classVIenglishGeneral Science Class VI

Transcription

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
1
is 12 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
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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
=1m
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
10 milligrams (mg)
10 c.gms
10 deci.gm
10 grams
10 deca. gms
10 hecto.gm
100 kg
10 quintals
General Science
= 1centigram (c.gm)
= 1 deci gram
= 1 gram (gm)
= 1 deca.gram (deca.gm)
= 1 hecto.gram
= 1 kilogram
= 1 quintal
= 1metric ton
= 1 mg = 1/1000 gram.
= 1 c.gm = 1/100 gram
= 1 deci gm. = 1/10 gm
= 1000 grams
= 100,000 gms
= 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
1
year. About 3654 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 onesixtieth 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
60 minutes
24 hours
7 days
30 days
12 months
= 1 minute
= 1hour
= 1 day = 86,400 seconds
= 1 week
= 1 month
1
= 1 year = 3654 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.
1
1
= 10 cm × 10 cm
1
= 100 square cm.
Measurement
11
1 square Km.
= 1 km. × 1 km.
= 1000m. × 1000m.
= 10,00,000 square m.
The area of any country is A
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
D
the figure.
B
C
Fig: 1.3 Finding areas with the help
of square boxes
Draw straight lines 1 cm apart.
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 Fig 1.5: Finding the volume with the
help of a measuring cylinder
piece of wood. Take a reading of the
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 –
mass
Density = 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.
What
Interrelation
In system International C.G.S system
measured Name of
Abbrevia Name of
Abbrevia
unit
tion
unit
tion
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
sq.cm.
1 cubic m. =
centimeter
1000000
cubic cm.
Volume Cubic metre cubic m. Cubic
cubc.cm. 1 kg/1cubic m.
centimeter
Density Kilogram per kg./cubic Gram per gm/cubic 1000
cubic metre -cmm
cubic
cm.
gm/1000000
centremtre
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
Fig 1.6: A metre scale
are longer and that of the
millimeters
are
smaller.
Perhaps there are metre scales
in your school. Your teacher
wrong process
will show them to you. You right process
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
right process
wrong process
scale to which other end
Fig 1.7: Process of measuring length with a
metre scale
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
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
Fig 1.8: An Ordinary Balance
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
c. 1000 kg .
b. 100
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
3
1
4
2
Figure
21
Measurement
5. Which of the above figure is used for determining the volume of a
piece of stone?
6.
a.
1
b. 2
c.
3
d. 4
The instruments of the figure are usedi.
in determination of length and mass
ii.
in determination of mass and density
iii.
in determination of area and density
a. i and ii
c. i and iii
b. ii and iii
d. i, ii and iii
Creative Questions (CQ)
1.
cm
A
B
Figure
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.
24
General Science
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
1. The matter which when broken
1.
Compounds
Compounds are substances
into smallest parts does not produce which when broken produce more
any other matter than itself is called than one element. For examplean element. For example- gold,
water, sugar, oil, salt, soap, soda
silver, copper, iron, hydrogen,
etc. are compounds
oxygen etc. are elements.
2. In free states elements can retain
2. The properties of the compounds
their respective properties or
are
characteristics.
properties
totally
different
of
its
from
the
constituent
elements.
3. The smallest part of the elements
3. The smallest parts of compounds
is atoms. Atoms retain properties of are the molecules. Molecules retain
the element itself.
4.
Similar
atoms
properties of the compound itself.
constitute 4. Molecules of compounds are
molecules of the elements.
constituted by different atom.
5. Total number of elements in this
5. Compounds are innumerable in
world is 109.
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
26
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?
General Science
Fig 2.1: Observation of iron filing
and sulphur powder
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.
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,
2. The properties of the constituent water vapour, dust particles etc are
elements of a compound get lost and a in it.
new substance of different properties is 2. In ordinary mixture the
formed.
constituents retain their own
3. In preparing a compound heat is properties and they remain side by
side.
needed to be applied or drawn out.
