Green Science and Environment 7 Final (2076)

c. What are non-metals? Give any five examples.

d. Write any four properties of non-metals.

e. What is meant by malleability and ductility?

f. Define alloys with any two examples.

g. Write any two properties of alloys.

h. Why are alloys made and used in our daily life?

i. Write any two properties and three uses of

i. brass ii. bronze iii. iodine iv. sulphur

j. Which non-metal is used to treat minor cuts and wounds?

k. Which non-metal is mixed with table salt?

5. Differentiate between: b. Metals and Alloys
a. Metals and Non-metals
c. Non-metals and Alloys

6. Write down the composition of the given alloys.

a. Steel b. Brass c. Bronze d. Stainless steel

GREEN Science and Environment Book-7 151

UNIT Some Useful

14 Chemicals

Weighting Distribution (Approximate) Teaching periods : 5 Marks (in %): 1

Before You Begin

Human beings use different types of chemical substances to fulfill
their needs. Soap, detergent, insecticides, chemical fertilizers,
dettol, phenol, plastics, paint, dyes, synthetic cleansers, colours,
etc. Soaps are used for bathing and washing clothes. Detergents
are used for washing clothes. Chemical fertilizers are used for
increasing the productivity of crops. Similarly, insecticides and
fungicides are used to kill insects and fungi respectively. In this
unit, we will study about detergent, dettol, phenol and chemical
fertilizers.

Learning Objectives Syllabus

After completing the study of this unit, students will be able to: • Detergent and its uses

i. introduce detergent, dettol, phenol and chemical • Dettol and its uses
fertilizers.
• Phenol and its uses
ii. state the uses of detergent, dettol, phenol and chemical
fertilizers. • Chemical fertilizers and their
uses

Glossary: A dictionary of scientific/technical terms

antiseptic : preventing or arresting the growth of micro-organisms
corrosive : tending to destroy something by chemical action.
detergent : a petrochemical which is used to wash clothes
fragrance : a sweet or delicate odour as of fresh flowers, pine trees or perfumes
fertilizers : the substances that increase the fertility of soil

152 GREEN Science and Environment Book-7

Useful Chemicals Fig. Fig. Fig.

Detergent

Detergent is commonly known as washing
powder. It is an important petrochemical
having a cleansing nature. It is used for
washing clothes. It produces lather when
dissolved in water. It is produced from
petroleum. It is more soluble than water.
High quality detergents contain fragrances,
brighteners, water softners, bleach, etc.
Detergents pollute water and affect aquatic 14.1
plants. Therefore, we should limit the use of detergents. Detergent is also used
for washing household utensils and dishes.

Dettol

Dettol is a very important chemical which
is used for cleaning cuts and wounds. It
kills germs that infect skin. Its colour is light
yellow. It is an antiseptic and disinfectant. It
is poisonous when ingested and inhaled. It
is used to clean the delicate skin of infants
to prevent skin infection. Dettol is also used
in soaps to protect skin infection. It is also 14.2
used for disinfecting clothes.

Phenol

Phenol is a useful chemical of alcohol group.
It is made from petroleum products. It is
also called carbolic acid. It is slightly soluble
in water. It is corrossive to eyes, skin and
respiratory tract and hence needs careful
handling. Phenol is used as a disinfectant.
It is used for killing bacteria and insects.
It is used for cleaning bathrooms. It is also
used for making medicines, plastics, thread, 14.3
colours, etc. It is found in bottles and in the
form of tablets.

GREEN Science and Environment Book-7 153

Chemical Fertilizers

The chemical substances which are used to increase the fertility of soil are
called chemical fertilizers. They are rich in minerals that are essential for the
growth and development of plants. Generally, we use two types of fertilizers
in soil. They are (i) organic fertilizers and (ii) chemical fertilizers.

Fig.14..4Chemical fertilizer
Fig. Organic fertilizer

Organic fertilizers are prepared by using dead and decaying parts of plants
and animals. They do not affect the quality of soil. Chemical fertilizers are
prepared by using different chemicals or minerals. Prolonged use of chemical
fertilizers affects the fertility and quality of soil. Therefore, over use of chemical
fertilizers should be avoided.

Green plants mainly require three types of chemicals, viz nitrogen (N),
phosphorous (P) and potassium (K). So chemical fertilizers are prepared by
using nitrogen, phosphorous and potassium.

On the basis of presence of minerals, chemical fertilizers are of three types.

They are: Do You Know
i. Nitrogenous fertilizers

ii. Phosphorus fertilizers The fertilizer containing nitrogen, phosphorus
iii. Potassium fertilizers and potassium is called NPK fertilizer. It is
called a complete fertilizer.

i. Nitrogenous fertilizers

The chemical fertilizers rich in nitrogen are

called nitrogenous fertilizers. They help in

growth of plants. They help in growth and

development of flowers, fruits and seeds. Urea,

ammonium chloride, ammonium sulphate,

are examples of nitrogeneous fertilizers. Due

to deficiency of nitrogen in soil, plants become

pale, flowers do not bloom properly, fruits 14.5
and seeds become small.

154 GREEN Science and Environment Book-7

ii. Phosphorus fertilizers Fig. Fig.14.6

The chemical fertilizers rich in phosphorus
are called phosphorus fertilizers.
Ammonium phosphate, calcium super
phosphate, bone meal, etc. are examples
of phosphorus fertilizers. These fertilizers
help in growth of roots, leaves and buds,
ripening of fruits and development of
seeds.

iii. Potassium fertilizers

The chemical fertilizers rich in potassium

are called potassium fertilizers. Potassium

cloride, potassium sulphate, potassium

fertilizers help in photosynthesis, formation

of protein and cell division. In the absence

of potassium in soil, the immunity of plants

decreases and leaves and buds of plants

wither. 14.7

Activity 1

Name any three chemical substances that are used at your home and school.

Write down the major uses of each of them.

Key Concepts

1. Human beings use different types of chemical substances to fulfill their
needs. Soap, detergent, insecticides, chemical fertilizers, dettol, phenol,
plastics, paint, dyes, synthetic cleansers, colours, etc.

2. Detergent is commonly known as washing powder. It is an important
petrochemical having cleansing nature.

3. Dettol is a very important chemical which is used for cleaning cuts and
wounds. It kills germs that infect skin.

4. Phenol is a useful chemical of the alcohol group. It is made from
petroleum products. It is also called carbolic acid.

5. The chemical substances which are used to increase the fertility of soil
are called chemical fertilizers.

6. Organic fertilizers are prepared by using dead and decaying parts of
plants and animals.

GREEN Science and Environment Book-7 155

7. Green plants mainly require three types of chemicals, viz nitrogen (N),
phosphorous (P) and potassium (K).

8. The chemical fertilizers rich in nitrogen are called nitrogenous fertilizers.
They help in growth of plants.

9. The chemical fertilizers rich in phosphorus are called phosphorus fertilizers.

10. The chemical fertilizers rich in potassium are called potassium fertilizers.

Exercise

1. Tick (√) the correct statement and cross (×) the incorrect one.
a. Detergent is used for washing clothes and utensils.
b. The colour of dettol is green.
c. Phenol is used for cleaning bathrooms.
d. Nitrogen is essential for growth of roots.
e. Potassium sulphate is rich in phosphrus.

2. Fill in the blanks using appropriate words.
a. Detergents are prepared from .......................... .
b. .......................... is used to clean bathrooms.
c. .......................... is used as an antiseptic and disinfectant.
d. .......................... are used to increase the fertility of soil.
e. Nitrogenous fertilizers are essential for the .......................... of plants.

