Science 8

5. Write down any four examples of acid with their molecular formula.
6. Explain the uses of salts.
7. What is an indicator? Give examples.
8. How do you prepare litmus paper? Explain in brief.

H. Complete the given table.

Indicator Colour in Colour in Colour in
acidic solution
Blue litmus paper basic solution salt solution
5HG OLWPXV SDSHU
Methyl orange
Phenolphthalein
(Colourless solution)

i. Prepare a table showing the change in colour of different indicators
when they are brought in contact with dilute HCl, dilute NaOH and
dilute NaCl solutions separately.

ii. Write down the name and molecular formula of a compound which
gives sodium ion and hydroxyl ion in water. What will be the colour
of phenolphthalein in the aqueous solution of this compound? Write
down the balanced chemical equation involved when this compound
is treated with dilute hydrochloric acid solution.

You eat several fruits and drink liquids in your daily life. Test whether they
are acidic, alkaline or salty with the help of indicators. Write down your
REVHUYDWLRQ LQ D SURMHFW ZRUN ÀOH

197 Times' Crucial Science & Environment Book - 8

16CHAPTER Some Useful
Chemicals

Nicolas Leblanc
Nicolas Leblanc was a French chemist and surgeon who
discovered how to manufacture soda from common salt

Estimated Periods : 4
Objectives: At the end of the chapter, the students will be able to:

H[SODLQ WKH SURSHUWLHV RI ZDWHU DQG GLIIHUHQWLDWH EHWZHHQ VRIW DQG KDUG ZDWHU
H[SODLQ WKH W\SHV RI KDUG ZDWHU DQG GHVFULEH WKH PHWKRGV RI WKHLU UHPRYDO L H ERLOLQJ

DQG XVH RI ZDVKLQJ VRGD
GHPRQVWUDWH PHWKRGV RI UHPRYDO RI SHUPDQHQW KDUGQHVV

Can you tell what hard water is?
Can hardness of water be removed?
Can you tell the advantages of hard water? Discuss.

Water

Water is the most available substance on the earth’s surface. It is available
in all three states, i.e. ice (solid), water (liquid) and vapour JDV 5DLQ ULYHUV
streams, lakes, oceans and seas are the natural sources of water. The water
obtained from natural sources may not be pure because it may contain some
GLVVROYHG RU VXVSHQGHG LPSXULWLHV :KLOH ÁRZLQJ RQ WKH VXUIDFH RI WKH HDUWK
or being stagnant on lakes or ponds, many soluble salts get dissolved in water
and make it impure. The impurities bring changes in the natural properties
of water.
The impure water can be made pure by the process of distillation. The pure
water has the following physical properties:
1. Water is a colourless liquid.
2. It is a tasteless liquid. It means that water does not have a particular taste.
3. It is odourless.
4. Its melting point is 0°C and boiling point is 100°C.

Times' Crucial Science & Environment Book - 8 198

5. Water is the best solvent for several solutes. It is regarded as a universal
solvent.

6. Water and its vapour can exist in several physical forms such as dew,
cloud, snow, fog, frost, etc.

Chemical properties of water

1. Water reacts with ammonia gas to form ammonium hydroxide.

:DWHU $PPRQLD ń $PPRQLXP K\GUR[LGH

H2O + NH3 ń 1+4OH
2. Water reacts with carbon dioxide gas to form carbonic acid.

:DWHU &DUERQ GLR[LGH ń &DUERQLF DFLG

H2O + CO2 ń +2CO3
3. Water reacts with sulphur trioxide to form sulphuric acid.

:DWHU 6XOSKXU WULR[LGH ń 6XOSKXULF DFLG

H2O + SO3 ń +2SO4
4. When steam is passed over red hot iron, hydrogen gas is evolved.

3Fe + 4H2O ¨ Fe3O4 + 4H2 Ń

5HG KRW LURQ 6WHDP )HUURVR IHUULF R[LGH

5. Aluminium reacts with steam to produce hydrogen gas and aluminium
hydroxide.

2Al + 6H22 ń $O 2+ 3 + 3H2Ń

Steam

Soft and hard water

The hardness of water is due to the presence of soluble salts of magnesium
and calcium in it. The presence of these salts in water reduces their capacity
to form lather with soap. Hence, the washing capacity of soap is also decreased
due to hardness.

The water which does not contain the soluble salts of magnesium and calcium
is called soft water. It produces lather with soap easily.

The water which contains the soluble salts of magnesium and calcium is called
hard water. It produces less lather with soap.

7\SHV RI KDUGQHVV

There are two types of hardness of water. They are temporary hardness and
permanent hardness.

199 Times' Crucial Science & Environment Book - 8

7HPSRUDU\ KDUGQHVV

The hardness of water due to the presence of calcium bicarbonate
[hCaar(dHnCesOs3o)2f]woratmera.gTnheesituemmpboicraarrbyohnaartden[Mesgs(cHaCnOb3e)2r]eims coavleldedetaesmilyp.orary

Removal of temporary hardness

The temporary hardness of water can be removed by using the following
methods:

a) Boiling

Heating decomposes the soluble magnesium and calcium bicarbonates
into the insoluble carbonates. Thus, the hardness is removed.

Calcium bicarbonate Heat Calcium carbonate + Carbon dioxide
+ Water

Ca(HCO3)2 ¨ CaCO3Ņ &22 + H2O

Magnesium bicarbonate Heat Magnesium carbonate + Carbon
dioxide + Water

Mg(HCO3)2 ¨ MgCO3Ņ &22 + H2O

E 7UHDWLQJ ZLWK OLPH ZDWHU &DOFLXP K\GUR[LGH

Lime water converts the soluble bicarbonates into insoluble
carbonates and removes the hardness.

Calcium bicarbonate + Calcium hydroxide Heat Calcium
carbonate + Water

Ca(HCO3)2 + Ca(OH)2 ¨ 2CaCO3Ņ +2O

Magnesium bicarbonate + Calcium hydroxide ¨ Calcium

carbonate + Magnesium carbonate + Water

Mg(HCO3)2 + Ca(OH)2 ¨ CaCO3Ņ 0J&23Ņ +2O

3HUPDQHQW KDUGQHVV

The hardness of water due to the presence of chlorides and sulphates of
calcium and magnesium is called permanent hardness. The permanent
hardness is caused by:

a. Magnesium chloride (MgCl2)
b. Magnesium sulphate (MgSO4)
c. Calcium chloride (CaCl2)
d. Calcium sulphate (CaSO4)

The permanent hardness of water cannot be removed by heating.

Times' Crucial Science & Environment Book - 8 200

Removal of permanent hardness

The soluble salts of calcium and magnesium are turned into insoluble
forms by the use of washing soda or permutit process.

D 7UHDWPHQW ZLWK ZDVKLQJ VRGD 1D CO3 + O)
When washing soda is added to the hard water, the soluble salts
of calcium and magnesium turn into insoluble salts and the water
becomes soft.

&DOFLXP FKORULGH 6RGLXP FDUERQDWH ń &DOFLXP FDUERQDWH
Sodium chloride

CaCl2 + Na2CO3 ń &D&23Ņ 1D&O
&DOFLXP VXOSKDWH 6RGLXP FDUERQDWH ń &DOFLXP FDUERQDWH

Sodium sulphate

CaSO4 + Na2CO3 ń &D&23Ņ 1D2SO4
0DJQHVLXP FKORULGH 6RGLXP FDUERQDWH ń 0DJQHVLXP FDUERQDWH

Sodium chloride

MgCl2 + Na2CO3 ń 0J&23Ņ 1D&O
0DJQHVLXP VXOSKDWH 6RGLXP FDUERQDWH ń 0DJQHVLXP FDUERQDWH

Sodium sulphate

MgSO4 + Na2CO3 ń 0J&23Ņ 1D2SO4

The sodium salts formed in the above reactions, i.e. NaCl and
BNuat2SsOa4ltasroef also soluble in water but they do not cause hardness.
insoluble in wcaaltceiruamndancadnmnoatgcnaeussiuemh,air.ed.nCesasC. O3 and MgCO3 are

b) Permutit process

The permanent hardness of Hard water Brine
water is removed in industrial
scale by the use of sodium ^ŽŌ ǁĂƚĞƌ
zeolite (permutit). The sodium Zeolite
zeolite (sodium aluminium Gravel
orthosilicate) is prepared by
fusing sodium carbonate, WĞƌŵƵƟƚ WƌŽĐĞƐƐ
fzmsSoieilroOoimlcle8iatcbaeuusal(ntaZNrdia=s2afZArole,lrup2wmSmrheiuiOesnlera8ae)n.tZi(esAdslt2NaiOnna3d)s2.shAofIotrlsrt2

201 Times' Crucial Science & Environment Book - 8

Na2Z + MgSO4 ń 0J= 1D2SO4
Na2Z + CaSO4 ń &D= 1D2SO4
In this process, hard water is passed into a cylinder packed with
permutit. The permutit forms insoluble compounds from the soluble
salts of calcium and magnesium responsible for the hardness of
water. Thus, the water becomes soft.

Advantages of hard water
1. Hard water is good for drinking. It contains calcium salts which help to

strengthen the bones and teeth.

2. The dissolved salts of calcium and magnesium add taste to water.

3. Hard water is useful in brewery (beer) industries.

Disadvantages of hard water
1. Hard water destroys the lather forming capacity of water with soap. It leads

to more consumption of soap while washing clothes.

2. The bright white clothes become dull if they are washed with hard water.

3. The calcium salts corrode the boilers in industries

Some water seems clean, but it may contain several micro-organisms which
can cause diseases in human beings. If water is boiled, its temporary hardness
is lost. This may degrade the natural taste of water. But boiling kills the germs
of diseases and makes water safe for drinking. Hence, drinking water must be
boiled.

Sodium carbonate

Sodium carbonate is a compound of sodium metal.
Its molecular formula is isNaa2lCsoO3k. noItwnis soluble in
water. Sodium carbonate as washing
soda because the hydrated form of sodium carbonate
a(Ns aa2CwOhi3t.e1p0oHw2Ode)ri.sAulsthedoutgohwsaosdhiucmlotchaersb.oIntaisteaivsaailsaabllte,
the aqueous solution of sodium carbonate is alkaline in
nature due to hydrolysis reaction.

Uses
1. It is used to manufacture paper.

2. It is used to remove the permanent hardness of water.

3. It is used to manufacture soap.

4. It is used to manufacture glass.

Times' Crucial Science & Environment Book - 8 202

5. Hydrated form of sodium carbonate (Na2CO3. 10H2O) is used as washing soda.
6. It is used as a weak base in laboratory activities.

