Modern Concept Science and Technology 7

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16.1 Introduction

The living beings found on the earth are divided into two major groups. They are
called kingdoms. These two kingdoms are Plant Kingdom and Animal Kingdom. All
those living beings that fall under the plant kingdom are called plants. Plants exist in
different forms. Most of the plants are multicellular but some are unicellular. Some
groups of plants bear flowers while others do not. Therefore, group of plants differ
from each other in different ways.

Mushroom Fern Spirogyra Volvox Chlamydomonas

Some of the chief characteristic features of plants are:
i. Leaves of most plants contain green pigments called chlorophyll.
ii. Green plants can synthesize their own food by a process called photosynthesis.
iii. Starch is the food prepared by most of the plants.
iv. Majority of the plants are multicellular and only few are unicellular.
v. Plants can be found in diverse habitats like sea water, deserts, wet areas, cold

areas, rocks etc.
vi. Developed plants have distinct root and shoot system.

16.2 Classification of Plants

For easy, fast and systematic study, the whole Plant Kingdom is classified into two
sub-kingdoms. They are Cryptogams and Phanerogams. Each sub-kingdom is divided
into different divisions. Divisions are further divided into sub-divisions and classes.
An outline of classification of plants is shown below.

Plant Kindgom

Cryptogams Phanerogams

Thallophyta Bryophyta Pteridophyta Gymnosperms Angiosperms

Algae Fungai Lichens Monocot Dicot

194 Living Beings: Plant Life

1. Sub-kingdom: Cryptogams

Cryptogams are the non-flowering plants that reproduce without seeds. They
are less developed plants. They are divided into three major divisions. They are:
Thallophyta, Bryophyta and Pteridophyta.
a. Division : Thallophyta
Division Thallophyta is the groups of primitive plants. Their body is not
differentiated into leaves, stem and roots. Thus, those plants whose body is not
differentiated into leaves, stem and roots are called thallophytes. Such a plant
body of thallophytes is called thallus. Plants belonging to this division contain
both unicellular and multicellular plants. It also contains both green as well as
non-green plants.

On the basis of presence and absence of chlorophyll, thallophytes are divided
into two sub-divisions. They are: Algae and Fungi. Algae are green thallophytes
while fungi are non-green thallophytes.

i. Sub-division: Algae

The sub-division Algae includes green thallophytes.

Some of their characteristics are:
i. They are autotrophic green thallophytes.
ii. They contain green pigment called chlorophyll.
iii. They are both unicellular and multicellular thallus plants.
iv. They are found in both fresh and marine water and even in moist

environment.
v. Their reserve food is starch.
vi. They have cell wall made up of cellulose.
Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, etc.

Chlamydomonas Spirogyra Volvox Ulothrix

FACT WITH REASON

Why is spirogyra considered an algae?
Spirogyra is considered an algae because it is a primitive form of life having green thallus as a
plant body.

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ii. Sub-division: Fungi

The sub-division Fungi includes non-green thallophytes.

Some of their characteristics are:
i. They consist of both unicellular (yeast) and multicellular (mushroom)

plants.
ii. They cannot prepare their own food themselves i.e. they are heterotrophs.
iii. They are found in water and moist places.
iv. They feed on dead and decayed organic matter. Some are parasitic.
v. Their reserve food is glycogen.
vi. They have cell wall made up of chitin.
Examples: fungi, yeast, mucor, mold, mushroom, etc.

Yeast Mucor Mushroom

Differences between algae and fungi

S.N. Algae S.N. Fungi
1. 1. Chlorophyll is absent in fungi.
Algae have chlorophyll in their
2. leaves. 2. Fungi derive their food from
dead or decayed matters or host.
Algae synthesize their own food.

3. Their reserve food is starch. 3. Their reserve food is glycogen.

4. Their cell wall is made up of 4. Their cell wall is made up of

cellulose. chitin.

FACT WITH REASON

Mushroom is a fungus, why?
Mushroom is a fungus because its body is non-green thallus which grows on dead organic
materials.

196 Living Beings: Plant Life

ACTIVITY 1

Observe the slides of algae and fungi. Draw their structures in your notebook. Compare
how they differ from each other.

b. Division : Bryophyta
Bryophytes are those cryptogams which do not have vascular bundles and

found in wet and shady places. They depend on water for sexual reproduction.
Hence, they are also called amphibian plants.

Salient features of Bryophytes are:
i. They are both thallus (e.g. liverwort) and non-thallus (e.g. moss) plants.
ii. They need water for reproduction.
iii. They bear simple hair like root structures called rhizoids. Rhizoids absorb

water and minerals from soil or water.
iv. They are slightly advanced than thallophytes but are mostly thallus.
Examples of bryophytes are: Mosses, Riccia, Marchantia (liverworts) etc.

Marchantia Riccia Moss

FACT WITH REASON

Bryophytes are also called amphibian plants, why?
Bryophytes grow in moist places on land but need water for fertilization. So, they are also known
as amphibian plants.

ACTIVITY 2

Observe the specimen of a moss and a liverwort and note how they are common and
different from each other.

c. Division : Pteridophyta

Plants of this division include most developed form of cryptogams. The body
of Pteridophytes is well differentiated into roots, stem and leaves. So, they are
non-thallus plants. Pteridophytes also contain conducting tissues (xylem and

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phloem) in their body. Xylem conducts water and dissolved minerals whereas
phloem conducts organic materials. Thus, pteridophytes are those cryptogams
which have vascular bundles in their body and feather like leaves.

Salient features of Pteridophytes:
i. They are advanced form of cryptogams i.e. their body is differentiated into

distinct roots, stem and leaves.
ii. They have vascular bundles (xylem and phloem) in their body.
iii. They reproduce with the help of spores.
Examples are: Fern, Horse tail, Lycopodium, etc.

Fern Lycopodium Horsetail

Differences between thallophytes and pteridophytes

S.N. Thallophytes S.N. Pteridophytes

1. They are the most primitive form 1. They are the most developed

of non-flowering plants. form of non-flowering plants.

2. Their plant body is thallus, i.e. 2. Their plant body is non-thallus,

cannot be differentiated into root, i.e. differentiated into root, stem

stem and leaves. and leaves.

3. They are both green and non- 3. They are totally green plants.
green plants.

4. They do not have vascular tissues. 4. They have vascular tissues.

FACT WITH REASON

Pteridophytes are also called vascular cryptogams, why?
Pteridophytes are also called vascular cryptogams because they contain vascular tissues, i.e.
xylem and phloem to conduct water and food materials respectively.

ACTIVITY 3

Observe a specimen of a pteridophyte like fern and note its salient features.

198 Living Beings: Plant Life

2. Sub-kingdom: Phanerogams

Phanerogams are the flowering plants which produce flowers and seeds. This sub-
kingdom contains plants with well-developed body. Plant body is well differentiated
into roots, stem and leaves. They also have well developed vascular tissues.

Differences between flowering plants and non-flowering plants

S.N. Flowering Plants S.N. Non-flowering Plants
1 They bear flowers in them.
1 They do not bear flowers in them.

