Oasis Science and Technology 7

Exercise

1 Choose the best answer from the given alternatives.
a. Which of the following is a metal?

(i) Copper (ii) Iodine

(iii) Brass (iv) Sulphur

b. Which of the following is a non-metal?

(i) Chlorine (ii) Bronze

(iii) Gold (iv) Steel

c. Which of the following is an alloy?

(i) Bronze (ii) Silver

(iii) Iodine (iv) Chlorine

d. Which substance is used for making gun powder?

(i) Sulphur (ii) Iodine

(iii) Brass (iv) Bronze

2 Tick (√) the correct statement and cross (×) the incorrect one.
a. Metals are malleable and ductile.
b. Non-metals are good conductors of heat and electricity.

c. Silicon and arsenic are metalloids.
d. Brass is the mixture of copper and tin.
e. Sulphur is used for curing skin diseases.

3 Fill in the blanks using appropriate words.

a. ................................. can be beaten into sheets.
b. Non-metals are bad conductors of ................................. and .................................
c. Bronze is the mixture of ................................. and .................................
d. ................................. is used for preventing goitre.
e. Brass and ................................. are called alloys.

4 Answer the following questions.
a. What are metals? Give any three examples.

b. What are non-metals? Give any three examples.

CHEMISTRY Oasis School Science and Environment - 7 143

c. What are metalloids? Give any two examples.
d. Write any four properties each of metals and non-metals.
e. What are alloys? Give any three examples.
f. Why do we use alloys? Give any three reasons.
g. Which substance is used for making insecticides and fungicides?
h. What happens due to the deficiency of iodine in our body?

5 Write any four differences between metals and non-metals.

6 Write any three uses of:
a. metals
b. metalloids
c. brass
d. bronze
e. sulphur
f. iodine

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Unit Estimated teaching periods: Th Pr
5 1
14
Dettol

Some Useful Chemicals

Objectives

After completing the study of this unit, students will be able to :

• introduce phenol, dettol, detergent and chemical fertilizers.
• tell the uses of phenol, dettol, detergent and chemical fertilizers.

Course of Study

• Some useful chemicals
– Phenol and its uses
– Dettol and its uses
– Detergent and its uses

– Chemical fertilizers and their uses

Points to be Focused / Questions to be Discussed

• What is phenol ? Why is it used?
• What is dettol? Why is it used?
• What is detergent? Why is it used?
• What are chemical fertilizers? Why are they used?

CHEMISTRY Oasis School Science and Environment - 7 145

14.1 Introduction

We use a variety of chemical substances in our daily life. Some of them are soap,
detergent, phenol, dettol, plastics, chemical fertilizers, etc. We use soap for bathing
and washing clothes. We use phenol for cleaning bathrooms and killing insects.
We use detergents for washing clothes. We use dettol to make our skin germ-free.
Similarly, we use chemical fertilizers to increase the fertility of soil. The sources of
these chemicals are plants and minerals. In this unit, you will learn about phenol,
dettol, detergent and chemical fertilizers in brief.

14.2 Phenol Fig. 14.1

Phenol is an aromatic organic compound. It is a useful chemical.
It is also known as carbolic acid. It is extracted from petroleum. It
is slightly soluble in water. It is mildly acidic and requires careful
handling as it is corrosive to the eyes, skin and respiratory tract.

Uses
(i) Phenol is used in wounds as a disinfectant.
(ii) It is used for making medicines, thread, bakelite (plastics),

colours, etc.
(iii) It is used for killing insects and bacteria.
(iv) It is used for cleaning bathrooms.

14.3 Dettol Fig. 14.2

Dettol is a trade name for a line hygiene product manufactured
by Reckitt Benckiser. It is an important chemical for cleaning cuts
and wounds. Dettol is an antiseptic and disinfectant of light yellow
colour. It is toxic to humans and many animals. It is poisonous
when ingested and inhaled.

Uses
(i) Dettol is used for washing cuts and wounds.
(ii) It is used to disinfect household floors, walls of slaughter

houses, etc.
(iii) It is used in soaps to protect skin infection.
(iv) It is also used for disinfecting clothes.

corrossive /kəˈrəʊsɪv/ - tending to destroy sth slowly by chemical action

slaughter /ˈslɔːtə/ - the killing of animals for their meat

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14.4 Detergent

Detergent is an important petrochemical having cleansing
properties. Its chemical name is alkylbenzenesulphonate.
Detergent is a chemical compound similar to the soap but it is
more soluble in water. Detergents are prepared from petroleum
products. Detergents contain water softeners, surfactants,
bleach, enzymes, brighteners and fragrances. Detergents pollute
water and affect plants. So, we should be careful while using
detergents. Fig. 14.3

Uses
(i) Detergent is used for washing clothes.
(ii) It is used for washing household utensils and dishes.

14.5 Chemical Fertilizers

Chemical fertilizers are the substances that are used
for increasing the fertility of soil. Chemical fertilizers
contain the minerals required by plants for their
growth and development. The fertilizer prepared
by using decayed plants and animal wastes is called
compost fertilizer. The fertilizers prepared with
minerals or various chemicals are called chemical
fertilizers. Green plants mainly require nitrogen,
phosphorus and potassium. Chemical fertilizers are
made by mixing compounds containing nitrogen,
phosphorus and potassium. Prolonged use and over Figure 14.4: Chemical fertilizers
use of chemical fertilizers affects the fertility and
quality of soil. Therefore, we should limit the use of chemical fertilizers.

Nitrogen is essential for growth of plants. In deficiency of nitrogen, plants become
pale and flowers do not bloom properly. Similarly, fruits and seeds become small
in size. Therefore, plants need nitrogenous fertilizers. Chemical fertilizers like urea,
ammonium chloride, ammonium sulphate, etc. are rich in nitrogen.

Phosphorus helps in the growth of roots, ripening of the fruits and development of
seeds in crops. It is also essential for growth of leaves and buds. Chemical fertilizers
like ammonium phosphate, calcium super phosphate and bone powder are rich in
phosphorus.

Potassium helps plants in preparing food, formation of protein and cell division.
In the absence of potassium, leaves and buds wither and immunity decreases.
Chemical fertilizers like potassium chloride, potassium nitrate, potassium sulphate,
etc. and ash are rich in potassium.



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Activity 1

• Prepare a list of chemicals that are used in your home.
• Also, write down their uses.

Summary

• We use a variety of chemical substances in our daily life. Some of them are soap,
detergent, phenol, dettol, plastics, chemical fertilizers, etc.

• Phenol is an aromatic organic compound.
• Dettol is an antiseptic and disinfectant of light yellow colour.
• Detergent is an important petrochemical having cleansing properties. Its

chemical name is alkylbenzenesulphonate.
• Detergents pollute water and affect plants. So, we should be careful while using

detergents.
• Chemical fertilizers are the substances made from minerals or various chemicals

that are used for increasing the fertility of soil.
• Nitrogen is essential for growth of plants. In deficiency of nitrogen, plants

become pale and flowers do not bloom properly.
• Potassium helps in preparing food for plants, formation of protein and cell

division.

Exercise

1 Choose the best answer from the given alternatives.

a. Phenol is used to ..........................

(i) wash clothes (ii) kill germs

(iii) increase the fertility of soil (iv) kill insects

b. Which chemical is used for washing cuts and wounds?

(i) dettol (ii) phenol

(iii) soap (iv) detergent

c. Which element is essential for the growth of roots in plants?

(i) potassium (ii) nitrogen

(iii) phosphorus (iv) oxygen

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d. Why are detergents used?

(i) to wash clothes

(ii) to clean cuts and wounds

(iii) to increase the fertility of soil

(iv) to protect skin against infection

e. Which element is essential for the growth of plants?

(i) phosphorus (ii) nitrogen

(iii) hydrogen (iv) potassium

2 Tick (√) the correct statement and cross (×) the incorrect one.
a. Phenol is used for cleaning surfaces.
b. Dettol is poisonous when ingested and inhaled.
c. Detergents cause environmental pollution.
d. Nitrogen is essential for the growth of plants.
e. Overuse of chemical fertilizers affects the fertility of soil.

3 Fill in the blanks using appropriate words.
a. Phenol is prepared from .................................
b. ................................. is used for washing cuts and .................................
c. The chemical name of detergent is .................................
d. Green plants need nitrogen, ................................. and .................................
e. The fertilizers rich in phosphorus are ................................. and ..............................

4 Answer the following questions.

a. What is phenol? Write any three uses of phenol.
b. What is dettol? Write any three uses of dettol.
c. What is detergent? Why is it used.
d. What are chemical fertilizers? Give any three examples.
e. Why do plants need chemical fertilizers?
f. Why is nitrogen essential for green plants? Name any two chemical fertilizers

rich in nitrogen.
g. Why is phosphorus essential for plants? Give any two reasons.
h. Why is potassium essential for plants? Give any two reasons.
i. What happens to the plants due to absence of nitrogen, phosphorus and

potassium?
j. Name any two fertilizers rich in phosphorus and potassium.

5 We should limit the use of chemical fertilizers. Justify this statement.

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Unit Estimated teaching periods: Th Pr
5 1
15
Peacock

Living Beings: Animal Life

Objectives

After completing the study of this unit, students will be able to :

• classify vertebrates and explain their characteristics.
• describe the life cycle of frog with a neat and labelled figure.

