Prescribed by the National Curriculum and Textbook Board as a Textbook for Class VI from the academic year 1997.

General Science

For Class VI

Written by Dr. A. K. M. Shamsudduha Dr. Md. Golam Rosul Miah Prof. Dr. Md. Abdul Wahab

Zohurul Islam Khan

Translated by S. M. Haider

Rukhsana Shaheen A. S. M. Lukman M. Rafiqual Islam Mrs. Irene Parveen

National Curriculum and Textbook Board, Dhaka

Published by National Curriculum & Textbook Board

69-70, Motijheel Commercial Area, Dhaka.

[All rights reserved by the Publisher]

First Edition : 1997 Revised Edition : 2007 Reprint : March’ 2009

Reprint : April’ 2010

Cover Ahmed Ullah

Computer Compose Mars Solutions Ltd.

Illustration Ranjit Das

Maniruzzaman Shipu Nasir Biswas

Design NCTB, Dhaka

For free distribution from academic year 2010 by the Government of Bangladesh

PREFACE

Education is the key to development. A progressively improved education system largely determines the pace and the quality of national development. To reflect the hopes and aspirations of the people and the socio-economic and cultural reality in the context of the post independent Bangladesh, new textbooks were introduced in the beginning of the 1980s following the recommendations of the National Curriculum and Textbook Committee. In 1994, in accordance with the need for change and development, the textbooks of lower secondary, secondary and higher secondary were revised and modified. The textbooks from classes VI to IX were written in 1995. In 2000, almost all the textbooks were rationally evaluated and necessary revision were made. In 2008, the Ministry of Education formed a Task Force for Education. According to the advice and guidance of the Task Force, the cover, spelling and information in the textbooks were updated and corrected. The aims & objectives of the study of General Science is to make the learners curious and observant about nature and its environment – science teaches a person to have clear and logical thinking ability. It also makes a person able to do things on his/her own. The General Science book has been prepared according to the general objectives and learning outcomes of the curriculum. Topics of physics, chemistry, botany, zoology, geography and population study have been included in this book. It is hoped that learners will be able to gain both theoretical and practical skills on these topics from study of this book. We know that curriculum development is a continuous process on which textbooks are written. Any logical and formative suggestions for improvement will be considered with care. On the event of the golden jubilee of the Independence of Bangladesh in 2021, we want to be a part of the ceaseless effort to build a prosperous Bangladesh. In order to develop learners interest in science, some modifications have been made in this book. This book of General Science for class VI is the English Version of the original textbook entitled ‘Sadharan Bijnan’ written in Bangla. In spite of sincere efforts in translation, editing and printing some inadvertent errors and omissions may be found in the book. However, our efforts to make it more refined and impeccable will continue. Any constructive suggestion towards its further improvement will be gratefully considered. I thank those who have assisted us with their intellect and efforts in the writing, editing and rational evaluation of this book. We hope that the book will be useful for the students for whom it is written. Prof. Md. Mostafa Kamaluddin Chairman National Curriculum and Textbook Board Dhaka

CONTENTS

Chapter Subject Matter Page

1. Measurement .................................................................... 1

2. Matters .............................................................................. 23

3. Air .................................................................................... 37

4. Metal and Non-Metal ........................................................ 54

5. Water ................................................................................. 65

6. Living World .................................................................... 78

7. Cell: Unit of Living Body ................................................ 90

8. Plant Kingdom .................................................................. 98

9. Morphology of Plants ....................................................... 114

10. Force, Pressure and Motion ............................................... 132

11. Work, Power, Energy ........................................................ 147

12. Electric Energy .................................................................. 159

13. Magnetic Energy ............................................................... 172

14. Surface of the Earth .......................................................... 182

15. Features of Invertebrate Animals ..................................... 194

16. Human Body: External Structure, Skin, Muscles, Bones

(Skeleton) ................................................................... 202

17. Health Rules: Skin Diseases .......................................... 213

18. Food and Nutrition ............................................................ 221

19. Population and Natural Environment.................................. 231

20. An Introduction to AIDS ................................................... 241

Chapter – 1

Measurement

What is your height? To answer this question it is necessary to measure your height with the help of a measuring tape or a measuring stick. What is your weight? It is necessary to weight your body with a weighing machine to answer this question also. What is the time now? Its answer is to be given by looking at a clock. What you have done to answer these three questions is measurement. At first your height, secondly your weight and thirdly time. The three answers may be as follows: the height

is 112 metre, the weight is 40 kg and the time is 11 am. If you observe you

will find that the three answers have been expressed in some numbers. This kind of scaling something and its expression in number is called measurement. Measurement is very essential and an important topic in learning science. In this chapter we will learn about measurement of length, mass and time.

Necessity of measurement It is questioned, whether a football is bigger or a cricket ball? You will immediately answer a football. But if it is questioned whether a cricket ball is bigger or a volleyball, or whether a cricket ball or a tennis ball and how big? You cannot answer then and there. Here you need measurement. In figure 1.1 there are two straight lines A and B, If it is asked which one is

2 General Science longer, you will answer either lines A or B is longer. Now you measure them with any device. You will see your finding is not correct. Length of both the lines is equal. So what we see or guess, may sometimes give wrong idea. Measurement is necessary to know the correct value or quantity. People need to measure various things in day-to-day life. What we eat, what we wear or the work we do, the game we play all involve measurement. If you want to buy rice, pulse etc. you will have to buy them by weighing. If you want to make a shirt, the tailor has to take your measurements. The ‘daftari’ (a peon) in the school rings bell as per time and the class breaks. Boundary of a football field is determined by measurement. Measurement has to be made for purchase or sale of a land. Various things have to be measured for making a chair or a table, in building a house and in preparing medicine. In a word, measurement is necessary for almost every work in the day-to-day life.

Units of Measurements Measure the length of a bench in you school by your forearm. Suppose, the length is equal to four forearms. What does this mean? It means that the length of the bench is four times the length of your forearm. The length of your fore arm is known. Here the unit of length is forearm a (cubit). Therefore a known length in comparison to which an unknown length is measured is called a unit of length. Similarly, when a mass of a body is said to be 40 kilograms, it means that its mass is 40 times that of standard mass considered as one kilogram. Here kilogram is the unit of mass.

Measurement 3

Generally, in order to measure things a certain part of the thing to be measured is taken as a standard. A convenient fixed length is taken as a standard to measure length; a convenient fixed mass is taken as a standard to measure mass, and a convenient fixed time is taken as a standard to measure time. The value of this known standard part is called the unit. Unknown length, masses and time are measured comparing them with the respective unit. Thus the fixed standard value or the quantity in comparison to which something is measured is called a unit of measurement. A number and a unit express a measurement.

Historical Background

Various units of measurement were used in different countries in different ages. About 5000 years ago the Egyptians used to measure length by forearm. The length of the arm from elbow to the tip of the middle finger was taken as one cubit. This procedure is still in practice in some places. Occasionally this is used in our country also.

The Romans or the English used to consider breadth of a thumb of an adult as one inch and the length of a foot as one foot (which is nearly equal to 12 inches). Keeping the head straight and extending an arm side ways, the length of the tip of the nose to the tip of the middle finger was taken as one yard. But this kind of

4 General Science measurement based on some specific parts of a human body cannot be accurate. Because length of all human bodies are not equal. For measuring rice, paddy etc. cane bowls of a certain size are sometimes used in our country. Again coins of various denominations are used to weigh gold and silver. Such as a coin of one taka is taken as weight of one tola, in ancient times shadows of things were used for measuring time. The sun rises in the east and sets in the west. For that, in the morning the shadow of a tree or a pole falls on to the west. As the daytime grows the length of the shadows becomes shorter and shorter. After mid-noon as the sun leans towards west the shadows fall on to the east. Thus an approximate calculation of time can be made from the observation of the position and length of a shadow. But this is not very accurate especially during night and cloudy days time cannot be measured by this process. Therefore for accurate measurement, unit should be such that it does not depend upon any particular person or time. Its value should be the same in all times. Few days ago mainly two systems of measurement were in practice in the world. These are (i) British system and (ii) Metric system. In the British system the unit of length is foot, unit of mass is pound and the unit of time is second. For that this system is also called the foot, pound, second, (F.P.S) system. Again the metric system is of two kinds - the centimeter, gram, second system or the CGS system and the metre, kilogram, second system or the M.K. S. system. Centimeter and metre are the units of length: gram and kilogram are units of mass and second is the unit of time.

In measurement use of various systems of units causes inconvenience. As for example, you go to a shop and ask for 10 kilograms of rice and another

Measurement 5

person asks for 20 pounds of rice. In this situation the shopkeeper has to have two sets of weights. The prices have to be set in two ways. The shopkeeper should know the relation between a kilogram and a pound. Again say a businessman wants to import cloth from a foreign country. He wants to buy in yards. The foreigners say that they do not know yard. They sell cloth in metres. If only a single system of units is used in all the countries, there will be no such convenience. All the scientists of the world who met in a session in the city of Paris, in France in 1968, agreed to introduce a single system for all countries. It is known as system international or briefly S.I system. In S.I system units resembles MKS system. Now-a-days system international is used all over the world. It is specifically used in scientific works. This system has also been introduced in Bangladesh.

Fundamental Units and Derived units Units of length, mass and time does not depend on other units. Units of these are called fundamental units. In the system international there are seven fundamental units. These are: (1) unit of length (2) unit of mass (3) unit of time (4) unit of electric current (5) unit of temperature (6) unit of luminosity of light and (7) unit of measurement of a body. We will discuss only about the units of length, mass and time in this chapter. Multiplying or dividing one fundamental unit by another obtains all other units except fundamental units. These units are derived units.

6 General Science Units of area and volume are examples or derived units. The area of the floor of a room is obtained by multiplying the lengthy of the room by its breadth. Units of both length and breadth in S.I. system are metre. Therefore unit of area = unit of length × unit of breath= metre × metre or square metre which is a derived unit.

Units of Length mass and time (System International and CGS. System) Units of length We have learnt that unit of length in the System International or S.I. system is metre. What length should be equal to one metre that was decided by the scientists from various countries, in a meeting in 1875. Two cut marks were made at the two ends of a bar made of platinum iridium alloy. Distance between these two fixed marks at 0oC was taken as one metre. This bar is preserved at the office of the International Agency of Weights and Measures, at Sevres near Paris. The length of a metre is determined by taking an equal length as of this standard in all the countries of the world. You may have some idea about the length of a metre. When you buy cloth, the shopkeeper uses the wooden bar for measuring cloth is one metre long. If you want to measure the length or the breadth of your classroom, you can measure it in metre. But if you want to measure the length of a small thing, you cannot measure it in metre. A small unit is necessary for that. This small unit is centimeter, which is one-hundredth part of a metre. Similarly small unit of mass is gram, which is one part of a kilogram thousandth. Unit of time is second in all cases. This system is called centimeter gram, second system or the C.G.S. system. Sometimes it may be necessary to measure very small lengths or very big length, such as the diameter of a wire or the distance from Dhaka to

Measurement 7

Dinajpur. To measure small and big lengths various fractions and multiples of a metre are used. These fractions, or the multiples are always the one tenth or ten times of the other. For this, the system is also called decimal system. Various decimals and multiples or a metre are given below: 1 millimetre (mm) = 1/1000 metre (m) = 1/10 centimeter (cm). 1 centimetre (cm) = 1/100 metre (m) = 1/10 decimetre (decim) 1 decimetre (decim) = 1/10 metre (m) 1 decametre (decam) =10 meters (m) 1 hectometre (he.m) = 100 metres (m) =10 decametres (decam) 1 Kilometre (km) = 1000 metres (m) = 10hectometres (he.m)

Reversely it can be said 10 mm = 1cm 10 cm = 1 decim 10 decim = 1 m 10 m = 1 deca.m 10 deca. m = 1 hecto.m 10 hecto.m = 1 km.

Unit of mass

In System International unit of mass is kilogram (k.gm. or kg.) Mass of a solid metal funnel made of platinum-iridium has been taken as one kilogram and is preserved along with the standard metre bar in the same office near Paris. You may have seen one-kilogram weights in grocer’s shop while purchasing commodities. These are made of the same weight as that of the standard kilogram. The unit of mass in C.G.S system is gram. One gram is equal to one thousandth part of a kilogram. Decimals and multiples of a kilogram and a gram are given below :

8 General Science 10 milligrams (mg) = 1centigram (c.gm) = 1 mg = 1/1000 gram. 10 c.gms = 1 deci gram = 1 c.gm = 1/100 gram 10 deci.gm = 1 gram (gm) = 1 deci gm. = 1/10 gm 10 grams = 1 deca.gram (deca.gm) 10 deca. gms = 1 hecto.gram 10 hecto.gm = 1 kilogram = 1000 grams 100 kg = 1 quintal = 100,000 gms 10 quintals = 1metric ton = 1000 kg

Gram, kilogram, quintal and metric ton are the most commonly used units in our day-to-day life. Gram is used to measure small quantities of things such as gold, silver etc. whereas kilogram is used to measure things like rice, pulse, vegetables etc. Again when rice, paddy, cement, rod etc. are to be loaded in gunny bags or trucks then quintal or metric ton is used as the unit. Thus, depending on the bulk and quantity of material to be measured, decimals or multiples of fundamental units are used.

Difference between mass and weight You may have question in your mind that kilogram is used to measure weight, then why is it used for measurement of mass always? Is mass called weight? Having such questions in your mind is quite natural. Because in general sense mass is called weight. But in the scientific terms mass and weight do not mean the same. Mass is the quantity of matter contained in a body. While the force of attraction of the earth on the body is its weight. Mass of a body is constant. It does not change from place to place. But the force of attraction of the earth is higher at some places and lower at others. Hence the weight of a body will be different at different places. If you go to the moon, your mass will remain the same but your weight will be reduced to almost one sixth. This is because, the force of attraction of the moon is one sixth of that of the earth. So when kilogram

Measurement 9

unit is used for measurement, it indicates mass of some body. Unit of weight is different. In the chapter ‘Force’ you will see that the unit of weight is Newton. A body of mass of one kilogram weighs about 10 Newton.

Unit of time Unit of time in both system International and C.G.S system is second. Time can neither be seen nor be touched. Hence unit of time is determined in a different way.

You know that the earth rotates on its own axis. As a result day and night occur. The time taken by the earth to make a single rotation on its own axis is called a solar day. The duration of each solar day is not equal. As such mean solar day is calculated from the mean of all the solar days in a

year. About 36514 solar days make a year. During this time the earth

moves round the sun. The time obtained by dividing mean solar day by 24 is called one hour. One-sixtieth part of an hour is one-minute and one-sixtieth part of a minute is one second, that is to say – 1 mean solar day = 24 hours. = 24 × 60 minutes = 24 × 60 × 60 Second = 86,400 seconds

In all the systems 60 seconds = 1 minute 60 minutes = 1hour 24 hours = 1 day = 86,400 seconds 7 days = 1 week 30 days = 1 month

12 months = 1 year = 36514 days

10 General Science

Units of Area, Volume and Density

Area: Your reading table is small. Reading room is bigger than that. Playground of the school is still bigger. What is the meaning of these words? It means that the area of floor of the room is larger than the area of the top of your reading table. Again the area of the playground is still larger than that. Therefore the spaces that have been occupied by the top of the table, the floor of the room or the playground of the school are called the areas. Area of any surface is obtained by multiplying its length and breadth. Therefore –

Area = Length × Breadth

In measuring unknown lengths as these, we are to compare them to a known length; similarly for measuring unknown areas these are compared to a known area. This known area of a square whose length of each side is one metre. This known standard area is the unit of area in the System International. This unit is called square metre. Therefore –

1 square metre = 1 metre × 1 metre

In the C.G.S system unit of area is square cm. One square cm. is equal to area of a square whose each side is one cm. Therefore –

1 square cm.=1 cm × 1 cm.

Fraction of this unit is used to measure small areas. Again multiple of this unit is used to measure very big areas. Such as – 1 square mm. = 1mm. × 1 mm.

= 110 cm ×

110 cm

= 1

100 square cm.

Measurement 11

1 square Km. = 1 km. × 1 km. = 1000m. × 1000m. = 10,00,000 square m.

A B

The area of any country is expressed in square km. Such as the area of Bangladesh is 147,570 square km. Experiment : Take a piece of paper, a measuring scale and a pencil. Draw a rectangle (ABCD) whose length is 10 cm. and breadth is 7 cm. as it is shown in the figure. D C

Draw straight lines 1 cm apart.

Fig: 1.3 Finding areas with the help of square boxes

Both lengthwise and breadth wise. Area of each of the square boxes formed is 1 square cm. What is the area of the rectangle ABCD? Count the total number of boxes in the rectangle. Multiply the length of the rectangle with its breadth. Result will be the same in both the cases. It is 70 square cm. Moreover you have observed that the same result is obtained by multiplying the length and the breadth. Therefore – Area of rectangle = length × breadth

Unit of volume A brick is bigger than a matchbox. It means that a brick occupies a larger space than that of a matchbox occupies. Every substance occupies some space. Space occupied by a substance is called its volume. The volume of

12 General Science a brick is larger than the volume of a matchbox. A water jug contains six glass of water. Volume of the jug is six times the volume of a glass.

Experiment Take three matchboxes of same size. Keep a matchbox on a table and place another (match box) on the first one. Volume of two matchboxes is double the third matchbox. Keep the third matchbox over the two boxes. What is the increase in height? What is the increase in volume? Both have increased three times. The bottom area of each of the matchboxes is the same. Number of times the volume has increased is the same as that of the height. Therefore, volume is obtained by multiplying, the area by height. Thus Volume = area× height [area = length × breadth] = length × breadth × height. In the System International unit of volume is cubic metre. The space occupied by a cube of 1 m. length, 1m breadth and 1m height is called 1 cubic metre. 1 cubic metre = 1m. × 1m × 1m. In the CGS system unit of volume is cubic centimeter. 1cubic cm = 1cm × 1cm × 1cm

Volume of liquid is measured in litres 1000 cubic cm. is equal to 1 litre. Volume of regular shaped bodies such as a brick, a matchbox or a room can be easily determined. For this

Measurement 13

purpose simply their lengths breadth and heights are measured and multiplied. But how can we determine the volume of an irregular shaped body, such as a piece of stone? A measuring cylinder is used for the purpose. Measuring cylinders have graduation in units of volume. As such volumes can be measured with them, directly.

Experiment Take a small piece of heavy wood of regular in shape. Measure, its length, breadth and height and determine its volume. Now take a measuring cylinder. Pour some water into it and take a reading. Tie the piece of wood with a thread and dip it into the measuring cylinder. Take reading of the height of water after the piece has completely been immersed. What is the volume of the piece of wood? Is this volume equal to the volume obtained by multiplying its length, breadth and height?

You will observe that the amount of increase in height of water is equal to the volume of the piece of wood. Take out the piece of wood. Take a reading of the

Fig 1.5: Finding the volume with the help of a measuring cylinder

height of water in the measuring cylinder. Now tie a piece of stone with a thread and dip it into the cylinder. Take a reading of the height of water. What is the volume of the piece of stone?

Unit of Density Ask your friend a puzzling question. Of one kilogram of iron and one kilogram of cotton, which one has a greater mass?

If he answers iron, he is befooled. Again, if he answers cotton then also he is befooled. Because masses of both are the same. But equal volume of iron is heavier than cotton. Hence masses of one-kilogram iron and one

14 General Science kilogram of cotton, though equal volume of cotton is by far greater. Density of iron is more. Density of cotton is less.

The masses of equal volume of different materials become different because of variation in their densities. The mass contained in unit volume of substance is called its density. Therefore –

Density = mass

volume

In the System International unit of mass is kilogram and unit of volume is cubic metre. Thus the unit of density is kilogram per cubic metre. Similarly in CGS system unit of density is gram per cubic cm. In the CGS system the density of water is 1 gram per cubic cm. This means that the mass of 1 cubic cm. of water is 1 gram. In the System International density of water is 1000 kg. per cubic metre. The more the density of a body the more it is heavy. The density of iron is 8 gm. per cubic cm and the density of wood is 0.8 gm. per cubic cm. Thus iron is much heavier than wood.

Comparison between the units of system International and the C.G.S. system.

In system International C.G.S system What measured Name of

unit Abbreviation

Name of unit

Abbreviation

Interrelation

Length Metre m. Centimeter cm. 1m = 100 cm. Mass Kilogram Kg. Gram gm. 1kg = 1000 gm. Time Second sec. Second sec. 1sq. m. =

10000 sq.cm. Area square metre sq.m. Square

centimeter sq.cm. 1 cubic m. =

1000000 cubic cm.

Volume Cubic metre cubic m. Cubic centimeter

cubc.cm. 1 kg/1cubic m.

Density Kilogram per cubic metre

kg./cubic-cmm

Gram per cubic centremtre

gm/cubic cm.

1000 gm/1000000 cubic cm.

Measurement 15

Some common measuring instruments : Various kinds of measuring instruments are used to measure length and mass of a body and to measure time. Descriptions of some simple instruments are given below.

Metre scale A metre scale is used to measure lengths. Generally it is made of a thin piece of metal or wood, 1 metre or 100 cm. in length. It has graduation marks at 1 cm. intervals. Again each cm. is divided into ten equal parts that is again into millimeters and are graduated. The graduation marks showing centimeters are longer and that of the millimeters are smaller. Perhaps there are metre scales in your school. Your teacher will show them to you. You may have also used scales for measuring things. In order to measure length of a body with a metre scale, it is placed lengthwise with the body in such a manner that one end of the body coincides with the zero mark on the scale. Now the reading of the mark on the scale to which other end

Fig 1.6: A metre scale

Fig 1.7: Process of measuring length with a metre scale

right process wrong process

wrong processright process

16 General Science of the body coincides is the length of the body. If for any reason it becomes difficult to make one end of the body coincide with zero mark on the scale, then it should be coincided with any other mark on the scale. Difference between higher and lower reading is the length of the body. In figure 1.6 length of the line AB is 5 cm. While taking reading it should be noticed that the eye is placed at a perpendicular position to the end at which reading is taken. If reading is not taken in this way or readings of both the ends are taken keeping eyes at one place, then the readings with be wrong. Again say, you want to measure length of your reading table. You will have to take measurement by placing the scale along the table in such a way that it remains by the edge or parallel to the edge of the table. If you place the scale in an oblique manner correct reading will not be obtained. So, for accurate measurement with a metre scale you will have to remember:

(a) Eye should be placed perpendicularly at the point on the scale whose reading is to be taken.

(b) The scale should be placed along the length of the body or parallel to that whose length is to be measured.

Ordinary Balance Balance is used to measure mass of any substance. The balance that the shopkeepers use for measuring rice, pulse etc. is an ordinary balance. You all have seen this balance. Some of you may have used it also. There is a wooden or an iron rod in this balance. Two dishes or bowls are hung from the two ends of the rod by means of cords which are called pans. Pan may be of iron, brass or cane also. A cord or an iron hook is fixed just at the middle of the rod.

Measurement 17

Fig 1.8: An Ordinary Balance

The balance may be hung by holding this cord on the hook. While hanging the rod remains horizontal, otherwise measure of mass will be wrong. The substance whose mass is to be measured is usually placed on the right pan. Weights are placed on the left pan. When the rod of the balance becomes just level after it is hung by holding the cord at the middle, masses of two sides become equal. The weights put on the left pan indicates the mass of the substance placed on the right pan. In order to obtain accurate measurement of masses by an ordinary balance it is to be noticed that (a) the mass of the empty pan of right side is equal to mass of the empty pan on left side. That is say, when the empty pans are hung by holding the cord at their middle, the rod remains parallel. (b) The cord or the hook holding by which measurement is made, must remain just at the middle of the rod. If the distance of either end of the rod from the hook is less or more than the other end, exact measurement of the mass cannot be obtained.

Clock Clock is used to measure time. You all have seen a clock and used it. Looking at a clock you get up from bed in the morning and you go to school. At bedtime also perhaps you look at the clock and then go to bed. There are various kinds of clocks. Such as a wristwatch, a wall clock, a

18 General Science table clock etc. Again these clocks are of two kinds, - a clock with hands and a digital clock. The former has hands for hours and minutes. Time is read by reading the positions of the hands on the graduation marks. There is no hand in a digital clock. Time is directly seen in numbers. While you want to observe time a glimpse at the clock gives you that in hours and minutes. In some of the clock time can be seen up to second also. Say at a certain time you observe a clock that reads 10:30:15. It means that the time at the moment is 30 minutes 15 seconds passed 10. Number of seconds changes at every second, number of minutes changes at every 60 seconds and that of the number of hours changes at every 60 minutes. These clocks are run by batteries and are called electronic clocks. Now a days most of the clocks with hand are also electronic clocks.

Figure 1.9: Different types of clock and watches.

One type of watch is used in the laboratory for measuring time. It is called stopwatch or stop clock. Pressing a button this can be run or stopped as per desire. The hand of the watch remains at zero position before starting. This button should be pressed at the moment from which counting of time should start. The watch starts running as soon as the button is pressed. As

Measurement 19

the counting of time is over the button is pressed again and the watch stops. The position of hand of the watch shows the time for which the watch ran. If the button is pressed once again the hand comes back to zero position. A stopwatch is used to measure the time taken by a runner in a race for fixed distance at the time of games and sports. A stopwatch is comparatively smaller and is like a wristwatch. A stop clock is slightly bigger and it looks like a table clock. It is kept on a table. Stop watch and stop clock may also be digital. New words in this chapter. measurement derived unit fundamental unit volume area

metre density second kilogram cubic metre

square metre balance metre scale unit clock

EXERCISE

Multiple Choice Questions (MCQ) 1. Which unit is fundamental?

a. of area b. of volume

c. of mass d. of density

2. The density of water is 1000 kilogram/cubic metre. What is the mass of 10 cubic metre of water?

a. 10 kg b. 100 kg

c. 1000 kg . d. 10000 kg

20 General Science

3.

Figure What can be measured out with the help of the instrument shown in the picture?

a. mass b. time c. weight d. volume

4. The instrument of the figure - 3 is widely used - a. in daily routine work b. in sports c. in research activities Of the following, which is correct? a. i and ii b. ii and iii c. i and iii d. i, ii and iii

From the figure below, answer the questions 5 and 6

Figure 1

3

4 2

Measurement 21

5. Which of the above figure is used for determining the volume of a piece of stone?

a. 1 b. 2

c. 3 d. 4

6. The instruments of the figure are used-

i. in determination of length and mass

ii. in determination of mass and density

iii. in determination of area and density

Of the following, which is correct?

a. i and ii b. ii and iii

c. i and iii d. i, ii and iii

Creative Questions (CQ)

1.

Figure

A B

cm

22 General Science

According to the figure, answer the following questions :

a. What is the meaning of ‘centimetre’?

b. How is measurement made with the help of the figure A.

c. Determine the volume with the help of figure B.

d. Explain whether apparatus - A is suitable for the measurement of diameter of a wire (or not).

2. A man weighing 60 kilogram landed on the moon. After landing he felt himself lighter than before. An object of 1 kilogram on earth is about 10 Newton.

a. What is kilogram?

b. Why did the man on the moon think himself lighter?

c. Determine the weight of the man on earth.

d. Explain the difference in mass and weight of the man on the earth and the moon.

Chapter – 2

Matters

Many things are scattered around us; as for example, chair, table, book, pen, brick, wood, trees and branches, rice, pulse, water, air etc. The general name of these things is matter. Take your book in hand, it has some weight. Keep it on the table, it occupies some space. Push your reading table slightly. The table will move but it will not change its position. This means, it has resisted the force you have applied. You can’t see air. But you can feel its existence. Thus all matters have more or less weight. They occupy some space and resist any external force. Matters can be seen, touched or felt with senses. So in science, matter is defined as something that has weight, occupies some space, can be sensed and resists forces applied to it. Different States of Matter There is countless matter in this world. These have been divided into three classes as per their states, such as solids, liquids and gases. Bricks, wood, stones, chair, table, book, exercise book etc. have definite shape and volume. In normal conditions, their shapes and volumes do not change. These are solids. Water, oil, milk etc. have definite volumes, but do not have definite shapes. They assume the shapes of the containers they are kept in. These are liquids. A gas has neither a definite shape nor a volume. Gaseous substances, whatever may be its amount, occupy the volume and assume shape of the container in which they are kept. Air, hydrogen, oxygen, carbon dioxide etc. are gaseous substances.

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Same substance can exist in three states The same substance can exist in three states such as solid, liquid and gaseous states. Water is the best example of this. At ordinary temperature water is liquid. Water when cooled becomes solid ice and when heated it becomes vapour. Thus water can exist in all three states, such as solid, liquid and gaseous states. Usually a solid substance when heated becomes liquid and a liquid when heated becomes gaseous. But the solid substances like camphor, salammoniac etc. when heated become directly gaseous without going through the liquid state. These substances are called volatile substances. Even at ordinary temperature, these volatile substances vaporize slowly.

Elements, Compounds and Mixtures All substances are made of particular matters. Matters are divided into three classes according to their constitution and properties or characteristics. These are elements, compounds and mixtures. We may take a piece of iron and divide it into smaller and smaller pieces. Whatever minute particle it may be, it retains the properties of iron. If hydrogen is analysed in this way, nothing of new properties other than hydrogen is obtained. So an element is a matter which, when broken or analyzed no other matter having different properties than the element itself is obtained. In this world there are 109 elements. Of them 92 are obtained in nature and remaining 17 can be prepared in the laboratory. Compounds are substances, which when broken or analysed, more than one elements having different properties are obtained. As for example, when water analyzed into its smallest parts, two matters, hydrogen and oxygen, having different properties are obtained. Similarly when common salt or sodium chloride is decomposed sodium and chlorine are obtained. Thus water, sugar, common salt, oil, clay etc. are compounds.

Matters 25

Distinction between elements and compounds.

Elements Compounds 1. The matter which when broken

into smallest parts does not produce

any other matter than itself is called

an element. For example- gold,

silver, copper, iron, hydrogen,

oxygen etc. are elements.

1. Compounds are substances

which when broken produce more

than one element. For example-

water, sugar, oil, salt, soap, soda

etc. are compounds

2. In free states elements can retain

their respective properties or

characteristics.

2. The properties of the compounds

are totally different from the

properties of its constituent

elements.

3. The smallest part of the elements

is atoms. Atoms retain properties of

the element itself.

3. The smallest parts of compounds

are the molecules. Molecules retain

properties of the compound itself.

4. Similar atoms constitute

molecules of the elements.

4. Molecules of compounds are

constituted by different atom.

5. Total number of elements in this

world is 109.

5. Compounds are innumerable in

this world (even more than 50 lacs)

Mixtures You know that iron and sulphur are elements having different properties. Iron filings look somewhat black and the sulphur dust is yellowish in colour. Take some iron filings and some sulphur dust on a piece of paper

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Fig 2.1: Observation of iron filing and sulphur powder

and mix them well. In preparing the mixture, you don’t need to weigh the iron filings and the sulphur dust. Mixing them well spread them over the paper and observe. If possible, you can observe through a magnifying glass. What do you see? The iron filings and the sulphur dust are lying side by side. Can we now separate the iron filing and sulphur dust from this mixture? Let us separate the elements from this mixture? Experiment 2.1:Separation of Elements from Mixture: Spread the mixture of iron and sulphur over a piece of paper now and draw a piece of bar magnet over the mixture several times. What do you see? Iron filings got stuck to the magnet due to its attraction. Draw the magnet over the mixture repeatedly until the iron filings are completely separated. A time will reach when no iron filings will stick to the magnet any more. Then you may be sure that iron filings have been completely separated from the mixture. Now if you observe well, you will see that only yellow coloured sulphur granules are lying on the paper. Thus you can easily separate the constituents of iron sulphur mixture.