2 They fall under the sub-kingdom 2 They fall under the sub-kingdom

Phanerogams. Cryptogams.

3 They consist of only the green plant. 3 They consist of both green and

non-green plants.

4 They are more developed compared 4 They are less developed.
to non-flowering plants.

This sub-kingdom is divided into two divisions. They are:
a) Division gymnosperms and
b) Division Angiosperms

a. Division Gymnosperms
Gymnosperms are the phanerogams that have naked seeds. The seeds of
gymnosperm are developed from the ovules which are not enclosed inside
the ovary. That is why they do not have fruits. They lack true flower. Instead,
they bear woody cones. So, they are also known as conifers. Gymnosperms are
usually found in cold areas where snowfall occurs.

Salient features of Gymnosperms
i. They have naked seeds i.e. seeds are not enclosed inside fruits.
ii. They bear separate male and female cones in them.
iii. They have long and pointed leaves.
Examples are Pine, Cycas, Fir, Spruce, Cedar etc.

Cycas Cedar Pine Cones of pine

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FACT WITH REASON

Why is pine called a gymnosperm?
Pine bears cone instead of a true flower. It has naked seeds developed from the ovules which are
not enclosed by any ovary wall. So, pine is called a gymnosperm.

b. Division Angiosperms

Angiosperms are the phanerogams that have seeds inside fruit. That is why, they
have seeds enclosed inside fruit. Angiosperms are the most advanced plants in
the whole plant kingdom.

Salient features of Angiosperms
i. They have closed seeds, i.e. seeds are enclosed inside fruits.
ii. They bear true flowers with reproductive parts in them.
iii. They have cotyledons in their seed.

Based on the number of cotyledons in the seed, angiosperms are divided into
two sub-divisions. They are:

i) Monocotyledons plants ii) Dicotyledons plants

i) Sub-division: Monocotyledons (Monocots): Angiosperms with one
cotyledon in their seed are called monocotyledons or monocots. Some
characteristic features of monocotyledons are:

i. They have only one cotyledon in MEMORY PLUS
their seed.
Unlike the roots in mustard, monocots
ii. They have long and narrow leaves have fibrous or adventitious roots in
with parallel venation. them which have no branches and
sub-branches. They grow as a cluster
iii. They have fibrous root system. from the base of stem and usually
have uniform size.
iv. They have distinct nodes and
internodes in their stem.

Examples: maize, bamboo, paddy, wheat, buckwheat, etc.

Sugarcane Maize Rice

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ii) Sub-division: Dicotyledons (Dicots): Angiosperms with two cotyledons
in their seed are called dicotyledons or dicots. Some characteristic features
of dicotyledons are:
i. They have two cotyledons in their seed.
ii. They have short and flat leaves with reticulate venation.
iii. They have tap root system.
iv. Nodes and internodes are not distinct.
Examples are: mustard, gram, soybean, rose, apple, etc.

Mustard Pea Mango

Differences between angiosperm and gymnosperm

S.N. Gymnosperms S.N. Angiosperms

1 Gymnosperms are open seeded or 1 Angiosperms are closed seeded

naked seeded plants. plants.

2 Cone is the reproductive part in 2 Flower is the reproductive part in

the gymnosperm. the angiosperm.

3 They do not have fruit. 3 They have fruit.

4 They have needle shaped leaves. 4 Leaves are usually flat, broad or
elongated.

ACTIVITY 4

Collect the different parts of plant of any two monocots and two dicots. List their
differences.

Differences between monocotyledons and dicotyledons

S.N. Monocotyledons S.N. Dicotyledons

1 Monocotyledons bear one 1 Dicotyledons bear two cotyledons
cotyledon in their seed. in their seed.

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2 They have fibrous root system. 2 They have tap root system.

3 Distinct nodes and internodes are 3 Distinct nodes and internodes

present in their stem. are not present in their stem.

4 They have long narrow leaves 4 They have short flat leaves with

with parallel venation. reticulate venation.

16.3 Structure of a Flowering Plant

Plants that bear flowers are called flowering plants. A typical flowering plant is
composed of root and shoot system. The shoot system is composed of parts like stem,
node, branch, leaves, flower, buds and fruits. Rose, mustard, soybean, sunflower, etc.
are the examples of flowering plants. In this unit, we will discuss some details of
mustard plant.

Mustard Plant (Brassica campestris)

Mustard is one of the important flowering plants cultivated in the Terai and Hilly
region of Nepal. It is mostly used for extraction of oil from its seeds. Its young leaves
are also eaten as vegetables.

Classification of Mustard Plant
Kingdom : Plant

Sub-kingdom : Phanerogams
Division : Angiosperm
Sub-division : Dicotyledon
Type : Mustard

Mustard plant is a herbaceous plant. Like other
flowering plants, the plant body of mustard is divided
into two major systems. They are root system and the
shoot system.

The Root System

Mustard is a dicot plant. It has a tap root system. The
main root in the tap root system is called primary root.
Primary root is thick at its base and tapers down to the
ground. It bears a number of branches that spread
wider in the soil. These branches are called secondary
roots. Secondary roots also bear number of other
branches. These branches are called tertiary roots. The
growing tip of the roots is called root tip or apex. It is system

202 Living Beings: Plant Life

very delicate and is covered by groups of dead cells called root cap. Root cap protects

the apex and also helps to penetrate deeper into the soil or rock layers to search for

water. Roots also bear fine unicellular hairs called root Primary root
hairs. These hairs absorb moisture from the soil. Secondary root

Function of roots Tertiary root

i. The main function of root is to absorb water and

minerals from the soil.

ii. It fixes the plant body to the soil.

iii. It anchors the soil and prevents soil erosion. Root hair

The Shoot System Root tip
Root cap

The parts of the plant that grow above the soil is called shoot system. Stem, branches,
leaves, fruits, flowers, buds etc. form the shoot system.

Flower Flower

Bud Fruit
Leaf

Node Stem

Stem Node

(a) Shoot system (b)

a) Stem

The stem of a mustard plant grows upright in the soil. It holds all the structures
of the shoot system. The shoot system grows with the help of stem and buds.
Apical bud and axillary bud are two types of buds responsible for the growth
and development of the shoot system. Apical buds are present at the tip (apex)
of the stem and axillary buds are present in the axil. The stem of a mustard plant
contains number of nodes and internodes. Axillary buds are found in the nodes.
In mustard plant, leaves arise from the nodes. The distance between two nodes
is called an internode.

Functions of stem
i. Stem holds the branches, leaves, fruits, flowers and buds.

ii. Stem transports food, water and minerals from one part to another.

iii. Stem keeps the plants upright in the soil.