4. Constituents of a compound can’t 3. In the preparation of a mixture
heat is neither applied nor removed.
be separated easily.
5. The constituents of a compound are 4. The constituents of an ordinary
same or homogeneous everywhere. As mixture can be separated by easy
for example, water collected from means.
anywhere contains equal proportion of 5. The constituents of a mixture may
hydrogen and oxygen.
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
30
General Science
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 sandmixed 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
34
General Science
EXERCISE
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
a. i
c. iii
b. ii
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
a. i
c. i and iii
b. i and ii
d. i, ii and iii
36
General Science
1.
aluminium, sand,
copper sulphate
Iron, Sand, Copper
Sulphate
B
A
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.
Pice of tin
Sand
Suger
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.
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
38
General Science
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.
Air
39
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.
40
General Science
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
Nitrogen
Oxygen
Moisture
Carbon dioxide
Inert gases
Percentage by weight Percentages by volume
75.50
77.16
23.10
20.60
0.06
1.40
0.04
0.04
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).
42
General Science
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:
44
General Science
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 onefifth 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
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?
Fig 3.5: Testing the presence of
carbon dioxide in the air exhaled
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
46
General Science
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.
Air
47
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.
48
General Science
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
Respiration
Conical flask
Moisture
Lungs
Methane gas
Helium
Waste materials
Argon
Inert gases
Calcium carbonate
Balance
Air pollution
Propulsion Method
Air circulation
Calcium hydroxide
Photosynthesis
Nitrate
Protein
Nitrogen cycle
Ammonium sulphate
Neon
50
General Science
EXERCISE
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
a. i
b. ii
c.
iii
d. i, ii and iii
From the diagram, answer the questions 7 and 8.
air
soil
nitrogen
soil
animal
Plant
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
figurei. due to mutual dependence on plants and animals
ii. due to leguminous plants
iii. due to presence of nitrate salt in soil
52
General Science
a. i
b. i and ii
c. ii and iii
d. i, ii and iii
1.
Air
Sun
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
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.
1
2
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
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.
58
General Science
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 oxyhydrogen 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 nonmetals, 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
1.
2.
Metals
Metals are generally bright
1.
Metals are hard and heavy in
mass
Metals emit clink when struck
with hammer.
Heat and electricity can pass
through metals.
Metals can be hammered to
thin sheets and can be drawn
into very thin wire.
The melting points of metals
are very high.
Metals are solid at normal
temperature.
2.
8.
Metals can reflect light
8.
9.
Metals usually dissolve in 9.
hydrochloric or sulphuric acid.
3.
4.
5.
6.
7.
3.
4.
5.
6.
7.
Non-metals
Non-metals are not generally
bright
Normally non-metals are soft
and light.
Non-metals do not emit clink
when struck with hammer.
Heat and electricity cannot
pass through non-metals.
Non-metals
cannot
be
hammered to thin sheets and
cannot be drawn into thin wire.
Non-metals melts at low
temperature.
At normal temperature nonmetals are generally solid or
gaseous.
Non-metals can not reflect
light
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
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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
Main Other elements Special
of alloy
metal in the mixture properties
element
Steel
Iron
0.25-1.5%
hard,
not
carbon and a brittle, does
little chromium not rust
Uses
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% does
not Cartidge of bullet,
Zinc 40-20%
rust
screw, ornaments,
utensils etc are made
of brass.
Bell
Copper Copper 75-90% attractive
Used in making coins,
metal
Tin 25-10%
colour
utensils, metalic
statues, bell, propeller,
equipment etc.
Duralum Alumi Aluminium 95% very light
Used in building
in
nium
Copper 4%
motorcars, and
Manganese 0.5%
aeroplanes.
Magnesium 0.5%
Metal and Non-metal
63
New words in this chapter
Conductor of electricity
Power tiller
Cavendish
Alloy
Tractor
Priestly
Molboard plough
Gasoline
Rutherford.
Exercise
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 balloona. 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
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General Science
a. i
b. ii
c. iii
d. i and ii
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.
b.
c.
d.