Matters 27

This mixture of iron filings and sulphur dust is an ordinary mixture. In preparing a mixture the constituents can be mixed in any proportion and it does not require any application of heat. The constituents of a mixture retain their own properties and characteristics fully. From the above experiment, you have also observed that constituents of a mixture can be easily separated. So we can say that, mixtures are those substances, which are produced when two or more elements or compounds are mixed in any proportions. The constituents do not change their own properties, the constituents lie side by side and can be separated easily. As for example – air comprises of nitrogen, oxygen, carbon-di-oxide, water vapour, dust particles etc. All these keep their own properties intact in the air. These constituents do not exist in air in definite proportions. Air at different places has the constituents in different proportions and they can be separated easily. That’s why, air is a mixture.

Experiment 2.2: Preparation of compound Take iron filings and sulphur granules in a definite proportion in a test tube, mix them well and heat slowly. After sometime, you will see that sulphur has melted, got mixed with iron filings and has produced a reddish mass. Cool the test tube, take out the mass on a piece of paper and observe it well. What do you see? No iron filing or sulphur granule is seen in the mixture any more. Because by application of heat chemical reaction has occurred between iron and sulphur and a new substance has

28 General Science

been formed. The name of this substance is iron sulphide. This new substance has colour and properties completely different form those of iron or sulphur. Can the constituents of the new substance, called iron sulphide, be separate easily? Let us try to do this with the following experiment.

Experiment 2.3: Effort for Separation of a Compound Take some iron sulphide on a piece of paper and draw a magnet slowly over it. What do you see? Does any iron filing get stuck to the magnet? No, no iron filing gets stuck to the magnet and no sulphur granule can also be seen on the paper. So from these experiment you see that iron and sulphur cannot be separated by any easy means from the new substance iron sulphide made of iron and sulphur. This iron sulphide is a compound. Therefore we can say that a new substance with different properties, formed by chemical reactions between two or more elements in a definite proportion by weight is called a compound. As for example, the iron filings and sulphur granules reacted chemically by application of heat to form a compound called iron sulphide. Application of heat is necessary for the formation of compounds, and the constituents of a compound can’t be separated easily. Water, salt, soap, soda, oil, sugar etc. are all compounds. The differences between ordinary mixtures and compounds are given in the table below.

Matters 29

Distinction between compounds and mixtures. Compounds Mixture

1. The weight of the constituents in a compound are in a definite proportion. As for example water contains on part by weight of hydrogen and eight parts by weight of oxygen. 2. The properties of the constituent elements of a compound get lost and a new substance of different properties is formed. 3. In preparing a compound heat is needed to be applied or drawn out. 4. Constituents of a compound can’t be separated easily. 5. The constituents of a compound are same or homogeneous everywhere. As for example, water collected from anywhere contains equal proportion of hydrogen and oxygen.

1. In a simple mixture the constituents may be present in any proportion by weight. As for example, air is a mixture and nitrogen, oxygen, carbon dioxide, water vapour, dust particles etc are in it. 2. In ordinary mixture the constituents retain their own properties and they remain side by side. 3. In the preparation of a mixture heat is neither applied nor removed. 4. The constituents of an ordinary mixture can be separated by easy means. 5. The constituents of a mixture may both be homogeneous or heterogeneous. As for example, solution of water and sugar is a homogenous mixture but mixture of salt and sand is heterogeneous.

General Methods of Separating Mixtures Sands and water can be separated from a mixture of sands and water by filtering. Salt can be separated by heating a solution of water and salt. Some common methods are applied for separating the constituents of a

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mixture in the laboratory. The common laboratory methods include sedimentation, filtration, vaporization etc. Below is the description of the methods. Sedimentation Take some water in a glass jar or beaker. Mix some sands in the water and stir it for sometime. The sand-mixed water looks muddy, isn’t it? Let this muddy mixture of sand and water stand for sometime. Now observe, what do you see? The sand particles have settled at the bottom of the jar and water above looks clear and transparent. This method of separating heavy, insoluble, solid particles from a mixture in a liquid is called sedimentation. After sedimentation of insoluble, heavy solid substances separating the clear and transparent liquid from the top by slanting the jar and pouring it into another container is called decantation. The heavy solid substance that settles at the bottom is called sediment.

Filtration Have you seen making a cup of tea at home? Tea-liquor is prepared by adding tea leaves to the hot water. Tea leaves do not dissolve in water. Isn’t it? Liquor is separated by straining the insoluble parts of the leaves. Often the dirty particles remain suspended in the water and sometimes they settle at the bottom of the pitcher if it is kept undisturbed. Dirty particles can be separated from water by filtering.

Matters 31

In the previous experiment, you have separated the constituents of a mixture of sands and water by sedimentation. It takes a long time to separate the constituents in this process. Without wasting such time, water and sands can be separated from the mixture by straining or flirtation. Let us do this.

Experiment 2.4: Separation of sands and water by the process of filtration Prepare a mixture of sands and water in a beaker or glass. Go on stirring the mixture with a stick. Take a filter paper. As shown in the figure first fold the paper into two and then again into two. Hold the paper with three folds on one side and one at the other to give it a conical shape. Now place it in a funnel and pour several drops of water so that the wet paper may stick to the funnel. As shown in the figure, now set the funnel in a ring clamped with a stand. Place the end of the funnel in an empty beaker, touching its inside wall. Now pour little by little the sand-mixed water on the three-folded part of the filter paper with the help of a glass rod. What do you see? Sands remain on the filter paper inside the funnel and clear water is collected in the beaker below. Thus filtration is the process of separating insoluble, solid substances from a liquid one by

32 General Science

pouring on the filter paper. In this experiment you have separated sand and water from their mixture by the method of filtration. Thus, the process of separation of heavy insoluble or suspended solid particles from liquid by filtering is called filtration. The solid substances collected on the filter paper after filtration is called residue. The transparent liquid that is collected in the beaker after filtration is called filtrate.

Vaporisation : In summer, canals, marshy lands, ponds etc. are dried up due to the heat of the sun. Wet cloths become dry in the sun by evaporation of water in it. A few drops of water on a plate kept in open air disappear within a short time. This vaporisation of water at normal temperature is called evaporation. Sea water is saline, as it contains lot of common salt dissolved in it. In the tropical zones of the world salt is easily produced by evaporation of seawater. You have seen cooking of rice and curry at home. For cooking, pots of rice or curry are placed on the hearth and heated. Water soon starts escaping as vapour due to heat. In this way, with the application of heat, transforming any liquid into vapour is called vaporisation. You have seen that insoluble solid solutes can be separated from a solution by the process of filtration or decantation. But solids such sugar, common salt, copper sulphate etc. are soluble in water. Hence straining can’t separate these soluble solid substances. Then how do you get back the soluble solids from a solution of water? Yes, vaporisation is the method by which you can separate the soluble solids from a solution of water? Let us do the following experiment to get back the solid solutes from a solution.

Matters 33

Experiment 2.5: Separating copper sulphate from the solution of copper sulphate in water Take some water in a beaker and mix some copper sulphate in it. If it is stirred with a stirring stick, a coloured solution of copper sulphate is prepared. How do you get back the copper sulphate from this solution? Heat the solution of copper sulphate in water with a spirit lamp as shown in fig 2.7. You will see that the solution gets heated soon and begins to vaporize. Continue heating until almost all the water vaporises. Now look at the bottom of the beaker. What do you see? Blue copper sulphate crystals are lying at the bottom. We have got back copper sulphate from the copper sulphate solution in the water back from this experiment. We want to get back both water and copper sulphate from the solution. But how do we get? A special process is adopted to get back both. This process is called distillation. You will know about this in detail in higher classes.

New Words in this chapter Compound Evaporation Mixture Volatile substances Chemical reaction Salammoniac Or Ammonium chloride Hydrogen

Oxygen Carbon di-oxide Homogeneous Filtration Decantation Vaporisation

Filtrate Sodium chloride Chlorine Sodium Distillation Condensation

Sulphur Nitrogen Iron sulphide Solution Solutes

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EXERCISE

Multiple Choice Questions (MCQ) 1. Classify the matters according to their composition.

a. one b. two

c. three d. four

2. What is the name of the substance when no other properties are found if it is broken?

a. fundamental substance b. liquid substance

c. compound substance d. mixed substance

3. From which of the following, both the solute and the solvent are obtained ?

a. distillation b. filtration

c. volatilization d. sublimation

4. By which process both salt and water will be recovered from common salt solution?

a. evaporation b. distillation

c. sublimation d. condensation

5. The components (ingredients) of which substance become homogeneous?

a. water containing dust b. pure water

c. a mixture of salt and sand d. a mixture of salt and water

Matters 35

6. The 2-4 drops of water when kept on the table becomes dry after a while. The process is -

a. evaporation

b. vaporisation c. sublimation

Of the following, which is correct?

a. i b. ii c. iii d. i, ii and iii

Salt cultivator Rahim made sea water confined by making a dam.

Salt is deposited in his land after a few days. After its purification,

he sales the salt in the market.

7. By which process does Rahim produce salt?

a. Evaporation b. Vaporisation

c. Sublimation d. Filtration

8. Rahim purifies salt

a. by filtration process

b. by thickening process

c. by distillation process

Of the following, which is correct?

a. i b. i and ii

c. i and iii d. i, ii and iii

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Creative Questions (CQ)

1.

Figure

a. What is the ingredients of container `A’ called together? b. Show two differences of osmosis with the process of separation of

copper sulphate from the container `A’. c. Describe how the ingredients of the container ‘A’ can be separated? d. Explain whether the separation of the ingredients of container `B’ is

possible as it in the case of the container `B’. 2.

Figure According to the figure above, answer the following questions: a. What is the substances in the beaker called together? b. Explain what will happen if water is poured in the beaker. c. How the components in the mixture are separated? d. Explain how such type of separation is used in daily life.

Iron, Sand, Copper Sulphate

aluminium, sand, copper sulphate

A B

Pice of tin Sand Suger

Chapter - 3

Air Existence of Air Air exists surrounding the earth. We are sunk into this air. We cannot survive even for two or three minutes in absence of air. It is not only the human beings, but also other living creatures and trees and plants also cannot exist without air. For this reason air is also called life. There is no living being on the moon as there is no air on it.

We cannot see air. But we can easily feel the movement of air. The leaves of trees move when air flows. In summer the cool air refreshes our body. Flow of air at a violent speed is called a storm. Storm uproots big trees and overturns houses. You observe festivals by filling in air into coloured ballons. You fill air into the tyre of a bicycle and ride it. Again you inflate football and volley balls with air and play with them. From all these we can easily realise the existence of air, although we cannot see it. Now the question is, whether the sea of air in which we are sunk is a matter or not. Air is a matter You have learnt earlier what is called a matter. Can you remember the three main characteristics of matter? Matter has weight, volume and it occupies space and it resists forces applied to it. Knowing these properties of matter, naturally you may ask whether air possesses these properties like matter. In a word, is air a matter?

You have learnt the answers to these questions in former classes. You have observed that when air is pumped into balloons, footballs, bicycle, tyres, etc they swell up. Do you know why they swell up? It is because, air

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occupies space inside them. You can do an experiment by filling air into a balloon. Air not only occupies space, but it has weight also. You inflate two balloons and fasten at the two ends of a stick. Then fasten a thread just at the middle of the stick and make it like a balance. Now perforate one of the balloons with a pin and you see that the other end of the stick leans down. Can you say why does it lean? Air goes out from the perforated balloon and it becomes lighter. The other balloon being heavier the stick at that end leans down.

Air resists any external force. Take a bucket of water and try to immerse in it an empty glass upside down. The more you try to dip it down into the water; you will see that water does not get into it. The reason is that the space inside the glass is already occupied by air, which resists water to rise up in the glass. This testifies that air resists any external force to act upon. So from the discussion above we can conclude that air occupies space, it has weight and it offers resistance to any external force. Therefore, air is a matter. Air is a mixture

In chapter two you have studied matters and their classification. Air is neither an element nor a compound. It is a mixture. Do you remember what a mixture is?

A mixture is a substance, which is formed of two or more elements of compounds, mixed together in any proportion; the components lie side by side and can be separated by easy mechanical means. The following arguments testify that air is a mixture.

1. The components of a mixture can be easily separated. As air is a mixture, its components can be separated easily.

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2. Experiment shows that when air is produced by adding 4 parts by

volume of nitrogen to I part by volume of oxygen, no change of

temperature takes place. The properties of this mixture are similar to

the properties of air. So it can be said that air is a mixture.

3. In air sometimes the amount of oxygen increases and sometimes that of carbon dioxide increases. The amount of these components do not remain the same in air at all places. In marshy lands air contains more of carbon dioxide and methane. In big towns also air contains more of carbon dioxide. It is because of dense population and large number of transports and factories in the town. The smoke emitted from the transports and factories contain more of carbon dioxide. Besides, there are fewer trees in towns than in villages. The amount of oxygen in air is more where there are more trees. For this reason in the forest areas and in the corn fields air contains more of oxygen and less of carbon dioxide. Again the air in the upper layer contains less amount of oxygen than that in the lower layer. This is why the mountaineers and the air passengers should have arrangement of additional oxygen supply to avoid problems in breathing due to shortage of oxygen in the air. These examples demonstrate that the amounts of the components of air vary from place to place. Hence air is a mixture. If it were a compound, the ratio of the components of air would remain the same at all places and at all times.

4. The density of air is not the same at all places. That is to say, air is a

heterogencous matter. If air were a compound, it would be

homogeneous and its density would be the same at all places.

5. The components of air do not lose their individual properties. The

properties of air are the sum total of the properties of its components.

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As for example, both oxygen and nitrogen are colourless and

odourless gases. Air, too, is a colourless and odourless gas. Oxygen

facilitates combustion and air also facilitates combustion. If air were a

compound, neither oxygen nor nitrogen could retain their properties,

they would lose them.

All these arguments prove that air is a mixture. Constituents of air We have learnt that air is a mixture. The two main ingredients of air are oxygen and nitrogen. Besides, air contains carbon dioxide, moisture, very little amount of inert gases like helium, neon, argon, etc and dust particles. The amount of different ingredients present in air, in approximate percentage by weight and by volume, is given below. Ingredients of air Percentage by weight Percentages by volume Nitrogen 75.50 77.16 Oxygen 23.10 20.60 Moisture 0.06 1.40 Carbon dioxide 0.04 0.04 Inert gases 1.30 0.80

Testing the presence of different ingredients in air. A. Testing the presence of oxygen and nitrogen in air: Burning a fire is not possible without air. The ingredient of air that helps burning is oxygen. Air

Air 41

is necessary for any burning or combustion. Besides, air is very essential for our respiration. Cover a burning candle with a glass or jar in such a way that air cannot enter (Fig: 3.1 a). After sometime you will see that the candle is extinguished. This experiment proves that burning a fire is not possible without air (Fig: 3.1 b). Now the question is: Does everything in air help combustion? To get answer to this question, do the following experiment: Place a flaming candle in a big bowl. Carefully pour water into the bowl so that water may rise up to half of the height of the candle. Carefully place an empty glass or jar (it is not really empty, but full of air inside), turning upside down, on the candle in such a way that the mouth of the glass remains under water. Put a mark on the glass at the level of water. Now observe the experiment closely and try to answer the following questions:

1. Does the candle extinguish? Does the extinction occur at once or slowly? 2. Does the water level rise in the glass or jar? How far does it rise?

If you observe carefully you will see that: 1. The candle extinguished. After burning for some time the candle

extinguished slowly. 2. The water level rose slowly inside the glass. After sometime water

occupied one-fifth of the empty glass (not really empty, it contained air).

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One-fifth of the glass is occupied with water and four-fifths remain empty. Due to combustion of the candle the whole of air in the glass is not utilized or burnt up. Water would occupy the entire glass if whole of the air had burnt up.

The one-fifth (or one part out of five parts) of the air has been utilized in combustion. The scientists have named it as oxygen. Therefore about one fifth of air is oxygen. Fire does not burn without oxygen, and without oxygen respiration cannot take place. So you have seen that one-fifth of air is oxygen. Then what are the remaining four-fifths?

Repeat the above experiment once again and when the candle extinguishes, carefully take out the glass or jar by covering its mouth with a lid keeping the glass upside down. Insert a flaming stick into it. What does happen? The flaming stick at once extinguishes. Thus it indicates that the remaining four-fifth of the glass is filled with such a gas that does not help combustion at all. Scientists have named this ingredient of the air as nitrogen. So we can say that four-fifths of air contains nitrogen and other ingredients. Nitrogen does not help combustion.

B. Testing the presence of carbon dioxide in air You can test the presence of carbon dioxide in air at home. Keep some clear limewater in a beaker. Do not cover the mouth of the beaker. After a day you see that a white film has formed on the surface of the water. The carbon dioxide present in air reacted with the limewater and formed this film. This white film is calcium carbonate. To prove that air contains carbon dioxide

Air 43

perform the following experiment in the class. You need a wide mouthed bottle or conical flask, two glass tubes and a quantity of limewater for doing the experiment. Take some clear limewater in the bottle or in a conical flask fitted into the mouth. One of the tubes should reach the bottom of the flask and the other should just enter inside. Now start sucking air with your mouth through the short tube. You see that air enters into limewater through the longer tube and bubbles up. After sucking air for sometime in this way, you will see that the clear limewater is getting turbid. This proves that there is carbon dioxide in air. C. Testing the presence of moisture in air Take some ice in a glass and keep it the air for sometime. Observe the outer surface of the glass. What do you see? Drops of water have accumulated on the outer surface of the glass. Where does this water come from? This water comes from the air. The moisture in the air coming in contact with the cold surface of glass gets cooled and condenses into drops of water and accumulate on the outer surface of the glass. So from this we can understand that there is moisture in air. D. Testing the presence of dust particle in air To test the presence of dust particles in air you are to do the following task:

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Observe carefully the sunlight that enters into the house through gaps in a window, you will see that lots of dust particles are floating on the air. This means that there are dust particles in air.

Necessity of air in Combustion and Respiration You have learnt in the experiment for testing the presence of oxygen and nitrogen in air that combustion doesn’t occur without air. The element of air, which helps combustion, is oxygen. You have also learnt that one-fifth of air is oxygen. Among the rest four-fifths parts of air, there are nitrogen and other elements. Nitrogen and other elements of air don’t help combustion. Only oxygen helps combustion. We are sunk into the sea of air. We cannot live without air. So another name of air is life. At every moment we inhale and exhale air. The air we inhale contains more oxygen (20 per cent) and the air we exhale contains comparatively less oxygen (16 percent) and more carbon dioxide (4 per cent). Amount of nitrogen remains the same in both cases. A portion of oxygen that take while inhaling goes to our lungs and get mixes with blood and purifies blood. As a result –

1. Energy is produced in our body. 2. Heat is produced and this heat maintains the temperature. 3. As carbon dioxide comes out of the blood to enter into the lungs,

the amount of carbon dioxide increases and that of oxygen decreases in the air we exhale.

Do the following experiment to test the presence of carbon dioxide in air.

Experiment: Take some clear limewater in a jar. Take a cup of limewater from the jar and keep it in the air. Slowly the limewater in the cup turns muddy and a

Air 45

Fig 3.5: Testing the presence of carbon dioxide in the air exhaled

white film is formed on the surface. In this way limewater takes much time to become white. So you may perform this experiment at home.

Now take another cup of clear limewater from the jar.

Dip one end of a jute stick or a hollow bamboo branch or a straw or a glass tube in this water and blow from the mouth. The limewater becomes muddy very quickly. Why does this happen so quickly?

The air we exhale contains more of carbon dioxide. This additional carbon dioxide when mixes with lime water makes it muddy or whitish quickly. It is carbon dioxide which makes clear lime water muddy. Air is an invaluable wealth. Without air, no animal or tree can survive. It is not only that we use air in respiration, but air supplies food to the whole of animal and plant kingdom. Plenty of carbon dioxide is being added to the atmosphere every moment from our exhalation. Plants and trees receive this carbon dioxide from the air and prepare their own food by themselves through photosynthesis process. Trees collect water from the soil with the help of roots. The reaction is as follows:

Sun-light

Water + Carbon-dioxide ⎯→ Starch + Oxygen

(From Soil) (From air) Chlorophyll (Food) Human beings and other animals receive their food from the trees. Carbon and oxygen combine together to form carbon dioxide. Plants use carbon

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dioxide of the air for producing food and leave oxygen in the atmosphere. We, the human beings and other animals, use this additional oxygen and leave additional carbon dioxide in the air again through respiration. In this way a wonderful balance is maintained in the kingdom of nature. Importance of nitrogen in the plant and animal kingdom We know that four-fifths of the air is nitrogen. This nitrogen is of immense value to animals and plants. Had there been no nitrogen in the air, we would get only oxygen for our respiration. We know that oxygen helps combustion. Pure oxygen received through inhalation would expedite combustion extremely, and as a result it would be impossible to survive.

Air becomes lighter due to the mixing of nitrogen with oxygen. As a result respiration and combustion inside the body occur smoothly and at a moderate speed. In absence of nitrogen in air, fire incidence at any place would be so severe that it would not have been possible to extinguish.

Nitrogen has a special need for nutrition of plant and animal body. Some plants such as the chickpea, pea, bean, etc take nitrogen directly from air. Besides these none of the members of the vast animal and plant kingdom can receive free nitrogen directly from air. Plants receive nitrogen from the nitrates mixed with the soil. Herbivorous animals directly from the plants and carnivorous animals from other animals receive nitrogen as protein. Thus plants and animals, all take nitrogen. Consequently nitrogen should have been exhausted from nature. But in fact such a situation does not occur. Through the natural process nitrogen goes from air to soil, from soil to plants, from plants to animals and then from animals to the soil and from soil to air again. As a result, the quantity of nitrogen in air always remains the same. This cyclic rotation of nitrogen is called nitrogen cycle. You will learn in detail about this in the next higher classes.

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Presence of nitrogen in some common fertilizers: Urea and ammonium sulphate are the nitrogenous chemical fertilizers. Urea contains 46% and ammonium sulphate contains 21% nitrogen. Use of these two fertilizers helps rapid growth of the branches and twigs of the trees. These give deep green colour to the trees and increase their yields. Air pollution and its prevention: Polluted air The air that contains poisonous gases, germs of diseases, dust particles, etc is called polluted air. Pure (or fresh) air Air that contains moderate amount of oxygen, nitrogen, moisture etc, and do not, contain dust particles, smoke, germs of diseases, poisonous gases or any other harmful substances in it, is called pure or fresh air. Reasons for pollution of air

The reasons for which air becomes polluted, are stated below:

1. Air is polluted by dust, sands, smoke, soot, jute fibres and other organic and inorganic substances.

2. Gases emitted from rubbishes, open drains, stagnant ponds, boggy swamps, open latrines, etc pollute air.

3. Smoke emitted from the mills and factories and the gases and smoke emitted from the railway engines, motorcars, launches, and other automobiles due to the combustion of fuel, oils pollute air.

4. Gas that is given out by the decomposed dead bodies of animals, pollute air.

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5. The sulphur dioxide and carbon dioxide gases produced due to the combustion of kerosene oil, pit coal etc, and the smoke from cooking pollute air.

6. Germs of various airborne diseases such as pox, TB, etc mix with air through sneezing, coughing and spitting of the patients and pollute it.

7. Gases that are given out from the brickfields, smoking of cigarettes, tannery, fish drying fields, cremation ground etc. pollute air.

Purification of air and prevention of pollution:

Air can be purified by the following two methods:

1. Natural process and

2. Artificial process.

1. Natural process:

A. By the rays of the sun: The ultra violet rays and heat of the rays of

the sun destroy the floating germs of diseases and other harmful germs in the air and purify it. Besides this, the sunshine dries up all moist things and checks their decay. Thus it helps keep the air fresh.

B. By the plants and herbs: In presence of sunlight the green leaves of

the plants and herbs take carbon dioxide from air and gives out oxygen. Thus air is purified.

C. By rainfall: Gases and floating substances in the air drop down with

the rain and get mixed with the soil. This purifies air. D. With the help of ozone: Ozone gas is formed due to thunderclap in

the sky. This ozone gas destroys the floating germs in the air, and thus air is purified.

Air 49

2. Artificial process:

Air in homesteads, industries and their surroundings become polluted due to various reasons. By arranging artificial circulation of air in these areas such pollution can be removed. This method is more suitable for town areas than rural areas. A. By circulating air: To remove the stagnant air from a closed space

and to bring dry, cool and blowing air in that place is called circulation of air.

B. By propulsion method: An electric fan is fitted in an opening made in wall on any side of the house. With the help of this fan fresh air is drawn in from outside and polluted air is driven out from inside.

C. By air conditioning: The air inside of a house may be kept fresh by air conditioning. Nowadays this method is widely used in railway carriages, motorcars, cinema halls, hotels, offices, residences, etc.

Besides these, for prevention of air pollution, the waste materials should be collected at a particular place and kept covered, they should not be thrown here and there, the premises should be kept neat and clean, the drains should be kept clean, and smoke should not be created unnecessarily by burning things. New words in this chapter:

Density Argon Calcium hydroxide Respiration Inert gases Photosynthesis Conical flask Calcium carbonate Nitrate Moisture Balance Protein Lungs Air pollution Nitrogen cycle Methane gas Propulsion Method Ammonium sulphate Helium Air circulation Neon Waste materials

50 General Science

EXERCISE Multiple Choice Questions (MCQ)

1. In which place is the amount of oxygen high? a. in the air of town area b. in the air of industrial area c. in the air of forest and crop fields d. in the air of marshy lands

2. What portion of air is helpful for combustion?

a. the whole part b. four fifth c. one fifth d. three fifth

3. In which air is the amount of carbon dioxide more? a. air in the upper zone b. air in the forests c. air above the sea d. air of the cities

4. Why do drops of water deposit on the outer surface of the glass when ice is kept inside? a. due to presence of oxygen in air b. due to presence of vapour in air c. due to melting of ice d. due to presence of carbon dioxide in air

5. From air, what is taken by plants for preparation of food?

a. oxygen b. hydrogen

c. nitrogen d. carbon dioxide

6. The amount of nitrogen in air remains always constant

i. because of nitrogen cycle

ii. animals do not use nitrogen

iii. nitrogen is not used in combustion.

Air 51

Of the following, which is correct? a. i b. ii

c. iii d. i, ii and iii

From the diagram, answer the questions 7 and 8.

Figure

7. What does the figure shown above indicate ?

a. nitrogen cycle b. the relation between animals and plants

c. the relation between soil and air d. the relation between plant and air

8. The equilibrium of the environment is maintained as shown in the

figure-

i. due to mutual dependence on plants and animals

ii. due to leguminous plants

iii. due to presence of nitrate salt in soil

air

nitrogen

soil

Plant

animal

soil

52 General Science

Of the following, which is correct?

a. i b. i and ii

c. ii and iii d. i, ii and iii

Creative Questions (CQ)

1.

Figure

a. Which component of air is taken by the plant in presence of the sun light?

b. Why is the sun light required as shown in the figure?

c. Explain, with the help of a diagram, how the plants prepare their food.

d. Explain what will happen if there is no carbon dioxide in that

environment.

Air

Sun

Air 53

2.

Figure

a. Which side in the diagram is force applied?

b. Why is force applied to that side?

c. According to the diagram, explain the condition of the paper inside the glass.

d. From the above experiment, give your opinion regarding air.

3.

Figure

a. Which candle as shown in the figure will go out at first? b. Why will the candle go out at first? c. Explain what will happen in case of figure -3 if a long burning candle

is covered with a second glass. d. In the light of experiment no. 1 and 2, write down the amount of

carbon dioxide in the air

1 2 3

Chapter - 4

Metal and Non – Metal

In chapter two you have learnt about the matters and its classifications. Try to remember what is called matter? What are the types of matter and what are these? We know there are 111 elements discovered so far. Out of these 92 elements occur in nature. Rest of them are man-made elements. These elements are classified into two groups on the basis on their properties. These are metals and non-metals. Hydrogen, Oxygen, Carbon, Nitrogen, Sulphur etc are the examples of non-metals. On the other hand, iron, copper, gold, zinc, aluminium, tin etc are the examples of metals. Now let us discuss what are metals and non-metals and uses of some of our known metals and non-metals. Metal The element which at ordinary condition, is hard, durable, bright, lustrous and can reflect light, heavy, conduct heat and electricity and when struck emit a sound clink is called metal. Iron, copper, gold, silver, zinc, tin, aluminum are the examples of some metal.

Non-metal The element which at ordinary condition, is solid, liquid or gaseous, light in mass, not bright or lustrous and do not reflect light, non-conductor of heat and electricity and does not emit clink sound when struck is called a non-metal. Such as- hydrogen, oxygen, sulphur, carbon, helium, neon, iodine etc are the examples of non-metal.

Metal and Non-metal 55

Some metals and non-metals having exceptional properties Mercury is a metal, liquid at ordinary temperature. Sodium metal is lighter than water. Carbon and sulphur are non-metal but solid at ordinary condition. Graphite (carbon) being non-metal is a good conductor of electricity. Diamond (carbon) is a non-metal but able to reflect light and the hardest one. Iodine is a non-metal but lustrous. Properties and uses of some metals used in everyday life

Iron Iron is most familiar and widely used of all metals. At ordinary condition, iron is black. But pure iron is a white in colour. Iron is attracted by magnet. We use iron in our everyday life for various purposes. Chopper, fish cutter knife, small spud, knife, scissors, spade, axe, plough-blade, weeding tool etc are used in our daily life and agricultural instruments are made of iron. Iron is used for making motor-cars, railway wagons and rail-line, various kinds of arms, launches, ships, bridges etc and to establish industries and buildings. The more is the quantity of iron used by a country the more developed it is. In short the consumption of iron per annum by a country is used as a parameter of development of that country.

Copper Copper is a peculiar reddish-brown bright metal. It is soft, malleable and ductile. It is a good conductor of heat and electricity. For this copper wire is widely used in houses and at other places for electric supply. If you examine a piece of electric wire, you see that there are many thin copper wires in it. We use copper for various purposes. Copper is used for telegraph, telephone and electric line. The importance of copper is seen in our various practical lives. It is used for making utensils, coins,

56 General Science

statues and propeller of ships. Alloys such as, bronze, brass and many metal are made of copper. The bell of your school is also made of copper. The main copper manufacturing countries of the world are America, Canada, Chilli, Mexico, Belgium, Rhodeshia, Spain, Germany, Russia, Japan and India.

Aluminium

Aluminium is a bluish-white light metal. It is a very good conductor of heat and electricity. Aluminium is used in making cooking utensils. Aluminium alloys are used for manufacturing aeroplane bodies, motor cars, bridges etc. Bright and lustrous frames of doors and windows are now made by mixing linseed oil with aluminium. Duralumin is an alloy of aluminium which is made mixing 95% aluminium, 4% copper, 0.5% magnesium and 0.5% manganese. Duralumin is used for making aeroplanes.

Silver From very ancient period of time people are using silver. Silver occurs in nature as a mineral ore. It occurs as ore in mine in South America, Canada, Peru, Mexico, Australia etc. Silver is a bright white metal. Very thin sheets and thin wires can be made of silver due to its malleable properties. Silver is the best conductor of heat and electricity. It is used for making ornaments and coins. Many household substances are made by mixing pure silver with copper. It is also used to make the coating on the back of the mirror.