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b) Leaf Blade (Lamina)
Leaf is a flat green structure that grows from the

stem or branches of the plant. Leaves contain green

pigment called chlorophyll. Different plants have Vein

different kinds of leaves. Dicots generally have Mid rib
short and broad leaves. The leaf of a mustard plant Petiole

is short, wide and tapered with uniform irregular Stem
edges. It arises from the nodes in the stem. It has
two main parts: petiole and lamina. Lamina is the Structure of leaf

flat green portion of the leaf. Petiole is a thin narrow stalk that joins lamina to the

stem. The leaf that has a petiole is called a petiolated leaf. Similarly, the leaf that

is directly attached to the node without a petiole is called a sessile leaf. Mustard

leaf also contains a midrib that runs from petiole to the leaf apex. The veins are

present on either side of the mid rib. These veins are further divided into small

veinlets that transport water, minerals and food in and out of the leaf. Veins are

also the skeletal framework of a leaf. The arrangement of veins and veinlets in a

leaf is called venation. The leaf of mustard has reticulate venation.

Functions of leaf

i. Leaves perform photosynthesis to prepare food.

ii. The stomata present in the leaves take in carbon dioxide during
photosynthesis and oxygen during respiration.

iii. Stomata of leaves lose excess water in the form of water vapour by the
process called transpiration.

ACTIVITY 5

Divide yourselves into four groups. Get a complete mustard plant for each group.
Observe its vegetative parts and discuss with your friends and teacher.

c) Flower MEMORY PLUS

Flower is the reproductive part of a plant. Different Rafflesia arnoldii is the largest flower
kinds of plants have different kinds of flowers. They found in Island of Indonesia. It is a
differ in shape, size and colour. The flower of a parasitic and has no distinct stems,
mustard plant is small in size and yellow in colour. leaves and branches. The flower is
It is a complete flower as it contains all four whorls about 100 centimetres in diameter,
namely; calyx, corolla, androecium and gynoecium. and weigh up to 10 kilograms.

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i) Calyx: The group of sepals that forms the outermost

whorl of a flower is called calyx. A mustard flower has

four free sepals. It is usually green in colour. Calyx

encloses and protects the flower during bud stage and

conduct photosynthesis for flower.

ii) Corolla: The coloured part formed by a group of petals

that form the second whorl of a flower is called corolla. A

mustard flower has four free petals. It surrounds the

androecium and gynoecium of the flower. It is usually

colourful. Corolla protects the reproductive organs

during their development and attracts insects and animals

for pollination.

iii) Androecium : The group of stamens or male Anther
reproductive parts that forms the third whorl of a

flower is called androecium. A mustard flower has Filament
six stamens. A stamen has two parts: anther and

filament. An anther is a top bi-lobed part of the

stamen. It contains numerous small sacs called pollen sacs. The pollen sacs

have tiny male reproductive units called pollen grains.

iv) Gynoecium : The carpel (pistil) or group of carpels that Stigma
forms the innermost whorl of a flower is called gynoecium. Style
It is also called the fourth whorl of a flower. Mustard flower

contains two fused carpels. This fused structure is called a Ovary
pistil. A pistil is divided into three different parts: stigma,

style and ovary. Stigma is the uppermost part of the pistil

which receives pollen grains. Style is a stalk that joins ovary

and stigma. Ovary is the swollen part at the base of the pistil.

It contains ovule. The ovule holds the female reproductive cell called egg

or ovum. Ovule after fertilization develops into seeds and ovary develops

into fruit.

Unisexual and Bisexual Flower

Some flowers may contain either male or female reproductive parts while other flowers
may contain both parts. Flower that contains only one reproductive part (either male
or a female part) is called a unisexual flower. Examples are pumpkin, cucumber etc.
A flower that contains both male and female parts in it is called a bisexual flower.
Examples are mustard, rose, tomato, sunflower, etc.

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Complete and Incomplete flowers

Some flowers have all the four parts while others have some missing parts. The flower
that has all the four parts, i.e. calyx, corolla, androecium and gynoecium is called a
complete flower. Mustard, rose, pea, etc. have complete flowers. Likewise, the flower
which does not contain all the four parts is called an incomplete flower. The flowers
of pumpkin, bottle gourd, etc. are incomplete flowers. Those flowers which contain
only stamens but no pistils are called staminate flowers. They are considered as male
flowers. Likewise, those flowers which contain only pistils but no stamens are called
pistillate flowers. These flowers are female flowers. Both staminate and pistillate
flowers are incomplete flowers.

16.4 Pollination

When the stamens of a mustard plant become MEMORY PLUS
mature, the anther dries out and bursts. During
bursting, it releases mature pollen grains from the About one-third of the human diet
pollen sac. The mature pollen grains fall on the is derived from insect-pollinated
stigma of the gynoecium. The process of transfer of plants, and honey bees are
pollen grains from the anther of androecium to the responsible for 80 percent of this
pollination.

stigma of gynoecium is called pollination. All pollen

grains do not fall on the stigma. They may also fall on other parts of a flower and get

wasted.

There are two types of pollination. They are:
a) Self-pollination and
b) Cross-pollination.

a) Self-pollination

Self-pollination is the transfer of the Self-pollination Cross-pollination
pollen grains from anther to stigma of the
same flower or flowers of the same plant. Stamen
This is a common process of pollination Pistil
in bisexual plants. Apricots, figs, peaches,
plum, apple, etc. are self-pollinating
plants.

b) Cross-pollination Pollination

Cross-pollination is the transfer of pollen grains from anther to stigma of different
flowers of different plants of the same species. Insects, animals, wind, water and
even human beings are the major agents of cross-pollination. This types of pollination
occurs in both bisexual and unisexual plants. Cross pollination is more common in
mustard, pumpkin, cucumber, sunflower, etc.

206 Living Beings: Plant Life

16.5 Fertilization

When the pollen grains inside the anther are Polar Pollen grain
matured, they burst out. Some of these pollen nuclei Stigma
grains land on the stigma of the flower. Out of
many pollen grains, one produces a long tube Egg Style
through the stigma, style and penetrates the ovary Pollen tube
and ovule. This tube is called a pollen tube. The Ovary
pollen grain travels through the pollen tube and Embryo sac
finally reaches the egg. Then, the male gamete Micropyle
within pollen grain fuse with egg cell. The process
of fusion of male gamete (sperm) with the female Fertilization of mustard plant
gamete (egg) to form a zygote is called fertilization.

After fertilization, there is formation of a zygote. A diploid cell resulting from the
fusion of a male and female gamete is called zygote. A zygote divides continuously
to form an embryo. An embryo is a multicellular structure formed by the growth of
a zygote. The fertilized ovule (embryo and endosperm) forms the seed. The embryo
is the baby plant inside the seed. Similarly, an
endosperm is a structure that provides nutrients for MEMORY PLUS
the growth and development of the embryo inside. A zygote is the first cell of the baby
The tissues of ovary develop into a fruit. Seeds plant which is formed from the
released from the fruit germinate in the soil under fusion of male and female gametes.
favourable condition.

ACTIVITY 6

Divide yourselves into four groups. Get a complete mustard plant for each group.
Observe its flower and discuss with your friends and teacher.