Sodium bicarbonate

Sodium bicarbonate is also a salt of sodium metal. Its molecular formula is
NbiacaHrCboOn3a. tIet is also available as a white powder. It is soluble in water. Sodium
is an important part of baking powder. The baking powder is prepared
by mixing sodium bicarbonate with potassium hydrogen tartarate. Baking powder
is used in bakery industries to make biscuit, cake, bread, etc light and puffy. It is
also used as edible soda to treat the hyper-acidity of stomach.

Uses

1. It is used to produce baking powder.

,W LV DQ LPSRUWDQW FKHPLFDO XVHG LQ ÀUH H[WLQJXLVKHU

3. It is used in the production of soft beverages.

4. It is used as edible soda to treat the hyper-acidity of stomach.

5. It can be used to increase the shining of table by rubbing and then wiping.

Glycerol (glycerine)

Glycerol is a thick and colourless liquid with sweet taste. It is soluble in water.
It is a trihydric alcohol having three 'OH' groups in a molecule. The molecular
ftohrrmeeuhlayodfrgoglyecneraotloims Cs 3oHf p5(rOoHpa)3n.eGblyyctehrroel eis'OsuHp'pgorsoeudptso. be formed by replacing

HHH +3[OH] OH OH OH
HC C C H -3 H
HC C C H
HHH HH H

Propane Glycerol

Uses

1. It is used to make medicines, printing ink and ink of stamp pad.

2. It is used as a sweetening agent in confectionery industries.

3. It is used to manufacture high quality toilet soap.

4. It is used to protect skin in winter season.

5. It can be used as a food preservative while storing or packing foods.

6. It is used as an important laboratory reagent.

203 Times' Crucial Science & Environment Book - 8

ĐƟǀŝƚLJ ϭϲ͘ϭ To identify glycerol

0DWHULDOV UHTXLUHG
A bottle of safe and clean glycerol, soap, water, towel, etc
3URFHGXUH
1. Wash your hands with soap and water. Let them dry under hot air or

wipe them with a towel.
3XW D OLWWOH JO\FHURO RQ \RXU SDOP 5XE LW JHQWO\ EHWZHHQ WZR SDOPV DQG

then rub gently over the skin. How do you feel?
3. Put two drops of glycerol on your tongue. What is its taste?
2EVHUYDWLRQ
Glycerol is a thick liquid. It makes skin moist and soft. It is sweet in taste.
&RQFOXVLRQ
*O\FHURO FDQ EH LGHQWLÀHG E\ REVHUYLQJ LWV YLVFRXV DQG VPRRWK QDWXUH DV ZHOO
as taste.

lather ͗ Ă ĨƌŽƚŚLJ ǁŚŝƚĞ ŵĂƐƐ ŽĨ ďƵďďůĞƐ ƉƌŽĚƵĐĞĚ ďLJ ƐŽĂƉ

ƉƌĞƐĞƌǀĂƟǀĞ ͗ Ă ƐƵďƐƚĂŶĐĞ ƵƐĞĚ ƚŽ ƉƌĞƐĞƌǀĞ ĨŽŽĚ ƐƚƵīƐ

sweetening agent ͗ Ă ƐƵďƐƚĂŶĐĞ ǁŚŝĐŚ ƐǁĞĞƚĞŶƐ ĨŽŽĚƐ

1. The water obtained from natural sources can contain dissolved and suspended impurities.
2. Pure water is colourless, odourless and tasteless.
3. The hardness of water is due to the presence of soluble salts of calcium and

magnesium in it.
4. The water which does not contain the soluble salts of magnesium and calcium is

called soft water.
5. The water which contains the soluble salts of magnesium and calcium is called hard water.
6. The hardness of water is of two types-temporary hardness and permanent hardness.
7. The hardness of water due to the presence of soluble magnesium bicarbonates and

calcium bicarbonates is called temporary hardness.
8. The hardness of water due to the presence of chlorides and sulphates of magnesium

and calcium is called permanent hardness.

Exercise

A. Answer these questions in very short.

1. What is soft water?
2. What is hard water?

Times' Crucial Science & Environment Book - 8 204

3. Name two types of hardness of water.
4. Name the salts and their molecular formulae which cause temporary

hardness of water.
5. Name the salts and their molecular formulae which cause permanent

hardness of water.
6. Name the methods of removing temporary hardness of water.

B. Answer these questions.
1. Is the water from natural sources pure? Explain with reasons.
2. Write down the physical properties of water.
3. Write down the chemical properties of water with balanced chemical
equations.
4. Explain the process of removal of temporary hardness of water with
chemical reaction .
5. Explain the process of removal of permanent hardness of water
with chemical reaction.

C. Complete the following chemical equations and balance them.

1. Ca(HCO3)2 ¨ ............... + ................. + H2O
2. Ca(HCO3)2 ń &D&23 + H2O
3. Mg(HCO3)2 + Ca(OH)2 ń
4. MgCl2 ń 1D&O
5. CaSO4 + Na2CO3 ń Ņ

D. Write down differences between.
1. Soft and Hard water
2. Temporary hardness and Permanent hardness
3. Sodium carbonate and Sodium bicarbonate

( :ULWH GRZQ VKRUW QRWHV RQ 2. Sodium bicarbonate
1. Sodium carbonate
3. Glycerol

Draw a water cycle that occurs in nature in a chart paper and display in your class.

205 Times' Crucial Science & Environment Book - 8

17CHAPTER Living Beings

Dmitri Ivanovsky
Dmitri Iosifovich Ivanovsky was a Russian botanist,
the discoverer of viruses and one of the founders of

virology

Estimated Periods : 7
Objectives: At the end of the chapter, the students will be able to:

H[SODLQ WKH VWUXFWXUH RI EDFWHULD YLUXV DQG IXQJL
H[SODLQ WKH YHJHWDWLYH SDUWV RI SODQWV OLNH URRW VWHP DQG OHDYHV

What is micro-organism? Can you give some examples of micro-organisms?
Have you heard about AIDS? What causes AIDS?
What are various parts of plants ? Which are vegetative parts?
Why are vegetative parts important for plants? Discuss.

Introduction

There are various types of living things on the earth. Some of them contain only
one cell in their body. They are called unicellular organisms. Some of them
contain many cells in their bodies. They are called multicellular organisms.
Cells contained in the body of living things also differ from organisms to
organisms. Fundamentally, cells are of two types. They are:
(i) Prokaryotic cell
(ii) Eukaryotic cell

i) Prokaryotic cell

This type of cells are primitive. Nuclear material is not bounded by
nuclear membrane. Such cells are present in bacteria, blue green algae,
etc.

ii) Eukaryotic cell

This type of cells are advanced. Nuclear material is bounded by a nuclear
membrane. Such cells are present in higher organisms.

Times' Crucial Science & Environment Book - 8 206

Some organisms are very small so that they cannot be seen with naked
eyes. They can be seen only with microscope. They are called micro-
organisms. Bacteria, virus and some species of fungi are some such
micro-organisms.

Bacteria Mesosome
Chromosome
Bacteria are the most primitive Cytoplasm
and the smallest cellular Plasmid DNA
organisms. They are single celled
and usually spherical, rod-like Ribosomes Flagella
Plasma
membrane

or spiral in shape. Their average Cell Wall Pili
size ranges from 0.5 to 10
microns. They are present almost
everywhere - in water, air and Capsule
soil. They are found in the body
Bacteria

of living things. The intestine of all animals contains a number of various
types of bacteria. Structure of bacteria differs from species to species. But
some common bacteria have the following structures:

They contain a distinct cell wall made up of proteins and carbohydrates.
Generally, they contain thread-like structures originated from the cytoplasm.
They are called ÁDJHOOD The cytoplasm is spread uniformly. There are many
vacuoles in the cytoplasm. The nucleus is not covered by nuclear membrane.
The nuclear material is present in the form of staining bodies called chromatin
materials.

Some bacteria are rod shaped. They are called bacilli. Some bacteria like
Mycobacteria are spherical. They are called cocci. For example, Micrococcus,
Azotobacter, etc. Some bacteria are spirally wound. They are called spiral
bacteria. For example, Spirillum, Spirochete, etc.

Bacilli Cocci Spiral

A few bacteria contain chlorophyll and can prepare their food themselves. But
most of the bacteria lack chlorophyll and cannot prepare their food themselves.
They are called heterotrophic bacteria. Saprophytic bacteria grow on dead and
decayed things. Parasitic bacteria absorb food from the body of living things
and infect them.

207 Times' Crucial Science & Environment Book - 8

%DFWHULD DUH ERWK EHQHÀFLDO DQG KDUPIXO
6RPH EHQHÀFLDO HIIHFWV RI EDFWHULD DUH DV IROORZV
a) They decompose and decay the body of dead organisms and clean the

environment
b) Some bacteria present in the root nodules of some plants absorb nitrogen

from the atmosphere and provide nitrogenous compounds to the soil.
c) They decompose the dead and decayed things and make the soil fertile.
d) Some bacteria like lactic acid bacteria convert milk into curd.
Harmful effects of bacteria
a) Bacteria cause the rotting and decaying of food, vegetables, etc.
b) They cause various types of diseases in animals and plants.

Virus

Viruses are the smallest and the most primitive micro-organisms. They are
much smaller than bacteria and cannot be detected even by a compound
microscope. They can grow and multiply only inside the body of living things.
They remain quite inactive outside the body of living things. They show the
characteristics of both living things and non-living things. So, they are called
the borderline between living things and non-living things.
Some living characteristics are as follows:
a. Viruses contain protein, which is the basis of living things.
b. They can infect and attack other organisms and cause various types of

diseases.
Some non-living characteristics are as follows:
a. They do not contain a complete nucleus.
b. They can be crystallized as a non-living thing.
Types of viruses
On the basis of host, viruses are of three types:
a. Plant virus: These viruses attack plants, e.g. TMV ( Tobacco Mosaic Virus)
b. Animal-virus: These viruses attack animals,e.g. Rabies virus, Rhino

virus, etc
c. Bacteriophage virus: These viruses attack and infect bacteria. Viruses

can be of two types on the basis of presence of nucleic acid. They are DNA
virus and RNA virus.

Times' Crucial Science & Environment Book - 8 208

Structure

Viruses are very small. Their size Nuclear material Capsid
varies between 25 nanometer to 250 dĂŝů ĮďƌĞ Head
nanometer. They do not contain nucleus Tail
but contain hereditary material, i.e,
DNA or RNA. They contain a coat of
protein called capsid.

Bacteriophage virus contains a head Basal plate
and a tail which are covered by a protein Bacteriophage virus
sheath. The end of the tail has a basal
SODWH ZKLFK EHDUV ORQJ WDLO ÀEUHV 6RPH
viruses are rod shaped and some are
spherical. Bacteriophage viruses are
tadpole shaped.

Harmful effects of viruses

a. Viruses cause various types of diseases in human. Common cold, mumps,
measles, polio, rabies, AIDS, etc are some common viral diseases.

b. Tobacco mosaic virus (TMV) causes diseases in the leaves of tobacco.