3. Tick (√) the best answer from the given alternatives.
a. Which of the given chemicals is used to increase fertility of the soil?

phenol dettol detergent fertilizer

b. Which of the given chemicals is used to kill germs and insects?

dettol phenol detergent soap

c. Which element is required for the growth of roots?

nitrogen oxygen phosphorus potassium

156 GREEN Science and Environment Book-7

d. Which of the given chemicals is rich in phosphorus?

ammonium chloride ammonium nitrate

ammonium phosphate potassium chloride

4. Answer the following questions.
a. Name any four chemicals that are used at your home.
b. What is detergent? Write any two properties of detergent.
c. Write any two uses of detergents.
d. What is dettol? Write its two properties and three uses.
e. What is phenol? Write its two properties and three uses.
f. What are fertilizers? Give any two examples.
g. What are chemical fertilizers?
h. What are nitrogenous fertilizers? Why do plants need nitrogen?
i. What are phosphorus fertilizers? Write their importance for plants.
j. What are potassium ferlitizers? Write their importance for plants.

5. Write any two symptoms in plants that are seen due to lack of
a. Nitrogeneous fertilizers
b. Phosphorus fertilizers
c. Potassium fertilizers

6. We should avoid the over use of detergents, why?

7. Write any two differences between organic fertilizers and inorganic
fertilizers.

GREEN Science and Environment Book-7 157

Biology

UNIT Living Beings

15

Weighting Distribution (Approximate) Teaching periods : 12 Marks (in %): 2

Before You Begin

Different types of living beings are found on the earth. These living
beingsarebroadlyclassifiedintotwokingdoms,viz(i)animalkingdom
and (ii) plant kingdom. All the animals present on the earth belong
to animal kingdom and all the plants present on the earth belong to
plant kingdom. To make the study of animals, scientists have divided
plant/animals into two categories, i.e. invertebrates and vertebrates.
Invertebrates are animals having no back bones or vertebral column
whereas vertebrates are the animals having backbones or vertebral
columns. Similarly, plant kingdom has been divided into two main
categories. They are cryptogams and phanerogams. Cryptogams are
plants that do not bear flowers and seeds whereas phanerogams are
plants that bear flowers and seeds.

Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce vertebrates with examples. • Vertebrates

ii. classify vertebrates and explain their characteristics. • Cold blooded and warm
blooded animals
iii. describe life cycle of frog with a labelled figure.
• Classes of vertebrates species,
iv. classify non flowering and flowering plants and state amphibia, reptilia, aves and
their characteristics. mammalia

v. describe the structure of a flowering plant with a • Life cycle of a frog
labelled figure.
• Classification of plants
vi. explain the structure of a flower.
• Cryptogams: Thallophyta,
Bryophyta and Pterodophyta

• Phanenorogams:
Gymnosperms and
Angiosperms

• Structure of a flowering plant

• Structure of a flower

• Pollination and fertilization

Glossary: A dictionary of scientific/technical terms

symmetrical : having two halves, parts or sides that are the same in size and shape
hibernate : to spend the winter in a state like deep sleep
streamline : a smooth or pointed or boat shaped structure that can move quickly
embryo : a young animal or plant in the very early stage of development
pollination : the transfer of pollen grains from anther to the stigma of a flower
fertilization : the fusion of a male gamete and a female gamete to form a zygote

158 GREEN Science and Environment Book-7

Living Beings

Vertebrates Fig.

Animals like fish, frog, snake, bird, cow, etc. have Vertebral column of
backbone or vertebral column in their bodies. human beings
These animals are called vertebrates. So, the
animals having backbone or vertebral column
are called vertebrates. They are found in water
and on land. The vertebrates that live in water
include fish, shark, whale, dolphin, turtle, etc.
whereas vertebrates like snake, lizard, parrot,
crow, peacock, horse, rhinoceros, elephant,
human beings, etc live on land. However, some
vertebrates like frog, toad, salamander, etc. can 15.1
live in water and on land. These vertebrates are
called amphibians.

The body of vertebrates is well developed having head, trunk and tail with
paired fins or limbs. They have well developed nervous system with a brain
and spinal cord. They breathe through gills or lungs.

Activity 1

Write the name of any ten animals that are found in your locality.

Study their structure and find out whether they have vertebral column or
not.

Classify these animals as invertebrates and vertebrates.

Some vertebrates can change their body temperature according to the
temperature of surroundings and others cannot. On this basis, vertebrates
have been classified into two categories. They are:

1. Cold-blooded vertebrates 2. Warm-blooded vertebrates

1. Cold-blooded vertebrates

The vertebrates whose body temperature changes according to the temperature
of the surroundings are called cold-blooded vertebrates. Fishes, amphibians
(frogs, toads, etc.) and reptiles (snake, lizard, crocodile, etc) are cold blooded
vertebrates. These animals go for hibernation as they cannot withstand
extreme cold or extreme hot temperature.

GREEN Science and Environment Book-7 159

15.2Fig. Fig.
Some cold-blooded vertebrates

2. Warm-blooded vertebrates

The vertebrates whose body temperature does not change with the temperature
of surroundings are called warm blooded vertebrates. Birds and mammals
are warm-blooded animals. These animals do not go for hibernation. Human
beings, cow, elephant, dog, crow, parrot, pigeon, dove, etc. are called warm
blooded animals as their body temperature remains constant.

15.3
Some warm-blooded vertebrates

160 GREEN Science and Environment Book-7

Classification of Vertebrates

Vertebrates are divided into Do You Know
following five classes on the basis of
their characteristics. The normal body temperature of human
beings is 37°C or 98.6°F. When we fall sick,
1. Pisces 2. Amphibia the body temperature may increase or
decrease.
3. Reptile 4. Aves

5. Mammalia

1. Class Pisces

This class consist of aquatic cold blooded vertebrates which are commonly
known as fishes. They live in water.

Fig.

15.4

Characteristics
1. Their body is boat-shaped or streamlined.
2. Their body is covered with waterproof scales.
3. They breathe through gills.
4. They move with the help of fins.
5. They have two chambered heart.
6. They lay eggs. So they are called oviparous animals.
7. Fertilization is external.
8. Their body can be divided into head, trunk and tail.
Examples: Shark, Rohu, Carp, Asla, Sea horse, Katla, etc.

2. Class Amphibia

This class includes the vertebrates that can live in water and on land. Most
amphibians lay eggs in water.

GREEN Science and Environment Book-7 161

15.5Fig. Fig.

Characteristics
1. Their body is covered with smooth or rough skin.
2. They breathe through lungs on land and through skin in water.
3. Their heart is three-chambered.
4. They move with the help of limbs.
5. They lay eggs. So they are called oviparous animals.
6. Their body can be divided into head and trunk. Neck and tail are absent.
Examples: Frog, toad, salamander, etc.

3. Class Reptilia

This class consists of cold-blooded vertebrates that crawl or creep on ground.
They are commonly known as reptiles. Most reptiles live on land. Different
types of snakes, lizards and crocodiles belong to class reptilia.

15.6

Characteristics Do You Know
1. The body of reptiles is covered
Reptiles are commonly known as
with hard, and dry scales. crawlers or creepers.

2. They have three chambered heart. All reptiles have three chambered heart
but crocodiles have four chambered
3. They lay eggs and fertilization is heart.
internal.

4. Their body can be divided into head, neck, trunk and tail.

162 GREEN Science and Environment Book-7

5. Breathing takes place with the help of lungs.
6. Two pairs of limbs are present but limbs are absent in snakes and some lizards.
Examples: snakes (cobra, python) lizards (garden lizard, house wall lizard,
monitor lizard), crocodiles, alligators, tortoirse, turtle, etc.

4. Class Aves

This class consists of warm blooded flying vertebrates which are commonly
known as bird.

Fig.