STEPS EXERCISE

STEP 1

1. Fill in the blanks with appropriate words.
a) ……………. is the group of autotrophic green thallus plants.
b) Examples of ……………. are yeast, mucor, mold, mushroom etc.
c) ……………. are also known as amphibious plants.
d) ……………. are the cryptogams that contain vascular tissues (xylem and
phloem) in their body.
e) ……………. protects the reproductive organs during their development
and attracts insects and animals for pollination.
f) ……………is formed after the fusion of male and female gametes.

Modern Concept Science and Environment - 7 207

2. Write True for the correct and False for the incorrect statements.
a) Angiosperms are also called conifers.
b) Transpiration is the process of losing water by plants through stomata.
c) Calyx is a group of petals.
d) Cucumber bears unisexual flower.
e) Mustard plant has incomplete flower.

STEP 2

3. Answer the following questions in one word.
a) Name the sub-kingdom of non-flowering plants.
b) Which group of plants do not have chlorophyll?
c) What is the term for single unit of calyx?
d) Which natural process produces zygote?
e) What kind of root system has branches and sub-branches on the main root?

4. Differentiate between:
a) Spirogyra and Mushroom
b) Fern and moss
c) Dicots and monocots
d) Stamen and Pistil
e) Calyx and corolla
f) Tap root and fibrous root
g) Pollination and fertilization

5. Give reasons.
a) Mushroom is a fungi.
b) Spirogyra is an algae.
c) Bryophytes are also called amphibian plants.
d) Pteridophytes are also called vascular plants.
e) Pea is a dicot but maize is a monocot.
f) Pine is a gymnosperm.

6. Classify the following plants:

a) b) c)

208 Living Beings: Plant Life

d) e) f)

STEP 3

7. Answer the following questions
a) Define cryptogams and phanerogams.
b) What is a bryophyte? Write any three examples.
c) What are fungi? Write down their main characteristics.
d) Define monocots and dicots.
e) Describe the structure of roots of mustard plant.
f) Describe the major structure and function of leaves.
g) Name the whorls of a flower and list their functions.
h) What is pollination? Define self-pollination and cross-pollination.
i) Define fertilization. Describe the process of fertilization in mustard plant.
j) Write two major characteristics of the following plants:
a) Marchantia b) Fern c) Pine
d) Wheat e) Mushroom f) Spirogyra
k) What is a zygote? How is it formed?

8. Draw a labelled diagram of the following:
a) Mustard plant
b) Mustard leaf
c) Androecium
d) Gynoecium

UNIT Estimated teaching periods TheoMryoderPnrCacotnicceapl t Science and Environment - 7 209
63
17
Cell and Tissue

Syllabus issued by CDC Plant cell

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

LEARNING OBJECTIVES

At the end 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).

Key terms and terminologies of the unit

1. Cell: A cell is the structural and functional unit of life.

2. Prokaryotic cell: Thecell thatlacks anorganized nucleusandothermembrane
bound cell organelles is called prokaryotic cell.

3. Eukaryotic cell: The cell that has well organized nucleus and membrane
bound cell organelles is called eukaryotic cell.

4. Unicellular organisms: Those organisms which are made up of a single cell are
called unicellular organisms.

5. Multicellular organisms: Those organisms which are made up of more than one cells
are called multi-cellular organisms.

6. Cell wall: Cell wall is the outermost tough covering of a plant cell.
7. Cell membrane:
Cell membrane or plasma membrane is the semi-permeable
membrane that surrounds the cytoplasm.

8. Cytoplasm: Cytoplasm is the substance that is present between the
nucleus and the plasma membrane.

9. Mitochondria: Mitochondria  are the rod or oval shaped cell organelles
which produce energy in the cell.

210 Cell and Tissue

10. Nucleus: Nucleus is a round cell organelle which controls the overall
activities of a cell. It is also called brain of the cell.

11. Vacuoles: Vacuoles are the single-membrane cell organelles that store
essential materials and wastes.

12. Plastid: Plastids are the double layered cell organelles that store food,
give colour to the petals and produce food.

13. Endoplasmic reticulum: Endoplasmic reticulum is the branching tubules and flattened
sacs that extend throughout the cytoplasm.

14. Ribosomes: Ribosomes are the small granular structures which are the
site of protein synthesis.

15. Lysosomes: Lysosomes are the membrane-bound sacs that contain
digestive enzymes.

16. Chloroplasts: Thegreenplastidspresentinplantcellsarecalledchloroplasts.

17. Plasmodesmata: Plasmodesmata are the pores in the cell wall that help to
transport substances from one cell to the another cell.

18. Tentacles: Tentacles are the small arm like projections around the
mouth of hydra.

17.1 Introduction

The body of living organisms is made up of tiny building blocks called cells. Cells are
the basic unit of life. They are responsible for performing living activities in organisms
such as growth, reproduction, excretion, etc. A single cell contains all the vital
structures and substances for their independent function. The body of living organism
as a whole is the sum of activities of all the cells. Hence, cell is called structural and
functional unit of life.

The word ‘cell’ was first coined by an

English scientist named Robert Hooke

in 1665 A.D. When he observed thin

slice of wooden cork under his own

crude microscope. He noticed the

rows of tiny boxes that are made up

the dead wood’s tissue and named a

box as cell. Antonie van Leeuwenhoek

invented an advanced microscope A compound microscope
during the same time and observed,

drew and described various cellular living forms. Later in 1839, German botanist

Matthias Jakob Schleiden and German zoologist Theodor Schwann proposed that all

living beings are made up of cells.

Modern Concept Science and Environment - 7 211

FACT WITH REASON

Why is a cell called the structural and functional unit of life?
Cell is called the structural and functional unit of life because the structure of an organism
depends upon the number of cells. Also, everything performed by an organism is the outcome of
the work done by the cells.

Prokaryotic and Eukaryotic Cells

On the basis of structure and composition, cells are divided into two major categories.
They are Prokaryotic cell and Eukaryotic cell.

Prokaryotic cell Eukaryotic cell

The cell that lacks an organized nucleus and other membrane bound cell organelles is
called Prokaryotic cell. Such cells are only found in Bacteria and Archaea.

The cell that has a well-organized nucleus and membrane bounded cell organelles is
called eukaryotic cell. Cells of plants and animals are the examples of eukaryotic cells.

FACT WITH REASON

Why are bacteria called prokaryotes?
Bacteria are called prokaryotes because they do not have an organized nucleus and membrane
bound cell organelles.

17.2 Cell Shape, Size and Number

Prokaryotic cells are rod like, spherical or spiral in MEMORY PLUS
shape. They are the tiniest cells and ranges from 1. Mycoplasma is the smallest cell.
0.0001 to 0.003 mm in diameter. Eukaryotic cells also 2. Egg of ostrich is the largest cell.
have different shapes like irregular (amoeba), oval, 3. Nerve cell in the neck of giraffe is the
circular, spherical (animals) or hexagonal (plants). longest cell.
Eukaryotic cells are typically about ten to hundred
times larger than the prokaryotic cells. Mycoplasma, a smallest prokaryotic cell, has a
diameter of about 0.0001mm. Similarly, an ostrich egg has the largest eukaryotic cell
measuring about 120 mm in diameter. Likewise, a nerve cell of Giraffe is the longest
cell which measures about 3m in length.