Fungi

Fungi is a group of organisms which generally Pileus
grow on dead and decayed organic bodies. Gills
Their body contains well developed cells called Annulus
eukaryotic cells. They lack chlorophyll. Therefore, Stype
they cannot prepare their food themselves. They
get their food either from other organisms as
parasites or from the dead and decayed organisms
as saprophytes.

Structure Velum

Some fungi like yeast are unicellular but most of Mushroom
them are multicellular. Their body is made up of a
number of elongated thread like hyphae. The hyphae develop in all directions
and form a network like mass called mycelium. The fungal cell contains cell
wall which is made up of chitin and lipids. Nucleus is small.

Mode of nutrition

Fungi cannot prepare their food themselves due to the lack of chlorophyll.
They are either saprophytic or parasitic. The fungi like mucor, moulds,

209 Times' Crucial Science & Environment Book - 8

mushrooms, etc get their food from dead and decayed organic bodies. They are
called saprophytic fungi.

The fungi like Puccinia, grow on the plants body and get
their food from them. They are called parasitic fungi.

Reproduction

Fungi mainly reproduce by asxual methods. The main
asexual methods are fragmentation, budding, fission,
sporulation, etc.

Harmful effects of fungi Mould in a bread

a. Fungi cause various diseases like ringworm, ear and lung infections in
humans, etc.

b. They cause the various diseases like yellowing in leaves, premature
falling of fruits, etc in plants.

c. They damage and decay fruits, vegetables, breads, food, leather, etc.

%HQHÀWV IURP IXQJL
a. Fungi decompose the organic matters and play important role for the

environmental balance.

b. Fungi decompose dead and decayed organic matters and make the soil
fertile.

c. Fungi like yeasts are used in bakeries and various food stuff factories.

d. Fungi like mushrooms are edible and are the sources of various types of
nutrients.

ĐƟǀŝƚLJ ϭϳ͘ϭ To study the growth of mould.

Materials required:
Bread
Procedure:
Take a piece of bread and keep it in a moist and dark place
for 3-4 days. What will you observe after 4 days?
Observation:
You will see blackish green coloured patches in the bread. This is mould.

0RGLÀFDWLRQ RI GLIIHUHQW SDUWV RI SODQWV

Root, stem and leaves are the main parts of plants. The roots grow under the
VRLO DQG DEVRUE ZDWHU DQG PLQHUDO VDOWV 7KH URRWV DOVR À[ WKH SODQW ÀUPO\ WR WKH
soil. The stem grows above the soil and supports the plant. The leaves prepare
food for the plant. These are the usual functions of roots, stem and leaves.

Times' Crucial Science & Environment Book - 8 210

6RPHWLPHV WKH URRWV VWHPV DQG OHDYHV RI SODQWV DUH PRGLÀHG WR SHUIRUP VRPH
additional functions. The change in the position, structure and function of
GLIIHUHQW SDUWV RI SODQWV WR SHUIRUP VSHFLÀF IXQFWLRQ LV FDOOHG PRGLÀFDWLRQ

0RGLÀFDWLRQ RI URRWV

%DVLFDOO\ URRWV À[ WKH SODQW ÀUPO\ WR WKH VRLO DQG DEVRUE ZDWHU DQG PLQHUDOV
IURP VRLO +RZHYHU VRPH URRWV DUH PRGLÀHG WR SHUIRUP VRPH VSHFLÀF IXQFWLRQV
The change in the position, structure and function of roots of plants to perform
D VSHFLÀF IXQFWLRQ LV FDOOHG PRGLÀFDWLRQ RI URRW 7KH URRWV DUH PRGLÀHG WR
perform the following functions:
1. To store food

7KH URRWV DUH PRGLÀHG LQ WKHLU VKDSH DQG VL]H WR VWRUH IRRG 7KH WDS URRWV
DUH PRGLÀHG DV IROORZV
a. Round and swollen beginning with sharply tapering end, e.g. turnip.
b. Swollen beginning part with gradually tapering lower end, e.g. carrot.
c. Wide or swollen middle part with narrow beginning and end, e. g.

radish.
d. Developed as side root but large size with both ends tapering, e.g. sweet

potato.

Turnip Carrot Radish Sweet potato

2. To provide mechanical support to the plant

Additional roots grow from the branches or stem in some plants such as
banyan, maize, bamboo, etc. These roots reach the ground and provide
mechanical support to the plant. Such roots are prominent in maize and
EDPERR 7KH ELJ WUHH RI EDQ\DQ LV À[HG ÀUPO\ WR WKH JURXQG ZLWK WKH
help of additional roots also.

The roots which grow from any part of plant (e.g. branch, node, etc.)
are called adventitious roots. Bamboo, maize, raspberry, sugarcane, etc.
have such roots. These roots provide mechanical support to the plant.
These roots also absorb water and minerals from the soil.

211 Times' Crucial Science & Environment Book - 8

3. To perform vital functions
The internal functions of organisms such as respiration, circulation,
reproduction, etc are called vital functions. The roots of some plants
contain chlorophyll to prepare food by photosynthesis. The plants of
marshy areas have their roots above the marsh surface to carry out the
process of respiration. Some plants such as hydrilla, water hyacinth, etc
KDYH DLU VSDFHV LQ WKHLU URRWV WR KHOS WKH SODQW LQ ÁRDWLQJ 7KH URRWV RI
parasitic plants absorb nutrients from their living host. Thus, the roots
of some plants perform vital functions.

0RGLÀFDWLRQ RI VWHP

Normally, a stem holds the plant upright and helps to transport water and
PLQHUDOV DV ZHOO DV SUHSDUHG IRRG +RZHYHU VRPH VWHPV DUH PRGLÀHG WR VXLW
the changed environment or to perform some additional functions. There are
WKUHH W\SHV RI PRGLÀFDWLRQ RI VWHP
8QGHUJURXQG PRGLÀFDWLRQ

7KH PRGLÀFDWLRQ RI underground part of some stems to store food by
WXUQLQJ LQWR WKLFN DQG ÁHVK\ SDUW LV FDOOHG XQGHUJURXQG PRGLÀFDWLRQ of
stem. For example, the underground stem of potato grows from its root
and becomes thick and ÁHVK\ to store food. Ginger and garlic are also the
XQGHUJURXQG PRGLÀFDWLRQ RI VWHP WR VWRUH IRRG

Potato Ginger Garlic

6XE DHULDO PRGLÀFDWLRQ

The stems of some plants such as strawberry, grass, etc have weak
running stems. Such runner stems grow parallel to the ground. New
plants with their own roots grow from the nodes of stem that touch soil.
6XFK VDSOLQJV FDQ EH SODQWHG LQ RWKHU SODFHV 7KXV WKH PRGLÀFDWLRQ RI
stem in which new plants grow from the nodes of stem that touch soil is
called VXE DHULDO PRGLÀFDWLRQ Grass, strawberry, sweet potato, etc have
VXE DHULDO PRGLÀFDWLRQ

Times' Crucial Science & Environment Book - 8 212

Grass Strawberry Sweet potato

$HULDO PRGLÀFDWLRQ

6RPH SODQWV KDYH WKLFN DQG ÁHVK\ VWHPV WKDW VWRUH ZDWHU 7KHLU OHDYHV
DUH LQ WKH IRUP RI WKRUQV WR UHGXFH WKH ZDWHU ORVV 7KH PRGLÀFDWLRQ LQ
WKH DHULDO SDUW RI VWHP WR VWRUH IRRG E\ WXUQLQJ LQWR WKLFN DQG ÁHVK\ SDUW
LV FDOOHG DHULDO PRGLÀFDWLRQ 7KH DHULDO PRGLÀFDWLRQ is found in cactus,
opuntia, nerium, etc.

ĂĐƚƵƐ KƉƵŶƟĂ EĞƌŝƵŵ
Tendril of pea
0RGLÀFDWLRQ RI OHDI

The usual function of leaves is to prepare food by
the process of photosynthesis. But the leaves of
VRPH SODQWV DUH PRGLÀHG LQ WKH IRUP RI tendrils,
thorns, stem, bladder, etc.

7KH OHDYHV RI FDFWXV RSXQWLD EDUEDU\ ÀJ HWF DUH
very much reduced to needle like thorns. Such
PRGLÀFDWLRQ RI OHDYHV KHOSV WKH SODQWV WR UHGXFH
water loss by the process of transpiration.

Pitcher plant Sundew Dionea

213 Times' Crucial Science & Environment Book - 8

The thorns also save the plants from herbivorous animals. In some plants
such as pea plant, the leaf gets elongated and coiled. It is known as tendril.
The tendrils help the plant to climb on a support. Similarly, the leaves of some
insectivorous plants are in the form of bladder. Such bladder helps to trap the
insects and digest them.

/LIH F\FOH RI D ÁRZHULQJ SODQW

$ ÁRZHULQJ SODQW FDQ EH GLYLGHG LQWR WZR SDUWV RQ WKH EDVLV
of structure and function. They are: vegetative part and
reproductive part. The root, stem, branches, and leaf are
called the vegetative SDUWV RI D SODQW 7KH ÁRZHU LV FDOOHG
the reproductive part because it takes part in reproduction
to produce seeds.

Flower

)ORZHU LV WKH UHSURGXFWLYH RUJDQ RI D ÁRZHULQJ SODQW
Flower has a stalk called pedicel with which it is attached
WR WKH VWHP RU EUDQFK 7KH ÁDWWHQHG WLS RI WKH SHGLFHO LV
called thalamus. 9DULRXV SDUWV RI WKH ÁRZHU JURZ IURP WKH WKDODPXV

Corolla Gynoecium
Androecium

Thalamus Calyx

Pedicel

ZĞƉƌŽĚƵĐƟǀĞ ƉĂƌƚƐ ŽĨ Ă ƉůĂŶƚ

$ W\SLFDO ÁRZHU FRQVLVWV RI IRXU SDUWV 7KH\ DUH FDO\[ FRUROOD DQGURHFLXP DQG
gynoecium.

Calyx

,W LV WKH RXWHUPRVW ZKRUO RI D ÁRZHU ,W LV
green in colour. One unit of calyx is called
sepal. The sepals may be free or joined.
7KH ÁRZHUV ZLWK IUHH VHSDOV DUH FDOOHG
SRO\VHSDORXV ÁRZHU 7KH ÁRZHUV ZLWK
joined sepals are called gamosepalous
ÁRZHUV 7KH VHSDOV SURWHFW ÁRZHUV LQ EXG 'ĂŵŽƐĞƉĂůŽƵƐ ŇŽǁĞƌ WŽůLJƐĞƉĂůŽƵƐ ŇŽǁĞƌ

stage. They also carry out photosynthesis.

