Modern Concept Science and Technology 9

Nature of Carbon

Carbon has four electrons in its valence shell. So, carbon attains stable electronic configuration
in the following ways:
a. By gaining four electrons in the valence shell
b. By losing four electrons from the valence shell
c. By sharing four valence electrons with other atoms
Carbon atom has small atomic size and more electronegativity. So it attracts electrons strongly
towards its nucleus. Therefore, loss or gain of four electrons by carbon atom is not possible.
As a result, carbon shares its valence electrons with other atoms to attain stable electronic
configuration. Hence, it forms four covalent bonds as shown in the given structure.

1p+

H
6p+ Or H C H

1p+ 6n0 1p+

H
Methane

1p+

Molecular structure of methane

Carbon shows mutual sharing of its four electrons with other carbon atoms or atoms of other
elements to form a large number of covalent compounds. Carbon is one of the unique elements
which can join with each other to form a long carbon chain which is called catenation property
of carbon. Due to this property of carbon, a large number of carbon compounds are found
in nature. In fact, the number of carbon compounds is more than the number of compounds
formed from other elements. This is the reason why we have a separate branch of chemistry to
study carbon compounds or hydrocarbons which is called organic chemistry.

FACT WITH REASON

Why do carbons make a covalent bond?
There are four valence electrons in carbon. Due to small atomic size, it can neither lose four electrons nor
gain four electrons to be stable. So, it forms covalent bond by sharing electrons.

Sources of Carbon

Carbon occurs in different forms in nature. The major sources of carbon are as follows:
a. All organic compounds which are obtained from living organisms contain carbon.

Modern Concept Science - 9 243

b. Rocks containing carbonate, minerals, petrol, natural gases contain carbon as one of the
constituents.

c. Carbon monoxide, carbon dioxide, etc. contain carbon as one of the elements.

The various forms (sources) of carbon in the form of element, compound and gas are given
below:

Carbon (in the Carbon (in the form of compounds)
form of element)
Organic Inorganic Carbon (in the form of gas)
compounds compounds

1. Coal 1. Carbohydrate 1. Carbonates 1. Carbon dioxide

2. Coke 2. Protein 2. Bicarbonates 2. Carbon monoxide

3. Charcoal 3. Fat (ghee, oil) 3. Carbides (e.g. 3. Hydrocarbon gases (e.g.

CaC2, SiC, etc.) methane, ethane, propane,
butane, LPG, CNG, etc.)

4. Graphene 4. Petrol 4. Minerals

5. Graphite 5. Diesel 5. Rocks

6. Diamond 6. Urine

7. Vitamins

8. Silk

9. Paper

10. Soap

11. Wool

Physical Properties of Carbon

1. It is present in amorphous and crystalline solids.

2 It is a non-metallic element. Memory Tips

3. It shows different allotropes. 1. Lampblack is the form
of carbon which can be
Allotropy of Carbon obtained from the flame of
the kerosene lamp. It is used
The different forms of an element having similar chemical to make black ink. Similarly,
properties but different physical properties are called it is also used as collyrium
allotropes. The characteristic by virtue of which carbon exists (gajal).
in various forms in nature is called allotropy.
ii. Coke is a fuel with few
Carbon is a non-metallic element which occurs in different impurities and high carbon
physical forms. Diamond, graphite, coal, charcoal, etc. are the content. Usually it is made
allotropes of carbon. Among them, some exist in crystalline from coal. It is used as a fuel.
form like diamond and graphite and some in amorphous form
like coal, charcoal, coke, etc.

244 Carbon and its Compound

Allotropes of Carbon

Crystalline forms Amorphous forms

Diamond Coal

Graphite or black lead Coke

Fullerene Charcoal

Lamp black

a. Diamond

Diamond is one of the purest forms of carbon. It is non-conductor, transparent, colourless
and precious crystalline solid. It is the hardest substance known. It is insoluble in all
ordinary solvents. It is used for making ornaments, cutting glass, drilling hard rocks, etc.

In a diamond crystal, each carbon atom is CC
combined to four other carbon atoms by C
covalent bonds. Hence all the four valence
electrons of each carbon atom are used up CC
in the bond formation without leaving free
electron/s. As a result, diamond cannot Structure of diamond
conduct heat and electricity. Therefore,
diamond is a bad conductor of heat and
electricity.

Properties of Diamond

i. Diamond is the purest allotrope of carbon. In its purest form, diamond is a colour-
less, lustrous, crystalline solid.

ii. It is the hardest substance known. Its specific gravity is 3.52 and its refractive in-
dex is 2.415.

iii. Natural diamond is transparent to X-rays whereas artificial diamonds are opaque.
This property is used for distinguishing natural and artificial diamonds.

iv. It is a non-conductor of electricity and is insoluble in all liquids.

v. It gets converted into graphite when heated at about 1800°C.

vi. When it is heated in the presence of excess air and at very high temperature, it
burns to from carbon dioxide.

vii. Diamond has extraordinary brilliance.

Modern Concept Science - 9 245

Uses of Diamond
i. Diamond is used for making valuable jewellery due to its extraordinary brilliance.

ii. It is used extensively for cutting, grinding and polishing as it is the hardest
substance known.

iii. It is also used for drilling hard rocks.
b. Graphite

Graphite is a soft and the purest form of carbon. It is Structure of graphite
dark grey and crystalline powder with metallic lustre.
It has free mobile electrons. So it is a good conductor
of heat and electricity. Graphite occurs in hexagonal
layers. One layer can slip over the surface of another
layer.

In a graphite crystal, each carbon atom is connected to only three other carbon atoms
by covalent bonds. The fourth valence electron of each carbon atom is free to move.
As a result, graphite can conduct heat and electricity. Therefore, graphite is a good
conductor of heat and electricity.

Properties of graphite
i. Graphite is a soft and greasy non-metal.

ii. It is dark grey in colour and has a metallic lustre.

iii. It crystallizes in the hexagonal form and has a specific gravity of 2.2 which is
much lower than that of diamond.

iv. Unlike diamond, it is a good conductor of heat and electricity.

v. Its melting point is 3527°C.

Uses of graphite
i. Graphite is used for making lead pencils, electrodes and electric furnaces.

ii. It is also used as a lubricant for machinery.

iii. It is used as a coating for iron to prevent rusting.

iv. In nuclear reactors, it is used as a moderator as it absorbs neutrons and helps in
controlling reactions.

v. It is also used in electrotyping.

FACT WITH REASON

Graphite can be used as a dry lubricant, why?

Graphite can be used as a dry lubricant because it is soft and slippery. There is weak bonding force among
its layers. The graphite layer can slide one upon another. So, it helps to reduce friction and used as a dry
lubricant.

246 Carbon and its Compound

Differences between Diamond and Graphite

S.N Diamond S.N Graphite

1. It is the hardest allotrope of carbon. 1. It is soft and slippery allotrope of carbon.

2. It is a bad conductor of heat and 2. It is a good conductor of heat and
electricity. electricity.

3. It is a transparent crystalline 3. It is a dark grey and opaque substance.
substance.

4. Its specific gravity is 3.52. 4. Its specific gravity is 2.2.

Chemical Properties of Carbon
a. Combustion in air

Carbon burns in excess air to give carbon dioxide gas.
C + O2 ∆ CO2
If the amount of oxygen is insufficient, it forms carbon monoxide.

2C + O2 2CO

b. Reducing nature of carbon

Carbon is a good reducing agent. It reduces less reactive metallic oxides into free metal.
PbO + C ∆ Pb + CO
ZnO + C ∆ Zn + CO

FACT WITH REASON

Carbon is called a reducing agent. Why?
Carbon is called a reducing agent because it reduces less reactive metal oxide into free metal.

c. Reaction with steam Memory Tips

When carbon is strongly heated with steam at about The mixture of carbon monoxide
900–10000C, a mixture of carbon monoxide and and hydrogen (CO + H2) is called
hydrogen gas is obtained which is called water gas. water gas. It is used in industries as
a source of heat.
C + H2O 900 – 1000ºC CO + H2 (water gas)

d. Reaction with calcium oxide (CaO)

When carbon reacts with calcium oxide or lime, it gives calcium carbide and carbon
monoxide.

3C + CaO CaC2 + CO (Calcium carbide)

Modern Concept Science - 9 247

e. Reaction with metal

Carbon reacts with calcium and forms calcium carbide.

2C + Ca CaC2 (Calcium carbide)

Organic and Inorganic Compounds

In ancient time, scientists believed that organic compounds are produced within the body of

living beings by the natural process. They also believed that formation of organic compounds

takes place under the influence of vital force and they cannot be prepared in laboratory. But

in 1828 AD, German chemist Friedrich Wohler synthesized urea in the laboratory by heating

ammonium cyanate.

NH4CNO ∆ NH2 – CO – NH2 Memory Tips

(Ammonium cyanate) (Urea) There are certain compounds like
CO2 and CO that contain carbon but
Here, ammonium cyanate is an inorganic compound are traditionally called inorganic
whereas urea is an organic compound. This experiment compounds. Compounds like
displaced the vital force theory of organic compounds. CaCO3, Na2CO3, etc. also contain
Thereafter many organic compounds were synthesized carbon atom but they have
artificially in the laboratory. The compounds formed by electrovalent bond and they do
reaction of carbon with elements like hydrogen, oxygen, not have hydrogen. So these
nitrogen, etc are called organic compounds. Examples: compounds are called inorganic
Methane, ethane, propane, butane, alcohol, ether, glycerol, compounds.

etc. The branch of chemistry in which we study about Memory Tips
organic compounds is called organic chemistry.
Organic compounds are usually
The compounds which are derived from minerals are called soluble in organic solvents, such
inorganic compounds. They contain other elements except as ether, alcohol, benzene, etc.
hydrocarbon. For example, water, sodium chloride, calcium and insoluble in water. Whereas
carbonate, hydrochloric acid, etc. The branch of chemistry inorganic compounds are soluble
in which we study about inorganic compounds is called in water, but insoluble in organic
inorganic chemistry. solvents.

FACT WITH REASON

Why is alcohol called an organic compound?
Alcohol is called an organic compound because carbon atoms and hydrogen atoms of alcohol are covalently
bonded.

Generally organic compounds burn, why?
Organic compounds have low melting and boiling points. So, they burn faster and easily when heated.

248 Carbon and its Compound

Differences between Organic and Inorganic compounds

S.N. Organic compounds S.N. Inorganic compounds

1. Carbon containing compounds are 1. Compounds of elements other than

called organic compounds. hydrocarbon are called inorganic

compounds.

2. They have covalent bond. So they 2. They have electrovalent bond. So they

are called covalent compounds. are called electrovalent compounds.

3. They have low melting and boiling 3. They have high melting and boiling

point. point.

4. They are soluble in organic solvents 4. They are soluble in water.
like ether, benzene, etc.

5. They burn easily. 5. They do not burn easily.

6. Organic compounds are generally 6. Many inorganic compounds are

covalent compounds and do not electrovalent and usually ionize in water.

ionize when they dissolved in water.