212 Cell and Tissue

Unicellular and multicellular organisms

On the basis of number of cells, organisms are divided into two groups. They are:
unicellular organisms and multicellular organisms. Organisms that are made up of a
single cell are called unicellular organisms. Examples: amoeba, paramecium, Euglena,
Chlamydomonas, etc. Organisms that are made up of more than one cells are called
multi-cellular organisms. Examples: Cow, dog, man, sunflower, ant, spider, mosquito,
etc. are the examples of multicellular organisms.

FACT WITH REASON

Euglena is a unicellular organism. Why?
Euglena is a unicellular organism because its body is made up of only one cell.
Hydra is called a multicellular organism. Give reason.
Hydra is called a multicellular organism because its body is made up of many cells.

Detailed Structure of a Typical Cell

Cells differ in shape, size and functions. But, most of the cells contain some basic living
structures inside them known as cell organelles. These cell organelles have specific
structure and functions. Some of the important cell organelles are discussed below.

Pinocytotic vesicle Mitochondrion Ribosome Cell wall
Lysosome Golgi apparatus Cell membrane
Nucleolus Endoplasmic Golgi apparatus
Endoplasmic reticulum (ER) Chloroplast
reticulum (ER) Nucleus Vacuole membrane
Nucleolus
Smooth ER Nucleus Raphide crystal
Druse crystal
Cell membrane Rough (ER) Mitochondria

Centrioles Cytoplasm

Large central vacuole
Microtubules

Cytoplasm
Ribosome

Animal cell Plant cell

a. Cell wall

Cell wall is the outermost tough covering of a plant cell. It is absent in animal
cell. Cell wall is mainly composed of non-living materials called cellulose. Cell
wall maintains rigidity of the cell. It is a permeable membrane. Plasmodesmata
are the pores present in the cell wall that help to transport substances from one
cell to the another cell.

Functions
i. Cell wall protects the cell from external injuries.

ii. It maintains the shape and size of the cell.

iii. It helps in transporting substances in and out of the cell.

Modern Concept Science and Environment - 7 213

b. Cell membrane or Plasma membrane

Cell membrane or plasma membrane is the semi-permeable membrane that
surrounds the cell. It is made up of phospholipids and proteins. It acts as a first
and outer covering in an animal cell. But in plant cell, it is the second covering
present inner to the cell wall. It is a thin and elastic membrane with numerous
pores on it. Cell membrane allows only selective substances to pass in and out
of the cell. So, it is also called a semi-permeable membrane.

Functions
i. It acts as a protective covering of a cell.

ii. It helps in the selective transport of chemical substances in an out of the cell.

iii. It also helps in communication among the cells in animals.

Differences between cell wall and cell membrane

S.N. Cell wall S.N. Cell membrane

1 Cell wall is made up of cellulose. 1 Cell membrane is made up of lipid
and protein.

2 Cell wall is dead and it is permeable. 2 Cell membrane is living and it is
semi-permeable.

c. Cytoplasm

Cytoplasm is the fluid-like substance that is present between the nucleus and
the plasma membrane. Cell organelles float freely in the cytoplasmic fluid. It is
made up of lipids, proteins, minerals and water. Proteins in cytoplasm are also
called the cytoskeleton as they maintain the shape of the cell.

Functions
i. Cytoplasm maintains the turgidity of the cell.
ii. It forms the skeleton of the cellular body.
iii. It anchors different cell organelles in it.
iv. It distributes nutrients and enzymes within the cell organelles.

d. Mitochondria

Mitochondria are the rod or oval shaped cell

organelles that produce and store energy in the

cell. They are found distributed in the cytoplasm.

All cells need energy to perform their functions.

In most of the cells, energy is produced in the

mitochondria. Without mitochondria, energy

cannot be produced from the food we eat. A

process called respiration occurs in mitochondria. Mitochondria

Respiration is the process by which energy is produced by utilizing food and

214 Cell and Tissue

oxygen in the cell. The inner membranes of the mitochondria have finger like
projections where respiration occurs. This produces energy in the cell in the form
of a chemical called adenosine triphosphate (ATP). So, mitochondria is also called
the powerhouse of a cell.

Functions
i. Mitochondria produces energy needed for various cellular activities.
ii. They also involve in synthesis of smaller units of proteins called amino acids.

FACT WITH REASON

Why are mitochondria called the powerhouse of the cell?
Mitochondria are called the powerhouse of the cell because they perform cellular respiration to
release energy and store it.

e. Nucleus

Nucleus is a double layered round Chromatin network

cell organelle. It contains nuclear Nuclear membrane

membrane, chromatin fibres, nucleolus Nucleolus

and nucleoplasm. Nuclear membrane is Nuclear pore Necleoplasm

the outermost covering of the nucleus.

A dark spot inside the nucleus is called Structure of nucleus
nucleolus. In a plant cell, nucleus lies at

the periphery of the cell membrane. But, in animal cell, nucleus lies at the centre

of the cell.

Functions
i. Nucleus controls the metabolic activities in the cell. So, it is also called the
control centre.

ii. Nucleus synthesis proteins.

iii. It helps in cell division which is necessary for the growth and development
of living body.

iv. The DNA present in the nucleus helps to transfer the hereditary information
from the parents to the offspring.

f. Vacuoles

Vacuoles are the membrane bound structure present
in the cytoplasm. The fluid inside the vacuole is
called cell sap. Cell sap is made up of mostly water
with various dissolved substances like sugar, salts
and other chemicals. The outer covering of vacuole is
called tonoplast. Plant cell has a large central vacuole
while an animal cell has many smaller vacuoles.

Modern Concept Science and Environment - 7 215

Functions
i. Vacuole stores water, sugar, salts and other waste materials of the cell.

ii. The space inside the vacuole helps to maintain the turgidity of the cell.

g. Plastids
Plastids are the disc shaped double layered cell organelles found only in the plant
cells. There are three kinds of plastids. They are chloroplast, chromoplast and
leucoplast. Chloroplasts contain chlorophyll. They are the site of photosynthesis.
Chromoplasts contain colour pigments. They give colour to the different parts
of the plants like fruits and flowers. Leucoplasts do not contain any pigments
and are colourless. They are found in roots and other storage organs.

Chloroplast Chromoplast Leucoplast

Functions
i. Chloroplast helps to trap sunlight for photosynthesis.

ii. Chromoplast helps to ripen fruits and provides colour to the flowers.

iii. Leucoplast is involved in the synthesis of starch, oils and proteins.

FACT WITH REASON

Chloroplast is called the kitchen of the cell. Give reason.
Chloroplast is called the kitchen of the cell because it prepares the food needed for the plant.

h. Endoplasmic reticulum Endoplasmic reticulum

Endoplasmic reticulum is the branching tubules
and flattened sacs that extend throughout the
cytoplasm. They act as skeleton of the cell and
provide mechanical support. They form pathways
inside the cell for the transportation of essential
chemicals and wastes. There are two types of
Endoplasmic Reticulum (ER). They are Rough ER
and Smooth ER. Rough ER has ribosomes attached
to it and smooth ER does not. Rough ER is the site
for protein synthesis.