Times' Crucial Science & Environment Book - 8 214

Corolla

7KH VHFRQG ZKRUO RI WKH ÁRZHU LV FDOOHG FRUROOD. One unit of it is called petal.
The petals are colourful and attractive. The petals may be free or joined with
HDFK RWKHU 7KH ÁRZHUV ZLWK IUHH SHWDOV DUH FDOOHG SRO\SHWDORXV ÁRZHUV While
WKH ÁRZHUV ZLWK SHWDOV MRLQHG ZLWK HDFK RWKHU DUH FDOOHG JDPRSHWDORXV ÁRZHUV

'ĂŵŽƉĞƚĂůŽƵƐ ŇŽǁĞƌ WŽůLJƉĞƚĂůŽƵƐ ŇŽǁĞƌ

Petals attract insects for pollination.

Androecium anther

$QGURHFLXP LV WKH WKLUG ZKRUO RI D ÁRZHU ,W LV WKH PDOH
UHSURGXFWLYH SDUW RI D ÁRZHU 2QH XQLW RI DQGURHFLXP LV ĮůĂŵĞŶƚ
called stamen. A stamen consists of stalk-like structure
called ÀODPHQW and swollen structure at the tip called pollen grains

anther. Anther produces a number of grains called
pollen grains. Male gametes develop inside the pollen
grains. Male gametes take part in sexual reproduction.
stamen

Gynoecium
Gynoecium is the innermost whorl of a ƐƟŐŵĂ
ÁRZHU ,W LV D IHPDOH UHSURGXFWLYH SDUW style
A gynoecium consists of one or more
carpels or pistils. The carpels may be free
or fused. A carpel consists of three parts: ovary
Ovary, style and stigma. The swollen base nucellus female
of a carpel is ovary. The ovary contains 2 polar gametes
ovules. Female gametes develop inside Ovule nuclei (n)
the ovules. Female gametes take part in egg call (n)

sexual reproduction. integuments
Style is a long and thread-like structure
Carpel

developed from the ovary. The tip of the style is little bit wider with lobes. It is
called stigma. The stigma catches the pollen grains during pollination.

215 Times' Crucial Science & Environment Book - 8

ĐƟǀŝƚLJ ϭϳ͘Ϯ 7R VWXG\ YDULRXV SDUWV RI D ÁRZHU

Materials required:
$ PXVWDUG RU KLELVFXV ÁRZHU
Procedure:
7DNH D PXVWDUG ÁRZHU RU KLELVFXV ÁRZHU
2. Observe its different parts. What do you see?
Observation:
You can see green leaf-like parts surrounding
the inner parts. These green parts are called
sepals. Remove these sepals carefully. You can
see colourful attractive parts. They are petals.
Remove these petals carefully. You can see stalk-like structure swollen at the
top. They are stamens. The sack like structure at the top is called anther. The
anther contains powdery yellow pollen grains.
Remove these stamens carefully. The remaining part is carpel. It contains
swollen base called ovary and elongated style. The ovary contains grain-like
ovules. The style ends with swollen top. It is stigma.

$ ÁRZHU KDYLQJ DOO IRXU ZKRUOV LV FDOOHG complete ÁRZHU. For example mustard,
KLELVFXV URVH SHD HWF 7KH ÁRZHU KDYLQJ WKH DEVHQFH RI RQH RU PRUH ZKRUOV LV
incomplete ÁRZHU )RU H[DPSOH PDL]H VXQ ÁRZHU HWF

Pollination ^ĞůĨͲƉŽůůŝŶĂƟŽŶ

The pollen grains produced in the anther ƌŽƐƐͲƉŽůůŝŶĂƟŽŶ
of androecium contain male gametes.
The pollen grains produced in the
anther of androecium are transferred to
the stigma of carpel by various agents
like water, air, insects, animals, etc.
The process of transfer of pollen grains
IURP DQWKHU WR WKH VWLJPD RI D ÁRZHU LV FDOOHG SROOLQDWLRQ It is of two types:
self pollination and cross pollination.

Self pollination is the process of transfer of pollen grains from anther to the
stigma of the same flower, whereas cross pollination is the process of transfer
of pollen grains of one flower to the stigma of another flower. External agents
like insects, animals, wind, water, etc are required for cross pollination.

Fertilization

After the pollen grains are transferred to the stigma of carpel, the pollen grain
develops a tube called pollen tube. The pollen tube grows downward through
style and finally reaches the ovule in the ovary.

Times' Crucial Science & Environment Book - 8 216

The male gametes contained in the pollen grain grow downward and fuse with
female gametes contained in the ovules. This process is called fertilization.
The process of fusion of male and female gametes is called fertilization. The
fertilization in angiosperms is double fertilization in
^ƟŐŵĂ

which one male gamete fuses with an egg cell to form Style

zygote and another male gamete fuses with the secondary Pollen tube

nucleus to form endosperm.

After fertilization, zygote divides and forms embryo Ovary

whereas the endosperm divides to form endosperm of the Ovule
seed. The embryo is the baby plant and the endosperm is
WKH IRRG VWRUDJH WLVVXH RI WKH VHHG 2YXOH ÀQDOO\ GHYHORSV Micropyle

into seed and the ovary into fruit.
&ĞƌƟůŝnjĂƟŽŶ

The fruit contains one or more seeds. The seeds when
become fully mature, fall to the ground and germinate into baby plants under
favourable conditions of water, air, temperature, etc.

ŇŽǁĞƌ

Adult plant ĨĞƌƟůŝnjĂƟŽŶ
'ĞƌŵŝŶĂƟŽŶ

seeds

njLJŐŽƚĞ ĨŽƌŵĂƟŽŶ

Ripe fruit Fruit

>ŝĨĞ ĐLJĐůĞ ŽĨ ŵƵƐƚĂƌĚ ƉůĂŶƚ

The baby plants grow into adult plants which contain various parts such as
OHDYHV VWHP EUDQFKHV ÁRZHUV URRWV HWF )ORZHUV GHYHORS LQWR IUXLWV 6HHGV
contained in the fruits again germinate. Thus, the same process repeats and
WKH OLIH F\FOH RI D ÁRZHULQJ SODQW FRPSOHWHV LQ YDULRXV VWDJHV

Structure of seeds

Size and shape of seeds differ from fruits to fruits. Some seeds are big and some
are small. Some contain only one cotyledon while others contain two cotyledons.
The seed containing only one cotyledon is called monocotyledonous seed and the
seed containing two cotyledons is called dicotyledonous seed. Maize, rice, wheat,

217 Times' Crucial Science & Environment Book - 8

etc have monocotyledonous seeds. Mango, papaya, pea, bean, grain, etc have
dicotyledonous seeds. Though the seeds differ in shape and size, they have some
common structures. Generally, seeds contain the following parts.

a) Seed-coat b) Embryo c) Endosperm

a. Seed coat Embryo
It is the outermost layer of the
seed. It consists of two layers Seed coat
in dicot seeds. The outer layer Radicle
is called testa and the inner
layer is called tegman. The Cotyledons
seed coat gives protection to (Seed leaves)
the embryo.
Parts of a seed (Bean seed)

The seed is attached to the fruit at hilum. Close to the hilum, there is
a small hole called micropyle. Water is absorbed to the seed through
micropyle.

Function: It protects embryos and endosperm.

b. Embryo

It is a part of the seed which grows into seedling. It is also called baby
plant. In dicot seeds, embryo is situated between two cotyledons. It
contains two parts-plumule and radicle. The plumule is surrounded by
small leaves. The radicle is protected by a cap. As the seed germinates,
plumule grows into shoot and the radicle grows into root. Cotyledons
DUH ÁHVK\ ERGLHV ,Q PRQRFRW VHHGV WKHUH LV RQO\ RQH FRW\OHGRQ ,Q GLFRW
seeds, there are two cotyledons.

Function: It develops into a new plant.

c. Endosperm

Endosperm is the food storage tissue. It forms the main part of the
grain in monocot seeds. It reserves food materials, particularly starch.
Endosperm is small or absent in dicot seeds. The seeds containing large
endosperms are called endospermic seeds.

Regions of embryo

The axis of embryo can be divided into three regions. They are: epicotyle,
mesocotyle and hypocotyle.

Epicotyle

It is the portion which lies just above the point of attachment of cotyledons.

Times' Crucial Science & Environment Book - 8 218

Mesocotyle Epicotyle
It is the portion at which the cotyledons are Mesocotyle
attached with the embryo.

Hypocotyle Hypocotyle
It is the portion which lies just below the point WĂƌƚƐ ŽĨ ĞŵďƌLJŽ
of attachment of the cotyledons.

ĐƟǀŝƚLJ ϭϳ͘ϯ To observe the various parts of a seed.

Materials required:
Some bean seeds, pea seeds, maize seeds, a beaker, water, etc.
Procedure:
1. Take some bean seeds, pea seeds and maize seeds in a beaker.
2. Put water to the beaker to soak the seeds.
3. Observe the various parts of the seeds after 1 day.

Observation:
All seeds contain outer cover called seed coat. When the seed coat is carefully
SHHOHG RXW WKH HQWLUH ÁHVK\ SDUW LV VHHQ ,W LV FRW\OHGRQ ,Q SHD DQG EHDQ VHHGV
there are two cotyledons. When these two cotyledons are carefully separated,
embryo is observed at either side of the cotyledon. But, in maize seed, the seed
coat is not easily peeled out. However, the two parts are distinctly observed.
The smaller portion is embryo and the bigger portion is endosperm.

Differences between monocot and dicot seeds

Monocot seed Dicot seed

1. It consists of single cotyledon, i.e. 1. It consists of two cotyledons, i.e.
single seed leaf in a seed. two seed leaves in a seed.

2. It bears a large endosperm. 2. It does not have endosperm.

3. A monocot seed bears a small embryo. 3. The embryo is comparatively
bigger.

4. Hilum and micropyle are not visible 4. Hilum and micropyle are easily
to our eyes. seen.

219 Times' Crucial Science & Environment Book - 8

5. Plumule of a monocot seed is very 5. Plumule of a dicot seed is big.
small.

6. The fruit cover and the seed cover are 6. Separate seeds are present inside
fused and the fruit and seed cannot be the pod or fruit.
separated.

