hydrotropism

The movement of parts of anorganism towards water is known ashydrotopism. Growth of rootstowards the source of water isexample for hydrotropism (Fig. 8.11).

Fig. 8.11

Hydrotropism

(iii) GeotropismThe movement of parts of

organism towards the gravity isknown as geotropism. The growth ofroots towards the direction of gravityis an example for geotropism (Fig.8.12).

Fig. 8.12 Geotropism

8.4.3 Sense organs

Sense organs are the organswhich help to communicate withenvironment. Lower organisms do notpossess well developed sense organs.But higher animals have welldeveloped sense organs such as eye,ear, nose, tongue and skin.

(i) Eye

When you observe an object, thelight rays coming out from the objectpass into the eyes through the pupiland eye lens. These light rays areconverged on the retina to form aninverted image. From retina themessage will be taken to the brainthrough the optic nerves. You are ableto see that object, when you get theinformation from the brain (Fig. 8.13).

Fig. 8.13 Eye1. Pupil 2. Light rays 3. Retina

4. Optic nerve 5. Eye lens

(ii) Ear

The waves of the sound passthrough the air and enter the ear. The

2 5 4

31


106

vibrations caused by the sound wavesover the ear drum will be passed onto the inner ear through ear ossicles.Organs of hearing present in the innerear will receive the vibrations of thesound waves. Then the informationsare sent to the brain through theauditory nerves. The brain ultimatelyhelps us to realise the sound(Fig. 8.14). The animal which hearsthe sound very sharply is the bat.

Fig. 8.14 Sense of hearing - Human Ear1. Sound wave 2. Ear 3. Ear drum

4. Inner ear 5. Nerve

(iii) Tongue

The taste buds present in thetongue are useful to discriminate thetastes of food such as bitter, salt, sweetand sour. Sensation of taste will besent to the brain through the sensorynerves which are leaving from thetaste buds of the tongue. The brainthen distinguishes the taste of the food(Fig. 8.15).

Fig. 8.15. Taste buds of tongue

1. Bitter 2. Sour 3. Slat 4. Sweet

(iv) Skin

We can feel the feelings likelight, touch, pressure, heat, cold andpain with the help of the nerve cellspresent in the skin.

(v) Nose

The nose functions as an organof differentiating the various types ofsmell and also acts as a nasal passageto inhale the air (Fig. 8.16).

Fig. 8.16 Nose

1. Brain 2. Nose

8.5 Locomotion

The movement of organismsfrom one place to another place iscalled locomotion. It is seen

5

4

32

1

1

2

3

4

1

2


107

commonly in animals and inChlamydomonas. In animals, spongesand coral reefs are immovable.

8.5.1 Reasons for Locomotion

Do you know why organismsmove from one place to another? Theymove from place to place in search offood and shelter ; for the purpose ofreproduction and protection. Animalshave locomotory organs likepseudopodia, flagella, fins, wingsand legs to move.

8.5.2 Locomotion of unicellularorganisms

There is no locomotory organ inthe plants. The movement in the algaelike chlamydomonas and volvox iseffected by means of flagella(Fig. 8.17).

Fig. 8.17 1. Chlamydomas 2. Flagellum

3. Volvox

(i) Locomotion in Amoeba

Amoeba has no permanentlocomotor organ. It moves by formingtemporary organs calledpseudopodia. These pseudopodia

can be formed from any part of thebody.

(ii) Locomotion in Euglena

The body of the Euglena isspindle shaped. In its anterior endthere is a flagellum. With the help ofthe flagellum, Euglena swims inwater restlessly (Fig. 8.18).

Earthworm moves by muscularcontraction.

Fig.8.18 Locomotion in unicellular organisms1. Locomotion in Amoeba2. Locomotion in Euglena

Activity 8.11

Compare the locomotion inearthworm, butterfly and snail.

8.5.3 Locomotion in higher animals

In higher organisms, differenttypes of locomotions are seen. Thelocomotion is effected by means offins, wings and legs. Locomotions likejumping, walking, crawling andrunning take place in animals. Thefins of fish help to swim in water.Median fins help for balancing, lateralfins for forward and backwardmovements and tail fins for changingthe direction. In land, frogs jump with

1

2

3

1

2


108

the legs and in water they swim withthe help of webbed feet. The web isa membrane which is present inbetween the fingers. Usually reptilesmove by legs (Fig. 8.19).

Birds fly with the wings fromplace to place. Man uses his legs towalk and run.

Infer

In one hour Amoeba crossesabout 2 cm. The fastest terrestrialanimal is cheetah. It is observed thatthis crosses 70 miles in one hour.

8.6 Reproduction

The sapling of plantain lookslike plantain tree. Similary the kittenslook like cats. The children resembletheir parents. What is the reason for this?

The capacity or ability of anorganism to produce offsprings of

their own kind for the continuance oftheir races, is known as reproduction(Fig. 8.20)

Fig. 8.20 Reproduction

1. Plantain and young plantain 2. Cat and kittens

Fig. 8.19 Locomotion higher animals1. Fish 2. Frog 3. Lizard 4. Bird 5. Human

Activity 8.12

Tabulate the locomotor organs ofthe following animals.

Sl.No. Animal Locomotor organ

1. Amoeba ..............................

2. Euglena ..............................

3. Earthworm ..............................

5. Fish ..............................

6. Man ..............................

1 2

5

43

1 2


109

8.6.1 Significance of reproduction

Due to reproduction plantsincrease in number. So foodproduction is also increased. Man andanimals can live. Reproduction helpsthe organism to retain their races onearth.

8.6.2 Types of reproduction in plants

Do you know how do plantsincrease their races?

Plants reproduce by threemethods. They are (i) Sexualreproduction (ii) Asexual reproductionand (iii) Vegetative reproduction.

(i) Sexual reproduction

In higher plants, the androeciumis male sex organ. The gynoecium isthe female sex organ. These two areinvolved in sexual reproduction.

(ii) Asexual reproduction

Some special structures areinvolved in the asexual reproduction.eg. Conidia in Penicillium (Fig. 8.21).

Fig. 8.21 Conidiain Penicillium

(iii) Vegetative reproduction

In certain plants new plantletsdevelop from various vegetative parts.

This type of reproduction is calledvegetative reproduction. InBryophyllum young plantless developfrom the leaf margins (Fig. 8.22).

Fig. 8.22 Vegetative reproduction - Bryophyllum

8.6.3 Reproduction in animals

Just like plants in animals alsothere are two types of reproductioncalled sexual and asexual.

Asexual reproduction

The unicellular organisms likeAmoeba and Euglena reproduce bymeans of binary fission. In hydrareproduction takes place by means ofbudding (Fig. 8.23).

(1)

Fig. 8.23 Reproduction in Amoeba and Hydra1. Amoeba - Binary fission

2. Hydra - Budding

(2)

Conidiain


110

Sexual reproduction :

It takes place in lower organismsas well as in higher organisms likefish, frog, snake, bird and man.

The testis which is a malereproductive organ produces sperm.The symbol O is a symbolicrepresentation of male. The ovary isa female reproductive organ whichproduces eggs. The symbol O is thesymbolic representation of female. Anorganism which developed by theunion of sperm and ovum is theproduct of the sexual reproduction.

8.6.4. Gestation period of animals

The period of time during whichthe female carries the growing embryoin uterus is called the gestationperiod. This period varies fromanimal to animal (Table 8.1).

Table 8.1

Gestation period of animalsS.

AnimalGestation

No. period

1 House rat 20-21 days

2 House dog 60 days

3 Goat 149 days

4 Cow 280 days

5 Man 280 days

6 Elephant 17-20 months

7 Tiger 155 days

8.6.5 Sexual dimorphism in animals

Externally there are differencesbetween male and female sexes. Thedifferentiation of organisms as maleand female on the basis of sex iscalled sexual dimorphism. Forexample, if we notice the abdomen ofcockroach, we can distinguish the sexof the animal.

The abdomen region of malecockroach is narrow and that of thefemale is slightly broader. Further apair of anal styles is present in the9th abdominal segment of the malecockroach, whereas this is absent inthe female cockroach (Fig. 8.24).

Fig. 8.24 Cockroach Differences between male

and female cockroach1. Male 2. Female 3. Anal style

Have you heard the sound madeby the frogs during rainy season? Thissound is produced by the two vocalsacs which are present in the jaws ofthe male frog. But these vocal sacsare not found in the female frogs. Anuptial pad is present in the first fingerof male frog whereas this organ isabsent in the female frog.

1 2

3

+


111

Activity 8.13

Tabulate the important male andfemale external differences for thefollowing animals.

Sl.Animal Male FemaleNo.

1 DeerPresence Absenceof horns of horns

2 Elephant ................ ................

3 Lion ................ ................

4 Peacock ................ ................

5 Chicken ................ ................

SELF EVALUATION


1. The branch of science that deals with the living organisms is called

(a) physics (b) chemistry (c) biology (d) zoology

2. Autorophic nutrition is

(a) parasitic life (b) saprophytic life

(c) symbiotic life (d) synthesising food by themselves

3. Goat is a / an

(a) herbivore (b) parasite (c) carnivore (d) omnivore

4. The plant that responds to the external stimulus is

(a) bryophyllum (b) touch me-not (c) amaranthe (d) shoe flower plant

5. Locomotory organs found in Amoeba are

(a) flagella (b) fins (c) legs (d) pseudopodia

6. Gestation period of man is

(a) 103 days (b) 60 days (c) 280 days (d) 149 days

7. The largest animal is _________________

8. The word photosynthesis means _______________

9. The plant which moves from place to place is ___________

10. Asexual reproduction is seen in __________ plant.


112

11. Amoeba reproduces by ______________ method.

12. In male cockroach __________ is seen.

13. Why we call plants as producers?

14. Define reproduction.

15. Define growth.

16. What is meant by metabolism?

17. What are the senses felt by skin?

18. What are the locomotory organs of higher animals?

19. What is meant by gestation period?

20. What is meant by nuptial pad?

21. Explain the fundamental aspects of photosynthesis?

22. Write different types of stimuli.

23. How do we hear sound?

24. How do plants reproduce?

25. Draw the structure of human eye and label the parts.


113

We studied the generalcharacteristic features of plants andanimals in the previous lesson. Wehave understood that the livingorganisms are made up of one to manycells. We will study in details about

the bio-diversity of organisms in thislesson.

9.1 Bio-diversity (different types oforganisms)

Write the names of the plantsand animals that you know. Several

Fig. 9.1 Organisms in different environment1. Monera 2. Protista 3. Fungi 4. Plantae 5. Animalia

9. Bio-Diversity

4 ––

2 ––

1

–– 5

3


114

millions of organisms live in ourearth. All organisms do not live in thesame environment. Some organismslive in water, some in land and few indeserts. According to the environment,the organisms have special structuresand functions. They attain individuality.

A classification becomes essentialto know about all these types oforganisms (Fig. 9.1). CarolusLinnaeus of Sweeden laid basisproperly for such a classification(Fig. 9.2).

Fig. 9.2 Carolus Linnaeus

Depending upon theenvironment, plants have developedsuitable adaptive features in them.

9.1.1 Significance of variousorganisms

Various types of plants, animalsincluding man and micro organismslive in our planet. These constitutethe biota.

Directly or indirectly plants arethe sources of food for all other kindsof organisms. No life is possible onearth without plants. Animals are usedin agriculture, dairy farming and forpulling the carts. Thus plants andanimals are useful in many ways.

9.1.2 Viruses - introduction

In tobacco plants, have you evernoticed the presence of pale greenpatches on the leaves? Do you knowthe reason for these changes?

Do you know the causes forcommon cold, mumps, small pox,chicken pox, jaundice, flu, fever,polio, rabies and AIDS?

The virus is responsible for suchdiseases in plants and animals.

The word virus is derived fromlatin. Virus means ‘poison’ or‘venom’. The virus can be seen onlyunder electron microscope. Virusespossess two characteristics namely(i) hereditary nature and(ii) multiplication. They live andmultiply only inside the living cells.So they are called obligate parasites.

The branch of science that dealswith viruses is known as virology.Viruses are 50 times smaller than thesmallest bacterium. In a modernsystem of classification viruses andbacteria are placed in the kingdomMonera.


115

Activity 9.1

Observe the symptoms of plantsaffected by viral diseases and also thesymptoms of viral fever in humanbeings.

9.1.3 Discovery of viruses

In 1796, Edward Jennercontrolled the viral disease calledsmall pox by vaccination. At that timethe causative organism for the smallfox namely virus was unknown. In1892 a Russian scientist DimitriIwanoski published his findings onTMV. The tobacco mosaic virusinfects the tobacco plant. He observedthe occurrence of etiolated and darkgreen patches on leaves of infectedplants. He called this disease asmosaic disease. After severalinvestigations, he discovered thatvirus was the cause of mosaic diseasein tobacco. He named the virus astobacco mosaic virus (TMV). In 1935W.M.Stanley obtained the tobaccomosaic virus in the form of crystals(Fig. 9.3). In 1983-84, Robert Gallo

and his associates in USA discoveredthe HIV viruses that cause the disease,AIDS (Acquired Immuno DeficiencySyndrome). It is a recent discovery ofgreat importance.

9.1.4 Structure of a virus

An intact virus particle capableof causing a disease in a particularhost is called a ‘viron’. Viruses aremade up of nucleic acids and proteins.The nucleic acid is called ‘nucleoid’and the protein coat is called as‘capsid’. The protein sub units ofcapsid are called capsomers. Thecapsid and the sub units capsomeremay be compared to a brick wall andbricks respectively. DNA (Deoxy ribonucleic acid) or RNA (Ribo nucleicacid) acts as hereditary material. Plantviruses possess RNA. Animal virusesand the bacteriophages possess DNAThe tobacco mosaic virus iscylindrical shaped. It appears underelectron microscope like a bunch ofgrapes. It has RNA surrounded by theprotein coat (Fig. 9.4).

Fig. 9.4 Structure of TMV1. RNA 2. Capsomere 3. CapsidFig. 9.3 W.M. Stanly

1

––2

–3


116

9.1.5 Virus - size and shape

How do we measure rice? Howdo we measure milk and cloth? Youknow that each of these materials ismeasured in different methods. Howmany millimetres are there in a metre?We have already studied that theviruses are very small and can be seenonly under electron microscope.Viruses are measured by the unitnanometre (nm) or millimicron. Thesize of the viruses ranges from 17 nmto 300 nm. 1 micrometre = 1/1000mm. 1 millimicron = 1/1000micronmetre. Satellite virus is thesmallest plant virus. Potato virus isthe biggest virus.