ANSWER WRITING SKILL

1. In which group and period of modern periodic table does carbon atom belong to?
Ans: Group of carbon – IV A and Period of carbon – 2nd period
2. Name any two organic sources of carbon.
Ans: Carbohydrate and protein are two organic sources of carbon.
3. Write the names of any two allotrope of carbon.
Ans: Two allotropes of carbon are diamond and graphite.
4. What are organic compounds? Give examples.
Ans: Those chemical compounds which have carbon atom in their molecular structure connected by a

covalent bond are called organic compounds. Examples: carbohydrates, proteins, fat, etc.
5. Define inorganic compounds with an example.
Ans: Those chemical compounds which do not have carbon atom in their molecular structure which is

connected by an electrovalent bond are called inorganic compounds. Examples: sodium chloride,
ammonium chloride, sulphuric acid, etc.
6. Why is a graphite good conductor of electricity?
Ans: In graphite, three electrons of each carbon atom are bonded by single covalent bond with other atoms of
carbon.Thereisafreeelectronineachcarbonatom. Suchfreeelectronsineachatomscanconductelectricity.
7. Diamond cannot pass electricity, why?
Ans: Diamond cannot pass electricity because all four electrons of each carbon atom in diamond are bonded
by single covalent bond. The electrons in single covalent bond are strongly localized. Hence, there are
no free electrons in diamond to transfer electricity.

Modern Concept Science - 9 249

8. Write down the uses of diamond.
Ans: Diamond is used for following purposes:

i) Diamond is used as a stone for rings.
ii) Diamond is used in jewelry like necklace and rings.
iii) Diamond is used to make windows of space craft.
iv) Diamond is attached in teeth or nails for decoration.

9. Write any four uses of graphite.

Ans: Graphite is used for following purposes:
i) Graphite is used as lubricant.
ii) Graphite is used to make lead of pencils.
iii) Graphite is used to make crucibles.
iv) Graphite is used to make electrodes for electrolysis.

10. When firewood burns with enough air, eye does not burn but if fire wood is wet or if air is less, then
smoke burns our eye? Explain the chemistry behind it with balanced chemical equation.

Ans: When firewood burns with enough air, there is enough oxygen, so carbon dioxide is produced

during the reaction. Carbon dioxide does not burn eyes.

C + O2 CO2+ heat

When firewood burns with less amount of air, there is less oxygen, so carbon monoxide is produced

which burns eye.

2C+ O2 2CO + Δ

STEPS EXERCISE

STEP 1

1. Define the following terms b) Allotropes
a) Catenation property of carbon d) Diamond
c) Allotropy f) Organic compounds
e) Graphite h) Inorganic compounds
g) Organic chemistry j) Hydrocarbons
i) Inorganic chemistry

2. Very Short Answer Questions
a) What is carbon?
b) What are the sources of carbon in nature?
c) Name two crystalline allotropes of carbon.
d) Name two amorphous allotropes of carbon.
e) Give two examples of organic compounds.

250 Carbon and its Compound

f) Give two examples of inorganic compounds.
g) Which type of chemical bond is present in each of organic compounds and

inorganic compounds?
h) What is the valency of carbon?
i) What is water gas?
j) Write the conditions to produce water gas.
k) What is reducing property of carbon?

STEP 2

3. Differentiate between:
a) Organic compounds and Inorganic compounds
b) Diamond and Graphite

4. Give reason:
a) Diamond cannot conduct electricity but graphite can.
b) Methane is called an organic compound.
c) Graphite is used for making lubricants.
d) Carbon forms covalent bond.

STEP 3

5. Draw the atomic structure of carbon with electronic configuration.
6. Describe an activity to prove that sugar contains carbon.
7. Write any three physical characteristics of carbon.
8. Describe the bonding nature of carbon in brief.
9. Mention any three characteristics each of diamond and graphite.
10. Write any three uses each of diamond and graphite.
11. Mention any three characteristics each of organic and inorganic compounds with any

three examples of each.
12. What are the sources of carbon in nature?

STEP 4

13. What happens when (write with balanced chemical equations)
a) Carbon burns in insufficient oxygen?
b) Carbon is heated with lead oxide?
c) Carbon is heated with steam?
d) Carbon reacts with lime?

Modern Concept Science - 9 251

UNIT Estimated teaching periods Theory Practical
4 2
14
Water

Syllabus issued by CDC River

 Sources of water (Surface and ground sources of water)
 Physical and chemical properties of water
 Solvent property of water
 Uses of water
 Types of water (Hard water and soft water)
 Methods to remove hardness of water

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 describe the sources, properties and uses of water.
 explain the methods of removing hardness of water with chemical equations.

Key terms and terminologies of the unit

1. Water : Water is one of the most important and abundant substances needed by living

beings. It covers approximately 70% of the earth's surface.

2. Sources of water : The sources from which we get water are called sources of water.

3. Surface water sources: The sources of water that are found on the surface of the earth are called surface

water resources.

4. Ground water sources: The sources of water which are found below the surface of the earth are called

ground water sources.

5. Solvent property of water : Water is a universal solvent. It dissolves various organic and inorganic substances

as well as different types of acids, bases, and salts, etc.

6. Soft water : The water that does not contain chloride, sulphate and bicarbonate salts of calcium

and magnesium is called soft water.

7. Hard water : The water that contains the chloride, sulphate and bicarbonate salts of calcium and

magnesium is called hard water.

8. Temporary hard water : The hard water containing bicarbonate salts of calcium and magnesium is called

temporary hard water.

9. Permanent hard water : The hard water containing chloride and sulphate salts of calcium and magnesium

is called permanent hard water.

Introduction

Water is one of the most important and abundant substances needed by living beings. It covers
approximately 70% of the earth's surface. All living beings need water to survive. Water makes
up about 70% of human body. We can survive for a month without food but cannot live more
than a weak without water. Therefore, we should drink water every day.

252 Water

About 97% of the water present on the earth is found only in the oceans. It consists of a lot of
salt dissolved. So it is unfit for drinking. The dead sea contains about 33.7% of salt. So it is too
salty and hence organisms cannot survive in dead sea. But living beings float on dead sea due
to high density of sea water.

In this unit, we will study the sources of water, properties and uses of water and methods of
removing hardness of water.

Sources of Water

The sources from which we get water are called sources of water. From these sources we get
water for drinking, cooking, bathing, irrigating, washing, cleaning, etc. The major sources of
water are given below:

1. Surface water sources

The sources of water that are found on the surface of the earth are called surface water
resources. They can be classified as follows:

a Rain : Rain is a very important source of water. It is the purest form of water.
Rain water can be stored in dams and later used for various purposes.

b Rivers lakes and ponds : Rivers, lakes and ponds are other sources of surface
water. Rivers are formed from the melting of snow lying on the Himalayas.
Similarly, rivers, ponds and lakes are also formed from rains. The rivers like
Koshi, Gandaki, Narayani, Karnali and Mahakali are the main rivers of Nepal.
Phewa lake, Shey Phoksundo lake, Tilicho, etc. are some famous lakes of Nepal.
Similarly, many ponds are found in different parts of the country. These sources
of water are very useful for human beings. The water obtained from these
resources is used for drinking, bathing, cleaning, running factories, generating
hydroelectricity, etc.

Karnali river Phewa lake Tau Daha
Langtang glacier
c Glaciers : Glaciers are other surface water sources
found in the Himalayas. They contain water in solid
state. When the snow or ice melts due to the heat of
the sun, glaciers are formed. Glacial ice is the largest
reservoir of freshwater on the earth. Khumbu is the
biggest glacier and Langtang is the longest glacier
in Nepal.

Modern Concept Science - 9 253

d Oceans : Oceans are the biggest sources of surface
water on the earth. The ocean (Sea) water contains a
lot of salts dissolved in it due to which it is not fit for
human use and irrigation. Ocean water is used for
transportation.

2. Ground water sources: The sources of water Ocean
which are found below the surface of the earth
are called ground water sources. Some of the
rain water which falls on the earth seeps through
the soil and goes down under the surface of the
earth. Ultimately this water is stopped by some
hard rocks and collects there. This underground
water can be taken out by digging well in the
ground.

An underground layer of permeable rock,

sediment, or soil that yields water is called an Ground water

aquifer. Aquifers can range from a few square

kilometers to thousand square kilometers in size. They contain thousand times more

water than that present in river, lakes and ponds. Ogallala aquifer is the largest aquifer

on the earth which is spread about 450,000 km2 in portions of eight states of United States

of America. The underground water does not become stagnant and may come out of the

earth's surface in the form of spouts, fountains, etc.

Physical Properties of Water

1. Pure water is colourless, odourless and tasteless.

2. It exists in solid, liquid and gaseous states.

3. Pure water is transparent.

4. It is a universal solvent.

5. Pure water is a bad conductor of electricity.

6. Its boiling point is 100 0C and freezing point is 00C.

Chemical Properties of Water

1. Pure water does not conduct electricity. But the water having dissolved substance like
salts, acids, etc. conducts electricity.

2. Water reacts with active metals like Li, Na, Ca, etc. and forms base and hydrogen gas.

2H2O + 2Li 2LiOH + H2

2H2O + 2Na 2NaOH + H2

2H2O + Ca Ca(OH)2 + H2

3. Water decomposes acids, bases and salts into their corresponding ions.

HCl H2O H+ + Cl–

254 Water

NaOH H2O Na+ + OH–
NaCl H2O Na+ + Cl–

Solvent Property of Water

Water is a universal solvent. It dissolves various substances like Sodium Chloride (NaCl),
Calcium Chloride (CaCl2), Sodium Nitrite (NaNO3), Copper Sulphate (CuSO4), etc. Different
types of acids, bases, and salts, etc. dissolve in water. Most of the organic compounds and
covalent compounds do not dissolve in water. But the covalent compound like HCl, alcohol,
glucose, urea, etc. dissolve in water. However, covalent compounds like carbon tetrachloride
(CCl4), methane (CH4), ether (CH3-O-CH3), etc. do not dissolve in water.

Uses of Water

1. Water is used for drinking, cooking, bathing, washing, cleaning, etc.

2. Water is used to run factories.

3. Water is used for irrigation.

4. Water is used to generate hydroelectricity.

5. Water is used by green plants for photosynthesis.

6. Water is used for swimming, rafting, boating, etc.

7. Water is used to produce various substances, metals and oil.

8. Water is used for jet cutting, i.e. the process of cutting wood, rubber, etc. by passing
water in very high pressure.

9. Water is used in laboratory to make solution.

Types of Water

On the basis of salts of calcium and magnesium, water is classified into two types, viz. soft
water and hard water.

Soap is used to wash clothes. Whenever we get enough amount of foam or lather by applying
a little soap, we say that the water is soft. But water from some sources like rivers, ponds,
lakes, instead of producing foam, forms sticky particles. Such water is called hard water.

Hardness of water is due to the presence of soluble salts of calcium and magnesium, viz.
chloride, sulphate and bicarbonate salts of calcium and magnesium.

The water that does not contain chloride, sulphate and bicarbonate salts of calcium and
magnesium is called soft water. It produces lather with soap easily. Rain water and distilled
water are some examples of soft water.

The water that contains the chloride, sulphate and bicarbonate salts of calcium and magnesium
is called hard water. It does not produce lather with soap easily. So hard water leads to wastage
of soap. The water of wells, rivers, oceans, etc. is hard.

Modern Concept Science - 9 255

On the basis of salts dissolved, hardness of water is of two types:

i. Temporary hardness

ii. Permanent hardness

i. Temporary hardness

The hard water containing bicarbonate salts of calcium and magnesium is called temporary
hard water. Such type of water is tasty while drinking and makes our bones healthy. This type
of hardness can be removed easily.