%
%
%
%
What is the name of the alloy?
Why is it called an alloy?
Explain what will happen if iron is used instead of aluminium.
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
Fig: 5.1 Analysis of water
of same size and fill them
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.
Electric
Water
→
analysis
Hydrogen Oxygen
+
2 vol
1 vol
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
Fig: 5.2 Water cycle
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
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.
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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.
Cavendish, insecticides, bleaching powder, sulphuric acid, chemical
fertilizer, watercycle, electrolysis, potassium permanganate, detergent,
hydroelectric centre, wastes,
Water
75
Exercise
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
76
General Science
4.
Cloud
Vapour
Rain
Pond
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
a. i
b. ii
c. iii
d. i and ii
Water
77
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
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
79
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
6.3: Sensitive plant
touch by folding its leaves; the
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
6.4: Plant growth
the capacity to respond to stimuli.
Growth
Living beings take food. This food is
digested and helps in the growth and
80
General Science
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.
Fig 6.5: Reproduction of living
organisms
Reproduction
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
1.
2.
3.
4.
5.
6.
7.
8.
9.
Nonliving
Living body is formed of
1. Nonliving things have no
protoplasm
protoplasm
Living beings can move around 2. Nonliving things cannot move on
its own
Living beings respond to
3. Nonliving things do not respond
stimuli
to stimuli
The food that living beings take
4. Nonliving things do not take
help in growth and repair
food
Living beings carry out
5. Nonliving things do not respire
respiration
Living beings can adapt with the 6. Nonliving things cannot adapt
environment
Living beings can reproduce
7. Nonliving things cannot
reproduce
Living beings have a definite
8. Nonliving things have no
lifecycle
lifecycle
Living bodies have definite size
9. Nonliving things have no definite
and shape
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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General Science
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
1. Cannot manufacture their own
pigment, with the help of which
food, as they do not have
plant manufacture their own
chlorophyll. So animals depend
food.
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
4. Animals take in oxygen and give
take in carbon dioxide and give
out carbon dioxide during
out oxygen. During respiration
respiration. It never takes in
it takes in oxygen and give out
carbon dioxide as
carbon dioxide.
photosynthesis does not occur in
animals.
5. Plants have a definite structure 5. Animals have a definite size,
and shape, but the branches are
shape and structure.
not well defined.
6. Plants do not have specific
6. Animals have specific organ
organ system.
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.
Living World
83
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
1.
2.
3.
4.
5.
No vertebral column
No endoskeleton
Have simple or compound eyes
Heart is not well developed
Usually have no tail
Invertebrate Animals
Earthworm
Cockroach
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.
2.
3.
4.
5.
6.
7.
Have vertebral column
Have endoskeleton
Heart is well developed
Do not have more than two pairs of legs or wings
Lungs or gills are used for respiration
Have simple or compound eyes
Have tail (except humans)
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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
Ruhi
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.
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General Science
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
1.
2.
3.
4.
5.
Invertebrates
No vertebral column.
Usually have no tail.
Heart is not well developed.
Eyes are either simple or
compound.
Usually
do
not
have
endoskeleton.
1.
2.
3.
4.
Vertebrates
Vertebral column present.
Except for humans, most have tail.
Heart is well developed.
Eyes are simple.
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
1. Which one flies?
a. buffalo
b. cow
c. magpie
d. golden frog
2. Which mammal can walk on standing?
a. man
c. leopard
b. chicken
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
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General Science
Of the following figure answer the questions 4 and 5.
A
Figure
4. The A marked portion of the above diagram isa. rostrum
b. compound eye
c. taleson
d. carapas
5. Applicable in case of the animal shown in the figurei. They have no internal skeleton
ii. Their tale is segmented
iii. They have no leg
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
Living World
89
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 Fig 7.1: Robert Hook’s
they can not be seen without the help
Microscope
of a 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.
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.
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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.
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.