15.7

Characteristics
1. The body is boat shaped which is covered with feathers.
2. Fore limbs are modified in the form of wings.
3. They have four chambered heart.
4. Breathing takes place with the help of lungs.
5. They lay eggs and fertilization is internal.
6. Their body can be divided into head, neck, trunk and tail.
Examples: Crow, dove, parrot, pigeon, peacock, hornbill, koel, ostrish, penguin,
etc.

5. Class Mammalia Do You Know

This class includes the most Most mammals directly give birth to their
developed warm blooded vertebrates young ones. But two mammals. i.e duck
that suckle their young ones. Most of billed platypus and sping ant eater lay eggs.
the mammals live on land and a few
live in water.

GREEN Science and Environment Book-7 163

Fig.

15.8

Characteristics
1. Mammary glands, i.e. milk producing glands are present.
2. They directly give birth to their young ones. Females suckle their babies.
3. Body is covered with hair
4. External ears, i.e. pinnae are present.
5. They have four chambered heart.
6. Breathing takes place through lungs.
7. Their body can be divided into head, neck, trunk and tail.
8. They are viviparous and fertilization is internal.
9. They have two pairs of limbs for locomotion.
Examples: Human beings, sheep, goat, tiger, elephant, monkey, bat, dolphin,
whale, rhinoceros, red panda, leopard, rat, cat, dog, etc.

Activity 1

Name any ten vertebrates that are found in your locality.

Study their characteristics and find out their class and fill in the given
table.

S.No. Pisces Amphiba Reptilia Aves Mammalia

164 GREEN Science and Environment Book-7

Life Cycle of Frog

A frog is a tailless vertebrate which can live
on land and in water. It is a carnivorous
amphibian which becomes active in
rainy season. Its body can be divided into
head and trunk. It has a stout body with
protruding eyes, cleft tongue and folded
limbs. The body remains covered with 15.9
moist skin. Frogs are generally found in
crop fields, rivers, lakes, ponds, streams, etc.
Fig. Rana Tigrina
Fig.
Reproduction

Frogs become active in the beginning Do You Know
of rainy season. They reproduce

during rainy season. Male frogs Life cycle can be defined as the series
of stages through which an organism
produce croaking sound while
passes.
raining and attract females. Male Frog completes its life cycle in three
frogs are slightly smaller than female stages, viz egg, tadpole and adult.

frogs. The abdomen of the female

frog appears swollen due to presence

of eggs. Female frogs lay eggs in water. A male frog mounts the female and

grips her tightly and the female lays eggs in a long chain in water.

The male frog covers the eggs with sperms. The fusion of an egg (ovum) and a
sperm takes place outside the body of a female (external fertilization).

The life cycle of a frog completes in three distinct stages. They are as follows:

1. Egg

2. Tadpole Egg Mass
3. Adult

Adult frog Tadpole

Young frog Tadpole with legs
15.10

Life cycle of frog

GREEN Science and Environment Book-7 165

1. Egg

Female frogs lay eggs on the surface of

water in a long chain. Eggs are oval in

shape. They remain covered with a jelly

like substance which forms a cluster of Fig. Fig.

eggs. The cluster of eggs floats on the

surface of water. The male disseminates Eggs of frog in water
sperms on the cluster of eggs. The fusion 15.11
of sperm (male gamete) and a female

gamete (egg) takes place in water. This process is called external fertilization.

After fertilization, a zygote is formed. The zygote divides and redivides and

forms an embryo. The embryo finally develops into a tadpole, i.e. larva stage.

2. Tadpole

A tadpole is the second stage of the life
cycle of a frog. It consists of a big head
and a tail. It breathes in water through
gills. The tadpole does not take any food
and it remains attatched to the leaves of
aquatic plants.

The tadpole develops mouth and teeth 15.12

on head after few days and then it feeds Tadpoles of a frog

on algae in water. This stage lasts for one week to several days in winter.

Later, the tadpole develops hind limbs and gills modify into lungs. The tail
shortens and disappears gradually. Finally, the tadpole metamorphoses into
an adult frog.

3. Adult
An adult frog starts breathing through moist skin in water and through lungs
on land. The adult frog has two pairs of well developed limbs for jumping and
swimming. The adult frog can live in water as well as on land.

In this way, the life cycle of a frog is completed.

Activity 2

In rainy season, pay a visit to a nearby crop field, river, pond, etc.
Observe the eggs, tadpoles and adult frog.
Study the structure of eggs, tadpoles and adult frogs.
Draw a neat figure showing the life cycle of frog.

166 GREEN Science and Environment Book-7

Classification of Plants

Different types of plants are found on the earth. Some may be microscopic
and some may be very large in size. Algae are small and trees are large. Some
plants produce flowers and some do not. On the basis of absence or presence
of flowers, plants are divided into two sub-kingdoms. They are as follows:

1. Sub-kingdom Cryptogams (non flowering plants)

2. Sub-kingdom Phanerogams (flowering plants)

Plant Kingdom
Sub-kingdom

Cryptogams Phanerogams
Division Division

Thallophyta Bryophyta Pteridophyta Gymnosperms Angiosperms

Sub-division Sub-division

Algae Fungi Monocot Dicot

Sub-kingdom Cryptogams

This sub kingdom consists of non-flowering plants. They are less developed
than flowering plants. On the basis of structure and development, sub kingdom
cryptogams is divided into three divisions. They are as follows:

1. Division Thallophyta 2. Division Bryophyta

3. Division pleridophyta

1. Division Thallophyta

This division includes primitive cryptogams without root, stem and leaves.
The plant body without root, stem and leaves is called thallus and the plants
are called thallophytes.

Thallophytes may be green or non green and unicellular or multicellular. On
the basis of absence or presence of chlorophyll, division thallophyta is divided
into two sub-divisions. They are (i) Algae and (ii) Fungi.

i. Algae
This sub-division consists of green thallophytes. They are found in water and
moist places.

GREEN Science and Environment Book-7 167

Fig. Fig.15.13 Chlamydomonas Volvox
Spirogyra

Characteristics

1. The plant body is a green thallus.

2. Chlorophyll is present. So they can prepare their own food by photosynthesis.

3. The cell wall is made of cellulose.

4. They may be unicellular (chlamydomonas) or multicellular (Spirogyra)

5. The mode of nutrition is autotrophic.

Examples: chlamydomonas, spirogyra, volvox, etc.

ii. Fungi

This sub-division consists of non green thallophytes. Most fungi are found on
dead and decaying organic matter whereas some live as parasites of plants
and animals.

15.14 Yeast Mucor
Mushroom

Characteristics

1. The plant body is a non-green thallus.

2. Chlorophyll is absent so they cannot prepare their own food.

3. The cell wall is made of fungus cellulose.

4. They may be unicellular (yeast) or multicellular (mushroom).

5. The mode of nutrition may be saprophytic or parasitic.
Examples: mushroom, yeast, mucor, etc.

168 GREEN Science and Environment Book-7

Differences between Algae and Fungi

Algae Fungi

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

2. Cell wall is made of cellulose. 2. Cell wall is made of fungus
cellulose.

3. They can prepare their own food 3. They cannot prepare their own

by photosynthesis. food.

Activity 2

Observe different types of algae and fungi in your locality. Collect them and
study their characteristics one by one.

Draw a neat and labelled figure of each.

2. Division Bryophyta Do You Know

This division includes multicellular Bryophytes grow on moist and they need
non-flowering plants that grow water to reproduce. Therefore, bryophytes
on moist land and need water to are also called amphibian plants.
reproduce.

Fig.

15.15 Riccia Moss
Marchantia

Characteristics
1. The plant body is multicellular which may be thalloid (e.g. liver worts) or

leafy (moss).
2. Chlorophyll is present.
3. True root, stem and leaves are absent.
4. They are attatched to the soil with the help of rhizoids.
5. Vascular tissues (xylem and phloem) are absent.
Examples: Marchantia (liverworts), Riccia, Moss, etc.