Dispersal of seeds
Plants are fixed to the ground. So, they cannot move from one place to another.
If fruits and seeds fall directly underneath the mother plant, the new seedlings
grow up close to one another. Due to this, there may be crowd of the plants
and there may be lack of sufficient space and food. To avoid from this, seeds
are scattered to different places far away from the mother plant naturally by
various means. This process is called dispersal of seeds.
Dispersal of seed is the process by which seeds are scattered to various places
far away from the mother plant by various means.
There are various ways of dispersal of seeds. Some of them are as follows:

a) by wind b) by water

c) by explosive fruits d) by man and other animals

a. By wind ŽƩŽŶ ƐĞĞĚƐ
Seeds of some plants contain wings, hairs, pappus,
etc. These structures make them light enough so
that they can be carried easily by the air from one
place to another.
Examples of the wind dispersed seeds are cotton,
simal, grass, poppy, sal, etc.

b. By water

6HHGV RI VRPH SODQWV FRQWDLQ ÁRDWLQJ GHYLFHV LQ WKH
IRUP RI VSRQJ\ RU ÀEURXV RXWHU FRDWV 6HHGV RI QXW
FRFRQXW HWF FRQWDLQ ÀEURXV FRDW DQG FDQ ÁRDW RQ
water for long distances without suffering any injury.

Examples of water dispersed seeds are coconut, nut, Coconut seed
walnut, lotus, etc.

c. By explosive fruits

Some fruits burst with a sudden jerk, so that >ĂĚLJΖƐ ĮŶŐĞƌ ƐĞĞĚƐ
the seeds are scattered on all sides. Ripe
IUXLWV RI ODG\·V ÀQJHU burst with great force
scattering the seeds. In the same way, fruit

Times' Crucial Science & Environment Book - 8 220

of camel’s foot climber explodes with a loud noise like cracker scattering
the seeds long distance away.

([DPSOHV RI H[SORVLYH IUXLWV DUH SHD ODG\·V ÀQJHU EDOVDP FDVWRU HWF

d. By man and other animals

Some fruits are provided with hooks, barbs,
spines, bristles, stiff hairs, etc on their surface.
These fruits attach with the body of animals
with these structures. Then the seeds or fruits
are carried to long distance by animals.

Germination of seeds ŝƐƉĞƌƐĂů ŽĨ ƐĞĞĚ ďLJ Ă ďŝƌĚ

When seeds get suitable conditions, they develop into new seedlings. This
process is called germination of seeds.

The process of development of an embryo of a seed into seedling is called
germination.

ĨŽůŝnjŐĞ ůĞĂǀĞƐ
ĐŽůĞŽƉƟůĞ

radicle

Seeds of some plants do not germinate immediately after they fall from the
parent plants. They require resting period to be ready for germination. Such
resting period is called dormancy period.
Seeds become active under favourable conditions and they germinate.
The favourable conditions required are adequate water, oxygen, suitable
temperature, etc.

ĐƟǀŝƚLJ ϭϳ͘ϰ To study the conditions required for germination

Materials required:
Three bean seeds, a beaker, ruler, thread, water.
Procedure:
1. Take a ruler and tie three bean seeds one above

another in three positions.
2. Keep the ruler in a beaker.

221 Times' Crucial Science & Environment Book - 8

3. Pour water into the beaker in such a way that the lowest seed is completely
under the water, middle seed lies partly immersed in the water and the
upper seed lies above the water.

4. Observe the seeds after 3 days.
Observation:
The seed under the water does not germinate but it decays. The middle seed
germinates into seedling. The uppermost seed does not show any sign of
germination.
Conclusion
The lowermost and the topmost seeds do not germinate due to lack of favourable
conditions of water and air. But, the middle seed gets favourable conditions
and it germinates.

ĐƟǀŝƚLJ ϭϳ͘ϱ To study the type of germination

Materials required:
Three maize seeds, three pea seeds, pot, soil
Procedure:
1. Take a pot and put some soil on it.
2. Sow the seeds of maize and pea in the soil.
3. Spray water to the soil to make it moist
4. Observe what happens after few days.
Observation:
The pea seeds germinate with cotyledons above the soil while the maize seeds
germinate with cotyledons inside the soil.
Conclusion:
The pea seeds show epigeal germination and the maize seeds show hypogeal
germination.

ƉĂƌĂƐŝƟĐ : living a parasite on other organisms body
decompose : break into small pieces
borderline ͗ ďŽƵŶĚĂƌLJ ƐĞƉĂƌĂƟŶŐ ƚǁŽ ĂƌĞĂƐ Žƌ ƐƵďƐƚĂŶĐĞƐ
ĐŚŝƟŶ : a chemical found in cell wall
lipid : a chemical found in cell wall
ŇĞƐŚLJ ͗ ŚĂǀŝŶŐ ůĂƌŐĞ ĂŵŽƵŶƚ ŽĨ ŇĞƐŚ

Times' Crucial Science & Environment Book - 8 222

1. The organisms which are composed of only one cell are called unicellular organisms.
2. The organisms which are composed of many cells are called multi-cellular organisms.
3. Nuclear material is not bounded by nuclear membrane in prokaryotic cells.
4. Nuclear material is bounded by nuclear membrane in eukaryotic cells.
5. Bacteria are primitive and the smallest unicellular organisms.
6. Bacilli, cocci and spiral are various shaped bacteria.
7. Bacteria cause various diseases in humans.
8. Viruses are the most primitive and the smallest micro-organisms.
9. Viruses are the borderline between living things and non-living things.
10. Viruses cause various diseases like mumps, measles, AIDS, rabies, etc in humans.
11. Fungi are those organisms which generally grow on dead and decayed organic matters.
12. Fungi cause various diseases such as ringworm, ear and lung infections in humans.
13. Fungi decompose dead and decayed organic materials and make the soil fertile.
14. Roots, stems and leaves are vegetative parts of plants
15. The part of the plants which grows under the soil is called root.
16. The roots fix the plants to the soil and absorb minerals from the soil.
17. The flat green outgrowths of stem or branches of plants are called leaves.
18. Leaves are the food factories of plants.
19. The part of the plant which grows upward from the ground and bears branches,

leaves and flower is called shoot.

20. Stem transports raw materials and prepared foods throughout the body.

Exercise

A. Fill in the blanks with appropriate words.
1. Unicellular organisms are composed of only one ……………...
2. Nuclear material is not bounded by nuclear membrane in ………….
3. The protein cover of virus is called ……………...
4. Dead and decayed materials decomposed by micro-organisms make
the soil ……………...
5. The fungi which get their foods from dead and decayed organic
bodies are called ……………...
6. Roots, stems and leaves are …………….. parts of plants.
7. …………….. the food factories of plants.

223 Times' Crucial Science & Environment Book - 8

B. Copy the correct statements and correct the wrong statements.
1. Viruses behave like both living and non-living things.
2. Prokaryotic cells are well developed cells.
3. Flagella are contained in virus.
4. The bacteria which get their food from the body of living things
are called parasitic bacteria.
5. Mushrooms, mucors, moulds, etc are viruses.

C. Answer these questions in short.
1. What are unicellular organisms? Give some examples.
2. What is an eukaryotic cell? Where is it present?
3. What is a micro-organism? Give some examples.
4. What is bacteria? Where are they found?
5. What is saprophytic bacteria? What are various shapes of bacteria?
6. What is virus? Why is it called borderline between living things and
non-living things.
:KDW LV FDSVLG" 'UDZ D ÀJXUH RI EDFWHULRSKDJH YLUXV
8. What is fungi? What is hypha?
9. What are various parts of a seed?
10. What are the various layers of a seed-coat? Mention the function of
seed-coat.
11. What is an embryo? What are the various parts of an embryo?
12. What is an endosperm? Name some seeds which contain large endosperm.
13. What is dispersal of seed? How is dispersal of seed carried out?
14. What is germination of seeds? Describe with suitable diagrams.
15. What is pollination? What are the various agents for pollination?
16. What is fertilization?

D. Give reasons:
1. Bacteria and virus are micro-organisms.
2. Fungi are called saprophytes.
3. Virus is borderline between living thing and non-living thing.
4. Yeast is unicellular fungus.

Times' Crucial Science & Environment Book - 8 224

E. Answer in detail:
([SODLQ WKH EHQHÀWV DQG KDUPV RI EDFWHULD IRU KXPDQ EHLQJV
([SODLQ EHQHÀFLDO HIIHFWV DQG KDUPIXO HIIHFWV RI YLUXVHV
([SODLQ KDUPIXO HIIHFWV DQG EHQHÀFLDO HIIHFWV RI IXQJL
4. Draw a diagram of mustard plant and label its important parts.
'UDZ D ÁRZHU VKRZLQJ LPSRUWDQW SDUWV DQG GHVFULEH WKHP
6. Explain the structure of a seed.
7. Explain the various means of dispersal of seeds.
8. Explain fertilization process in detail.
([SODLQ YDULRXV VWDJHV RI OLIH F\FOH RI D ÁRZHULQJ SODQW

F. Name the parts shown in the diagram.

A
B
C

D

G. Give reasons:
3HWDOV RI ÁRZHUV DUH FRORXUIXO DQG DWWUDFWLYH
2. Animals play important role for the dispersal of seeds.

7DNH D PXVWDUG RU KLELVFXV ÁRZHU DQG REVHUYH LWV YDULRXV SDUWV DQG SDVWH
each part in your project work copy separately and name them.

225 Times' Crucial Science & Environment Book - 8

18CHAPTER Cell, Tissue
and Organ

Zacharias Janssen

Zacharias Janssen was a Dutch spectacle-maker from Middelburg
DVVRFLDWHG ZLWK WKH LQYHQWLRQ RI WKH ÀUVW RSWLFDO WHOHVFRSH -DQVVHQ LV
VRPHWLPHV DOVR FUHGLWHG IRU LQYHQWLQJ WKH ÀUVW WUXO\ FRPSRXQG PLFURVFRSH

Estimated Periods : 7
Objectives: At the end of the chapter, the students will be able to:

GHILQH FHOO WLVVXH DQG RUJDQV
H[SODLQ WKH UHODWLRQVKLS RI FHOO WLVVXH DQG RUJDQV
H[SODLQ YDULRXV W\SHV RI DQLPDO WLVVXH DQG SODQW WLVVXH
H[SODLQ WKH UHODWLRQVKLS RI FHOO WLVVXH DQG RUJDQV RI D KXPDQ ERG\

What are buildings made up of?
What is body of animals or plants made up of?
How are cells, tissues and organs related?
What are the various types of tissues present in human body? Discuss.

Introduction

Buildings are made up of bricks. Bricks are joined together by cement or mud.
Similarly, body of every living thing is made up of cells. Body of an organism
may be made of one cell or many cells. Various functions taking place inside
the body of living things take place inside the cells. Respiration, digestion,
growth, cell division, etc take place inside the cells. The structure of the body
of an organism depends upon the arrangement of the cells. Thus, FHOO LV GHÀQHG
as structural and functional unit of life. You have already studied about the
structure of cells in earlier classes.

In unicellular organisms, all the processes like respiration, growth, excretion,
reproduction, etc are performed within the single cell. But, in multicellular
organisms, there are separate groups of cells responsible for separate functions.
Such group of cells are called tissues. Thus, tissue is the group of cells which
have similar structure and perform the similar function.