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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:
95
a) nuclear membrane
Nuclear membrane
b) nucleoplasm
c) chromosome
Nucleolus
Nucleoplasm
d) nucleolus
Nucleus controls all
physiologic activities of
a cell. It is the life
centre of the cell.
chromosome
Fig 7.5: Nucleus
Difference between plant and animal cell
Topics
1. Cell wall
Plant cell
Animal Cell
1. Plant cell has cellulos 1. In animal cell, cellulose
cell wall outside the cell
cell wall is absent; only
membrane
cell membrane is present.
2. Vacuole
2. In mature cells large 2. Usually animal cell has no
vacuole is present.
vacuole; if present it is
small.
3. Plastid
3. Usually plant cells 3. Usually animal cells do
contain plastids.
not contain plastids.
4. Centrosome 4. Usually in plant cells 4. Usually in animal cells
centrosomes are absent.
centrosomes are present.
5. Position of 5. In plant cell vacuole is 5. In animal cells the nucleus
nucleus
large and the nucleus
is centrally placed.
lies near the cell wall.
New words of this Chapter
Transverse
Plastid
Nucleoplasm
Chromoplast
Cell
Respiration
Glycerin
Leucoplast
Cytoplasm
Plasma membrane
Chloroplast
Mitochondria
Nucleus
Cellulose
Centrosome
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General Science
Exercise
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
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)
ii)
iii)
A
gives the size of the cell
is made of two-leyer membrane
B
prevents liquid substances from coming out of the cell
97
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
a. i and ii b. ii and iii
c. i and iii
d. i, ii and iii
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.
C
A
B
a.
b.
c.
d.
What is the picture about?
Explain the characteristics of the A marked portion.
Explain what would happen if the C marked portion would not be in the cell.
The B marked portion shown in the picture bears a special
characteristics of the above cell. Discuss.
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).
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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 nongreen 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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General Science
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 Dicotyledonous 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
Phanerogams
Cryptogams
(Non flowering)
Protophyta
(Acellular or
primitive
cells.)
Thallophyta
(Body not
differentiated
into root
and leaf)
(Flowering)
Bryophyta
(Body differ
entiated into
stem and leaf but
not root)
Gymnosperms
(Fruits not formed and seeds
not covered in fruits.)
Monocotyledons
(Only one cotyledon
in the seed)
Pteridophyta
(Body divided
in
stem, root and
leaf)
Angiosperms
(Fruits formed and seeds
covered in fruits)
Dicotyledons
(Two cotyledons
in the seed)
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General Science
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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General Science
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.
Plant Kingdom
107
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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General Science
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.
Plant Kingdom
109
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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General Science
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
Plant Kingdom
111
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
1.
2.
3.
In how may classes the cryptogamia is divided?
a. one
b. two
c. three
d. four
Which of the following is not (available) in bryophyte?
a. stem
b. root
c. leave
d. vein
Perinnial (plant) is –
a. ginger
c. pea
b. carrot
d. mustard
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General Science
4.
Applicable in case of dying planta. penicillium
b. black band of jute
c. blue cheese
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
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 picturei. There is vitamin in their body
ii. Blue cheese is made with its help
iii. is used in bread making industry
a. i and ii
b. i and iii
c. ii and iii
d. i, ii and iii
Plant Kingdom
113
1.
figure 1
a.
b.
c.
d.
figure 2
What is the type of the plant shown in the picture?
Write down two characteristics of this sort of plant
Explain the necessity of cultivation of the plant (as shown) in the picture.
The plant in picture-2 is useful as well as harmful. Put arguments.
2.
Figure 1
Of which order is the plant in Figure 1?
a.
b.
c.
Figure 2
Why is their stem soft?
Which of the above plants is called annual, herb and dicot? Explain.
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.
115
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 downwards. 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 internode, 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. ExampleCarrot.
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. ExampleSweet potato, Four o΄clock plant (Sandhya malati) etc.
Functions of a root:
Roots usually perform two types of work, such asa) 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.
b)
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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 asa) 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). ExampleMast 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. ExampleMango, 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 asa) 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 asBasella (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.