Shape (Fig. 9.5)

(i) Spherical (a) HIV virus

(ii) Cylindrical (b) TMV

(iii) Tadpole (c) Bacteriophage

(iv) Brick (d) Pox virus

Fig. 9.5 Shapes of viruses

9.1.6 Classification of viruses

Viruses cause diseases to plants,animals and human beings. Theviruses are classified based on their

hosts as follows :

(i) Plant viruses - Viruses thatcause diseases to plants.

eg. TMV, potato - leaf rolldisease virus and bunchy top bananavirus.

(ii) Animal viruses - Viruses thatcause diseases to animals and humanbeings. eg. polio virus, small poxvirus, foot and mouth disease virus.

(iii) Bacteriophages - Virusesthat attack bacteria.

eg. T4 bacteriophage

9.1.7 Living and non-livingcharacteristics of virus

Viruses do not multiply outsidetheir host. They lack metabolicactivities. They can be crystalised.These are the non-living characteris-tics of the viruses. Capable ofmultiplying inside the living host,presence of DNA and protein coat arethe living characteristics of viruses.

9.1.8 Diseases caused by viruses

Viruses cause various types ofdiseases in plants and animals.

In plants

Sl.No. Plant Disease1. Tobacco - Mosaic disease2. Banana - Bunchy top disease3. Potato - Leaf roll disease4. Beet root - Yellow disease5. Chick - Pox disease6. Cow - Foot and mouth

disease

(d)(c)

(a) (b)


117

In man viruses cause a varitiesof diseases like AIDS, Jaundice, smallpox, chicken pox, polio, rabies,mumps, common cold, etc.

AIDS (Acquired ImmunoDeficiency Syndrome) is a killerdisease. Specific medicine for AIDShas not yet been discovered. But adrug called Azitothyamidine (AZT) isused to prolong the life of the affectedperson.

9.2 Classification of differentorganisms

In 1969 Robert H. Whittakerclassified the organisms into fivekingdom. This classification has beenaccepted by all scientists.

Divisions :

(i) Monera - Primitive unicellularorganisms without typicalnucleus. eg. bacteria and viruses.

(ii) Protista - Primitive unicellularoganisms with prominentnucleus. Eg. Amoeba,chlamydomonas

(iii) Fungi - Unicellular andmulticellular plants withoutchlorophyll. eg. Agaricus

(iv) Plantae - Multicellular plantshaving chlorophyll.eg. algae toall higher plants

(v) Animalia - Multicellular animals.

eg. sea sponges, earthworm,elephant, human beings.

9.2.1 Monera eg. Bacteria

Do you know which convertsmilk into curd? Do you know themicro organism which is responsiblefor the fermentation of dosai and idlyflour? Do you know the reasons forthe diseases in man like cholera,tuberculosis, typhoid and leprosy?

Many people died in Surat ofGujarat state in the year 1994 dueto plague. Do you know the reasonfor this?

9.2.2 Discovery of Bacteria

In 1675 Anton Von Leewvenhoek, a Dutch scientist, discoveredbacteria. He called the bacteria as‘animalicules’. The branch of sciencethat deals with the bacteria iscalled bacteriology. Anton VonLeewvenhoek is called as the fatherof bacteriology.

Bacteria are considered as firstformed organisms in the world.Except one or two types of bacteria,others do not have chlorophyllpigment. So majority of them obtaintheir food from other livingorganisms, dead plants and animalssubstances. They live as parasites aswell as saprophytes. Some bacteriaalso lead symbiotic mode of life.


118

9.2.3. Structure of Bacteria

Bacteria are found in water, air,soil, sewage, food materials and theyalso live in plants and animals asparasites. Each bacterium is made upof single cell. They spread throughwater and air. Some bacteria possesshair like structures for movement.

The hair like structures found onthe surface of the bacterium are calledflagella. The number of flagella andtheir arrangements differ in varioustypes of bacteria. Well defined nucleusand nuclear membrane are absent.Cytoplasm is present. Chloroplast isabsent. RNA is present. The hereditarymaterial DNA is present. A thickcovering present around the cell wallin some bacteria (Fig.9.6) is knownas capsule.

Fig.9.6 Structure of bacteria

1. Flagellum 2. Capsule 3. Nucleus

Size of bacteria

Bacteria can be seen only under

the compound microscope. The width

of bacteria ranges from 0.2 μm to

1.5 μm and the length from 3 to 5μm

(μm means micrometre) 1 micrometre =

1/1000 mm.

Shape of Bacteria

The shape of bacteria varies in

different species (Fig. 9.7).

The important shapes are

(i) rod (ii) spherical(iii) spiral and

(iv) comma

Fig. 9.7 Shapes of the bacteria

9.2.4 Classification of bacteria

On the basis of cell structure,

flagellation, nutrition and respiration,

bacteria are classified into many types.

On the basis of shape, they are

classified into four types and on the

basis of flagellum, they are classified

into four types as shown in theFig. 9.8.

–1

2

3

(i)(ii) (iii)

(iv)

Fig. 9.8 Classification of bacteriabased onflagellation

1. Monotrichous2. Lophotrichous3. Amphotrichous4. Pertrichous

9.2.5 Beneficial bacteria

Many bacteria are useful inindustries, medicines, recycling ofwaste materials and agriculture.

1 2 3

4


119

How is curd formed from themilk? When a small amount of curdis added to the milk, the bacteriumLacto bacillus present in the curd,multiplies several times and fermentsthe milk. Due to fermentation, milkis converted into curd.

A type of bacterium known asLeuconostoc is responsible for thefermentation of flour of dhosa andidly. Certain bacteria convert thedomestic wastes into good manure.Bacteria are responsible for thetanning of leather and processing oftea and tobacco leaves.

Activity 9.2

Fruits, vegetables and greensdecay and get spoiled. What is thereason for this? Bacteria areresponsible for this. With the help ofthe teacher, observe the rotten partsof fruits or vegetable under compoundmicroscope.

Activity 9.3

Cut and burn the bacteriaaffected portion of the plants that areavailable in the garden. So that otherplants can be protected from thediseases.

Activity 9.4

The vegetables bought frommarket must be used at once.Otherwise they should be stored insuch a way that they are not spoiledby the bacteria. The spoiled

vegetables must be discorded aspathogenic bacteria might be presentin the rotten vegetables.

Activity 9.5

Keep a drop of curd on a cleanglass slide and observe through acompound microscope. Many rodshaped Lactobacillus can be seen.

9.2.6 Harmful Bacteria

Bacteria cause many diseases inplants and human being.

Sl.No. Plant Disease

1 Citrus Canker disease

2 Potato Ring rot disease

3 Apple Fire blight disease

4 Tomato Wilt disease

In man bacteria cause a varietyof diseases like diptheria, plague,tetanus, cholera, tuberculosis, typhoid,leprosy, etc.

9.3 Protista

Animals and plants of protistaare of one celled and they live in seaas well as in fresh water. Some areparasites. Though the body is of onecelled, they have the capacity ofperforming all the body activities.

There are many types ofunicellular organisms (Fig. 9.9). TheParamecium, which consists of cilia,belongs to class Ciliata.


120

Fig. 9.9 Unicellular organisms1. Amoeba 2. Paramecium 3. Euglena

4. Plasmodium

Euglena which consists of aflagellum belongs to classMastigophora (Fig. 9.9). Amoebawhich consists of pseudopodiabelongs to class Sarcodina and theparasite Plasmodium whichreproduces through spores belongs toclass Sporozoa.

The dreadful disease malaria iscaused by the Plasmodium which isa parasite. The Plasmodium affectsthe red blood cells. Malaria will notdirectly spread from one person toanother. Mosquitoes act as a maincarriers in spreading this disease. Themalarial fever spreads from theaffected person to another personthrough the anopheles femalemosquitoes. Symptoms of malaria arecold with shivering, followed by fever,severe head ache and vomitingsensation. Malaria is a big healthproblem. If we want to prevent andcontrol malaria, we should destroy themosquitoes, which is responsible fortransmiting the parasites.

Activity 9.6

Take a drop of pond water, keepit on a slide and observe it under acompound microscope.

9.3.1. Micro-algae

Micro-algae can be seen onlyunder microscopes. They occur assingle cells or filaments or colonies.eg. Chlamydomonas, Volvox, etc.(Fig. 9.10) Algae are autotrophs.

Fig. 9.10 Micro-algae(a) Chlamydomonas (b) Volvox

Activity 9.7

Observe the growth of algae incanals and in water stagnating areas.

9.3.2 Pyrrophyta - Dianoflagellates

Algae belonging to this categoryare greenish brown in colour. Mostof the algae are motile. They occur insea water. Two flagella are useful forthe movement. Out of two flagella,one is longer than the other(Fig. 9.11).

Fig. 9.11 Exuviaella

9.4 Fungi Ascomycetes

eg. Penicillium and Yeast

Penicillium is a simple organism.It lacks chlorophyll. It lives as

1 2 3 4


121

saprophyte. The body consists offilamentous structures. The antibioticpencillin is extracted from the funguscalled Penicillium. The pencillin isalso known as “the queen of drugs”.

Yeast is an unicellular organismand oval in shape. It is a saprophysicfungus. It is useful for the preparationof alcohol by fermentation process.Conversion of sugar solution intoalcohol with the release of carbon-di-oxide is called fermentation. It is alsoused in bakery (Fig. 9.12).

Fig. 9.12 Structure of yeast

Acitivity 9.8

Mix the yeast powder with the

sugar beet’s extract. After few days

you can see the formation of whitish

layer on the surface of the extract.

When it is observed under the

microscope, yeasts can be seen.

9.5. Plantae

In our earth as per the statistical

estimate there are 4,00,000 species of

plants existing. Among these,

2,86,000 species are flowering plants.

They all differ in structure, habit,

habitat and life cycles.

9.5.1. Bio-diversity among plants

The plants are broadly divided

into two groups. They are

1. non-flowering plants or

cryptogams

2. flowering plants or

phaenarogams. The two groups

are further divided into many

divisions as shown in below.

9.5.2 Classification of plants

Plant kingdom

Cryptograms Phanerrogams

(non-flowering plants) (flowering plants)

Thallophyta Bryophyta Pteridophyta

Gymnosperms Angiosperms

Monocotyledons Dicotyledons

9.5.3. Macro-algae

Among the algae, some of themhave leaf like and stem like structures.They grow several metres long. Thealgae which are visible to our nakedeyes are called macro algae. They aregreen algae, brown algae and redalgae.

(i) Green algae : eg - Enteromorpha

They are green in colour. Theyare attached to the rocks of the sea oftemperate regions. Some are presentin fresh water. The filament has a


122

single layered cells. The stored foodis starch. The pigment chlorophyllis present (Fig. 9.13).

Fig. 9.13. Enteromorpha

(ii) Brown Algae : eg - Sargassum

Mostly they grow in salt water.They show dichotomous branching.They are called sea weeds. Thepigment phycoxanthin occurs in thecells. The reserve food materials ofthese algae are laminaran starch(Fig. 9.14).

Fig. 9.14 Sargassum

(iii) Red Algae : eg - Grenella

They are present in seas oftemperate regions. Thallus is flat andfilamentous. They are red in colourdue to the presence of the pigment,phycoerythrin. The reserve food isknown as floridian starch (Fig. 9.15).

Fig. 9.15. Grenella

9.5.4. Non-flowering plants

Eg. Riccia and Funaria

Riccia is a simple and very smallplant. It has no root system and shootsystem. The plant body is representedby ribbon shaped structure. It is foundon the surface of wet lands. In doesnot produce flowers (Fig. 9.16).

Funaria has root but not welldeveloped. It has leaves but not welldeveloped. It also does not produceflowers (Fig. 9.17).

Those plants having vasculartissue are called vascular plants. eg.Cycas, Amaranthes, etc.

In Riccia and Funaria thevascular tissue is absent. So they areexamples for non-vascular plants.

Activity 9.9

If you go to hill stations likeOoty, Kodaikanal and Yercaud,observe the occurrence of liver shapedbryophytes in the shady slopes.

Infer

Riccia and Funaria are called non-vascular cryptogams. Why?

Fig.9.16 Riccia Fig.9.17 Funaria


123

9.5.5. Vascular cryptogams

Have you seen the plantsSelaginella and Nephrolepis? Someplants do not produce flowers. Theyhave the vascular tissues xylem andphloem. The tissues which transportwater and food materials in plants arecalled vascular cryptogams. Xylem andphloem are the consituents of vasculartissue. Xylem trnsports water fromroot to stem and leaf. Phloemtransports food material to storageregion of the plant.

Selaginella and Nephrolepis areexamples for vascular cryptogams(Fig. 9.18 and 9.19)

Fig. 9.18. Selaginella

Fig. 9.19 Nephrolepis

9.5.6. Gymnosperms

The word gymnosperm isderived from the greek language. Innature several kinds of plants produceseeds. Bean, citrus, mango, guava, etc.

are seeded plants. In all these plantsthe seeds are found in fruits. i.e. theseeds are surrounded by soft tissues.The plants in which the seeds occurwithin the fruit are calledangiosperms. But in some plants,the seeds are naked i.e. the seeds are notsurrounded by any tissue. The seedsare exposed. These plants are calledgymnosperms. Gymno meansnaked. Sperm means seed. eg. Cycas(Fig. 9.20).

Fig. 9.20 Cycas

9.5.7 Angiosperms

Most of the plants that we see inour day today life are floweringplants. Angiosperm constitutes a largegroup of plants. In angiosperms seedsare present inside the fruits. So theyare called closed seeded plants.Angiosperms are classified intomonocotyledons and dicotyledons

Activity 9.10

Observe the trees in and aroundyour house and on the streets, youwill find the majority of them areflowering plants.


124

9.6 Animalia

Animals seen in animal kingdom

are classified into many phyla on the

basis of cell, tissue and external

structure. All the animals come under

animalia kingdom are made up of

many cells. But the organisms differ

in their structure and functions.

Phylum is a unit of classification

comprising a group of animals having

similar common characteristic features.

9.6.1 Porifera

eg. Sea sponge

The organisms of this phylum

have pores through out the body. So

they are called porifera. They have

no locomotory organs. They live in

fresh water as well as in sea water.

Some of these animals are used for

ornamental purposes.

9.6.2 Phylum : Coelenterata

eg. Hydra, Jelly fish, Coral reefs

The body of these animals is

made up of tissues. The body wall is

made up of two layers of cells called

the ectoderm and the endoderm. The

body has stinging cells by which they

paralyse the prey and eat. Some can

move and some cannot move. The

animals which produce coral reefs are

found in this phylum.