Course of Study

• Vertebrates
– Cold-blooded animals
– Warm-blooded animals
• Pisces - Characteristics and examples
• Amphibia - Characteristics and examples
• Reptilia - Characteristics and examples
• Aves - Characteristics and examples
• Mammalia - Characteristics and examples
• Life cycle of frog

Points to be Focused / Questions to be Discussed

• What are vertebrates ?
• What are cold-blooded and warm-blooded animals?
• What are the salient features of different classes of vertebrates?
• What are the stages of life cycle of frog ?

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15.1 Introduction

A large number of animals are found in our surroundings. They differ from one
another in structure, size, habit, habitat, characteristics, etc. Snail, mosquito,
earthworm, slug, butterfly, honeybee, cockroach, fish, toad, frog, snake, crow,
parrot, dog, cat, cow, etc. are some of the animals that live in our surroundings.
Among them, some animals have backbone while some don’t. On the basis of
absence or presence of backbone, animals are divided into two major groups, viz.
Invertebrates and Vertebrates. In this unit, you will learn about vertebrates.

Activity 1

To identify invertebrates and
vertebrates

• Observe at least 15 animals in your
surroundings.

• Study their external structure and find
out whether the backbone is present in
them or not.

• Classify them in terms of invertebrates Figure. 15.1: Vertebral column of humans
and vertebrates.

15.2 Vertebrates

The animals having backbone or vertebral column are called vertebrates. Fish,
frog, snake, lizard, bird, cow, dolphin, bat, human, tiger, etc. are some examples
of vertebrates. Some vertebrates are found in water and some are found on land.
However, some vertebrates can live on land as well as in water. Vertebrates cannot
tolerate extreme hot or extreme cold temperature.
Salient features of vertebrates
(i) Vertebral column or backbone is present.
(ii) Well developed nervous system is present. It includes brain and spinal cord.
(iii) The body is well developed having head, trunk and paired fins or limbs.
(iv) Gills or lungs are present.
(v) Their body is bilaterally symmetrical and triploblastic (having three germ layers).
(vi) Various organs and systems are present.

Some vertebrates can change their body temperature according to the temperature
of the surroundings and some cannot. On this basis, vertebrates are divided into
two groups: cold-blooded animals and warm-blooded animals.

trunk /trʌŋk/ - the main part of the body apart from the head, arms and legs
symmetrical /sɪˈmetrɪkl/ - having two halves, parts or sides that are the same in size and shape

BIOLOGY Oasis School Science and Environment - 7 151

15.3 Cold-blooded Animals

Animals like fish, frog, snake, lizard,
etc. can change their body temperature
according to the temperature of the
surroundings. Such animals are called Shark Rohu

cold-blooded animals. They cannot
tolerate extreme cold or extreme
hot temperature. So these animals Salamander
Cobra Frog

usually hibernate to escape very cold Figure 15.2: Some cold-blooded animals
temperature. During winter, most of
the cold-blooded animals go under the soil in burrows, in warmer places. When
the temperature of the surroundings is suitable for their body, they come out of the
hole and become active. Those animals whose body temperature changes according
to the temperature of the surroundings are called cold-blooded animals. Fishes,
amphibians and reptiles are the cold-blooded animals.

15.4 Warm-blooded Animals

Animals like cow, horse, bat, crow,
dog, monkey, etc. do not change
their body temperature according
to the temperature of their
surroundings. Such animals are Pigeon Parrot Peacock

called warm-blooded animals. Their
body temperature remains constant
in any climate. The normal body
temperature of human body is 37°C
Elephant Tiger Bear

or 98.6°F. When this temperature Figure 15.3: Some warm-blooded animals
changes due to fever, we feel unwell.
To maintain the body temperature
to a constant level, we wear thin and light clothes during summer and thick and
warm clothes during winter. The animals whose body temperature remains constant
and does not change according to the temperature of the surroundings are called
warm-blooded animals. Different types of birds and mammals are warm-blooded
animals.

Activity 2

• Observe at least ten vertebrate animals in your surroundings.
• Study their external morphology and write any two salient features of

each.
• Classify them in terms of cold-blooded or warm-blooded animals.


hibernate /ˈhaɪbəneɪt/ - to spend the winter in a state like deep sleep

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On the basis of structure and development, vertebrates are divided into the
following five classes.

1. Pisces 2. Amphibia

3. Reptilia 4. Aves

5. Mammalia

Class 1. Pisces
Class Pisces includes cold-blooded vertebrates commonly known as fishes. They

are found in water.

Salient features
(i) The body is streamlined or boat–shaped which remains covered with smooth,

slippery and waterproof scales.
(ii) Breathing takes place with the help of gills.
(iii) Locomotion takes place with the help of fins and tail.
(iv) The body is differentiated into head, trunk and tail.
(v) Heart is two-chambered.
(vi) They are oviparous (i.e. egg laying) and fertilization is external.

Examples: Shark, Rohu (Labeo), Sea horse, Katla, etc.

Seahorse Shark Rohu
Figure 15.4: Some fishes

Class 2. Amphibia

Class Amphibia includes cold-blooded vertebrates which can live on land as well
as in water. Amphibians form the first group of vertebrates adapted to live out of
water. Most amphibians lay eggs in water where the eggs develop into tadpoles.
Salient features
(i) The body is divided into head and trunk. Neck is absent.
(ii) The body remains covered with smooth or rough skin which is moist and
rich in glands.
(iii) They breathe through skin in water and through lungs on land. However,
tadpoles breathe through gills.

streamline /ˈstriːmlaɪn/ - to give something a smooth even shape so that it can move quickly
BIOLOGY
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(iv) Two pairs of limbs are present.
(v) Heart is three-chambered.
(vi) They are oviparous and fertilization is external.
Examples: Frog, Toad, Salamander, Tree frog (Hyla), etc.

Frog Toad Salamander Hyla

Figure 15.5: Some amphibians

Class 3. Reptilia

Class Reptilia includes creeping cold-blooded vertebrates. Most of the reptiles are
found on land. Different types of snakes, lizards and crocodiles are kept in this
class.

Salient features

(i) The body remains covered with hard, dry and horny scales.
(ii) The body can be divided into head, neck, trunk and tail.
(iii) Heart is three-chambered but crocodiles have four-chambered heart.
(iv) Two pairs of limbs with clawed digits are present. But limbs are absent in

snakes and some lizards.
(v) They are oviparous and fertilization is internal.

Examples: Cobra, Garden lizard, House wall lizard, Gharial, Monitor lizard,
Python, Tortoise, etc.

Wall lizard Tortoise Crocodile Snake
Figure 15.6: Some reptiles

Class 4. Aves

Class Aves includes warm-blooded vertebrates having feathers and wings. Various
types of birds are kept in this class.
Salient features
(i) The body is streamlined which remains covered with feathers.
(ii) The body can be divided into head, neck, trunk and tail.
(iii) Fore limbs are modified in the form of wings.

154 Oasis School Science and Environment - 7 BIOLOGY

(iv) Toothless beak is present.
(v) The heart is four-chambered.
(vi) Breathing takes place with the help of lungs.
(vii) They are oviparous and fertilization is internal.
Examples: Pigeon, Sparrow, Crow, Owl, Peacock, Vulture, Parrot, Koel, etc.

Giant Hornbill Koel Crow

Saras (Crane)

Sparrow Peacock

Danphe
Figure 15.7: Some birds

Class 5. Mammalia
Class Mammalia includes the most developed vertebrates which directly give birth

to their young ones and suckle them. However, two mammals, viz. duck-billed
platypus and spiny ant eater, lay eggs.


Bat Kangaroo Squirrel

Ghoral Tiger Great Tibetan Sheep

Elephant Yak Rhinoceros
Figure 15.8: Some mammals

suckle /ˈsʌkl/ - to feed a baby or young animal with milk from the breast or udder

BIOLOGY Oasis School Science and Environment - 7 155

Salient features
(i) Females have mammary glands (i.e. milk producing glands) which secrete milk.
(ii) Body is covered with hair. Sweat glands and oil glands are present in the skin.
(iii) External ears (pinnae) are present.
(iv) Heart is four-chambered.
(v) They are viviparous and warm-blooded animals.
(vi) Body can be divided into head, neck, trunk and tail.
(vii) Two pairs of limbs are present.
(viii) Breathing takes place with the help of lungs.

Examples: Human, Buffalo, Whale, Bat, Dolphin, Dog, Rat, Cat, Cow, Horse, Sheep, etc.

Activity 3

• Study the structure of some birds and mammals in your locality and
differentiate between them. Also, classify them with two salient features
of each.



15.5 Oviparous and Viviparous Animals

The animals that lay eggs are called oviparous animals whereas the animals that give
birth directly to their young ones are called viviparous animals. Fishes, amphibians,
reptiles and birds are oviparous animals whereas mammals are viviparous animals.

Activity 3

• Observe different types of vertebrates found in your surroundings.
• Study their characteristics and identify the class to which they belong.
• Draw neat diagram of each and label the main body parts.
• Also, find out any two similarities among them.