Tin People are using tin from ancient period. People of Egypt and China used to be use bronze; which is an alloy of tin and copper. Large amount of tin occur in Burma (Mayanmer). 80% of the total tin contain of the world

Metal and Non-metal 57

occur in South-East-Asia. Tin is a white metal of high malleable properly. Thin sheets can be made from it. Alloys, utensils sheets, tin-plating and tin soldering etc are made from tin. In the rural and urban areas of our country tin are generally used to make houses.

Gold Gold is a precious metal. Almost all of you are familiar with gold. It is

lustrous and of golden colour. The women in our country use gold

ornaments. Not only in our country, women in abroad also use gold

ornaments. The value of currency of a country is determined on the basis

of gold deposits.

The use of iron and steel in agricultural instruments

Bangladesh is an agricultural country. About 80% of the population depends on agriculture. The instruments, which are used, for cultivation purpose are called agricultural instruments. Iron and steel are used for making local and modern agricultural instruments. Steel is an alloy, made from iron. Axe, spade, knife, chopper, sickle, small spud, weeding tool,

Fig 4.1: Some agricultural instruments.

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crowbar, plough blade etc are all used in agriculture and they are made

of iron.

Molboard plough, power tiller, tractor, power pump, sowing machine, spray machine, threshing machine etc are modern agricultural instruments. Can you tell with which elements these instruments are made of? All these are made of steel. Now you can understand that small and heavy, local and foreign, all these agricultural instruments are almost made of iron and steel. In short, we talked about the role of iron and steel, which is essential to make agricultural instruments.

Properties and uses of non-metals At the beginning of this chapter you have learent what is non-metal. Hydrogen, oxygen, nitrogen, carbon, sulphur, chlorine, iodine, helium, neon, krypton etc are the examples of some non-metals. The properties and some uses of these non-metals are discussed below.

Hydrogen

Hydrogen is the lightest of all the elements. The British scientist Cavendish first discovered it in 1756. ‘Hydro’ means water and ‘gen’ means producer. Hence, hydrogen means water producer. Small amount of elementary hydrogen occurs in air, oil mine and in volcanoes. In laboratory hydrogen is prepared by the action of metals with acids.

Hydrogen is colourless, odorless and test less gas. Hydrogen is the lightest element of all substances in the world. For this hydrogen gas is used for flying balloons and aircrafts. Hydrogen burns itself but does not help others to burn. Hydrogen chemically combines with oxygen to produce water. Water contents are 2 parts by volume of hydrogen and 1 part by volume of oxygen. The flame of hydrogen with oxygen is called oxy-

Metal and Non-metal 59

hydrogen flame. It used for melting of metals and welding. Hydrogen is also used for manufacturing ammonia, hydrochloric acid and urea fertilizer. Hydrogen combines chemically with carbon to produce various types of compounds. Sugar, soap, oil, petroleum, gasoline etc. contain sufficient quantity of hydrogen.

Oxygen Oxygen discovered by British scientist Priestly in 1774. Swedish scientist Schell and French scientist Lavisher discovered it independently at the same time. ‘Oxy’ means acid and ‘gen’ means producer. That is oxygen means acid producer. Oxygen is one of the components almost of all the acids. Air contains 1 part by volume of oxygen and 4 parts by volume of nitrogen of its per 5 parts. Oxygen can be prepared in the laboratory. Oxygen is a colourless, odour less and taste less gas. It is soluble in water. Fishes and other aquatic plants can perform their respiration due to the dissolved oxygen in water. Oxygen does not burns itself but help to burns others substances. Oxygen is very essential for the survival of plants and animal kingdom. We take oxygen in respiration. Oxygen is used to help respiration of dying patients. Space travelers, mountaineers and divers use oxygen for respiration. Large quantity of oxygen is used for the production of oxy-hydrogen flame. Liquid oxygen is used as rocket fuel. Large quantity of oxygen is also used in iron and steel industries.

Nitrogen In 1772 Daniel Rutherford discovered nitrogen. Air contains large amount of nitrogen. 4 parts are nitrogen in air out of its 5 parts. Nitrogen is

60 General Science

essential for the nutrition of plant and animals. Nitrogen gas can be prepared in laboratory.

Nitrogen is a colourless, odorless and taste less gas. Nitrogen is an inert gas. It does not burn it self and does not help to burn other substances. Vast amount of nitrogen is required to produce chemical fertilizer. The roll of nitrogen for plants and animals are very important. You have learnt this in the chapter air.

Sulphur Sulphur occurs in nature as elementary sulphur ore. Egg, mustard seed, onion, garlic, hair, wool etc contain sulphur. Sulphur is a light yellow crystalline solid. It is used in the manufacture of matches. Sulphur is also used in production of ointments, medicines, insecticides, dyes and paper.

Coal Carbon occupies an important position among all the elements on the earth. Diamond, graphite etc are the varieties of carbon. Proteins, carbohydrates and fats are also carbon compounds. In nature the existence of carbon is mostly found in the plant and animal kingdoms. The primary and essential components of plant and animal bodies is carbon. Every portion of plant and animal bodies is made of carbon compounds. Charcoal, animal coal, lamp black coke and gas carbon are the different forms of carbon. Carbon is used as fuel. It is also used for making of shoe-polish, antiseptics, gunpowder, printing ink etc.

Comparison between metals and non-metals You have learnt about the properties and uses of some metals and non-metals, which are used in our daily life. Some distinctions between metals and non-metals are given below in tabular form.

Metal and Non-metal 61

Difference between Metals and Non-metals

Metals Non-metals 1. Metals are generally bright 1. Non-metals are not generally

bright 2. Metals are hard and heavy in

mass 2. Normally non-metals are soft

and light. 3. Metals emit clink when struck

with hammer. 3. Non-metals do not emit clink

when struck with hammer. 4. Heat and electricity can pass

through metals. 4. Heat and electricity cannot

pass through non-metals. 5. Metals can be hammered to

thin sheets and can be drawn into very thin wire.

5. Non-metals cannot be hammered to thin sheets and cannot be drawn into thin wire.

6. The melting points of metals are very high.

6. Non-metals melts at low temperature.

7. Metals are solid at normal temperature.

7. At normal temperature non-metals are generally solid or gaseous.

8. Metals can reflect light 8. Non-metals can not reflect light

9. Metals usually dissolve in hydrochloric or sulphuric acid.

9. Non-metals do not usually dissolve in hydrochloric or sulphuric acid.

Alloys For what purposes the alloys are used? Let us discuss about the uses of alloys. What is the meaning of alloy? The terms alloy means mixture. When two or more metals are mixed together by melting and the solid mass that is obtained on cooling it is called Alloy. Steels, brass, bell

62 General Science

metals and duralumin etc are alloys. Alloys are stronger than the constituent metals. Alloys do not rust or not errode if they are exposed to air for a long period of time. The properties and uses of some alloys are given in the table below:

Table of Alloys Name of alloy

Main metal

element

Other elementsin the mixture

Special properties Uses

Steel Iron 0.25-1.5% carbon and a little chromium

hard, not brittle, does not rust

Used in making railway line, wheels of railway train, ship crane, frames of buildings, war equipment, medical equipment, engine, utensils spoon etc.

Brass Copper Copper 60-80% Zinc 40-20%

does not rust

Cartidge of bullet, screw, ornaments, utensils etc are made of brass.

Bell metal

Copper Copper 75-90% Tin 25-10%

attractive colour

Used in making coins, utensils, metalic statues, bell, propeller, equipment etc.

Duralumin

Aluminium

Aluminium 95% Copper 4% Manganese 0.5%Magnesium 0.5%

very light Used in building motorcars, and aeroplanes.

Metal and Non-metal 63

New words in this chapter Conductor of electricity Alloy Molboard plough Power tiller Tractor Gasoline Cavendish Priestly Rutherford.

Exercise

Multiple Choice Questions (MCQ) 1. Which is a metal?

a. carbon b. sulphur c. graphite d. mercury

2. Which is a non-metal? a. sodium b. iodine c. copper d. zinc

3. Though nonmetal, which is conductor? a. graphite b. diamond c. sulphur d. carbon

4. Which property is applicable in case of nonmetal? a. a sound is produced when it is hurt b. thermal and electric conductor c. low melting point d. bright and glittering

5. What compound are sugar, soap, oil, petroleum, etc. made of? a. oxygen and hydrogen b. carbon and hydrogen c. carbon and nitrogen d. carbon, oxygen and hydrogen

6. A balloon full of gas was flown away when it was released. There is in the balloon- a. hydrogen gas b. oxygen gas c. nitrogen gas d. carbon dioxide gas

7. The gas in balloons of question number 6 i. helps in combusting others ii. burns itself iii. helps in putting the fire off

64 General Science

Of the following, which is correct? a. i b. ii c. iii d. i and ii

Creative Questions (CQ) 1. Mariam Begum is a housewife. She lives in the town. She goes to

her village house, if required. Prior to her departure, she kept her utensils, crockeries, chopper, spoons etc under lock and key. She returned home after a few days. She saw that there was deposition of brown colour on her chopper. The cooking pots, spoons, remained the same as they were. Of the crokeries, some are made of metal and some are of nonmetals. a. What is the name of brown coloured coating on the chopper and knife

(boti)? b. Classify the used crockeries according to the properties of metal and

alloy. c. Why was brown coating not developed on the other crockeries? D. Explain the causes of using different metals and alloys on crockeries.

2. In an alloy, there is

aluminium ………………. 95 % copper …………………… 04 % magnesium ……………… 0.5 % manganese ……………… 0.5 %

a. What is the name of the alloy? b. Why is it called an alloy? c. Explain what will happen if iron is used instead of aluminium. d. Explain the cause of using such type of metal in the construction of

aeroplane.

Chapter-5

Water Water is the most easily available liquid of all the liquids present on the earth. Three fourth of the earth surface consists of water. Human body contains about 70% water. Fish, meat vegetables contain almost 60% to 90% water. None can survive without water. That is why the other name of water is life.

Water is a compound Water is a liquid. It has no definite shape, it takes the shape of the container in which it is kept. You have learnt about the elements. Compounds and mixtures in chapter number two. Now, the question is raised what class of substance is water? An element, a compound or a mixture? In ancient period, water was considered to be an element to the people. In 1781 a scientist, Cavendish proved that water is a compound and he was produced water by the chemical reaction between oxygen and hydrogen. Water is a compound; this can be proved by the following arguments.

1. By pure sample of water taken from different parts of the world, it has been found that nine parts by mass of water contain 1 part oxygen and 8-part hydrogen. If water was a mechanical mixture, the proportion of mass of oxygen and hydrogen would be different.

2. Water is produced by the combination of oxygen and hydrogen. The individual properties of each component are absent in water.

3. Heat energy is produced during the formation of water. If water was a mixture of oxygen and hydrogen no heat would evolve.

66 General Science

4. If water was a mechanical mixture, its constituent’s oxygen and hydrogen could be separated easily while oxygen and hydrogen cannot be separated without chemical operation.

5. A chemical compound is always homogeneous. But oxygen and hydrogen that remain in water are homogeneous.

6. After chemical analysis of a compound it produces different elements having different properties. Electrolysis of water produces two elements oxygen and hydrogen having different properties.

From the above point of view it is to say that water is a compound and not a mechanical mixture. Constituents of water: Separation of hydrogen and oxygen

Water is composed of two elementary gases hydrogen and oxygen. When electricity is passed through a slightly acidulated water, it decomposes into two gases; oxygen and hydrogen. This method of decomposition of a compound into its components by chemical reaction is called chemical analysis. Water can be decomposed chemically into its component elements. For this, let us perform the following experiment.

Experiment To perform this experiment you require a glass or plastic bowl with two holes at the bottom, rubber stoppers, four dry cell, two carbon rod collected from two rejected dry cell, some copper wire, sulphuric acid, water and two test tube for collecting gas. First of all close the two holes of the glass bowl with the rubber stoppers. Introduce two copper wires into the bowl through rubber stoppers. Connect the two copper wires with the copper caps of carbon rod, which is taken out from the reject dry cell. Now connect the other two ends of copper wire with four dry cell out side the bowl. The four dry cell should be kept in wooden case. Insert the two

Water 67

carbon rods inside the bowl appropriately. Now pour water in the bowl, acidified with a little sulphuric acid. After a few moments you will see that gas bubbles are evolving from the carbon rods. Take two test tubes of same size and fill them Fig: 5.1 Analysis of water

with water. Place them on the carbon rods inertly and clamp them. Observe that gas is deposited into the two test tubes by down wards displacement of water.

You will also observe that gases deposited in the test tubes are not equal. The amount of gas in one tube is one half the amount of gas in the other tube. After filling both the test tube with gases, bring them out, closing their mouths with your fingers. Now enter a lighted jute stick into tube in which gas will be deposited quickly. The stick extinguishes and the gas burns at the mouth of the tube with a blue flame. This proves that the gas is hydrogen. Similarly insert another lighted stick without flame in the other tube, in which gas will be deposited slowly. You see that the stick kindles and burn brightly. This proves that the gas in the rube is oxygen. From this experiment, it is understood that water dissociates to produce two volumes of hydrogen and one volume of oxygen, when electricity is passed into it. This means that water is a compound and it is composed of two elements as hydrogen and oxygen.

volOxygen

volHydrogen

analysis

ElectricWater

12+→

68 General Science

Importance of water for saving the animals and plants and in our daily life Another name of water is life. No life can exist without water. Plants and animals need water for different purposes. Some of its requirement of water for plants and animals are discuss below: Water is required to build the cells of a body. The water secreting from mouth helps to swallowing food. The food components dissolve in water and then absorb in body. The fluid of blood transports food items to different organs and then it produces energy and builds body. Similarly, the toxic substances are leaving out through this water. Sufficient amount of water are required to washing cloth, bathing, cooking and cleaning of utensils. There is a hydroelectric power station at Kaptai in our country. In this power station water is used to run generator to produce electricity and this electricity is supplied to different places. We use this electricity to lighting bulbs, running fan, radio, television etc. Again, large quantity of water is required in different small and heavy industries. Cultivation of lands is not possible without water. Cultivation of land in our country mostly depends upon rainfall. But at the time of requirement sufficient rainfall do not occur. Thus, the farmer cultivates their lands by irrigation. Water is essential for plant kingdom. From the time of germination of seeds sufficient quantity of water is required, until end of the life of plants. Plants receive required quantity of water from soil by their roots. This water reacts with carbon dioxide in air in presence of chlorophyll and sunlight to produce food. The plant and animal world live by taking this food.

Water 69

Sources of water From the following four sources we get water in nature. (1) Rain water (2) Fountain water (3) River water (4) Sea water.

1. Rain water Rainwater is the purest form of natural water. Water in the sea, river canal, lake, pond etc vaporise due to sunshine and go into the air. In contact with the upper cold air this vapour condenses into cloud and make rainfalls from the cloud. As a result, the rivers, ponds, canals, lakes, swamps etc fill with water. In the hill track area there is more rainfall. This rainwater goes into the river and sea. This cycle of water is called water cycle. This water cycle is shown in figure.

2. Fountain water Rainwater enters into the soil after rain. Sand, clays and stones filter when it passes water through them. After a long storage in the ground this water comes up on the surface as fountain. This water is also obtained from wells and tube-wells. Various substances present in the soil get dissolved in this water. For this reason, fountain water is not always pure. But as it comes out through the layers of sand and stone, it looks almost clear. 3. River water Molten snow from mountains, rain and fountain water flow into the river. There are floating and dissolved material present in river water waste

Fig: 5.2 Water cycle

70 General Science

materials from surroundings also fall in to the river water. For this river water looks muddy and un-clean in rainy season. The river-flow carries various materials with it. Some of these materials are soluble and some are insoluble. Soluble materials contain different salts and insoluble materials contain sand, clay etc. In rainy season river water looks turbid due to the presence of clay and mud.

4. Sea water Sea is the main source of water. River flow into the sea. Seawater looks clear. But it contains the largest amount of dissolved impurities. Excess amount of different salts contain in seawater. For this seawater is undrinkable and salty. Besides these, we get water from wells, tube-wells, ponds, lake. Water from these sources is used for drinking and other domestic purposes. Now a day’s water is supplied to the city areas and in cultivating land from deep tube-wells.

Pure and impure water We should be very careful about the purity of our drinking water. Water is polluted in various ways. The water which contains germs of diseases, waste materials, darts etc. and which by drinking causes diseases in our body is called impure water. Pure water cannot be obtained except rainwater. Rain water generally pure. But rainwater at the beginning of rain remains dirty due to the presence of dust particles in the air. The rainwater in industrial areas is not pure. Water in ponds, ditches, canals and rivers become polluted in different ways. Some of the common causes of pollution of water are mentioned here.

Water 71

Causes of pollution of water (1) River and pond water is polluted by washing of household utensils, taking bath, washing of dirty clothes, giving bath to cattle’s, rotting of jute, defeating and throwing dead bodies in water. (2) Washing of clothes, urine and stools of patients attacked by cholera, typhoid, dysentery and diarrhoea, contaminates water with germs of these diseases. (3) Plants and herbs, leaves of trees straws, moss etc pollute water by decay and decomposition. (4) When the walls of wells are very low, then due to washing of utensils, clothes etc around it, and also due to percolation from the nearby waste pits privies the well water becomes polluted, use of soap and detergents also pollute water to a high extent. (5) The waste of industries contains toxic and poisonous chemicals. When the wastes thrown to lake and river are water pollutes by it and fishes are killed. (6) Various insecticides are applied on a large scale. These poisonous chemicals are washed by the rainwater and fall into pond and river. Thus water is polluted and fishes are die in it. (7) Excess use of chemical fertilizers in the land is harmful to different living bodies in pond and river. These excess chemical fertilizers are washed down by rainwater and brought into the pond or river. As a result moss and other aquatic weeds grow more in the river and pond.

These weeds use dissolved oxygen in water. Due to this fishes die for oxygen deficiency. Dead fishes make water polluted. This polluted water is harmful to use. Production of masses and weeds in water are decreased due to shortage of oxygen.

72 General Science

Pure water The water which is transparent, colourless, odourless, there is no floating organic or inorganic matter and is free from any germs is called pure water. There is no risk to drink pure water. We should always drink pure water. Tube-well water is usually pure.

Methods of purifying water Meanwhile, you have known the causes of pollution of water. Water pollution can be prevented by not doing such things by which water pollution occurs usually water can be purified by two methods. Such as – natural method and artificial method.

Natural methods of purification of water In nature, water is being purified through natural process but it is being polluted the next time. Hence one cannot depend on natural methods of purification of water for drinking purpose. Water from preserved pond, well or tube-well, that cannot be polluted easily, can be used for drinking purpose. Usually, water is purified by the following natural methods, - such as- (1) Sunlight damages the bacteria in water and removes bad smell. (2) The dissolved oxygen in water makes organic substances in water

harmless and removes bad smell. (3) Minute aquatics live in water. They eat dirty particles of water and

thus water is about purified. (4) Aquatic plants produce oxygen in water by which water is purified. (5) When bacteria is present in great extent in preserved water, they

destroy themselves. So water is purified.

Water 73

Artificial methods of purification of water There are several artificial methods by which water is purified. The following three methods are most commonly used to make water pure and germless. viz- (1) By boiling : At first insoluble floating substances, muds, clays etc contained in water are filtrate out. Then the water is boiled for 20-25 minutes. All the germs are killed due to boiling. It is now free from germs and ready for drinking. But the boiling container should be cleaned and then dried by heating. This method of purifying water is dependable, cheaper and suitable. (2) Potassium, bleaching powder, potassium permanganate, chlorine etc are added to water and allowed to settle down the impurities. Then decant the clear water from upper portion and then it is ready for use. (3) Some tablets are available for the purification of water, are called water-purifying tablets. Using these tablets can purify water. Sometimes floodwater enters into the tube-wells and wells etc and pollutes water. At that time water-purifying tablets can be used to purify water.

Prevention of wastage and pollution of water Water is the most valuable natural asset. Excessive use of any asset ended once upon a time. Deposit of water is not also unlimited. So never misuse water. To avoid wastage of water carefully close the water tap. You have observed that there is much difference between the water in the rural area and town. You will astonish to know that the layer underground water in our country is gradually going down. That is why the rivers, and canals of our country become dry in summer. For that

74 General Science

reason our country is going to be a desert. So you need to be conscious that there is no wastage of water. In this chapter you have known about the various information of water. You should use pure water for different activities such as cooking, washing, bathing, drinking etc. You must drink boiled water after cooling. In the big cities the water is first purified with chlorine and other chemicals and then it is supplied. Bacteria may form in the water tanks in the city if it is not cleaned periodically. For that water should be boiled to drink. By using polluted water you can be attacked by diseases like dysentery, cholera, typhoid and jaundice. Water should not be polluted. You must be take care of it. Avoid those activities, which may cause pollution of water. Water is polluted by leaving stools or urine near the rivers and ponds, washing clothes of patients, washing utensils and bathing of cattle’s in the ponds. So try to avoid such activities. Now a days the farmers in our country use chemical fertilizers and insecticides in a large extent. These chemicals are drainage away by the rainwater and cause pollution of river and ponds water. Farmers need to be motivated not to use excess chemical fertilizers and insecticides out of necessity. Following the above-mentioned steps are can prevent pollution of water and you can obtain pure water easily.

New words in this chapter Cavendish, insecticides, bleaching powder, sulphuric acid, chemical fertilizer, watercycle, electrolysis, potassium permanganate, detergent, hydroelectric centre, wastes,

Water 75

Exercise

Multiple Choice Questions (MCQ) 1. Which is the stage of water cycle ?

a. river → rain → vapour → sea → cloud

b. sea → cloud → vapour → rain → water

c. water → river → cloud → rain → vapour → sea

d. water → vapour → cloud → rain → river → sea

2. Why do the fishes die when water of the pond is polluted by chemical

fertilizer?

a. the fish takes polluted water

b. the food of the fish becomes poisonous

c. there is scarcity of oxygen in water

d. the amount of oxygen in water increases

3. Why chlorine is added in drinking water?

a. to make water tasty

b. to destroy harmful germs of water

c. to remove the insoluble matter of water

d. to increase the nutritious value of water

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4.

Diagram

The diagram above indicates -

a. water cycle

b. the relation between vapour and cloud

c. the relation between vapour and rain

d. the relation between cloud and rain

5. Relatively more safe source of water in diagram 4 as shown is

i. pond

ii. rain water

iii. cloud

Of the following, which is correct?

a. i b. ii

c. iii d. i and ii

Cloud

Rain Vapour

Pond

Water 77

Creative Questions (CQ)

For drinking purposes, Sajal takes boiling water to his school. One day

he did not take water with him and he was attacked with diarrhoea by

drinking polluted water from the tap. The doctor advised him to drink

always boiled water. He advises all to take saline water. He also says,

‘the other name of water is life’.

a. What is water pollution?

b. Why is Sajal attacked with diarrhoea by drinking tap water?

c. How is tap water made safe?

d. Explain why the doctor has said that ‘the other name of water is life’?

Chapter-6 Living World

All that is seen around, that is, houses, roads, doors, windows, chairs, tables, soil, water, rivers, mountains, vehicles, tree, birds, insects, flowers, and so on, all together constitute the environment. All these things can be broadly divided into living and nonliving things.

Things like tree, birds, animals, insects, humans have life, and so are called living. Again, chairs, tables, soil, water, rivers, mountains, sun, moon, stars, and so on do not have life, and so are called nonliving.

It is thus evident that the basic difference between living and nonliving is the presence or absence of life. Because of the presence of life, the living things show certain characteristics, that nonliving things do not posses. What follows is a brief discussion on the characteristics or features of living things.

Movement and locomotion

Living body is made up of innumerable cells. These cells contain a jelly-like substance, the protoplasm. The protoplasm in the cell is in continuous motion. It is because of this protoplasm that there is movement in living bodies. The movements shown by living bodies come from within. The change of position is not movement.

6.1: Movement in animals

Living World 79

The change of position is locomotion. All living things show movement and locomotion. Locomotion is easily observed in humans, birds, animals, insects, fish, and so on. Some animals move with the help of legs on land, while

6.2: Plants some swim in water with the help of fins. The movement of plants is not easily observable as they are found to be fixed in one place on the soil. Plants too exhibit movement. For example, the roots grow and move in search of water; the stem grows and moves towards light. This shows that living beings exhibit movement and locomotion. Nonliving things do not exhibit movement and locomotion.

Sensation Living organisms respond to stimuli. In fact, sensation and the ability to respond to stimuli is the basic property of protoplasm itself. For example, the sensitive plant (e.g., lajjaboti) responds to touch by folding its leaves; the

6.3: Sensitive plant

dog barks at the sight of a stranger; when touched, a snail curls itself within the shell. Similarly, living beings feel the presence of light or heat, and respond as required by the body. Nonliving things do not have the capacity to respond to stimuli. Growth Living beings take food. This food is digested and helps in the growth and

6.4: Plant growth

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repair of the body. Trees, humans, birds, insects are all seen to slowly grow bigger from a very small size. There is increase in size and weight. This increase in size and weight comes from within through the increase in number of cells and thus of protoplasm, and is called growth. The diagram shows the growth of a seed → sapling → tree.

Nonliving do not grow from within. Things may be added from outside but that is not growth.

Respiration

All living bodies take in oxygen during inspiration and give out carbon dioxide during expiration. The oxygen is needed to carry out the metabolic functions of the living cells. The nonliving things do not need oxygen and so do not respire.

Reproduction

Fig 6.5: Reproduction of living

organisms

Reproduction is a process whereby all living organisms produce offspring. Trees produce seeds, these seeds then grow into saplings and then trees again. The hens lay eggs from which a chicken comes out. Humans, cow, goat, cat and so on give birth to babies. Reproduction is one of the essential functions of plants, animals, and single celled organisms, for the preservation of the species.

Death Plants and animals do not live forever. The life of living beings have three stages childhood, youth or adulthood, and old age. Both plants and animals grow rapidly in childhood, reproduce in adulthood, and then still later all life processes end, that is, death occurs. Nonliving things have no death.

Living World 81

Difference between Living and Nonliving Living Nonliving

1. Living body is formed of protoplasm

1. Nonliving things have no protoplasm

2. Living beings can move around 2. Nonliving things cannot move on its own

3. Living beings respond to stimuli

3. Nonliving things do not respond to stimuli

4. The food that living beings take help in growth and repair

4. Nonliving things do not take food

5. Living beings carry out respiration

5. Nonliving things do not respire

6. Living beings can adapt with the environment

6. Nonliving things cannot adapt

7. Living beings can reproduce 7. Nonliving things cannot reproduce

8. Living beings have a definite lifecycle

8. Nonliving things have no lifecycle

9. Living bodies have definite size and shape

9. Nonliving things have no definite size and shape

Features of Plants and Animals Living things include both plants and animals. Those living beings that can move from one place to another, such as dog, cat, cow, goat, elephant, horse, camel, buffalo, fish, snake, fly, dragon fly, earthworm are animals.

The living things that usually do not move from one place to another, rather remain fixed at some point on the soil, are called plants. But some parts of the plant body do move, such as roots, leaves, stem, branches, and so on.

Important Features of Plants: Plant are usually green coloured; produce their own food, they are food producers; cannot take in solid food; cell is

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surrounded by cell wall; usually unable to move; and have no organ systems for respiration, excretion, and digestion.

Important Features of Animals: Animals usually cannot manufacture their own food, they are food consumers; have locomotion; can take food in any form–solid, liquid; the cells do not have cell wall; and they have organ systems for respiration, excretion, digestion, nervous functions. Plants and animals have few features in common, while other do not match.

Differences between Plants and Animals

Plants Animals 1. Have chlorophyll, a green

pigment, with the help of which plant manufacture their own food.

1. Cannot manufacture their own food, as they do not have chlorophyll. So animals depend on plants for food.

2. Most plants cannot move. 2. Almost all animals can move. 3. Plants cannot take solid food. 3. Animals can take solid, liquid

and other forms of food. 4. During photosynthesis plants

take in carbon dioxide and give out oxygen. During respiration it takes in oxygen and give out carbon dioxide.

4. Animals take in oxygen and give out carbon dioxide during respiration. It never takes in carbon dioxide as photosynthesis does not occur in animals.

5. Plants have a definite structure and shape, but the branches are not well defined.

5. Animals have a definite size, shape and structure.

6. Plants do not have specific organ system.

6. Animals have specific organ systems.

7. Most plants are food producers. 7. Most animals are food consumers.

8. Plants grow till before they die. 8. Animals grow up to a certain age. 9. Plant cells have cell wall. 9. Animal cells do not have cell wall.

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Animal Kingdom Animal kingdom may be divided into invertebrates and vertebrates.

Invertebrates: Animals that do not have vertebral column or spinal cord are called invertebrates. For example: earthworm, spider, crab, scorpion, cockroach, prawn, snail, fly, mosquito, and so on.

Features of invertebrates: Like humans the invertebrates have certain features, such as

Earthworm

Cockroach

1. No vertebral column 2. No endoskeleton 3. Have simple or compound eyes 4. Heart is not well developed 5. Usually have no tail

Invertebrate Animals Mosquito

Prawn

Crab 6.6: Invertebrate animals

Vertebrates: Animals that

have vertebral column or spinal cord are called vertebrates or chordates. For example: goat, elephant, horse, tiger, lion, frog, snake, cattle, fish, crocodile, monkey, cat, humans, and so on.

Features of vertebrates: Like invertebrates, vertebrates have certain features, such as

1. Have vertebral column 2. Have endoskeleton 3. Heart is well developed 4. Do not have more than two pairs of legs or wings 5. Lungs or gills are used for respiration 6. Have simple or compound eyes 7. Have tail (except humans)

84 General Science

Vertebrates in Our Near Environment

6.7: Vertebrate animals

The vertebrates found in our near environment have been grouped into five classes. What follows is identifying features of the animals in each class.

a. Pisces or fishes: All fishes are included in this group. They live in water. Examples include, hilsa, ruhi (salmon), catla, mrigel, puthi, koi, boal, shul, gojar, shing, magur, ayer, tangra, meni, roopchanda (pomfret), ritha, coral, shark, and so on.

Features 1. Most fish have scales. Some do not have scales, like boal, shing,

magur 2. Gills present, lung absent 3. Odd or even number of fins present that help in swimming 4. Carries out respiration by gills 5. Are cold-blooded

b. Amphibia: Vertebrates that can live in both water and land are called amphibians. For example, toad, golden frog, tree frog, and so on. The eggs and larvae of the amphibians do not survive without water.

Living World 85

6.8: Pisces or fish Features

1. Skin is bare, that is, hairless, featherless, scaleless. 2. Has four legs but no nail 3. Gills present when young. In adult,

the gills are replaced by lungs 4. Are cold-blooded animals

Golden frog Toad

6.9: Amphibia c. Reptiles: Vertebrates that move on the ventral aspect of the body are

called reptiles. For example, lizard, snake, crocodile, and so on. Features 1. Body is covered by scales or by some other hard material. 2. Move on their ventral aspect. 3. Have nails on their fingers. 4. Lay eggs. 5. Gills present, with which

respiration is carried out. 6. Cold-blooded animal. 6.10: Reptiles

d. Aves or birds: Vertebrates that have feathers are called birds. For example, crow, cuckoo, myna, duck, hen, pigeon, sparrow, weaver bird, parrot, kite, vulture, and so on.