Removal of temporary hardness of water

Temporary hardness of water can be removed easily by boiling the water or treating with
lime-water.

a. By boiling water : When the temporary hard water is boiled, the soluble bicarbonate

salts of calcium and magnesium get converted into water insoluble carbonate salts and

settle down at the bottom of the container. These insoluble salts can be filtered away.

Calcium bicarbonate heat Calcium carbonate + Water + Carbon dioxide

Ca(HCO3)2 ∆ CaCO3 + H2O + CO2↑

Magnesium bicarbonate heat Magnesium carbonate + Water + Carbon dioxide

Mg(HCO3)2 ∆ MgCO3 + H2O + CO2↑

b. By treating with lime-water : Temporary hardness of water can also be removed

by adding lime water or slaked lime into the hard water. Calcium hydroxide, i.e. lime

water reacts with bicarbonate of calcium and magnesium and forms insoluble calcium

carbonate which makes the water soft. This method is called Clark's method.

Calcium bicarbonate + Calcium hydroxide Calcium carbonate + Water

Ca(HCO3) 2 + Ca(OH)2 2CaCO3 + 2H2O

Magnesium bicarbonate + Calcium hydroxide Calcium carbonate + Water + Magnesium hydroxide

Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + 2 H2O + Mg(OH)2

ii. Permanent hardness

The hard water containing chloride and sulphate salts of calcium and magnesium is called
permanent hard water.

Removal of permanent hardness of water

Permanent hardness of water can be removed by treating the hard water with
washing soda and permutit process.

a. By treating hard water with washing soda : When permanent hard water is treated
with washing soda or sodium carbonate, the salts present in it change into carbonates

256 Water

and water becomes soft. The chemical reactions involved in this process are given below:

Calcium chloride + Sodium carbonate Calcium carbonate + Sodium chloride

CaCl2 + Na2CO3 CaCO3 + 2NaCl

Calcium sulphate + Sodium carbonate Calcium carbonate + Sodium sulphate

CaSO4 + Na2CO3 CaCO3 + Na2SO4

Magnesium chloride + Sodium carbonate Magnesium carbonate + Sodium chloride

MgCl2 + Na2CO3 MgCO3 + 2NaCl

Magnesium sulphate + Sodium carbonate Magnesium carbonate + Sodium sulphate

MgSO4 + Na2CO3 MgCO3 + Na2SO4

b. By permutit process : In permutit process, the Hard water Sodium chloride

permanent hard water is passed through sodium Soft water

aluminosilicate (Na2Al2SiO8) or sodium zeolite Zeolite
(Na2–Z). When hard water passes through the zeolite
or permutit, the calcium and magnesium ions of Column

hard water get replaced by sodium ions of permutit. Finegravel

As a result, water becomes soft. Permutit process to remove
hardness of water
The chemical reactions involved in permutit method
are given below:

Sodium zeolite + Calcium chloride Calcium zeolite + Sodium chloride

Na2–Z + CaCl2 Ca – Z + 2NaCl
Sodium zeolite + Magnesium chloride Magnesium zeolite + Sodium chloride

Na2 – Z + MgCl2 Mg–Z + 2NaCl
Sodium zeolite + Calcium sulphate Calcium zeolite + Sodium sulphate

Na2 – Z + CaSO4 Ca–Z + Na2SO4
Sodium zeolite + Magnesium sulphate Magnesium zeolite + Sodium sulphate

Na2 – Z + MgSO4 Mg–Z + Na2SO4

ANSWER WRITING SKILL

1. What is water?

Ans: Water is a transparent, odourless and tasteless liquid. It is a compound of hydrogen and oxygen (H2O).
2. Name two salts that cause temporary hardness of water.

Ans: Salts that cause temporary hardness of water are calcium bicarbonate and magnesium bicarbonate.

3. W hat do you mean by permanent hardness of water?

Ans: Hardness of water caused by chloride and sulphate salts of calcium and magnesium is called permanent
hardness of water.

Modern Concept Science - 9 257

4. What is permutit method?

Ans: Permutit method is a process of removing permanent hardness of water by the use of sodium zeolite.

5. Write any two ways of removing temporary hardness of water. (Name only)

Ans: Temporary hardness of water can be removed by the following methods:
i) It can be done by boiling water.
ii) It can be done by the use of lime water.

6. What is the principle of permutit process?

Ans: The principle of permutit process is to replace magnesium or calcium ions by sodium ions.

7. What are the advantages of hard water?

Ans: Advantages of hard water are:
i) Hard water is useful for drinking because it supplies important salts.
ii) Hard water is good for irrigation because it supplies minerals.
iii) Hard water contains salts, which may help to reduce skin diseases.

8. Differentiate between soft water and hard water.

Ans: Differences between soft water and hard water are:

SN Soft water SN Hard water

1 If water does not contain chlorides, 1 If water contains chlorides, sulphates or

sulphates or bicarbonates of magnesium bicarbonates of magnesium or calcium,

or calcium, then it is called soft water. then it is hard water.

2 Soft water produces more lather with soap 2 Hard water does not produce more lather
with soap but it is good for drinking.
but it is not good for drinking purposes.

9. Write any two differences between temporary hardness of water and permanent hardness of water.
Ans: Differences between temporary hardness of water and permanent hardness of water are:

SN Temporary hardness of water SN Permanent hardness of water

1 Hardness of water due to presence of 1 Hardness of water due to presence of sulphate

bicarbonates of calcium or magnesium and chloride of magnesium and calcium is

is called temporary hardness of water. called permanent hardness of water.

2 Temporary hardness of water is usually 2 Permanent hardness of water is usually removed

removed by boiling or using lime water. by using washing soda or sodium zeolite.

10. Explain the solvent property of water.

Ans: Water is a universal solvent. Most of the organic and inorganic compounds dissolve in water. So, it is
called universal solvent. Electrolytes like acid, base and salt dissolve easily in water.

11. How does washing soda remove permanent hardness of water? Mention the chemical formula.

Ans: Washing soda converts soluble chloride and sulphates of Mg and Ca into insoluble carbonates. So,
water becomes soft.

Calcium chloride + Sodium carbonate Calcium carbonate + Sodium chloride

CaCl2 + Na2CO3 CaCO3 + NaCl

258 Water

Magnesium chloride + Sodium carbonate Magnesium carbonate + Sodium chloride
Calcium carbonate + Sodium sulphate
MgCl2+ Na2CO3 Mg CO3 + NaCl
Magnesium carbonate + Sodium sulphate
Calcium sulphate + Sodium carbonate

CaSO4 + Na2CO3 CaCO3 +Na2SO4

Magnesium sulphate + Sodium carbonate

MgSO4+Na2CO3 Mg CO3 +Na2SO4

STEPS EXERCISE

STEP 1

1. Define the following terms:

a) Water b) Sources of water
c) Surface water sources d) Ground water sources
e) Solvent property of water f) Soft water
g) Hard water h) Temporary hard water
i) Permanent hard water

2. Very Short Answer Questions

a) What is water?

b) Name any four sources of surface water.

c) What is underground water?

d) What is surface water?

e) Name two salts that cause temporary hardness of water.

f) What is temporary hardness of water.

g) What do you mean by permanent hardness of water?

h) Name any two chemicals dissolved in hard water..

i) What is Acquifer?

j) What are the two salts that cause permanent hardness in water?

k) Write two examples of soft water.

l) What is permutit method?

m) Name two methods to remove permanent hardness of water.

n) Name the chemical used during permutit process and write its molecular formula.

o) Name the hardness of water caused by bicarbonate of calcium and magnesium.

Modern Concept Science - 9 259

STEP 2

3. What do you mean by soft water? Give an example.
4. Define hard water and list its type.
5. Write any two use of hard water.
6. Write down the uses of soft water.
7. Name the salts with their molecular formula that cause permanent hardness in water.
8. Write any four physical properties of water.
9. Differentiate between:

a) Rain water and Sea water
b) Soft water and Hard water
c) Temporary hard water and Permanent hard water

STEP 3

10. Write any two chemical properties of water with balanced chemical equations.
11. Write a short note on 'solvent property of water'.
12. Write any five uses of water.
13. What is soft water? Write one advantage of soft water.
14. Write any two methods of removing temporary hardness of water.

STEP 4

15. What happens when (write with a balanced chemical equation):
a) Lithium reacts with water?
b) Calcium reacts with water?
c) Calcium hydroxide is kept in water?
d) Sodium chloride is dissolved in water?

16. Write any two methods of removing permanent hardness of water.
17. What is permutit process? Describe it in brief

260 Water

UNIT Estimated teaching periods Theory Practical
5 0
15
Chemical Fertilizers Used in
Agriculture

Syllabus issued by CDC Chemical fertilizer

 Introduction to fertilizers
 Type of fertilizers
 Green organic fertilizers and animal organic fertilizers
 Advantages and disadvantages of organic fertilizers
 Inorganic fertilizers
 Advantages and disadvantages of inorganic fertilizers
 Points to remember while using chemical fertilizers
 Use of chemical fertilizers and its impact on environment

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 introduce chemical fertilizers and state their types with examples.
 describe the uses of nitrogen, phosphorus and potassium fertilizers.

Key terms and terminologies of the unit

1. Fertilizers : Fertilizers are those water soluble substances which are used in the soil to increase
crop production by supplying essential nutrients.

2. Organic fertilizers : Fertilizers which are obtained from dead, decayed and decomposed parts of animals
and plants or their waste products are called organic fertilizers or manure.

3. Green manures : Green manures are the green plants which are grown, ploughed and mixed in the soil
to provide essential nutrients to the growing plants.

4. Compost manure : Compost manure is an organic fertilizer which is made from dead, decayed and
decomposed parts of animals and plants or their waste products.

5. Chemical fertilizers : The man-made chemical (or inorganic) substances which are added to the soil to
increase crop production by supplying essential elements are called chemical fertilizers.

6. Nitrogenous fertilizers: Fertilizers which contain nitrogen are called nitrogenous fertilizers.

7. Phosphorus fertilizers : Fertilizers which contain phosphorus are called phosphorus fertilizers.

8. Potassium fertilizers : Fertilizers which contain potassium are called potassium fertilizers.

9. Single fertilizers : The fertilizers which supply only one basic nutrient, i.e. nitrogen or phosphorus or
potassium are called single fertilizers.

10. Mixed fertilizers : The fertilizers which supply more than one basic nutrient are called mixed fertilizers.

11. NPK fertilizers : The fertilizers which supply all the basic nutrients, i.e. nitrogen, phosphorus and
potassium are called complete fertilizers.

Modern Concept Science - 9 261

Introduction Chemical fertilizer

Farmers use a variety of organic and inorganic
substances to increase the fertility of soil. These
substances are called fertilizers. These substances
supply nutrients which are essential for the growth
and development of plants. Fertilizers are those
water soluble substances which are used in the soil
to increase crop production by supplying essential
nutrients. A good fertilizer or complete fertilizer
always provides essential elements to the growing
plants as well as nourishes the micro-organisms.

FACT WITH REASON

It is necessary to use fertilizers in soil, why?

When the same types of plants are grown for a long time, the fertility of soil decreases. So, for the purpose of
continuous use of soil and to maintain crop production, it is necessary to use the fertilizers.