GREEN Science and Environment Book-7 169

3. Division Pteridophyta

This division consists of well developed cryptogams having feather shaped
leaves. Pteridophytas are commonly found in moist, shady and cool places.

Fig. Fig.15.16 Lycopodium Horsetail
Fern

Characteristics

1. The plant body can be divided into rhizoids (root), rhizome (stem) and leaves.

2. Feather-shaped leaves are present.

3. Vascular tissues (xylem and phloem) are present.

4. The mode of nutrition is autotrophic.

5. Flowers and seeds are absent.

Examples: Fern, Lycopodium, Horsetail (equisetum) etc.

Sub-kingdom phanerogams

This sub-kingdom consists of well developed plants that bear flowers and
seeds. Cycas, pine, mango, apple, sal, sunflower, rose, orange, etc are the
examples of phanerogams. They may or may not bear fruits. Sub-kingdom
phanerogams is divided into two divisions. They are as follows:

1. Division Gymnosperms 2. Division Angiosperms

1. Division Gymnosperms

This division consists of conebearing plants having naked seeds. They are
commonly found in cold and dry places.

15.17 Pine Pine cone
Cycas

170 GREEN Science and Environment Book-7

Characteristics
1. Seeds are naked.
2. Cones are present instead of true flowers.
3. Needle-shaped leaves are present.
4. They do not have fruits due to absence of ovary.
5. Male cones and female cones are separate.
Example: Cycas, pine, cedar, juniper, etc.

2. Division Angiosperms
This division consists of the most developed flowering plants having fruits.
They are found on land and in water.

Fig.

15.18 Maize Mango Rose
Pea

Characteristics

1. True flowers are present.

2. Seeds are enclosed inside the fruit.

3. They may be herbs, shrubs or trees.

4. Vascular tissues are well developed.

5. These plants may be small to very large in size.

Exmaples: Maize, rose, apple, mustard, sugarcane, onion, garlic, orange,
mango, sal, sissoo, simal, etc.

On the basis of number of cotyledons in a seed, division, angiosperms is
divided into two sub-divisions. They are as follows:

1. Sub-division Monocotyledons 2. Sub-division Dicotyledons

1. Monocotyledons

This sub division includes flowering plants having only one cotyledon in their
seeds.

GREEN Science and Environment Book-7 171

Fig. Fig.15.19 Bamboo Sugarcane Onion
Maize

Characteristics
1. A seed contains only one cotyledon.
2. Fibrous root system is present
3. Leaves are elongated having parallel venation.
4. Nodes and internodes are distinct.
Examples: Maize, sugarcane, bamboo, onion, garlic, grass, paddy, wheat,
barley, etc.

2. Dicotyledons

This sub-division includes well developed flowering plants having two
cotyledons in their seeds.

15.20 Sunflower Mango Apple
Beans

Characteristics
1. A seed contains two cotyledons.
2. Tap root system is present.
3. Leaves are broad having reticulate venation.
4. Nodes and internodes are not distinct.
Examples: Rose, mango, apple, bean, pea, mustard, orange, lotus, sunflower,
etc.

172 GREEN Science and Environment Book-7

Differences between Gymnosperms and Angiosperms

Gymnosperms Angiosperms

1. Cones are present. 1. Cones are absent.

2. Fruits are absent. 2. Fruits are present.

3. Seeds are naked. 3. Seeds are enclosed.

4. Leaves are pointed. 4. Leaves are flat and broad.

Differences between Monocot and Dicot

Monocot Dicot

1. A seed contains only one 1. A seed contains two cotyledons.
cotyledon.

2. Fibrous root system is present. 2. Tap root system is present.

3. Leaves are elongated having 3. Leaves are broad having reticulate

parallel venation. venation.

Activity 3

Observe different types of flowering plants in your locality.

Study their morphology and classify them in terms of gymnosperms,
angiosperms, monocot and dicot and fill in the given table.

Flowering plants Gymnosperms Angiosperms
1. 1. 1.

2. 2. 2.

3. 3. 3.

4. 4. 4.

5. 5.

6. Monocot Dicot
7. 1. 1.
8. 2. 2.
9. 3. 3.
10. 4. 4.

5. 5.

GREEN Science and Environment Book-7 173

Differences between Non-flowering and Flowering plants

Non-flowering plants Flowering plants

1. They do not bear flowers and 1. They bear flowers and seeds.
seeds.

2. They may be green or non green. 2. All flowering plants are green.

3. They may be unicelular or 3. All flowering plants are

multicellular. multicellular

4. They may or may not bear roots, 4. They bear roots stem and leaves.
stem and leaves.

Activity 4

Observe any three non flowering and three flowering plants in your locality.
Study their morphology (external structure). Write any three similarities and
three differences between them and fill in the given table.

Similarities

S.N. Non-flowering plants S.N. Flowering plants
1. 1.
2.
2. 3.

3.

Differences

S.N. Non-flowering plants S.N. Flowering plants
1. 1.
2.
2. 3.

3.

Most flowers have four distinct whorls. They are calyx, corolla, androecium
and gynoecium. Such type of flower is called a complete flower or bisexual
flower. Flowers of tomato, ornage, mango, mustard, bean, etc. are examples
of bisexual or complete flowers. Flowers of same plants like cucumber, gourd,
pumpkin, etc contain either androecium or gynoecium along with calyx and
corolla. These flowers are called unisexual or incomplete flowers.

174 GREEN Science and Environment Book-7

Structure of a Flowering Plant

Different types of non-flowering Flower
and flowering plants are found Fruit
in our surroundings. The plants
that bear flowers, fruits and Leaf
seeds are called flowering plants. Stem
Sunflower, lotus, rose, marigold, Root
pea, bean, mustard, mango, apple,
etc. are some common examples A flowering plant
of flowering plants. A flowering
plant consists of various parts like
root, stem, branches, leaves, buds,
flowers and fruits. These parts
perform specific functions.

A flowering plant can be divided

into two parts, viz. root system

and shoot system. Root system is

the part of a plant below the soil Fig.

whereas shoot system is the part

of a plant above the soil. Stem, 15.21
branches, leaves, flowers and fruits

are the parts of the shoot system.

Flowering plants produce flowers of various colours like red, pink, purple,
orange, yellow, white, blue, etc. They have green leaves and brown or white
roots. The leaves of the plants appear green due to the presence of chlorophyll.

Activity 1

Visit a nearby garden or cropfield.

Uproot a flowering plant such as marigold, pea, mustard, soyabean, etc.

Observe the plant and identify its various parts.

Draw a neat and labelled figure of the plant on your practical file and submit
to your science teacher.

Root system

The underground part of the plant is called the root system. Flowering plants
have two types of root system, viz. (i) tap root system and (ii) fibrous root
system.

GREEN Science and Environment Book-7 175

The root system having primary root, its

branches and sub-branches is called and sub-

branches is called tap root system. The

branches of primary root are called secondary

roots and the branches of secondary roots are
Fig.
Fig.
called tertiary roots. Tap root system is found

in dicot plants like bean, pea, mustard, apple,

mango, rose, soyabean, orange, etc. 15.22

Tap root system

15.23 The root system having cluster of roots of the
Fibrous root system same size and thickness is called fibrous root
system. These roots grow from the base of
the stem and spread in all directions. Fibrous
root system is found in monocot plants like
sugarcane, onion, maize, bamboo, paddy,
wheat, garlic, etc.

Functions of roots
1. Roots absorb water and minerals from the soil.

2. They fix the plant to the soil.

Shoot system

Shoot system is the part of the plant which is found above the ground. It consists
of stem and its branches, sub-branches, leaves, buds, flowers and fruits.