Ruhi

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Features 1. Almost all birds can fly. 2. Body is covered with

feathers. 3. Have a pair of wings, and

a pair of legs. 4. Have strong beaks but no

teeth. 5. To have a lighter body

weight the big bones are hollow.

6. Lungs and air sacs present.

7. Warm-blooded animal.

6.11: Aves or birds

e. Mammals: Vertebrates that give birth to live young ones or babies that feed on mothers' milk are called mammals. For example, human, cat, cow, buffalo, dog, goat, horse, tiger, monkey, donkey, and so on.

Features 1. Body is covered with hairs 2. Have external ears 3. Mothers give birth to young ones that feed on breast milk 4. Warm-blooded animal

Difference between Vertebrates and Invertebrates Invertebrates Vertebrates

1. No vertebral column. 1. Vertebral column present. 2. Usually have no tail. 2. Except for humans, most have tail. 3. Heart is not well developed. 3. Heart is well developed. 4. Eyes are either simple or

compound. 4. Eyes are simple.

5. Usually do not have endoskeleton.

5. Have endoskeleton.

Living World 87

Place of Humans in the Animal Kingdom Among the animals, humans are the best. Human is the only animal that can walk upright. Human brain is bigger than those of other animals, so they are more intelligent. Using the intelligence, humans are ruling everywhere. In today's world, humans are moving freely in space, moon, highest mountain, and in the depth of oceans. Thus, human occupy an unique and superior position among all living things.

New Words Learned in This Chapter Protoplasm Reptile

Reproduction Mammal

Chlorophyll Compound eye

Exercise

Multiple Choice Questions (MCQ) 1. Which one flies?

a. buffalo b. cow c. magpie d. golden frog

2. Which mammal can walk on standing? a. man b. chicken c. leopard d. rhinoceros

3. Which is the characteristic of an animal ? a. green and autotroph b. has definite system c. unable to eat solid food d. cell wall is surrounded by nonliving material

88 General Science

Of the following figure answer the questions 4 and 5.

Figure 4. The A marked portion of the above diagram is-

a. rostrum b. compound eye c. taleson d. carapas

5. Applicable in case of the animal shown in the figure- i. They have no internal skeleton ii. Their tale is segmented iii. They have no leg

Of the following, which is correct? a. i b. ii c. iii d. i, ii and iii

6. They have gills at minor stage but they are converted to lung in matured stage

i. catfish ii. frog iii. crocodile

Of the following which is correct? a. i b. ii c. iii d. i, ii and iii

A

Living World 89

Creative Questions (CQ) 1. Figure A Figure B Figure C a. What is the type of the two animals in the figure A and B? b. Describe the main characteristics of this type of animal. c. Explain the similarity and dissimilarity of the above three animals. d. Discuss how the animal in figure B influences our environment and

economy. 2.

Figure –A Figure –B

a. What is plant? b. Explain the function of the portion marked - A c. What are the characteristics for which the animal in fig B is different

from the crocodile ? d. Write the difference between A and B.

Chapter – 7

Cell: Unit of Living Body

Many of you might have seen the construction of a building. You might have also seen that the mason lays bricks one after another while constructing the building. Each single brick is the unit of the building. Like a building the body of a plant or an animal is build with one or more structure, called a cell. It is the functional unit also. So the structural and functional unit of a body is called a cell. May be you are interested to know how and when the cell was discovered. In 1665, an English scientist, Robert Hooke discovered the cell. He observed the thin transverse section of a bottle cork under a microscope. There he saw hundreds of honey comb like small chambers surrounded by walls. He termed each chamber as cell. It is the unit centre of all basic activates of the body. Most of the cells are so small that they can not be seen without the help of a microscope.

Fig 7.1: Robert Hook’s Microscope

Observation of plant and Animal cell Let us observe plant cells (Onion cells) and animal cells (human cheek cells) under a microscope and draw their diagrams showing different parts.

Cell: Unit of Living Body 91

Observation of Onion cells

Take a fleshy scale leaf of Onion. Now separate the outer skin and place it on a glass slide. Add one drop of water or dilute glycerin and cover it with a small thin glass called cover slip. Now place it under a microscope and observe the structure of cells. Remove the cover slip and add a drop of iodine solution, place the cover slip and again observer the cells under the microscope. The light brown structure you observed is the nucleus. Observe the cell walls also. Now draw a diagram of what you have observed and label the structures. Observation of human cheek cells Wash your hands with safe and clear water. Now gently wipe the inside wall of your cheek with a finger. Your will notice some white particles sticking to your finger. Now spread the whitish saliva stick to your finger on the glass slide. You can see these as sticky film on the slide. Now put a drop of methylene blue stain. Put the cover slip and observe under a microscope. You will see some grey coloured granular cells. The thick structure inside is the nucleus. Now draw a diagram of the cells and label the parts you can identify.

92 General Science

Mark the differences between a plant cell and an animal cell

Structure of a cell Plant and animal cells are very small. They cannot be seen with unaided eyes. But it can be observed under a microscope. Now a days with the help of an electron microscope fine structures of the cell can also be observed well. As a result few small organelles were discovered in the cell. Let us discuss the structures and functions of different parts of a cell.

A. Cell wall Only plant cells have cell walls. The animal cells do not have any wall. The wall is made of nonliving materials. It gives shape of the cell. It also regulates movement of fluid between outside and inside of a cell.

Fig 7.4: The Living cell B. Protoplasm Protoplasm is a jelly like semi fluid, translucent living matter surrounded by cell membrane. It is termed as the physical basis of life. Protoplasm contains 70-90 percent water. Without water it stops functioning. Protoplasm has three parts, such as-cell membrane or plasma membrane, cytoplasm and nucleus.

Cell: Unit of Living Body 93

1. Cell membrane or plasma membrane Thin and soft membrane around cytoplasm is called cell membrane or plasma membrane. It is a two layered membrane with occasional inward foldings. It regulates movement of water, minerals and other materials between outside and inside of the cell.

2. Cytoplasm

Portion of a protoplasm surrounded by cell membrane outside the nucleus is called cytoplasm. Its main function is to hold the organelles or small organs and perform few physiological functions.

Discussion on some of the organelles found in cytoplasm Plastid: Plastids are also called chromatophores. Usually they are not found in animal cells. It is a characteristic of a plant cell. Leaves, flowers and fruits of different colours that we see are due to plastids. The colour borne excessively by the plastids is reflected outside and the organ bearing those plastids, show the colour. When the quantity of chlorophyll is high, tha plastied is green. It is called a chloroplast. Plastids bearing colours like yellow, red, blue etc. in excess, is called chromoplast. It is due to the chromoplasts that the china rose red. Oleander is yellow, and Butterfly pea is blue. But when plastids bear no colour, they are termed as leucoplasts.

Shape of plastids may be ring like, round, flat, filamentous, star like, biscuit shaped etc. Each cell may contain one or more plastids. A plastid is covered with two layered membranes. Different colours are embedded within these layers. Green plastids help in manufacturing food. The coloured plastids make plant parts clolurful and attractive. Colourless plastids store foods.

94 General Science

Mitochondria It is called the power house of the cell. Most of the energy producing reactions take place inside it. Its shape may be rod like, globular, star like etc. each mitochondrion is bounded by double membrane: the outer one is smooth while the inner one has many foldings towards the cavity of mitochondrion. Main function of mitochondrion is to help respiration. It is the major site of respiratory activities in the cell. So it helps releasing energy through respiration. It is also called the reservoir of energy.

Vacuole The open space inside a cell is the vacuole. In plant cells the size of vacuoles is bigger while in animal cell the vacuoles are usually absent; when it is present; it is very small in size. The fluid present inside the vacuole is called the cell sap. To bear cell sap is the main function of vacuoles.

Ribosome It is a very small globular structure. Its number is high in every cell. Its main function is to participate in protein synthesis.

Centrosome There is a small structure beside the nucleus called centrosome. It is absent in plant cell. It helps and participates in animal cell division.

3. Nucleus Comparatively dark and spherical body surrounded by cytoplasm is the nucleus. It is the most important structure of the cell. In absence of nucleus normally a cell cannot function. A nucleus has following parts:

Cell: Unit of Living Body 95

a) nuclear membrane

b) nucleoplasm c) chromosome d) nucleolus Nucleus controls all physiologic activities of a cell. It is the life centre of the cell.

Nuclear membrane

Nucleolus

Nucleoplasm

chromosome

Fig 7.5: Nucleus

Difference between plant and animal cell Topics Plant cell Animal Cell 1. Cell wall 2. Vacuole 3. Plastid 4. Centrosome 5. Position of

nucleus

1. Plant cell has cellulos cell wall outside the cell membrane

2. In mature cells large vacuole is present.

3. Usually plant cells

contain plastids. 4. Usually in plant cells

centrosomes are absent. 5. In plant cell vacuole is

large and the nucleus lies near the cell wall.

1. In animal cell, cellulose cell wall is absent; only cell membrane is present.

2. Usually animal cell has no vacuole; if present it is small.

3. Usually animal cells do not contain plastids.

4. Usually in animal cells centrosomes are present.

5. In animal cells the nucleus is centrally placed.

New words of this Chapter

Transverse Cell Cytoplasm Nucleus Plastid Respiration Plasma membrane Cellulose Nucleoplasm Glycerin Chloroplast Centrosome Chromoplast Leucoplast Mitochondria

96 General Science

Exercise

Multiple Choice Questions (MCQ)

1. Who discovered cell? a. Leuyen Hook b. Robert Hook

c. Heksly d. Mendel 2. The more dense material of the cell is

a. nucleus b. mytocondria c. chloroplast d. ribosome

3. The main work of the colourless plastid is a. to prepare food b. to store food c. to prepare colour of the flower d. to prepare colour of the leaves

4. The organelle which is found in animal cell but not in plant cell is - i. plastids ii. centrosome iii. mytochondria

Of the following, which is correct? a. i b. ii c. i and ii d. ii and iii

From the figure below, answer the questions 5 and 6 5. The A-marked portion -

i) gives the size of the cell ii) is made of two-leyer membrane iii) prevents liquid substances from coming out of the cell

A

B

Cell: Unit of Living Body 97

Of the following, which is correct? a. i and ii b. ii and iii c. iii d. i, ii and iii

6 The B-marked portion - i. resides in both animal and plant cells ii. helps in cell division iii. helps in protein synthesis

Of the following, which is correct? a. i and ii b. ii and iii c. i and iii d. i, ii and iii

Creative Questions (CQ) 1. An incomplete picture of an animal cell is given below- a. What organelle of the cell is the above picture ? b. Explain the position of the upper portion in animal and plant cell c. Draw the complete picture of the above incomplete one and mark its

different portions. d. Explain why the upper portion of the cell is called an essential part. 2. a. What is the picture about? b. Explain the characteristics of the A marked portion. c. Explain what would happen if the C marked portion would not be in the cell. d. The B marked portion shown in the picture bears a special

characteristics of the above cell. Discuss.

C

A

B

Chapter – 8

Plant Kingdom The world of Biology includes plant and animal kingdoms. According to the botanists at present there are about four and a half lakh plants in the world. You know that some plants produce flower while others do not. Some plants are very big and some are small. Few others are so small that they are not visible without a microscope. Mango, Black berry, Jack fruit etc. have root, stem, branches leaves, flowers and fruits. There are plants that have no root, stem and leaves. These plants do not bear flowers and fruits. We take Rice, “Wheat, Pulses, Brinjal, Cabbage etc. as our food. We get fibre from Jute, Cotton etc. Clothes are made from these fibres. We make furniture and houses by using these timbers. Arjun, Sacred basil (Tulshi), Akanda, Thankuni, Asparagus, Malabar nut (Bashak). Create (Kalomegh) are medicinal plants. We get life saving drugs also from some of the plants. If we want to use the plants for the benefit of the humanity we must get perfect knowledge about plants. To know about all types of plants we are to follow a process. Depending upon size and shape, longevity, capacity of bearing flowers and fruits, nature of stem and food habit, morphological similarity and dissimilarity etc. scientists have divided the plants into different groups. The process is known as classification. Necessity of plant classification

Plant kingdom is very vast and full of variety and diversity. Every individual plant is different from the other. It is not possible to know every

Plant Kingdom 99

thing of every plant individually. Some plants are used as medicine, while some are used as manure for the crop field. There are plants which are helpful for fish culture. It is easier for some plants to produce improved variety. Few plants can grow in dry condition while others require saline water. Few plants grow faster than the others. There are plants which are suitable for plantation in the forests. To get all these information accurately and easily, with less effort in a short span of time, it is necessary to classify all the plants known. Classification of plants Scientist proposed a name for every plant known and divided them into different groups. Now let us discuss the classification of plants based on flowering ability. Classification based on flowering ability You have learnt that few plants bear flowers and fruits while others bear no flower or fruit. Based on flowering ability, plant scientists divided plant kingdom into two groups:1) Cryptogams (nonflowering plants) and 2) Phanerogams (flowering plants).

100 General Science

1. Cryptogams or Non flowering plants Plants who never bear flowers are grouped in one subkingdom, Cryptogams. These plants reproduce by forming spores. This group is again divided into four subgroups: such as a) Protophyta, b) Thallophyta, c) Bryophyta and d) Pteridophyta. a) Protophyta Plants of this group are microscopic. Some of them are so small that one needs an electron microscope to see them. They are usually non- green heterophytes. Body is simple and composed of primitive type of cells. Virus, bacteria etc are included in this group. They are responsible for causing most of the diseases. b) Thallophyte It is a group of plants whose body is not divisible into root, stem and leaf. It is of two types; such as - Algae and Fungi.

1) Algae: Thallophyte having chlorophyll in their body are known as algae. They are unicellular or multicellular. They grow in rivers, ditches, drains, damp or wet soil, stagnant water etc. Algae need sun light to survive. Spirogyra and Chlorella are examples of two green algae.

Plant Kingdom 101

2) Fungi: Thallophytes without chlorophyll are called fungi. They cannot manufacture their own food. They grow on rotten things and in damp places. Bread when left for few days, often show some white cottony growth. It is a kind of fungus known as mould or Mucor. Penicillin, a life saving drug is prepared from a fungus, calls Penicillium. c) Bryophyta: Bryophytes have stems and leaves but no roots. They can manufacture their own food. They grow on damp soil and brick walls. Riccia, Marchantia, Moss are few examples of Bryophytic plants.

d) Pteridophyta: Pteridophyta are the most advanced type of Cryptogamic (non flowering), plants. Its distribution is world wide. They grow profusely near houses on damp or wet soil or walls of old buildings. It is popularly known as fern plants. Dryopteris and Pteris are most common ferns found in every where. It can manufacture its own food because it contains chlorophylls. Ferns are planted in earthen pots as ornamental plants. Dryopteris is taken as vegetables.

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2. Phanerogams or flowering plants Plants bearing flowers and fruits are grouped as phanerogams or flowering plants. Usually they reproduce by producing seeds. Mango, Litchi, Jackfruits etc are examples of Phanerogamic plants. All flowering plants are divided into two groups: a) Gymnosperms and b) Angiosperms. a) Gymnosperms There are plants where ovary is absent. Here fruits are not formed, so seeds remain open. These plants are Gymnospermic plants such as Pinus, Cycas etc b) Angiosperms These plants have ovary. A mature ovary forms a fruit. Seeds are borne within the fruit. So seeds are covered. Plant with seeds borne inside fruit are called angiosperm plants; such as Litchi, Mango,

Guava etc. Angiospermic plants are divided on the basis of cotyledon in

their seeds into two groups; such as 1) Monocotyledons and 2) Dicotyledons

1) Monocotyledons:

These plants bear one cotyledon in the seeds; such as Rice, Wheat, Sugarcane, Maize, Coconut etc. Usually stems of these plants are hollow at inter nodal regions. Venation is parallel. Stigma is feather like and

Plant Kingdom 103

stems mostly unbranched. Food, sugar, perfume and antiseptic medicines are produced from monocotyledonous plants. 2) Dicotyledons: Plants having two cotyledons in their seeds are called Dicotyledo-nous plants. Stems are branched, venation of leaves is reticulate or net like. Mango, jackfruit, mustard, gram, jute, pea nut, sesame are few examples of Dicotyledonous plants. Cabbage, cauliflower, turnip, radish etc. are good vegetables. All pulses are Dicotyledonous plants.

Classification of plants in tabular from Plant kingdom

Cryptogams (Non flowering)

Phanerogams(Flowering)

Protophyta (Acellular or

primitive cells.)

Thallophyta(Body not

differentiated into root and leaf)

Bryophyta (Body differ

entiated into stem and leaf but

not root)

Pteridophyta (Body divided

in stem, root and

leaf)

Gymnosperms

(Fruits not formed and seeds not covered in fruits.)

Angiosperms (Fruits formed and seeds

covered in fruits)

Monocotyledons

(Only one cotyledon in the seed)

Dicotyledons (Two cotyledons

in the seed)

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Classification of plants based on stem nature

Stems and branches of mango, jackfruit etc. are hard. Why it is so? Because they contain wood inside. What about Basella (puin), bottle gourd or gourd? Are the stems of these plants strong? Why not? Yes, they do not contain wood inside. Mango and jackfruit plants have distinet main stem. It is erect, thick and woody. It bears the weight of branches, leaves, flowers and fruits. Do plants like rose, lemon and gardenia have distinct main stems? Based on these variations in stem nature scientists classified plants into three categories; such as 1) Herbs 2) shrubs and 3) Trees. 1. Herbs: These plants are small with soft stems. Examples are gram, mustard, radish etc. 2. Shrubs: These are medium sized plants. The production of branches starts from near soil level. So the main stem cannot be identified. Stem and branches are woody and hard. Rose, Lemon, Gardenia etc. are examples of shrubs. 3. Trees: These are medium to large plants. Their main stem is very much distinct. It is called stump. The main stem bears branches and leaves Examples are Mango, Jackfruit, Teak, mahogany etc.

Plant Kingdom 105

Observe few plants around you. Now write down their names and note nature of their stems. Try to separate three categories of plants into herbs, Shrubs and trees.

Classification of plants based on longevity You might have observed that few plants grow rapidly, produce seeds and die within a short period of time. While other plants live for a very long time. Based on longevity scientist divided plants with soft stem into three groups; like-(1) Annual, (2) Biennial and (3) Perennial. 1) Annual Plants: Plants which live for one year or one season are called annual plants; such as gram, pea, mustard, etc. 2) Biennial Plants: These plants live for two years. In cold countries radish, cauliflower etc. are biennial plants. 3) Perennial Plants: These plants live for more than two years. Zinger, turmeric, doob grass etc. are some perennial plants. It may be mentioned here that all shrubs and trees are perennial in nature.

Classification of plants based on mode of nutrition We know that most plants are autophytes. It means that they can manufacture their own food. But there are plants who cannot manufacture their own food. They are heterophytes. Plants are classified on the basis of mode of nutrition into two groups- (1) Autophytes and (2) Heterophytes 1. Autophytes: Usually these are green plants. These plants contain chlorophylls. So they can manufacture their own food. They

Fig 8.13: An autophytic

unicellular algae

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Prepare carbohydrate food with water taken from soil and carbon dioxide from

environment, in presence of light with the help of chloroplasts. This food is

carbohydrate or sugar. A portion of this is used by the plants for their own

purpose. Rest portion is left for man, other animals and heterophytic plants.

2. Heterophytes: Non green plants cannot manufacture their own food. So

they are dependent on other plants for food. They are called heterophytes.

These plants are of two types; such as (a) Parasites and (b) Saprophytes.

a) Parasites: These plants are not green and

cannot prepare their own food. The plants

live on or inside other organisms. They

collect food from the host organism by

various mechanisms. They sometimes

develop special sucking roots. Example

Dodder. They sometimes cause diseases of

the host plant or animal. Black band disease

of jute, late blight of potato and blast disease

of rice are caused by parasitic fungi.

b) Saprophytes: These are plants that collect food from dead remains of

plants and animals. These are saprophyhtes. Have you seen white powdery

things on rotten bread? These white dot like things soon turn black. It is a type

of fungus. Mucor is a saprophytic plant.

Saprophytes decompose dead remain of plant and animal and mix it up with

soil as organic matter. This process is of great help to us. They act as natural

scavengers.

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Some Saprophytes There are many saprophytes around us. But we do not recognize them as plants. Yeast, mushroom, Penicillium etc. are examples of saprophytes.

1. Yeast Some of you must have heard about yeasts which are used in bakery. It is a fungus (Plural-fungi) and saprophyte. They release carbon dioxide during respiration. This carbon dioxide is used in bread for raising of it. This plants can ferment alcohol from sugar. It is very rich in vitamin ΄B΄. So they are valued as good food. Yeasts are used in making bread and biscuits, wine and medicines.

Yeast is a group of unicellular plants. Its cells may be arranged in a line. Thus it forms a filament or band like structure. Each cell produce buds. These buds when get separated, new yeast plant is produced. It is a process of reproduction. Yeast cells may divide by direct cell division. Each cell become separate yeast plant. It is also a process of reproduction. 1. Mushroom ΄Frog΄s umbrella΄ is an incidental remark. Frogs do not use umbrella. When talk about ΄frog΄s umbrella΄you may think about some white and soft umbrella like things. In English they are called mushrooms. In rainy season, they grow on the soil with decomposed leaves, straw and other organic matter.

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Now mushroom is cultivated for human consumption. Some people eat mushroom by choice. You must not take naturally growing mushrooms from bushes or fields. Few mushrooms are very poisonous. Mushrooms are fungal plants. Small umbrella like fleshy part is the fruit body of the fungus. Small powdery spores are produced inside the fruit body. The body of this fungus is like a fine thread. This thread like body remains beneath the growing soil. The fruit body comes out above the ground and is visible without microscope. We can see only this fruit body in the field. We call it mushroom. 3. Penicillium Many of you have taken penicillin as medicine. Penicillin tablets are taken by many to cure common cough and cold, throat pain etc. It is the first discovered antibiotic medicine. Alexander Fleming discovered this life saving drug from Penicillium fungus. With its help blue cheese is prepared. Penicillium is a saprophytic fungus. Its spores float in the air. They are also found in soil. They grow on citrus fruits, vegetables and other foods. When a piece of lemon is kept is a dark place, blue spots are visible in few days. These are Penicillium fungi. It is a beneficial fungus. It is also the cause of human disease.

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Disease of economic plants

We have learnt that parasitic plants cause diseases. Now let us know about such

specific diseases.

a) Black band diseases of Jute

The disease is identified as black band

around the stem at ground level. The band

start as black patch and finally develop as

band. When touched the hands become

dirty black. At the final stage the stem

breaks at this point. The plant falls on the

ground.

This disease is caused by a parasitic

fungus. The spores of this fungus look deep brown under a microscope. It is an

elliptical two celled structure. At the prevalence of the disease, fungicides are

to be spread over. Fungicides are chemicals that kill fungi. As a preventive

measure disease free seed should be used. The infected plant remains should be

burnt in the field. It helps avoiding fresh attack of the disease.

b) Blast disease of rice

Walking by the rice field you might have seen brown or yellow scar on leaves. These scars are broad at the middle and tapering at two ends.

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Gradually scar become whitish at the middle point. When spikelet is affected at its base, it breaks down. The disease is caused by one type of parasitic fungus. Spraying of Brodeux mixture controls the disease. Control of weeds and burning of debris are effective preventive measures. C) Red rot of sugar cane

While chewing sugar cane you might have seen long red scar inside. These type of scar may be the cause of a fungal attack. The stems and leaves are affected. When a diseased stem is divided lengthwise, a red scar is visible at the middle along the length. Shrinkage appears at nodal region. The apex and sides of leaves become dry. This disease is caused by a parasitic fungus. The micro seeds or the conidia are curved and transparent. You know planting of top end portion with few leaves produce new plant. If this cutting is washed with fungicides before plantation, the attack of this disease can be minimized. Burning of debris of previous year and using disease resistant stock saves the crop from disease. D) Late blight of potato It is a very deadly disease of potato. Once it caused famine in Ireland. Black patches appear on stem and

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leaves on diseased plants. Gradually all leaves and branches are affected. The

plants soon droop down. On large scale attack of the disease, the field spread

bad smell all around. Potato tubers show brown scars. A kind of parasitic

fungus is responsible for the disease.

Use of healthy seeds (tubers) and early variety are good preventive measures.

Use of appropriate fungicide minimizes the attack of the disease.

New words of this chapter

Virus, Bacteria, Fungi, Gymnosperm, Angiosperms,

Monocot Dicot, Autophytes, Heterophytes, Parasite,

Saprophyte, Thallophyte, Bryophyte, Pteridophyte, Herb,

Shrub, Penicillium Chlorophyll, Algae.

Exercise

Multiple Choice Questions (MCQ) 1. In how may classes the cryptogamia is divided? a. one b. two c. three d. four 2. Which of the following is not (available) in bryophyte? a. stem b. root c. leave d. vein 3. Perinnial (plant) is – a. ginger b. carrot c. pea d. mustard

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4. Applicable in case of dying plant- a. penicillium b. black band of jute c. blue cheese Of the following, which is correct? a. i and ii b. i and iii c. i and iii d. None of the above From the picture below, answer the questions 5 and 6.

figure

5. What kind of plant is shown in the picture? i. dying ii. heterotrophic iii. autotrophs Of the following, which is correct? a. i and ii b. ii and iii c. i and iii d. i, ii and iii 6. Applicable in case of plant shown in the picture- i. There is vitamin in their body ii. Blue cheese is made with its help iii. is used in bread making industry Of the following which is correct? a. i and ii b. i and iii c. ii and iii d. i, ii and iii

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Creative Questions (CQ) 1.

figure 1 figure 2 a. What is the type of the plant shown in the picture? b. Write down two characteristics of this sort of plant c. Explain the necessity of cultivation of the plant (as shown) in the picture. d. The plant in picture-2 is useful as well as harmful. Put arguments. 2.

Figure 1 Figure 2 Of which order is the plant in Figure 1? a. Why is their stem soft? b. Which of the above plants is called annual, herb and dicot? Explain. c. Discuss the comparative studies regarding two characteristics of the plants

above.

Chapter-9

Morphology of Plants

Flowering Plant We find innumerable plants around us. One finds variations in there size and structure. Some plants do not bear flowers or fruits; such as algae, mushroom, moss, fern etc. Some other plants bear flowers and fruits; such as Paddy, wheat, Mango, Mustard etc. We have already learned a bit about nonflowering and flowering plants. Now we shall learn about different parts of a typical flowering plant. Parts of a typical flowering plant A typical flowering plant has root, stem, leaves, flowers and fruits. Let us take a chili plant as a representative of a flowering plant. Now let us describe its different parts. This plant is divided into two parts; the root and the shoot. The root Part of the plant that grows under the soil level is called the root. The part of root system which is attached to the stem and comparatively thick and strong, is called the main root. The main root gives rise to branch roots. These branch roots in turn produce branchlets. It is called tertiary roots. Each root bears at its tip a cap like structure, called root cap.

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The Shoot The portion of the plant that remains above the ground level is called the shoot. The shoot includes stem, branches, branchlets, leaves, flowers and fruits. In chilli plant a single flower grows at leaf axil. The flower has calyx, corolla, androecium and gynoecium.

Root

The part of a plant that have no apical bud, nodes and inter nodes; is called root. Normally root is formed from the first root called the radicle. It does not bear leaves, flowers and fruits. Normal roots grow down- wards. Of course it is not true that at all times the underground parts are the roots. Prop roots of Banyan and aerial roots of Orchid remain above the ground level. While stems of Zinger, Turmeric, Onion etc grow under the soil level. The radical grows as main root. It is the primary root. Branches of main root is called branch roots or secondary roots. Branches from secondary roots are the tertiary roots. The main roots is also known as tap root. A root can be divided into few regions. At root tip there is a cap like structure, known as root cap. This is the root cap region. Root cap protects the smooth apical region from any probable injury caused by friction with hard soil particles.

Behind this, there lies a soft region, called growth region. In this area cell division and cell elongation occurs. The region behind this is the root hair region. Very fine hairy growth appears around the root. Above this region is the permanent region. From the permanent region the branch roots are developed.

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Classification of roots Different plants have different types of roots. On the basis of origin and position: roots are classified into two major types; such as 1) Tap root and 2) Adventitious root. 1. Tap root: This root originates from the radicle of the embryo. It goes down inside the soil. It gives rise to branches. It is also called main root. In Mango, Basella, Spinach, Neem, Gram etc. we find this type of roots. 2. Adventitious root: Roots developed from stem, branches, leaves or any part other than the radical, are called adventitious roots. It is of two kinds; such as (a) Fibrous roots and (b) non fibrous roots. a) Fibrous roots: When the radical is lost and a group of fibre like roots grow from the same place, it is called fibrous root; such as Paddy. It is the characteristics of monocotyledonous plants. b) Non Fibrous roots: When adventitious roots grow separately from one another; it is called non fibrous roots. Example-stilt roots of Screw pine, roots of Bryophyllum.

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Different kinds of root systems

Main root and its branch together make a root system. It is of two kinds, such as 1) Tap root system and 2) Adventitious root system.

1) Taproot system or Main root system

In dicotyledonous plants, the main root along with its branch roots and tertiary roots make the Taproot system. Example-Mango, Jackfruit, Mary gold, Rose etc. 2) Adventitious root system In monocotyledonous plants, the fibrous roots make the adventitious root system.

Modified roots When roots are modified, are called modified roots. Both tap root and adventitious roots are modified. The roots are modified to perform the function of storage of food, giving mechanical support and physiological functions. Now let us discuss about modification of roots for food storage.

We all have seen Radish, Turnip and Carrot. We also have taken them as vegetables. Do you find any node, inter node, leaf or bud in them? No, there is nothing of the sort. The crown of leaves you see arise from a very small and compressed stem. A normal root does not have any node inter-node, leaf or bud. These structures are very fleshy and juicy. Why it is so? These roots store food. So they are fleshy and juicy. The main root (tap root) swells up due to storage of food and can not be identified as roots.

Based on shape, modified tap roots are of four types: such as 1. Fusiform. 2. Conical, 3. Napiform and 4. Tuberculer.

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1. Fusiform: By storing of food, when the tap root becomes swollen at the middle and tapering at both ends and take the shape of a Radish, it is called fusiform root. Example-Radish.

2. Conical: When the tap root sotre food and is much swollen at the upper end and gradually tapering towards the lower end like a carrot, it is called conical root. Example- Carrot.

3. Napiform: Due to storage of food when the tap root become very much swollen at its upper end and abruptly become tapering towards the lower end, like a turnip it is called napiform tap root. Example-Turnip.

4. Tubercular: When a tap root store foods and swells up irregularly and does not have any definite shape: it is called Tubercular root. Example-Sweet potato, Four o΄clock plant (Sandhya malati) etc. Functions of a root:

Roots usually perform two types of work, such as-

a) Normal functions

i) Fixing the plant to the soil

ii) Absorbing water and mineral salts

iii) Transportation of water and mineral salts absorbed by the root to the stem.