15.6 Life Cycle of Frog

A series of stages through which an organism passes is
called the life cycle. Frog is a short-bodied and tailess
carnivorous amphibian which can live on land and in
water. A frog is an animal with a stout body, protruding
eyes, cleft tongue, folded limbs and no tail. Frogs Fig. 15.9

generally become active during rainy season. They are commonly found in ponds, lakes,
rivers, crop fields, etc.

Frogs generally reproduce in rainy season. Male frogs attract female frogs by

protrude /prəˈtruːd/ - to stick out from a place or a surface

156 Oasis School Science and Environment - 7 BIOLOGY

producing a ‘croaking’ sound. The female frog is slightly larger than the male. Many
frogs migrate to the bodies of water in which they develop as larvae or tadpoles.
At breeding site, the male mounts the female and grips her tightly round the body.
Then the female lays her eggs and the male covers them with sperms. There are
three stages in the life cycle of frog. They are egg, tadpole and adult.

Tadpole

Metamorph
Eggs

Frog (adult)

Fig. 15.10: Life cycle of frog

Eggs

Frogs typically lay eggs in water. Eggs are oval Fig. 15.11: Eggs of frog
and covered with a jelly like substance which
expands when immersed in water and forms
a cluster of eggs. The cluster of eggs remains
floating on the surface of water. The male
disseminates a large number of sperms on the
eggs and fertilization of sperm and egg takes
place in water. This process is called external
fertilization. After fertilization, a zygote is
formed in water.

After a few days, the nucleus of zygote divides and develops into an embryo and the
embryo finally develops into larva, i.e. tadpole of a frog.

Tadpole

Tadpole is the larval stage of the frog. It has a big head and
a short tail. It has adhesive glands on the base of the head. It
has gills for breathing. The tadpole remains attached to the
surface of leaves but does not take any food. It depends on
the nutrition stored in its body.

After a few days, the head develops mouth with teeth
and then the tadpole feeds on algae in water. The tadpole
stage may be as short as a week to one or more winters. Fig. 15.12: Tadpole

embryo /ˈembrɪəʊ/ - a young animal or plant in the very early stage of development
adhesive /ədˈhiːsɪv/ - a substance that is used to make things stick together

BIOLOGY Oasis School Science and Environment - 7 157

At the end of tadpole stage, it develops hind limbs, well developed mouth and gills
metamorphose into lungs. The tail becomes short and then disappears gradually. As
a result, a tadpole metamorphoses into an
adult frog.

Adult

The adult frog has a short stout body, two
pairs of limbs for jumping, swimming,
running and walking. The adult frog can live
on land and in water.

Fig. 15.13: Adult frog develops from a tadpole

Summary

• Vertebrates are the advanced animals having vertebral column.
• Those animals whose body temperature changes according to the temperature

of the surroundings are called cold-blooded animals.
• The animals whose body temperature does not change according to the

temperature of their surroundings are called warm-blooded animals.
• Different types of fishes are kept in class Pisces.
• Amphibians are the cold-blooded animals which can live on land as well as in

water.
• Reptiles are the creeping cold-blooded vertebrates.
• Class Aves includes warm-blooded vertebrates adapted for flight.
• Mammals are the most developed animals which directly give birth to their young

ones.
• Fishes, amphibians and reptiles are cold-blooded animals whereas birds and

mammals are warm-blooded animals.
• The animals which lays eggs are called oviparous animals and the animals

which directly give birth to their young ones are called viviparous animals.
• Frog completes its life cycle in three stages. They are: egg, tadpole and adult.

Exercise

1 Choose the best answer from the given alternatives.

a. Which of the following animals cannot live in water ?

(i) Sea horse (ii) Horse

(iii) Rohu (iv) Frog

metamorphose /ˌmetəˈmɔːfəʊz/ - transform, to change into sth completely different

158 Oasis School Science and Environment - 7 BIOLOGY

b. Which of the following is a viviparous animal ?

(i) Toad (ii) Dog (iii) Snake (iv) Fish

c. Which of the following is an animal having four-chambered heart ?

(i) Cow (ii) Asla (iii) Lizard (iv) Toad

d. The heart of reptiles contains ______.

(i) one chamber. (ii) two chambers

(iii) four chambers. (iv) three chambers

e. Which of the following is a mammal ?

(i) Bat (ii) Crow

(iii) Pigeon (iv) Sparrow

2 Tick (√) the correct statement and cross (×) the incorrect one.

a. Bat is a viviparous animal.
b. Salamander is a kind of reptile.
c. Earthworm is a vertebrate animal.
d. Mammary glands are found in dolphin.
e. Parrot is a cold-blooded animal.
f. Frog has a two-chambered heart.
g. Tortoise is kept in class reptilia.
h. Sea horse breathes through gills.

3 Fill in the blanks with appropriate words.

a. Fishes have................... chambered heart.
b. The body of mammals is covered with..........................
c. Frogs and snakes lay...............................
d. External ears are found in........................
e. Parrot is kept in the class......................
f. Horse is a .................blooded animal.
g. Frogs generally reproduce in .......................... season.

4 Answer the following questions:
a. What are vertebrates ? Give any five examples.
b. Write any three salient features of vertebrates.
c. What is meant by cold-blooded and warm-blooded animals ? Give any three
examples of each.
d. Why do cold-blooded animals go for hibernation ?
e. Mention any three characteristics of Pisces.
f. What are amphibians? Write any two salient features each of amphibians and reptiles.

BIOLOGY Oasis School Science and Environment - 7 159

g. Write any two characteristics of the animals belonging to class Aves. Also,
write any three examples of Aves.

h. What are mammals ? Write their salient features with any three examples.
i. Where do frogs lay eggs? What is a tadpole?

5 Differentiate between:
a. Invertebrates and Vertebrates
b. Cold-blooded animals and Warm-blooded animals
c. Fish and Frog
d. Sea horse and Horse
e. Bird and Bat
f. Fish and Dolphin

6 Match the following:

A B
Bat Aquatic mammal
Snake Two-chambered heart
Birds Having backbone
Mammals Three-chambered heart
Vertebrates Flying vertebrate
Fishes Having mammary glands
Dolphin

7 Draw a neat diagram of each of the following animals and label their main parts.

(a) fish (b) toad (c) snake

(d) bird (e) bat

8 Name the habitat of the given animals.
(a) shark (b) frog (c) lizard
(d) crocodile (e) tiger (f) bat

9 Name the locomotory organs of each of the following animals.

(a) whale (b) sparrow (c) lizard

(d) frog (e) sea horse

10 Classify the following animals in terms of cold-blooded and warm-blooded
animals.

(a) cat (b) pigeon (c) rohu

(d) toad (e) mouse (f) snake

(g) frog (h) human

11 Draw a neat and labelled figure showing the life cycle of frog.

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Unit Estimated teaching periods: Th Pr
7 1
16
Lotus

Living Beings: Plant Life

Objectives

After completing the study of this unit, students will be able to :

• classify non-flowering and flowering plants and state their characteristics.
• explain the structure of a flowering plant with a labelled figure.
• describe the structure of a flower.

Course of Study

• Classification of plants
• Cryptogams and its divisions
• Phanerogams and its divisions
• Structure of a flower

Points to be Focused / Questions to be Discussed

• What are cryptogams?
• What are phanerogams?
• What are the different parts of a flowering plant?
• What are the different parts of a flower?
• What is meant by pollination and fertilization?

BIOLOGY Oasis School Science and Environment - 7 161

16.1 Introduction

The earth is inhabited by a large number of living organisms. All organisms that
live on the earth are broadly categorized into two Kingdoms - Plant Kingdom and
Animal Kingdom. Different types of plants like thallophytes, liverworts, mosses,
ferns, gymnosperms and angiosperms are kept in the Plant Kingdom. Spirogyra,
mushroom, yeast, moss, fern, pine, orange, mustard, mango, etc. are some examples
of plants. Most of the plants are found in land whereas some are found in water.

Mushroom Fern Rose
Fig. 16.1: Some plants

16.2 Salient Features of Plants

(i) Most of the plants appear green due to the presence of chlorophyll.
(ii) Most of the plants are made up of eukaryotic cells.
(iii) Their cells contain cell wall which is made up of cellulose.
(iv) Most of the plants are multicellular.
(v) Most of the plants (except non-green plants) prepare their own food by

photosynthesis.
(vi) Most of the plants remain fixed to the soil with the help of roots. So they

cannot show locomotion like animals.
(vii) Developed plants contain roots, stem, leaves, branches, flowers and fruits.

Thousands of different species of plants are found on the earth. Some of them do
not produce flowers and some do. On the basis of absence or presence of flowers
and seeds, Plant Kingdom is divided into two sub-kingdoms.

(i) Sub-kingdom Cryptogams

(ii) Sub-kingdom Phanerogams

16.3 Sub-kingdom Cryptogams [Gk., crypto-hidden, gamous-marriage]

The Sub-kingdom cryptogams includes less developed plants which do not bear
flowers and seeds. Therefore, cryptogams are regarded as the flowerless or seedless
plants. The members of this sub-kingdom may be unicellular or multicellular and
green or non-green.

On the basis of structure and development, Sub-kingdom Cryptogams is further
divided into three divisions.
1. Division Thallophyta 2. Division Bryophyta 3. Division Pteridophyta

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1. Division Thallophyta [Gk., thallus–without roots, stem and leaves; phyton–plant]
This division contains lower cryptogams whose plant body is not differentiated into

roots, stem and leaves. Such plant body is called a thallus and the thallus-bearing
plants are called thallophytes. The plant body of thallophytes may be unicellular or
multicellular and green or non-green.