The population of the world is increasing at a high rate but the productivity of crops is
decreasing which results in food crisis. Therefore, a variety of fertilizers should be used to
increase the productivity of crops.

Fertilizers enhance the growth and development of plants. Plants need three main macronutrients,
viz. Nitrogen (N), Phosphorus (P) and Potassium (K), three secondary macronutrients, viz.
calcium (Ca), magnesium (Mg) and sulphur (S) and micronutrients like copper (Cu), iron
(Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B), etc. These macronutrients and
micronutrients are found in soil which are absorbed by roots of green plants.

In this unit, we will study the fertilizers used in agriculture, types of fertilizers, organic or
inorganic fertilizers, chemical fertilizers, their types with examples and effects on plants due
to lack of these fertilizers in brief.

Types of Fertilizers

Fertilizers are classified in many ways. On the basis of source or chemical nature, fertilizers
are of two types, viz. (i) organic fertilizers and (ii) inorganic fertilizers or chemical fertilizers.

1. Organic Fertilizers

Fertilizers which are obtained from dead, decayed and decomposed parts of animals and
plants or their waste products are called organic fertilizers or manure. Organic fertilizers are
soil suitable fertilizers. There are two types of organic fertilizers or manures.

a) Green manure : Green manures are the green plants which are grown, ploughed and
mixed in the soil to provide essential nutrients to the growing plants. Green manures
supply essential elements which are required for the growing plants and also check
soil erosion. The leguminous and non-leguminous plants are grown, ploughed and
decomposed to get organic matter which is also called humus.

262 Chemical Fertilizers Used in Agriculture

b) Compost manure : Compost manure is an organic fertilizer which is made from
dead, decayed and decomposed parts of animals and plants or their waste products. To
prepare compost manure, mixture of dead plants, animals or their waste products are
kept in a pit with altering layers of soil. Sometimes, little amount of lime is also added
to the mixture. Due to microbial action, the mixture gets decomposed into compost
manure. It is used in the soil to provide essential elements for the growing plants.

Advantages of Organic Fertilizer

The main advantages of organic fertilizer are given below:

i) It increases the fertility of soil. Memory Tips
ii) It increases water retaining capacity of the soil.
iii) It helps to control soil erosion. Organic fertilizer is a biodegradable
iv) It helps to control environment pollution. fertilizer. So, natural fertilizer
v) It does not affect the quality of soil. (organic fertilizer) does not pollute
environment.

FACT WITH REASON

Organic fertilizer is good for plants but also farmers are attracted towards chemical fertilizer, why?
Organic fertilizer is good for plants but farmers are attracted towards chemical fertilizer because:
i) Chemical fertilizer is easily absorbed by plants and immediate result is seen. But organic fertilizer is

solely absorbed by plants and cannot give immediate result.
ii) Chemical fertilizer is available easily in market but organic fertilizer is not produced in industrial scale.
iii) Chemical fertilizer is rich in nutrients but organic fertilizer has low concentration of nutrients.
iv) Different types of chemical fertilizers can be used depending upon the nature of soil.

Disadvantages of Organic Fertilizer
The major disadvantages of organic fertilizer are as follows:
i) It does not dissolve completely in water. So plants cannot absorb it easily.
ii) It does not contain all nutrients required for plants.
iii) It is difficult to collect and transport due to its large mass.

Green manure Compost manure

FACT WITH REASON

Organic fertilizers are soil suitable fertilizers, why?

Organic fertilizers are soil suitable fertilizers because they provide all the essential elements to the growing
plants without changing the composition of soil.

Modern Concept Science - 9 263

2. Inorganic Fertilizers or Chemical Fertilizers

The man-made chemical (or inorganic) substances which are added to the soil to increase crop
production by supplying essential elements are called chemical fertilizers. Chemical fertilizers
(or inorganic fertilizers) supply mostly Nitrogen (N), Phosphorus (P) and Potassium (K) as
the chief elements. They are needed for growth, development and seed production. On the
basis of element present, there are three types of chemical fertilizers. They are (i) Nitrogenous
fertilizers (ii) Phosphorus fertilizers and (iii) Potassium fertilizers.

Nitrogenous fertilizer Potassium fertilizer Phosphorus fertilizer

i) Nitrogenous fertilizers : Fertilizers which contain nitrogen are called
nitrogenous fertilizers. For example,

i. Urea [NH2CONH2]
ii. Ammonium sulphate [(NH4)2SO4]
iii. Ammonium nitrate [NH4NO3]
iv. Calcium cyanide [Ca(CN)2]

Importance of nitrogen (Nitrogenous fertilizer)

Nitrogen helps in the formation of protein, protoplasm and chlorophyll in the

plants. It is essential for rapid growth and to Memory Tips
yield more crops. Deficiency of nitrogen results
in poor development of flowers, fruits and Nitrogenous fertilizer is necessary
seeds. Leaves become yellow and flowers do for plants if the leaves are yellow and
not bloom properly. flower does not bloom properly.

ii) Phosphorus fertilizers : Fertilizers which contain phosphorus are called
phosphorus fertilizers. For example,

i. Ammonium phosphate [(NH4)3PO4]
ii. Calcium super phosphate [Ca(H2PO4)2.2CaSO4]
iii. Triple super phosphate [3Ca(H2PO4)2]
iv. Bone meal

Importance of phosphorus (Phosphorus fertilizer)

Phosphorus helps in the ripening of fruits and Memory Tips
development of seeds. It is also important in
synthesis of protein, cell division and growth of If plants have poorly developed roots,
leaves and buds. Phosphorus also helps to resist then Phosphorous containing fertilizer
are necessary for these plants.

diseases.

264 Chemical Fertilizers Used in Agriculture

FACT WITH REASON

Why is bone used to make a fertilizers?
Bone is a tissue present in the animal's body. It is very rich in salts of calcium and phosphorus. Since, bone
can supply calcium and phosphorus to the plants, it is used as a fertilizer.

iii) Potassium fertilizers : Fertilizers which contain potassium are called potassium
fertilizers. For example,

i. Potassium chloride (KCl)
ii. Potassium nitrate (KNO3)
iii. Potassium sulphate (K2SO4)
iv. Potassium carbonate (K2CO3)

Importance of potassium (Potassium fertilizer)

Potassium helps in photosynthesis and growth of flowers. It also helps in protein
synthesis, cell division, food production, etc. Due to deficiency of potassium,
leaves and buds wither and immunity is also reduced.

Differences between Organic fertilizers and Chemical (inorganic) fertilizers

S.N. Organic Fertilizers S.N. Chemical (Inorganic) Fertilizers

1. They are obtained from dead, decayed 1. They are man-made inorganic

and decomposed parts of animal and substances.

plant or their waste products.

2. They are not soluble or less soluble in 2. They are soluble in water.
water.

3. They do not supply sufficient amount 3. They supply sufficient amount of

of nitrogen, phosphorus and potassium nitrogen, phosphorus and potassium

to the growing plants. to the growing plants.

4. Plants absorb them very slowly. 4. Plants absorb them very fast.

Groups of Fertilizers

According to the number of basic nutrients supplied, there are three groups of fertilizers. They are:

a. Single fertilizers
The fertilizers which supply only one basic nutrient, i.e. nitrogen or phosphorus or
potassium are called single fertilizers. Examples: Calcium nitrate, potassium chloride,
potassium sulphate, etc.

b. Mixed fertilizers
The fertilizers which supply more than one basic nutrient are called mixed fertilizers.
Examples: Potassium nitrate, ammonium phosphate, etc.

Modern Concept Science - 9 265

c. Complete fertilizers (NPK fertilizers)

The fertilizers which supply all the basic
nutrients, i.e. nitrogen, phosphorus and
potassium are called complete fertilizers. They
are made by mixing two or more than two
single fertilizers or mixed fertilizers.

FACT WITH REASON NPK fertilizer

Compost manure is a complete fertilizer, why?

Compost manure (organic fertilizer) is a complete fertilizer because it contains nitrogen, phosphorous and
potassium along with other essential elements.

Disadvantages of Using Fertilizers

We should not use excessive amount of chemical fertilizers because it causes water and soil
pollution. When nitrogenous fertilizers reach the water body, they cause deficiency of oxygen
in water. So, aquatic animals die due to the lack of oxygen. Similarly, when children drink
nitrogen containing water, they become dwarf.

FACT WITH REASON

Aquatic animals die due to excessive use of nitrogen fertilizers, why?
When nitrogenous fertilizers reach to the water body, they cause rapid growth and development of aquatic
plants. They use up available oxygen of the water and create deficiency of oxygen in water. So, aquatic
animals die due to the lack of oxygen.

Precautions While Using Fertilizers

i. We should not use excessive amount of fertilizers which may damage the plants.

ii. Nitrogenous fertilizers having easy burning nature cause fire when they come in contact
with wooden dust, coal, dry leaves, etc.

iii. Hygroscopic fertilizers like urea should be stored away from the moist places.

iv. Chemical fertilizers should be stored away from the reach of the children.

v. They should be used after testing the soil.

Advantages of Inorganic/Chemical Fertilizers

The major advantages of chemical fertilizers are as follows:

i. Chemical fertilizers are easy to collect and transport from one place to another.

ii. They increase the fertility of soil. Memory Tips

iii. They contain most of the nutrients essential for Chemical fertilizers are good for
growth and development of plants. immediate results in the growth,
development and productivity of
iv. They are water soluble. So, they can be absorbed by plants.
plants easily.

266 Chemical Fertilizers Used in Agriculture

Disadvantages of Inorganic/Chemical Fertilizers

i. Chemical fertilizers cause environment pollution.
ii. They increase acidity or alkalinity of soil.
iii. They affect the quality of soil.

ACTIVITY 1

• Pay a visit to your locality and meet some local farmers.
• Ask the technique of making compost manure and green manure to the farmers.
• Prepare a short report and submit to your science teacher.
• Also, prepare a list of inorganic or chemical fertilizers that are used in your locality.

ANSWER WRITING SKILL

1. Name three primary macro nutrients important for plants.
Ans: Nitrogen, potassium and phosphorous are main primary nutrients required for plants.
2. What does it mean by that fertilizer is nutrient specific? Give an example.
Ans: A fertilizer is nutrient specific. It means that fertilizer can supply only one kind of nutrient for plants.

Example, urea which supplies nitrogen only.
3. Which fertilizer supplies each and every type of nutrients? Give an example.
Ans: The complete fertilizer supplies each and every type of nutrients. Example, NPK fertilizer
4. Name the type of a biodegradable fertilizer.
Ans: Organic fertilizer is a biodegradable fertilizer. It does not pollute environment.
5. Which type of fertilizer is easily absorbed by plants? Why?
Ans: Chemical fertilizer is easily absorbed by plants. It is because chemical fertilizer is highly soluble in water.
6. Organic fertilizer is better than chemical fertilizer for environment. Why?
Ans: Organic fertilizer is better than chemical fertilizer for environment because:

i) Organic fertilizer increases fertility of soil but chemical fertilizer decreases quality of soil.
ii) Organic fertilizer is biodegradable so it does not pollute environment but chemical fertilizer does

not decay and pollutes environment.
iii) Since, Nepal is an agricultural country with lots of forest, compost manure can be easily prepared

at low cost but chemical fertilizer is to be imported from foreign country.
iv) Organic fertilizer contains complete set of macro nutrients and micro nutrients but chemical

fertilizer is usually nutrient specific.
7. Why are framers suggested to use organic fertilizer?
Ans: Farmers are suggested to use organic fertilizers because:

i) Organic fertilizers make soil porous and increase fertility.
ii) Organic fertilizer supplies every type of essential nutrients for plants.
iii) Organic fertilizer is biodegradable and does not pollute environment.
iv) Raw materials to produce organic fertilizer is easily available in Nepal.