Stem

The part of a flowering plant that grows upwards from the soil is called a stem.
It forms the main axis of the shoot system. Trees and bushes have hard and
strong woody stem but most of the small plants have green, soft and weak
stem. Trees and shrubs have many branches and sub-branches in their stem.
These branches and sub-branches have leaves, thorns, buds, flowers and fruits.

The stem is thick in its base and it tapers gradually towards the tip. The stem
consists of certain points from where branches and leaves sprout. These points
are called nodes. The portion of the stem between two nodes is called internode.

176 GREEN Science and Environment Book-7

Functions of stem
1. Stem transports water and minerals from roots to the leaves.
2. It keeps a plant upright or erect.
3. It transports prepared food from leaves to various parts of the plant.
4. It bears and supports branches, leaves, flowers and fruits.

Leaf Vein

The flat and green part of a plant that sprouts Lamina
from a node is called leaf. Flowering plants
have leaves of various shapes and sizes. Mid rib
Lamina, petiole and leaf base are the three Petiole
main parts of a leaf. Lamina or leaf blade is
the flat and wide green portion of the leaf. Leaf
Green plants prepare food in the lamina as it
has chlorophyll, i.e. green pigment. 15.24
Chlorophyll traps solar energy and helps
plants in photosynthesis.
Fig. Fig.
Fig.
Petiole is a narrow, short stalk of a leaf which Parallel venation
remains attached to the stem. Similarly, leaf
base is the portion of the stem from which a
leaf grows. The petiole extends into the
lamina in the form of mid rib. The mid rib
gives branches and sub-branches that form a
network in the leaf. The network is formed by
veins and veinlets which distribute water, 15.25
minerals and prepared food to the lamina.

15.26 Flowering plants have two types of venations
Reticulate venation in their leaves. They are parallel venation and
reticulate venation. The arrangement of veins
and veinlets in a leaf is called venation. In
parallel venation, veins are arranged parallel
to each other towards the tip of the leaf.
This type of venation is found in leaves of
sugarcane, bamboo, rice, maize, wheat, grass,
onion, garlic, etc.

In reticulate venation, the veins give rise to lateral veinlets in all directions
and form a network. This type of venation is found in leaves of rose, mustard,
apple, mango, papaya, orange, bean, sunflower, etc.

GREEN Science and Environment Book-7 177

Functions of leaves
1. Leaves prepare food by using carbon dioxide and water in the presence of

sunlight.

2. They remove excess water during transpiration.

Activity 2

Observe the stems of various flowering plants in your surroundings and
study their structure.

Collect leaves of some flowering plants.

Study venation present in those leaves and differentiate between parallel
venation and reticulate venation.

Flower Fig. Fig. Flower

We see a variety of flowers in our
surroundings. Flowers are colourful. They
have bright and attractive colours like red,
yellow, pink, purple, white, blue, orange, etc.
Flowers are the colourful and most attractive
parts of plants. Flowers have different
shapes, sizes and colours. They help in sexual 15.27
reproduction.

A flower consists of four distinct parts. They are sepals, petals, stamen and
pistil or carpel. Some flowes contain only one type of reproductive organ, i.e.
either stamen (male) or carpel (female). These flowers are called unisexual
flowers. Plants like pumpkin, maize, paddy, cucumber, etc. have unisexual
flowers.

Some flowers contain both male and female
reproductive organs. These flowers are called
bisexual or complete flowers. Plants like pea,
chinarose, orange, tomato, apple, bean, etc.
contain bisexual flowers.

A flower is connected to the stem by a narrow 15.28

stalk called pedicel. A flower has a swollen Unisexual flower

basal portion called thalamus. A complete flower consists of four distinct

whorls or rings. They are as follows:

178 GREEN Science and Environment Book-7

(i) Calyx

(ii) Corolla Pistil Stigma Anther Stamen
(iii) Androecium Style Filament
Fig. Ovary
Fig. Petal
Ovule

(iv) Gynoecium Receptacle Sepal

15.29

i. Calyx Bisexual flower

Calyx is the outermost whorl of a flower. It is made of a number of green leaf

like structures called sepals. Calyx protects a flower in the bud stage.

ii. Corolla

Crorolla forms the second whorl of a flower. It consists of colourful petals.
Petals surround and protect the reproductive parts of a flower. Similarly, petals
attract insects and help in pollination.

iii. Androecium

Androecium forms the third inner whorl of a flower. It consists of a number
of male reproductive organs called stamens. Each stamen consists of anther,
filament and connective. Anther produces pollen grains and filament supports
the anther.

iv. Gynoecium

Gynoecium forms the fourth innermost whorl of a bisexual flower. It represents
the female reproductive part called pistil or carpel. Each carpel consists of three
parts, viz. stigma, style and ovary. Stigma receives pollen grains and ovary
consists of ovules in it. The ovary develops into a fruit and ovules develop into
seeds with maturity.

Pollination Cross-pollination
Pollination
The transfer of pollen

grains from anther to Self-pollination
the stigma of the same

flower or different

flower is called

pollination. Various

external agents like

air, water, insects,

birds, animals etc. 15.30

help in pollination.

GREEN Science and Environment Book-7 179

Pollination is of two types, viz. self-pollination and cross-pollination.

i. Self-pollination

It is the transfer of pollen grains from the anther to the stigma of the same
flower. This process is common in bisexual flowers like pea, chinarose, tomato,
etc.

ii. Cross-pollination

It is the transfer of pollen grains from the anther of a flower of one plant to the
stigma of a flower of another plant of the same species. This process is common
in unisexual flowers like pumpkin, cucumber, gourd, etc. and bisexual flowers.

In flowering plants, pollination is followed by fertilization.

Seed

Flower Germinating seed

Fig. Adult plant Seedling

15.31
Life cycle of a flowering plant

Fertilization

The process of fusion of a male gamete and a female gamete to form a zygote
is called fertilization. After pollination, pollen grains germinate and form
pollen tubes which grow towards ovary through style and finally reaches the
ovule in the ovary. Ovule consists of female gametes. In ovule, fusion of a
male gamete and female gamete takes place and forms a zygote. This process
is called fertilization. After fertilization, the zygote divides and forms embryo.
The embryo of a seed grows into a new plant on favourable condition.

In this way, the life cycle of a flowering plant is completed.

180 GREEN Science and Environment Book-7

Key Concepts

1. The animals having backbones or vertebral columns are called vertebrates.

2. The body of vertebrates is well developed having a head, trunk and tail
with paired fins or limbs.

3. The vertebrates whose body temperature changes according to the
temperature of the surroundings are called cold blooded vertebrates.

4. The vertebrates whose body temperature does not change with the
temperature of surroundings are called warm blooded vertebrates.

5. This class consist of aquatic cold blooded vertebrates which are commonly
known as fishes.

6. Different types of snakes, lizards and crocodiles belong to class reptilia.

7. This class includes the most developed warm blooded vertebrates that
suckle their young ones.

8. Frog is a tailless vertebrate which can live on land and in water. It is a
carnivorous amphibian which becomes active in rainy season.

9. Life cycle can be defined as the series of stages through which an organism
passes.

10. On the basis of structure and development, sub kingdom cryptogams is
divided into three divisions. They are as follows: a. Division Thallophyta,
b. Division Bryophyta, c. Division Pteridophyta.