On the basis of presence or absence of chlorophyll, Division Thallophyta is further
divided into two sub-divisions, viz. Algae and Fungi.

a. Sub-division Algae [L., alga–sea weed]
This sub-division includes green thallophytes. Most of the algae are found in water

(both fresh water and marine water) whereas some are found in moist places.
Salient features

(i) The plant body is a thallus which may be unicellular or multicellular.
(ii) They contain green pigment, i.e. chlorophyll for photosynthesis.
(iii) They are autotrophic due to the presence of chlorophyll.
(iv) The cell wall is made up of cellulose.
(v) Reserve food is generally starch.
Examples: Spirogyra, Chlamydomonas, Volvox, Ulothrix, etc.

Chlamydomonas Spirogyra Volvox Ulothrix

Figure 16.2: Some algae

Activity 1

To observe the filaments of spirogyra
• Visit a nearby pond and collect some green filaments.
• Keep one of the filaments on a glass slide and cover it with a cover slip.
• Observe the slide under the compound microscope. You can see the
multicellular spirogyra.
• Draw a neat diagram and label its main parts on the basis of your
observation.

cellulose /ˈseljʊləʊz/ - a natural substance that forms the cell walls of plant cells
BIOLOGY
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b. Sub-division Fungi [L., fungus–mushroom]

This sub-division includes non-green thallophytes. Most of the fungi are found on
dead and decaying matters whereas some are parasites.

Salient features
(i) Fungi are non-green thallophytes which do not contain chlorophyll.
(ii) The plant body may be unicellular (e.g. yeast) or multicellular (e.g. mushroom,

Mucor, etc.).
(iii) The cell wall of a fungus is made up of cellulose.
(iv) Their mode of nutrition is heterotrophic which may be either saprophytic or

parasitic.
(v) The reserve food is glycogen.

Examples: Yeast, Mucor, Mushroom, etc.

Yeast Mucor Mushroom

Figure 16.3: Some fungi

Activity 2

To observe yeast (bread mould)
• Take a piece of bread and keep it in the warm

and moist place for 3 - 4 days.
• You will observe the white cotton-like structures

on the bread. It is called yeast or bread mould. Fig. 16.4: Yeast grown on bread
• Prepare a temporary slide of the yeast and

observe it under the compound microscope.
• On the basis of your observation, draw a neat

diagram.

2. Division Bryophyta [Gk., bryon-a moss, a liverwort]
Bryophytes form a group of higher cryptogams. They grow on old damp walls,

on moist ground and on the bark of trees; however, they need water for their
reproduction. Therefore, bryophytes are also called the amphibians of Plant
Kingdom.

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Salient features

(i) The plant body may be thalloid (e.g. liverworts) or leafy (e.g. moss).
(ii) True roots, stem and leaves are absent.
(iii) Bryophytes are attached to the soil by means of hair-like outgrowths called

rhizoids. They absorb water and minerals from the soil.
(iv) Vascular tissues (i.e. xylem and phloem) are absent.
Examples: Marchantia (liverworts), Riccia, Moss, etc.

Marchantia Riccia Moss
Figure 16.5: Some bryophytes Riccia

3. Division Pteridophyta [Gk., pteron - feather, phyton - plant]

This division includes the most developed cryptogams whose body can be divided
into roots, stem and leaves. Pteridophytes are more advanced than bryophytes since
their plant body contains vascular tissues and roots, stem and leaves. Pteridophytes
are mostly found in damp, cool and shady places.

Salient features
(i) The plant body can be differentiated into roots, stem and leaves.
(ii) They have well developed vascular tissues (i.e. xylem and phloem tissues).
(iii) Flowers and seeds are absent.
(iv) Chlorophyll is present.
Examples: Fern, Lycopodium, Equisetum (Horsetail), etc.


Fern Lycopodium Horsetail
Figure 16.6: Some pteridophytes

vascular /ˈvæskjʊlə/ - containing tubes or veins
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165

Activity 3

• Visit a garden and observe various types of cryptogams.
• Collect some thallophytes, bryophytes and pteridophytes.
• Study their structure and differentiate among them.
• Write their division and draw the labelled diagrams.
• Also, write at least two important features of each which helped you to
decide the division in which the plant should be kept.

Differences between Algae and Fungi

S.N. Algae S.N. Fungi

1. Chlorophyll is present. 1. Chlorophyll is absent.

2. Cell wall is made up of 2. Cell wall is made up of chitin
3. cellulose. and cellulose.

The mode of nutrition is 3. The mode of nutrition is either
autotrophic. saprophytic or parasitic.
4.
Reserve food is starch Reserve food is glycogen.
(glucose). 4.

Differences between Bryophytes and Pteridophytes

S.N. Bryophytes S.N. Pteridophytes

1. The plant body may be thalloid 1. The plant body is clearly
with rhizoids or having rhizoids, differentiated into roots,
stem (seta) and leaves. stem and leaves.
2. Vascular system is absent. 2. Vascular system is present.

16.4 Sub–Kingom-Phanerogams (Greek, phaneros–visible, gamous–

marriage)

This sub-kingdom includes developed plants having flowers and seeds. They are
commonly known as flowering plants. Phanerogams are more developed than
cryptogams.

Salient features
(i) The plant body contains well developed roots, stem and leaves which can

produce flowers and seeds.
(ii) Well developed vascular system (xylem and phloem tissues) is present.
(iii) The sex organs are multicellular.

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Examples: Cycas, pea, apple, pine, maize, bamboo, etc.
On the basis of absence or presence of fruits, Sub-kingdom Phanerogams is divided

into two divisions-Gymnosperms and Angiosperms.

Division–Gymnosperms [Gk., gymno-naked, sperma-seed]
This division includes cone-bearing plants having naked seeds. They are commonly

known as conifers.

Salient features
(i) Cones are present instead of true flowers. Male cones and female cones are

separate.
(ii) Seeds are not enclosed in the fruit. They develop in the woody scales of cones.
(iii) Needle-shaped leaves are present.
(iv) There is no fruit due to the absence of ovary.
Examples: Cycas, pine, cedar, fir, etc.

Cycas Cedar Pine Cones of pine

Figure 16.7: Some gymnosperms

Division – Angiosperms [Gk., angion - case, sperma - seed]
This division includes well developed flowering plants having seeds enclosed

within the fruit. Angiosperms are the most developed flowering plants.

Salient features
(i) Well developed flowers are present. The reproductive organs are aggregated

in a flower.
(ii) Seeds are enclosed within the fruit.
(iii) Vascular tissues are present.

Examples: Grass, bamboo, pea, mango, bean, etc.
On the basis of number of cotyledons in a seed, Division Angiosperms is further

divided into two sub-divisions–Monocotyledons and Dicotyledons.

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Sub-division – Monocotyledons (Monocot)

(i) The seeds of these plants bear only one cotyledon.
(ii) Leaves are elongated with parallel venation.
(iii) Fibrous root system is present.
(iv) Distinct nodes and internodes are present in the stem.
Examples: Bamboo, grass, maize, wheat, onion, rice, sugarcane, etc.

Sugarcane Maize Rice

Figure 16.8: Some monocot plants

Sub-division – Dicotyledons (Dicot)

(i) The seeds of these plants contain two cotyledons.
(ii) Tap root system is present.
(iii) Leaves are broad having reticulate venation.
(iv) Distinct nodes and internodes are absent.
Examples: Mustard, pea, sunflower, bean, mango, rose, orange, apple, etc.

Mustard Pea Mango

Figure 16.9:Some dicot plants

Activity 4

• Visit a forest and observe various types of gymnosperms and angiosperms.
Study their external structure and differentiate between them.

• Visit a cropfield and collect some angiosperms. Study their external
structure and separate them in terms of monocots and dicots.



fibrous /ˈfaɪbrəs/ - made of many fibres; looking like fibres

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Differences between Gymnosperms and Angiosperms

S.N. Gymnosperms S.N. Angiosperms

1. Cones are present instead of true 1. Well developed flowers are
flowers. present.

2. Seeds are naked. 2. Seeds are enclosed inside the
3. Generally, leaves are elongated fruit.

and pointed. 3. Generally, leaves are flat and
broad.

Differences between Dicot and Monocot

S. N. Dicot S.N. Monocot

1. A seed contains two cotyledons. 1. A seed contains only one
cotyledon.
2. Leaves contain reticulate
venation. 2. Leaves contain parallel venation.

3. Tap root system is present. 3. Fibrous root system is present.

4. Distinct nodes and internodes 4. Distinct nodes and internodes
are absent. are present.

Differences between Non–flowering and Flowering Plants

S.N. Non–flowering plants S.N. Flowering plants

1. Non-flowering plants may be 1. All flowering plants are green.
green or non green.
2. Flowering plants produce
2. Non-flowering plants do not flowers and seeds.
produce flowers and seeds.
3. All flowering plants are
3. Non-flowering plants may be multicellular.
unicellular or multicellular.
4. Flowering plants are more
4. Non-flowering plants are less developed.
developed. Examples: Cycas, pine, pea, rose,
Examples: Spirogyra, mushroom, bamboo, apple, etc.
moss, fern, etc.