Multifoliate
1. Bifoliate palmate: Bignonia
2. Trifoliate palmate: Oxalis (amruli), Woodapple etc.
3. Quadrifoliate palmate: Marsilea (Shushni).
4. Multifoliate: Silk cotton (Shimul).
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Differences between simple leaf and compound leaf
Simple leaf
Compound leaf
1. It bears a single lamina
1. It bears a number of leaflets.
2. Its lamina may be lobed but the 2. Here the leaflets are completely
incision is not complete and the
separated from one another.
pieces are not completely
separated
3. It has midrib or main vein
3. It has rachis or axis in place of
midrib.
4. It may bear stipules at the leaf 4. It may have stipules at the base
of leaflets. Of course stipules
base.
may be present at the base of
compound leaves
5. It bears axilary bud.
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
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 stemi. 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
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 isa. 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 picturei. 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
a. i b. ii
c. iii d. i, ii and iii
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.
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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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General Science
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.
Force
Therefore, Pressure = Area
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 bicycle 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 50metre 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.
Distance
Therefore, Speed = 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.
Displacement
Therefore, velocity =
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
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 abouta. 1 Newton
b. 2 Newton
c. 10 Newton
d. 20 Newton
5. The sort of motion of the wheel of the carriera. 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 isa.
10 Newton
b. 20 Newton
c.
40 Newton
d. 30 Newton
2. In B-marked fig, the pressure of the brick per square metre isa.
1000 Newton
b. 2000 Newton
c.
3000 Newton
d. 4000 Newton
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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 –
Work, Power, Energy
149
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 joule
1 watt = 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
Amount of work done
His power =
Time
600
= 60
= 10 watts.
The second man does a work of 1200 joules in the same time so –
Amount of work done
His power =
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.
Power =
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
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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.
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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.
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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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157
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
1. What is the name of the unit of the energy?
a. Newton
b.
c. Watt
d.
Joule
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
(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
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
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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.
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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.
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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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General Science
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-inone, 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 storedup 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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General Science
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.
Electron
Positive charge
Negative charge
Statical electricity
Current electricity
Conductor
Non-conductor
Electric cell
EXERCISE
1. Electricity is produced in electric cellsa. from mechanical energy
b. from chemical energy
c. from thermal energy
d. from the sun energy
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General Science
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.
b.
c.
There are charges of similar properties (similar charges) in
glass rod and rubber rod
The glass rod is charged and the rubber rod is not charged
There are charges of opposite properties (opposite charges)
in the glass rod and rubber rod.
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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
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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173
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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General Science
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.
Magnetic Energy
175
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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General Science
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
Magnetic Energy
177
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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General Science
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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179
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.
Natural magnet
Direction finding instrument
Artificial magnet
Electro magnet
Horse-shoe magnet
Magnetic substance
Attraction
Non-magnetic substance
Repulsion
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General Science
EXCERCISE
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 calleda. 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?
Magnetic Energy
4.
181
Which of the above material cannot be artificially converted to
magnet?
5.
a. iron
b. nickel
c. copper
d. steel
Which of the above is used for making electric magnet?
a. steel
b. zinc
c. nickel
d. iron
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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General Science
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,
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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General Science
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.
Fig 14.6: Laccoliths Mountain
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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General Science
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.
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.
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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.
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Exercise
1. The large portion of water body surrounded by land on the three sides is
calleda. 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 aa. 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
1.
a.
b.
c.
d.
What is the name of the portion in picture A?
Write two differences regarding the form of the land as shown in B and
C portions of the picture.
How is the region D created?
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
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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 Animals
Phyla
Includes
1. Protozoa Amoeba,
malarial
parasite
2. Porifera
Spongilla
Common features
These are unicellular animals, and were
the first ones to be created. They live
individually or in groups.
Some, like malarial parasite and microorganism causing dysentery, live in other
organism as they are parasitic in nature.
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.
196
3.