216 Cell and Tissue

Function
i. Endoplasmic reticulum transports molecules to specific destination.

ii. Rough ER transports proteins to various parts of the cell.

iii. Smooth ER helps in lipid formation.

iv. Endoplasmic reticulum also provides mechanical support to the cell.

i. Golgi bodies or golgi apparatus

Golgi bodies or Golgi apparatus are the Vacuole
network of flattened layers of membrane-
bound sacs. They are located near the Cisternae
nucleus.
Secretory
vesicle

Function Golgi complex

i. They store, package, and distribute the proteins and lipids made in the
endoplasmic reticulum.

ii. They also manufacture substances like cellulose and pectin.

j. Ribosomes

Ribosomes are the small granular structures that Ribosomes
float freely in the cytoplasm or are bound to the
endoplasmic reticulum. They are the site of protein
synthesis.

Function

Ribosomes synthesis proteins.

k. Lysosomes

Lysosomes are membrane-bound sacs that contain digestive enzymes. These
enzymes are manufactured in the rough endoplasmic reticulum. If the lysosome
breaks open, the enzymes can destroy the cell by digesting the cellular organelles.
So, it is also called suicidal bag.

Function MEMORY PLUS

a) Lysosomeshelp in intra-cellular Lysosomes  are called  suicidal
bags because if lysosome breaks open,
digestion. the enzymes can destroy the cell by

b) They engulf viruses or bacteria and digesting the cellular organelles with

protect the cell organelles from foreign their digestive enzymes.

bodies.

Modern Concept Science and Environment - 7 217

ACTIVITY 1

To observe onion cells under a compound microscope.
Take an onion and remove its outer dry scales. Cut a small
section of it or take its fleshy layer out from the onion bulb.
Peel a thin transparent layer carefully with forceps which
can be seen on the bulb layers. Place it in a watch glass
containing water. Transfer the slice of thin layer into the
glass slide. Add a drop of saffron for colour and wash it
with distilled water. Observe the slide under a compound
microscope.
Draw the diagram you observe and list some features of
the cell including the parts of the cell you can distinguish
and their functions.

Differences between plant cell and animal cell

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

1 Plant cell is usually larger than an 1 Animal cell is comparatively

animal cell. smaller in size.

2 It has cell wall. 2 It does not have cell wall.

3 Plastids are present in plant cell. 3 Plastids are absent in animal cell.

4 It contains a large central vacuole. 4 It contains many small vacuoles.

5 Nucleus lies on one side in the 5 Nucleus lies at the centre.
peripheral cytoplasm.

6 Centrioles are usually absent. 6 Centrioles are present.

7 Reserve food is in the form of 7 Reserve food is in the form of

starch. glycogen.

8 Lysosomes are rare. 8 Lysosomes are always present.

17.3 Unicellular and Multicellular Organisms

Unicellular organisms are those microscopic organisms which are composed of
a single cell. Examples: amoeba, euglena, paramecium, etc. In these organisms,
respiration occurs through general body surface. They have different organs like
flagella (euglena), pseudopodia (amoeba), cilia (paramecium), etc. for movement.

218 Cell and Tissue

Multicellular organisms are those organisms which are made up of two or more
cells. Examples: most plants and animals like cow, man, ant, fly, mosquito, banyan
tree, grass, etc. Based on the development of multicellular animals, they have tissues,
organs and systems for specific activities to support life processes.

Amoeba

Introduction

Amoeba is a unicellular microscopic organism.
The scientific name of a common amoeba
is Amoeba proteus. Amoeba is a freshwater
organism and it is found in pond, ditches, wet
soil and even as parasites in animals. The name
amoeba comes from the Greek word amoibe,
which means change.

Anatomy of amoeba Amoeba

An amoeba consists of transparent and gelatin like irregular shaped body surrounded

by a thin, elastic and semi-permeable membrane called plasmalemma. It contains a

nucleus and membrane bound organelles such as food vacuole, contractile vacuole,

Golgi apparatus, mitochondria, etc. Its size ranges from 0.2 mm to 1mm in diameter.

Locomotion and Food habit

Amoeba moves by changing the shape of its body by forming temporary false feet
called pseudopodia. It eats algae, bacteria, plant cells and protozoa. They engulf food
particles by surrounding them with their pseudopodia forming a bubble-like food
vacuoles. The food vacuole digests the food. Wastes and excess water are transported
outside the cell by contractile vacuoles.

Reproduction

Amoebas reproduce asexually by binary fission. The nucleus of a parent cell divides
first and then the cytoplasm divides into two portions. Finally, a parent cell produces
two smaller daughter cells. Each cell develops into a new amoeba.

Respiration

Amoeba breathes through general body surface. MEMORY PLUS
The plasmalemma contains small pores which allow
dissolved oxygen to pass inside and carbon dioxide A species of amoeba called the
outside of their body. Naegleria fowleri is known as the
brain-eating amoeba. They are
found in warm fresh water. If infected

Effects of amoeba on Human Beings with this species of amoeba, then it
will slowly destroy the brain tissue. It
All species of amoeba are not harmful to us. Some results in death within a week.
amoeba species are endoparasites in human beings

that cause different health problems. Some of them are discussed below:

Modern Concept Science and Environment - 7 219

a) Entamoeba histolytica

Entamoeba histolytica is the parasitic amoeba

that causes amoebiasis or amoebic dysentery.

E. histolytica enters the wall of the intestine that

causes intestinal ulcers, bleeding, increased

mucus production and diarrhoea. These amoeba

may also pass into the bloodstream and travel to

the liver or rarely to the brain. In the liver and Entamoeba histolytica
brain, they form pockets of infection (abscesses).

Amoebiasis is most common in developing countries that have poor sanitary

conditions. Mild Amoebiasis is associated with stomach pain and stomach cramping.

But a severe form of amoebiasis is amoebic dysentery. Amoebic dysentery can cause

stomach pain, fever and bloody stool. Other health complications arise when amoeba

infects brain and lungs.

Control measures of amoebiasis

Drinking boiled or disinfected water is a safe way to avoid Entamoeba histolytica. Taking
contaminated water, ice cubes, vegetables without treatment and non-pasteurized
dairy products should also be avoided.

b) Entamoeba gingivalis

Entamoeba gingivalis is another amoeba that is found in the oral cavity and causes
pyorrhoea. Pyorrhoea is the inflammation of gum with discharge of pus. This
protozoan lives in the oral cavity of humans and feeds on teeth tissue. It can be found
within the spaces of the teeth, gums or tonsils. It transmits from one person to another
through mouth to mouth kissing and sharing of eating utensils.