Similarities between Non–flowering plants and Flowering plants

1. Cells of both non-flowering and flowering plants contain cell wall.
2. Most non-flowering (except thallophytes) and flowering plants prepare their

own food by photosynthesis.
3. Both non-flowering and flowering plants grow on moist, cool, humid and

shady places.

16.5 Structure of a Flowering Plant

Various types of flowering plants are found in our surroundings. Flowering plants
contain roots, stem, leaves, buds, flowers and fruits. Among them, roots, stem and

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leaves are vegetative parts whereas buds, flowers and fruits are reproductive parts.
Such plants are propagated from their seeds. Various parts of the flowering plants
perform different functions.
A variety of flowering plants are found on the earth. However, their basic structure
is similar. In this chapter, you will learn about the parts of a flowering plant by
taking mustard plant as an example.

Activity 5

• Visit a nearby crop-field and uproot a mustard plant or a pea plant.
• Observe various parts of the plant like roots, stem, leaves, buds, flowers, etc.
• Draw a neat figure and label the main parts on the basis of your observation.


Mustard Plant

In our country, mustard plant is grown in the winter
season. It is cultivated for yielding oil as its seeds are
rich in oil content. The tender leaves of the mustard
plant are also used as vegetable. It is grown in the Terai
and hilly regions of Nepal.

The plant body of a flowering plant can be divided in
the following two main parts.

1. Root system
2. Shoot system

1. Root system Figure 16.10: Mustard plant

The underground part of a plant is called the
Primary root root system. It consists of a main root called
Secondary root primary root, its branches and sub-branches.
Tertiary root Mustard is a dicotyledonous plant. It contains
a primary root from which a number of
branches arise. Such root system is called
tap root system. Primary root directly grows
downward in the soil. The branches and sub-
branches of primary root are called secondary
Root hair and tertiary roots. The growing portion in the

Root tip root is called root tip which is very delicate.

Root cap So it remains covered with a root cap. The

Figure 16.11: Root system root cap is made up of dead cells. It protects

the root tip as it grows downward through the
soil. A number of unicellular thread-like structures arise from each root. They are
called root hairs.

Some plants like onion, bamboo, sugarcane, maize, etc. contain fibrous root system.

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Fibrous roots are of the same size and structure. They do not have branches and
sub-branches. They arise from the lower end of stem in the form of clusters.

Functions of roots
(i) Roots absorb water and minerals from the soil.
(ii) Roots help to fix the plant to the soil.
(iii) Roots also bind the soil particles together and help to prevent soil erosion.

2. Shoot system

The green part of a plant above the ground is called the shoot system. It consists
of stem and its branches, leaves, buds, flowers and fruits. The stem, its branches and
leaves are the vegetative parts whereas the flowers are the reproductive parts of a plant.

The stem
The stem grows vertically upward from the soil. It forms a main axis of the shoot

system. Stems of different plants vary greatly in their size, structure and appearance
but all of them contain nodes and internodes. Stem of a mustard plant also contains
nodes and internodes. The points in the stem from which the leaves arise are called
nodes whereas the portion of the stem between the two nodes is called an internode.
The stem of a tree is called trunk which is thick, woody and strong.

The stem contains two types of buds. They are apical buds and axillary buds. The
bud present at the tip of the plant is called an apical or terminal bud. A plant grows
in height due to the growth of the apical bud. Leaves make an angle with the node
which is called axil. The buds present in the axil are called axillary buds. Those
buds help the plant to develop new branches and flowers.

Functions of stem
(i) The stem keeps a plant upright.
(ii) It transports water, minerals and food to different parts of a plant.
(iii) The stem supports branches, leaves, buds, flowers and fruits.

Flower Flower

Bud Fruit
Leaf

Node Stem

Stem Node

(a) (b)
Figure 16.12: Shoot system
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BIOLOGY

Activity 6

• Take a balsam plant and cut it at the base.
• Place the plant in a beaker half-filled with water.
• Put a few drops of red fountain pen ink in the water and stir it.
• Leave the plant in the beaker for one day.
• Examine the plant next day and check the presence of thin red lines on the

stem and leaves.
• Where did the lines come from? How did the red water rise through the

stem to reach the leaves ?
• Write down the conclusion of this experiment.


The Leaf

A leaf is a green and flat lateral outgrowth of the Blade (Lamina)

stem. Like stem, leaves also show a great variety in
shape and size. Mustard plant consists of a simple
leaf. A leaf mainly consists of three parts: leaf base,
Vein

petiole and lamina. The portion of the stem from Mid rib
which a leaf arises is called the leaf base. Petiole is
a narrow, short stalk of the leaf which is attached to Petiole

the stem. Leaf blade or lamina is the flat and green Stem
portion of the leaf. The lamina of the mustard plant is
serrated (having irregular margin). The petiole in the Figure 16.13: Structure of a leaf
lamina acts as mid-rib which branches out as veins
to form a network. The arrangement of veins in the mustard leaf is called reticulate
venation. Veins transport water, mineral and food to various parts of a leaf and also
provide mechanical support to the leaf. Leaves appear green due to the presence of
chlorophyll which traps the solar energy for photosynthesis.

Functions of leaf
(i) Leaves prepare food by using water and carbon dioxide in the presence of

sunlight. This process is called photosynthesis.
(ii) Leaves provide food to the entire living world.

Flower
Flower is a sexually reproductive organ of a mustard plant. The flower is pedicilated,

complete and bisexual. The flower is yellow in colour which contains four distinct
whorls: calyx, corolla, androecium and gynoecium.

bisexual /baɪˈsekʃʊəl/ - having both male and female reproductive organs in the same body

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Stamen Pistil
Petal

Sepal Thalamus

An entire flower L.S. of a flower

Figure 16.14: Mustard flower
Calyx

Calyx forms the outermost whorl of a mustard flower.
It contains four light green sepals. The sepals are free
(polysepalous) which synthesize food for the flower and
protect the flower in the bud stage.

Corolla Figure 16.15: Calyx

Limb Corolla forms the second whorl of a mustard flower. It
consists of four bright yellow petals with fragrance. The
Claw petals are free (polypetalous). They attract insects towards
them and help indirectly in pollination. Each petal consists of
Figure 16.16: Corolla two parts: claw and limb.

Androecium

Androecium forms the third whorl of a mustard flower. Anther
It consists of six stamens arranged in two rings. The outer

ring consists of two short stamens whereas the inner ring Filament

consists of four long stamens. Each stamen consists of

two distinct parts: filament (slender structure) and anther

(swollen structure). Stamen is the male reproductive organ Figure 16.17: Androecium
of a mustard flower which produces pollen grains at

maturity.

Gynoecium Stigma

Gynoecium forms the fourth and innermost whorl of a Style
mustard flower. It represents the female reproductive organ. Ovary
Gynoecium consists of two fused carpels. The carpel consists
of three distinct regions, i.e. stigma (uppermost spreading
part), style (middle slender stalk) and ovary (lowermost
cylindrical part). At maturity, ovary produces female gametes
in ovules.

Fig. 16:18 Gynoecium

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Activity 7

• Collect the leaves of different flowering plants from your surroundings.
• Observe their size, shape, colour, edges, venation, etc. carefully.
• Draw their labelled diagrams and colour them.
• Classify the leaves into two groups on the basis of venation.


16.6 Unisexual and Bisexual Flowers

Most of the flowers have all the four whorls, i.e. calyx, corolla, androecium and
gynoecium. Such flowers are called complete flowers. They are also called bisexual
or hermaphrodite flowers. For example, flowers of orange, mustard, tomato, etc.
Some flowers contain either male (androecium) or female (gynoecium) reproductive
organs. Such flowers are called unisexual flowers. For example, flowers of cucumber,
pumpkin, etc.

16.7 Pollination Cross-pollination

Self-pollination

At maturity, anthers begin to

dry and burst open to release

pollen grains. The pollen grains Stamen
are transferred to the stigma of a Pistil
flower by many external agents

like insects, wind, birds, water,

animals, etc. Pollination is the

process of transfer of pollen grains Figure 16.19: Types of pollination

from the anther to the stigma of a

flower. It is of two types: self-pollination and cross-pollination.

Self-pollination is the process of transfer of pollen grains from the anther to the
stigma of the same flower or to the stigma of another genetically identical flower of
the same plant. This process is common in bisexual flowers, e.g. China rose, pea, etc.

Cross-pollination is the process of transfer of pollen grains from anther of a flower of
one plant to the stigma of a flower in another plant of the same species. This process
is common in both unisexual and bisexual flowers. External agents of pollination
are essential for cross-pollination. In flowering plants, pollination is followed by
fertilization.

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16.8 Fertilization

Fertilization is the process of fusion of a male gamete and a female gamete to form
a zygote. In flowering plants, pollen grains absorb secretions from the stigma and
undergo germination after pollination. The germinating pollen grain produces a
pollen tube which grows down towards style and finally reaches the ovule in the
ovary.

The fertilization in flowering plants involves the fusion of two male gametes
separately. One male gamete fuses with the egg cell (ovum) and forms zygote.
Similarly, another male gamete fuses with the secondary nucleus and forms
endosperm nucleus. Therefore, the fertilization in flowering plants is called double
fertilization. After fertilization, the zygote divides and forms embryo whereas the
endosperm nucleus develops into endosperm of the seed.