Times' Crucial Science & Environment Book - 8 226

Animal tissue

On the basis of structure and function, animal tissues are divided into the
following types:

a) Epithelial tissue b) Muscular tissue

c) Connective tissue d) Nervous tissue

7KHVH WLVVXHV DUH IXUWKHU FODVVLÀHG LQWR WKH IROORZLQJ W\SHV

Animal tissue

Epithelial tissue Muscular tissue Connective tissue Nervous tissue

Pavement epithelium Voluntary muscle
Cubical epithelium Involuntary muscles
Columnar epithelium Cardiac muscles
Glandular epithelium
Ciliated epithelium

Epithelial tissue

Epithelial tissue is found in the outer and inner lining of various organs of a
human body. It is found in the inner walls of blood vessels, ducts or cavities.
It is composed of single or many layers of cells. Epithelial tissues have the
following features:
a) The epithelial tissues are attached with basement membranes at the

lower part.
b) Cells are closely packed without intercellular space.
c) Cells are arranged either in a single layer or multiple layers.
d) There are no blood vessels in this tissue.

Functions:

a) Epithelial tissues protect the underlying tissues from mechanical
injuries, entry of germs, and harmful chemicals.

b) They help in absorption of digested foods, water, etc to the body.

227 Times' Crucial Science & Environment Book - 8

c) They help to secrete hormones and enzymes.

d) They excrete unnecessary and waste things from the body.

Types of epithelial tissue

a) Pavement epithelium Apical Surface

Pavement epithelium is a single Basement
layered epithelial tissue. The cells Membrane
DUH WKLQ EURDG DQG ÁDW ZKLFK DUH
arranged like mosaic tiles on the Nucleus Pavement epithelium
ÁRRU 7KHUHIRUH WKH\ DUH FDOOHG
pavement epithelium.

They are also called squamous epithelium.

Location: It is found in skin, blood vessels, lungs, heart, kidneys, body
cavities, etc.

Functions: 3URWHFWLRQ ÀOWUDWLRQ PDNLQJ SDVVDJH IRU OLTXLGV DQG JDVHV

b) Cubical epithelium

It is also single layered epithelial tissue. The
cells are cubical having similar dimensions
in each side. The cells are attached with
each other at lateral surfaces.

Location: It is found in tubules of kidney, Basement
thyroid glands, ducts of excretory glands, Membrane
inner parts of ovary, etc. Cubical epithelium

Functions: Protection, secretion, germination, etc.

c) Columnar epithelium

It is also found in a single layer. It consists Columnar epithelium
of elongated cells which are placed side by
side like columns. The cells are attached
to the basement membranes.

Location: It is found in the form of lining layer of stomach, intestine,
reproductive organs, gall bladder, salivary glands and their ducts, etc.

Function: Absorption, secretion, etc.

d) Glandular epithelium

,W LV D PRGLÀHG IRUP RI FROXPQDU HSLWKHOLXP LQ ZKLFK FHOOV DUH specialized
for the manufacture and secretion of chemical substances such as
hormones, enzymes, mucus, etc.

Times' Crucial Science & Environment Book - 8 228

Pavement epithelium of different parts Goblet cell Tall Columnar Cell
Location: It is located in various types
of glands such as pancreas, liver, sweat
gland, etc.

Functions: Secretion of hormones,
enzymes, mucus, etc.

e) Ciliated epithelium

,W LV DOVR D PRGLÀHG IRUP RI FROXPQDU EƵĐůĞŝ Ăƚ ĚŝīĞƌĞŶƚ ůĞǀĞůƐ Basal cell

epithelium. Cells are arranged in a single Glandular epithelium

OD\HU ,W KDV ÀQH KDLU OLNH VWUXFWXUHV Cilia
called cilia at the free structure. The cilia
are always in motion. Thus, they sweep
away dust and other particles.

Location: It is found in the lining of
buccal cavity, neck of urinogenital
tubules, retina of eyes, etc.

Functions: Making passage for ova, Ciliated epithelium
making the part sensitive, etc.

ĐƟǀŝƚLJ ϭϴ͘ϭ To observe the chicken skin under microscope

Materials required:

A piece of skin of chicken, foreceps, slide,
methyl blue, cover slip, microscope, toothpick,
water glass, etc.

Procedure:

1. Take a piece of skin of chicken and scratch
it with a pointed toothpick.

2. Place the scratched part on a clean watch glass.

3. Put a drop of methyl blue on the scratched part.

4. Put the scratched part on a clean slide and cover it with a cover slip.

5. Observe the slide under the microscope. What do you see?

Observation:

<RX FDQ ÀQG WKH WLVVXH FRQWDLQLQJ WKH FHOOV DWWDFKHG WRJHWKHU ,W LV HSLWKHOLDO WLVVXH

Plant tissue

Plant body is composed of various types of tissues. The plant tissue can be
divided into three types. They are:

i) Meristematic tissue ii) Permanent tissue iii) Special tissue

229 Times' Crucial Science & Environment Book - 8

Meristematic tissue

It is made up of the cells which have the capacity of cell division. The cells
are closely attached to each other. The cells contain protoplasm with large
nucleus. Vacuoles are absent in them and the cell wall is thin. Meristematic
tissue LV IXUWKHU FODVVLÀHG LQWR WKUHH W\SHV RQ WKH EDVLV RI ORFDWLRQ
i) Apical meristematic tissue
ii) Lateral meristematic tissue
iii) Intercalary meristematic tissue

Apical meristematic tissue

It is present at the apex of stem, root or branch. It is responsible for increasing
the length or height of a plant.

Lateral meristematic tissue

It is present along the side of the stem or root. Due to its location at the side,
it is called lateral meristem. It is responsible for the increase of thickness or
girth of stem and root.

Intercalary meristemic tissue

7KH PHULVWHPDWLF WLVVXH ZKLFK LV ORFDWHG DW WKH EDVH RI OHDYHV RU ÁRZHUV DERYH
the node is called intercalary meristematic tissue. It increases the length of
internodes.

Apical meristem Apical meristem

Intercalary meristem

Lateral meristem
dLJƉĞƐ ŽĨ ŵĞƌŝƐƚĞŵĂƟĐ ƟƐƐƵĞ

Permanent tissue

It is the tissue which is composed of cells that have lost the capacity of cell
division. The cells may be either living or dead and thin walled or thick walled.
They have intercellular space ÀOOHG ZLWK DLU 7KH SHUPDQHQW WLVVXHV DUH RI
three types. They are:
i) simple permanent tissue
ii) complex permanent tissue
iii) special permanent tissue

Times' Crucial Science & Environment Book - 8 230

Simple permanent tissue

A simple permanent tissue consists of similar type of cells. They perform
FRPPRQ IXQFWLRQ ,W LV IXUWKHU FODVVLÀHG LQWR parenchyma, collenchyma and
sclerenchyma.

Parenchyma

It is composed of oval, spherical or
polygonal cells. It is found in root,
stem and leaves of plants. The cells
are living and thin walled. These
cells may contain chlorophyll. The
parenchyma containing chlorophyll is
called chlorenchyma. It is responsible
for photosynthesis. Its main function ƉĂƌĞŶĐŚLJŵĂ

is to conduct water, food, etc. It protects and keeps the plant in turgid condition.

Collenchyma

It consists of living cells with thick Wall thickenings
cell wall. In these cells, corners
are thick due to deposition of extra
Nucleus

cellulose and protein at the edges of
the cells.
Vacuole

It is located below the epidermis of Cell wall
stem and petiole of leaves. It provides
mechanical support to the plant body. dƌĂŶƐǀĞƌƐĞ ƐĞĐƟŽŶ
ŽůůĞŶĐŚLJŵĂ

The collenchyma containing chlorophyll is responsible for photosynthesis, too.

Sclerenchyma

The cells of sclerenchyma are very long, narrow and thick
walled dead cells. The cytoplasm is little or absent. The cell
wall is thick due to deposition of cellulose and lignin.

It is located at the the hard parts of plant like seeds, cover
of seeds, shells of nuts, etc. It provides mechanical support
and hardness to the various parts of plants.

The permanent tissue which consists of various types of ^ĐůĞƌĞŶĐŚLJŵĂ
cells that work together is called complex permanent tissue.
Xylem and phloem are examples of complex permanent
tissue. Xylem and phloem are responsible for the conduction
of materials in various parts of plant. Therefore, xylem and
phloem is collectively called vascular or conducting tissue.

231 Times' Crucial Science & Environment Book - 8

Relationship between cells, tissues and organs

All living things are composed of cells. Some living things are composed of
only one cell. They are called unicellular organisms. In such organisms, all life
activities take place within a single cell. But, most of the organisms are made
up of many cells. They are called multicellular organisms. In such organisms,
various organs and systems are formed for carrying out various functions.
For example, for breathing and respiration, organs like nose, lungs, pharynx,
bronchi, trachaea, etc come into use. These organs collectively form respiratory
system. The organs are formed by the combination of tissues. Thus, organ can
EH GHÀQHG DV D SDUW RI V\VWHP ZKLFK LV IRUPHG E\ WKH FRPELQDWLRQ RI WLVVXHV
of various types. Tissues are formed by the combination of cells of similar or
different types. In human beings too, cells of similar type or origin combine
together to form tissue. Tissues carry out certain functions. Tissues of various
types remain in group to form organs. An organ is a part of system which
performs a particular function. Group of various organs work together to form
a system.
&HOOV ń 7LVVXHV ń 2UJDQV ń 6\VWHPV ń %RG\
Body of an organism functions due to interrelationship among cells, tissues,
organs and systems. For example, digestive system of human being consists of
organs like mouth, tongue, throat, foodpipe (oesophagus), stomach, intestine,
salivary gland, liver, pancreas, etc. The main function of the digestive system
is to digest food and absorb the digested food.
The following table shows the systems in human body, their organs, tissues
and functions.