11. This division includes primitive cryptogams without root, stem and leaves.

12. Most fungi are found on dead and decaying organic matter whereas some
live as parasites of plants and animals.

13. Bryophytes grow on moist and they need water to reproduce. Therefore,
bryophytes are also called amphibian plants.

14. This division consists of well developed cryptogams having feather shaped
leaves.

15. This division consists of conebearing plants having naked seeds.

16. This division consists of the most developed flowering plants having fruits.
They are found on land and in water.

17. This sub division includes flowering plants having only one cotyledon in
their seeds.

18. This sub-division includes well developed flowering plants having two
cotyledons in their seeds.

GREEN Science and Environment Book-7 181

19. The plants that bear flowers, fruits and seeds are called flowering plants.
20. A flowering plant can be divided into two parts, viz. root system and shoot

system.
21. The underground part of the plant is called root system. Flowering plants

have two types of root system, viz. (i) tap root system and (ii) fibrous root
system.
22. The root system having primary root, its branches and sub-branches is
called tap root system.
23. Tap root system is found in dicot plants like bean, pea, mustard, apple,
mango, rose, soyabean, orange, etc.
24. The root system having cluster of roots of the same size and thickness is
called fibrous root system.
25. Fibrous root system is found in monocot plants like sugarcane, onion, maize,
bamboo, paddy, wheat, garlic, etc.
26. Shoot system is the part of the plant which is found above the ground.
27. The part of a flowering plant that grows upwards from the soil is called
stem.
28. The portion of the stem between two nodes is called internode.
29. The flat and green part of a plant that sprouts from a node is called leaf.
30. Chlorophyll traps solar energy and helps plants in photosynthesis.
31. The arrangement of veins and veinlets in a leaf is called venation.

32. Flowers are the colourful and most attractive parts of plants.

33. A flower consists of four distinct parts. They are sepals, petals, stamen and
pistil or carpel.

34. The transfer of pollen grains from anther to the stigma of the same flower or
different flower is called pollination.

35. Pollination is of two types, viz. self-pollination and cross-pollination.
36. The process of fusion of a male gamete and a female gamete to form a zygote

is called fertilization.

182 GREEN Science and Environment Book-7

Exercise

1. Tick (√) the correct statement and cross (×) the incorrect one.
a. The animals having backbones are called vertebrates.
b. Cow and elephant are cold-blooded animals.

c. Crocodile belongs to class reptilia.

d. In frogs, fertilization is internal.

e. In algae, chlorophyll is present.
f. The transfer of pollen grains from anther to stigma is called

fertilization.

2. Fill in the blanks using appropriate words.
a. In ..................... animals, body temperature changes according to the
surrounding temperature.
b. In ....................., fore limbs are modified into wings.
c. ..................... directly give birth to their young ones.
d. The plants that do not bear flowers are called .....................
e. Cones are present in .....................
f. ..................... is the second whorl of a flower.

3. Tick (√) the best answer from the given alternatives.
a. The vertebrates that can live on land and in water are called ........

pisces amphibians reptiles aves

b. Mammary glands are present in ......

crow bat parrot dove

c. Chlorophyll is absent in ..........

mushroom moss fern riccia

GREEN Science and Environment Book-7 183

d. Which of the given plants has tap root system?

onion maize pea bamboo
corolla
e. Which of the following is the third whorl of a flower?

calyx gynoecium androecium

4. Answer the following questions:

a. What are vertebrates? Give any five examples.

b. Define cold-blooded and warm-blooded animals with any two
examples of each.

c. Name the five classes of vertebrates.

d. Write any two salient features and two examples of

i. pisces ii. amphibia iii. aves iv. mammalia

e. What are reptiles? Give any two examples.

f. What are cryptogams? Give any three examples.

g. Name three divisions of cryptogams.

h. What are thallophytes? Give any two examples.

i. What are bryophytes? Write any two characteristics of pteridophyts.

j. What are phanerogames? Give any five examples.

k. Write any two characteristics of the plants belonging to division
angiosperms?

l. What is a flower? Name the four whorls of a flower.

m. Define pollination and fertilization.

5. Differentiate between:
a. Fish and Frog
b. Reptiles and Mammals
c. Cryptogams and Phanerogams
d. Algae and Fungi
e. Grymnosperms and Angiosperms

184 GREEN Science and Environment Book-7

f. Monocot and Dicot
g. Calyx and Corolla
h. Self-pollination and Cross-pollination
6. Give reason:
a. Frog is called an amphibian.
b. Bat is kept in class mammalia.
c. Algae are called autotrophs.
d. Maize is called a monocot.
e. Mustard flower is called a complete flower.
7. Draw a neat and labelled figure of a flowering plant.
8. Draw a neat and labelled figure of a bisexual flower.
9. What is pollination? Draw a neat figure showing self-pollination and
cross-pollination.
10. What is meant by fertilization?
11. Write down the major functions of roots, stem and leaves.

GREEN Science and Environment Book-7 185

UNIT Cell and Tissue

16

Weighting Distribution (Approximate) Teaching periods : 6 Marks (in %): 3

Before You Begin

A house is made of many bricks. Similarly, the body of plants and
animals is made of many cells. A cell is the basic, structural and
functional unit of life. Cells are the building blocks of living organisms.
A cell has its own structure and cell gives shape to the body of an
organism. So a cell is called the structural unit of life. A cell performs
various functions like respiration, excretion, reproduction, etc. which
are essential for the survival of an organism. So a cell is called the
functional unit of life. A cell is capable of independent existence and
it acts as the smallest complete unit of life. So a cell is called the basic
or fundamental unit of life.

Learning Objectives Syllabus

After completing the study of this unit, students will be able to: • Cell – Introduction
i. introduce cell and explain the structure of a typical
• Parts of a cell
plant cell and animal cell.
• Cell organelles and their
ii. introduce cell organelles and state the functions of functions
various cell organelles.
• Unicellular and multicellular
iii. describe the structure of a unicellular animal (amoeba) animals
and a multicellular animal (hydra).
• Structure of amoeba and hydra

Glossary: A dictionary of scientific/technical terms

cell : the basic, structural and functional unit of life.
cell organelles : living and membrane bound structure of a cell, e.g. nucleus
inclusions : non-living structures present in a cell, e.g. vacuole
unicellular : having only one cell
multicellular : having many cells
metabolic : related to chemical processes in living things that change food into energy

permeable and materials for growth
turgid : allowing a liquid or gas to pass through
contractile : swollen, containing more water than usual
: able to contract or become narrower

186 GREEN Science and Environment Book-7

Cell and Tissue

Cell

A cell is the basic, structural and Fig. Fig.16.1
functional unit of life. The bodies of all
plants and animals are made up of cells. Compound microscope
Cells are also called building blocks of
life and can be compared with the bricks
of a house. A cell can perform various
metabolic activities and the function of
an organism as a whole is the outcome of
combined activities of the cells present
in the body.

A cell is the smallest unit of life made of life giving substances called cytoplasm.
A cell is capable of independent existence. Cells are very small, i.e. microscopic
and cannot be seen with naked eyes. Therefore, we use compound microscope
to see the detailed structure of a cell. The bodies of living organisms consist
of cells and cell products. All new cells are formed by division of pre-existing
cells. Basically, cells are alike in chemical composition and metabolic activities.
Cells form the bodies of living beings. They have their own structure and
perform various functions. Therefore, cell is called the basic, structural and
functional unit of life.

Discovery of cell

Cell was discovered by Robert Hook
in 1665 AD. He built a microscope and
observed a thin slice of cork. He observed
numerous compartments connected
together in a honey-comb like structure.
He named these comparts as cells.

Types of cell Robert Hooke

On the basis of nuclear organization, 16.2
there are two types of cells. They are as
follows:

1. Prokaryotic cell

2. Eukaryotic cell

GREEN Science and Environment Book-7 187

1. Prokaryotic cell Fig. Fig.

A cell having a primitive nucleus is called
prokaryotic cell. It does not contain various
membrane bound cell organelles such as
mitochondria, endoplasmic reticulum,
lysosome, etc. Bacteria, blue-green algae,
etc. have prokaryotic cell.

16.3

2. Eukaryotic cell

A cell having well organized nucleus is
called eukaryotic cell. It consists of various
cell organelles and inclusions. Most plants
and animals contain eukaryotic cell.