Polar Pollen grain
nuclei Stigma

Egg Style
Pollen tube

Ovary
Embryo sac
Micropyle

Figure 16.20: Fertilization in a flowering plant

The embryo is the baby plant in the very early stage of its development before
coming out of its seed whereas the endosperm is the food storage tissue of the seed.
The embryo and endosperm together make a seed. After fertilization, the ovule
forms seed and ovary forms the fruit. A seed is a reproductive unit of a plant which
can germinate to produce a new plant in favourable condition.

Activity 8

To observe various parts of flowers
• Visit a garden and collect different types of flowers.
• Separate the sepals, petals, stamens and pistils of each flower.
• Draw diagrams of each and label them.
• Also, write down the similarities and differences among them.


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Summary

• Plant kingdom includes different types of plants like thallophytes, bryophytes,
pteridophytes, gymnosperms and angiosperms.

• Thallophytes are the primitive plants without roots, stem and leaves.
• Bryophytes grow on damp and moist land but they require water for

reproduction. So, they are called amphibian plants.
• Pteridophytes are the most developed cryptogams having feather-shaped leaves.
• Gymnosperms are cone-bearing plants having naked seeds.
• Angiosperms are the most developed flowering plants having enclosed seeds.
• A flowering plant has two parts - root system and shoot system.
• Roots fix the plant to the soil, absorb water and minerals from the soil, and

also bind the soil particles together.
• Stems transport water, mineral and food to all parts of the plant.
• Leaves of the green plants prepare their own food by photosynthesis.
• Most of the flowers consist of four separate whorls: calyx, corolla, androecium

and gynoecium.
• Flowers are the most attractive parts of flowering plants.

Exercise

1 Choose the best answer from the given alternatives.

a. The plant which does not bear flowers is _______.

(i) pea (ii) cycas

(iii) moss (iv) wheat

b. The plant which cannot prepare its own food is _______.

(i) yeast (ii) volvox

(iii) fern (iv) rose

c. The colourful and attractive part of a flower is _______.

(i) stamen (ii) sepal

(iii) pistil (iv) petal

d. The part of carpel which changes into a seed is _______.

(i) ovary (ii) anther

(iii) ovule (iv) style

e. The _______ has tap root system.

(i) mustard (ii) grass

(iii) rice (iv) maize

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2 Tick (√) the correct statement and cross (×) the incorrect one.

a. Mushroom is a flowering plant .
b. Fern is kept in the division pteridophyta.
c. Chlorophyll is found in fungi.
d. Mustard plant is a dicot
e. Shoot system is an underground part of a plant.
f. Sepals are colourful and beautiful.
g. Androecium is the male part of a flower.

3 Fill in the blanks with appropriate words.
a. The plant body of thalloophytes is called.........................
b. Non-flowering plants are kept in the sub-kingdom........................
c. ................ are also called amphibian plants.
d. In gymnosperms, ................ are present instead of flowers.
e. A seed of mustard contains ............... cotyledons.
f. The flat and green part of a leaf is called.......................
g. The bud present at the tip of a plant is called...........................

4 Answer the following questions.
a. Name the two sub-kingdoms of Plant Kingdom.
b. Write any three salient features of plants.
c. What are cryptogams? Give any three examples.
d. What are thallophytes? Write any three characteristics of thallophytes.
e. What are bryophytes and pteridophytes ? Give any two examples of each.
f. What types of plants are kept in Sub-Kindom Phanerogams? Write any two
features of gymnosperms.
g. What are angiosperms ? Give any four examples.
h. What do you mean by root system and shoot system ?
i. Explain various parts of a leaf with labelled diagram.
j. Name various parts of a mustard plant.
k. What are nodes and internodes ?
l. Write down the major functions of roots, stem and leaves.

5 Differentiate between:
a. Non-flowering plants and Flowering plants
b. Algae and Fungi
c. Dicot and Monocot
d. Apical bud and Axillary bud
e. Androecium and Gynoecium

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6 Match the following:

A B
Spirogyra angiosperms
Pine reticulate venation
Apple tip of stem
Moss gymnosperms
Horsetail thallophyta
Apical bud bryophyta
Dicot leaf pteridophyta
monocot

7 Name the parts A, B, C and D shown in each of the given figures.
A

A
BB
CC
DD
(a) (b)

8 Draw the neat figures of the following plants:

(a) Mushroom (b) Fern (c) Moss (d) Cycas

9 Draw a neat figure of a mustard plant showing its various parts.

10 Name the parts A, B, C and D shown in the given figure. Also, mention the major
function of each.

A
B

C

D

11 Write short notes on:
a. Bryophytes
b. Root system
c. Androecium

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Unit Estimated teaching periods: Th Pr
6 3
17
Plant cell

Cell and Tissue

Objectives

After completing the study of this unit, students will be able to :

• explain the structure of a typical plant cell and animal cell.
• describe the structure and functions of various cell organelles.
• describe the structure of a unicellular organism (amoeba) and a

multicellular organism (hydra).

Course of Study

• Cell and cell organelles
• Structure and functions of cell organelles
• Unicellular and multicellar animals
• Structure of amoeba and hydra

Points to be Focused / Questions to be Discussed

• What is a cell? Why is it called basic unit of life?
• What are cell organelles?
• What are unicellular and multicellular animals?
• Where are amoeba and hydra found?

BIOLOGY Oasis School Science and Environment - 7 179

17.1 Introduction

All living organisms are Eye piece
made up of microscopic
units called cells. These cells Coarse adjustment
are called building blocks knob

of life. A cell is defined as Fine adjustment Objective lenses
the basic, structural and knob
functional unit of life capable Stage clip
of independent existence. A Stage
cell is made up of life giving
substance called protoplasm. Mirror

Stand

Cell was discovered by Figure 17.1: Compound microscope
Robert Hooke in 1665 AD.
He observed a thin slice of cork under his self-built microscope and found
that the cork piece had numerous compartments connected together
in a honeycomb-like structure. He named these compartments as cells
(L., cella- compartments).

All living organisms are composed of cells or cell products. All new cells arise as
a result of divisions of pre-existing cells. All cells are basically alike in chemical
composition and metabolic processes. The function of an organism as a whole is the
outcome of combined activities and interactions of the constituent cells. Cells are
the structural and functional units of all living beings. Therefore, cell is called the
fundamental, structural and functional unit of life.

17.2 Prokaryotic Cells and Eukaryotic Cells

On the basis of nuclear organization, cells are of two types: Prokaryotic cell and
Eukaryotic cell.

The cell that lacks a well organized nucleus is called a prokaryotic cell. It lacks
several membrane bound cell organelles like mitochondria, lysosome, endoplasmic
reticulum, etc. Such type of cell is found in bacteria, blue-green algae, etc.

The cell having a well organized nucleus is called a eukaryotic cell. It contains
nuclear membrane, nucleolus and membrane bound cell organelles. Such type of
cell is found in most of the plants and animals.

17.3 Cell Shape, Size and Number

Generally, plant cells are rectangular and animal cells are oval. However, they show a
great variation in their shapes. Cells may be oval, polygonal, cubical, elongated, etc.
Cells show a great variation in their sizes. Most of the cells are tiny and microscopic
whereas a few cells are macroscopic. The smallest known cell is mycoplasma. Its
size is 0.5 to 5 mm (micrometer). The largest cell is the egg of ostrich. Its size is
170 × 135 mm. Microscope is used to observe the internal details of a cell.

metabolic /metəˈbɒlɪk/ - related to chemical processes in living things that change, food into
energy and materials for growth

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Many organisms are made of a single cell. They are called unicellular organisms,
e.g. amoeba, Plasmodium, bacteria, etc. Most of the plants and animals are made of
multiple cells. They are called multicellular organisms.

17.4 Detailed Structure of a Typical Cell

Cells of different organisms differ in their structure. Cells even within a body of
multicellular organisms differ in their shape, size and function. In spite of these
differences, every cell shows the same basic structure as discussed below.
Cell wall

It is the outermost rigid and protective covering layer of plant cells. It is absent in
animal cells. It is made of non-living secretion called cellulose. It is metabolically
active and is capable of growth. It is freely permeable in nature.

Figure 17.2: Typical structure of a plant cell

Functions
(i) Cell wall provides a definite shape and rigidity to the plant cell.
(ii) It protects plasma membrane and internal parts of the cell.

Plasma membrane
Every cell is surrounded by a living, elastic and delicate membrane called plasma

membrane. In plant cells, it is found inner to the cell wall. It is made up of lipid
and protein molecules. It contains numerous small pores in it. It is a selectively
permeable or semi-permeable membrane as it allows only selected substances to
enter or leave the cell.
Functions
(i) Plasma membrane provides an outer boundary to a cell and protects it from

external injury.

(ii) It helps in transport of materials in and out of the cell.

permeable /ˈpɜːmɪəbl/ - allowing a liquid or gas to pass through

rigid /ˈrɪdʒɪd/ - stiff and difficult to move or bend

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Cytoplasm
The space between cell membrane and nuclear membrane is filled with a translucent

liquid called cytoplasm or protoplasm. It consists of carbohydrates, proteins,
lipids, nucleic acids, sodium and potassium salts, water and enzymes. Various cell
organelles and inclusions remain floating in the cytoplasm.