Control measures of pyorrhoea

Elimination of this protozoa from the oral cavity is the treatment to this disease.
Maintaining proper oral hygiene can also prevent this disease.

c) Entamoeba coli

Entamoeba coli lives inside the large intestine of the human body. They never enter into
the mucosa or sub-mucosa layers or other tissues of the intestine to cause intestinal
wounds. But, they occasionally ingest red blood cells. Large population of E. coli
inside the gut lumen may cause dyspepsia, hyperacidity, gastritis and indigestion in
humans. E. coli is not only harmful but also useful to us. It consumes undigested food
and helps us in digestion.

Entamoeba gingivalis Entamoeba coli

220 Cell and Tissue

Hydra

Structure

Hydra is a multicellular aquatic invertebrate. It belongs to the Hydra
Phylum Coelenterate. It is a simple two-layered animal with
cylindrical body. It is surrounded at one end by 6-10 tentacles.
Most hydra range in size from 0.25 to 2.5 cm. The body of
a hydra is made up of two layers of cells: an outside layer is
called ectoderm and an inside layer is called endoderm. Hydra
is equipped with poison-containing structures in the ectodermal
layer. These are called stinging cells or nematocysts. Stinging
cells in the tentacles paralyze the prey. Respiration and excretion
occurs through the general body surface.

Food habits and Locomotion

Tentacles are the small thread-like projections around the mouth of the hydra. Hydra
catches its prey, paralyzes it and eats it.

Hydra is usually sessile. But, it can also move from one place to another by swimming,
looping and somersaulting.

Looping

During looping, the head of hydra stretches to bend on the side. Then, the tentacles
attach themselves to the substratum. It then releases its foot and pulls it to attach near
the tentacles. Then, it releases the tentacles to become erect again. Hydra does looping
to travel short distances.

Somersaulting

In somersaulting, the head with tentacles bend over to the side and attach to the
substratum. Then, it releases its basal foot, makes a 180 degrees turn to the same
direction and releases its tentacles to become erect again. This process is repeated
many times. Hydra somersaults to travel long distances.

Somersaulting

Reproduction

Hydra reproduces asexually by budding. Buds develop from the body surface of
the hydra and grow into full-sized adults. Eventually, the buds leave the parent and
become independent. Hydra also regenerates into new individual from its larger
fragments.

Modern Concept Science and Environment - 7 221

Reproduction of hydra

Differences between amoeba and hydra.

S.N. Amoeba S.N. Hydra

1 Amoeba reproduce asexually by 1 Hydra reproduce asexually by

binary fission. budding.

2 Amoeba move with the help of 2 Hydra move with the help of

pseudopodia. tentacles.

STEPS EXERCISE

STEP 1

1. Fill in the blanks with appropriate words.
a) …………… cells are found only in bacteria and archaea.
b) …………… produces energy in the cell.
c) ……………is a control centre of the cell.
d) …………… gives colour to different parts of the plants.
e) Amoeba reproduce asexually by ……………
f) Entamoeba histolytica is the parasitic amoeba that causes ……………

2. Write True for the correct and False for the incorrect statements.
a) A single cell contains all the vital structures and substances for its
independent function.
b) The main material of the cell wall is wax.
c) Lysosomes are called suicidal bags of the cell.
d) Vacuoles synthesize proteins.
e) Entamoeba gingivalis causes diarrhoea.
f) Hydra reproduces asexually by budding.

222 Cell and Tissue

3. Select the best answer from the given alternatives.
a) Which on is a prokaryotic organism?
i) Paramecium ii) Hydra iii) Bacteria iv) Amoeba
b) ………………… is the largest cell.
i) Ostrich leg ii) Bacteria
iii) Ostrich egg iv) Neuron
c) The molecule produced in mitochondria is

i) ATP ii) DNA iii) RNA iv) NTP
d) What causes amoebic dysentery?

i) E. coli ii) E. gingivalis
iii) E. histolytica iv) Hydra

e) ...................... is capable of digesting even the cell organelles.
i) Ribosome ii) Lysosome iii) DNA iv) Nucleus

f) Which one of the given cell organelles is a non-living?
i) Mitochondria ii) Cell wall
iii) Nucleus iv) Plastids

4. Match the following. i) Control centre of the cell
a) Cell wall

b) Cell membrane ii) Tentacles
c) Cell sap iii) Cellulose
d) Nucleus iv) Plasmalemma
e) Amoeba v) Vacuole

f) Hydra vi) Pseudopodia

STEP 2

5. Answer the following questions in one word.
a) Which material makes the cell wall?
b) Which cell organelle produces energy for the cell?
c) Which cell organelle controls the cell.
d) Which plastid is colourless?
e) Which plastid helps in photosynthesis?
f) What is the outermost layer of plant cell called?
g) Name the site for the production of energy in the cell.

6. Differentiate between:
a) Cell wall and cell membrane
b) Amoeba and hydra

Modern Concept Science and Environment - 7 223

c) Unicellular organisms and multicellular organisms
d) Eukaryotic cell and prokaryotic cell

7. Give reasons.
a) Cell is the structural and functional unit of life.
b) Bacteria are called prokaryotes.
c) Euglena is a unicellular organism.
d) Hydra is called a multicellular organism.
e) Lysosome is called suicidal bag.
f) Mitochondria are the powerhouse of the cell.
g) Chloroplast is the kitchen of a plant cell.

8. Identify the cell organelles and write their major functions.

a) b) c) d)

STEP 3

9. Answer the following questions
a) What is cell? Why is it called structural and functional unit of the life.
b) What are unicellular and multicellular organisms? Give any two examples
of each.
c) Mention the major functions of the following:
i) Cell wall ii) Cell membrane iii) Mitochondria
d) Write the scientific names of any two harmful amoebas along with the
diseases they cause.
e) Describe structure of an amoeba with the help of a diagram.
f) Explain the structure of a hydra with the help of a diagram.
g) Explain the locomotion in amoeba and hydra.
h) Explain reproduction in amoeba and hydra?

10. Draw the well labelled diagram of the followings:

a) Plant cell b) Animal cell

c) Amoeba d) Hydra

224 Life P roEcsteimssaetesd teaching periods Theory Practical
UNIT 10 2

18 Life Processes

Syllabus issued by CDC Lungs

 Respiration – Introduction
 Respiration in animals and plants
 Digestive system in human beings
 Process of digestion
 Excretion in plants and animals
 Excretion in human body

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 introduce respiration and explain various breathing organs of organisms, viz. skin,

gills, trachea, spiracles, lungs and stomata.
 explain breathing in plants and animals.
 introduce digestive system in human body and explain it in brief.
 introduce excretion and explain the excretion process in plants and animals in brief.

Key terms and terminologies of the unit

1. Life process: The set of all the metabolic activities that are performed by
the organisms to make them living are called life processes.

2. Respiration: The process of breaking down the food materials in the
mitochondria with the help of oxygen to release energy is
called respiration.

3. External respiration: External respiration is the process of inhaling oxygen and
exhaling carbon dioxide.

4. Internal respiration: Internal respiration is the process of breaking down of glucose
in the mitochondria of the living cell to produce energy.