16.4

Structure of cell Cell wall Cytoplasm

Generally, animal cells are round Cell membrane Rough ER
or oval and plant cells are Vacuole Smooth ER
rectangular or hexagonal.
However, cells of different Nucleus Ribosomes
organisms differ in shape, size Nucleolus Golgi body
and structure. Similarly, cells of
the same organisms differ from Fig. Chloroplast
one another. In spite of these
differences, all cells are basically 16.5 Mitochondrion
similar in structure and functions. Chromatin

Plant cell

A cell consists of various parts, Lysosome Golgi apparatus
i.e. membranes, cell organelles Golgi vesicles Mitochondrion
and inclusions. A brief
description of different parts of Rough ER Nucleolus

a cell is given below: Fig. Smooth ER Nucleus
Cell membrane Microtubules
1. Cell wall

A cell wall is the outermost, 16.6 Centrioles Cytoplasm
thick, rigid and protective layer Ribosome
of plant cells. It is made of a non- Animal cell
living structure called cellulose.

188 GREEN Science and Environment Book-7

It is freely permeable in nature. A cell wall is absent in animal cell.

Functions
1. It provides a fixed shape to a plant cell.
2. It protects cell membrane and internal parts of a cell.
3. It helps various materials to enter and leave a cell.

2. Cell membrane

Cell membrane is a living, elastic and delicate membrane that forms the
outermost covering layer of an animal cell. In plant cells, it is found just inside
the cell wall. Cell membrane or plasma membrane is made up of protein and
lipid. It contains numerous pores and is semi-permeable or selectively
permeable in nature.

Functions Do You Know
1. It provides a fixed shape to an
Cell membrane or plasma membrane
animal cell. is called semi-permeable or selectively
permeable membrane because it allows only
2. It protects internal parts of a cell. selected substances to enter or leave a cell. It
allows only the required materials to enter a
3. It helps in transport of materials in cell and waste materials to leave.
and out of a cell.

3. Cytoplasm

Cytoplasm is a living, jelly-like substance found between cell membrane and
nuclear membrane. It is made of water, protein, fats, carbohydrates, minerals,
etc. It is translucent and semi-liquid in nature. It provides space for various
cell organelles and inclusions.

Functions
1. It consists of various cell organelles and hence, provides space for various

metabolic activities.

2. It helps in exchange of materials among various cell organelles.

3. It helps in distribution of molecules, nutrients and enzymes inside tahe cell.

GREEN Science and Environment Book-7 189

4. Nucleus

Nucleus is a spherical or round cell
organelle found at the centre of a cell. It
consists of nuclear membrane, nucleolus,
nucleoplasm and thread-like structures
called chromosomes. The chromosomes
contain heredity information.
Fig.
Fig.Functions 16.7

1. Nucleus controls various metabolic activities of a cell.

2. It helps in cell division.

3. It helps in reproduction.

4. It helps to transmit hereditary information from parents to their offspring.

5. Mitochondria

Mitochondria are thread-like, rod-shaped or spherical cell organelles present
in cytoplasm. They may be small or large. They are enclosed by an outer
membrane and inner membrane. They contain different types of enzymes.

Do You Know

Mitochondria produce energy during
cellular respiration and store it. So they are
called the power house of a cell.

16.8

Functions
1. Mitochondria produce and store energy required for a cell.
2. They synthesize amino acids

6. Endoplasmic reticulum

Endoplasmic reticulum is a network of membrane bound flat tubules present
in the cytoplasm. It connects cell membrane to the nuclear membrane. It fills
up the intracellular cavity and forms the endoskeleton of a cell. Endoplasmic
reticulum is of two types, i.e. smooth endoplasmic reticulum and rough

190 GREEN Science and Environment Book-7

endoplasmic reticulum. The endoplasmic reticulum in which ribosomes are
attached is called rough endoplasmic reticulum.

Functions

1. It increases surface area for various
metabolic activities.

2. It helps in formation of cell plate during
cell division.

3. It helps in intracellular transport. Fig. Fig.

4. It provides mechanical support to the

cytoplasm. 16.9

5. It forms the supporting framework of a cell.

7. Ribosomes

Ribosomes are small spherical structure. They are found attached to the
surface of endoplasmic reticulum and some are found freely distributed in the
cytoplasm. They consist of RNA and protein.

Function
1. Ribosomes help in protein synthesis.

8. Plastids

Plastids are oval, round or elongated

cell organelles found only in plant

cells. On the basis of pigments, there

are three types of plastids. They are

i) Chloroplasts, ii) Chromoplasts and iii)

Leucoplasts. 16.10

i) Chloroplasts

Chloroplasts are green plastids. They are found in leaves, green parts of stem,
sepal and young fruits.

Functions

1. Chloroplasts trap solar energy and help in photosynthesis.

ii) Chromoplasts
Chromoplasts are colourful plastids. They are found in petals of flowers and
pericrap of fruits.

GREEN Science and Environment Book-7 191

Fig.Function
1. Chromoplasts impart various colours to flowers and attract insects for

pollination.

iii) Leucoplasts
Leucoplasts are colourless pigments found in cells of underground storage
tissues of plants.
Function
1. Leucoplasts store food in the form of carbohydrates, protein and fat.

9. Golgi bodies

Golgi bodies consist of a set of membrane
bound tubules, fluid-filled vesicles and
vacuoles. It is found in the cytoplasm near
the nucleus.

Function
1. It helps in cell division.
2. It helps in synthesis and storage of 16.11

proteins, carbohydrates and enzymes.
3. It helps in formation of cell wall and membrane.

10. Vacuoles

Vacuoles are non-living fluid filled spaces present in the cytoplasm. In animal
cell, vacuoles are smaller but more where as in plant cell, vacuoles are larger
but less. Vacuoles remain enclosed by a membrane called toroplast. Vacuoles
remain filled with a fluid which contains water, minerals, waste products, etc.

Functions
1. Vacuoles help a cell to remain turgid.
2. They balance the amount of water in a cell.
3. They balance the amount of glucose in a cell.
4. They store waste products, water and minerals.

11. Lysosomes

Lysosomes are spherical sac-like structures found in the cytoplasm. They
contain powerful enzymes that can digest various substances. They are capable

192 GREEN Science and Environment Book-7

of digesting entire dead cell or damaged cell. Therefore, lysosomes are called
suicidal bags of the cell.

Functions
1. They help in intracellular digestion.
2. They provide energy to a cell during starvation.

12. Centrosome

It is a small naked structure found only in animal cells. It is located in the
cytoplasm near the nucleus. It contains two small centrioles and astral rays.

Functions
1. It helps in cell division in animal cells.
2. It gives rise to cilia and flagella.
Activity 1
To observe onion cells under a compound microscope:

Take a bulb of onion and remove outer dry scales. Cut the bulb into small
pieces vertically.

Take a fleshy scale and bend its outer surface and pull the broken thin layer
using foreceps.

Place the thin layer in a watch glass containing water and sefranin.
Take a glass slide and put a drop of glycerine at the middle of the slide.
Place the thin layer of onion, cover it gently with a cover slip and observe it

under the compound microscope.

Draw a neat figure after your observation.

Unicellular Animals

The animals having only one cell in their bodies are called unicellular animals.
They are very less developed. They do not have tissues, organs and systems.
Examples: Amoeba, Paramecium, Euglena, Plasmodium, etc. In unicellular
organisms, all life processes like respiration, digestion, excretion, etc take
place in a single cell.

GREEN Science and Environment Book-7 193

16.12 Fig.ParameciumEuglena
AmoebaFig. Fig.

Multicellular Animals

The animals having many cells in their bodies are called multicellular animals.
They are more developed than unicellular animals. They have tissues, organs
and systems. Examples: Hydra, tapeworm, earthworm, butterfly, fish, frog,
snake, crow, elephant, etc. Multicellular organisms have different organs and
systems to perform various life processes.