Modern Concept Science - 9 267

8. How do chemical fertilizers pollute environment?

Ans: Chemical fertilizers pollute environment in the following ways:
i) Chemical fertilizer decreases population of the earthworms and other micro-organisms in the
soil.
ii) Chemical fertilizer increases acidity of soil and decreases agricultural product.
iii) Chemical deposit is found in the food products which causes serious health hazard.
iv) Chemicals dissolved in water pollute water resources, drinking water and kills aquatic life.

9. My grandmother uses ash of fire in fields. Will it help to make soil fertile?

Ans: Yes, use of ash helps to make soil fertile because ash is an organic plant matter which is rich in potassium.

10. Farmers complain that if urea fertilizer is used more in plants, plants grow very tall and fall during
winds. Explain the possible reason behind it.

Ans: If excess amount of urea is used, plants grow very tall and fall during winds. It is reasonable complain
because urea is not a complete fertilizer. Urea supplies large amount of nitrogen. So, plants grow rapidly
and become very tall. But due to lack of phosphorous, roots become weak and cannot support the weight
of the plant. Hence, they fall in wind.

STEPS EXERCISE

STEP 1

1. Define the following terms:

a) Fertilizers b) Organic fertilizers
c) Green manures d) Compost manure
e) Chemical fertilizers f) Nitrogenous fertilizers
g) Phosphorus fertilizers h) Potassium fertilizers
i) Single fertilizers j) Mixed fertilizers

k) Complete fertilizers (NPK fertilizers)

2. Name any two macronutrients and three micronutrients essential for growth and
development of plants.

3. Name two types of fertilizers on the basis of chemical nature.
4. Define organic fertilizers with any two examples.
5. What are inorganic fertilizers? Give any three examples.
6. What are nitrogenous fertilizers? Give any three examples.
7. What are phosphorus fertilizers? Give any three examples.
8. What are potassium fertilizers? Give any three examples.

268 Chemical Fertilizers Used in Agriculture

STEP 2

9. Differentiate between:
a) Organic fertilizers and Inorganic fertilizers
b) Green organic fertilizers and Animal organic fertilizers
c) Nitrogen fertilizers and Potassium fertilizers
d) Phosphorus fertilizers and Potassium fertilizers

10. Give reason:
a) Fertilizers added to the soil
b) Organic fertilizers are better than chemical fertilizers.
c) NPK fertilizer is a complete fertilizer.
d) Inorganic fertilizers affect environment.

STEP 3

11. Write any three advantages of organic fertilizers.
12. Write any three disadvantages of organic fertilizers.
13. Write any three advantages and two disadvantages of chemical/inorganic fertilizers.
14. Write down the importance of nitrogenous fertilizers. Write any two effects on plants

due to deficiency of nitrogenous fertilizers.
15. Write down the importance of phosphorus fertilizers. Write any two effects on plants

due to deficiency of phosphorus fertilizers.
16. Write down the importance of potassium fertilizers. Write any two effects on plants due

to deficiency of potassium fertilizers.
17. Write any three precautions while using chemical fertilizers.

STEP 4

18. Explain the use of chemical fertilizers and its impact on environment.
19. What is a fertilizer? Is compost manure organic fertilizer or chemical one? How is

compost manure prepared? Explain in detail.
20. Side effects of chemical fertilizer are now easily seen in the fields. Soil is acidic and

agriculture production has been decreased. what can be done to save fertility of soil and
increase crop production. Write in detail.

Modern Concept Science - 9 269

UNIT Estimated teaching periods Theory Practical
8 3

16 Classification of Plants and Animals

Syllabus issued by CDC Carl Von Linnaeus

 Introduction to classification
 Classification of flowering and non-flowering plants
 Classification of vertebrates and invertebrates
 Mosquitoes: features and life cycle
 Disadvantages of mosquitoes
 Control measures of mosquitoes
 Types of mosquitoes

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 classify plants up to class, invertebrates up to phylum and vertebrates up to class and explain

their characteristics with examples.
 explain the life cycle of mosquito with a neat and labelled figure.
 list the adverse effects of mosquito bite on human beings.

Key terms and terminologies of the unit

12. Classification of organisms: Classification is the act of grouping of organisms on the basis of their similarities and
dissimilarities.

13. Taxonomy: Taxonomy is the branch of biology which deals with identification, classification and
nomenclature of organisms.

14. Taxon: A taxon is a generally accepted category under which the organisms having similar

characteristics are grouped. e.g. kingdom, phylum etc.

15. Genus: Genus represents the group of those organisms that have similar physiology,
anatomy and feeding habit.

16. Species: Species represents the organisms that are completely similar to each other and can
interbreed to produce a fertile offspring.

17. Epithet: Epithet is the second word of the scientific name of the organism, i.e., species.

18. Unicellular organisms: Organisms which have a single cell in their body to perform life functions are called
unicellular organisms.

19. Multicellular organisms: Organisms having more than one cell in their body are known as multicellular organisms.

20. Microscopic organisms: The organisms that are too small to be seen through unaided eyes (naked eyes) are
called microscopic organisms.

21. Macroscopic organisms: Macroscopic organisms include those which can be seen with our naked eyes.

270 Classification of Plants and Animals

22. Prokaryotes: The organisms that lack a well-organized nucleus and membrane covered structures
in their cells are known as prokaryotes.

23. Eukaryotes: The organisms having a well-organized nucleus and membrane bound structures in

their cells are known as eukaryotes.

24. Autotrophs: The organisms that can prepare own food by themselves are known as the autotrophs.

25. Heterotrophs: The organisms that cannot prepare own food by themselves are termed as heterotrophs.

26. Saprophytes: The heterotrophs that depend on dead and decayed organic matter are called

saprophytes, e.g. mushroom, mucor etc.

27. Parasites: The heterotrophs that live in the body of host organism for their food are known as

parasitic organisms, e.g. puccinia, leech, roundworm etc.

28. Algae: Algae are green small thallophytes that are autotrophic in nature.

29. Bryophytes: Bryophytes are the non-flowering (cryptogams) green plants that grow in moist,

shady, damp and watery places.

30. Tracheophyta: Tracheophyta is the division which includes vascular plants.

31. Closed circulatory system: Closed circulatory system is the type of circulation in which the blood is transported
throughout the body through the blood vessels from and to the heart.

32. Open circulatory system: The circulatory system in which blood is transported directly into the tissues without

blood vessels is called open circulatory system.

33. Diploblastic animals: An organism which is developed from two germ layers is called diploblastic animals.

34. Triploblastic animals: The animal developed from three germ layers is called triploblastic animals.

35. Hermaphrodites: The animals that have both male and female sex organs in the same body are called

hermaphrodites. Example, earthworm

36. Invertebrates: Invertebrates are the groups of animals which do not have vertebral column in their

body.

37. Chordates: Chordates are those animals which bear notochord in some stages of their life.

38. Vertebrates: Vertebrates are those animals that have notochord in their embryonic stage which

modifies into backbone or vertebral column.

39. Cold blooded animals: The animals whose body temperature changes according to the surrounding

temperature are called cold-blooded animals. Examples, pisces, amphibian and

reptiles.

40. Warm blooded animals: The animals whose body temperature does not change according to the surrounding

temperature are called warm-blooded animals. Example, birds and mammals.

41. Oviparous animals: Animals that reproduce by laying eggs are called oviparous animals.

42. Viviparous animals: Animals that reproduce by directly giving birth to the young ones are called viviparous

animals.

43. Metamorphosis: The process of completion of the life cycle through different distinct stages is called

metamorphosis. During complete metamorphosis, insects involve four distinct life

stages. They are egg, larva, pupa, and adult.

44. Moulting : The process of shedding the skin by the organisms during metamorphosis or during
their lifetime is known as moulting or ecdysis.

45. Malaria: Malaria is a mosquito-borne disease which is characterized by fever, headache, chill,

vomiting, seizures or even death.

Modern Concept Science - 9 271

Introduction

Classification of organisms is the act of grouping organisms Memory Tips
on the basis of their similarities and dissimilarities. It was

first done by Swedish biologist Carolus von Linneaus 1. There are about 8.7 million species

in the 1750s. Carolus introduced a system known as the of living things in the earth.

Binomial system of Nomenclature in which the plants and 2. Taxonomy is the branch of biology

animals were given a unique name called the scientific which deals with identification,

name. The scientific name consists of two Latin words: the classification and nomenclature

first word is called the genus or the generic name and the of organisms.

second one is called the species or specific name or epithet.

Today, all known organisms in the world have a universal scientific name that every biologist

understands irrespective of his language and country. The system Carolus started is well

developed into a branch of biology known as the Taxonomy. Carolus von Linnaeus is known

as the father of taxonomy.

FACT WITH REASON

Carolus von Linnaeus is known as the father of taxonomy, why?

Carolus von Linnaeus started the systematization in the classification process through Binomial system for
the first time. So, Carolus von Linnaeus is known as the father of taxonomy.

Discovery, Identification, Classification and Nomenclature

When a new species of an organism is discovered, its Kingdom
characteristics are studied and the kind of organism is Phylum or Division
identified. Identification is the process of distinguishing the Sub-phylum or Sub-division
type of organism on the basis of its characteristics. Then, Class
the discovered organism is classified under a proper taxon. Order
After that, the organism is given a binomial name which Family
completes the process of the systematic classification. The Genus
advantages of classification of organisms are as follows: Species

i) It helps us to learn about the characteristics of large Memory Tips
number of plants and animals in a group.

ii) It is systematic and scientific. Hence, it is an easy Phylum and sub-phylum: for animals
and understandable method of studying the Division and sub-division: for plants
characteristics of organisms.

iii) It projects a basic idea about the inter-relationship between similar and dissimilar species.

iv) Classification helps to study trend of diseases, evolution, growth and decline in the
population of creatures.

FACT WITH REASON

Why is classification of organisms necessary?

Classification of organisms is necessary to identify, group, and properly name the organisms with the help
of a standardized system based on similarities found in the organisms.

272 Classification of Plants and Animals

Common name and Scientific name Common name Scientific name

An organism can have several names depending on Human Homo sapiens

the country or its native region. These multiple names Tiger Panthera tigris

are not universal, and they make communication in Lion Panthera leo

biology difficult. These names are called common Cat Felis catus

names. To avoid the confusion of common names, Pea Pisum sativum

every organism under the Binomial System is given Rice Oryza sativa

a scientific name. Every single organism on this earth Apple Malus domestica

has a scientific name that every biologist understands. Potato Solanum tubersum

Some of the plants and animals and their scientific Maize Zea mays

names are given in the table alongside. Memory Tips

The genus or generic name The scientific name consists of two Latin
or Greek words. the first word is called
The genus is the first word of the scientific name. the genus or the generic name and the
Genus represents the group of those organisms that second one is called the species or specific
have similar physiology, anatomy and feeding habit. name or epithet.
For example, tiger and lion belong to the similar genus
called Panthera. The organisms of the same genus but

different species generally do not interbreed with each other.