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b) Special function:

i) Bear weight of branch and branch lets. Example-Prop roots of Banyan (Bot).

ii) Keep a plant erect. Example-stilt root of Screw pine (Keya). iii) Help climbing of a climber. Example-climbing root of Betel leaf

(Pan) iv) Store food for the plant. Example-Fusiform root of Radish. v) Help plant to float. Example-Floating root of jussiaea (Keshor dam) vi) Help plants in reproduction. Example-Tubercular root of sweet

potato. vii) Help plants in respiration. Example-breathing roots of Sundary. Stem

The part of a plant, that bears branches, leaves, flowers and fruits is called stem. Normally a stem remains above the soil. But there are stems that grows beneath the soil surface, such as Zinger, Garlic etc. Different parts of a stem

Examine a plant taken from any place near you. You will see that is has node, inter-node, leaves, axillary and apical bud on the stem. 1. Node: From where leaves grow is called node. In mature stems nodes

are located at almost equal distance. It is the node from where leaves,

axilary buds, branches flowers and fruits grow.

2. Inter node: The portion in between two nodes is called an inter-node.

It helps the plant to stand erect. It also helps plant growing.

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3. Bud: Buds grow at the apex of a branch or at the axil of a leaf. The angle between the stem and a leaf is called an axil. It is found growing on stem, branches and branchlets. Based on location they are of two kinds, such as-a) Apical bud, that grows at the apical position of a branch or stem, and b) Axilary bud, that grows at the axil of a leaf.

Structure of stem: Various kinds of stems are found in plants around us. Some are strong while others are weak. Stems of Jackfruit, Litchi are example of strong stems. Bottle gourd, Cucumber, Gourd are plants with soft and weak stems. Among these stems some are round or quadrangular, while flat and triangular stems are also found. In Sacred basil (Tulshi), Bottle gourd (Lau), Cucumber (Shosha) stems are found. Opuntia (Phonimonsha), Shama etc. have flat stems. Stem of Eucalyptus is round and smooth. All trees have round stem. On the basis of stem nature, it is classified into two groups, a) Erect (strong) stems and b) Weak stems.

1. Erect (strong) stems: Erect stems are on four types. Such as- a) Caudex: The stem is erect, strong and has a crown of leaves at the top. Example-Coconut, Pamyra palm, Betel nut. b) Culm: Erect, unbranched stems with hollow inter nodes are called culm. Example-Bamboo, Sugarcane etc.

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c) Excurrent: When the stem produces branches in such a way that it becomes a cone like structure and looks like a temple (mot). Example-Mast tree (Debdaru). d) Deliquescent: These stems are simple and short. It give rise to lateral branches. Growth of apical bud is weak. It gives a look like a dome. Example-Mango, Jackfruit etc.

2. Weak stem: When stems are soft and

weak and can not grow erect, are called weak stems. They are of three types; such as-

a) Creeping stem or creepers: Stems which grow horizontally on the soil surface and produce roots from each nodal zone, such as-Doob grass (Durba). b) Trailing stem or trailers: The stems that spread on the soil parallel to soil surface but do not produce roots, such as-Basella (Puin), Pig weed (Punarnava) etc.

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c) Climbing stem or Climbers: Weak stems that grow upward with the help of any support is called climbers: such as-Betel leaf (Pan), Cucumber (Shosha) etc.

Functions of stems: 1. It bears branches, leaves, flowers and fruits. 2. It keeps the branches and leaves in proper position for getting

maximum sunlight. 3. It transports water and mineral salts to branches and leaves, flowers

and fruits. 4. Foods prepared in leaves are carried by the stem to different parts of

the plant. 5. Stems, when young and green, manufacture food. 6. Some stems store foods. 7. Stems gives mechanical support to the plant. 8. Stem helps in storage of food, self defense, help surviving in

unfavourable season and conditions and vegetative reproduction.

Leaf Lateral flattened green outgrowth of stem and branches at nodal region is called a leaf. Older leaves remain at the base of stem while the younger ones grow at the upper level. In algae and fungi there is no leaf at all. In moss plants leaf like flat structures are found. These are not actual leaves. Leaves of flowering plants are the true leaves.

Different parts of a leaf: The leaf, which bears leaf base, petiole and leaf blade or lamina is called a typical leaf. Example-Leaves of china rose, mango plants etc.

If we observe a leaf of Mango or China rose, we will see parts 1) Leaf base, 2) Petiole and 3) Leaf blade or lamina.

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1) Leaf base: The part of leaf which is attached to the stem, is called leaf base. In Mango, Krishna chura, Gold mohor etc. the leaf base is swollen. Swollen leaf base is called pulvinus. In Coconut, Betel nut and Pamyra palm the leaf base is flat and surrounds the stem. It is called a sheathing leaf base. In some plants flat leaf like small growth arise from the leaf base. It is called stipule. Example-pea. 2) Petiole: Petiole connects leaf blade or lamina with leaf base. It is the stalk of the leaf; such as Mango, Jack Fruit, Betel leaf etc. When petiole is absent the leaf is called sessile leaf; such as Ulat chandal, Rangan etc. 3) Leaf blade or lamina: Thin and flat part of leaf is the leaf blade or lamina. It is broad at the base and tapering at the apex. This tapered cone like part of lamina is called the leaf apex. Marginal line of lamina is called leaf margin. At the middle of the blade a rib like structure runs from the petiole to the apex It is called the mid rib or main vein. Midrib of religious tree (Aswatha) is very prominent. Branches from main vein or mid rib are the veins. Branches from the veins are called veinlets. Shape of leaf blade may be of various types. Base on the shape of leaf blade, leaves are classified into some types. Let us discuss some common types. When the lamina is long and thin like a needle it is called acicular; such as Casuarina. In paddy and Wheat, leaves are linear. In Bamboo, Mango etc. the leaves are like a lens (ballam). So they are called lenceolate leaf. Bettle leaf,

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Religious tree etc. bear leaves like heart. So they are cordate. Arum leaves are arrow shaped. So they are called sagittate. Likewise we get ovate in China rose, rotund in Lotus. Cucurbita leaf is irregularly lobed like duck΄s foot. Kinds of leaves We see various types of leaves in plants. Few of them with only one lamina, while others may have more than one lamina which are smaller in size. This small lamina is actually the part of the main lamina. It is called leaflet. Based on lamina or presence of leaflet; leaves are classified into (1) Simple leaves and (2) Compound leaves.

(1) Simple leaf: Leaf that contains only one leaflet is called a simple leaf. Example: Black berry, Mango, Jackfruit, Banyan, etc. the margin of a simple leaf is entire or may be incompletely incised. It is also divided into two types; (a) Leaf with entire lamina and (b) leaf with lobed lamina. (a) Leaves with entire lamina: When the lamina is not lobed the margin is entire. Litchi, Mango, Banyan, Jackfruit etc.

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(b) Leaves with lobed lamina: In some leaves the margins are lobed. The incision of the lamina is such that is does not reach the mid rib. Example;Mustard, Papaya, Arun etc. (2) Compound leaf: A leaf composed of more than one leaflet is called compound leaf. Rose, Wood apple and Tamarind leaves are compound leaves. Each small leaf blade of a compound leaf is called a leaflet. The branch like structure bearing the leaflets is called the rachis or axis. It is of two kinds such as (a) Pinnate compound and (b) Palmate compound. (a) Pinnate compound: When a compound leaf bears leaflets on its two sides it is called a pinnate compound leaf. It is of four types. 1. Unipinnate compound: When the rachis is unbranched and leaflets are directly attached to the rachis, it is called unipinnate compound leaf. It is again grouped into two types. (i) Paripinnate and (ii) Imparipinnate. (i) Paripinnate: In this type leaflets are in pairs and there is no apical leaflet. Example: Shonalu, Goldmohor etc. (ii) Imparipinnate: Here the leaflets are present in even number and the single leaflet is borne at the apex of the rachis. Example: Rose, Clitoria etc. 2. Bipinnate compound: In this case the rachis is branched. Leaflets are arranged on this branches. Example: Sensitive plant (Lajjabati). 3. Tri Pinnate compound: When the branches of rachis again produce branches and leaflets are arranged on the branchlets, it is called tri pinnate. Example: Nim, Moringa (sajina) etc. 4. Decompound: Here the incision of leaf blade is of higher order than that is found in tripinnate. Example: Carrot, Coriandrum (Dhoney) etc.

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(b) Palmate compound leaf: When compound leaf bears leaflets in a point and looks like a palm, it is called palmate compound leaf. Based on number of leaflets palmate compound leaves are grouped into following types.

1. Bifoliate palmate: Bignonia 2. Trifoliate palmate: Oxalis (amruli), Woodapple etc. 3. Quadrifoliate palmate: Marsilea (Shushni). 4. Multifoliate: Silk cotton (Shimul).

Multifoliate

Morphology of Plants 127

Differences between simple leaf and compound leaf Simple leaf Compound leaf

1. It bears a single lamina 2. Its lamina may be lobed but the

incision is not complete and the pieces are not completely separated

3. It has midrib or main vein 4. It may bear stipules at the leaf

base. 5. It bears axilary bud.

1. It bears a number of leaflets. 2. Here the leaflets are completely

separated from one another. 3. It has rachis or axis in place of midrib. 4. It may have stipules at the base of leaflets. Of course stipules may be present at the base of compound leaves 5. It does not bear any axillary bud.

Functions of leaf: 1. Green leaves manufacture food for the plant. 2. During photosynthesis leaf takes carbon dioxide and oxygen is

released. During respiration oxygen is taken in and carbon dioxide is released. So gaseous exchange is another important function of leaf. This exchange of gases occur through small pores, called stomata.

3. Plants release excess water in the environment in the form of vapour during transpiration.

4. Leaves store food and water. Example: Basella (Puin), Bryophyllum (Pathar kuchi) etc.

5. When leaves modified into tendril it helps plant in climbing. Example-Garden pea.

6. It takes part in vegetative reproductions. Example: Bryophyllum (Pathar kuchi.)

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Importance of roots, stems and leaves in human life:

For different purposes man use roots, stems and leaves in our everyday life. For food, clothes and shelter we are dependent on plants. We take fish, meat, egg and milk as our favourite food. Indirectly these animal products are also the contribution of plants. Because poultry, cattle & fishes feed on plants. It means animal world is mostly dependent on plants for food. Specific contributions of roots, stems and leaves are described below: a) Importance or utility of roots: We use root everyday for different purposes. Some roots are used as food, such as Sweet potato, Radish, Carrot, Turnip etc. Roots of Indian pennywort (Thankuni), Asparagus, and Silk cotton are used as medicine. Roots of Bamboo, Banyan, Silk cotton, Tamarind, Mango, Jackfruit etc are used as fuel. b) Importance or utility of stems: We get food, medicine, fibre, timber, spices and fire wood from stems of various plants. From Sugarcane stems we get sugar, fire wood and raw material for paper pulp. Drugs are extracted from stems of Arjun, Cinchona, and Camphor. We get timber from plants liked Teak, Sal, Mahogani, Mango, Jackfruit, Gamari, Chaplash etc. Paper is made from Jute, Bamboo, Gewa, Goran and Sugarcane stems, Jute and Silk cotton stems are used in making chip boards and match boxes. Fibre, gum and fire woods are collected from stems of some other plants. c) Improtance or utility of leaves: We get various daily necessities from leaves. From Amaranth (Danta), Dryopteris (Dhenki shak), Spinach, Basella, Cabbage, Lettuce, Coriander etc. we get vegetables. Medicines are extracted from the leaves of Sacred basile, Bashak, Thankuni, Bellandonna etc. We use tea leaves for making tea.

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Exercise Multiple Choice Questions (MCQ) 1. Which is a sessile leaf?

a. shial Kata b. mango c. lotus d. pumpkin

2. The shape of trunk of jhao tree is a. branchless b. runner c. temple shaped d. tomb shaped

3. What is the root called that originates from the basic root? a. Adventitious root b. main root c. fibrous root d. shandhamalati

4. Which root is of elongated shape? a. radish b. turnip c. Shandhamalati d. beet

5. In case of stem- i. medicine is available from cinconna and arjun ii. valuable wood is obtained from gewa and garam iii. partex and match are made from black berry and jackfruit Of the following, which is correct? a. i b. i and ii c. ii and iii d. i, ii and iii

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From the picture below, answer the questions 6 and 7.

6. The leaf (as shown) in the pictures is- a. simple leaf with incised margin b. simple leaf with entire margin c. simple palmate leaf d. pinnate compound leaf 7. Applicable in case of the picture- i. leaves are decorated at the top of the rachis. ii. there is a leaf at the top of the rachis iii. leaves are decorated at both sides of rachis

Of the following which is correct? a. i b. ii c. iii d. i, ii and iii Creative Questions (CQ) 1.

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a. What is the name of the portion B in the figure? b. Write two differences between C and D c. Explain what would happen to the plant if portion-B is injured. d. Discuss the necessity of the portion A for the growth of the seedling. 2.

a. What is called root? b. Explain the characteristics of the root A in the picture. c. Explain what would happen if portion-C from figure B is cut off. d. Discuss what plant shown in picture A and B can absorb more water from the soil.

Chapter - 10 Force, Pressure and Motion

What is force?

What do you do to open a door? You push or pull. A cart man pushes a cart from the back or pulls it from the front to move it on. Again in order to stop the cart, he pulls it from the back or pushes it backward from the front. This push or pull is called force.

Fig 10.1: Push or pull is the force

You can bend, twist or stretch the piece of rubber you use for erasing pencil marks. This will change the shape of the rubber. Also the volume will decrease on pressing it a little hard. This bending, twisting, pressing or thrusting is also kinds of push or pull − that is force.

Force, Pressure and Motion 133

The beginning of the football game, the football is kept at middle of the field. It remains then motionless until any player displaces that. Again suppose, a player changes the course of a football passing over his head towards the goal, by heading. Both the speed and direction of the football are changed. Goalkeeper catches the football. The football is stopped. Force has been applied to hit, head and catch (stop) the football.

Force can neither be seen with eyes, nor can be touched or felt. But the change of a body can be seen when the force is applied on it. Hence to understand what is force, you have to observe and understand the changes a body undergoes on application of force. You have seen that a football at rest, can be put into motion, direction of that motion can be changed, the motion can be speeded up or slowed down and the football can be stopped, by the application of force. Again suppose, you push a pushcart loaded with bricks, but do not succeed. So it is not that a body at rest, always moves, on application of force, but it tends to move. If one of your friends join you and you push together the cart may start moving. So it can be said in short, that which acting on a body changes or tends to change its state of rest or of motion is called force.

Force may be of many kinds such as, frictional force, gravitational force, magnetic force, static electrical force etc.

Working with a husking pedal, grinding spices, picking up of load, throwing stones, rowing boats, walking and moving etc. are all examples of application of force in our daily life. Beginning from motorcar, railway train, aeroplane to push cart, rickshaw, and bicycle etc. all moves with the help of this force.

Till now we have learnt that force⎯ (a) can put a body at rest into motion and can bring a moving body at rest;

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(b) can speed up or slow down the motion of a moving body ; (c) can change the direction of motion of a moving body ; (d) can change the shape or volume of a body. Measurement of force: Unit of force You know that force cannot be seen but its effect can be seen. For that force cannot be measured directly and it is measured by measuring the effect caused by it. What does happen when a rubber tape or a spring is pulled? It becomes longer. The greater is the pull the longer it becomes. In other words the greater is the force applied, the more is the increase in length of the rubber tape or spring. This amount of increase in length can be seen and measured. Thus an easy way of measurement of force is to measure amount of increase in length of a spring on application of force.

For measurement of any thing we need to know its unit. Thus a standard force or unit of force needs to be known, in comparison to which other forces can be measured. In the System International unit of force is Newton.

Now how much force is equal to one Newton? To have an idea of this, keep in mind that a mass of one kilogram weighs about 10 Newton.

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Hence. 1 Newton is equal to the weight of mass of about 100 gram.

Units of weight and force are the same. Because weight of a body is the force of attraction or the pull of the earth on it. Thus weight is force.

Force can be measured with the help of a spring balance. In this machine there is a graduated scale fixed with a spring. Graduation in the scale is such that a single change in graduation is equivalent to one Newton of force. There is a pointer or an indicator attached to the spring. The pointer comes down when the spring increases in length on application of force. The reading of the pointer directly gives the measurement of force in Newton.

What is Pressure? We use the word pressure in various meanings. Such as, the pressure of study, mental pressure, social pressure, political pressure etc. But in the language of science the word pressure has a special meaning, which is different from the ordinary meaning. When force is applied on a body, then many things depend on how much area this force is applied on. The same force applied on a small area and on a larger area makes a lot of difference. You take a board pin or a flat-headed nail. Put the sharp end of the pin vertically on your exercise book and press it with your thumb. You will see that the pin has pierced through the pages of the exercise book. Turn the nail or the pin up sided own and place the flat end on the exercise book. Now try to press the pin with your finger. You can't press it hard, as it will pierce through your finger. What is the reason for it? The reason for it is that the area of

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the sharp end of the pin is very small. It is almost a dot. While the other end is flat and its area is many times larger than the sharp end. When force is applied on the flat head, it gets concentrated on a small dot like area of the sharp end. As a result, its influence increases. On the other hand when the force is applied on the sharp end it gets spread over a larger area. As a result its influence decreases. That is to say the pressure decreases. So, influence of force depends on the extent of area on which it is applied. Pressure is obtained by dividing force by the area.

Therefore, Pressure = ForceArea

In other word, force exerted on a unit area is called pressure. The same force can exert a high pressure, as well as low pressure. When force is concentrated on a small area, the pressure increases. Again, when the force is spread over a bigger area, the pressure decreases. Such as the pressure obtained by application of 10 Newton of force on an area of 1 square cm. is ten times greater than the pressure obtained by application of the same force on an area of 10 square cm. Unit of force is Newton and unit of area is square metre. So, unit of pressure is Newton/square metre. This unit has been named as Pascal. Therefore, 1 Pascal = 1 Newton per sq. metre.

You can now surely understand why, the point of a pin or a nail is made so sharp. The sharper the knives, scissors, axes, fish knives are easier to work with them. That is to say, more work can be done with the application of less force. Here pressure has been increased by decreasing area. Again, you have surely noticed that in the construction of a building the lowermost wall is made wider. Here the amount of pressure has been

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decreased by increasing the area. It is for this reason that the wheel of a truck is much wider than the wheel of a rickshaw. The rear wheels of buses and trucks are also used in pairs. Some of you may have seen physical feats demonstrated by some men. They lie down on the points of nails, placed in rows. They lie down bare bodied. This is possible as the weight of the man that is the force gets distributed over a number of nails. As a result the pressure becomes much less. Otherwise it would not be possible to lie down over a single nail.

Rest and Motion There are some bodies around us, which are at rest. Such as the houses, trees, hills and mountains. Again, there are some bodies, which are in motion. Such as the moving train, motorcar, rickshaw etc. Thus all bodies may be divided into two groups according to their position: (a) Bodies at rest (b) Bodies in motion. Rest Your school building is at the same place today as it was yesterday. And it will remain at the same place until it is broken or removed for some reason. Similarly other houses or trees will be seen to be at the same place, as they are now, after one hour, one day or one month also. These are called static bodies and this state of the bodies is called rest. Therefore, if a body does not change its position with the change of time, with respect to surrounding bodies, the body is said to be a static body and the state of the body is called rest. Motion While a bus or a train remains standing at a station, then they are static. But as soon as they begin to move their positions also go on changing.

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They will be seen at some places after ten minutes and at some other places after one hour. Therefore their positions change with the change of time. These are called bodies in motion or moving bodies. And this moving condition of the body is called motion. Therefore, when a body changes its position, with the change of time, with respect to surrounding bodies, then the body is said to be a moving body and the state of the body is called motion. By now you have noticed that whether a body is at rest or in motion that can be understood by comparing it with the surrounding bodies. Suppose, you are going from one place to another by a train. The train has started to move. Will there be any change in your position with respect to door, window or passengers of the train? There will be no change, and everything within the compartment will appear to you to be at rest, although the train is in motion. Again houses and trees are at rest, with respect to the earth. But you know that the earth rotates about its own axis at a mean speed of about 1200 kilometers per hour. As a result of this day and night occur. The earth revolves round the sun also. So, all bodies on earth are in motion. In real sense, nothing in this universe is at rest. The earth, the moon, the sun, the stars all are moving. Thus there is nothing like absolute motion or absolute rest. Whether a body is at rest or in motion can only be understood by comparing it with other bodies. Therefore, all motions and rests are only relative. Motion of a moving body changes on application of force on it. That means, the motion increases or decreases. What does happen if force is not applied? The motion neither increases nor decreases, and the body moves with the same uniform motion. How long will it move in this way. The body will move in this way until any force is applied on it. It will continue to move forever if no force is applied on it to change it.

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So a body at rest will remain at rest forever if no force is applied on it. Similarly a moving body will continue to move forever at uniform speed if no force is applied on it. Is it surprising? You will learn many surprising things, like this in your science classes. Many kinds of Motion Motion of a train, rotation of a wheel of a bi-cycle, movements of the hands of a clock, and swinging of a cradle are all different kinds of motion. Names of different kinds of motion are different. Linear Motion You lift a body up and let it fall. The body will fall down straight. If a body moves along a straight line in this way, the motion of the body is said to be linear motion. The motion of a bullet fired from a gun is linear motion.

Curvilinear Motion While coming to school from home you come along a zigzag way and do not come straight, your motion will be curvilinear motion. Therefore, if

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the course of a moving body is curved, the motion of that body is called curvilinear motion. Motion of a moving rickshaw, van, bus, truck etc. is curvilinear motion. Because, perfectly straight road can hardly be seen. Rotational Motion Take a rope of one metre length. Tie a piece of brick or stone at one end. Wind other end of rope with your finger and revolve the stone. Motion acquired by the stone is called rotational motion. Therefore, when a body rotates about a point or an axis, then the motion of the body is said to be rotational motion. The motion of the wheels of a moving bi-cycle, motion of a moving electric fan, rotation of the earth along its own orbit etc. is all rotational motion. Periodic Motion At the time of revolving the stone with a rope, if you revolve it in such a way that time of each revolving always be the same, then that motion is called periodic motion. Sometimes a bi-cycle moves faster and sometimes it moves slower. Thus the time taken by the wheel of a bi-cycle to revolve once is sometime less and sometimes more. So the motion of

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the wheel of a bi-cycle is not periodic motion. Time taken by the earth to make one complete rotation about its own axis is always 24 hours. So the motion of the earth is periodic motion. Therefore, if a body moves in such a way that after a specific interval of time, it moves through the same point along its path of motion in the same direction, then the motion of the body is said to be periodic motion. Motion of the hands of a clock, motion of a electric fan, motion of a gramophone record etc. are periodic motion. Oscillatory Motion Hold the rope to which a stone is tied in such a way that it hangs downwards. Holding the rope with right hand, pull the stone with your left hand slightly and let it go. You will observe that the stone will have a pause after moving a distance from left to right, then again it will go to left moving in opposite direction. The stone will be oscillating in this way. That is to say, at a specific interval of time, the motion of the stone will be reversed. This motion of the stone is called oscillatory motion. The motion of pendulum of a clock and the motion of a cradle are also oscillatory motion. Oscillatory motion is a kind of periodic motion. Difference is that the motion of a body, having oscillatory motion, is reversed at a specific interval of time. All oscillatory motions are periodic motions but all periodic motions are not oscillatory motions. The motion of the pendulum of a clock is oscillatory as well as periodic motion. But the motion of the hands of a clock is not oscillatory it is only periodic motion.

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Complex Motion Whenever a bi-cycle moves along with the rotation of its wheels it gains a forward motion also. In this way when a body has linear as well as rotational motion at a time, then the body is said to have complex motion. The motion of the wheels of a moving motorcar, train or rickshaw is complex motion. Displacement, speed and velocity.

Displacement You keep your book on the table, a distance apart. The position of book is changed. The change of position of a body is called displacement. But this change of position should be in a definite direction. The linear distance between first and second positions of the object is the magnitude of displacement. Suppose a body moves from position A to position B. The body may move directly along a straight line, or it may go along a zigzag and upward or downward paths. But whichever path it follows, its displacement will be the linear or least distance AB, between the first position A and last position B. Displacement does not depend upon path along which the body traverses. The direction of displacement will be from A to B. So we can say that the change of position of a moving body in a definite direction is called displacement. While the amount or magnitude of

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displacement is the linear or least distance between first and last positions of the body. Displacement is a distance, so units of displacement and length are the same. Therefore unit of displacement is metre. Speed Suppose the distance of your school from your house is 1000 metres. You take 20 minutes to go there on foot. That is to say, you can walk a 50-metre path in a minute. Thus your speed is 50 metres per minute. Speed does not depend on traversing straight or curved path. It depends upon the total distance traversed and the time taken to traverse it. In a word, distance traversed by a body in unit time is called speed. Unit of speed is metre per second.

Therefore, Speed = Distance

Time

Velocity Speed having a definite direction is called velocity. Therefore distance traversed by a body in a definite direction in unit time is called velocity.

Therefore, velocity = Displacement

Time

Suppose you took part in a 100-metre race in the annual sports of your school. You took 20 seconds to run 100 metres. You ran straight, without moving this side or to that side. Therefore, your direction of motion was fixed. Your velocity was 5 metres per second. Unit of velocity and speed is one metre per second. The difference between speed and velocity is that, speed has no definite direction, but the direction of velocity is definite.

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New words in this Chapter Force Rest Newton metre Pascal Displacement, Velocity

Speed Pressure Oscillatory Motion Periodic Motion Complex Motion Motion

Exercise Multiple Choice Questions (MCQ) 1. What is the unit of the force? a. metre b. kilometre c. Newton d. Pascal 2. Which is the unit of Pascal? a. of force b. of pressure c. of acceleration d. of velocity 3. Of the following, which is force? a. Energy b. Mass c. Weight d. Speed

4. A bag of 2 kilogram mass weights about- a. 1 Newton b. 2 Newton c. 10 Newton d. 20 Newton

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5. The sort of motion of the wheel of the carrier- a. is complex b. is liner c. is rotational d. is periodic

The two positions of the same brick is shown in the picture. 1. The weight of the brick in B position is- a. 10 Newton b. 20 Newton c. 40 Newton d. 30 Newton 2. In B-marked fig, the pressure of the brick per square metre is- a. 1000 Newton b. 2000 Newton c. 3000 Newton d. 4000 Newton

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Creative Questions (CQ) 1. Everyday Rahim goes to school by crossing the above way on foot. Rahim takes 30 minutes to reach his school. a. What is distance? b. Explain how Rahim’s speed is separated from periodical speed c. Calculate the average speed of Rahim. d. What would be the change in Rahim’s speed and velocity if the

distance of the school from his house is measured in displacement? Put mathematical arguments.

2. With the help of a hammer, 10 Newton force is applied on the head of a pin spreading ovel an area of 2 square millimeter. As a result the pin enters into the wood upto distance of 2 centimeter. a. What is the meaning of 10 Newton force? b. Explain the cause of entering the pin into the wood. c. Determine how much pressure is felt by the pin. d. Write what change would occur in pressure that would be felt in

case of increase and decrease of area at the head of the pin.

Chapter - 11 Work, Power, Energy

Work, power, energy – these words we always use in our daily life. Such as, the boy is very hard working, the man is very powerful and the lion is a strong and energetic animal, etc. But the general and scientific meanings of these words are not always the same. Work, power and energy have special meanings in the language of science. What is work? What is the unit of work? You take a book from the table and lift it up on your head. What work do you have to do for this? You have to apply a force against the weight of the book. In this way the displacement of a body from one place to another, with the application of force is called work in the scientific language. Here there are two things that need to be noticed. Firstly force and secondly motion of the body or displacement. When the body changes its position on being in motion by application of force, only then work is done. You push a wall with all your strength. The wall does not move even a bit. Have you done any work? No, because although force has been applied there is no displacement. A cart driver drives his cart. He does work. Because, as a result of application of force, the cart moves from one place to another. Therefore, there is displacement of the cart. A porter lifts up a load from the ground to his head. He does some work. But when he remains standing with the load on his head, no work is done. So, the displacement of a body from one place to another, with the application of force is called work. The product of force and displacement

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measures amount of work done. Therefore, work done = force x displacement. Name of unit of work is joule. You know that unit of force is Newton and unit of displacement is metre. So,

1 joule = 1 Newton × 1 metre

Therefore, if a force of 1 Newton acting on a body produces a displacement of 1 metre, then amount of work done will be 1 joule. Suppose, to lift up your book, a force of 10 Newton need to be applied. You have raised the book up through a distance of 1 metre. Then the work done by you is – 10 × 1 = 10 joules.

What is power? What is the unit of power? Two men are lifting up bricks from the same place and loading a truck. One man is lifting 6 bricks in a minute, and the other man is lifting 12 bricks in a minute. Whose power is greater? Power of the second man is greater. Because he is working twice the work of the other man in the same time. In other words one, who works quicker, has a greater power. How quickly a work can be done, can be understood from power. In a word, work done in unit time is called power. Therefore –

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Power = Amount of work done

Time

Unit of work is joule and unit of time is second. So unit of power is joule per second. Name of this unit of power is watt. Therefore –

1 watt = 1 joule

1 second

As this unit of power is rather small, sometimes kilowatt is used as practical unit. 1 kilowatt = 1000 watt. In the example given above (Figure no. 11.1), if the first man does 600 joules of work in one minute that is in 60 seconds, then

His power = Amount of work done

Time

= 60060

= 10 watts. The second man does a work of 1200 joules in the same time so –

His power = Amount of work done

Time

= 1200

60

= 20 watts. So, the power of the second man is twice the power of the first man. Power does not depend upon total amount of work, but it depends upon the time in which it is done. What is energy? What is the unit of energy? You and one of your friends started to run together. Your friend sat down after he had run one kilometre. He was unable to run further. You also sat down after you had run one kilometre further. Who is more powerful? You

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will surely say, 'I am'. You are right. But how is it so? You both have done work during running. Your friend could not run further after he had run one kilometre. That means he has lost his capacity for doing work. But your capacity still remained. Hence you could run one kilometre further. But after that your capacity was also exhausted.

This capacity for doing work is called energy. Therefore energy is necessary for doing work. The more the energy a person has, the more the amount of work he can perform. None can do any work without energy. A man or a machine can perform that amount of work, which his energy permits. Hence energy is measured by work. So unit of work is the unit of energy. Therefore – unit of energy is also joule.

We cannot live even a moment without energy. In fact, this universe also cannot survive without energy. Nothing is static in the universe. The earth revolves round the sun, and the moon revolves round the earth. Always something or the other is happening, therefore, work is done. For performing any work you may think, energy is necessary. Energy is necessary for production of food, cooking, movement of cars and carts, running mills and factories, playing games, and even when you read books. Many forms of energy We get our energy from food. This is one kind of energy. Motorcar or train move with another kind of energy. Again lamp burns, fan rotates or mills, factories run with another kind of energy. Energy has many forms like this and each of the forms has a particular name. Mechanical Energy Movement means work. Therefore, any moving body has capacity for doing work. That is to say, they have energy. You are walking, a car is

Work, Power, Energy 151 moving, you or the car has a kind of energy. This energy is called kinetic energy. Because, capacity for doing work has developed due to motion. Therefore, capacity for doing work is generated by a moving body by virtue of motion is called kinetic energy.

You lift up a brick from the ground. You do some work. Has the brick any energy while you hold it up? It has; because if you now let the brick fall, it will fall on the ground on its own, and hence it will perform some work. If there is no energy how this work can be performed? So while you are holding up the brick, although it has no motion, it possesses a kind of energy. This energy is called potential energy. Therefore, energy that is generated by a body by virtue of its special position or configuration is called potential energy.