Figure 17.3: Typical structure of an animal cell

Functions
(i) It helps in intracellular distribution of molecules, enzymes and nutrients

within the cell.
(ii) It contains many cell organelles and provides space for various metabolic activities.
(iii) It helps in the exchange of materials between many cell organelles.

Nucleus

Nucleus is a round or spherical cell Chromatin network
organelle present almost at the centre of Nuclear membrane
a cell. It consists of nuclear membrane,
nucleoplasm, nucleolus and chromatin Nucleolus Necleoplasm
network. Nuclear pore

The nuclear membrane is double

membraned porous structure which Figure 17.4: Structure of nucleus
separates nucleus from the cytoplasm.

Nucleoplasm is a transparent semifluid substance containing nucleolus, chromatin

network and various enzymes. The chromatin network contains hereditary information.

Nucleolus is a dense and round structure attached to a chromatin fibre.

Functions
(i) Nucleus controls various metabolic activities of the cell. So, it is also called

the director of the cell.
(ii) It helps in cell division and hence in reproduction.

enzyme /ˈenzaɪm/ - a substance produced by living beings which helps a chemical
hereditary /həredɪtri/ change happen more quickly

- given to an offspring by its parents before it is born

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Endoplasmic reticulum

Endoplasmic reticulum is a system of

flattened membrane bound tubules Membranes

enclosing a fluid filled lumen. It almost

fills up the intracellular cavity. On one end

endoplasmic reticulum is connected to the

nuclear membrane and on another end it is Ribosomes

connected to the plasma membrane. It forms Figure 17.5: Rough endoplasmic reticulum

the endoskeleton of the cell.

Endoplasmic reticulum is of two types: smooth endoplasmic reticulum and rough
endoplasmic reticulum. Ribosomes are attached to the surface of rough endoplasmic
reticulum whereas they are absent on the surface of smooth endoplasmic reticulum.
Functions

(i) It forms the supporting framework of the cell and provides mechanical
support to the cytoplasm.

(ii) It helps in intracellular transport.

(iii) It provides a large surface area to the cytoplasm for various metabolic
activities.

Mitochondria

Mitochondria are spherical, rod-shaped or thread- Matrix Cristae Inner Outer
like cell organelles present in the cytoplasm. Each membrane membrane

mitochondrion is enclosed by an outer membrane
and an inner membrane. Mitochondria are sites of
energy production and storage of energy during
cellular respiration. So, they are also called power
plant of the cell.

Functions Figure 17.6: Mitochondrion

(i) Mitochondria use molecular oxygen to oxidize the carbohydrates and fats to
release energy for the cell.

(ii) They synthesize many amino acids.

Ribosomes

Ribosomes are minute, spherical granules attached to the tubes of endoplasmic
reticulum. But they may occur free in the cytoplasm. Ribosomes are composed of
RNA and protein.
Function
Ribosomes are responsible for protein synthesis.

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Golgi complex

Golgi complex consists of a set of membrane-bound Vacuole
fluid-filled vesicles, tubules and vacuoles. It is
generally found near the nucleus in the cytoplasm.
The golgi apparatus arises from the membrane of Cisternae
the smooth endoplasmic reticulum and originates
from the rough endoplasmic reticulum. Secretory
vesicle

Figure 17.7: Golgi complex

Functions

(i) It acts as a way station for storage, processing and packaging of various
cellular secretions like enzymes, proteins, etc.
(ii) It produces vacuoles or secretory vesicles that contain cellular secretions.
(iii) It is responsible for the synthesis of cell wall, cell membrane and lysosomes.

Lysosomes

Lysosomes are sac-like spherical structures present in the cytoplasm. Each lysosome
is surrounded by a single membrane. Lysosomes contain powerful enzymes which
can digest all types of substances. They may even digest the entire damaged cell or
dead cell. So, lysosomes are also called suicidal bags of the cell.

Functions
(i) Lysosomes help in intra-cellular digestion.
(ii) They provide energy during starvation by controlled breakdown of stored food.

Vacuoles

Vacuoles are non-living, fluid-filled spaces present in the cytoplasm. They are
enclosed by a membrane called tonoplast. In plant cells, vacuoles are larger in size
and less in number whereas they are smaller but more in animal cells. Vacuoles are
filled with a fluid which contains water, minerals, carbohydrate, organic acids, etc.
In animal cells, vacuoles are temporary.

Functions
(i) Vacuoles help the cell to remain turgid.
(ii) They store water, minerals and waste products.
(iii) Vacuoles help in growth of the cell.

Plastids

Plastids are disc-shaped cell organelles only in plant cells.
All plants contain plastids except fungi. Plastids are of
three types: chloroplast, chromoplast and leucoplast.

Chloroplasts are green plastids. They appear green due to Figure 17.8: Plastid
the presence of photosynthetic pigment called chlorophyll.
Chloroplasts are involved in the synthesis of food. So they are also called 'kitchens
of the cells'. Chloroplasts are found in leaves, young stem, sepal and young fruits.

vacuole /ˈvækjʊəʊl/ - non-living, fluid-filled space found in cytoplasm

starvation /stɑːˈveɪʃn/ - the state of suffering and death caused by no food

turgid /ˈtɜːdʒɪd/ - swollen; containing more water than usual

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Chromoplasts are colourful plastids. They are found in petals of flowers and pericarp of
fruits. They do not contain chlorophyll. They contain red, yellow and orange pigments.

Leucoplasts are colourless plastids. They are found in the cells of underground
storage organs. If exposed to light for a considerable period, leucoplast may change
into chloroplast.
Functions
(i) Chloroplasts trap solar energy and utilize it for photosynthesis.
(ii) Chromoplasts impart various colours to flowers and attract insects for pollination.
(iii) Leucoplasts store food in the form of carbohydrate, protein and fat.
Centrosome

Centrosome is a small naked protoplasmic structure. It is located in the cytoplasm
near the nucleus of animal cells. It contains astral rays and two small granules
called centrioles.
Functions
(i) Centrosome initiates and regulates cell division in animal cells.
(ii) It acts as a basal body to give rise to cilia and flagella.

Differences between Plant cell and Animal cell

S.N. Plant cell S.N. Animal cell

1. Plant cell is usually larger in size 1. Animal cell is comparatively
and rectangular in shape. smaller in size and oval in shape.
2. Cell wall is absent.
2. Cell wall is present. 3. Centrosome is present.
3. Centrosome is absent. 4. Plastids are absent.
4. Plastids are present. 5. Vacuoles are smaller and
5. Vacuoles are larger and well scattered.
6. Golgi bodies are well developed.
developed. 7. Food is stored in the form of
6. Golgi bodies are diffused. glycogen.
7. Food is stored in the form of starch

or oil.


Activity 1

Microscopic examination of onion peels to study plant cells
• Take an onion bulb and remove the outer dry scales.
• Cut the bulb into small pieces vertically and remove the fleshy scale.
• Bend the outer convex surface of the fleshy scale and pull the broken thin

transparent layer with forceps.
• Place the peel (i.e. thin layer) in a watch glass containing water.
• Prepare a temporary slide of the peel and observe it under the compound

microscope.

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• Draw a neat labelled figure and comment on it.

piece of Onion cells under L.P. cytoplasm
epidermal Figure 17.9 nucleus
layer vacuole
cell wall
Onion scale
Single cell under H.P.

17.5 Unicellular and Multicellular Animals

The animals having a single cell in their bodies are called unicellular animals, for
example, amoeba, paramecium, euglena, etc.

The animals having many cells in their bodies are called multicellular animals, for
example, hydra, butterfly, fish, bird, human being, etc.

In unicellular animals, all the activities like respiration, excretion, reproduction,
sensation, etc. occur in the single cell. But multicellular animals have tissues, organs
and systems for performing specific functions.

17.6 Amoeba (Amoeba proteus)

Amoeba is a popular protozoan creature. The name Amoeba proteus has been
derived from two Greek words – amoibe which means change, and proteus after the
name of mythical sea-god Proteus, who could change shape.

Habitat

Amoeba is commonly found in freshwater pseudopodium
ponds, pools, slow running streams, ectoplasm
ditches, soil, etc. It occurs in abundance in digestive vacuole endoplasm

those waters which contain bacteria and cell membrane

decayed organic substances. nucleus

Structure food vacuole

contractile vacuole

Amoeba is a unicellular microscopic Figure 17.10: Amoeba
organism which measures about 250 to 600

m (microns) in diameter. To the naked eye, the largest amoeba is just visible as a

whitish blob. Under the microscope, it appears as an irregular, colourless mass of

protoplasm. The body of amoeba is covered externally by a very thin, elastic and

semi-permeable layer called plasmalemma. Cytoplasm is distinguished into an

outer clear dense ectoplasm and an inner granular endoplasm.

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A small spherical nucleus is present at the centre of endoplasm. A large contractile
vacuole, many food vaculoes, water globules, endoplasmic reticulum, mitochondria,
golgi bodies, ribosomes, etc. are distributed in the endoplasm. The contractile
vacuole is enclosed by a unit membrane which remains filled with watery fluid.
It helps in excretory and osmoregulatory activities. Food vacuoles are spherical
spaces filled with water. They help in digestion of food. The nucleus is flattened
and biconcave which contains nuclear membrane, nucleoplasm, some nucleoli and
chromosomes.