The species or specific name or epithet Memory Tips

The species forms the second word of the scientific In some organisms, interbreeding
name. Species represents the organisms that are between different species of same genus
completely similar to each other and can interbreed is also possible. Example:
to produce a fertile offspring. For example, a male a. Male tiger + female lion = tigon
cat and a female cat belong to the same species. They b. Male lion + female tiger = liger
can interbreed with each other to produce the same c. Female horse + male donkey = mule
species type. d. Male horse + female donkey = hinny
These animals are called hybrids. They
Rules for writing the scientific name have selected qualities of their parents.

The scientific names of organisms should be written
with the following rules:

a) The first letter of the genus should be capital and rest all the letters should be small.

b) A space should be given between the genus and the species.

c) Both the genus and the species should be separately underlined in the handwritten form.

d) The genus and the species should be italicized (as in Panthera) in printed form.

The Five Kingdom System

The two kingdom system (Plantae and Animalia) could not distinguish between prokaryotes/
eukaryotes, autotrophs/heterotrophs and unicellular/multicellular. There were many
organisms that did not fit in the two kingdom system satisfactorily. Therefore, American
Biologist Robert H. Whittaker proposed the five kingdom system, adding three more
kingdoms: Monera, Protista and Fungi, in addition to the earlier two kingdoms: plantae and
Animalia. The five kingdom system is explained in brief below:

Modern Concept Science - 9 273

5 Kingdom System

Monera Protista Fungi Plantae Animalia
Unicellular Unicellular Non-green uni/ Multicellular Multicellular
autotrophic heterotrophic
prokaryotes eukaryotes multicellular eukaryotes eukaryotics
eukaryotes

FACT WITH REASON

Why is the two kingdom classification system inadequate?

On the basis of two kingdom classification system, grouping of diverse organisms into only two kingdoms
is not satisfactory. This system puts together Eukaryotes and Prokaryotes. It also groups together non-pho-
tosynthetic fungi with photosynthetic green plants.

1. Monera Memory Tips

This kingdom includes all types of bacteria (e.g. cyanobacteria Kingdom monera consists of one-
or blue-green algae, coccus, bacillus, etc.). They are single- celled organisms, both autotrophs
celled microscopic prokaryotes having no nuclear membranes. and heterotrophs that are
They are both autotrophic and heterotrophic. extremely simple in structure.

Bacteria Coccus Blue-green algae

2. Protista

This kingdom includes single-celled microscopic

eukaryotes. i.e. they contain a well-defined nucleus

with membrane bound cellular structures. They

have a nuclear membrane and are both autotrophic

and heterotrophic. For example, amoeba,

paramecium, euglena, dinoflagellates, etc. Their Amoeba Paramecium Euglena
locomotory organs are primitive.
Memory Tips
3. Fungi
Fungi are useful in our daily life too.
Fungi is the kingdom of non-green eukaryotes. They may The fungus called yeast is used to
be single or multi-celled. They cannot prepare food by prepare beer and bread. Similarly,
themselves and are heterotrophic. Hence, they have to antibiotics are extracted from a fungus
depend upon dead and decayed matter for food. Most of called penicillium. Mushroom is a
the fungi are filamentous and thread-like in structure. fungus which has several medicinal
values. But, some fungus are parasitic
too e.g. puccinia, yarshagumba etc.

274 Classification of Plants and Animals

Mushroom Yeast Mucor

4. Plantae

These are well-developed multicellular Mango Moss Fern
organisms. They have a eukaryotic cell
and can prepare food by themselves
(autotrophic). Plants lying in this
kingdom are both higher and lower
type. The herbs, shrubs and trees are
parts of this kingdom. They have a
long life cycle. Their bodies are made
up of tissues and organs.

5. Animalia

The organisms lying in this kingdom are multicellular, eukaryotic and heterotrophic. They
have different forms of habitats. Most of them have well developed tissue, organ and body
systems. They swallow their food as a whole and have a digesting column in the body (holozoic
in nature). Their cells do not have a cell wall.

Dolphin Frog Starfish

FACT WITH REASON

Why is the five kingdom classification system most accepted?

In five kingdom classification system, grouping of diverse organisms is done into five kingdoms. This system
groups organisms on the basis of complexity of Cell Structure (Prokaryote or Eukaryote), Complexity of the
Organism’s Body (Unicellular or Multicellular and Complex) and Mode of their Nutrition (Photosynthesis,
Absorption or Ingestion). So, five kingdom classification is the most accepted system of classification.

Kingdom Plantae [Latin: 'planta'- shoot]

The kingdom plantae includes the multicellular, autotrophic eukaryotes. This kingdom contains
plants living in all types of habitats. They may vary in shape, size and body features. On the
basis of their habitats there are two types of plants: terrestrial and aquatic. All herbs, shrubs,
trees, creepers, etc. fall under this category. The plant kingdom is divided into three divisions:

Modern Concept Science - 9 275

i) Division Algae – thalloid colourful plants
ii) Division Bryophyta – mosses
iii) Division Tracheophyta – plants bearing xylem and phloem

Division algae [Latin: 'alga'- sea weed]

Algae are the wide range of small, thalloid and green plants that are autotrophic in nature.
They are mostly seen as green, red, brown, yellow-green, golden and purple patches in the
sea, pond, and rivers. They may cover up the entire pond or seacoast that gives a colourful
effect to the water. Their bodies are thalloid i.e. cannot be differentiated into roots, stem and
leaves. Hence, they are called thallophytes. Their main characteristics are given below:

i) The plant body of algae is thallus which be unicellular or multicellular.
ii) They are mostly green coloured as they contain chlorophyll.
iii) They have chlorophyll in their body. So, they make their own food. Due to this, algae

are also known as autotrophs.
iv) Their cell wall is made up of cellulose.
v) They store their food materials in the form of starch.
vi) They are found in water or in moist places.
vii) They reproduce asexually or sexually.
Example: volvox, spirogyra, chlamydomonas, anabaena, nostoc, ulothrix, etc.

Spirogyra Chlamydomonas Ulothrix Volvox

Anabaena Nostoc Batra Lamnaria

FACT WITH REASON

Why do some sea-coasts and pond look colourful?

In some sea-costs and ponds, there is a growth of various types of algae having different pigments in their
cells. So, some sea-coasts and ponds look colourful.

276 Classification of Plants and Animals

Differences between algae and fungi

SN Algae SN Fungi

i. Algae are found in well lighted areas. i. Fungi are found in dark places.

ii. They are autotrophs. ii. They are heterotrophs.

iii. They have chlorophyll. iii. They do not have chlorophyll.

iv. They store their food in the form of iv. They store their food in the form of glycogen.
starch.

v. Their cell wall is made up of cellulose. v. Their cell wall is made up of chitin. Example:

Example: spirogyra, volvox, etc. mushroom, mucor, etc.

Division Bryophyta [Greek: bryon – moss and phyton - plant]

Bryophytes are the flowerless plants (cryptogams) that grow in moist, shady, damp and

watery places. They are commonly divided into three groups of plants: liverworts, mosses

and hornworts. Mosses form the largest family of bryophytes. Some of their common

characteristics are: Memory Tips

i) Bryopytes grow in moist, cool and shady places. Bryophytes are more advanced than

ii) These plants are essentially terrestrial but they green algae but more primitive than
require water for every step in their life cycle and for ferns.

fertilization. So, they are also known as amphibian plants.

iii) Their vascular tissues (xylem and phloem) are completely absent.

iv) They contain chlorophyll and produce their own food. Hence, they are autotrophs.

v) Their main body part is green, flat and thallus. They remain attached to the substratum
by the hair like structures called rhizoids.

vi) They possess alternation of generations in their life cycle.

Examples: Riccia, Marchantia, Moss (Funaria), Anthocerous, etc.

FACT WITH REASON

Bryophytes are called amphibian plants, why?

Most of the bryophytes are found in terrestrial habitat but they depend on water for completion of their
sexual reproduction. So, bryophytes are also called amphibian plants.

Marchantia Riccia Moss

Modern Concept Science - 9 277

Division Tracheophyta [Greek: 'trakheia' - windpipe and ‘ophyta’ - to produce]

Tracheophyta is the division which includes vascular plants. Vascular plants are those which
have vascular tissues called xylem and phloem. These tissues conduct food and minerals
throughout the plant body. Xylem tissues conduct raw materials from the roots to the leaves
while the phloem tissues conduct food prepared in the leaves to all parts of the plant body.

The division Tracheophyta is further divided into three sub-divisions:

a) Sub-division Pteridophyta : feather like plants Seed lacking plants

b) Sub-division Gymnosperms : cone bearing plants Seed bearing plants

c) Sub-division Angiosperms : flower, fruit and seed bearing plants Fruit and seed
bearing plants

FACT WITH REASON

Plants with xylem and phloem are called vascular plants, why?

Xylem and phloem are the vascular bundles in the plants that help in the transportation of water and
minerals throughout the body. So, the plants with xylem and phloem are called vascular plants.

Sub-division Pteridophyta [Greek: ‘pteris’ - fern like and ‘phyton’ - plant]

Pteridophytes are the most developed non-flowering Memory Tips
plants. They do not bear flowers, fruit and seeds. As they
are tracheophytes, they bear vascular tissues: xylem and Fern is an advanced crotyptogam.
phloem. Some of the characteristics of pteridophytes are Its body is differentiated into roots,
given below: stem and leaves.

i) Pteridopytes include first vascular plants i.e. they have vascular tissues (xylem and
phloem) in their body.

ii) They are the most developed non-flowering plants.

iii) They do not have flowers and seeds.

iv) They have feather-like leaves.

v) The plant body is completely differentiated into roots, stem (rhizome) and leaves.

vi) They reproduce through spores.

vii) They have distinct alternation of generation.

Examples: fern, lycopodium, horsetail, equisetum, azola, etc.

Fern Lycopodium Equisetum Selaginella Marsilea

278 Classification of Plants and Animals

FACT WITH REASON

Why is fern classified in the division tracheophyta and sub-division pteridophyta?
Fern consists xylem and phloem which is the characteristic feature of tracheophyta. On the other hand it
has feather like leaves which is the characteristic feature of pteridophyta. So, fern is classified in the divi-
sion tracheophyta and sub-division pteridophyta.

Sub-division: Gymospersms [Greek: 'gymno'-naked and 'sperma'- seed]

Gymnosperms are the plants that do not bear fruits but Memory Tips
they have naked seeds. Their seeds are not enclosed inside
the fruits. That is why they are called naked seeded plants. Gymnosperms grow on dry places.
Their characteristics are given below: They have long roots to search
water, pointed leaves to reduce
i) Gymnosperms are vascular plants which bear naked transpiration and dry scales to
seeds i.e. seeds are not enclosed within the fruits. prevent loss of water.

ii) They do not bear fruit.

iii) They bear cones instead of flowers. So, they are also known as conifers.

iv) They form the evergreen forest.

v) True vessels are absent in their xylem.
vi) They have small and needle shaped leaves.
vii) They are found in extreme climate (extreme cold or dry). They are also known as

xerophytes. Examples: Pinus, Cycas, Cedrus, Ephedra, Taxus, Ginkgo.