You may have plucked mangoes or guavas or hunted birds by a catapult. Along with stone, while you lengthen the rubber band of a catapult, by stretching, then potential energy is stored in that. As soon as you release the rubber band, the stone shoots out with a tremendous speed. These occur for kinetic energy. These kinetic energy and potential energy are together called mechanical energy.

Chemical energy

Energy stored in food or fuel is called chemical energy. We get energy from food. Petrol, gas, wood, coal as they all have chemical energy. The batteries that you use in the torch and radio also have chemical energy. Heat energy

Energy used in cooking, driving of motorcars or railway engines is called heat energy. This energy is obtained by burning coal, gas, wood, petrol or diesel. Again heat comes directly from the sun also. This heat energy

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keeps the earth warm. No animal or tree can survive without heat energy.

Magnetic energy

Another form of energy is magnetic energy. A magnet attracts articles made of iron with this energy from a distance. We will discuss about the magnetic energy in the next chapter.

Light energy

The other energy, which comes along with heat energy from the sun directly, is light energy. We could not see anything in absence of light energy.

Sound energy

While you speak, sing or play on a flute, you generate a kind of energy. This is called sound energy. We can hear the voice of one another with the help of sound. Sound energy is used in telephone, radio and television. The vibration of substances produces sound.

Electrical energy

A very well known and useful form of energy is electrical energy. We light lamp, turn the fan on, run mills and factories by electrical energy. Trains are also run by electrical energy in many countries. Electrical energy can be transmitted from one place to another with the help of wire.

Solar energy

Energy received from the sun in the form of heat and light is called solar energy. In fact the sun is one of the main sources of our energy. We use solar energy for drying of clothes, jute and paddy everyday.

Work, Power, Energy 153 Wind energy Energy generated by the flow of air is called wind energy. Boats with lifted sails move with help of air energy. Windmills are run by the use of air energy. These mills produce electricity and also grind wheat, maize, etc. This energy is not used much as the generation and uses of electrical energy by other processes are much easier and cheaper. Atomic energy You know that matter is composed of atoms. The inner content of this atom is bound together by a very powerful force. If this binding can be broken by any means, then a very powerful energy called atomic energy is obtained. This energy can be transformed into electrical energy and is used in our work. It can also be used for destruction of world by making atom bomb. Transformation of energy When using some energy one performs some work, then what does happen to that energy? Is that energy destroyed? No energy is neither lost nor destroyed. It is only transformed from one form into another. You rub your palms several times by pressing them together. You will observe that your hands become warm. You will also hear sound during rubbing. Rubbing of palms is a kind of work. For this you have to use your muscle energy or mechanical energy. This energy you have received from the chemical energy of your food. So here at first chemical energy has been transformed into mechanical energy and then mechanical energy has been transformed into heat energy and sound energy. Many examples can be cited in respect of such transformation of energy from one form into another. When coal or oil burns, its chemical energy is transformed into heat energy. This heat energy is transformed into mechanical energy while

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trains or motorcars run. Electrical energy can again be generated from heat energy. When we light an electric lamp, electrical energy is then transformed into light energy. When an artist sings at a radio station, sound energy is transformed into electrical energy. When you listen to that song in your radio, that electrical energy is further transformed into sound energy.

Conservation of energy Is some energy consumed during its transformation from one form into another? No, though it may appear surprising, energy is neither lost nor is destroyed. Total amount of energy before and after transformation remains the same in one form or the other. In fact, the scientists have shown that total amount of energy in this universe is constant. No more amount of energy than this can be created also. Amount of energy that remains cannot be destroyed also. Only it can be transformed from one form into another form, or into more than one form. This is called conservation of energy.

Fig 11.2: Energy from air-sailing of boat and wind mill

In brief, we can state the principle of conservation of energy in this way: The sum total of the amount of energy in the universe is constant and unchangeable. Energy can neither be created nor can be destroyed; it can only be transformed from one form into another or into more than one form.

Work, Power, Energy 155 Sources of energy Where do we get energy? How essential the energy is! Now where do we get this energy? You or any man receives his energy from food. Energy, which is needed for the mills and factories or vehicles, comes from fuel. Then where do these foods or fuels come from? Source of most of energy of the earth is the sun. Energy comes in the form of light and heat from the sun. This light of the sun is utilized for production of food. Again, coal, oil, gas or petrol has been produced from remains of the trees and animals of thousands and thousands years ago. Trees or animals are converted into coal, gas or oil after they remained under pressure inside earth for thousands and thousands of years after their death. Again by burning this coal, oil or gas most of the electrical energy is being produced. Energy is also obtained from air. The power of air can be understood during cyclone. Energy of air can uproot trees and houses and blow them all away. Air energy actually causes destruction during storms, and it is not utilized in any work. But during other times air energy can be utilized. Boats with lifted sails move with the help of air energy, with the lifted sails. Fan can be rotated by air, which in turn can rotate grindstones for crushing rice, or wheat. There was a kind of wind driven mill in many countries of Europe, about two or three hundred years ago, by which people used to grind wheat. The name of this machine or mill is windmill. The windmills can also generate electricity. Burning coal or oil can generate electricity more easily and cheaply. Hence windmills are not used as before.

Another main source of energy is water. Water current can also be utilized to rotate fan or wheel. Water can be increased to a great extent by constructing dams in the river. Water rushes out downward with a

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tremendous speed when gates of the dam are opened. Electricity can be generated from this. Electricity generated in this way is called hydroelectricity. In Bangladesh, there is a hydroelectric generation centre at Kaptai, in the Chittagong Hill Tracts. Renewable and non-renewable energy You have learnt that we get energy from coal, oil, gas, sun, water or air. The amount of coal, oil, gas burnt to generate energy is spent away. These cannot be used again. The amount of these fuel deposits in the world is not unlimited. Perhaps one day these deposits will be exhausted altogether due to the continuous use. Coal, oil or gas is called sources of non-renewable energy. On the other hand, rays of the sun, air or water are unlimited. They can be used again and again. These are called sources of renewable energy. Ocean-current and tides can also be used as sources of renewable energy. In brief we have learnt:

Main source of energy is the sun. Other sources of energy are: coal, gas, oil or petrol, water and air. Sun, water and air are sources of renewable energy. Coal, gas and oil are sources of non-renewable energy.

Till now most of the energy is generated in the world from non-renewable sources. Because it is easy and can be done with less expense. Demand of energy is increasing day by day. For this reason, coal, oil and gas deposit are being quickly exhausted. In view of this, scientists have been trying to generate useful energy at a low expense, from renewable sources, specially the sun. Perhaps energy, in future, will be obtained from renewable sources. But none can say in how

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many days that will be possible. For this reason we must be careful and should not waste energy. Hardly there is any coal or oil in our country. There is some gas. This gas is used in many of your houses for cooking. You must see that gas is not wasted by burning gas-ovens without any purpose. You will not keep electric lamps lighted or put electric fans on unnecessarily.

New words in this chapter.

Work Joule Renewable Energy Energy Watt Non-Renewable Energy Power Conservation of energy

EXERCISE

Multiple Choice Questions (MCQ) 1. What is the name of the unit of the energy? a. Newton b. Joule c. Watt d. Meter

2. What one is the source of renewable energy? a. Coal b. Gas c. Oil d. Sun 3. The weight of you and one of your friends is almost same. It took 20

second for you to run for 100 metre distance. Your friend took 25 seconds. Which is correct?

a. your force is more b. your power is more c. your energy is more d. the amount of your work is more

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4. A man can work equivalent to 25, joule in 10 seconds. What is the power of the man in watt? a. 2.5 b. 2/5 c. 250 d. 50

5. Which energy is transformed for production of sound energy while a small drum (tabla) is slapped? a. heat b. chemical c. electrical d. mechanical

6. A mango fell on the ground from 10 meter height. At 5 meter height in case of falling mango-

(i) kinetic energy is converted into potential energy. (ii) potential energy is converted into kinetic energy.

(iii) no conversion of energy Of the following, which is correct? (a) i (b) ii (c) iii (d) i, ii and iii 7. From the statement of question 6 if the mango falls on the ground, the

mango a. will have no potential and kinetic energy b. will have potential energy a. will have kinetic energy d. will have mechanical energy

Creative Questions (CQ) Rahim, a labourer, can raise 20 bricks at a time in two minutes upto a height of 15 metre from the ground. But Barek requires 3 minutes to raise 20 bricks upto the same height. Each brick weight 1 Newton.

a. What is the unit of meter? b. Explain how the work is occurring from the above incidence. c. Calculate the work of Barek? d. Put mathematical arguments for your assumption for more working

power between Rahim and Barek.

Chapter - 12

ELECTRIC ENERGY

We all know electricity. Application of electricity is seen in almost every area of our daily life. Lamps are lighted and fans rotate in the houses, offices and shops with the help of electricity. Mills and factories are run by electricity. It has become possible for us to hear songs on radio, see pictures on television and speak to any body at distant places over telephone, by the use of electricity. Trams and trains are run by electricity in many countries for communication. All these are various kinds of work. Therefore, electricity has the capacity for doing work. So, electricity is a kind of energy. Story of discovery of electricity

The story of discovery of electricity dates back to about 2600 years ago. A wise man named Thales used to live at a place called Miletas in Greece. He observed first that hard yellow gum of a pine tree named amber, when rubbed with wool, attracted small bits of paper or light substance like dust of wool. He used to show this to his friends as a game of fun in order to give them pleasure. But he did not actually know that he discovered electricity, which would create a revolution in the world afterwards. About 2200 years passed since then and it is not known whether anyone thought seriously on that or not. About 400 years ago, that is in 1600 AD, an English scientist named Gilbert discovered that not only amber but there were many other substances, when rubbed, attracted light substances like small bits of paper. That is to say, an invisible energy developed in them. Electron is the synonym of amber in Greek language. From that

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Gilbert was the first to name this property of the substance as electricity whose Bengali synonym is biddut. Scientists started to carry on researches on electricity after Gilbert had discovered it.

Statical electricity is produced by friction

Experiment: Take a plastic

or rubber comb. If your hair is dry comb your hair several times with some pressure, it will be found that the comb is attracting small bits of paper if it is held near them. By rubbing the comb with a woolen cloth. You can also perform this experiment if your hair is not dry. When a glass rod or a bottle is rubbed with a silk cloth, a rod of sealing wax is rubbed with wool, they are also found to attract light substances like small bits of paper, pieces of cork, bird's feather, parched rice (muri), etc. It is understood from these that power of attraction generates in some special substances when they are rubbed with some other

Electric Energy 161 special substances. Scientists have named this invisible energy as electrical energy. This electricity is called statical electricity, as it remains static at the place where it is produced. This electricity is also called frictional electricity, as it is produced by friction. Thus, rubbing some special kinds of substances with each other produces statical electricity. Statical electricity can be produced by rubbing glass, rubber, plastic, gutta-percha, sealing wax, ebonite etc. with wool, silk etc. To observe the attractive power of statical electricity, light substances such as, cork or small piece of sponge wood, dry hair, piece of paper, parched rice (muri) parched paddy (khoi) etc. can be used. What is charge? Positive and Negative Charges. Experiment: A glass rod is suspended by a thread of silk after rubbing it with silk cloth (Figure 12.2). Another glass rod is rubbed with silk cloth in a similar way. This rod is brought near the end of the first rod, which is rubbed with silk. It will be observed that the end of the suspended rod has moved farther. Therefore, the two rods repel each other. This time a hard rubber rod is brought near the same end of the suspended glass rod after rubbing it with a woolen cloth. It will be observed that there is attraction between them. Then by a thread, another rubber rod is suspended after rubbing it with wool. The first rubber rod is brought near the second suspended rod. It will be observed that there is repulsion between them. In order to explain these facts, it is said that electric charge is produced in glass and rubber rods due to friction. Charges of the two rods exert force on each other. It clearly shows that the nature of the charges in the glass rod and that in the rubber rod is not the same. About 250 years back, Benjamin Franklin named the charge produced in glass rod due to its rubbing with silk as positive (+) charge and the charge produced in rubber

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rod due to its rubbing with wool as negative (−) charge. This name is in use till today. Whether an unknown charge is positive or negative, can be known by comparing it with a charged glass rod or charged rubber rod. We cannot see charges but we can observe their influences. We can observe that the two charged bodies attract or repel each other. We can understand the existence of charge by observing this influence. So, we have learnt 1. By virtue of which a body acquires power of attraction, that is to say statical electricity is produced in the body, is called charge. 2. Charge is produced in a body due to rubbing. The body is called a charged body. 3. The cause of electrical energy is the charge. The effect of charge is electricity. 4. Charges are of two kinds− (i) positive charge and (ii) negative charge. Properties of charge⎯Attraction and Repulsion We have seen from the above experiment that two glass rods rubbed with silk repel each other. Again two rubber rods rubbed with wool also repel each other. But the glass rod and the rubber rod attract each other. We have also learnt that charge of the glass rod is positive and charge of the rubber rod is negative. Therefore charges of same nature that is positive charges of two glass rods repel each other. Similarly charges of same nature that is negative charges of two rubber rods also repel each other. But the positive charge of glass rod attracts the negative charge of rubber rod. So it can be concluded that⎯ 1. Charges of same nature repel each other. 2. Charges of opposite nature attract each other.

Electric Energy 163 Statical Electricity and Current Electricity You have learnt that statical electricity is produced in a plastic comb, rubbed with woolen cloth. Is this statical electricity always static? You will get answer to this question from a small experiment. Experiment: Rub a plastic comb with a woolen cloth. The comb attracts small bits of paper. Therefore statical electricity has been produced in it. Now touch comb with your hand. Bring the comb near the pieces of paper again. It will be seen that it no longer attracts pieces of paper. What can be understood from this? It is understood that there is no more electricity in the comb. Where did this electricity go? This electricity has gone elsewhere, flowing through the metallic substances or through the hand. Electricity that goes from one place to another or one body to another by flowing through a substance is called current electricity. The electricity that we always use for lighting lamps, rotating fans, running mills and factories, lighting torches is current electricity. Electricity flows through the bulb or an electric lamp if we press the switch. As a result lamp is lighted. Lamp remains lighted so long as electricity flows. Flow of electricity stops when the switch is turned off. To keep the lamp lighted, flow of electricity needs to be maintained. It is necessary to remember here that a definite amount of electricity is produced in a body by friction. This charge goes to earth as soon as it is touched with hand or with any metallic substance. Flow of electricity ceases when there is no charge. So temporary flow of electricity is produced in this way. In order to maintain supply of electricity, there should be a source, which can supply electricity continuously. You will learn about source of electric current a bit later. So, we have learnt that electricity is of two kinds ⎯ statical electricity and current electricity.

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1. Statical electricity: The electricity which is confined or which remains static within a body is called statical electricity. 2. Current electricity: The electricity, which flows through a body continuously and in a definite direction, is called current electricity. Conductors and Non-conductors Can electricity flow through all substances? In order to get the answer to this question another little experiment is to be performed. Experiment: A wood, a glass, a piece of porcelains or plastic is touched with a plastic comb after producing electricity in it by rubbing with wool. It will be observed in bringing the comb near the pieces of paper that it still attracts them. What is understood from this? It is understood that electricity of the comb remains in it. That is to say, electricity does not go elsewhere by flowing through wood, glass, porcelain or plastic. Electricity cannot flow through these substances. On the other hand, we have observed earlier that electricity can flow through iron, copper or brass. Therefore, electricity can flow through some substances and cannot flow through some other substances. Substances have been divided into two groups on the basis of flow of electricity: 1. Conductors: Substances through which electricity can easily move or flow are called conductors. Some examples of conductors are: iron, copper, gold, silver and other metallic substances, human body, earth, mercury, most air and water. 2. Non-conductors or Insulators: Substances, through which electricity cannot flow, are called non-conductors or insulators. Some examples of non-conductors are: glass, wood, porcelain, plastic, paper, silk, rubber, ebonite, dry air, etc.

Electric Energy 165 Now you will be able to understand by a bit of careful observation that substances in which statical electricity is produced due to friction are non-conductors. For that reason electricity remains static at the place where it is produced. Had it been a conductor on production of electricity it would go elsewhere by flowing through it. Generally the body is held by hand. For that electricity goes through hand and body to earth. For the same reason it appears that no electricity is produced, when a metallic substance is rubbed with wool or silk. American scientist Benjamin Franklin showed it by his experiment that electricity is produced in a metallic substance fitted with rubber or glass handle, when it is rubbed with wool or silk. Electricity can be produced in all substances by rubbing them in appropriate methods. Statical electricity is turned into current electricity whenever it comes in contact with a conductor. Source of Current Electricity. If your houses or schools have electrical connection, lamp is lighted just pressing a switch. Again a torch can also be lighted by pressing its switch. Electrical energy has been transformed into light energy in both the cases. But source of electricity of house and source of electricity of torch are not the same. Electrical connection is made in a house by drawing wire from a long distance. But perhaps two or three batteries have been used in torch. Source of electricity of torchlight is the battery or electric cell. Whereas electricity comes to houses from electricity generating centre. The machine by which electricity is produced at the electricity-generating centre is called generator. Electric generator and electric cell are the sources of electrical energy in our day to day work. Mechanical energy is transformed into electrical energy in electric generator. Any device to maintain continuous supply of electricity by producing electrical energy from chemical energy is called an electric cell. Two

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metallic substances are partially immersed in a chemical substance in an electric cell. Due to chemical reaction with metal an excess of positive charge occurs in one of metallic substances and an excess of negative charge occurs in the other. Electricity flows through a conducting wire that connects the two metallic substances. There are many types of electric cells. The cell commonly used by us is called dry cell or liquid-free fell. General people know this cell as torch battery. In various shapes these cells are used in torches, radio, two-in-one, clock, calculator, etc. You have seen another type of cell used in motorcars or mikes. These look different from torch batteries, and they are also big and heavy. These are called storage cells. In this cell at first electrical energy is stored as chemical energy by passing electric current from some external source through chemical substance. Electric current is obtained by transforming again this stored chemical energy into electrical energy. Advantage of this cell is that when stored-up chemical energy is exhausted on being transformed into electric energy, chemical energy can again be stored up by passing electric current. As a result, the same chemical substance can be used again and

Electric Energy 167 again. Transformation into chemical energy by passing electric current is called charging of battery. Chemical energy of torch batteries being exhausted by use, these cannot be charged again. Old batteries need to be replaced by the new ones. Advantage of electric cell is that its size is small; as a result it is convenient to carry. It can be used at any place. Electric cell is ideal for use in wristwatch, calculator or motorcar. But where much energy is required, electric cell cannot be used there. Then electricity produced from generator is required. Electric generator can produce electrical energy of thousands and thousands of watts. This electricity can be taken to hundreds and hundreds of kilometres away by means of wires. As a result electrical connections can be given to thousands and thousands of houses and mills and factories. You will learn in higher classes the principle on the basis of which electricity is produced by a generator.

Lightning, Thunder It is rainy season. The sky is overcast with dense black clouds. Suddenly you see a flash of glaring light in the sky. Terrible deafening sound is heard after a little while. You all have this experience. This flash of glaring light is called lightning and terrible sound you hear is called rumbling of clouds or thunderclaps.

What is lightning? There are particles of water, dust and various gases in air. Statical electricity is generated among these particles due to friction. Therefore, the particles are charged. Clouds are produced from the accumulation of such crores and crores of charged water particles. A cloud may either be positively or negatively charged. Electricity produced in air due to various natural reasons is also deposit over the particles of water in the clouds.

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Amount of electricity increases very much in cloud in this way. As a

result, due to powerful attraction between positively charged cloud and

negatively charged cloud, electricity rushes from one cloud to another.

Heat, light and sound are produced simultaneously due to this. As

velocity of light is many times greater than velocity of sound, hence we

see light first and hear sound later. This flash of light is called lightning.

Thunder

Sometimes highly charged clouds come near to the earth. The lightning discharge occurs between the clouds and the earth, piercing the atmosphere. This is called thunder. The higher a body is over the surface of earth, the nearer it is to the cloud. For this thunder generally strikes on top of high buildings and trees. Thunder may strike even head of a man standing in the field. Building crack and trees or men die due to occurrence of thunder. It is not safe to remain standing under a tree during storm and rain. It is not essential for

Electric Energy 169 cloud to come very close to earth for occurrence of thunder. There may be thunder from a cloud lying at a distance of four to five kilometres. Sound heard along with thunder is called thunderclap. Benjamin Franklin discovered first that electricity in cloud is the cause of thunder. Lightning conductor In order to protect high buildings from ravages of lightning discharge, a metallic rod is fitted at the highest place of the building. Sharp and tapering upper end of this rod remains high above the roof. Other end, connected to a thick metal wire, is buried under the earth. This rod is called lightning conductor. This rod remains closer to cloud than other parts of building. As a result, while there is thunder, it strikes this rod. The rod is a metallic substance; therefore, it is a conductor. So electricity contained in thunder passes directly to the earth through the rod. As a result there is no harm to the building.

New words in this chapter Electron Current electricity Positive charge Conductor Negative charge Non-conductor Statical electricity Electric cell

EXERCISE

Multiple Choice Questions (MCQ)

1. Electricity is produced in electric cells-

a. from mechanical energy b. from chemical energy

c. from thermal energy d. from the sun energy

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2. If repulsion occurs between the two, it is confirmed that

a. the two material / objects are charged

b. one is charged and another is not

c. one is positively charged and the other is negatively charged

d. none of the above

3. Which is not the source of the direct current?

a. battery b. amber

c. generator d. electric cell

4. Why is the sound of the cloud heard after a while of thundering? a. the velocity of the electricity is more b. the velocity of sound is more c. the velocity of light is higher than that of the sound d. the velocity of light is less than that of the sound

In the light of the following paragraph, answer the questions 5 and 6. The two glass rods repel each other when they are rubbed with silk. Again the two rods made of rubber repel each other when they are rubbed with the same. But the glass rod and the rubber rod attract each other.

5. Why do the glass rod and the rubber rod attract each other?

a. There are charges of similar properties (similar charges) in glass rod and rubber rod

b. The glass rod is charged and the rubber rod is not charged c. There are charges of opposite properties (opposite charges)

in the glass rod and rubber rod.

Electric Energy 171 6. Of the following, which is correct?

a. The glass rod is positively charged

b. The rubber rod is negatively charged

c. The glass rod is positively charged

d. Both glass and rubber are Positively charged

Creative Questions (CQ)

Fig: 1 Fig: 2

In the light of the above figures, answer the following questions:

1. What is called the system of fig-1?

2. Why is the bulb not lightning in fig-2?

3. Explain the flow of electricity of the circuit.

4. Give your opinion regarding suitable of such sort of electric flow in

a house.

Chapter – 13

MAGNETIC ENERGY

Story of discovery of magnet

This is a story of many years ago. There was a shepherd named Magnes who used to live at a place named Magnesia in Asia Minor. A mountain named Ida was there. One day, Magnes wished to climb up the mountain. He noticed that his legs could not be lifted up any more from the ground while climbing up the mountain. Nails of shoes got stuck to the ground. He found a kind of stone after he had dug the ground there. He observed that this stone attracted iron nails of his shoes.

A strange kind of stone, which attracts iron or ferrous substances, was discovered at first in such a way. Another peculiarity of this stone was also observed. He found that when a long stone was allowed to hang freely in open space that always remained pointing towards north and south. Name given to this stone was magnetite, after the name of Magnes. Some people's opinion was that the name magnetite was given as it was first found in Magnesia. Word magnet is derived from the word magnetite. Bengali word of magnet is chumbak. This is the most common story about the discovery of magnet. However it is not definitely known that how many years ago this occurred. But it is known that small magnets were also used to find out direction, in China, about four thousand five hundred years ago. Magnet has power to attract iron. Attraction is a kind of force. Work can be done by force. Therefore a magnet has capacity for doing work. So magnet is a kind of energy.

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Natural and Artificial Magnets Magnetic stone discovered by Magnes is a kind of grey black coloured compound substance. It is a compound of iron and oxygen (chemical notation is Fe3O4). This stone is still now available in the mines of Canada, Norway and Sweden besides Asia Minor. As these are available in nature, hence they are called physical or natural magnets.

Natural magnet has no definite shape. Besides, its magnetic strength, that is attractive power is not very much. For this reason magnets are also prepared by artificial processes. Specialty of artificial magnet is that its strength is as per requirement and it has a convenient shape for working purpose. Artificial magnets are prepared by some special methods. As they are prepared artificially, hence they are called artificial magnets. So magnets are of two kinds ⎯ natural magnet and artificial magnet. Magnets which are available in nature are called physical or natural magnets. Magnets prepared artificially are called artificial magnets. Different kinds of artificial magnets Artificial magnets of different shapes and sizes are prepared for using them conveniently. A few kinds of artificial magnets in respect of their shapes are : 1. Bar magnet When a rectangular steel bar is converted into a magnet, it is called a bar magnet. This kind of magnet is used in laboratory. 2. Magnetic needle It is made of very light steel sheet. Its two ends are tapering. Middle point of this sheet is pivoted on a pin. For that the needle can move freely in a horizontal plane. As a result, a magnetic needle at rest always points

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towards north and south. Magnetic needle is used as a direction indicating instrument.

3. Horseshoe magnet This magnet looks bent, as that of a horse's hoop and the English letter U, hence its name is such. Generally it is made of steel bar. Its two poles remain side by side. Strong magnetic field can be produced between two poles.

Properties of magnet : Magnetic pole Experiment: Sprinkle some iron fillings over a white paper, placed on a table. If iron fillings are not available, a box of pins will also serve the purpose. Keep a bar magnet over the sprinkled iron fillings or the pins, and lift it up after moving it a few times. You will observe that iron fillings or pins remain stuck to the body of the magnet. It is understood from this that the magnet has power of attraction. This power of attraction of a magnet is called its attractive property.

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It will be seen by careful observation that most of the iron fillings or pins remain stuck to the two ends of the magnet. Amount of iron fillings stuck to the magnet gradually decreases from the end to its middle. Iron fillings or pins do not stick to its middle place at all. It is understood from this, that the power of attraction of the magnet is not the same at all places. Power of attraction is maximum at two points near the two ends of the magnet. These two points are called two poles of the magnet. Remove iron fillings or pins from the magnet by shaking and rubbing them off. Touch the magnet with your plastic ball pen, wood pencil and erasing rubber one by one. You will observe that there is no attraction between them. It will be seen that if the magnet is brought near to silver, copper or piece of glass, these also do not stick to the body of the magnet. It is understood from this, that a magnet does not attract all kinds of substances. Magnet attracts ferrous substances such as, steel, cobalt and nickel. But it does not attract plastic, wood, rubber, glass, silver or copper.

Substances attracted by a magnet are called magnetic substances. And the substances which are not attracted by a magnet are called non-magnetic substances. Property by virtue of which a magnet attracts a magnetic substance is called attractive property of a magnet.

Now suspend the bar magnet by tying it with a thread at the middle. The magnet will come to rest after swinging from one side to the another. It will be seen that the magnet will practically lie pointing north and south. Again rotate the magnet and let it go. When it will come to rest after swinging from one side to the another, it will remain

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pointing towards north and south as before. It is understood from this, that a hanging magnet, without obstruction, always lie pointing towards north and south. This property of a magnet is called directive property. People knew this property of magnetite in ancient times. So, the sailors used magnetite stone for determining direction in sea. They named this stone as leading stone or lode stone or direction finding stone. One particular end of a magnet always tends to lie pointing towards north. This end is called north seeking pole or briefly north pole. The end which always tends to lie pointing towards south is called south seeking pole or south pole. Now you take two bar magnets. Suspend one of them by means of a thread as before. Now bring north pole of the other magnet near north pole of the suspended magnet. You will see that, the north pole of the suspended magnet moves farther. Therefore, repulsion occurs between them. Now bring south pole of the second magnet near north pole of the suspended magnet. You will observe that they attract each other. Similarly it will be observed that there is repulsion if the south pole of the other magnet is brought near the south

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pole of the suspended magnet. And there will be attraction if north pole of other magnet is brought near the south pole of the suspended magnet.

Now bring an iron bar, or a bar of any magnetic substance, at first near north pole and then near south pole of the suspended magnet. It will be seen that there is attraction in each case. So it is understood that⎯

Like poles of magnets repel each other. Unlike poles of magnets attract each other. Both the poles of a magnet attract a magnetic substance.

Methods of Magnetisation You have learnt earlier that magnets are of two kinds ⎯ natural magnet and artificial magnet. Artificial magnet can only be prepared by magnetic substances. Method of conversion of a magnetic substance into an artificial magnet is called magnetisation. You will learn now two easy methods of preparing artificial magnets. Method of rubbing A steel bar can be converted into a magnet by rubbing it with a magnet. AB is a steel bar (Fig. 13.5a). Keeping the bar on a table it is rubbed from end A to end B, in the same direction several times, by means of a powerful bar magnet. Each time the bar magnet is to be lifted up, after rubbing the steel bar with it upto end B. Again rubbing should be started from the end A. The steel bar is then turned upside down. It is rubbed from end A to end B in a similar way several times.

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Now it will be seen that the steel bar attracts pins or pieces of iron. Thus, it has been converted into a magnet. End A of the steel bar acquires polarity of the same kind as that of the bar magnet end B acquires the polarity of opposite kind to that of the bar magnet pole. Electrical method A long iron nail is coiled with ordinary electrical wire, covered with plastic (that is, covered with an insulating material), available in market. Electric current is passed through the wire by connecting its two ends to a battery. Now it is seen that the nail can attract a pin or a piece of iron. Thus, the nail has been converted into a magnet. Again on disconnecting the battery, it is seen that the nail has no attractive power. Therefore magnetism of the nail remains so long electric current flows, through the wire. Any soft iron bar can be converted into a temporary magnet by coiling wire like this and passing electric current through it. This kind of magnet is called an electromagnet. Strength of electromagnet depends on the flow of electric current through it. Strength of magnet increases with increase in flow of electric current. Uses of magnet Perhaps many of you use magnet in your everyday life, some knowingly and

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some unknowingly. Electric fan moves and electric bell rings on pressing switches. Electromagnets are used in electric fans and electric bells. Here attractive property of magnet is utilised. Magnetic energy is converted into mechanical energy with the help of electrical energy.

In ancient times sailors used to find out direction in the seas by utilising

the directive property of a magnet. That is done still today. Name of the

instrument used for this purpose is direction finding instrument or the

compass. Compass needle is made of magnets. Aeroplanes also determine

direction with the help of compass while flying through the vast sky.

So you have learnt that magnet is used in our everyday life in the electric

fan, electric bell and compass. You will learn about many other uses of

magnet later.

New words in this chapter Natural magnet Direction finding instrument Artificial magnet Electro magnet Horse-shoe magnet

Magnetic substance Attraction Non-magnetic substance Repulsion

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EXCERCISE

Multiple Choice Questions (MCQ)

1. Where is the power of attraction of magnet more?

a. at the north pole of the magnet

b. at the south pole of the magnet

c. at both the south and north pole of magnet

d. equal at all places of the magnet

2. Which of the following is correct in case of repulsion if two rods are

brought near?

a. both rods are of magnetic materials

b. one is magnet, the other is magnetic materials

c. both rods are non-magnet

d. both rods are magnet

3. Those attracted by magnet are called-

a. natural magnet b. artificial magnet

c. magnetic material d. nonmagnetic material

In the light of the following paragraph, answer the questions 4 and 5.

Which will be attracted by iron, nickel, steel, copper and zinc etc. when

they are brought to a magnet, and which will not be?