9.6.3 Phylum : Platyhelminthes

eg. Tape worm

9.6.4 Phylum : Aschelminthes

eg. Round worms, hook worms

The animals which belong to theabove two phyla are mostly parasites.The body wall of these animals hasectoderm, mesoderm and endoderm.The organism in which the parasitelives is called host. From the host,the parasite gets its food and shelter.It also causes harmful effects to thehost. For example, the round wormsand tape worms are found in thedigestive system of man as parasites.Here man is the host. Tape worms arepresent not only in man but also inother vertebrates as parasites. Becauseof these parasites, anaemia, vomitingsensation, stomach ache andnervous disorders are caused in man.

9.6.5 Phylum : Annelida

eg. Earthworm, Leech

The body of the animals of thisphylum is made up of segments. Thebody is three layered and has closedcirculatory system which is animportant character. The blood is redin colour, because of the presence ofblood pigment in the red blood cells.The excreta of these animals enrichthe fertility of the soil.


125

The earthworm which is calledas the “friend of farmer” belongs tothis phylum. It plays an important rolein the conversion of wastes. Itconverts the decaying wastes intonatural manure. This type of naturalmanure is better than the chemicalfertilizers.

9.6.6 Phylum : Arthropoda

eg. Prawns, crabs, spider,centipede, millipede, scorpion,cockroach, butterfly, house fly,mosquito and honey bee.

The animals which belong to thisphylum possess joints in their legs.So they are called arthropods. Thebody is divided in to head, thorax andabdomen. The exoskeleton of theseorganisms are made of chitin. Opentype circulatory system is present.Blood is colourless, because there isno blood pigment. Presence ofantennae and compound eyes is one

of other salient features of theseanimals.

Arthropods are economicallysignificant and some cause harmfuleffects. Prawns and crabs are proteinrich foods. Honey bees producehoney. Butterflies and other insectshelp in cross pollination. House flysspread the micro-organisms whichcause diseases like cholera, typhoid,anthrax, diarrhoea and dysentry.Mosquitoes spread malaria andelephantiasis (Fig. 9.21).

9.6.7 Phylum : Mollusca

eg. Octopus, snail and freshwater muscle.

They are soft bodied organisms.They move with the help of muscularfoot. In some molluscs, a hard shellis present outside the body. Thecalcarious shell present in somemolluscs is protective and external.This shell is called exoskeleton. In

1 2

5 6

3

7 8

4

Fig.9.21 Lower animals1. Sponges 2. Jelly fish 3. Tapeworm 4. Round worm

5. Earthworm 6. Butterfly 7. Snail 8. Starfish


126

this phylum the valuable pearlproducing species are found. Somemolluses are used as food for man,fish and water birds.

9.6.8 Phylum : Echinodermata

eg. Star Fish, sea cucumber andsea Lillies.

These animals have spines on theupper surface of the body. So theyare called as echinoderms. The body

has no segments. They move with thehelp of tube feet. The animals of thisphylum pushes their stomach outsidethe body and digest the food eaten bythem. Many molluscs are used as foodfor man and for ornamental purposes.

9.6.9 Phylum : Chordata

All the animals having backbonecome under this phylum. Back boneis a long chain which is formed bythe union of small vertebrae.

Fishes, amphibians, reptiles, avesand mammals are the vertebrates(Fig. 9.22). They have skeleton madeof bones. For example

(i) Fishes which live in water. Theymove with the help of fins.

(ii) Amphibians like frogs live bothin water and on land.

(iii) Crocodile, tortoise, snake, lizardand garden lizard are examplesfor reptile.

Activity 9.11

Tabulate the economicallyimportant and harmful arthropods.

Sl. Economically HarmfulNo. important arthropods

arthropods

1. ................... ...................

2. ................... ...................

3. ................... ...................

4. ................... ...................

Fig. 9.22 Chordates1. Fish 2. Frog 3. Snake 4. Pigeon 5. Rabit

1 2

4 5

3


127

(iv) Birds like sparrow, eagle, ostrich,peacock and crow are examplesfor aves.

(v) Mammals like cat, dog, rat,squirrel, bat, tiger, lion, elephant,cow and man are examples formammals.

Infer

Ostrich is a bird and it cannotfly. Bat is a mammal which can fly.

9.7 Anthropology

The study of human race is calledanthropology. Human race has beendistributed world wide. Human raceis distributed from the apex region ofNepal to the lower level of Dead seaof Israel.

Thus the man who has beendistributed all over the world is notsimilar in their appearance. Men differin skin, colour and structure of skull.For example the black people livingin Africa are called Negroes. Themelanin pigment is more in their skinand the skull has square shaped eyesocket and big jaw bones. Mangoloidsof China are yellowish in complexion.They have oval eye socket and smalljaw. The white people are calledcaucasians. The reason for thedifference in complexion among thepeople is due to the geographical andenvironmental conditions in whichthey live. The zoological name of manis Homo sapiens

SELF EVALUATION


1. The virus which causes AIDS is

(a) T4 (b) TMV (c) HIV (d) animal virus

2. The genetic material present in plant virus is

(a) RNA (b) tRNA (c) DNA and RNA(d) rRNA

3. An example for anemalia is

(a) bacteria (b) earthworm (c) Amoeba (d) yeast

4. The organism which causes malaria

(a) Euglena (b) Paramecium (c) Plasmodium (d) Amoeba

5. Example for micro-algae is

(a) Clamydomonas (b) Sargasam (c) Chara (d) Hydrilla


128

6. ______________ is known as the “Father of bacteriology”.

7. __________ is called the queen of drugs.

8. The number of species present in angiosperms is _________.

9. An example for vascular cryptogams is _______________ .

10. The parasite which is present in the digestive system of man is _________.

11. The exoskeleton of arthropods is made of ___________.

12. Bacteria is a plant. Give reason.

13. Difine parasite.

14. Why do negroes appear black in colour?

15. What are the diseases caused to man by virus?

16. What are the symptoms of malaria?

17. What is brown alga? Give example.

18. What is anthropology?

19. What is meant by fermentation?

20. Explain the structure of T4 virus.

21. Explain the merits and demerits of bacteria.

22. Explain the general characters of annelids and arthropods.

Few informations ...

Giraffe has the longest neck among all the animals.

All kinds of snakes have short-sight problems.

Chimpanzee is considered to be the most intelligent animal.

Before going to sleep, dog will revolve three times around itssleeping place

There are no scorpions in Newzealand.


129

The study of external structureof plants is called plant morphology.It includes the study of structure andfunctions of shoot system, root systemand leaves. In higher plants andanimals, to perform various functions,well developed organ systems arefound. In this lesson, let us study theprocesses like photosynthesis,respiration and transpiration that aretaking place in plants and digestion,circulation, excretion, etc. related tohuman system.

10.1 Root system - structure andfunction

Root system is seen generallybelow the soil. It is continuation ofthe shoot system. Roots absorb waterand minerals from the soil. It anchorsthe plants firmly in the soil. Rootsprevent the soil erosion. In someplants food material is stored in rootsystem and used as food.

10.1.1 Two types of root systems

Have you seen the roots of thetrees growing around your house?Have you seen the roots of tamarindand mango trees? Have you seen the

roots of grass, coconut, banana andpalm trees? Did you observe anysimilarity in these structures?

Root system is of two types.(i) Normal or tap root system and(ii) Fibrous root system.

10.1.2 Tap root system

Tap root system is thecharacteristic feature of dicot plants.The radicle that comes out at the timeof germination of seed, grows into taproot system. It consists of primaryroot, secondary roots and tertiaryroots. This constitutes tap rootsystem (Fig 10.1). Generally roots arepositively geotropic. They are brownin colour eg. Mango and Hibiscus.

Fig. 10.1Tap root system1. Primary root2. Secondary root

3. Tertiary root

10. Structure and functions of theliving organisms

1

2

3


130

10.1.3 Fibrous root system

It is the characteristic feature ofmonocot plants. First formed rootdeveloping from the radicledegenerates. Later on bunch of rootshaving same length develops. This isknown as fibrous root system(Fig. 10.2). These roots do not growvery deep into the soil. eg. Maize,sugarcane and paddy.

Fig. 10.2 Fibrous root system

10.1.4 Functions of root

(i) Anchorage of plants

Roots profusely give outbranches and spread in the soil. Theyhelp plants to be rooted firmly in thesoil. Besides that, trees are protectedfrom being toppled down during highvelocity of the wind and during soilerosion.

(ii) Absorption of mineral salts andwater

Roots absorb water and mineralsalts which are dissolved in the soilwater.

(iii) Conduction

Water and mineral salts absorbedby the roots are conducted to stem,branches and leaves.

10.1.5 Root modifications

Apart from the normal functionslike anchorage, absorption andconduction, roots undergo certainmodifications for the purpose ofstorage and other functions. Suchadaptive features are called rootmodifications. Root modifications areof two types. 1. Tap root modificationand Adventitious root modification

(i) Tap root modifications

Have you seen carrot, radish andbeet root? Observe their shape.

Conical : Top of the rootbroadens like a cone and lower parttapers down. eg. carrot (Fig. 10.3).

Fig. 10.3Conical - Carrot

Fusiform : Middle part broadensand both ends are tapering like aspindle. eg : radish (Fig. 10.4).

Fig. 10.4Fusiform - Radish


131

Napiform : The modified rootresembles a top and the lower parttapers suddenly eg. beet root(Fig. 10.5).

Fig. 10.5Napiform - Beet root

(ii) Adventitious roots

The roots developing from anypart of the plant other than the radicleare called adventitious roots.

Adventitious root modifications

Adventitious roots also undergomodifications like the tap roots. Theycarry out the functions like support,absorption of atmospheric moisture,etc.

Have you seen a banyan tree?Have you seen the roots hangingdown from the branches?

Prop roots

Roots develop from thehorizontal branches in banyan tree andgrow towards the soil. After reachingthe soil they grow deeper into it andform pillar like branches of the tree.So they are called prop roots(Fig. 10.6).

1

2

Fig. 10.6 Prop roots - Banyan tree1. Prop root

Epiphytic roots

In nature some plants grow onthe branches of trees. Such plants areknown as epiphytes. Unlike parasites,they do not absorb food from the hostplant. They depend on the host onlyfor the shelter. They produce a specialtype of adventitious roots having aspongy tissue called velamen. Thistissue absorbs moisture and rain waterfrom atmosphere eg.Vanda (Fig.10.7).

Fig. 10.7 Epiphytic roots - Vanda1. leaf 2. Adventitious root

10.2 Shoot system and functions

Stem develops from theplumule. Shoot system is seen abovethe surface of the soil. It bears variousparts of the plant such as stem,branches, buds, flowers and fruits.

1


132

10.2.1 Parts of the shoot system

The shoot system has the mainaxis called stem. The part of the mainaxis from where the branches andleaves develop is called node. The partbetween two successive nodes isknown as internode. The anglebetween the leaf and the central axisis called axil. Buds can be seen in theseangles. These are called axillary budsand develop into axillary flowers orbranches (Fig. 10.8).

Fig. 10.8 Parts of a plant1. Axillary bud 2. Internode 3. Stem 4. Node

10.2.2 Characteristics of shootsystem

(i) Stem always grows towardssunlight. Hence they arepositively phototropic. As itgrows away from gravity thestem is described as negativelygeotropic.

(ii) Presence of nodes andinternodes.

(iii) They are green in colour.

(iv) Branches, buds, flowers andfruits are present.

(v) Lateral branches are exogenousin origin.

(vi) Foliage leaves or scale leaves arepresent.

Functions of stem

(i) Generally the stem conductswater, mineral salts and food.

(ii) Stem gives support to branches,leaves, flowers and fruits.

(iii) Stem undergoes modificationsand stores food.

(iv) Green stem prepares food.

10.2.3 Modifications of stem

Apart from the usual functions,the stem undergoes modifications toperform special functions like storage,anchorage, etc.

Fig. 10.9 Twinner - Bean

1

2

34

The stem of bean is thin andunable to stand errect. So it coilsaround on some support and grows.So it is called twinners (Fig. 10.9).The other types of sub aerial stem arerunner, stolon, offset andsucker (Fig. 10.10).

Activity 10.1

Observe the twining habit of beanthat grows on adjacent fence or treesin the garden.


133

Fig. 10.10 Sub aerial stems

Activity 10.2

Pluck a monocotyledonous anda dicotyledonous plants from the fieldor from your garden and observe theirmorphological characters. Tabulate thedifferences between monocotyledonsand dicotyledons.

Underground stems are of fourtypes. (i) Rhizome (ii) Corm(iii) Tuber and (iv) Bulb

(i) Rhizome eg. Ginger

Nodes, internodes, scale leaves,axillary buds and terminal buds arepresent in rhizome. Because of thisrhizome is considered as a modifiedstem. This stores food (Fig. 10.11(a))

Fig. 10.11(a)Rhizome-Ginger

(ii) Corm eg. Amorphophallus

In Amorphophallus axillarybuds and scale leaves are present. Soit is considered as stem. A large

(a) Runner - Hydrocotyle (b) Stolon - Colocacia

(c) Offset - Eichhornia

(d) SuckerChrysanthemum

Fig. 10.11(b) CormAmorphophallus

terminal bud is present at the centre.The corm is subspherical and semicircle small depressions occur(Fig.10.11(b)).

(iii) Tuber eg. Potato

Many "eyes" are present on thepotato tuber. Scale leaves can be seen.Axillary buds are found along witheyes. Each eye develops into anindependent plant (Fig. 10.11(c)).

Fig. 10.11(c)Tuber - Potato

(iv) Bulb eg. Onion

Bulb is cone shaped. Node,internode, axillary bud and terminalbud are present along with scaleleaves. Food materials are stored inthe bulb (Fig. 10.11(d)).

Fig. 10.11(d)Bulb - Onion

Activity 10.3

Keep a part of potato with some"eyes" in the moist soil. After few


134

days, you can observe that new plantsdevelop from the "eyes". So it isinferred that "eyes" have buds.

10.2.4 Parts of a flower and itsfunctions

Tell the names of some flowers.Some flowers are large and some aresmall. Some flowers are beautiful.Flowers are the structures producedfor the purpose of reproduction. Ifflowers are not there, reproductionwill not take place in higher plants.Flowers are generally defined asmodified shoots. Flowers involve inthe process of reproduction andproduce seeds. Flowers areimportant structures among variousparts of the plant (Fig. 10.12).