6 1 6\VWHP Organs of system Kinds of Major functions
1. tissues Grinding,
Digestive digestion,
System Mouth, stomach, Columnar absorption of foods
2. liver, pancreas, epithelium, Inhale and exhale
Respiratory intestine involuntary of oxygen
System muscle
3. Excretion of waste
Excretory Nasal chamber, Pavement products
System trachea, bronchus, epithelium,
lungs, etc. cubical
epithelium

Kidney, liver, Pavement
ureter, urinary and cubical
bladder, gall epithelium
bladder

Times' Crucial Science & Environment Book - 8 232

4. Circulatory Heart, blood Cardiac muscle, To supply food and
connective R[\JHQ ÀJKW ZLWK
System vessels, blood tissue, pavement disease germs.
epithelium

5. Skeletal Bones and Connective To give frame
System Cartilage tissue work, to help in
locomotion

6. Reproductive Male: Testes, penis Cubical and
System columnar
Female: Vagina, epithelium Reproduction
ovary

7. Nervous Brain, spinal cord Nervous tissue To control all
System and nerves (neuron) activities of the
body

8. Glandular Liver, Pancreas, Digestion, growth
system thyroid, etc Secretory tissue & development of

body

9. Muscular Muscles Muscle cells & Giving shape and
system PXVFOH ÀEUHV movement of body

epithelial ͗ ƚŚŝŶ ƟƐƐƵĞ ĨŽƌŵŝŶŐ ŽŶ ƚŚĞ ŽƵƚĞƌ ůĂLJĞƌ
intercellular : between cells
mechanical : related to machine or force
tubules : small tubes
gall bladder : a small sac shaped organ below liver
lignin : a chemical found on cell wall

1. Tissue is a group of cells which have similar structure or origin and perform a
particular function.

2. Epithelial tissue is found in the outer and inner lining of various organs of human
body.

3. Epithelial tissues protect the underlying tissue from mechanical injuries, entry of
germs and harmful chemicals.

4. Pavement epithelium is a single layered epithelial tissue which consists of thin,
broad and flat cells.

5. Cubical epithelial tissue consists of the cells having similar dimensions in each side.

6. Columnar epithelial tissue consists of elongated cells which are placed side by side
like columns.

233 Times' Crucial Science & Environment Book - 8

7. Glandular epithelial tissue is modified form of columnar epithelial tissue which is
modified for the manufacture and secretion of various chemicals.

8. Ciliated epithelial tissue is a modified form of columnar epithelial tissue in which
hair-like cilia are present at the free structure of cells.

9. Nervous tissue builds up nervous system which controls and co-ordinates the
activities of human body.

10. The plant tissue which contains the cells having capacity of cell division is called
meristematic tissue.

11. Apical meristematic tissue is located at the apex of stem, root or leaves.

12. Lateral meristematic tissue is located at the lateral side of stem, root or leaves.

13. The tissue which contains the cells that have lost the capacity of cell division is
called permanent tissue.

14. Parenchyma, collenchyma, sclerenchyma, etc are simple permanent tissues.

Exercise

A. Answer the following questions in short.
1. What is tissue? Mention various types of animal tissues.
2. What is epithelial tissue? Mention its features.
3. What are various functions of epithelial tissue?
4. Mention location and function of pavement epithelial tissue.
5. What is cubical epithelial tissue? Mention its location and function.
6. What is columnar epithelial tissue? Mention its location and function.
7. What are various types of muscular tissue?
8. What is cardiac muscular tissue? What is its function?
9. What is meristematic tissue? Mention its types.
10. What is apical meristematic tissue? Mention its functions.
11. What is permanent tissue? Mention the various types of simple
permanent tissue.

B. Give reasons.
1. Skeletal muscular tissue is called voluntary muscle.
2. Plant stops growing in length when its tip is cut.
3. Cell is called functional and structural unit of life.
4. Cover of coconut, walnut, etc is hard.

Times' Crucial Science & Environment Book - 8 234

& ,GHQWLI\ WKH IROORZLQJ ÀJXUHV c)

a) b)

d)

e)

D. Draw labelled diagrams of:

1. Parenchyma 2. Columnar epithelium

E. Explain relationship of cells, tissues, organs and systems.

7DNH WKH JURZLQJ WLS RI VWHP RI D GLFRW SODQW &XW D YHU\ WKLQ ÀOP IURP LW
using a sharp blade and study its cells and tissues under microscope. Draw
WKH GLDJUDP DQG H[SODLQ \RXU ÀQGLQJV

235 Times' Crucial Science & Environment Book - 8

19CHAPTER Life
Processes

Jean-Baptiste Lamarck
Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, often known

VLPSO\ DV /DPDUFN ZDV D )UHQFK QDWXUDOLVW +H LV IDPRXV IRU ODPDUFNLVP

Estimated Periods : 14

Objectives: At the end of the chapter, the students will be able to:

GHILQH OLIH SURFHVVHV
WHOO WKH PHDQLQJ DQG W\SHV RI UHSURGXFWLRQ
H[SODLQ PHWKRGV RI VH[XDO DQG DVH[XDO UHSURGXFWLRQ
H[SODLQ SURFHVV RI EORRG FLUFXODWLRQ LQ KXPDQ ERG\
H[SODLQ SKRWRV\QWKHVLV SURFHVV LQ SODQWV

What is life process?
Do life processes take place in non-living things?
Why is reproduction important?
Can you say various types of reproduction?
What is blood circulation? Why is it important?
What is photosynthesis? Why is it important? Discuss.

19.A Reproduction

The number of living things of a certain species does not decrease, even though
they die of various reasons. This is possible due to reproduction. Reproduction
is the process by which all living things produce new offspring of their own
kind. It is needed for the continuity of race. It is of two types:

a) Asexual reproduction b) Sexual reproduction

a) Asexual reproduction

The reproduction which takes place without fusion of male and female gamete
is called asexual reproduction.

Times' Crucial Science & Environment Book - 8 236

In this reproduction, there is no involvement of both male and female parents.
Only one individual is able to produce new offspring.

Asexual reproduction occurs in organisms by the following methods:

i) Fission ii) Budding iii) Regeneration

iv) Sporulation v) Vegetative propagation

Fission

In this method, a unicellular organism divides into two or more cells. Each
newly formed cell is new unicellular organism. The offspring are totally similar
to their parents.

Parent amoeba Division of nucieus Division of cytoplasm New amoeba

ŝŶĂƌLJ ĮƐƐŝŽŶ ŝŶ ŵŽĞďĂ

Amoeba, Paramecium, Euglena, unicellular fungi, etc reproduce by ÀVVLRQ.

Budding

In this process, an outgrowth is developed from the parent body. The outgrowth
is called bud. The bud when becomes fully mature, gets detached from the
parent body and grows into a new individual.

Bud

Parent hydra Growing Bud New hydra

ƵĚĚŝŶŐ ŝŶ ŚLJĚƌĂ

Yeast, hydra, cactus, etc reproduce by budding.

Regeneration Grows new
head
In lower animals like sponges, Anterior
FRHOHQWHUDWHV ÁDWZRUPV WDSHZRUP half with
and echinoderms, small parts get
detached from the parent body. Each Flatworm no tail
part develops into complete organism. divides in two
This process is called regeneration. Posterior half Grows
with no head new tail

ZĞŐĞŶĞƌĂƟŽŶ ŝŶ WůĂŶĂƌŝĂ

237 Times' Crucial Science & Environment Book - 8

Sporulation Sporangium
Spores
,Q VRPH QRQ ÁRZHULQJ SODQWV OLNH IHUQV
bryophytes, mushroom, mucor, etc, spores are
produced. These spores are produced inside
sacs called sporangia. These spores germinate
into new individuals under favourable
conditions.

Mushroom, mucor, fern, bryophytes, etc ^ƉŽƌƵůĂƟŽŶ ŝŶ ŵƵĐŽƌ
reproduce by this method.

Vegetative propagation

Some plants reproduce by vegetative parts such as root, stem, leaves, etc.

By roots: Plants like sweet potato, dahlia, etc propagate by roots.

By stem: Some plants like rose, potato, onion, ginger, etc propagate by stem.

By leaves: Plants like bryophyllum, begonia, etc reproduce by leaves. In the
margins of leaves of these plants, buds are developed. These buds get detached
from the leaves when they become mature. These buds grow as individual
plants later.

WƌŽƉĂŐĂƟŽŶ ďLJ ƐƚĞŵ WƌŽƉĂŐĂƟŽŶ ďLJ ƌŽŽƚ WƌŽƉĂŐĂƟŽŶ ďLJ ůĞĂĨ

Importance of asexual reproduction

a) Large number of organisms can be grown from a single organism.

b) The offspring are similar to the parents.

c) Some plants like bamboo, sweet potato, etc do not bear seeds. They
reproduce by asexual method only.

Sexual reproduction

It is a type of reproduction which involves the fusion of male and female
gametes. Developed plants and animals reproduce by sexual method.

Male gametes are produced in the body of male organisms and female gametes
are produced in the body of female organisms. Male gamete and female gamete
fuse together to form a zygote.

Times' Crucial Science & Environment Book - 8 238

The process of fusion of male gamete and female gamete is called fertilization.

The zygote divides and forms embryo. The embryo ^ƟŐŵĂ
grows into new individual. Style
In plants, male gametes are produced inside the pollen Pollen tube
grains which are developed in the anther of stamen.
Similarly, female gametes are produced inside the ovule Ovary
which are developed inside ovary. After pollination, Ovule
pollen grains are transferred to the stigma of carpel. The Micropyle
pollen grain develops pollen tube which grows towards
ovule. The male gamete moves through the pollen tube &ĞƌƟůŝnjĂƟŽŶ
towards the female gamete (ovule). They get fused and
a zygote is formed. The ovule changes into seed and the
zygote into embryo.

The seed germinates under favourable conditions of heat, light, air, etc. to
produce new offspring.

In animals, male gamete called sperm is produced inside the testes and
female gamete called egg is produced inside the ovary. The sperm and egg fuse
together to form a zygote. This process is called fertilization. The fertilization
may be either external or internal. If the fusion of male and female gamete
takes place outside the body of organism, the fertilization is called external
fertilization ,W WDNHV SODFH LQ IURJ ÀVK HWF ,I WKH IXVLRQ RI PDOH DQG IHPDOH
gamete occurs inside the body of female organism, the fertilization is called
internal fertilization. Internal fertilization takes place in reptiles, aves and
mammals.

The zygote divides and develops into a new baby.

6LJQLÀFDQFH RI VH[XDO UHSURGXFWLRQ

a. Offspring produced by sexual reproduction are different from parents.
Hence, new types of offspring are developed.

b. The offspring produced by sexual reproduction are more advanced than
the parents.

Differences between internal fertilization and external fertilization

Internal fertilization External fertilization

1. In this fertilization, male gamete 1. In this fertilization, male gamete
and female gamete fuse inside and female gamete fuse outside the
the body of female. body of female.

2. It occurs in cow, dog, man, duck, ,W RFFXUV LQ IURJ ÀVK HWF
etc.

239 Times' Crucial Science & Environment Book - 8

Differences between sexual reproduction and asexual reproduction

6H[XDO UHSURGXFWLRQ Asexual reproduction

1. The reproduction which takes 1. The reproduction which takes
place by the fusion of male and place without fusion of male and
female gamete is called sexual female gamete is called asexual
reproduction. reproduction.

2. Two individuals, i.e. one male 2. Only one individual is able to
and another female is needed to carry out this reproduction.
accomplish this reproduction.