4.
5.
6.
7.
8.
9.
General Science
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.
Platyhelminthes Tapeworm They are flat soft-bodied, and
or flatworms
and flukes usually parasitic in nature. Has a
mouth but no anus.
Nematoda or
Hookworm, Roundworms are cylindrical,
tapering animals with simple bodies.
roundworms
trichina,
Have both mouth and anus. Many
filarial
nematodes, live as parasites in plants and
whip worm animals, where they may cause
disease.
Annelida
Earthworm, These are soft bodied animal with
leech
mouth and anus. The body is
divided into ring-like segments.
The body is covered by a durable
Arthropoda
Prawn,
shell. It has mouth and jaws. Has a
crab,
centipedes, pair of articulated legs, and
cockroach, compound eyes.
fly
Echinodermata Starfish,
These are marine animal. The body
sea urchin, has numerous spiny projections, and
sea lily
has a body tube.
Mollusca
Snail,
These are soft-bodied, and are
oyster,
covered by a hard external shell.
octopus
Have large muscular organ used for
locomotion called the foot
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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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General Science
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.
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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
Phylum
Appendages
Cephalothorax
Segmented
Jointed
Golda
Bagda
Vertebral column or spinal cord
Gills
Parasite
Tentacles
Telson
Excretory opening
Anus
Malarial parasite
Antennae
Carapace
Rostrum
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General Science
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.
a. i
b. ii
c. i and iii
d. i, ii and iii
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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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General Science
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
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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
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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
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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General Science
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-
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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
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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.
Skin
Involuntary muscle
Thorax
Joints
Melanin
Cardiac muscle
Vertebral column
Upper limb
Sweat gland
Skeleton
Bones
Lower limb
Cartilage
Bone marrow
Voluntary muscle Skull
Exercise
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
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
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
a. i and ii b. i and iii
c. ii and iii d. i, ii and iii
1.
fig: A
fig: B
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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.
B
A
D
C
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.
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
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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
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.
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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.
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.
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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
219
times a day. It is necessary to keep the towel and other articles as bed
linen and clothes clean too.
Scabies
Benzoic acid
Microsporon
Vesicle
Tissue
Salicylic acid
Trichophyton
Mycobacterium
Iodine
Ampicillin
Sarcoptis
Ointment
Fungus
Benzyl benzoate
Griseofulvin
Chlorpheneramine
Exercise
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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General Science
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
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-
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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 asa) 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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General Science
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
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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226
General Science
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:
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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
New words of this chapter:
Nutrition
Protein
Beriberi
Anemia
Calcium
Iodine
Preservation Refrigerator
229
Carbohydrate
Scurvy
Constipation
Cold storage
Vitamins
Goiter
Diarrhoea
Pasteurization
Exercise
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 babiesa. 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
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General Science
1.
A
C
a.
b.
c.
d.
B
D
What sort of ingredients of food remains in vegetable?
Explain the necessity of food marked-A.
Explain how the body weight is increased by food marked-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.
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
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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
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
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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
Comment
(times
Year1961 Year 1974 Year 1981 Year 1991 Year 2001
increase in
40 years)
5,21,941 16,79,972 34,40,178 61,05,160 99,12,908 19 times
Population
City
Dhaka
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
56,885
90,909 2,53,726
Rajshahi
8,77,388 12,27,239 10 times
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
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
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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.
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
Bare
Population
Highway robbery
Population density
Per capita land
Census
Per capita income
Exercise
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
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
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
1.
Table – 1
Table -2
Population of
Population of cities
Bangladesh
1961 5,520,0000
City
1961
2001
(approx)
2001 12,93,00000
Dhaka
521941
9912908
(approx)
Chittagong 354206
3202710
Khulna
1,27,970 12,27,239
Rajshahi
56,885
6,46,716
Increase
19 times
10 times
10 times
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
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
a. i
c. ii and iii
b. ii
d. i, ii and iii
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

classVIenglishGeneral Science Class VI

Transcription

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