Fig. 10.12 - Parts of a flower1. Calyx 2. Corolla 3. Androecium

4. Gynoecium

The stalk of a flower is calledpedicel. At the top of the pedicel,other floral parts are present. It iscalled thalamus or receptacle. Theouter whorl of the flower is calledcalyx. It is made up of sepals whichare generlly green in colour. It protects

the flowers when they are in budcondition. The second whorl of theflower is known as corolla. It is madeup of petals. It attracts insects forpollination. Both calyx and corolla arecalled accessory whorls. They do notinvolve directly in the process ofreproduction.

The third whorl is androecium.This is the male reproductive organof the flower. It is made up ofstamens. Each stamen has a filamentand an anther lobe. The antherproduces pollen grains.

The fourth whorl is gynoecium.This is the female reproductive organof the flower. The gynoecium consistsof ovary, style and stigma.

10.3 Leaf - structure and functions

Leaf is the external outgrowth ofthe stem and it is green in colour. Itis meant for photosynthesis. This isalso called as foliage leaf. Generallyleaves originate from nodes of thestem. The stalk of the leaf is calledpetiole. The flat and expandedstructure of the leaf present at the tipof petiole is called lamina or leafblade. Lamina has a midrib and manylateral veins. The arrangement ofveins and vienlets is called venation.Veins give support to the lamina. Theyalso conduct water and food materials(Fig.10.13).

4

32

1


135

Fig 10.13 Parts of leaf1. Apex 2, Leaf margin 3. Lateral vein

4. Veinlet 5. Midrib 6. Lamina

Functions of leaf

1. Green leaves prepare food byphotosynthesis.

2. They perform respiration.During this process oxygen istaken inside and carbondioxideis given out. So leaves areinvolved in the exchange ofgases.

3. Leaves release the excess ofwater in the form of watervapour. It is called transpiration.

10.3.1 Internal structure of a leaf

Fig.10.14 Internal structure of a leaf1. Upper epidermis 2. Xylem 3. Phloem

4. Lower epidermis

When the cross section of a dicotleaf is observed under microscope, thefollowing parts can be seen.

(i) Upper epidermis (ii) Lowerepidermis and (iii) Mesophyll tissue

(i) Upper epidermis

It is made up of single layer ofcells. The cells do not haveintercellular spaces. Above the upperepidermis, a waxy coating is present.This is called cuticle. Cuticle checksthe rate of transpiration.

(ii) Lower epidermis

It is made up of single layer ofcells. It is interrupted by the presenceof small pores. They are calledstomata. The stoma is surrounded bytwo bean seed shaped cells. They arecalled guard cells. Through stomata,transpiration takes place.

(iii) Mesophyll tissue

The tissue present in between theupper and lower epidermis is calledas mesophyll tissue. The upper partof mesophyll is made up of palisadeparenchyma and the lower part ismade up of spongy parenchyma. Inthe centre of the mesophyll vascularbundles are present. In the vascularbundle, water and food conductingvascular tissues are present.Surrounding the vascular bundle,bundle sheath is present. Vascularbundles are nothing but veins(Fig. 10.14).

10.3.2 Role of stomata

Stomata play an important roleat the time of respiration,photosynthesis and transpiration.

1

2

3

4

1

2

345

6


136

10.3.3 Transpiration

The removal of excess water inthe form of water vapour through theaerial parts of the plant is calledtranspiration. The body temperatureof the plant is maintained constant dueto transpiration. More over it enhancesthe absorption of water by the plantsfrom soil.

Transpiration is of three types.(i) Stomatal transpiration (ii) Cuticulartranspiration and (iii) Lenticulartranspiration.

(i) Stomatal transpiration

Stomatal transpiration takesplace through stomata. Maximumtranspiration occurs through stomata.Stomata are present on the uppersurface of the leaves in thehydrophytes. Sunken stomata arepresent in xerophytic plants.Transpiration takes place by theopening and closing of guard cells inthe stomata.

(ii) Cuticular transpiration

The waxy coating which ispresent in the upper surface of theleaf is called cuticle. Lesser amountof water vapour is released duringcuticular transpiration.

(iii) Lenticular transpiration

The small opening in the stem iscalled lenticel. Only less amount oftranspiration takes place through

lenticels. More transpiration takesplace through stomata. It can beproved by Bell-Jar experiment.

Bell-Jar experiment

Two potted plants are taken.Leaves are removed from a plant.Vaseline is applied in the detachedparts of the stem. Both the pots arecovered by polythene bags and tiedat the bottom. Then both the pottedplants are covered by bell-jars. Laterthey are kept in the open sun light.

Fig. 10.15 Bell-jar experiment

After few hours if we observethe bell-jar, droplets of water can beseen on the inner surface of the bell-jar which has the plant with leaves.Water droplets cannot be seen in thebell-jar having the plant withoutleaves.

So from this experiment, it isinferred that the transpiration takesplace through the leaves in plants(Fig. 10.15).

10.3.4 Photosynthesis

Photosynthesis is defined as thepreparation of starch by the greenleaves of the plants using the Sun light

(1) (2)

1. Bell jarplant withleaves

2. Bell jarplantwithoutleaves


137

with the help of chlorophyll,carbondioxide and water.

Photosynthesis is the bio-chemical reaction. By using carbon-dioxide, sun light and water, energyrich chemical compounds areprepared. As it is prepared in livingcells, it is called bio-chemical reaction.Oxygen needed for human beings isproduced during this process. So thisreaction may be called as Bio-industry.

Sunlight is necessary forphotosynthesis. This can be provedby Ganong's light screen experiment.This apparatus is fixed to the plantleaf and kept in sunlight for few hoursas shown in the figure. Then the leafis tested for starch. Except the portion‘A’, the remaining portion will notanswer for starch test. Since theremaining part did not get sunlight,they could not prepare starch. Thisshows that sunlight is necessary forphotosynthesis (Fig. 10.16).

Fig. 10.16 Light Screen Experiment1. The region of the leaf with starch2. The region of leaf without starch

Mohl’s half leaf experiement

Corbon-di-oxide is necessary forphotosynthesis. As shown in the Fig.10.17 set the apparatus so that half ofthe leaf is inside and half outside thebottle. The part of the leaf which ispresent outside the bottle gets sunlight,Corbon-di-oxide and water. But thepart that’s present inside the bottle getsall the factors except corbon-di-oxide,as the pottassium hydroxide absobrscarbon-dioxide. So the part that ispresent outside the bottle can preparestarch and the part which is presentinside the bottle cannot prepare starch.From this it is proved that corbon-di-oxide is necessary for photosyntheis(Fig. 10.17).

Fig 10.17 Mohl's half leaf experiment1. Region of leaf with starch 2. Region of leaf

without starch 3. Potassium hydroxide

10.3.5 Respiration

Respiration is an importantreaction that takes place in all livingorganisms. The starch obtained at theend of photosynthesis is oxidised bybio-chemical reactions and energy isreleased. The released energy is usedfor various metabolic activities of theplants.

1

2

3

1

2


138

Respiration is of two types.(i) Aerobic respiration and(ii) Unaerobic respiration. Aerobicrespiration is the process during whichoxygen is utilised. During thisreaction starch is completely oxidisedand energy is obtained. Generally thistakes place in higher organisms.eg. trees, animals, birds and humanbeings.

Anaerobic respiration takes placein the absence of oxygen. During thisprocess starch is incompletelyoxidised and less energy is obtained.Generally this takes place in lowerorganisms eg. Fungi and bacteria.

Aerobic respiration takes placein higher organisms. Mitochondriapresent in the cells play an importantrole during aerobic respiration. Energyis produced during the process ofrespiration by mitochondria. So themitochondria are called power housesof the cell (Fig. 10.18).

Fig 10.18 Mitochondrin

10.4 Organ system of man

In man and higher animals, thereare separate organs for performingdifferent body functions. The union

of many organs to perform a particularbody function constitutes an organsystem. Organ systems like digestivesystem, respiratory system, circulatorysystem, excretory system, repro-ductive system are seen in animals.

10.4.1 Digestive system of man

Digestive system of man consistsof mouth, oesophagous, stomach, liver,pancreas small intestine, large intestineand anus as shown inFig. 10.19.

10.4.2 Process of digestion

You know that we need moreenergy to do work. Where from dowe get this energy? We get this energyfrom the food that we eat. But yourbody cannot get energy directly fromthe food. The food should be brokeninto simple particles. This takes placeby the process called digestion. Theconversion of complex foodsubstances into simple particles iscalled digestion. Enzymes (bio-chemical substances) are necessary fordigestion. The various parts of thedigestive system secrete various typesof enzymes. Each enzyme acts on aparticular substance and helps indigestion.

10.4.3 The changes that take placeon food in the digestive system

The digestion starts, as we chewthe food. The food that enters themouth are ground by the teeth and


139

mixed with saliva. The enzymeptyalin which is present in saliva actson starch and converts it into maltose.

The chewed food is swallowedand it enters the stomach through theoesophagus. The stomach is amuscular bag like structure. The foodremains in the stomach for about fourhours. The gastric juice which issecreted by the stomach acts on theprotein and starts the proteindigestion.

When this food reaches the smallintestine, again the food is mixed withthe secretion of the intestinal juices.By the time, the food reaches thesmall intestine, it is fully digested(Fig. 10.19).

In the duodenum, the bilesecreted by the liver participates infat digestion. The bile secreted by theliver and the intestinal juices secretedby the duodenum change the food into

simpler forms. The digested food isabsorbed by the villi of the smallintestine.

10.4.4 The end products of digestion

Protein is converted into aminoacid, carbohydrate into glucose andfat into fatty acid and glycerol. Allthe food cannot be digested. Theundigested matter is stored in the largeintestine and sent out as waste throughthe anus.

Have you seen the frogprotruding its tongue and capturingits prey? How do birds pick up theirfood grains by their beaks? You mighthave noticed the mastication of cowsafter eating their food. Do you knowhow digestion takes place in theseanimals?

The bifurcated sticky tongue ismuch useful in capturing the prey infrogs. In frog, the stomach has twoparts namely the cardiac region andpyloric region. Here the digestiontakes place as in man.

In order to fly, birds need moreenergy. So birds have to take morefood. As there are no teeth in the beak,the birds swallow the food as suchinto their crop without chewing withsaliva. The crop is present in front ofthe neck region. The food collectedby the crop is ground in the gizzardand then digested in the stomach.

1

2

3

45

6

7

8

Fig. 10.19 Digestive system

1. Mouth2. Oesophagus3. Stomach4. Liver5. Pancreas6. Small intestine7. Large intestine8. Anus


140

There are four chambers in thestomach of cow. The food that cowsfeed on, has plant fibers. The fibrescontain more cellulose material. Thiscellulose is digested by the bacterialiving in the stomach. The swallowedfood is stored in the stomach for sometime. When the cow is at rest, theswallowed food is again taken backto the mouth and chewed. Thisprocess is known as mastication.Then the masticated food getsswallowed again and passes back intothe stomach where it is completelydigested.

Activity 10.4

Arrange the following organs ofthe digestive system in sequence.

Stomach, large intestine,oesphagus, deuodenum, anus, mouthand small intestine.

Activity 10.5

Match the following

(i) Large intestine - Secretion of bile

(ii) Stomach - Teeth grind thefood

(iii) Liver - Digestion ofprotein

(iv) Mouth - Storage of waste

(v) Deuodenum - Digestion of fat

Activity 10.6

Correct the following

Bile juice is the juice secretedin the mouth. It contains mineral

salts. This begins the digestion ofprotein. The carbohydrate digestionstarts in stomach.

In deuodenum, saliva andgastric juice are secreted. Hereprotein, fat and starch are convertedinto simple sugar, amino acids andfatty acids respectively. Undigestedfood is eliminated from smallintestine through the anus.

10.5 Circulatory system of man

How do we get food and oxygento all the tissues and cells of ourbody? The blood which is present inthe blood vessels of our body takesthese materials to all parts of the bodyby means of circulation. Heart is theorgan which pumps blood to all partsof the body.

Fig. 10.20 Logitudinal section of human heart1. Right auricle 2. Right ventricle

3. Left auricle 4. Left ventricle

The heart which is present inbetween the lungs consists of fourchambers. There are two auricles onthe upper side and two ventricles onthe lower side. The heart is coveredby a membrane called pericardium.The wall of the heart is made of strong

4

3

2

1


141

muscles. This helps for the contractionand relaxation of the heart and forpumping the blood with force in theblood vessels.

When the heart contracts, bloodfrom the heart enters the blood vessels.When the heart expands the bloodfrom all parts of the body enters theheart. Since the heart functions like apump, blood circulates continuouslythrough out the body.

Every time when the heartcontracts, the blood from the heart issent to the blood vessel called artery.The arteries are made up of elasticand thick walked muscles. The arteriescarry pure blood (Fig. 10.20).

The arteries then give rise to formcapillaries. The capillaries are minuteblood vessels. The arteries are thevessels that carry the food and oxygento the cells.

The walls of the veins are thin

and less elastic in nature. The veins

carry the impure blood to the heart.

The heart sends the impure blood to

the lungs for purification. In lungs the

blood releases carbon-dioxide and

receives oxygen. Then the blood is

taken back to the heart for further

ciculation (Fig. 10.21).

Do you know why the blood is

red in colour? The presence of

haemoglobin in the red blood cells

gives red colour. Red blood cells

(RBC), white blood cells (WBC) and

platelets are present in the blood.

Heart, artery, capillaries and veins

together form the circulatory system.

William Harvey (1628) wasthe first who discovered thefunctions of heart and thecirculation of blood.

The average heart beat of man is

70-72 times per minute. The heart beat

rate increases while running fast or at

the time of doing exercises. The

stethoscope is an instrument used to

hear the heart beat.

Activity 10.7

Keep your right hand behind thewrist of your left hand, just below thethumb. You can feel the pulse beat.

5

42

1

3

6

7

Fig. 10.21 Circulatory system1. Lungs 2. Carries blood to upper part of the

body 3. Carries blood to lower part of the body4. Carries blood to lungs 5. Blood reaches fromlower apart of the body to heart 6. Organs above

the heart 7. Organs below the heart


142

Find out how many times the pulsebeats per minute? This is your pulserate (Fig. 10.22).

Fig. 10.22Pulse rate

Infer

(i) The heart of the fish is made upof two chambers.

(ii) In amphibians there are threechambers eg. Frog.

(iii) Completely separated two atriaand two incompletely separatedventricles are present in reptileseg. Garden lizard.