16.13

Amoeba

Amoeba is a unicellular animal. It is
commonly found in fresh water, ponds,
pools, slow running streams, soil, etc. It
feeds on bacteria and other microscopic
organisms.

There are different types of amoeba. They
are microscopic. We need a compound
microscope to see the detailed structure of 16.14
an amoeba.

The shape of an amoeba is irregular. The body of an amoeba remains covered
with a thin elastic and semi-permeable plasmalemma. The cytoplasm can be
distinguished into outer ectoplasm and inner endoplasm. A small spherical
nucleus is found at the centre of endoplasm. The endoplasm also consists

194 GREEN Science and Environment Book-7

of a large contractile vacuole, many food vacuoles, mitochondria, golgi
complex, endoplasmic reticulum, ribosomes, water droplets, etc. The nucleus
controls various metabolic activities in amoeba and also helps in growth and
reproduction.

The plasmalemma of amoeba is semi-permeable which allows only selected
substances to enter or leave the cell. Two types of vacuoles are found in
amoeba. They are:

i. Contractile vacuoles ii. Food vacuoles

Food vacuoles store food and water. Similarly, contractile vacuole stores waste
materials and helps in excretion.

Most amoebas are harmless to human beings. But entamoeba histolytica infects
inner lining of human intestine and causes dysentery. Entamoeba coli is a non-
pathogenic species of amoeba which is found in human intestine but does not
cause any disease. It feeds on bacteria and indigested food particles.

16.15 Fig. Entamoeba coli
Entamoeba histolyticaFig.

Hydra

Hydra is a small aquatic invertebrate. It
belongs to the phylum coelenterata of
Animal Kingdom. Hydra has a hollow
body of about 10 mm length. It has a mouth
but no anus. In hydra, the mouth remains
surrounded by tentacles. Tentacles help in
movement and catching food.

Hydra moves with the help of tentacles.
While moving, hydra bends its body 16.16
attaching itself to the substratum with the
tentacles and then releases the basal disc, which provides usual attachment.

GREEN Science and Environment Book-7 195

This process is called somersaulting or looping. The hydra then bends its bodyFig.
and makes a new place for attachment with the basal disc.Fig.

16.17
Movement of hydra

Hydra is a diploblastic animal, i.e. it has two body layers. They are epidermis
(outer) and dermis (inner). A gel-like substance is found between two layers
which are called mesogloea. In hydra, digestion of food takes place in the
coelenteron.
The hydra reproduces asexually by budding. In this process, a small outgrowth,
i.e. bud grows in the body. The bud develops into a baby hydra. The bud finally
separates from a parent hydra. In this way, reproduction takes place in hydra.

16.18
Budding in hydra

Differences between plant cell and animal cell

Plant cell Animal cell

1. Cell wall is present. 1. Cell wall is absent.

2. Centrosome is absent. 2. Centrosome is present.

3. Plastids are present. 3. Plastids are absent.

4. Vacuoles are larger. 4. Vacuoles are smaller.

5. It is hexagonal or rectangular in 5. It is round or oval in shape.
shape.

196 GREEN Science and Environment Book-7

Activity 2

Observe the structure of amoeba under a compound microscope.

Draw a neat and clean labelled figure after your observation.

Key Concepts

1. A cell is the basic, structural and functional unit of life.
2. A cell performs various functions like respiration, excretion, reproduction,

etc. which are essential for the survival of an organism. So a cell is called
the functional unit of life.
3. A cell is the smallest unit of life made of life giving substances called
cytoplasm.
4. Cell was discovered by Robert Hook in 1665 AD.
5. A cell having a primitive nucleus is called prokaryotic cell.
6. A cell having a well organized nucleus is called eukaryotic cell.
7. A cell wall is the outermost, thick, rigid and protective layer of plant
cells.
8. Cell membrane is a living, elastic and delicate membrane that forms the
outermost covering layer of an animal cell.
9. Cytoplasm is a living, jelly-like substance found between cell membrane
and nuclear membrane.
10. Nucleus is a spherical or round cell organelle found at the centre of a cell.
11. Mitochondria are thread-like, rod-shaped or spherical cell organelles
present in a cytoplasm.
12. Endoplasmic reticulum is a network of membrane bound flat tubules.
13. Ribosomes are small spherical structure. They are found attached to the
surface of endoplasmic reticulum.
14. Plastids are oval, round or elongated cell organelles found only in plant
cells.
15. Golgi bodies consist of a set of membrane bound tubules, fluid-filled
vesicles and vacuoles.
16. Vacuoles are non-living fluid filled spaces present in cytoplasm.
17. Lysosomes are spherical sac-like structures found in cytoplasm.
18. The animals having only one cell in their bodies are called unicellular
animals.

GREEN Science and Environment Book-7 197

19. The animals having many cells in their bodies are called multicellular
animals.

20. Amoeba is a unicellular animal. It is commonly found in fresh water,
ponds, pools, slow running streams, soil, etc.

21. Most amoebas are harmless to human beings. But Entamoeba histolytica
infects inner lining of human intestine and causes dysentery.

22. Hydra is a small aquatic invertebrate. It belongs to the phylum
coelenterata of Animal Kingdom.

23. The hydra reproduces asexually by budding. In this process, a small
outgrowth, i.e. bud grows in the body. The bud develops into a baby
hydra.

Exercise

1. Tick (√) the correct statement and cross (×) the incorrect one.
a. A cell is the basic, structural and functional unit of life.

b. Eukaryotic cell contains primitive nucleus.

c. Ribosomes help in protein synthesis.

d. Plastids are absent in plant cells.

e. Amoeba is a multicellular animal.

2. Fill in the blanks using appropriate words.

a. Cell was discovered by …………….

b. ………… is made of cellulose.

c. ………… controls metabolic activities of a cell.

d. Centrosome is found only in …………… cell.

e. Hydra moves with the help of ………….

198 GREEN Science and Environment Book-7

3. Tick (√) the best answer from the given alternatives.

a. ………………… forms the outermost covering layer of plant cell.

Nucleus Cell wall Cell membrane Ribosome

b. …………… are absent in animal cells.

Centrosome Vacuoles Plastids Ribosome

c. Which of the given cell organelles help in photosynthesis?

centrosome plastid nucleus ribosomes

d. Which of the given animals is unicellular?

hydra tapeworm amoeba crab

4. Answer the following questions.

a. What is a cell? Why is cell called the basic unit of life?
b. Name the scientists who discovered the cell?
c. What is a prokaryotic cell?
d. What is a eukaryotic cell?
e. What is a cell membrane? Write its two functions.
f. What is a cell wall? Write its two functions.
g. What is a cytoplasm? Write its functions.
h. What is a nucleus? Write its two functions.
i. What are mitochondria? Write the major functions of mitochondria.
j. What is endoplasmic reticulum?
k. What are ribosomes? Write down their major function.
l. Name three types of plastids. Also, write their major functions.
m. What are golgi bodies ? Write their major functions.
n. What are lysosomes? Write down the function of centrosome.

GREEN Science and Environment Book-7 199

5. Match the following: B
A Help in protein synthesis
Cell wall Help in photosynthesis
Cell membrane Release and store energy
Nucleus Gives shape to animal cell
Plastids Gives shape to animal cell
Mitochondria Controls metabolic activities


6. Draw a neat and labelled figure of a

i. Plant cell ii. Animal cell

7. Given reason:
a. A cell is called the fundamental unit of life.
b. Nucleus is called the controller of a cell.
c. Mitochondria are called power house of a cell.

8. Describe the structure of amoeba with a neat and labelled figure.

9. Describe the structure of a hydra with a neat figure.

200 GREEN Science and Environment Book-7