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4. Which of the above material cannot be artificially converted to

magnet?

a. iron b. nickel

c. copper d. steel

5. Which of the above is used for making electric magnet?

a. steel b. zinc

c. nickel d. iron

Creative Questions (CQ)

1.

a. What sort of current is flowing in the circuit?

b. Explain the activities of diagram B.

c. Explain what change would happen if the use of electric flow in the

circuit ′A′ is made less.

d. Which process of the above will you give preference in case of

making magnet?

Chapter -14

Surface of the earth Land Mass The earth, our living place was initially in a hot gaseous state. Later it became gradually cool and then liquid. After cooling further more it became solid. In this way a hard crust was created on the surface of the earth. During the time of solidification, the crust became uneven in some places due to the contraction of rust of the earth. The upper portion of the earth crust is called land mass and water containing lower portions are called water body.

Fig 14.1: Position of the ocean

Surface of the Earth 183

Five (71%) of seven parts of the earth crust is covered by water and rest of two (29%) builds the landmass. That is, the area of land mass is smaller. This land mass is further divided into several biggest parts. Each such biggest part of land mass is called continent. There are seven continents covering the different areas of the earth crust. These are (i) Asia, (2) Africa, (3) Europe, (4) South America, (5) North America, (6) Australia and (7) Antarctica.

Fig 14.2: Plain, Plateaus, mountain and hill

The land forms of the earth crust

The landforms of the different parts of the earth’s crust are different. Some places it is high, in some places it is low and somewhere there are vast area of the plain lands. Besides, the nature of the lands of the different parts of a country may be different. Land of the eastern part of Chittagong division in Bangladesh is hilly terrain. The land of northwestern part of Rajshahi division is upper plain and those of southern area of Khulna and

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Barisal division are low land. The land deformating natural energies are

earth quakes, volcanic eruptions, heat, winds, rains, snow, glaciers, river,

seas etc. The change of earth crust is the result of their single or

combined effect. In such ways land deformation occurs. On the basis of

land deformation, the earth crust is divided into three categories. These

are (a) Mountains (b) Plateaus and (c) Plains.

(a) Mountain

Very high and far-flung rocky mounds with sharp inclines are called

mountains. Such as the Himalayas.

Rocky mounds comparatively lower and smaller than the mountains are

called the hills. Such as- Sitakund hill of Chittagong. Another landform is

found between two hills is called valley. Classification of mountains Mountains are found in many countries of the world in different shapes and sizes. These mountains have been formed in different ways. The mountains are classified into four groups depending upon their structure and characteristics. On the other hand these mountain after erosion, can be formed another mountain. This mountain is called Erosional mountain. Fold Mountain Certain places of the earth’s crust may subside or gain attitude due to earthquake or land upheaval or shaking. Fold Mountains are created when the layers of rocks get folded and gain attitude.

These mountains are called Fold Mountains as they are created with folds (fig 14.3). The Himalayas of Asia, the Alps of Europe, the Atlas of Africa,

Surface of the Earth 185

the Rocky of North America, the Andes of South America etc. are fold

mountains.

Side Pressure Side Pressure

Side Pressure Side Pressure

Fig 14.3: Fold Mountain

2. Block Mountain

Sometimes the earth’s crust gets

cracked vertically and on side of the

crack subsides. Such subsidence of

the earth’s crust is called fault.

Sometimes the layers of rocks

between two faults create mountain

by uplifting the land due to side or

low pressure. The type of mountain is

called Block Mountain.

Fig 14.4: Block Mountain

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Fig 14.6: Laccoliths Mountain

Again if the land mass is dropped down and as a result a low land mass is

formed then it is called as Rift valley. The salt mountain of the Punjab in

Pakistan and the western mountain of the Deccan in India are the

examples of Block Mountain.

3.Volcanic Mountain

The mountains which are created by the cooled and solid state of lava, ashes, gas etc erupted by the volcanoes are called volcanic mountains (fig 14.5). The Fujiama of Japan, the visuvias of Italy, the Kilimanjaro of Africa etc. are volcanic mountains. Fig14.5: Volcanic mountain 4. Laccoliths Mountain

The high hooted liquid in the inner side of the landmass is called ‘Magma’. Sometimes magma tries to come out from the centre of the earth by gaseous pressure. But these when encounter abstraction make solidification under the earth crust and take the shape of dome. The mountain is formed in such way is called Laccoliths mountain (fig 14.6). The Henry Mountain in Utah State of the America is the example of Laccoliths Mountain.

Surface of the Earth 187

Erosional Mountain

The soft mounds of rocks of the mountain may be eroded by the sun, rain,

wind etc. Then the unevoded mound of hard rock remains as a small

mountain. This hard rock mountain is called Erosional mountain. The

Bindhya mountain of India and the kong mountain of Africa are the

examples of Erosional mountain.

Valley The low land in between two hills or two mountains is called valley. The valleys are formed by four ways. 1. Mountain valley

Lowland between the two mountains is called mountain valley. The

mountain valleys are seen between the folds of the Fold Mountains.

2. Glacial valley Valley in the mountainous area takes the shape of glacial valley due to rubbing action of the glaciers. The hard ice of the glacier moves straight. As such the inclines of their two sides stand very steep like ‘U’. 3. Rift valley The valley created by the depressions between two parallel of the earth’s crust due to earthquakes are called rift valleys (fig 14.4).

4. River valley

The intense flows of the river create deep gorges in their path. Such gorges are called river valleys. Over a long time, the river flows erodes land of both sides. As a result river gorges gradually become wide and shallow.

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B. Plateau or Tableland Extensive elevated plain land above the sea level is called the plateau or

tableland. Usually Tableland is created by land upheaval, weathering and

deposition of lava. Such as- the Decan plateau.

Classification of plateaus Depending upon the location, the plateaus are divided into three

categories, such as (1) Intermountain (2) Piedmont and (3) Continental

plateaus.

(1) Intermountain plateaus

The plateaus, which are surrounded by mountains, are known as intermountain plateaus. The palmer plateaus in Tibet are one of the examples. The palmer is the highest plateau of the world. The attitude of palmer plateau is 4877 metre. For this the palmer is called the roof of the world. (2) Piedmont plateau The mountain is eroded by rain, river flow, glacier etc. The plateau, which is created by this eroded material deposited at the base of the mountain, is known as piedmont plateau. The Colorado of North America is a piedmont plateau. (3) Continental plateau The plateau which is usually surrounded by sea or low land, but these

have no connection with the mountains is called continental plateau.

Indian peninsulas, Arabia, Spain etc are continental plateau.

Surface of the Earth 189

Environments of plateau Trees grow and cultivation of land is carried out in the plateau, which has sufficient rainfall. The people of dry plateau live by rearing livestock. The plateaus are suitable for rearing lambs. Now the cultivation is done by irrigation in the plateaus. C. Plains The vast landmasses, which have almost same level of the sea surface, are called plains. The surface of the plains could be plain or gently sloping or slightly uneven. The plains on the crust of the earth were formed in different ways. Such as- (1) Coastal plain The coastal plain was created due to deposit of sands, stones and various tinny matters from the landmass, which were brought in different ways. Chittagong of Bangladesh and Chenni of India are the examples of coastal plains. (2) Flood plain Deposits of sediments on both sides of the river produce the flood plain during flood. Such as- the coastal plains of the Jamuna in Bangladesh and the Indus of Pakistan both are the examples. (3) Delta plain The delta plains are formed due to deposit of sediments in estuaries of the rivers. Such as the Ganges delta plain of southern part of Bangladesh. (4) Glacial plain Due to the rubbing action of the glacial moraine the uneven landmasses are turned into plains. The prairie in Canada is a glacial plain.

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(5) Loess plain

Loess plains are formed by dust particles carried by winds. Loess plain was created over a vast area in northern China (6) Lava plain The plain, which are formed due to deposit of lava from volcanic eruptions, are called lava plains. The plain with black soil in southern India is lava plain. (7) Pen plain The Pen plains are formed when the natural forces like winds, rains, heat of sun etc such as the pen plains of Siberia erode the plateaus and mountains. Besides plains may be formed in many other ways. Influence of plains Cultivation can easily be done and production of crops also abundant in the fertile plains produced by alluvial deposits. Living is easier and scopes of development of culture and civilization are more in the plain. Men can travel from one place to another easily. Various products such as agricultural products can be transported to other places. From ancients times human living place establish in the plains. It is easier to build up roads, market, ports, cities and industrial plants in the plains. The ancient Egypt civilizations were established in the bank of the river ‘Neil’ due to its much drinking water and vast alluvial deposits. As such 90% population of the world live in the plains.

Surface of the Earth 191

Water area

You have already known that 71% of the total area of the Earth’s crust is contained with water. The whole water area of the world has been divided into five bigger parts on the basis of their location; each part of these is called the ocean. Water areas smaller than the ocean are called the seas. The large water areas surrounded land on three sides is called the bays. Water areas surrounded by land on all sides are called lakes. Ocean There are five oceans in the world. These are – (1) The Pacific Ocean – it is the largest in size and depth. (2) The Atlantic Ocean – this Ocean is second in size and third in depth. (3) The Indian Ocean – it is third in size but second in depth. (4) The Northern Ocean – fourth in both size and depth and (5) The Southern Ocean – fifth in both size and depth. The nature of the bottom of the oceans The land formation of the bottom of the oceans is not similar in everywhere. In some areas there are long stretched coast where water level rise and fall with the tidal movement. The land formation of the bottom of the ocean can be divided into four categories in terms of depth. (1) Continental shelf The parts of the continents remain stretched in the water of the sea from the coastline. The gradual sloping area of the continent immersed in the shallow depth of the sea are known as continental shelves (fig 14.7). The wider the plain in the coastal areas the wider is the continental self. For this reason the continental self in Africa is relatively narrower than that in Europe and Asia.

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Fig: 14.7 Landform of the Ocean

(2) Continental slope

The area beyond the edges of the continental shelf, which suddenly becomes steeply deep and stretches up to the bottom of the ocean are known as the continental slopes (fig-14.7). The depth of the continental slopes varies between 183 meters to 3600 meters. (3) The plains in the deep sea

The area where the continental slope gradually runs to the deep ocean

bottom is called the plains of the ocean (fig 14.7). The depth of ranges of

this area from 3,660 to 5,490 meters.

(4) Deep Ocean troughs

The trenches in the deep ocean bottom are known as deep ocean troughs.

These troughs find over very small areas. The Mindanao trough of

Philippine Islands is the deepest trough and is deep 10,870 meters from

the sea surface.

Surface of the Earth 193

Exercise Multiple Choice Questions (MCQ)

1. The large portion of water body surrounded by land on the three sides is called-

a. gulf b. peninsula c. lake d. delta 2. Which is broken mountain? a. Rocky b. kong c. Bindha d. West Ghat 3. What is the name of the extensive elevated plain land of the sea level? a. Kong b. Plateau c. Glacial plain d. Mountain Henry 4. The prairie of Canada is a- a. plain land b. glacial plain c. erosional pain land d. coastal plain land 5. What sort of valley are Sindha and Ganga? a. mountain valley b. rift valley c. glacial valley d. river valley Creative Questions (CQ) 1.

a. What is the name of the portion in picture A? b. Write two differences regarding the form of the land as shown in B and

C portions of the picture. c. How is the region D created? d. Explain the contribution of portion C in the development of human

civilization.

Chapter 15

Features of Invertebrate Animals Prawn

There are various types of animal in this world. The cow, goat, elephant, horse, humans walk on their legs. Again, robin, crow, stork, kite, fly in the air with their wings spread out. Still other animals like, duck, fish, and so on swim in the water; and snake, crocodile, lizard move on their ventral surface. Some animals, like that of malarial parasite, are so small that they can not only be seen by naked eye. Again, some animals are very big, like the blue whale, which may even weigh 150 tons. On the other hand, some animals do not have a skeleton or vertebral column, while other have skeleton and a vertebral column or notochord. Based on the presence of the vertebral column, the animal kingdom is divided into invertebrates and vertebrates. Chapter six dealt with what are invertebrates and vertebrates. This chapter deals with the invertebrates in greater details. Animals that do not have vertebral column or spinal cord are called invertebrates. For example: earthworm, spider, crab, scorpion, cockroach, prawn, snail, fly, mosquito, and so on. There are more invertebrates than vertebrates in this world. Based on the various characteristics, the animal kingdom is divided into ten phyla, nine of which are invertebrates.

Common features of invertebrates Like vertebrates, the invertebrates have some common features, which are enumerated below. 1. Invertebrates do not have vertebral column or spinal cord. 2. They range from unicellular to multicellular organisms 3. Usually their organ of respiration is skin 4. Their alimentary canal is simple

Features of Invertebrate Animals 195

5. Some invertebrates do not have blood, or else have blood that is red

and have blood vessels

Brief description of the invertebrates: Nine out of the ten phyla, into

which the animal kingdom is divided, are the invertebrates. The names of

the phyla along with a brief description of their main features is given

below.

Name of Phyla

Animals Includes

Common features

1. Protozoa Amoeba, malarial parasite

These are unicellular animals, and were the first ones to be created. They live individually or in groups. Some, like malarial parasite and micro-organism causing dysentery, live in other organism as they are parasitic in nature.

2. Porifera Spongilla These animals live in water. They contains numerous perforations on their body. Water and nutrients enter the body through the pores. Commonly known as "sponge". Most remain stationary in one place.

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3. Cnidaria Coral,

jellyfish, hydra

These are marine animals. They have a hollow body, known as coelenteron. Has a mouth but no anus. This opening used to take food and excrete waste. Has six to ten tentacles that surround the mouth.

4. Platyhelminthes or flatworms

Tapeworm and flukes

They are flat soft-bodied, and usually parasitic in nature. Has a mouth but no anus.

5. Nematoda or roundworms

Hookworm, trichina, filarial nematodes, whip worm

Roundworms are cylindrical, tapering animals with simple bodies. Have both mouth and anus. Many live as parasites in plants and animals, where they may cause disease.

6. Annelida Earthworm, leech

These are soft bodied animal with mouth and anus. The body is divided into ring-like segments.

7. Arthropoda Prawn, crab, centipedes, cockroach, fly

The body is covered by a durable shell. It has mouth and jaws. Has a pair of articulated legs, and compound eyes.

8. Echinodermata Starfish, sea urchin, sea lily

These are marine animal. The body has numerous spiny projections, and has a body tube.

9. Mollusca Snail, oyster, octopus

These are soft-bodied, and are covered by a hard external shell. Have large muscular organ used for locomotion called the foot

Features of Invertebrate Animals 197

Prawn/ Shrimp: An Invertebrate Animal

Prawn, common name applied to numerous species of shrimp-like, ten-legged crustaceans. There are over 60 species in the world. The most notable among the species is the golda prawns. Bangladesh has earned a place for itself in the world for cultivating prawn in fresh water. Currently, prawn is being cultivated in ten southern districts of Bangladesh. Though prawn is commonly called a fish, it is not a fish. The prawns vary in size. They live in the fresh waters of pond, rivers, canals and lake, and also in the salty sea waters. It has a long, serrated rostrum, or beak, that projects from the shell. A exoskeleton that is segmented only from the outside, covers the body. The body is divided into two parts–a fused head and thorax the cephalothorax, and abdomen. A hard covering called carapace covers the head and thorax part. The shrimps have thirteen pairs of appendages on the cephalothorax. The abdomen contains six pairs of appendages. Some of the appendages may have pincers. These appendages have various function, like sensory, swimming, feeding, and walking. It has a long, serrated rostrum, or beak, that projects from the head in the midline. This is used as a defence organ. The appendages in the head is called antennae, which works as sensory organ. On either side of the rostrum, the head usually has a pair of compound eyes.

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The abdomen is formed of six segments. A tail portion–telson–bears the anus, an elongated opening that is occasionally used in swimming. Abdominal appendages may be used in locomotion but frequently have other functions, such as respiration. A pair of excretory openings that serve as kidneys are located near the antennae, or the second appendage. This is the organ of excretion of waste products. The shrimps can live in both fresh and saline water. They usually crawl along the bed of the water bodies, and can swim from one place to another too. They do not move much during the daytime, at night they look for their food. Habitat, diet, and growth: Shrimps eat both organic and inorganic food. Many of them eat small plants and animals, such as corals, insects, small snails, tadpole take, small fish. Many strain take small particles of organic and inorganic food from the water. The mouth parts is in the rostrum, which is used to take all sorts of food. The exoskeleton protects the body maintains the shape of the body, and protects it from external injury. The exoskeleton does not grow, so at intervals, the shrimps shed the exoskeleton and grow a new one. The shrimp grows during the time between shedding of one exoskeleton and the growth of the new one, in other words the growth is not continuous.

Features of Invertebrate Animals 199

Economic Importance of Shrimps

1. Shrimps are a source of protein which is very tasty.

2. There is a great demand of shrimp in the foreign countries.

Bangladesh is earning huge amount of foreign exchange through

export of shrimps. Hence, it is called the silver crop of Bangladesh.

About 7.6 percent of the foreign exchange earned by Bangladesh

comes from the export of shrimps.

3. Lots of people are engaged in the cultivation of, and businesses

related to

shrimp. This serves as employment for them. So this industry helps to

reduce unemployment in the country.

4. The shrimp industry has the potential to employ more people and

further reduce unemployment, in addition to bringing in more foreign

exchange.

New Words Learned in this Chapter

Bones Parasite Phylum Tentacles Appendages Telson Cephalothorax Excretory opening Segmented Anus Jointed Malarial parasite Golda Antennae Bagda Carapace Vertebral column or spinal cord Rostrum Gills

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Exercise Multiple Choice-,.Questions (MCQ) 1. Which phylum does the shrimp belong to?

a. Porifera b. Arthropoda

c. Annelida d. Mollusca

2. How many appendages are there in thoracic region of Shrimps -

a. 11 pairs b. 13 pairs

c. 16 pairs d. 19 pairs

3. The name of saw-like organ at the front of the head of the shrimp is

a. carapas b. telson

c. rostrum d. Appendage

4. Applicable in case of shrimp

i. fish type animal

ii. delicious protein food

iii. Though the body is covered with hard coating; their eyes

are of simple ' nature.

Of the following, which is correct?

a. i b. ii c. i and iii d. i, ii and iii

Features of Invertebrate Animals 201

Creative Questions (CQ)

figure

1. a. Which phylum do the shrimp belong to?

b. Shrimp is not fish. Explain

c. Draw a diagram of such an animal having similar

characteristics with the shrimp and label the two portions.

d. Of the two portions of the shrimp marked A and B, which one

is more important? Discuss.

Chapter 16 Human Body: External Structure, Skin,

Muscles, Bones (Skeleton)

External Structure

The human body consists of head, neck, trunk, upper limbs and lower

limbs. The trunk can be divided into three parts: the thorax or chest, the

abdomen, and the pelvis or lower end of trunk associated with hip. Hairs

cover the external surface of the body. The major organs, seen from

outside, are limbs, eyes, ear, nose, and so

on. Organs are formed of groups of tissues.

Tissues are again formed of groups of cells.

The origin of these cells and their function

are same. Integrated function of two or

more organs form systems. For example, the

digestive system digests food, the skeletal

system gives the body its shape and form.

There are several other systems in the body,

the coordinated outcome of which is human

being as a whole.

The skeleton forms the structural framework of the body. On this

framework attached are the muscles which together give the body its form

Human Body: External Structere, Skin, Muscles, Bones (Skeleton) 203

and shape. The muscles are in turn covered by skin. All these together

give the external structure of the human body. Besides, cartilage, blood,

nerves all contribute to the buildup of the body.

Skin

The skin forms a continuous

layer over the surface of the

body. The skin consists of two

main layers, an outer epidermis,

and an inner dermis.

Epidermis: This is the outer layer of the skin. The skin is thickest on areas of the body that regularly rub against objects, such as the palms of the hands and the soles of the

feet; it is thin on the lips and other parts of the skin. Specialised parts of the skin are the nails and hairs. This layer also contains hairs. Dermis: The dermis is thicker than the epidermis. Blood capillaries, nerves, lymphatics, apocrine sweat glands, eccrine sweat glands, sebaceous glands, and hair follicles are present in this layer. The eccrine sweat glands are more numerous in the palm and sole. General Functions of the Skin: 1. It protects the tissues beneath from mechanical injury, cold, heat,

ultraviolet rays in sunlight and drying. 2. It forms a barrier that helps prevent harmful microorganisms and

chemicals from entering the body

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3. The skin also helps to regulate body temperature through sweating 4. It excretes some waste products 5. The melanin in the skin protects the body from the harmful ultraviolet

rays of the sun.

Special Functions of the Skin: The dermis contains numerous different types of specialised nerve cells or sensory receptors at the base of the hair follicles. These sensory receptors detect various stimuli, including pain, heat, cold, itch, and pressure. Sensory receptors are more dense in hairless areas, such as the fingertips and lips. This makes these areas especially sensitive, and one can understand the texture of the surface; the form, liquid or solid; and the shape of objects.

Scattered in the epidermis are a dark pigment called melanin. This pigment gives colour to the skin, and protects it from the sun’s ultraviolet rays. Differences in skin colour among people of different race is due to the differences in the amount of melanin in the skin. Melanin is more in dark skinned people particularly in those who live in hot and humid climatic conditions. Just below the dermis is a layer of fat. This fat gives the body its external contours. The sweat gland of the skin produce sweat, which is a mixture of water, salt, and small amounts of metabolic waste products. If dust and dirt collect on the skin, the openings of the sweat glands are blocked, this cause retention of waste product in the body, and leads to certain skin diseases, such as infection. Hence, one should take daily baths to keep the body clean.

The skin also helps to regulate body temperature. The capillaries in the skin dilate during summer and constrict during winter. During summer the blood flow through the skin is more, more blood gets the opportunity to give off its heat to the surrounding, and the body cools down. During winter, the blood flow through the capillaries is less and so less heat is lost

Human Body: External Structere, Skin, Muscles, Bones (Skeleton) 205

and the body is kept warm. In fact, the skin helps to maintain a uniform

temperature in the body, whatever is the temperature of the surrounding.

Muscle

The bones of the skeleton are covered by the muscles, which in turn is covered by fatty tissue and skin. Muscle characterised by the ability to contract, usually in response to a stimulus from the nervous system. The muscle covering the bones is the skeletal muscle or flesh. It is reddish in colour, the muscle cells are arranged in layers. The end of the muscle form thick white bundles before attaching to the bones. There is about 75 percent water in the muscles. In general, the muscles contract as required and then return to its original state. This contraction and relaxation of muscles help the body to move from one place to another, and also to carry out the function of respiration.

Types of Muscular Tissue: Some of the muscles in the body can be brought into action at one's will or consciously. For example, muscles of the limbs. There are some muscles that are not under one's voluntary control. These muscles work on their own, for example, the muscles in the intestine and stomach. Basically, muscles are of two kind-voluntary and involuntary. * Voluntary muscle: When the elbow is flexed or bent, the muscles in the front of the upper arm contract and pull the forearm upwards. Similarly, when the elbow is Fig 16.3: The contraction and

expansion of voluntary muscle

206 General Science

extended or straightened, the muscles in the back of the upper arm contract and at the same those in the front relax and so the elbow is extended. This bending or straightening of the elbow is under one's control or wish. Muscles that respond to conscious effort, that is, they can be moved at will, are the voluntary muscles. Most of the muscles in the body are voluntary in nature. They are attached to the bones of the skeleton and so they are also known as skeletal muscles. They help in movement of different parts, and also in locomotion.

* Involuntary muscles: The digestive tract has the responsibility to transport the food from mouth to anus. This job is done by the help of muscles in the walls of the alimentary canal, by a special movement called peristalsis. The muscles of the alimentary canal contract and relax to propel the food forward. But the action of this muscle is not one's control. The propulsion of food cannot be stopped at will at any point. Such muscles that are not under one's conscious control are called involuntary muscles. The muscle in the alimentary canal are called smooth muscle.

There is another type of involuntary muscle, the cardiac muscle. This muscle forms the wall of the heart. It contracts and relaxes at its own rhythm and thus propel the blood throughout he body.

How muscles can be strengthened: The muscles of the neck, limbs, abdomen all work in different ways. The more these are used the healthier

Human Body: External Structere, Skin, Muscles, Bones (Skeleton) 207

and strong they are. Those who are sedentary workers, do not have to do physically exhaustive work, should exercise to keep themselves fit and strong. Swimming is a very good exercise. It brings all the muscles of the body into action and thus keep all parts active. Function of the muscles: 1. It gives the body its shape and contour, and help to move the bones 2. Help in movement and locomotion 3. Protects the internal organs 4. Cardiac muscle helps to circulate the blood throughout the body Skeleton Children frequently play with dolls. These dolls may be made of clay,

cotton, jute fibre. To these dolls, first two strong sticks are tied together such that they cross each other. This forms the framework over which clay, cotton or jute are moulded to give the required shape of a doll. It is then coloured and made attractive for children. Similarly, human body has a framework too, which is formed by the bones joined together as the skeleton. Muscles, fat and skin cover this skeleton.

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Thus, skeleton is the rigid or semirigid structures supporting the soft tissues of an animal's body and providing leverage for muscular action. In vertebrates, such as humans, the skeleton is known as the endoskeleton as it is formed within the body.

Function of skeleton: 1. Skeleton provides the framework, and supports the soft tissue.

Without a skeleton the body would have been a mass of flesh only 2. It helps humans to stand upright and move about. 3. It affords special protection to highly important structure and organs.

For example, the skull protects the brain, the thorax protects the heart and lungs.

4. It bears the weight of the body. The weight of the different parts pass through different bones and finally through the lower limb to the ground.

5. It provides attachment for muscles so that movement may take place at the joints.

6. The bones are a storehouse for minerals such as calcium and phosphorus.

Human body is formed of 206 big and small bones. The bones are of different size and shape. Some are long, some short, again some are flat. The longest bone is femur, and the smallest is stapes, a small bone in the middle ear. According to the arrangement the skeleton is made of four main parts–the skull, trunk, upper and lower limbs.

Skull: The skull is a bony covering that protects the brain from external

injury. In it lodges the ear, nose, and eye.

Trunk: The middle part consisting of the vertebral column, and the ribs

and their cartilage–the thorax. The vertebral column consists of thirty-

Human Body: External Structere, Skin, Muscles, Bones (Skeleton) 209

three small bones–the vertebrae–attached to one another. The vertebral column keeps the body upright, and bears the weight of the skull.

Thorax: This is like a cage. It is formed by the vertebral column behind and twelve pairs of curved ribs that pass to front and attach to the sternum in front. Thorax protects the heart and lungs.

Upper and lower limb: The upper limb is formed of 64 bones, and the lower limb is formed of 62 bones. They help in movement

The bones join one another to form the complete skeleton. The regions of union between bones or cartilages is the joints. Joints are two types: moveable and immovable.

In moveable joints: the bones forming the joint can move against each other. For example, elbow joint, wrist joint.

In immovable joints: the bones are fused together and so cannot move against each other. For example, the skull bones.

Structure of bone: The bones are formed of bone cells or osteocytes. The bones are very strong. It is composed of calcium and phosphorus, along with water. The ends of the bones are covered by cartilage, which are formed of softer tissue than bones. The tip of the nose, the pinna of

external ear are formed of cartilage. Cartilage is softer, more elastic, and more compressible than bone. The skeleton is formed of bones and cartilage. The bones are covered by the periosteum, and inside it are the blood vessels and nerves. At the two ends of long bones are a region of soft bone with pores. This is the spongy

210 General Science

bone. In the central hollow of the long bones is the bone marrow.

Between the spongy bone and the cartilage is the cortex. It is the hardest

part of bone.

New Words Learned in this Chapter

Skin Involuntary muscle Thorax Joints

Melanin Cardiac muscle Vertebral column Upper limb

Sweat gland Skeleton Bones Lower limb

Voluntary muscle Skull Cartilage Bone marrow

Exercise

Multiple Choice Questions (MCQ)

1. What is present in the epidermis? a. hairs b. sebaceous gland c. apocrine sweat gland d. ecorine sweat gland

2. On which muscle of the organ we have no control? a. of hand b. of jaw c. of leg d. of intestine

3. Which salt is more available in bone? a. calcium b. sulphur c. iron d. phosphorous

4. Cartilage is present in which part of the bone? a. inside b. outside c. at the end d. in all places

Human Body: External Structere, Skin, Muscles, Bones (Skeleton) 211

From the diagram below, answer the questions 5 and 6.

figure

5. The diagram is - a. a bone of upper part b. a bone of lower part c. of an ordinary bone

Of the following which is correct? a. i and ii b . i and iii c. ii and iii d. i, ii and iii

6. Applicable in case of diagram above i. composed of innumerable bone cell ii. there are calcium and salt in it iii. there is bone marrow in it

Of the following, which is correct? a. i and ii b. i and iii c. ii and iii d. i, ii and iii

Creative Questions (CQ)

1.

fig: A fig: B

212 General Science

a. What type of muscle is (shown) in fig: A?

b. How does the muscle as shown in fig: A work?

c. The muscle shown in fig: B is a special type of muscle. Explain.

d. What would happen if there would be one type of muscle instead of

two? Discuss.

2.

Fig: Skin

a. What is the name of portion-A?

b. Why is pain not felt if the portion-B as shown in picture is cut off?

c. Explain the activities of portion C of the body.

d. Discuss the relation between the two portions A and D as marked in

the diagram.

B

A

D

C

Chapter -17

Health Rules: Skin Diseases

Human disease is any harmful change that interferes with the normal appearance, structure, or function of the body or any of its parts. Many disease causing micro-organisms are present in the environment. These micro-organisms enter the body through food, water, respiration, hands, legs, even skin, and cause disease. Diseases like cholera, diarrhoea, dysentery, helminthiasis affect the abdomen, and so are called abdominal diseases. Diseases like scabies, eczema, ringworm, leprosy affect the skin and so are called skin diseases. Scabies, ringworm, and other skin infections are very contagious. These conditions are not very serious and debilitating so they are often not given importance. But no disease should be ignored. All diseases should be treated with equal importance.

A. Scabies Causes of Scabies: Scabies is a contagious skin disease caused by small parasites called itch mites that infest the outer layers of the skin, where their waste products cause irritation. Such mites are usually transmitted by close body contact with another person. Scabies is particularly prevalent where there is overcrowding and unhygienic conditions. The most common itch mite is the female of Sarcoptes scabiei. The mite burrows into sensitive folds of the skin, such as between the fingers or in the genital area. It lives about six weeks and lays 40-50 eggs at a time in the burrows which mature in a week; a new generation is produced about every three weeks. Intense itching begins about one month after the initial infestation, and the

214 General Science

resultant scratching may lead to secondary bacterial infections. Also itching of the affected parts allows some of the eggs to lodge in the nails, and when the same nail is used to itch another place, the eggs may lodge there, and thus spread the disease. Children and old people are more affected by scabies during winter season.

Symptoms of scabies: Scabies is a distressing and embarrassing condition. The main symptom is itching. This usually occurs in the interdigital or between the fingers, wrist, elbow, axilla, around the umbilicus, and upper thigh. The itching occurs more at night, because in the warm environment of the bed, the mite moves around more. Itching and scratching may injure the skin which may facilitate secondary bacterial infections causing fever and body ache.