3. New types of offspring are 3. It produces similar offspring as
produced. parent

ŽīƐƉƌŝŶŐƐ : babies
spores ͗ ƐŵĂůů ƌĞƉƌŽĚƵĐƟǀĞ ĐĞůů

1. Reproduction is the process of production of offspring by an organism.

2. Asexual reproduction is the reproduction which takes place without fusion of male
and female gamete.

3. In fission, one unicellular organism divides to form two or more new cells.

4. In budding, small buds are developed from the parent body and grow into individual
when detached from the parent body.

5. Reproduction that occurs through vegetative parts like leaf, stem or root is called
vegetative propagation.

6. The reproduction which takes place by the fusion of male and female gametes is
called sexual reproduction.

7. The fusion of male and female gametes is called fertilization.

8. External fertilization takes place outside the body of female.

9. Internal fertilization takes place inside the body of female.

Exercise

1. Answer these questions in short.
1. What is reproduction? Mention differences between sexual and
asexual reproduction.
2. Mention various methods of asexual reproduction.

Times' Crucial Science & Environment Book - 8 240

3. What is budding? Name any four organisms which reproduce by
budding.

4. What is sporulation? Name any two plants that reproduce by
sporulation.

5. What type of reproduction occurs in amoeba? Explain.
:KDW LV VH[XDO UHSURGXFWLRQ" :KDW DUH LWV VLJQLÀFDQFH"
7. What is fertilization? Distinguish between internal and external

fertilization.
2. Mention the mode of reproduction in the following organisms.

Amoeba, hydra, cactus, mushroom, rose, potato, tapeworm, bryophyllum

Visit the garden of your school or home and observe the vegetative propagation
of different plants. Write the parts through which the plants are being
propagated. Also draw the relevant diagrams and explain them.

241 Times' Crucial Science & Environment Book - 8

19.B Blood Circulation

Every organism needs oxygen, water, hormones, nutrients, etc to be supplied
to every cell. The waste materials such as carbon dioxide, urea, uric acids,
waste products, etc need to be removed from the cells. This is done by transport
system ,Q DQLPDOV WUDQVSRUWDWLRQ RI WKRVH WKLQJV LV GRQH E\ EORRG DQG ÁXLGV
whereas it is done in plants by xylem and phloem.

,Q KXPDQ EORRG DQG ÁXLGV DUH WUDQVSRUWHG E\ D V\VWHP QDPHG EORRG FLUFXODWRU\
system.

The circulatory system consists of mainly three parts: blood, blood vessels and
heart.

Blood

%ORRG LV D ÁXLG FRQQHFWLYH WLVVXH ZKLFK NHHSV RQ FLUFXODWLQJ WKURXJKRXW WKH
body. It consists of blood cells suspended in plasma.

Plasma

It is liquid portion of blood. It constitutes 55% of the total blood volume. It is
a straw coloured transparent liquid. It contains more than 90% water, and
about 10% other substances like dissolved food, mineral salts, waste products
like urea, uric acid DPPRQLD HWF ,W DOVR FRQWDLQV SURWHLQV OLNH ÀEULQRJHQ
albumen, globulin, various types of hormones, etc. It also contains heparin
which prevents blood circulating in the blood vessel from clotting.

Functions

i) It transports digested food such as glucose, amino acids, etc to various
parts of the body.

ii) It transports excretory products to the excretory organs.

iii) It transports carbon dioxide to the lungs.

iv) It carries hormones secreted by the endocrine glands to the various parts.

Blood cells

There are three types of blood cells RBC
suspended in the blood. They are: WBC
erythrocytes, leucocytes, and platelets.

Erythrocytes (Red blood cells or RBCs) Plasma
Platelets

These are disc-shaped cells. They are
biconcave, i.e. pressed inwards in
Structure of Blood

the middle. They do not contain nucleus. They are covered by highly elastic
PHPEUDQH ZKLFK HQDEOHV WKHP WR SDVV WKURXJK ÀQH FDSLOODULHV WRR $ERXW 4.5

Times' Crucial Science & Environment Book - 8 242

to 5 million RBCs are present in 1 cubic millimeter of blood. They are formed
in red bone marrow and are destroyed in spleen and liver.
They contain haemoglobin which is iron rich pigment. It makes the blood red
in colour. Haemoglobin carries oxygen from lungs to the different cells. The
decrease in the number of red blood cells causes the disease named anaemia.

Leucocytes (White blood cells or WBCs)
Leucocytes are larger in size but fewer in number. Generally 8,000 to 11,000
WBCs DUH SUHVHQW LQ FXELF PLOOLPHWHU RI EORRG 7KH\ KDYH QR À[HG VKDSH
They contain large nucleus.
:%&V DUH SURGXFHG LQ ERQH PDUURZ 7KH\ ÀJKW ZLWK GLVHDVH JHUPV DQG
destroy them.

Functions
D 7KH\ ÀJKW ZLWK GLVHDVH JHUPV
b. They produce antibodies against different pathogens and protect the

body against various diseases.

Thrombocytes (Platelets)

Platelets are fragments of larger cells. They are smaller in size. They lack
nucleus and are irregular in shape. They are also produced in red bone marrow.
Their number ranges between 2 to 4 millions in one cubic millimeter of blood.

Functions
They clot blood during injury and prevent excessive bleeding.

Differences between red blood cells and white blood cells

RBCs WBCs

1. RBCs are small and biconcave in 1. WBCs are large and irregular in
shape. shape.

2. They are about 4 to 5 millions in 1 2. They are about 8000 to 11000 in 1
cubic millimeter of blood. cubic millimeter of blood.

3. Haemoglobin is present in it. 3. Haemoglobin is absent in it.

4. They carry oxygen from lungs to 7KH\ ÀJKW ZLWK GLVHDVH JHUPV
various cells.

5. They do not have nucleus. 5. They have nucleus

Blood vessels

Blood vessels are network of tube-like structures that carry blood to various
parts. They are of three types: arteries, veins and capillaries.

243 Times' Crucial Science & Environment Book - 8

Arteries Tunica

They carry blood pumped by heart externa Tunica
to different parts. The arteries media
Tunica
further divide into smaller vessels interna

Lumen

called arterioles 7KH EORRG ÁRZLQJ
through them has high pressure.
To withstand high blood pressure,
the walls of the arteries are thick
and elastic. All arteries carry /ŶƚĞƌŶĂů ƐƚƌƵĐƚƵƌĞ ŽĨ ĂƌƚĞƌLJ

oxygenated blood except pulmonary artery.

Veins

Veins are blue coloured blood vessels. They collect blood from different organs
and pour to the heart. They carry blood with low pressure. They have thin
walls and valves 7KH YDOYHV SUHYHQW WKH EDFN ÁRZ RI WKH EORRG 7KH RSHQLQJ
of the valve is in the direction of
KHDUW ZKLFK FDXVHV WKH ÁRZ RI Tunica Tunica
externa interna

blood towards heart only.

Veins are formed by joining Valves
of smaller blood vessels called
venules. All veins carry Lumen
deoxygenated blood except Tunica
pulmonary veins. media

Internal structure of vein

Capillaries

Capillaries are very thin hair-like blood vessels Capillaries
which supply blood to every cell. They connect
arterioles and venules in the form of network.
They help to exchange nutrients, gases, etc
between blood and cells of the body.
Differences between arteries and veins

Arteries Vein

1. They are blood vessels which 1. They are blood vessels which carry
carry blood from heart to different blood from different organs to the
organs. heart.

2. They are thick walled. 2. They are thin walled.

%ORRG ÁRZLQJ WKURXJK WKHP KDV %ORRG ÁRZLQJ WKURXJK WKHP KDV
high pressure. low pressure.

4. Valves are absent in them. 4. Valves are present in them.

Times' Crucial Science & Environment Book - 8 244

Heart

It is the main part of blood Aorta
circulatory system. It is
roughly conical in shape Superior venacava
and located in the middle
of the chest cavity. It is Right auricle >ĞŌ ĂƵƌŝĐůĞ

made up of thick cardiac
muscles. It is covered by
double walled membranous Inferior venacava >ĞŌ ǀĞŶƚƌŝĐůĞ

sac called pericardium. In Right ventricle
this sac, there is a liquid
External Structure

FDOOHG SHULFDUGLDO ÁXLG
which protects the heart from mechanical injury like jerks and shock. Heart of
human body consists of four chambers. The upper two chambers are called
auricles and lower two chambers are called ventricles. The heart is divided
into left and right by a septum.

Two large veins called
superior venacava and Superior venacava
inferior venacava open Aorta
to right auricle. A valve Pulmonary artery
named tricuspid valve Pulmonary vein
is present between >ĞŌ ĂƵƌŝĐůĞ
Right auricle Bicuspid valve
>ĞŌ ǀĞŶƚƌŝĐůĞ
right auricle and right Tricuspid valve
ventricle. It lets the blood Right ventricle Septum
ÁRZ IURP ULJKW DXULFOH WR Inferior venacava
right ventricle but not in
opposite direction. Internal Structure

Pulmonary artery originates from right ventricle and grows towards lungs.
Pulmonic valve is present between pulmonary artery and right ventricle. Left
auricle is connected with four pulmonary veins which carry blood from lungs
to the heart. Left auricle opens to left ventricle through bicuspid valve. A large
blood vessel named aorta originates from the left ventricle. It carries blood
from the heart to various part of the body. Aortic valve is present between
aorta and left ventricle.

Flow of blood

Deoxygenated blood is collected from upper parts of the body by superior
venacava and from lower parts by inferior venacava to the right auricle. From
ULJKW DXULFOH EORRG ÁRZV WR WKH ULJKW YHQWULFOH WKURXJK tricuspid valve. The
right ventricle pumps the blood to the lungs through pulmonary artery. The
pulmonary artery divides into left and right pulmonary arteries to carry blood

245 Times' Crucial Science & Environment Book - 8

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carbon dioxide.
The oxygenated blood is carried from each lung to the left auricle by two
pulmonary veins. The oxygenated blood passes from the left auricle to the left
ventricle through bicuspid valve. From the left ventricle, blood is carried by
aorta to the various parts when the left ventricle contracts.
The aorta divides into small arteries then to the arterioles. The arterioles
further divide into capillaries in the organs. The capillaries supply oxygen to
the organs. Some capillaries collect carbon dioxide and supply to the veins.
Veins combine together to form venacava. From the venacava, blood comes to
the right auricle.

Aorta

Right auricle Arteries
Arterioles
Left ventricle Capillaries

Vena cava

Veins Systemic Circulation of
Blood

Venules Tissues

Capillaries

In the same way, blood circulation continues.
Functions of blood circulation
1. It supplies dissolved food, oxygen, hormones, water, etc to the various parts.
2. It removes waste things from the cells to the excretory organs.
3. It helps to keep temperature of the body uniform.
4. It maintains the various compositions of the blood in right amount.

hormones : chemicals produced by glands
Urea : chemical thrown by kidney through urine

Times' Crucial Science & Environment Book - 8 246