FACT WITH REASON

The seeds of gymnosperms are not enclosed inside fruits or seed covering, why?

Gymnosperms are the plants that do not bear fruits but they have naked seeds. Instead of flowers, they bear woody
scales called the cones. They do not have ovary. So, the seeds are naked and not enclosed inside fruits or seed covering.

Cycas Pine Cedar

Sub-division: Angiosperms [Greek: 'angion' - coat and 'sperma' - seed]

Angiosperms belong to about 300,000 species of the most Memory Tips
advanced flowering plants of the Plantae kingdom. They are
found both on land and in water and are the most advanced Angiosperms are more advanced
plants. Some of the reasons why they are considered the than gymnosperms. The seeds of
most advanced plants are as follows: angiosperms are enclosed inside
fruits or seed covering, whereas
i) They have well developed vascular tissues: xylem gymnosperms do not possess this
and phloem. structure.

Modern Concept Science - 9 279

ii) They bear well developed flower, fruit and seed.

iii) They are all multicellular, non-thalloid and green plants.

iv) Seeds are enclosed inside the fruits and ovules are enclosed inside the ovary of the
flowers.

FACT WITH REASON

The seeds of angiosperms are enclosed inside fruits or seed covering, why?
Angiosperms bear flowers with ovule inside an ovary. The ovary changes into fruit and the ovule changes
into seed. So, the seeds of angiosperms are enclosed inside fruits or seed covering.

v) Flowers are both unisexual and bisexual.
vi) Their size ranges from small herbs to large trees.

Differences between gymnosperm and angiosperm

SN Gymnosperm SN Angiosperm

i. Gymnosperm bear naked seeds i. Seeds are enclosed inside a seed coat and

and do not bear fruits. bear fruits or pods.

ii. They bear cones. ii. They bear flowers.

iii. They are mostly unisexual. iii. They are mostly bisexual.

iv. Xylem does not consist of true iv. Xylem consists of true vessel. Example:

vessel. Example: pine, cedrus, maize, pea, bean, etc.

cycas, etc.

On the basis of the number of leafy parts of a seed (cotyledon), the angiosperms are divided
into two major classes:

a) Class: Monocotyledon/monocotyledonous/monocot plants

b) Class: Dicotyledon/dicotyledonous/dicot plants
Monocotyledon: [mono - one]

The monocots are those plants which have a single cotyledon or leafy part in Monocot
their seeds. They are found in various habitats and grow in wide ranges of
climates. Their stems and branches are soft and do not contain woody parts.
They constitute about 60,000 species.

Characteristics of monocotyledons (monocot)
i) Monocots bear single cotyledon in their seeds.

ii) They have fibrous or adventitious root system.

iii) They have long and narrow leaves with a parallel venation.

iv) Their vascular bundles are scattered in the stem.

v) They have trimerous flowers.

Examples: maize, oat, rice, barley, sugarcane, bamboo, etc.

280 Classification of Plants and Animals

Dicotyledon: [Di - two]

The dicotyledons are the plants which bear two cotyledons in their seeds.
They mostly are terrestrial plants and have woody stems. There are about
200,000 species of dicots on earth.

Characteristics of dicotyledons (dicot)

i) Dicots have two cotyledons in their seeds.

ii) They bear the tap root system. Dicot

iii) They have broad and short leaves with a reticulate venation.

iv) Vascular bundles are arranged in a ring system.

v) They have tetramerous or pentamerous flowers.

Examples: gram, pea, bean, mustard, sunflower, etc.

A short comparison between monocots and dicots along with their characteristics on the basis
of various features are given below:

Differences between monocots and dicots

SN Monocots SN Dicots

i. Monocots bear only one cotyledon i. Dicots bear two cotyledons in their seeds.
in their seeds.

ii. They have a fibrous root system. ii. They have a tap root system.

iii. Leaves are long and narrow with a iii. Leaves are short and broad with reticulate

parallel venation. venation.

iv. They have trimerous flowers. iv. They bear tetramerous or pentamerous
flowers.

v. Vascular bundles are scattered. v. Vascular bundles are arranged in a ring.

vi. Secondary growth does not occur. vi. Secondary growth occurs. Example: soyabean,

Example: sugarcane, bamboo, maize, mustard, apple, mango, etc.

wheat, etc.

Kingdom Animalia [from Latin – animalis meaning ‘having breath and soul’]

Animals are the multicellular, non-green eukaryotes having no cell wall in their cells. They are
mostly found in marine water (e.g. seas, oceans), fresh water (e.g. lake, pond, river), deserts,
grasslands, jungles etc. The animal kingdom is simply divided into two parts:

a) Chordates Memory Tips

Chordates are animals which possess a notochord in the All chordates have blood enclosed
embryonic stage of their life. A notochord is a dorsal (towards in blood vessels, although they
the back of animal) structure of rod-like cells that runs from may not have blood cells.
head to tail in the embryonic stage. In some animals, the

notochord remains same throughout their lifetime (in urochordates and cephalochordates)

while in some animals it changes into vertebral column or backbone (in vertebrates: fishes,

birds, reptiles, amphibians and mammals). About 3% of animals on earth are chordates.

Modern Concept Science - 9 281

b) Non-chordates
These are the animals which do not have notochord in the embryo during their development.
Since they do not have notochord, they do not bear a backbone. The non-chordates include
the phylum of invertebrates: Porifera, Coelenterata, Platyhelminthes, Nemathelminthes,
Annelida, Arthropoda, Mollusca and Echinodermata. They occupy about 97% of all animal
species on earth.

A chart below illustrates the classification of animals in an understandable manner.

Animal Kingdom

Group Non-chordata Group Chordata

(no notochord) (notochord present)

Phylum: Porifera e.g. sycon Phylum Chordata
Phylum: Coelenterata e.g. hydra
Phylum: Platyhelminthes e.g. tapeworm Sub-phylum: Hemichordata
Phylum: Aschelminthes e.g. round worm Sub-phylum: Urochordata
Phylum: Annelida e.g. earthworm Sub-phylum: Cephalochordata
Phylum: Arthropoda Sub-phylum: Vertebrata

Class: Crustacea e.g. prawn Class: Pisces e.g. rohu
Class: Insecta e.g. butterfly Class: Amphibia e.g. frog
Class: Myriopoda e.g. millipede Class: Reptilia e.g. snake
Class: Arachnida e.g. spider Class: Aves e.g. parrot
Phylum: Mollusca Class: Mammalia e.g. human

Phylum: Echinodermata e.g. starfish

Classification of non-chordates

The non-chordates are divided into eight phyla (singular-phylum) altogether which are
explained below:

1. Porifera [Greek: 'porus' – pore, 'ferre'– to bear]

The poriferons are the most primitive multicellular animals which have pores all over their
bodies. They live in both fresh water and marine water but not on land. They are commonly
known as the sponges. The general characteristics of poriferons are listed below according to
their body features:

i) Porifera are mostly marine animals but demospongiae is a fresh water-living creature.

ii) They are the first multicellular animals.

iii) Some of them are vase- like and some are flat, globular or irregular shaped.

282 Classification of Plants and Animals

iv) They are attached to the substratum and cannot move throughout their life. So, they are
also called sessile.

v) They are diploblastic animals as they have two layers in their skin.

vi) Their body bears number of small pores (ostia) with a single large opening called the
osculum on the top.

vii) The current of water along with food enters through ostia and comes out from the body
through osculum.

viii) They possess an internal skeleton consisting of tiny calcareous or siliceous spicules or
the fine sponging fibres. These structures make the body rigid.

Example: sycon, spongilla, euspongia, euplectella, etc.

Sycon Spongilla Euspongia

FACT WITH REASON

Poriferons are called the simplest multicellular organisms, why?

Poriferons are called simplest multicellular organisms because they are just a group of cells and do not have
true tissues, organs and systems.

2. Coelenterata [Greek: 'koilos' – hollow, 'enteron' – gut]
Coelenterata are also known as cnidarians as they have cnidoblasts in their body. The main
characteristics of coelenterate are given below.

i) Coelenterata have a single cavity called the gastro-vascular cavity or coelenteron.

ii) They have a mouth but no anus.

iii) The mouth often bears slender, flexible processes called the tentacles which help them
to capture food.

iv) Their body wall is supplied with special stinging cells called cnidoblasts or nematocyst
for offence and defense purpose.

v) They are mostly aquatic.

Examples: hydra, sea-anemone, corals, obelia, jellyfish, etc.

Hydra Jelly fish Coral

Modern Concept Science - 9 283

FACT WITH REASON

Why is hydra called a coelentrate?
Hydra is called a coelenterate because it has hollow cavity called coelenteron in it.

3. Platyhelminthes [Greek: 'platys' – flat, 'helminth' – worm]
Platyhelminthes includes the bilaterally symmetrical flat worms. The main characteristics of
these animals are given below.

i) The body of platyhelminthes is dorsoventrally flattened and bilaterally symmetrical.
ii) Their body is soft and has a leaf-like or ribbon-like structure.
ii) Most of them are parasite and few are free living. The parasitic animals are attached to

their hosts by their hooks and suckers.
iii) They are the triploblastic animals (it means they have three layers of skin).
iv) Their body does not have a cavity or coelom.
v) The digestive system is incomplete.
vi) The excretory system includes flame cells (protonephridia).
vii) They are mostly hermaphrodite (bisexual) i.e. both male and female sex organs are

present in the same animal.
Examples: planarian, liver fluke, tapeworm, blood fluke, etc.

Tapeworm Liverfluke Planaria

FACT WITH REASON

Why is tapeworm called a hermaphrodite?
Male and female sex organs are in the same body of a tapeworm. So, a tapewrom is called a hermaphrodite.

4. Aschelminthes Aschelminthes or Nematoda or Nemathelminthes [Greek: 'ascus'
– bladder, 'helminth' – worm]

Aschelminthes are the cylindrical, unsegmented and triploblastic animals. The main
characteristics of these animals are given below.

i) Aschelminthes are the cylindrical, unsegmented and triploblastic animals.
ii) Their body length varies from microscopic to several centimetres.
iii) The body wall is covered with a tough and resistant cuticle.
iv) They have a pseudocoelom (false coelom) in their body.
v) They have a mouth and an anus with a complete digestive system.

284 Classification of Plants and Animals

vi) Sexes are generally separate.
vii) They are mostly parasitic and some are also free living.
Examples: ascaris , pinworm, hookworm, filarial worm, etc.

male female

Ascaris Hookworm Wuchereria

FACT WITH REASON

Roundworm is an aschelminth but not annelid, why?

Roundworm is called an aschelminth but not annelid because it is unsegmented body. An annelid must
have metamerically segmented body which is absent in a roundworm.

5. Annelida [Latin: 'annelus' – ring]
Annelida is the phylum of animals with metamerically segmented body.

Annelida are the cylindrical, segmented and triploblastic animals. The main characteristics of
these animals are given below.

i) Annelida are the cylindrical, segmented and triploblastic animals.
i) Their body is divided into segments or circular ring-like grooves called annuli.
ii) Locomotion takes place with the help of parapodia or setae.
iii) Their body cavity is a true coelom.
iv) The alimentary canal of annelida is complete.
v) The excretory organs are metanephridia.
vi) They may be unisexual or hermaphrodite.
Example: earthworm, leech, nereis, etc.