Mode of spread of scabies: Close bodily contact with scabies infested person allows the itch mite to pass from the affected person to the healthy one. Besides, the articles of daily use such as bed, clothes, plate, towel of an affected person may also contain the mite. Using these articles too, may spread the disease to a healthy person. The nails of the affected person may also contain the mite, and when the person handles articles used by other healthy person, then the disease may spread.

Prevention: The following preventive measures need to be taken to prevent the spread of the disease from an affected person to a healthy one–

1. Not to come in close contact with a person affected by scabies 2. The articles of daily use of the affected person should be kept separate 3. The articles of daily use should be washed with soda, or dried in

bright sunlight 4. The nails should be cut short 5. Treatment of the affected person

Health Rules: Skin Diseases 215

Treatment:

1. The patient should be scrubbed and bathed with warm soap water.

2. After drying the body, a solution of 25 percent benzyl benzoate mixed

with two parts of water is applied all over the body from neck down to

the toes. This solution is to be applied on three consecutive days. On

the fourth day, the patient is scrubbed and bathed with soap water. At

the same time, all articles used by the patient should be washed with

soda, and dried in sunlight.

3. To reduce the itching, chlorpheneramine tablets may be taken orally

thrice a day. If there is secondary bacterial infection then penicillin

or ampicillin group of medicine, in appropriate dose for the age of the

patient, should be taken.

4. Physician's advice should be taken.

B. Ringworm

Ringworm is a infection of the skin, hair, or nails caused by various kinds of fungi. The infection spreads from one person to another by close contact. it is a contagious disease. It is more common among children.

Cause of ringworm: Ringworm is caused by parasitic fungi that belong to the genera Trichophyton, Epidermophyton, and Microsporum.

Symptoms: Ringworm tends to infect moist areas of the body, such as the groin, between the toes, and under the arms. The affected area usually becomes inflamed and itchy, because of sensitivity to the fungus, or a secondary infection by bacteria. Ringworm on the limbs, trunk, and face causes raised circular patches, which heal in the centres out as the patches widen. The condition derives its name from this circular pattern.

216 General Science

Mode of spread: The pus discharged from the ringworm infection

contains fungus. This pus comes in contact with the articles used by the

patient. These articles when used by a another person, the healthy person

will be infected too. Close contact is also a mode of spread. Sharing

clothes, combs, or towels may result in the spread of the infection.

Prevention:

1. The articles if daily use of the patients should be washed everyday with soda water

2. After drying up the body, 25% Benzyl benzoate lotion with 2 portion of water should be applid from just below the throat to the whole body consecutively. After three days, a fresh bath is to be taken with soap. With this, the used clothes of the patient must be washed with soda and dried in the sun

3. In case of itching, Chlorpheneramine tabled should be taken thrice in a day. And if the germ is infected then tablets from penicillin or Ampicillin group have to be taken according to age.

4. To follow the physicians’s advice for treatment. Treatment: 1. If the ringworm is on the scalp, the hairs should be shaved and salicylic

acid applied on the skin twice a day till the hairs re-grow. 2. To apply iodine, or ointment containing salicylic acid, benzoic acid

should be applied on the skin in case of ringworm on other parts of the body.

3. If the ringworm is in the nail, then the dead part of the nail should be removed and tincture iodine applied regularly. The modern drug griseofulvin may be taken orally to cure the disease.

Health Rules: Skin Diseases 217

C. Leprosy Causes of Leprosy: Leprosy is a chronic infectious disease caused by the bacterium Mycobacterium leprae. Leprosy has two main forms, known as tuberculoid and lepromatous disease. In tuberculoid leprosy, the skin lesions are few and small, with only a few bacteria present in each, and is less infectious. In lepromatous leprosy, which is the more infectious and severe form of the disease, the lesions may be much more widespread and contain many leprosy bacteria. Leprosy is neither caused by curse, nor is a genetic disease.

Mode of spread: Nasal droplets released when a person with untreated lepromatous disease sneezes may contain large numbers of leprosy bacteria. These released bacteria could infect a new person who inhales the droplets, or the bacteria could invade through a cut or abrasion on the person’s skin. Scientists now know that leprosy is not easily transmitted, but they are still not sure how it is spread from person to person.

Symptoms: As the disease is slowly progressive, the symptoms develop gradually. In the early stage there may be slight fever, body ache, and weakness. As lepromatous leprosy progresses, hard nodules and folds of skin may appear on the skin specially in the face, nose, ear lobule. In some places the skin may be thickened. In places the skin becomes pale or reddish, and there is lack of sensation in affected areas. Disfigurement of various organs is one of they symptoms of leprosy. Such as, curved fingers and toes, emaciated muscles of the hands, wounds on limbs or other places, inability to close eye lids, weakness of limbs, paralysis of specific parts of the body etc.

Signs: Patches of skin with lack of sensation, and the presence of hard nodules may lead the physician to suspect leprosy. Presence of the bacteria in tissue scraping and fluid, confirms the diagnosis.

218 General Science

Treatment:

With modern treatment leprosy is a curable disease. In Bangladesh, free treatment for the disease is given at all Thana health facilities and leprosy hospitals across the country. There are three leprosy hospitals in the government sector. These are:

1. Institute and Hospital for Leprosy Control, Mohakhali, Dhaka 2. Leprosy Hospital, Nilphamari 3. Leprosy Hospital, Sylhet

Besides, eleven non-government organisations are working in the area of leprosy control and treatment. Multi-drug therapy is currently used as specific treatment. These drugs must be taken for a long period–six months to two years.

D. Care of the Skin The whole body is covered by skin, which protects the soft parts and organs. It regulates temperature through dissemination of excess heat from the body. The skin is also a sensory organ by which one can understand the heaviness or coldness of an object. There are minute opening of sweat glands and hair follicles on the surface of the skin. Some waste products are excreted through these openings. The dirt and dust from the environment settles on the body and with the sweat forms a layer, which blocks the openings on the skin and leads to accumulation of waste products in the body. This layer should be cleaned everyday. One should take bath everyday with clean water, and scrub the body with a towel to clean and open the pores. Soap should be used at least twice a week. It is better to use a toilet soap rather than cloth washing soap. The washing soap is more alkaline and may be harmful for the skin. Besides daily bath, one should wash the hands and face with clean water at least three to four

Health Rules: Skin Diseases 219

times a day. It is necessary to keep the towel and other articles as bed linen and clothes clean too. New Words Learned in this Chapter Scabies Benzoic acid Microsporon Vesicle Tissue Salicylic acid Trichophyton Mycobacterium Iodine Ampicillin Sarcoptis Ointment Fungus Benzyl benzoate Griseofulvin Chlorpheneramine

Exercise

Multiple Choice Questions (MCQ) 1. Which is the function of the skin?

a. to permit to grow leprosy b. not to allow sweat through the pores of the hair c. to protect from external injury. d. to keep body diseaseless

2. Washing soap should not be used in the body because - a. there is no scent (fragrance) in this soap b. there is no formation of lather c. the amount of fat is more in this soap d. the amount of base is more in the soap

3. Oral medicine for ringworm is - a. gryseofulvin b. riphampicine c. tetracycline d. iodine

4. Grain like pimple and fibre are seen a. if leprosy grows b. if one suffers from skin diseases c. if one suffers from ringworm d. if one suffers from vomiting

5. The symptom of leprosy is - a. Wheel-like swelling on the skin b. to become hands and legs weak c. to suffer from itching d. nodules between two fingers

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6. The symptom of ringworm is i. there grow pimples and fibre ii. drying of muscles iii. swelling of skin around ring or spot

Of the following, which is correct a. i b. i and ii c. i and iii d. i, ii and iii

Creative Questions (CQ) 1. From Dhaka Sohel came to visit his grandfather’s house during summer vacation. He spent 7-8 days there by playing with his cousin. But after his return to his residence, his mother saw that he had been suffering from itching at his hands and legs. His mother identified it as skin disease. a. What is skin disease? b. What would be the name of the skin disease from which Sohel has

been suffering and why will it be so called ? c. Explain the causes of Sohel’s skin disease. d. Discuss how Sohel will be quickly recovered from this disease. 2. Anis has been suffering from fever for about a month. Then he found

that there were black spots on different parts of his body. There were somewhere ulcer on his skin and his body became weak. His neighbours identified it as leprosy and prevented them from mixing with him.

a. What is called leprosy? b. Why leprosy is called infectious disease? c. Explain the justification of the above symptoms of leprosy grown

on the skin of Anis. d. Give your opinion on the behaviour of neighbours with Anis.

Chapter-18

Food and Nutrition

No living organism can survive without food. Food is indispensable for any organism to remain alive. Taking food is an instinct nature of all organisms. Food supplies energy for work to all organisms. In other words it is the source of all energy. Food that we take is digested and stored as energy. When we work a part of this stored energy is spent. We compensate this loss by taking food. So we can say food is the secret of keeping good, strong and disease free health. It also helps rebuilding and growth of the body. You learned in you previous class that whatever you take to keep the body healthy and strong, is called food. Of course this statement is not totally correct. Man cannot take everything. Whatever he takes is not always digested properly. So materials taken and digested; compensate loss or decay and help growth of the body; and that produce heat and keep the body disease free, is called food. From the above discussion we now understand that the main aim of taking food is to keep the body strong and workable. Health of a body depends on the process of nutrition. We may take nutritious food but it will not help us keeping good health if the nutrition process is not proper. So we must know what nutrition is. The process by which the food is digested, transformed into energy and finally contribute in compensation of loss or decay, growth, production of heat and keep the body disease free is called nutrition. Necessity of Food: Food is necessary for continuing different activities in living body. In short of these activities are mentioned below-

222 General Science

1. Food is necessary to compensate decay and for the growth and

nutrition of the body.

2. To satisfy appetite, food is necessary.

3. Loss caused by activities of the body is compensated by taking food.

4. Foods save the body from diseases.

5. Food keeps the body healthy and fit.

Kinds of food:

Food are of three kinds; such as Carbohydrate, Protein and fat

Constituents of food are of six types, such as-

a) Carbohydrate, b) protein, c) fats and oils d) Vitamin e) Mineral salts

and f) Water.

A) Carbohydrate:

Flour, Rice, Potato, sugar etc are carbohydrate foods.

Function:

1. Carbohydrate food supply energy for different activities and produce heat.

2. Cellulose type Carbohydrates help in

clearing bowels. 3. Taking high amount of

carbohydrate may result in fatty body. So it may

cause heart diseases. Carbohydrate deficiency cause loss of weight, enhance appetite and weakness of the body.

Fig 18.1: Starchy foods

Food and Nutrition 223

B) Protein

Fish, meat, egg, milk products such as cheese, card (doi), posset (sana),

beans, pulses etc.

Functions

1) Its functions are growth and

compensation of decay of the body.

2) To produce energy.

3) To produce antibody for disease

resistance.

Protein deficiency causes weakness of

muscles. So ultimately it results in fall

of working ability. It also causes anemia

and indigestion.

C) Fats and Oils

Ghee, butter, oil, fats etc. are fatty foods.

Functions

1) It increases production of heat and

energy for work.

2) It helps to save carbohydrate loss.

3) It helps supply of vitamin A, D, E and K.

4) It increases beauty of the body

5) It resists skin diseases.

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D) Vitamins These are few constituents of food which are essential for the body in a very small dose. These are called vitamins. Depending on the solubility, it is of two kinds:- 1) Water soluble vitamins such as vitamin-B complex and vitamin-C. 2) Fat soluble vitamins-vitamin A, Vitamin D, Vitamin E and Vitamin K. Water soluble vitamins Origin of vitamin B complex: This complex includes: Vitamin B1 : It is found in aleuronic layer of rice kernel, germinating Gram seed and fresh flour. Vitamin B1 deficiency causes Beriberi disease. Vitamin B2 : Milk, egg, liver, kidney, various cereals, vegetables etc. contain vitamin B2. Its deficiency causes ulceration at the joining of two lips, cataract, hair fall etc. Vitamin B6 : Liver, kidney, egg, various cereals, vegetable etc. contain vitamin B6. Its deficiency causes loss of weight, nervous breakdown and anger Vitamin B12 : Liver, egg, vegetable etc. are the source of vitamin B12. It is now extracted from a particular mushroom. Its deficiency causes anemia. Vitamin C: It is found in all citrus fruits (like Lemon, Orange, Shaddock etc), Tomato, Mango, Guava, Amloki, Pine apple, Papaya, Cabbage, Cauliflower, Lettuce, Spinach, germinating Gram seeds etc. Its deficiency causes scurvy disease, bleeding from capillary below the skin. The gum swells

Food and Nutrition 225

Up and finally bleeds. The bone and teeth become deformed. Healing of wounds is delayed. Fat soluble Vitamins: Vitamin A: Milk, butter, egg, fish, cod fish, carrot, leafy vegetable. Yellow fruits etc. contain vitamin A. Its deficiency causes night blindness. Vitamin D: Egg, milk, food made from milk, fish oil etc. contain Vitamin D. Its deficiency causes rickets in children. Vitamin E: Green vegetables, Spinach, Cabbage, Cauliflower, Lettuce etc. contain this vitamin. Its deficiency causes fall in reproductive ability and miscarriage. Vitamin K: Cabbage, Tomatoes, Soybean, Spinach etc. contain vitamin K. Its deficiency hampers coagulation of blood. E) Mineral salts: Mineral salts are indispensable for building and regulating internal functions of the body. Salts of

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Sodium, calcium, phosphorous, iodine,

iron, copper, chlorine, sulfur etc. are

found in liver, milk, egg, fish, green

vegetable and fruits. Goiter is the

cause of iodine deficiency. Iron

deficiency causes anemia and calcium

deficiency causes rickets in children.

Water Water is an important constituent of food. Every food contains some water. Drinking is a method of fulfilling demand of water. Activities like swallowing, digestion and absorption of food needs water. It maintains fluidity of blood. It helps in excretion process to expel body wastes. Two third of our body weight is water. Water deficiency causes constipation and hampers metabolic activities of the body.

Balanced diet and unbalanced diet: Balanced diet: Food that contains carbohydrate, fat, protein, vitamin, mineral salts and water in quantities optimum for the body is called balanced food. Milk is a balanced food.

Any food fulfills the appetite. But if all the essential constituents in ideal quantities are not found in the food it cannot help keeping healthy body. If the food is deficient in any type of constituent, it may cause any of the deficiency disease. The body will become nonfunctional. So for normal growth and functioning of the body, balanced diet (food) is essential.

Food and Nutrition 227

Unbalanced diet: The food where one or more essential constituent is missing totally or partially is called unbalanced food. In our country most of the people take unbalanced foods. The common man΄s food is almost totally carbohydrates. This food is deficient in fat, protein, mineral salts and vitamins in proper quantities. It causes the disease called anemia. How to get cheap balanced foods 1. By acquiring common knowledge about food and nutrition. 2. By preparing a list of balanced foods affordable for the family. 3. By selecting less costly balanced foods from the list. Bad effects of taking rotten, adulterated and staled food: If the cooked foods are not properly covered dirt may fall on it. When cockroach fly and rats feed upon any food; microbes get into it. And the food is polluted. If cooked foods are not properly preserved it becomes decomposed. When these foods are taken it may cause diseases like diarrhoea, cholera, dysentery etc. Parasitic microbes come with dust and agents like cockroaches, rate etc. Normally the food is spoiled by bacteria or fungal type of microbes. Dishonest businessmen add various low graded food or inconsumable materials with food for more profit. This is called adulteration. When consumed these foods may cause diarrhoea, cholera, dysentery, constipation etc. It causes loss of health or even death. Necessity of food preservation: Storage of food without rotting or change of any nature and keeping the Quality of food intact is called food preservation. The aim of food preservation is given below:

228 General Science

1) To prevent the decomposable food from rotting and keeping them fresh. 2) To ensure availability of food for future use. 3) To enhance economic condition of the family and the country. 4) To bring variety in the food list of the family. 5) To earn foreign exchange by exporting preserved foods. 6) To prevent Waste of food materials. Process of food preservation: Usually the food can be preserved in the following ways: 1. By drying in the sun: Paddy, rice,

fish etc. are preserved in this process.

2. By applying low temperature: Food can be preserved in cold storage, refrigerator or by ice blocks.

3. Using preservatives: Using preservatives like vinegar, salt,

sugar etc. Fish, olive, pea, shrimps etc. are preserved in this method.

4. Preserving in a can: When cooked in high temperature it can be preserved in metallic can. 5. Pasteurization: It is also a process of preservation. When milk is

boiled at 1400 F to 1600 F for 15 to 20 minutes; germs of cholera, typhoid etc. are killed

Food and Nutrition 229

New words of this chapter: Nutrition Protein Carbohydrate Vitamins Beriberi Anemia Scurvy Goiter Calcium Iodine Constipation Diarrhoea Preservation Refrigerator Cold storage Pasteurization

Exercise

Multiple Choice Questions (MCQ)

1. Which vitamin is soluble in water? a. Vitamin A b. Vitamin B c. Vitamin C d. Vitamin K

2. What amount of our body is water? a. one third b. two third

c. one fourth d. two fifth 3. Which one plays the main role in producing energy of the body?

a. hilsa fish b. chicken c. potato d. sweet pumpkin

4. For want of fatty food of the babies- a. the body weight decreases b. the skin becomes rough c. the preparation of antibody is obstructed d. constipation disease occurs

5. As a result of pasteurization the food materials - a. remains cold b. becomes free from germs c. remains dry

Of the following which is correct ? a. i b. ii c. i and ii d. i, ii and iii

230 General Science

Creative Questions (CQ)

1.

a. What sort of ingredients of food remains in vegetable? b. Explain the necessity of food marked-A. c. Explain how the body weight is increased by food marked-D. d. Give your opinion on the suitability of food as shown in the picture

as balance diet 2. Basu’s house is (situated) at Barisal. As people of the region, they eat

marine fish relatively more. One day Basu went to Rangpur with his uncle. He saw some people whose side of the throat was somewhat swollen. He cannot remember whether he has seen such type of people in Barisal. a. What is the name of the disease Basu saw? b. Why do the people of the north generally suffer much from this

disease? c. Explain how the people of this locality can be made free from such

disease. d. Explain why Basu did not see such disease in Barisal.

A B

C D

Chapter 19

Population and Natural Environment

Population Situation in Bangladesh Bangladesh is a small country with an area of 1,47,570 square kilometre.

It is a highly populated country, but previously it was not so populated. A

close look at table-1 given below will give an idea of the population in

the last sixty years.

Table-1

Year Population

1941 4 crore 20 lakh 1951 4 crore 19 lakh 1961 5 crore 52 lakh 1974 7 crore 64 lakh 1981 8 crore 99 lakh 1991 12 crore 14 lakh 2001 12 crore 93 lakh∗

The above table shows that the population decreased between 1941 and

1951. This was because during the partition of the country in 1947, many

people migrated out. But from 1961 to 2001 the population has been

rapidly increasing, and has more than doubled in the last 40 years.

∗ Preliminary population census report 2001

232 General Science

Influence of Increased Population on Environment

The rapid increase of population in Bangladesh is causing adverse effect on the social and natural environment. This effect is observed both in the rural and urban settings.

A. Rural area: Food comes up as the first issue. The production of crop and other agricultural products is not increasing at the same rate as the population. The demand for housing, roadways, market place, schools and colleges is increasing. This in turn is decreasing the cultivable land, and thus decreasing per head production of crop.

To increase the crop production, increased amount of fertiliser and pesticides are being used. But most of the farmers are illiterate, so they cannot use the fertilisers and pesticides in the right amount, thus damaging the crop and decreasing fertility of the land. Again, some of the fertiliser and pesticide is washed into the rivers, lakes, canals and ponds with rainwater, which in turn kill the young fishes. So the fish population is also decreasing. Due to the use of pesticides and other disinfectants, the number of beneficial insects, and frogs, are decreasing. This is leading to the increase of insects that are harmful for crops. The barren and unfertile land is being forced into cultivation, leading to decrease in grazing and forest land, and thus decrease in the number of cattle, goat, sheep. This is one of the reasons for the decrease in protein food. Again, increased attention to growing paddy, decreases attention to production of pulses or lentils, which is further decreasing the production of protein rich food.

To meet the increased demand of housing and roadways, increased number of gardens and forests are being cleared. The land is becoming bare and more of the topsoil is being washed into rivers and lakes with the rainwater. The water retaining capacity is also decreasing for the same

Population and Natural Environment 233

reason. As soon as the monsoons are over, the ponds and lake become dry, thus hampering crop production. Again, increasingly deep tube-wells are used to compensate for the dryness in winter season. This in turn is decreasing the underground water table, so sometimes the tube-wells are also unable to extract the underground water. Plants are not getting enough water so their number is also decreasing.

The natural resource of Bangladesh is not being used efficiently. Increasingly, trees are being cut indiscriminately to be used as fuel, for housing and furniture making, and brick burning. To maintain a healthy environment, enough trees are not being planted. A comprehensive aforestation plan is also not in place. The insects and pests that usually live in forests are increasingly turning to crops. The natural habitat of wildlife is being destroyed gradually. Too much, or too little rain is turning into a normal phenomenon. Crop cannot be produced in draught. Food is less and people become under-nourished. Less crop means less hay, that is less fodder and food for cattle. The cattle become weak and cannot pull the plough, and milking cows give less milk.

Most of the people in Bangladesh live in the rural area, and most are farmers. Population is increasing day by day, but the land is not. When the father dies, the land is distributed among his children, thus the per capita land is gradually decreasing. Similarly, the number of homestead is also increasing and living quarters are becoming congested, resulting in deterioration of social and natural environment. In congested living conditions less air and light reach individual living quarter. It becomes difficult to arrange for sanitary disposal of urine and faeces. People practice open-air defecation and pollute the environment. In the rural area pond water is used for all purpose including human bathing, cattle bathing and all other agricultural and household activities. The water rapidly

234 General Science

becomes polluted and unsuitable for use. this polluted water also becomes the source of many diseases.

B. Urban area: Because of increased population, there is scarcity of jobs in the rural area. So many people move to urban areas in search of food and job. As a result the rate of increase of population is much higher than the national figures. Rapid increase in urban population compels people to live in congested unhealthy slums. Non-availability of jobs also compel people to look for alternate source of income and so all sorts of unlawful activities like dacoity, thievery, highway robbery, and terrorism are on the rise. Living in unhealthy conditions is giving rise to different diseases.

The rate of increase in urban population over the last 40 years is shown in table-2.

∗Table-2

Population City Year1961 Year 1974 Year 1981 Year 1991 Year 2001

Comment (times increase in 40 years)

Dhaka 5,21,941 16,79,972 34,40,178 61,05,160 99,12,908 19 times

Chittagong 3,54,206 8,89,760 13,90,680 20,40,663 32,02,710 10 times

Khulna 1,27,970 4,37,344 6,52,000 8,77,388 12,27,239 10 times

Rajshahi 56,885 90,909 2,53,726 5,17,136 6,46,716 12 times

Basic Concept of Demography The term population refers to the total human inhabitants of a specified area, such as a city, country, or continent, at a given time. Population study as a discipline is known as demography. Demography is concerned with the size, composition, and distribution of populations; their patterns of change ∗ Preliminary population census report 2001

Population and Natural Environment 235

over time through births, deaths, and migration; and the determinants and consequences of such changes. Demographic information is important for planning, particularly by governments, in fields such as health, education, housing, social security, employment, and environmental preservation. Such studies also provide information that is needed to formulate government population policies, which aims to modify demographic trends in order to achieve economic and social objectives.

Density of population: The distribution of people in different areas is different. In some places more people live compared to others. In order to understand how many people live in a place, the number of people living in one square kilometre area is used as a standard indicator. For example, if in a village there are 4000 people living in an area of 4 square kilometre, then the number of people living in each square kilometre will be how much? The density of population will be (4000/4) 1000 per square kilometre. Again if the same village has an area of 5 square kilometre then the density of population will be (4000/5) 800 per square kilometre. Thus, the average number of people living in a square kilometre of a country is termed the population density for that country.

Total population of a country Population density = Total area of the country Example: A population of 1,20,000 lives in an area of 150 square kilometre (15 km in length and 10 km in breadth). What is the population density in that area?

Total population of a country Population density = Total area of the country 1,20,000 = = 800 persons per square kilometre 150

236 General Science

Per Capita Land:

The amount of land owned by the number of families living in a place is not the same. Some have more land, while some have less. Suppose, a 10 membered family has 10 acres of land. Then how much land is there per person of the family. In this case it is easy to calculate, as 10 persons own 10 acres, so for each person there is 1 acres of land. When the total land of a place or a country is equally distributed among the total population of that place or country, the amount of land allocated per person is the per capita land for that place. Per capita land is also termed as average land. Per capita land is measured in acres or hectares. 1 acre is equal to 100 decimal or 43560 square foot, and 2.47 acres is equal to 1 hectare.

Total land (in acre) Per capita land = Total population Suppose, the population in a place is 2,40,000 and the total land is 72,000 acres, then the per capita land can be calculated by

Total land (in acre) Per capita land = Total population

72,000 acre = = 0.30 acres or 30 decimals/person 240,000 person The per capita land in Bangladesh is much less than that of many other countries. According to the census of 1981, the per capita land in Bangladesh was 0.33 acres. In 1991 it became 0.29 acres, and as of 2001 this stands at 0.28 acres. If the present conditions persist, then soon the per capita land will further decrease. What are the reasons for such a situation? The total land is more or less constant, it is the population that is increasing rapidly, and so the decrease in per capita land. An exercise may be done where the students collect information from two localities, and calculate and compare the per capita land for the said two localities.

Population and Natural Environment 237

Per capita income: All the persons in a family do not earn. One or two members may earn, but it is consumed by all the members. In other word, the income by one or two persons is considered the income of the family. The family income when distributed evenly among all the members, then the income allocated to each is the per capita income or average income of the family. Similarly, when the same is considered for a larger population, then the total income in one year when equally distributed among the total population of the place will give the per capita income of the place. Total income in one year Per capita income = Total population Suppose, the salary of a service holder of a family, added to the annual profit from business or agricultural activity, all together amounts to Tk. 1,20,000. That family is composed of 10 members. Then the per capital income of the family is Total income in 1 year Per capita income (average income) = Total population 1,20,000 = = Tk. 12,000 10 The per capita income of every family can be thus calculated. As an exercise, the students may ask about the income and family size of each family in their locality, and thus calculate the per capita income of their locality. For convenience and uniformity the per capita income world-wide is calculated in dollars. The per capita income in Bangladesh, as per 2001 census, is US dollar 377∗. In 2001, US dollar 1 was equal to Tk. 57.33. From this the per capita income in Bangladesh may be calculated in Bangladeshi currency. Per capita income or average income is not constant, it may increase or decrease. The total income of rich and poor determines the average income. ∗ Bangladesh at a Glance 2001, BBS.

238 General Science

New Words Learned in this Chapter

Bare Population

Highway robbery Population density

Per capita land Census

Per capita income

Exercise

Multiple Choice Questions (MCQ) 1. What is the cause of decreasing the population of the country in 1951?

a. partition of the country b. war c. epidemic d. unawareness about the increase of population

2. The number of people who live in per square kilometre in any country is called a. population b. total population b. density of population d. average population

3. One acre is equivalent to i. 40 decimal ii. 100 decimal iii. 43560 square feet

Of the following, which is correct a. i b. ii c. i and iii d. ii and iii

Population and Natural Environment 239

4. Per head income is equal to total income

i. total population total yearly income

ii. total population yearly income of the total population in the country

iii. total population Of the following, which is correct?

a. i b. i and ii c. i and iii d. ii and iii

5. The population of a locality is 360000 and the amount of total land is 96000 acre. What is the amount of land in acre per head? a. 0.27 b. 0.28 c. 0.29 d. 0.30

Creative Questions (CQ) 1.

Table – 1 Table -2 Population of Bangladesh

Population of cities Increase

1961 5,520,0000 (approx)

City 1961 2001

2001 12,93,00000 (approx)

Dhaka 521941 9912908 19 times

Chittagong 354206 3202710 10 times Khulna 1,27,970 12,27,239 10 times

Rajshahi 56,885 6,46,716 12 times

240 General Science

a. What is population? b. What is the cause of increase in population of town area? c. Calculate how many times population of Bangladesh has been

increased in the last 40 years. d. According to table -2, discuss the influence of increase in population

in the urban area. 2. The father of Shuva and father of Nafiz are govt employees in same

rank of the same office. Though Shuva has one sister yet the number of brothers and sisters of Nafiz are six. Nafiz’s grandmother also stays with them. The father of Shuva and father of Nafiz each receives taka 16,000/- per month as their salary. Yet the father of Nafiz faces difficulties in payment of tuition fee of Nafiz’s school.

a. How many members are there in Nafiz’s family? b. Why does the difficulty arise in payment of tuition fee for Nafiz’s

school? c. Determine the income of Nafiz’s father? d. Determining the per head income of Shuva’s family and compare the

similarities of the two families.

Chapter 20

An Introduction to AIDS

Many of us have heard about some deadly diseases. For example, tuberculosis (TB) is a deadly disease that causes death to many people. However, a TB patient gets completely cured if treated timely. Besides, there is a vaccine which prevents TB. But today we will know about a new disease for which no vaccine or treatment has been discovered as yet. This disease has created panic throughout the whole world. It is called AIDS. A virus named HIV, entering into human body, gradually destroys the immune system of the body. When the immunity of an HIV infected person is reduced too much, the person becomes an easy victim of various types of diseases. This stage of HIV infection is called AIDS. Since there is no cure of AIDS as yet, death is the only consequence. For this reason, AIDS is termed as the fatal disease. All of us should have ideas about how does AIDS spread, how it does not spread and how can we be saved from this disease. HIV may be transmitted into human body through various means, like: 1) Receiving blood of an HIV infected person 2) Sharing the infected needle and syringe 3) Through breastfeeding of an HIV infected mother.

Learners’ task (homework): The learner will identify a few of her/his friends, relatives, and neighbours who did never go to school and who do not know about AIDS. The learner will talk to them about AIDS and will record their opinions. Finally, she/ he will exchange this experience with classmates in the classroom.

242 General Science

AIDS is not a contagious disease. It does not spread through air or water. So people do not get AIDS from living with and caring for the AIDS patients, talking to the patient, mixing and shaking hands with the patient or sharing meals. Remember that adherence to religious and social customs reduces the chances of being affected by AIDS. Everyday innumerable people are being affected by AIDS and countless people are also dying all over the world. For various reasons, the people of Bangladesh also are at high risk of being affected by AIDS. So, all of us will have to be careful before it is late. We shall inform our friends, partners and associates, family members and other persons about AIDS. We shall be careful about the ways through which AIDS spreads and will also ask others to be careful.

Exercise Multiple Choice Questions (MCQ)

1. The fatal disease is -

a. infleunza b. tuberculosis

c. AIDS d. HIV

2. The cause of infection of Aids is

a. bacteria b. drinking polluted water

c. HIV d. to come in touch with AIDS patients

3. HIV / AIDS spreads

a. through food b. through HIV infected blood

c. through air d. through shaking hands with AIDS patients

An Introduction to Aids 243

4. HIV

i. creates a few diseases

ii. destroys preventive power of the body

iii. creates AIDS disease

Of the following, which is correct?

a. i b. ii

c. ii and iii d. i, ii and iii

Creative Questions (CQ)

Fig

a) What is HIV? b) Why is such type of indication / symbol given below the word

AIDS? c) Explain whether there is any possibility of infection of HIV

(AIDS) to the healthy man in the figure. d) Give your opinion regarding the suitability of the poster with the

AIDS patient.

244 General Science