(iv) In birds and mammals the heartis made up of four chambers.There are the two atria and twoventricles.

10.6 Excretory system in man

The removal of waste productsfrom the cells of the body is knownas excretion.

10.6.1 Waste products

Carbon-di-oxide, the undigestedfood materials, excess of water, saltsand nitrogenous wastes which are theend products of protein metabolismare the important waste productsexcreted from the body.

10.6.2 Excretory organs

The imporotant excretoryorgans are the skin and kidney.

Kidney of man

The most important excretoryorgans in man are kidneys. There aretwo kidneys one on either side of thevertebral column in the lumbar region.Nephrons are the important functionalunits of kidneys. In the nephron thereare two parts namely the Bowmann'scapsule and uriniferous tubules(Fig. 10.23).

The blood enters into kidneythrough renal artery. Nephrons,separate the waste products and excessof water from the blood. The pureblood after the removal of the wasteproducts comes out from the kidneyby renal vein. The urine formed ineach kidney is stored collected in theurinary bladder through ureters.When the urinary bladder is filledwith urine, it comes out throughurethra (Fig. 10.24).

1

2

3

4

1. Kidney2. Ureter3. Urinary bladder4. Urethra

Fig. 10.23Man-Excretory

system


143

Fig. 10.24 Structure of Nephron1. Malpighian capsule 2. Uriniferous tubule

The important functions ofkidneys are the removal of wasteproducts and to maintain the waterand salt balance of of the body.

If kidney fails to perform itsfunctions, the toxic materials in the

blood are stored in the cells of thebody. This is called kidney failure.

Do you know how much of urineis excreted daily in man? The amountof urine excreted per day ranges from1.5 – 2.0 litres.

During rainy season urine isexcreted more than in summer. Butmore sweat is given out duringsummer season. Do you know thereason?

During summer skin receivesmore amount of blood. So more sweatand less urine is excreted. Sincekidney receives more blood, more ofurine and less of sweat are excretedin rainy season. Thus water balanceis maintained in our body.

SELF EVALUATION


1. The example for tap root modification is

(a) potato (b) beet-root

(c) onion (d) Colacacia

2. The plant part that is especially meant for reproduction is

(a) leaf (b) root

(c) internode (d) flower

3. The spongy tissue present in epiphytic roots is called

(a) velamen (b) vascular

(c) mesophyll (d) cuticle

4. The conversion of complex food into simple food is called

(a) respiration (b) excretion

(c) nutrition (d) digestion

1

2


144

5. Food is ground in birds by

(a) mouth (b) crop

(c) gizzard (d) beak

6. The human blood appears red due to the presence of

(a) oxygen (b) carbon-di-oxide

(c) haemoglobin (d) plasma

7. In monocots __________________ root is seen.

8. Velamen tissue is present in ____________ plant.

9. __________________ is called power house of the cell.

10. The saliva contains ___________ enzyme.

11. Heart is covered by a covering called _______________.

12. _____________________ are the important functional units of kidney.

13. What is root modification?

14. Define prop roots.

15. What are the types of sub aerial stem?

16. Why does food remain four hours in the stomach?

17. What happens if urine is not excreted properly?

18. Name the chambers of human heart.

19. Define tap root system.

20. What are the functions of stem?

21. What is the function of stomata?

22. What is meant by mastication?

23. What are veins?

24. What is kidney failure?

25. Explain the modifications of tap root system.

26. How do plants respire?

27. Draw and describe the parts of a leaf.

28. Draw the structure of urinary system and label the parts.

29. Draw the structure of flower with label.

30. Draw and label the structure of a plant.


145

11. Our Environment11. Our Environment11. Our Environment11. Our Environment11. Our EnvironmentIn our environment, different

kinds of living and non-living thingsare seen. Can you tell what are thosethings? They are herbs, twiners,shrubs, trees, man, animals, water,soil, stones etc. Among these, plantsand animals including man are livingbeings. Water, soil etc. are non-livingthings. The living organism and theenvironment have close relationshipbetween them.

When you observe keenly, youwill realise that there is an inseparablerelationship between living organisms

and non-living things. In this lessonlet us discuss how the livingorganisms and non-l iving areinter-related with each other.

Ecology

In nature, plants and animalsdepend on one another. The termecology was coined by the zoologistReiter and it was defined by ErnestHaeckel in 1869. According to hisdefinition ecology is a branch ofscience dealing with the relationshipbetween living and non-livingcomponents of the environment(Fig. 11.1).

Fig. 11.1. Ecosystem


146

Activity 11.1

With your teacher, visit a pondor water pool and observe the plantsand animals in the water. Based onyour observation prepare a list ofplants animals and insects.

Activity 11.2

Have you seen how the fishesare reared in glass tanks? Observe itand make a list of things found in it.

11.1 Ecosystem

An ecosystem is a part of natureconsisting of biotic and abioticfactors. Shall we study about theecosystem in this chapter?

Ecological factors

Each and every living organismdepends on the environment for food,shelter and reproduction (Fig. 11.2).

The biotic components areaffected by the environmental factors.

The ecological factors may beclassified into two components viz.(1) Biotic factors and (2) Abioticfactors.

11.1.1 Abiotic factors

In an ecosystem, the abioticfactors play an important role. Water,air, Sunlight, temperature, pressure,carbon-di-oxide, oxygen, nitrogen aresome important abiotic factors.

11.1.2 Biotic factors

Micro organisms, plants andanimals constitute the bioticcomponent.

Biotic factors

The biotic factors are classifiedinto three groups. They are

Fig. 11.2. Terrestial ecosystem showingthe activities of (a) feeding (b) dwelling

and (c) selecting mates.

(b)

(c)

(a)


147

(i) Producers (ii) Consumers and(iii) Decomposers.

(i) Producers

Plants which synthesise theirown food material by the presence ofchlorophyll are called producers.eg. All types of green plants.

(ii) Consumers

Organisms which make use ofthe food produced by the producersare also called consumers. Consumersare classified into three types.

a) Hebrivores

The animals which eat onlyplants are called herbivores and theyare also called primary consumers. eg.deer, rabit, cow and rat.

b) Carnivores

Animals which feed on theherbivores are called secondaryconsumers or carnivores. eg. fox,wolf, snake.

c) Omnivores

Those organisms which feed onboth plants and animals are calledomnivores. eg. man, dog.

(iii) Decomposers

Organisms which decompose thedead bodies of producers, consumers,and waste food substances are calleddecomposers. eg. bacteria

Producer Pri. consumer Sec. consumer Tertiary consumerPlants Rat Snake Eagle

Fig. 11.3 Food Chain

In an ecosystem, one can observethe transfer or flow of energy fromone organism to other in succession.The organisms which feed on primaryand secondary consumers are calledtertiary consumer eg. eagle.

Transfer of energy from oneorganism to another is called foodchain. The energy flows fromproducer to tertiary consumer asshown in Fig. 11.3.

Activity 11.3

Along with your teacher, visit apond near your school. Observe thebiotic and abiotic factors. Tabulateyour findings.Table of a

S.No. Biotic factors AbioticPlants Animals factors

1 ................... ................... ..................

2 ................... ................... ..................

3 ................... ................... ..................

4. ................... ................... ..................

11.1.3 Types of ecosystem

Based on the nature of livingbeings and the environmental factorssurrounding them, the ecosystemcosists of following types (Fig. 11.4).

1. Fresh water ecosystem

2. Marine ecosystem.

3. Forest ecosystem

4. Grass land ecosystem

5. Desert ecosystem

→ → →→ → →→ → →→ → →→ → →


148

11.2. Aquatic organisms

Remember the organisms youhave observed in a pond. Eichhornia,Vallisneria, Pistia, lotus, lilly etc. areexamples for aquatic plants. Frog,fish, snake etc. are some of theanimals living in water. The place inwhich an organism lives in known ashabitat.

Aquatic habitat is divided intofresh water and sea water dependingupon the salts and other materialsdissolved in it. So different types ofanimals live in sea water as well as infresh water.

11.2.1 Hydrophytes

Plants living in ocean, pond,lake, river and marshy places arecalled hydrophytes.

The hydrophytes haveadaptations suited for living in aquaticenvironment. The root system is notwell developed. In the stem and leaflarge inter–cellular air spaces or

cavities are found. For dispersal ofseeds the fruit is weight less with airfilled fibrous tissues.

Activity 11.4

Arrange the students to see waterbodies and show the adaptations ofthe aquatic plants such as lilly,Eichhornia etc. growing on it. Whydoes Eichhornia float on water? Showthe floating Eichhornia leaf. Taketransverse section of petiole ofEichhornia leaf and show theoccurrence of large air spaces in it.

Based on the nature of theiroccurrence, the hydrophytes arefurther classified into four kinds asfollows.

(i) Free floating (ii) Submerged(iii) Floating and rooted(iv) Amphibious

(i) Free floating plants

eg. Eichhornia

This plant floats on the surfaceof water. This is not rooted in the soil(Fig. 11.5.)

Fig. 11.5

Eichhornia

(ii) Submerged plants

eg. Vallisneria

This plant is completely sub-merged into the water and is alsorooted to the mud (Fig. 11.6).

Fig. 11.4. Types of ecosystem1. Terrestial ecosystem 2. Aquatic ecosystem

1

2


149

Fig. 11.6 Vallisneria

(iii) Floating and rooted plants

Nymphaea

This plant is rooted to the mud.But the leaves and flowers float onthe surface of water (Fig. 11.7).

Fig. 11.7 Nymphaea

(iv) Amphibious plant

eg. Limnophila heterophylla

This plant isrooted to the mud. Theupper portion of thestem is projected intothe air (Fig.11.8).

Fig. 11.8 Linnophilaheterophylla

11.2.2 Mesophytes (plants of fertilelands)

Write the names of the plantsaround your school and house. Plantsgrowing under average conditions oftemperature and moisture are calledmesophytes. Mesophytes are ordinaryland plants (Fig. 11.11). eg. mango,jack fruit, guava, banana, drumstick,Hibiscus, etc.

Activity 11.5

Have you seen the shoe - flowerplant Hibiscus? Observe that plantwhere it grow?

11.2.3 Xerophytes

Plants that grow in places ofwater scarcity are called xerophytes.These plants have adaptations suitablefor living in dry places. These plantshave succulent tissues and in whichlarge amount of water is accumulated.The number of leaves are reduced andthe leaves are modified into spinesand scale leaves.

eg. Opuntia (Fig. 11.9)Casuarina and tirucalli.

Fig. 11.9. Opuntia


150

11.2.4 Aquatic animals

In fresh water habitat like ponds,lakes, streams different types ofanimals are living. The plankton likecopepods, rotifers, astrocods,swimming organisms like fish,tortoise, organisms like water spiders,mosquito, larvae, snails, Hydra andflat worms are seen (Fig.11.10) here.

11.2.5 Terrestrial animals

In terrestrial habitat differenttypes of animals with various typesof adaptations are found. It is due tothe presence of various terrestrial ecosystem. The habitats like forests, grasslands, tundra regions and deserts areexamples for terrestrial ecosystems.

The animal which is present inone habitat will not be in anotherhabitat. In forests, organisms likewood peckers, squirrels, Elk deers,rabbits, foxes, dotted deers, elephants,monkeys, toads, snakes, eagles,different types of insects and lowerorganisms like leeches, snails,millipedes and centipedes are present(Fig. 11.12).

The grass land animals includebison, antelope, zeebras, sparrows,kangaroos, birds and locusts(Fig. 11.13).

Treeless plain arctic region iscalled Tundra. Here animals likearctic rabbits, arctic fox, reindeer,migratory birds, penguins and polarbears are seen.

In desert, which is the dry regionof the earth, animals like rats, camels,

2

3 4

Fig. 11.10 Fresh water animals

Fig. 11.12 Terrestrial Animals

In sea water, organisms like seasponges jelley fishes, sea horses,crabs, neries, star fishes seacucumbers, sharks, whales, sea birdssea snakes are present (Fig. 11.11).

Fig. 11.11 Sea water animals1. Crab 2. Prawn 3. Sea cucumber 4. Shark

1


151

Fig. 11.13 Grass land and Desert animals

hedge hog, porcupine and insects likelocusts are found.

11.3 Role of plants in theenvironment

The role played by the plants inthe environment is very important.They are as follows : 1) For all livingorganisms, directly or indirectly plantsare the only sources of food. 2) Theyenrich the oxygen supply in theenvironment. 3) They subside theenvironmental temperature 4) Plantscontrol air pollution.

Contamination of environment isknown as pollution.

11.3.1 Purification of air duringphotosynthesis

During photosynthesis carbon-di-oxide is utilised from the atmosphereand oxygen is given out by plants andthe air is purified.

Why are the hill stations calledhealth resorts? Because the large

number of plants available on the hillsreleases large amount of oxygen. Asa result the air surrounding the hillstation becomes purified.

Role of plants in pollution control

Some plants are useful for thetreatment of sewage water. Forexample plants such as Eichhornia,Chlorella (Fig. 11.14) are reported toabsorb the toxic substances fromsewage water. Their occurenceindicates the presence of pollutantsin the water. Hence, they are calledpollution indicators.

Fig. 11.14

Chlorella

Trees reduce air pollution. Inareas where industries areconcentrated, the air is very muchpolluted. Such polluted air causesserious respiratory and other health

KangarooDeer

SparrowCamel

Snake

Bison


152

problems. To prevent air pollution,plants particularly, trees have to begrown in large numbers. They protectthe environment. Growing trees liketamarind, neem, mango, etc. on bothsides of the road will reduce pollutionof air and provide shade to us. Fallingof trees and deforestation are thecauses for low rainfall. Henceprotection of forest is very importantone (Fig. 11.15).

Fig. 11.15 Deforestation

At our gardens, we should growas many plants as possible includingornamental plants. The forest depart-ments plant a number of avenue treesin the streets and on road sides. Weshould take care of them, since thetrees give us good oxygen supply andcontrol the temperature of theenvironment.

Trees for fire wood andcommercial purposes may be grownseparately. In the school also trees andother plants should be planted andprotected. Will you do it?

11.3.2 Source of rainfall

No living organisms can existwithout air.

Forests are the important sourcesof rain. Continuous and heavy rainfall in the bigger mountainous regionsis due to the occurrence of thickforests. Transpiration takes place inplants. The water vapour that isreleased during transpiration iscollected in the sky and transformedinto clouds. On condensation, theclouds pour down water as rain. Thusforests are the important sources forrain. As a result of rainfall, the waterin the ground raises up. The lakes,ponds, pools, wells, etc. get filled withrain water. Thereafter this water ismade use for so many activities. Therain water may be stored in dams andlakes for future use. In addition, therain water falling on earth flows asrivers. This water is availablethroughout the year for agriculture,drinking and domestic purposes(Fig. 11.16).