Earthworm Leech Nereis

6. Arthropoda [Greek: 'arthros' – jointed, 'podos' – feet]

Arthropods are bilaterally symmetrical and triploblastic animals which have multiple paired
feet. The phylum arthropoda is the largest phylum which includes 84% of all known species
of animals. Some of their common features are:

Modern Concept Science - 9 285

i) Arthropoda are the invertebrates which have jointed appendages.
ii) The body is externally segmented.
iii) The body may be divided into two regions, i.e., cephalothorax (jointed head and thorax)

and abdomen, or three regions; head, thorax and abdomen.
iv) The head contains brain and sensory organs.
v) Exoskeleton is made of a thick chitinous cuticle. This hard cuticle restricts the growth.

Thus, this cuticle gets changed periodically during their growth. This process is called
moulting or ecdysis.
vi) Their body cavity contains blood. It is called haemocoel.
vii) Alimentary canal is complete.
viii) Sexes are usually separate. They reproduce by sexual method.
ix) Respiration takes place through gills, trachea, book-lungs, book-gills, etc.
x) Locomotion takes place with the help of legs or wings or both.
Examples: prawn, lobster, spider, ant, butterfly, millipede, centipede, cockroach, etc.
There are four classes in phylum Arthropoda. Which are divided on the basis of the number
of legs and habitat.They are:

a) Class: Crustacea
i) Crustaceans are the aquatic arthropods except for few which are terrestrial
(woodlice) and parasitic (fishlice).

ii) The body is divided into two parts: cephathorax (fused head and thorax) and
abdomen.

iii) They have five or more pairs of legs.

iv) They bear compound eyes.

v) Breathing takes place with the help of gills.

Examples: prawn, crab, lobster, woodlice, fish lice, etc.

Prawn Crab

b) Class: Insecta
i) Insects are mostly terrestrial in nature.

ii) They have three pairs of legs and one pair of antennae.

iii) Breathing takes place with the help of trachea.

iv) The body is divided into three parts: head, thorax and abdomen.

v) They have compound eyes.

286 Classification of Plants and Animals

Examples: butterfly, housefly, grasshopper, bee, termite, ant, cockroach, wasp, etc.

Mosquito Butterfly

FACT WITH REASON

A mosquito is called an insect, why?

A mosquito has three pairs of legs and one pair of antennae which is the characteristic feature of the class
insecta. So, a mosquito is called an insect.

c) Class: Arachnida
i) They are terrestrial in nature.
ii) They have four pairs of legs fused together inside their body.
iii) Breathing takes place with the help of trachea or book lungs.
iv) Antennae and compound eyes are absent.
v) The body is divided into cephalothorax and abdomen.
Examples: spider, scorpion, tick, mite etc.

Memory Tips

Most of arachnids are flesh eating
predators.

Scorpion Spider

FACT WITH REASON

Spider is not an insect but an arachnoid, why?

Spider possesses four pairs of legs and its body is divided into two parts: cephalothorax and abdomen un-
like the body features in insects. So, spider is not an insect but an arachnoid.

d) Class: Myriopoda
i) They are terrestrial in nature.
ii) They have multiple pairs of legs fused together inside their body. Each trunk
segment has one or two leg pairs.
iii) Breathing takes place with the help of trachea.
iv) Simple eyes and antennae are present.
v) The body is divided into head and trunk.
Examples: centipede, millipede, etc.

Modern Concept Science - 9 287

Centipede Millipede

The summary of the four classes of the phylum arthropoda is given below for comparison:

Feature Crustacea Insecta Myriopoda Arachnida
Habitat Mostly aquatic Terrestrial Terrestrial
Terrestrial +
Body section Cephalorax aerial Head and trunk Cephalorax
and abdomen and abdomen
Antennae Two pairs Head, thorax One pair Absent
and abdomen

One pair

No. of legs Five or more Three pairs Multiple pairs with Four pairs
pairs one or two pairs on Absent
each segment
Presence of wings Absent Present
Absent

Respiratory organ Gills Trachea Trachea Trachea or
book lungs

FACT WITH REASON

Why is the arthropoda largest phylum?

Arthropoda is the largest phylum of invertebrates because arthropods have high rate of reproduction. So,
they are billions in number and found all over the earth in any climate and habitat.

7. Mollusca [Latin: 'molluscus' – soft]
The animals of phylum mollusca have soft-body. They mostly live on land and in water. They
are both free living and parasitic. Their salient features are explained below:

i) They have a soft and unsegmented body without external appendages.
ii) The body is usually differentiated into three regions. i.e., anterior head, visceral mass

and foot.
iii) Their body is generally protected by a hard shell made up of calcium carbonate.
iv) Mantle covers the body.
v) Breathing usually takes place with the help of gills or lungs.
vi) Digestive system, excretory system, blood vascular system, nervous system, and

reproductive system are present.
vii) They are unisexual and reproduce by sexual method.

288 Classification of Plants and Animals

Examples: chiton, pila, limax or slug, snail, octopus, unio, squid, cuttlefish, etc.

Snail Slug Pila

Squid

Octopus Sepia

8. Echinodermata [Greek: 'echinos' – spiny, 'derma' – skin]

The animals having spiny skin are kept under the phylum Echinodermata. They are completely

marine and lie at the bottom. Memory Tips

i) Echinodermata includes aquatic invertebrates having Starfish (echinoderm), jellyfish
spiny skin (calcareous spines). (coelenteron), cuttlefish (mollusk),

ii) The shape of these animals may be star-like, crayfish (arthropod), devilfish
cylindrical, melon-like or disc- like or flower- like. (mollusk) and silverfish (arthropod)

iii) Their body is unsegmented, triploblastic and radially are not fishes because they are all
invertebrates and do not possess
symmetrical.
backbone.
iv) They do not bear a head.

v) Peculiar tube feet (podia) are developed for the locomotion.

vi) They have water-vascular systems in their body.

vi) Their sexes are separate. They can reproduce by regeneration.

Examples: starfish, brittle star, basket star, sea-urchin, sand dollar, sea-cucumber,
feather star, etc.

Starfish Sea urchin Sea cucumber Brittle star

Chordates

The group chordates include only one phylum: chordata.

Phylum Chordata

Chordates are those animals which bear notochord in some stages of their life. In sub-phylum
Vertebrata, the notochord changes into vertebral column in the adult stage. But in Urochordata
and cephalochordata, the notochord remains unchanged throughout their lifetime. Some of
the distinguishing features of chordates are:

a) Notochord is present at some stage of their life.

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b) A dorsal nerve cord is present above the notochord in the embryonic stage.
c) The notochord changes into spinal cord in vertebrates.
d) Pharyngeal gill slits and post anal tail are present in the embryonic stage.
e) The circulatory system is closed type
f) They are bilaterally symmetrical and triploblastic animals.

Balanoglossus-Hemichordate Herdmania-Urochordate Amphioxus-A Cephalochordate

Sub-phylum Vertebrata
This sub-phylum includes all the vertebrates. Vertebrates are those animals that have a
backbone or vertebral column. The backbone helps to protect the spinal cord enclosed inside
it. The common characteristics of sub-phylum vertebrata are as follows:

a) The bones and the vertebrae surround the spinal cord.
b) They have a skull that protects their brain.
c) Notochord is present in the earlier stage of their life which converts into spinal cord later.
d) They have an endoskeleton made up of bones and cartilage.
e) A dorsal nerve cord is present above the notochord in the embryonic stage.
f) Pharyngeal gill slits and post anal tail are present in the embryonic stage.
g) The circulatory system is closed type.

FACT WITH REASON

All vertebrates are chordates but all chordates are not vertebrates, why?
All vertebrates are chordates but all chordates are not vertebrates because all vertebrates have a notochord
in the embryonic stage of their life while all chordates do not possess vertebral column.

The sub-phylum Vertebrata is divided into five classes namely: Pisces, Amphibia, Reptilian,
Aves and Mammalia.

Class Pisces (fishes) (Latin: 'piscis' – a fish)
Pisces are the vertebrates that are aquatic and cold-blooded. Their body is specially modified
so that they can live in water. Some of their important characteristics are:

a) Body is differentiated into head, trunk and tail. Most of them have hard waterproof
scales on their body. The body somewhat tapers on both sides making them streamlined.

290 Classification of Plants and Animals

b) Body temperature changes with the change in the temperature of the surroundings, i.e.
they are cold-blooded animals.

c) Locomotion takes place with the help of paired fins and tail.
d) Breathing occurs with the help of gills.
e) Heart is two chambered (one atrium and one ventricle).
f) Reproduction takes place by laying eggs i.e. they are oviparous.
g) Fertilization is external.
Examples: Dog fish, saw fish, great white shark, rohu, katla, sea horse, flying fish, etc.

Sea horse Shark Rohu

Class Amphibia (Greek: 'Amphi'- dual, 'bios' - life)

The amphibians are those creatures that can breathe both on land and inside water. The
females lay eggs inside water which hatch and develop gradually into an adult in different
stages. Some of its characteristics are:

a) Body is differentiated into head and trunk. They have two pairs of limbs with webbed
feet for walking and swimming. The skin is moist and doesn’t contain scales.

b) Body temperature changes with the change in the temperature of the surroundings, i.e.
they are cold-blooded animals.

c) Locomotion takes place with the help of webbed feet. The limbs are pentadactylated, i.e.
with five digits.

d) Breathing occurs with the help of lungs in air, skin in water and gills in tadpole stage.

e) Heart is three-chambered (two atria and one ventricle).

f) Reproduction takes place by laying eggs i.e. they are oviparous. Sexes are separate.

g) Fertilization is external.

Examples: Frog, toad, salamander, tree frog (hyla), ichthyophis etc.

Salamander Toad Frog Ichthyophis

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FACT WITH REASON

Why is frog called an amphibian?
Frog is called an amphibian because it lives in land but must return in water for fertilization and to keep its
skin moist. Amphibians far away from water bodies will die of dehydration.

Class Reptilia: (Latin: 'repere or reptum' - to creep or crawl)
Reptiles are those creatures that crawl on the ground with their ventral surface. Some of its
characteristics are:

a) Body is differentiated into head, neck trunk and tail. They have two pairs of limbs with
webbed feet for walking and swimming. The skin is dry and contains tough scales. They
do not have ear holes.

b) Body temperature changes with the change in the temperature of the surroundings, i.e.
they are cold-blooded animals.

c) Locomotion takes place with the help of limbs (except in snakes and lizards like glass lizard)
d) Breathing occurs with the help of lungs.
e) Heart is three- chambered except in crocodile which has four chambered heart.
f) Reproduction takes place by laying eggs i.e. they are oviparous. Sexes are separate.
g) Fertilization is internal.
Examples: crocodile, tortoise, turtle, wall lizard, garden lizard, snake like Cobra, krait etc.

Wall lizard

Tortoise

Snake

Crocodile

Turtle

Class Aves: (Latin: 'avis' - bird)

Aves or birds are animals that spend most of the time in air. They are well modified for aerial
adaptation. Salient features of aves are:

a) Body is differentiated into head, neck trunk and tail. Their forelimbs or wings are
modified for flying and hind limbs for walking, grabbing or swimming. They have a
toothless beak modified for their feeding habit.

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