Amoeba shows characteristic amoeboid movement by the formation of finger-
like temporary projections called pseudopodia. They are formed as a result of
the flowing forward of the cytoplasm. Amoeba is a carnivorous animal. Its mode
of nutrition is holozoic (i.e. a mechanism in which the food is engulfed in a solid
form). Amoeba, even in the absence of special sense organs, is able to select its food.
It captures and engulfs its food by means of pseudopodia. Pseudopodia are formed
at the points where the food comes in contact with the body surface. The digestion
of food takes place inside food vacuoles and the products of digestion are diffused
into cytoplasm. Finally, egestion of undigested residue takes place at any point in
plasmalemma.

In amoeba, breathing takes place through the general body surface. It reproduces
asexually by binary fission and multiple fission.

Effect of Amoeba on Human Beings

Apart from free-living forms, certain Plasmalemma
amoebae lead a parasitic life in the
intestine and buccal cavity of human
Nucleus

beings. Entamoeba histolytica lives as an Ectoplasm Nucleolus

endoparasite in the upper part of the Endoplasm Pseudopodium
large intestine, i.e. colon of human beings. Ingested RBC
It causes amoebic dysentery. The amoeba Food vacuoles
infects intestinal tissue and dissolves
them. So, it is called histolytica (histo -
tissue, lysis - to dissolve). This parasite Figure 17.11: Entamoeba histolytica

mainly feeds on the tissues of intestinal
wall. The symptoms of amoebic dysentery are the passing out of stool with blood
and mucus, abdominal pain, nausea, flatulence, headache, etc.

In a person suffering from amoebiasis, numerous minute ulcers can be seen in
the intestinal wall. Entamoeba reproduces rapidly by binary fission and feeds on
bacteria, RBC and tissue debris. In chronic cases, amoebae get into blood circulation
and migrate to the liver, lungs, spleen, brain, etc. where they produce secondary
complications.

contractile /kənˈtraktaɪl/ - able to contract or become narrower

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Entamoeba gingivalis is found in the mouth, usually between the teeth and the gums.
This amoeba occurs in mouths of nearly 70% of human population. It has been a
belief for a long time that E. gingivalis causes pyorrhoea but it has been established
that pyorrhoea is caused by bacteria. However, Entamoeba gingivalis aggravates the
pyorrhoea by destroying the tissues in the gums. It is directly transmitted from
mouth to mouth by contact during kissing.

Entamoeba coli is Plasmalemma Food vacuole
a non-pathogenic Ingested bacteria
species of amoeba.
It does not invade Endoplasm Nucleus Endoplasm

the host tissue.
However, its
presence in the Figure 17.12: (a) Entamoeba gingivalis and (b) Entamoeba coli

lumen of intestine
may cause digestive complications. E. coli occurs in the intestine of about 50%
population. It is transmitted from one person to another by means of contaminated
food and water. E. coli lives in lumen of colon and does not enter the tissues of the
wall. It is a harmless species which feeds on bacteria and indigested food particles.

17.7 Hydra

Hydra is a smalll, multicellular invertebrate animal. It
belongs to the phylum coelenterata of Animal Kingdom.

Hydra has a tubular body up to 10 mm. At the free end of
the body, it has a mouth which remains surrounded by a
ring of tentacles. The tenlacles contain stinging cells which
can paralyse the prey. Tentacles help in locomotion and
catching food.

Hydra has two main body layers. So it is called a diploblastic Fig. 17.3: Hydra
animal. The outer layer is called epidermis and the inner
layer is called gastrodermis as it lines the stomach. Those
layers are separated by mesoglea, i.e. a gel like substance. Hydra has a mouth but
no anus. In hydra, breathing and excretion occur through the general body surface.

In hydra, locomotion takes place with the help of
tentacles. Hydra moves by the process of looping or
somersaulting. In this process, hydra bends its body
attaching itself to the substratum with the tentacles
and then releases the basal disc, which provides usual
attatcment. This process is called looping. The body then
bends over and makes a new place of attatchment with
the basal disc.

Fig. 17.14 Hydra reproduces asexually by budding. In this process,
a bulb-like outgrowth, i.e. bud grows in the body of

hydra. This bud grows into a baby hydra and gets separated from the parent hydra.

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In this way, hydra reproduces by budding.

Tentacles

Bud separates

Bud

Fig. 17.15: Budding in hydra

Summary

• Cell is the basic, structural and functional unit of life.
• Unicellular organisms are made-up of a single cell whereas multicellular

organisms are made-up of many cells.
• Every cell contains a cell membrane, a nucleus, cytoplasm and cell organelles.
• Cell membrane is a porous membrane which allows the entry and exit of

cellular materials.
• Cytoplasm is a jelly-like fluid having several cell organelles embeded in it.
• Nucleus is a membrane–bound cell organelle which controls various

activities of a cell.
• Mitochondria are rod-like or spherical cell organelles which act as sites of

energy production.
• Golgi complex contains a hollow tubular system responsible for the secretion

of enzymes, hormones and proteins.
• Plastids are found only in plant cells which contain coloured pigments like

chlorophyll.
• Centrosome is present only in animal cell which initiates and regulates cell

division.
• Plant cell can be distinguished from animal cells due to the presence of cell

wall, plastids, a large central vacuole and absence of centrosomes in the
former.
• Amoeba is a unicellular and microscopic protozoan found in water.
• Hydra is a multicellular invertebrate that belongs to phylum coelenterata.

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Exercise

1 Choose the best answer from the given alternatives.

a. The cell wall is made of ________.

(i) cellulose (ii) fat

(iii) protein (iv) minerals

b. An organelle called suicidal bag is ________.

(i) vacuole (ii) lysosome

(iii) ribosome (iv) plastid

c. Proteins are synthesized by ________.

(i) nucleus (ii) cell wall

(iii) ribosome (iv) vacuole

d. The power house of a cell is ________.

(i) nucleus (ii) golgi body

(iii) chromosome (iv) mitochondrion

e. The cell organelle which is not found in animal cells is ________.

(i) centrosome (ii) plastid

(iii) golgi body (iv) vacuole

f. The shape of an amoeba is ________.

(i) spherical (ii) cubical

(iii) irregular (iv) oval

g. In hydra, locomotion takes place with the help of

(i) jointed legs (ii) tentacles

(iii) cilia (iv) flagella

2 Tick (√) the correct statement and cross (×) the incorrect one.

a. In a plant cell, photosynthesis takes place in chloroplast.

b. Animal cell is bound by cell wall.

c. Nucleus controls various activities of a cell.

d. Respiration occurs in ribosomes.

e. Chromoplast is the kitchen of the plant cell.

f. Ostrich egg is the largest known cell.

g. In amoeba, locomotion takes place by means of pseudopodia.

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3 Fill in the blanks with appropriate words.
a. Cell wall is found only in ........cells.
b. The term ‘cell’ was given by .................
c. Various activities of a cell are controlled by..............
d. ...............is found only in animal cell which initiates cell division.
e. Vacuoles are .............in plant cells than that in animal cells.
f. .....................is called basic unit of life.
g. Ribosomes are responsible for..................synthesis.
h. Hydra reproduces asexually by ..................

4 Answer the following questions.
a. What is a cell ? Name the scientist who discovered cell.

b. Why is a cell called basic, structural and functional unit of life ?

c. What are unicellular and multicellular organisms ? Give any two examples of each.

d. Why do cells differ in their shape and size ?

e. Describe the importance of cells for living beings.

f. What are cell organelles? Give any four examples.

g. What is cell wall ? Write down its functions.

h. Describe the structure of nucleus with a labelled figure.

i. What are plastids ? Name their types and functions.

j. What are golgi bodies ? Write down the function of ribosomes.

k. What are mitochondria? State their function.

l. Where are amoeba and hydra found?

m. Which amoeba causes dysentery in human beings?

n. What are locomotory organs of hydra?

5 Differentiate between:
a. Unicellular organism and Multicellular organism
b. Cell organelles and Cell inclusions
c. Plant cell and Animal cell
d. Chloroplast and Chromoplast

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6 Match the following: B
Helps in photosynthesis
A Synthesizes proteins
Lysosome Releases energy
Nucleus Helps in digestion
Vacuole Keeps cell turgid
Centrosome Controls cellular activities
Endoplasmic reticulum Transports materials
Ribosomes
Mitochondrion
Plastids

7 Draw a neat and labelled diagram of a plant cell.
8 Name the parts A, B, C, D and E shown in the given figures. Also, identify the

type of cell given below with any two reasons for each.

A
AB
B

C C
D

E
D

E

9 Write any three cell organelles which are found in both plant and animal cell.

10 Write down the major function of each of the given parts of a cell.

(a) Nucleus (b) Cell membrane (c) Leucoplast

(d) Lysosome (e) Vacuole (f) Centrosome

11 Give reasons:
a. Cell membrane is called selectively permeable membrane.
b. Plastids are called the kitchen of plant cells.
c. Lysosomes are called suicidal bags.
d. Mitochondrion is called the power house of a cell.
e. Hydra is called a diplobastic animal.

12 Name the cell organelles which are found only in plant cells.

13 Draw a neat and labelled figure showing:
a. Amoeba
b. Hydra

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