Because of destruction of forestsrainfall decreases resulting in thelowering of ground water level anddrought condition sets in. To avoidsuch adversity, our Government has

Fig. 11.16 Forests

Don’tcut me


153

introduced ‘rain water harvestingplan’. Accordingly, everyone of usmust carryout the rain waterharvesting plan.

11.3.3 ‘Rain water harvesting’ inindividual home.

“There is no living organismwithout the water”. Water is essentialone for existence.

The ultimate source of drinkingwater is the rain. Hence withoutwasting the rain water, it may bestored in the underground for futureuse. This is the aim of rain waterharvesting.

The rain water is collected bytwo methods.

1. Collection of rain water fromthe surface of terrace.

2. Collection of rain water fromthe open space.

In order to make the rain waterreaching the water table, cementflooring must be avoided around thedwelling place and particularly aroundthe well.

Rain water that falls on terraceis carried through pipes to a filtertank. The size of this tank must be1 m × 1.5 m. This filter tank is filledhalf with pebbles and broken bricks.Water from this filtertank is carriedby pipes to the bore well for storageand future use (Fig.11.17).

Fig. 11.17 Rain water harvesting

11.3.4 Conservation of soil fertility

Fertility of the soil must beproperly protected. If fertility isreduced, growth of plants particularlythe agricultural crops and their yieldsare affected. It results in the decreasein yield. Soil erosion is an importantreason for decreasing fertility of soil.Because of soil erosion caused byrain, the fertile soil is washed away.The soil particles thus washed awayby rain water fills up on waterreservoirs and reduce the waterholding capacity. Excess usage ofchemical fertilizers and insecticidesalso reduce the soil fertility and makesit unfit for cultivation. By using greenmanure and by the practise of croprotations, the fertility of the soil maybe protected and increased. Thisresults in the increase of the yieldconsiderably.

11.3.5 Role of animals inEnvironment

You know that both beneficialas well as harmful animals are presentin the land.

The most important among theharmful animals are the Cockroaches


154

and rats. Do you know the reasonsfor their successful life? The mainreason lies in destroying thebelongings of man.

Cockroach

Do you know where cockroacheslive? (Fig. 11.18). They live in toilets,ditches and crevices of the wall. Theyare seen only in dark places. Youwould have also seen cockroachesroaming about very fastly by the sidesof the rice bags, between the vesselsand between the groceries stored inhouses, where cleanliness is lacking.Their flattened body helps them toenter the crevices on the walls. Thebody of the cockroach consists of apair of compound eyes, a pair ofantennae, three pairs of legs and twopairs of wings. The mouth has manyparts and they are called the “Bitingand chewing mouth parts”. So withthe help of these mouthpartscockroach can bite and chew hardfood-stuffs. This is an omnivorousanimal.

Fig. 11.18 - Cockroach1. Head 2. Compound eye 3. Leg 4. Thorax

5. Abdomen 6. wing

Cockroach as a scavanger

What are scavangers? Theorganisms which help to keep thesurroundings clean are called asscavangers.

Cockroach spoils the food itemsIt also acts as scavanger. It eats the verysmall insects found on fruits andvegetables. It consumes the foodpoisoning insects.

Rat

Let us see the causes for thesuccessful life of rats.

Rat is a herbivore mammal.(Fig. 11.19). Hairs are found on theskin. A pair of fore limbs and hindlimbs are seen and they are meant forlocomotion. Though the life span isshort, it has the fast rate ofreproduction. In a year a pair of ratmultiplies into two hundred of rats.At a time, a single rat gives birth toten to fifteen young ones. Withinthree months, they attain theirreproductive capacity.

Rat eats both tender paddy aswell as paddy grains. The amount ofgrains damaged by the rat will bemore than the amount of grains eatenby them. They excrete their faecalmatter on the grains stored by us andmake them unfit for use. Rat storesabout 2 - 2½ kg of grains in the holewhere it lives.

1

23 4

6

5


155

Fig. 11.19 - Rat

Plague is an important diseasespread by the rat. This disease iscaused by a bacteria “Ercinia pestis”A type of mite by name “Xenopsylla”is the vector of this infectant. Thesemites live and reproduce on the skinof rat and cause lethel effect by itsinfection on the rat itself. Thexenopsylla infected by the bacteriabecome contagious. The infected mitesand infected rats cause plague in man.Since plague is transmitted to man byvertebrate animal, it is zoonoticdiesease.

Chironomous larva which livesin drainage is one of the decomposers,because it decomposes the wastes inthe water and eats the same. Sincemosquito larve feed on dead andwaste matter, they are called detritusfeeder.

11.3.6 Recycling by earthworm

The convesion of used wastematerials into useful product is calledrecycling. Earthworm, plays a majorrole in this process (Fig. 11.20).

It is a known fact thatearthworms are the “Friends of thefarmer”. But you should know why

it is called so? The inter relationshipbetween the earthworm and the soilwas found by Charles Darwin. Theearthworm eats the soil and theundigested soil comes out as excrete.This excrete increases the fertility aswell as the air circulation of the soil.They also play an important role inthe conversion of natural wastage intomanure. So the crops grow healthy.Therefore the earthworms are called“Friend of the farmer”.

Fig. 11.20 (a) Earthworm (b) Millipede

Infer

Mites, millipedes and centipedesalso decompose the dead organismsand increase the soil fertility.

Activity 11.6

List out the beneficial andharmful animals to man.

S.No. Beneficial Harmfulanimals animals

1 .................. ..................

2 .................. ..................

3 .................. ..................

4 .................. ..................

5 .................. ..................

6 .................. ..................


156

11.4 Role of man in environment

Man is a terrestrial organism. Itis an undeniable fact that man is theonly “Master of the environment”. Letus see how man plays a vital role forthe changes in the environment.

Population growth is animportant factor, which affects theenvironment. Due to increase in thenumber of factories the environmentis being polluted. Now let us knowhow the environment is polluted bythe industries.

Fig. 11.21 Factory

The wastes from the industriespollute the land, water and air. Thepoisonous waste materials, that arereleased from the factories are mixedwith pure water. So the water ispolluted and the organisms living inthe water and the man who uses thewater are affected badly. Every year2.2 millions of people die, because ofpolluted water. About 40% of theworld’s population is struggling forthe need of water.

Gases like carbon-di-oxide,Sulphur-di-oxide, methane are present

in the smoke that comes out from theindustries. These pollutants not onlypollute the atmosphere, but also therain water, which in turn reaches theearth and thereby the land is alsopolluted. Every year three millionpeople die out of air pollution(Fig. 11.21).

Activity 11.7

Make a trip to a nearby industryalong with your science teacher, andknow how lands and air are polluted?

Man cuts down the trees forfirewood and house construction. Sothe rainfall decreases and causes thedrought. Destruction of the forests andpaddy fields by man to constructhouses and industries are certainexamples how the scarcity of foodoccurs and affects the ecosystem.

You should realise that in thismodern world, as the need increases,the hazardous factors are alsoincreasing.

What are the measures to betaken to control the pollution? youshould follow the followingcontrolling measures.

(i) You should plant more treesinstead of cutting trees.

(ii) You should not pollute thewater reservoires and land by thewaste materials and instead, we shouldrecycle the wastes and use them.


157

SELF EVALUATION


1. The word environment was defined by

(a) Reiter (b) Ernest Haeckel (c) Odum (d) Darwin

2. Which one of the following is an example for xerophyte?

(a) Opuntia (b) bean (c) pea (d) Hibiscus

3. The source of rain is

(a) land (b) forest (c) animal (d) sunlight

4. The gas given out during photosynthesis is

(a) oxygen (b) carbon-di-oxide

(c) nitrogen (d) carbon-monoxide

5. Which of the following is plankton?

(a) Frog (b) Fish (c) Rotifer (d) Tortle

6. Which is a scavanger?

(a) Cockroach (b) Rat (c) Lizard (d) Dog

7. Which is the “Friend of the farmer”?

(a) Leech (b) Ant (c) Earthwarm (d) Snake

8. _________________ is a abiotic factor.

9. Primary consumers are otherwise known as _____________.

10. ___________________ is a vector for plague.

11. The number of young kids given birth by a rat at a time is ________.

12. What is photosynthesis?

13. Give two examples for xerophytes.

3) You should avoid using ofpolythene bags. The gases whichcome out, on burning the plasticthings are poisonous. It is found that

these gases cause cancer. Non-conventional energy and solar energyshould be used.


158

14. What is meant by rain water harevesting?

15. Define Ecology.

16. What is the role of Chlorella in ecology?

17. Why should we protect the forests?

18. What are the types of aquatic habitat?

19. Why is earthworm called as the “Friend of the farmers”?

20. How do the rats spoil the grains?

21. Write about the biotic components of environment.

22. Describe hydrophytes.

23. Describe rain harvesting system.

24. Rat is a harmful organism. Discuss.

25. Explain the man made changes in the environment.

Few informations ...

Snakes can live without food for several months.

The crocodile can sleep keeping its eyes open.

Kangaroo is not found in any other country except in Australia.

Hippopotamus is an herbivore.


159

Plants are very useful for ahealthy life. Similar to the plantsanimals are also useful in many ways.In this lesson let us discuss that howthe plants and animals are helpful forour healthy life.

12.1 Uses of plants and animals

The plants are the sources offood, clothing and shelter. Foodgrains, vegetables, fruits, oil seeds,drugs, cosmetics, cotton and rawmaterials for various industries areobtained from plants. Similarly milk,butter, ghee, leather, silk, honey etc.are obtained from the animals.

Due to the cutting of trees,hunting of animals and such otherharmful activities, the forests aredestroyed. It is our duty to protectour forests and animals living in them.

12.1.1 Rubber : Uses of rubber

Nowadays the usage of rubberproducts is indispensable. The rubberis derived from plants only.

It has been found that as manyas 35 species of plants yield rubber.The botanical name of the importantspecies among these is Hevea

brasiliensis. The rubber plant whichis growing as tree, was firstdiscovered by ChristopherColumbus. It was Joseph Priestlywho gave the name rubber to thesubstance obtained from rubber plant.Hevea brasiliensis is also called aspara rubber plant. As much as 99%of rubber produced in the world isobtained from Hevea brasiliensisonly. This plant is a native of Amazonvalley in South America. At present,rubber is cultivated widely in Africa,Malaysia, Thailand and India.

In our Tamil Nadu state rubberis cultivated extensively inKanyakumari district. The milkyliquid substance obtained from rubbertree is known as latex. It contains therubber substance that can be separatedby processing the latex.

Quite a number of industries isworking based on rubber. Rubber isused in tyre industries, in makinghousehold articles, electrical goods,hospital instruments, telephonecomponents, toys, writing materials,sports goods, foot wears, etc.(Fig.12.1).

12. Applied Biology


160

Fig. 12.1 Rubber tree

1. Latex 2. Collection of latex

12.1.2 Ornamental plants

Plants which are beautiful arecalled ornamental plants. They giveus pleasant appearance. Some of theornamental plants are shoe flower,Ixora, Mussaenda, Dahlia, Orchids,Heliconia, Sunflower, Crotons, etc.are grown in the garden (Fig.12.2)

Fig. 12.2. Ixora

12.1.3 Pollination by insects

Have you noticed insects flyingaround the flowers? Can you tell thereason why insects visit the flowers?The reason is this. Flowers producenector and pollen grains. They are thefood for many kinds of insects. The

insects visit the flowers. They sit onthe flowers to suck the nector. Duringsuch times, pollination takes place.

The transfer of pollen grains tothe stigma of a flower is known aspollination. It is of two types. (i) Selfpollination and (ii) Cross pollination.

The transfer of pollen grains tothe stigma of the same flower isknown as self pollination. Thetransfer of pollen grains from antherof one flower to the stigma of anotherflower found in the another plant ofthe same kind is called crosspollination. In number of plants, crosspollination takes place by insects.Among the insects butterflies andhoney bees are important agents forpollination.

Cross pollinated flowers possesscertain features, such as attractivebright colour, smell and nector.

A good amount of honey issecreted in the flowers of Leucasaspera (Thumbai chedi - Fig. 12.3).Insects visiting these flowers forhoney help in cross pollination. In aplant called Yucca, pollination takesplace only by a specific insect.

Fig. 12.3.Leucas aspera

1

2


161

12.1.4 Dispersal of seeds

If the seeds produced by a plantfall around it and germinate, theycannot grow normally. For normalhealthier growth of a plant suitablespace is required. The nutrients, waterand sun light are also necessary. Thesemay not be available to all plantswhen they are found in crowd. Incontrast to this, if seeds are dispersedto different places, there are moreopportunities for them to growvigorously. Because of this, manykinds of seeds have adaptive features.Dispersal of seeds and fruits takesplace by different methods.

(i) Dispersal by air

(ii) Dispersal by water

(iii) Dispersal by animals

(iv) Dispersal by explosion.

(i) Dispersal by air

Seeds and fruits dispersed by air aregenerally smaller, winged and they areprovided with long hairs. eg. Drumstick,cotton, Calotropis, Tridax, etc.

(ii) Dispersal by water

The seeds float on the water. eg.Coconut.

(iii) Dispersal by animals

There are two types of dispersalof seeds by animals.

The seeds attached on the surfaceof animals are dispersed to longdistances. eg. Achyranthes(Naayuruvi)

Fruits of some plants with seedspass through the alimentary canal andcome out along with the excreta.eg. Ficus

(iv) Disposal by Explosion

In some plants fruits burst andliberate seeds. eg. Castor (Fig.12.4).Calotropis, bean, cotton etc.

Cotton Calotropis Been

Fig.12.4 Dispersal of seeds by explosion

12.1.5 Cattle rearing, Chickenrearing and Aquaculture

Cattle rearing

Milk is an important food. If werear the cows, we can increase ourincome as well as the economy of thenation. Among the milching cows,Thioni, Kir Red and Sahival are goodmilk yielding cows. Bulls likeKangayam, Nagori and Holiga areused to drive the carts and plough thelands (Fig. 12.5).

Fig. 12.5 Uses of cattle1. Milching cow 2. Bull 3. Ploughing

4. Bull pulling the cart

1 2

3 4


162

The cows of Oongoal, Hariyanaand hybrid cows like Jersy, BrownSwiss are used for milching. Thebeneficial animals must be potectedand managed properly without beingattacked by any diseases.

Chicken Rearing

Chicken are reared for eggs andmeat. We can increase the income byrearing chickens. Some of the foreignbreeds are known as Polymouth,Newhamshir, Brama, Susex,Leghorn and Minarca (Fig.12.6).

Fig. 12.6 Lehorn hen and Lehorn cock

Azeel, chitagong and kakal areIndian breeds. Sun light is essentialfor their health. Poultry farm shouldbe constructed where there is propersunlight.

Aquaculture

Aquaculture refers to the practiceof cultivation of economicallyimportant aquatic animals and plantsin a suitable body of water undercontrolled condition.

We can culture pearl producingmolluscan forms, arthropods such asprawns, crabs and severaleconomically important fishes in asuitable body of water. India shows

more interest in culturing andexporting prawns and artificial pearlsfor earning foreign exchange. Fisheslike Tilapia mossambicus, Mullet,Mugil cephalus and catla areartifically reared.

Activity 12.1

Make a visit to a cattle form andpoultry farm along with your teacherand try to know about the differentvarities of cows and chickens rearedthere.

12.1.6 Prevention of cruelty toAnimals

Though history says that Ashokathe great created shelter for animals,certain ashrams have been there fromthe time immemorial to protect theanimals. It is our duty to protect thenatural animals with utmost concern.

Man uses animals for variouspurposes like food, skin, milk,transport, dragging carts, research andas pets. We should not illtreat them.India is one among the countries,which adapts the animal welfare asthe Government policy. A separateministry is functioning to protect theenvironment, forest and animals.

The first Animal Protective Lawcalled Society for Preventionand Cruelty to Animals (SPCA)was enacted in the 1890 A.D.Mrs. Arundale served as the chief ofthe Animal Welfare Board.


163

12.2 Medicinal Plants

At present, there is a greatdemand for medicines prepared fromplants. Researches are being carriedout throughout the world on themedicinal plants. In our country, fromancient times, plants have been usedfor curing various diseases.

12.2.1 Importance and uses ofmedicinal plants

Aristotle, the Greek philosopher,recorded the important medicinalplants. Dr. William Withering,indicated and used a drug preparedfrom Digitalis plant for treating heartdisease. Tribals make use of plantsonly for curing all kinds of diseases.For the preparation of drugs used inAyurveda and siddha, plants are verymuch useful.

Amino acids, oils, resins, gums,mucilages, alkaloids, steroids, etc. aresome of the important substances ofmedicinal value obtained from plants.Quinine is an important drug to curemalaria. It is obtained from CinchonaOfficinalis tree.

Kizha - nelli is a good medicinalplant for curing jaundice. Thebotanical name of this plant isPhyllanthus fraternus.

12.2.2 Ginger

Zingiber officinalis is thebotanical name of ginger. Ginger isgood for health and we may take it

along with our meals everyday. It isthe best medicine for gastric and bileproblems. A drink called ‘SukhuNeer’ prepared from dried gingerpowder is good for digestion. Thedried ginger rhizome is known assukku.

The sukku drink is good forpreventing cold and vomiting. Gingeris added to soft drinks, sweets, foodadditives, masala powders anddifferent kinds of foods (Fig.12.7).

Fig. 12.7 Ginger

12.2.3 Babul tree - Karuvela Maram

There is an adage in Tamil. Thetooth sticks of banyan and Acaciagive strength to the teeth (Alum velumPallukku Urudhi). Acacia arabica isthe botanical name of Babul tree. InTamil it is called Karuvela Maram.This plant is a Xerophyte, generallygrowing in drought prone regionsAcacia is a thorny tree. The adhesivecalled acacia gum is obtained fromthis plant. Another substance calledtannin is useful for processing leather.The Acacia wood is useful formanufacturing parts of wooden cartand several kinds of modern articles.


164

The leaves and fruits are eaten bygoats and sheep.

12.2.4 Garlic

Allium sativum is the botanicalname of garlic. This belongs to thegroup of plants with undergroundstem. The stem of this plant is knownas bulb.

Garlic is good for general health.Several kinds of essential oils arepresent in garlic. It is reported thatthe extract of garlic has antibacterialproperties. Garlic is good for treatingdigestive problems, common cold etc.(Fig. 12.8).

Fig. 12.8 Garlic

12.2.5 Madar

Calotropis gigantia is thebotanical name of this plant. This iscalled ‘Erukku’ in Tamil. This plantgrows in dry lands. It is an herb. Thefruits of Calotropis at maturity burstopen to release seeds. The seeds areprovided with thin long hairy fibresby which the seeds float in the airand dispersed to other places. Whenscrached, a milky latex out flows outfrom the leaves and stems. This

substance contains numerous chemicalsubstances (Fig.12.9)

Fig. 12.9 Calotropis

12.2.6 Nithiya Kalyani

Cathyranthes roseus is thebotanical name for this plant. Extractobtained from this plant is reportedto be useful for treating cancer. Drugprepared from this plant is used toreduce excess sugar in urine. Italso reduces body temperatre.(Fig. 12.10).

Fig.12.10. Cathyranthes roseus

12.3 Food plants

Directly or indirectly we obtainfood from plants only. For someanimals also, plants are the onlysources of food. Each and every partof a plant is useful in different ways.Specifically the stem, root, fruits, etcare used as food (Fig.12.11).


165

Fig. 12.11 (a) Tomato (b) Apple

(c) Mango (d) Grapes (e) Orange (f) Banana

12.3.1 Root tubers

Root tuber is a root modification.The part of root in which the starch isstored becomes enlarged. This iscalled root tuber.

e.g. Carrot, Beet root, etc.

12.3.2 Stem tubers

The stem tuber is the modifiedpart of a stem. eg. Potato. In potato,the tips of underground branches ofstem are swollen due to the accu-mulation of starch. These branches donot bear roots. The swollen parts areoval or spherical shaped.

12.3.3 Greens – leafy vegetables

The leaves of many plants areuseful as greens. They contain fibres,iron, vitamins and mineral salts. Theseare important for good health. Forgood vision and digestion, greens arevery important.

eg. Manjal karisalan kanni,Araikeerai, Murungai keerai,Pudina, Manathakkali, Curryleaves, Agathi keerai,Kothumalli, etc.

12.3.4 Food from algae and fungi

Few algae and fungi are used asfood.

(i) Agar-agar : It is a culturemedium used in laboratories forgrwoing bacteria, fungi, algae andplant tissues. It is extracted from thered algae called Gellidium andGracilaria.

(ii) Diatomite : This is formedby the deposition of algae known asdiatoms. This deposit is calleddiatomite earth. This is used in sugarfactories for filtering the cane juiceand in the manufacture of paints.

(iii) The marine algae : They aregood sources of iodine andpotassium.

(iv) Algae such as Nostoc andAnabena are very much useful formaking the soil fertile. They absorbnitrogen from the air and convert intouseful products. These algae are usedas biofertilizers.

(v) In Japan different kinds ofalgae foods including Kombu, Aramiand Miru are prepared.

(vi) In Norway, France, America,Denmark and Newzealand, themarine algae are used as fodder.

(vii)As several marine algaecontain iodine, different kinds of medicines and ointments are prepared fromthem. Algae such as Chlorella and

(a) (b) (c)

(f)(e)(d)


166

spirullina are grown for their proteins.These constitute single cell protein.

Fungi

Among fungi, Agaricus bisporus(Mushroom) (Fig.2.12) andVolvariella. Volvacea (Oystermushroom) are important edible fungi.These fungi are producedcommercially. The unicellular fungus,yeast is used in beverages andin bakery. Yeast is source of VitaminB Complex and Vitamin C.

Fig. 12.12. Agaricus

12.3.5 Importance of vegetarian diet

The vegetarian diet contains allnutrients, including starch, protein,

fibres, iron, vitamins, fats etc. (Table12.1) It prevents the several kinds ofdiseases.

12.4 Fibre yeilding plants

Fibre yeilding plants are cotton,jute, hemp, sun-hemp, etc.

12.4.1 Importance of fibres

Fibres obtained from stems,roots, fruits, seeds of different kindsof plants satisfy the various needs ofhuman beings. Animal fibres such assilk and wool are also useful.

The fibres are used in textile,paper and coir industries. Based onthe source of fibres, they are classifiedas stem, fruit, seed, and leaf fibres.

Fibre is a thin but strong andlong thread like structure. Fibresobtained from the stem are used forthe manufacture of paper, cellophanepaper, rayon, paper boards etc.(Fig. 12.13)

S.No. Plant food Nutrients Uses

1. Green vegetables Mineral salts Bone growth

2. Root tuber (Carrot) Vitamin A To treat xeropthalmia disease

3. Cabbage, cauliflower Vitamin K For better blood clotting

4. Unpolished rice, whole grains Vitamin B1 Remedy for beri beri

5. Pulses Vitamin B6 To treat anaemia and nervous disorder.

6. Tomato, orange Vitamin C To cure scurvy

7. Tubers Carbohydrate, Body growth and energy source mineral salts

8. Stem, sugarcane Fibres sugar Growth, energy

Table 12.1 Food yielding plants


167

Fig. 12.13 (a) Cotton (b) Coir

12.4.2 Stem fibers

These fibers are obtained fromthe stem cortex and epidermis. eg.Manilahemp and pulichainar. Thesefibres are used for manufacturingropes, gunny bags, etc. These ropesare useful in construction purposes.

12.4.3 Leaf fibres

These are obtained from leavesof plants such as Agave (Katrazlai)Fibres of Agave are utilized for themanufacture of strong ropes.

12.4.4 Surface fibres

Fibres obtained from the surfaceof seeds of certain plants are calledsurface fibres. Eg. Cotton fibres.These are used in textile industries.

12.5 Oil yielding plants

Vegetable oils are obtained fromdifferent kinds of plants. eg. Groundnut, soya beans, palm, gingely, castor,etc. Some of them are edible oils. Thevegetable oils are classified asfollows:

12.5.1 Plant fats

Eg. Coconut oil, ground nut oil,gingely oil, Sunflower oil.

These oils are extracted fromseeds (Fig.14a & b).

Fig. 12.14 (a) - Coconut

(b) Ground nut (c) Sunflower

12.5.2 Easily evaporating oils

Eg. Soya

This is extracted from seeds. Onexposure to the air the oil dries outeasily.

12.5.3 Slowly evaporating oils

Eg. Sunflower. Sunflower oildoes not evaporate easily. This oil isused for cooking. This isrecommended for heart patients.

12.5.4 Non-drying oils

Eg. Castor oil, ground nut oil,etc.

This type of oil does notevaporate. Ground nut oil is used formanufacture of vanaspathi. Castor oilis used in soap and lubrication oilindustries. It is a good purgatieconstipation substance.

12.5.5 Oil extraction

Oil is extracted by differentmethods (1) by automatic machinesand (2) by country treadmill.

(a)

(b)

(b)

(a)

(C)


168

Activity 12.2

With your teacher visit an oilextracting factory and observe howoil is separated.

12.6 Pet animals

We live in an atmosphere ofanimals and plants. Look at theanimals around you. We keep someanimals and birds at home for fun andlove. They are harmless. They becomepart of our family also.

Dog, cat, rabbit, love birds andfishes are the important pet animals(Fig. 12.15).

Fig. 12.15 Pet animals

Activity 12.3

List out the pet animals of yourhouse.

12.6.1 Dog and Cat

If you are asked about thecommon pet animals of your house,you’ll readily answer as dogs and cats.Pet animals like cats and dogs can betamed to play. They play with themembers of our families. Children

love to play with them. They give joyto us.

Cat plays an important role inkilling the rats, which spread diseaseslike plague and Leptospirosis andthus they protect us from the infectionof diseases (Fig. 12.16).

Fig. 12.16. A cat chasing a rat

Activity 12.4

Notice how your cats and dogsare helpful to you in your house.

Dog is a faithful animal. Dogsare our favourite friends. They chasethe strangers and theives out. It guardsthe house. Since dog’s sense of smellis thousand times greater than us, dogsare trained and used in modernsecurity system (Fig. 12.17).

Fig. 12.17 Dog barking at a stranger

12.6.2 Rabbits and love birds

You know that rabbits andlove birds are also pet animals. Rabbitis a weak an timid animal. Rabbitsare very lovely to look at withdifferent colours. Their ears are very

Rat

Cat


169

large and look like ear-trumpet. Therabits are always alert with their longears moving around to receive thesound.

They are very sensitive to the senseof smell. As their hind limbs are long,they are capable of running fast (Fig.12.18(a)).

Like wise, the love birds arebrightly coloured to look at. Theirchirps are pleasant to hear and it givesus relief from tensions. They feed ongrains and grams (Fig. 12.18b).

Fig. 12.18(b) Love birds

Activity 12.5

Make a cage and keep one pairof love birds in it and watch theiractivities.

12.6.3 Aquarium

Fish is a familiar organism tous. Now let us learn how fishes arereared as pet animals. Do you know

where fishes are reared in houses?Have you seen fishes of differentcolours in glass tub? If not ask, yourscience teacher to arrange a picnic toa nearby aquarium and notice them(Fig. 12.19).

Fig. 12.19 Fish tank

Activity 12.6

Arrange a fish tub with differentcolours of fish in your class room andobserve their growth and movements.

Here is a list of aquarium.(1) Guppies (2) Fighter (3) Gourami(4) Black molly (5) Golden fish(6) Tiger fish (7) White molly (8) Angelfish.

Learn how to maintain a fish tank.Take a clean glass tank of thedimensions 45 cm × 30 cm × 30 cm.Put some cleanly washed sand into it.Water plants like Vallisnaria andHydrilla have to be grown inside thetank. Then leave the fishes in to thetank.

Many fishes are capable oflaying eggs. Some fishes directly givebirth to young ones. Fishes build theirnest with foam and lay eggs on them.The male fishes guard the nests.

Fig. 12.18(a) Rabbit


170

Rearing of aquarium fishes is notonly a time passing aspect, but it isan earning activity also.

Uses of pet animals.

(i) Pet animals give us joy.

(ii) They give an entertainment forus.

(iii) Rearing of dogs and aquarium

fishes are considered asprofitable business.

(iv) Dog guards our house. With thehelp of trained dogs of its subtlesniffing capacity, they are usedby police to trace the criminals.

(v) Cat destroys the rats of ourhouses.

SELF EVALUATION


1. Rubber plant was first discovered by

(a) Galileo (b) Christopher Columbus

(c) Aristotle (d) Socrates

2. Plant used to cure jaundice is _________

(a) Grass (b) Kizhanelli (c) Bean (d) Hibiscus

3. The oil recommended to heart patient is ___________

(a) coconut oil (b) gingely oil

(c) castor oil (d) sun flower oil

4. Which among the following chicken belongs to foreign breed

(a) Azeel (b) Plymouth (c) Kakal (d) Chitakong

5. The pet animal which runs fast

(a) Cat (b) Cow (c) Rabbit (d) Bull

6. Which among the following is an aquarium fish

(a) Catla catla (b) Gourami (c) Thilapia (d) Cebalus

7. In _______________ plant, pollination takes place by one specific insect.

8. The botanical name of ginger is ____________.

9. ______________ is an example for plant surface fibre.


171

10. ______________ is a hybrid cow.

11. The sense of smell of dog is ___________ times that of man.

12. The nest of the fish is formed by ________________.

13. What are the factors necessary for the growth of seeds?

14. Define self pollination.

15. How are the fibres classified according their structures?

16. Mention the types of seed dispersal mechanisms.

17. Name five plants whose leaves are used as food.

18. What are the medicinal uses of ginger and garlic?

19. What are pet animals?

20. How are dogs helpful to us?

21. What is the importance of medicinal plants?

22. Give an account of oil and importance.

23. Explain the uses of any two medicinal plants.

24. What are the uses of pet animals?


172

13. Health and HygieneWe have studied the functions of

different organs of our body. In orderto have smooth functioning of theseorgans and to lead a disease freehealthy life, good health and hygienichabits are essential. Good health givesnecessary energy to do all activitiessuch as exercise, over comingtiredness etc., and it requires goodnutrition. Hygenic habits includecleanliness of external and internal lifestyle of the human body.

13.1 Health - General features

“Health is wealth” is a knownproverb. The happiness of a man liesin his health. It is an invaluablebelonging to him. The widelyaccepted definition for health givenby World Health Organization (WHO1948) is as follows.

Fig.13.1. Appearanceof a healthy child

“Health is a stage of completephysical mental and social well beingand not merely the absence of diseaseor infirmity”. See the height - weight

relationship (Table 13.1).

Table 13.1

Age Weight(kg) Height(cm)

At birth 3 501 year 8 72.505 years 14.5 101.5010 years 23.5 128.515 years 39 149.520 years 43.5 151.5

13.1.1 Health factors

Some of the parameters whichreveal the healthy condition are

i) Height and weight according tothe age.

ii) Bright eyes

iii) Lustre hair

iv) Healthy teeth and

v) Wrinkle free skin

Fig. 13.2 Appearance of unhealthy child

See the appearance of healthyand unhealthy children in Fig. 13.1and 13.2 respectively.


173

Appearance of unhealthy child

We should follow certainmeasures to maintain healthy body.We should take nutritious food intime. We should take adequate rest.We need relaxation and rest afterexercising some work. Sound sleep isessential for the proper functioningof brain and other body activities.Since the body is in complete restwhile sleeping, it can function veryactively after the sleep.

The important organ whichcommunicates us with ourenvironment is the eye. Our eyes mustbe taken care of properly. Vitamin Ais highly essential for eyes. VitaminA is available more in carrot andpappaya. We should take suchvegetables in plenty. We must washour eyes twice a day with pure water.If we read in dim light it will affectour eye sight. We should avoidwatching T.V. for a long while.

By eating nutritious food anddrinking pure water, we can protectourselves from diseases.

Fig. 13.4 Playing games

Our mind should be free frommental conflicts. Proper exercise andout-door games are helpful to regulatethe body activities such as circulation,digestion and respiration (Figs. 13.3and 13.4).

13.2 Health related values

Your mental health is also a partof your health. A person having goodhealth and mind is very active withgood physique. They can acquiregoodwill at home as well as from

(a) Eating healthy food (b) Taking rest (c) Reading in bright light

Fig. 13.3 Certain guide lines for good health


174

public. Such persons alone can adjustwith others without any selfishness.

You should have love for yourparents and others around you. Beinghelpful to one and all is essential tobe a good human being. Beingtruthful, having friends with goodhabits, being regular to school,learning the lessons well and fulfillingyour responsibilities are all importanthealth related values.

13.2.1 Care for others

When you step out of your houseyou should be ready to help others.

i) If you come across a blindperson, you must be ready tohelp him.

ii) If you happen to witness anaccident, you should immediatelyinform to the nearby hospital andto the victim’s relatives helpthe injured in time.

iii) Help the aged person to crossthe road (Fig. 13.5).

iv) When you happen to travel intransport buses you may leaveyour seat to the aged andhandicapped people.

Fig. 13.5 Some good habits

13.3 Nutrition and the importanceof food

Food is necessary for the survivalof organisms, because they areessential for the growth of the healthybody. It is also essential for creatingresistance against the disease causinggerms and for giving energy to thebody. Activities like in take of food,digestion, absorption, metabolism andexcretion together constitute nutrition.Nutrition enables us to grow well andenjoy good health.

13.3.1 Constitutents of food

Everyday, we eat varieties ofsmall food items like idli, dosa,chappati, pulses, greens, vegetables,fruits and milk. The nutrients likecarbohydrates, proteins, lipids,vitamins and mineral salts are presentin these food items and they performsome important functions (Fig. 13.6).

Fig. 13.6 Food items(a) Body builder (b) Energy producer

(c) Regulator

(a)Proteins

(b)Carbohy-

drates

(c)Vitamins


175

Activity 13.1

Make a list of the food items inthe table 13.3 that you eat every day.After seven days just check whetherthe food items you had eaten containall the essential nutrients. All thenutritious food should be in your dailyfood. If not, try to a balance the dietatleast hereafter.

13.3.2 Balanced diet

A particular type of food itselfdoes not give all required nutrients.So, taking different type of diet

containing different nutrients isessential.

A nutritionally adequate dietcontaining proportionate quantity ofsix essential nutritions namelycarbohydrates, proteins, fats, vitamins,minerals and water are known asbalanced diet. It should also containsome quantity of indigestable fibrecontent food to avoid constipation.

By the following tabulation(Table 13.4) we know how much ofcarbohydrates, proteins and fat are

The food items which contain various six types of primary nutritions andtheir uses are tabulated below (Table 13.2).

Table 13.2

S.No. Food items Constituent Uses

1. Rice, wheat and potato Carbohydrate Gives energy

2. Oil, butter and ghee Fat Gives energy

3. Egg, milk, soya beans pulses, Protein promotes growthfish and meat

4. Vegetables, meat, fish and egg. Mineral salts Regulate body

5. Fruits, greens and vegetablesVitamin activities

6. Water Water Transport medium

Table 13.3 The varities of food that you eat daily

Sl.No. Date Food items that you have eaten Energy producer Body builder Regulator

Morning Noon Night


176

present in 100 gms of the foodmaterials.

Table 13.4

S.No. Food Carbo- Protein Fatitems hydrate

1. Grains 70 10 0

2. Pulses 60 20 0

3. Soya beans 20 40 20

4. Fruits and

vegetables 10 01 0

5. Cow’s Milk 3 3 3

7. Hen Egg 0 13 13

8. Fish and meat 0 20 0

9. Ghee 0 0 100

10. Sugar 100 0 0

11. Nuts 20 20 50

13.4 Personal hygiene

Personal hygiene is anindispensable for hygienic society.Because, the society is formed byindividuals. Personal hygiene is thatkeeping our body, belongings andenvironment neat and clean. Youshould remember that hygiene ishighly essential for a person to lead adisease free and healthy life.

13.4.1 Methods of taking care ofoneself

Shall we see how to keep ourbody clean?

Taking bath everyday andwearing washed clothes by which wecan prevent spreading of diseases.

Our teeth are the most importantpart of our body. Teeth are arrangedin such a way that they giveappearance for the face, for speechand to eat the food. One should brushhis teeth on every morning as well asafter taking meals so as to keep histeeth in good condition. Otherwise thebacteria develop on the food particlesthat have been entangled between theteeth and cause damages to our teethand gums (Fig.13.7 & 13.8).

Fig. 13.7 Some ways for personal hygiene

Fig. 13.8 Some products useful inpersonal hygiene.

We can protect our skin in abetter way by taking bath two or threetimes a day during hot summer, bycleaning our hands and legs as soonas we get into our home from outside,


177

by avoiding the applications ofunwanted cream and powder on ourface.

Besides neat and clean, if wefollow the hygienic habits we canprevent the skin diseases like scabies,itches, etc.

In order to avoid falling of hairand to maintain its lustrous nature, itis essential to comb our hair to removelies and dandruff by applying oilregularly without fail. Moreover, bytaking nutritious food we can havehealthy hair growth.

Always the nails must betrimmed and kept clean. Otherwisethe dirt in the nails will also enterinto our stomach along with the foodwe eat and cause diseases. So it isessential to have the food only afterwashing our hands.

The infection called cold isformed in the upper respiratory regionby more than hundreds of viruses.This disease has the tendency ofspreading very easily. Over crowd andlack of aeration can spread thisdisease easily. The hand-kerchief andclothes used by the people who aresuffering from cold should not be usedby the other. By closing our mouthand nose with cloth while sneezingand coughing, we can avoid infectingof cold to others.

Activity 13.2

Classify the following habits as

good or bad.

Covering the face while sleeping,

eating without washing the hands,

cleaning the teeth after every meal,

putting finger inside the nose,

watching TV for long time, wearing

clean cloths.

13.5 Health and environment

Air, water and sunlight which are

considered as the nature’s gift are

essential for a healthy life.

13.5.1 Environmental factors

affecting health

The harmful gases discharged

from factories; the exhaust from the

automobiles, rocket, aeroplanes; the

smoke emitted by burning of tyres,

garbages and rubber materials are the

major factors for the pollution of the

air in the surrounding in which we

are living. As a result of which

diseases such as allergy, cough, cold,

heart ailments and many types of

cancer are caused.

Pollution contaminate the water

sources also. The wells and ponds in

the villages are polluted due to lack

of proper maintenance and misuse.

For example the washing of clothes,


178

vessels with detergents and bathing

of animals in near by the wells and

ponds.

World Environment Day June 5

Apart from this, the other sourceswhich influence the pollution aresewage water, industrial effluents,usage of insecticides, herbicides andfertilizers. Due to water pollution,diseases such as cholera, typhoid,dysentery, jaundice andleptospyrosis are caused (Fig. 13.9).

Fig. 13.9. The ways of water and air pollution

Noise is also another importantfactor for sound pollution. Theunwanted sound is known as noise.Some of the sources for noise arecompressor, grinder, generator, radioand television, aeroplanes, loudspeaker, trains etc. (Fig. 13.10).Deafness, heart ailments, intestinewound and the damage to the nervoussystem are caused due to noisepollution. The measure of soundto hear, ranges from 81 decibel to120 decibel.

Fig. 13.10 Noise and Land pollution

Land Pollution

Throwing of solid wastes,plastic, polythene, domestic sewage,usage of fertilizers and disinfectantsare causing land pollution.

13.5.2 Control of contamination offood and water

Due to unhygienic humanpractices, water and food arecontaminated. Following controllingmeasures can be followed to preventthe spreading of diseases (Fig. 13.11).

i) Drink boiled water.

ii) When fresh vegetables and fruitsare eaten, it should be washedbefore eating.

iii) Don’t eat contaminated food soldby street hawkers.

iv) Don’t eat the food items whichare exposed to house fly.

(a) (b)

Fig. 13.11 (a) Ways for transmission of diseases

(b) Ways to prevent diseases


179

13.5.3 Care for the environment andControl of pollution

Nowadays, concern about theconservation of water, management ofwaste and awareness for the protectionof environment are indispensable. Toprotect our environment we shouldfollow certain regulations.

i) Whenever we come across waterdroping from the tap which isnot closed properly, see that thetap is closed tightly withoutspilling water.

ii) To water the plants in the garden,we should use buckets insteadof pipes.

iii) Rain water may be stored insome containers for some of ourdomestic purposes.

iv) Instead of using the continuousrunning of water from the tapsall along brushing of our teethand washing of our face andhands, it is better to take thewater in a vessel for usage.

v) We should avoid excess using ofinsecticide and herbicide in ourgardens.

It is your environment andits protection starts from you.

The important things to beobserved during waste management.

Fig.13.12 (a) Collection of garden wastes

(b) seggregation of wastes

i) To reduce formation of wastes

ii) Reuse

iii) Recycling of wastes

You would have seen thedumping of garbage in our day to dayactivities at home. Segregate thegarbage as bio-degradable and nonbio-degradable (Fig. 13.12).

We should find out the ways andmeans whether the non bio-degradablewastes such as plastics can be usedfor further utilities by recyclingmethods.

Whatever we use, we should useit in a proper way.

For example, usage of cloth bagsinstead of plastic bags can avoid theaccumulation of plastic things in ourhouses. The leaves and garbages fromour houses can be heaped up in thegarden and let it to decompose untilthey are converted into manure. If wefollow the above mentioned goodhabits, we can lead a healthy life anddevelop a good environmentalcondition.


180

SELF EVALUATION(For the examination, teachers are instructed to frame their own questions

from the text matter and activities)

1. The vitamin essential for eyes is(a) vitamin A (b) vitamin D (c) vitamin E (d) vitamin B

2. The food which is useful for growth of the body is(a) fat (b) water (c) mineral salt (d) protein

3. The food which is essential to avoid constipation(a) tuber (b) fibre food (c) nut (d) meat

4. Respiratory problem is caused by(a) air pollution (b) water pollution(c) land pollution (d) noise pollution

5. Cold is caused by more than hundreds of(a) bacteria (b) parasites (c) viruses (d) unicellular organisms

6. Food is needed for ________ ____________ ___________ and_________

7. There are __________ types of chief components found in our food.8. To maintain the health ___________is needed.9. _______________ is essential to lead disease free life.10. We should keep our ______________ cut and clean.11. We should not use _______ from the people who are suffering from cold.12. For a healthy life ________ is needed basically.13. The unwanted sound is called ________.14. What should we do before we eat?15. How is cold caused?16. Give four examples of regulators.17. Define - balanced diet.18. Write two methods to protect our body.19. Write two diseases caused by noise pollution.20. What are the factors causing water pollution?21. How is land polluted?22. How will you keep your body clean?23. Write the methods adopted to save rain water.24. Explain the role of waste management in our environment.25. Name the diseases caused by water pollution.

tnpsc - science text book 6th standard

Documents