5. Cutaneous respiration: The respiration which occurs through moist body surface is
called cutaneous respiration.

6. Digestion: Digestion is a process of breaking down of complex
substances in the food into simpler and absorbable forms.

7. Alimentary canal: Modern Concept Science and Environment - 7 225

8. Digestive glands: The passage along which food passes through the body from
9. Ingestion: mouth to anus during digestion process is called alimentary
canal or digestive tract.
Digestive glands are organs that secrete enzymes for the
digestion of food.
Ingestion means the intake of food through the mouth.

10. Absorption: The process of extraction of water and other nutrients by the
small intestine into the bloodstream is called absorption.
11. Egestion:
12. Excretion: The removal of faeces through the anus is called egestion.

The process of throwing out of unwanted and harmful
substances from the body through excretory organs is called
excretion.

18.1 Introduction

The set of all the metabolic activities that are performed by the organisms to make
them living are called life processes. Respiration, digestion, circulation, transportation,
excretion, etc. are the examples of life processes. In this unit, we will discuss about
respiration, digestion, excretion, etc.

18.2 Respiration

The body of living beings need energy for all the metabolic activities occurring in the
body. Food is the main source of energy to our body. The food releases energy when
it is oxidized (burnt) in the living cell.

FACT WITH REASON

Why is respiration essential for living beings?
Respiration is essential for living beings because it releases energy that is required to perform
various metabolic activities in the body.

The process of breaking down of food materials in the living cells with the help of
oxygen to release energy is called respiration. Simply, respiration is the process of
oxidation of food to release energy. The group of organs that are involved in the
respiration are called respiratory organs.

There are two types of respiration. They are: external respiration and internal
respiration (cellular respiration).

226 Life Processes

External Respiration

External respiration is the process of inhaling oxygen and exhaling carbon dioxide.
External respiration takes place in the lungs through various parts. It is also called
breathing. In human beings, nose, larynx, pharynx, trachea, bronchi, bronchioles and
lungs comprise the breathing organs. Exchange of oxygen and carbon dioxide takes
place in the lungs. Energy is not produced in external respiration. It just enables us to
take oxygen to the blood and throw out carbon dioxide.

Internal Respiration

Internal respiration is the Breathing Cellular
process of oxidation of respiration
glucose in the mitochondria O2
of the living cells. Oxidation CO2 Mitochondria
means reaction with oxygen.
CO2

Internal respiration is also O2
called cellular respiration. Eating
Internal respiration burns

glucose and produces energy Water vapour
in the form of Adenosine

triphosphate (ATP). This

energy is used for performing various life processes in the living organisms. Carbon-

dioxide and water are also formed as the by-products during internal respiration.

Carbon dioxide is excreted through the lungs while the water is used up in various

processes. Excess water is thrown out through the kidneys.

Glucose + Oxygen Water + Carbon dioxide + Energy

C6H12O6 + 6O2 6H2O + 6CO2 + Energy

Differences between internal respiration and external respiration

S.N. Internal Respiration S.N. External Respiration

1 It is the oxidation of glucose in the 1 It is the inhaling of oxygen and

mitochondria of the cells. exhaling of carbon dioxide.

2 It releases energy in the form of 2 It does not release energy.
ATP.

3 It is also called cellular respiration. 3 It is also called breathing.

4 It takes place inside of a cell. 4 It takes place outside of a cell.

Modern Concept Science and Environment - 7 227

Exchange of Gases in Simple Animals

a) Exchange of gases through general body surface

Unicellular organisms like amoeba, paramecium, O2 inside CO2 outside
euglena, etc. and multicellular organisms like sponge,
sycon, hydra, tapeworm etc. do not have specialized Breathing in Amoeba
organs or systems for breathing. So, these organisms
breathe through their general body surfaces. During
breathing, oxygen gas is diffused inside their cells or

tissues and carbon dioxide gas is diffused out.

b) Breathing through tubes (spiracles)

Insects breathe through a set of branching air

filled tubes called trachea. These air passing

tubes are connected with the outside of the

insect’s body through paired circular openings

called spiracles. These spiracles and trachea are

the organs for respiration in insects. Oxygen

passes from spiracles to trachea and reaches

deep inside their body. Oxygen diffuses inside

the body and reaches to every cell and carbon Spiracle
dioxide releases from the same path. In larger Breathing in grasshopper
insects like wasp and grasshopper, there are

internal air sacs connected to trachea. These insects exchange gases by squeezing

the sacs to suck air from outside.

c) Breathing through gills

Fishes, molluscs and some other water animals breathe

through gills. Gills consist of a membrane containing many

blood vessels and capillaries. Gills are specialized organs to Gills
absorb dissolved oxygen from the water. When fish breathes

in oxygen through its gills, oxygen gets diffused in the Breathing organ in fish

blood capillaries. Blood capillaries carry oxygen to every cell and releases carbon

dioxide. Carbon dioxide excretes out through the same path into the water. Fishes

have internal gills but some molluscs and tadpoles have external gills.

d) Breathing through moist skin CO2 outside
Some animals like frogs, earthworm,

leech, etc. can breathe through moist
body surfaces. The respiration which O2 inside

occurs through moist body surface is

called cutaneous respiration. The skin of Breathing in earthworm and frog

228 Life Processes

frog is rich in blood capillaries. When the frog is in the water, it cannot breathe
through lungs. So, it breathes through skin in which oxygen gas gets diffused
into the blood capillaries through its skin. Similarly, carbon dioxide is diffused
out into the water. When frog comes out from the water, it breathes with its
lungs. Respiration through lungs is called pulmonary respiration.

e) Breathing through lungs

Amphibians, reptiles, birds and mammals MEMORY PLUS
breathe through lungs. Lungs have numerous
air sacs called alveoli. Alveoli are enriched 1. Our lungs always hold about 1
with blood capillaries. When animals take in litre of air in the airway no matter
oxygen into the lungs, it is diffused inside the how much we inhale or exhale. This
alveoli to blood capillaries. Likewise, the makes the lung to float on water.
carbon dioxide is released out from blood
capillaries to alveoli. Exchange of gases takes 2. Human lungs breathe in and out
place in lungs. about 8,000 to 9,000 litres of air
every day.

The respiratory system of human is

composed of nose, pharynx, larynx,

wind pipe, bronchi, bronchioles,

diaphragm and lungs. Air rich in oxygen

passes from the nose to pharynx and

larynx. Then, air passes through wind

pipe to bronchi. Bronchi are divided into

bronchioles that lead to right and left

lungs. Lungs contain alveoli which are

small air sacs rich in blood capillaries.

Oxygen diffuses into the blood stream in Human respiratory system

alveoli and carbon dioxide is diffused out from blood to alveoli. Thus, external

respiration takes place.

18.3 Respiration in Plants

Like animals, plants also take in oxygen and throw out carbon dioxide during
respiration. Stomata present in the upper and lower surfaces of leaves, lenticular cells
and general root surface are the structures for respiration in plants. Respiration is a
process just opposite to that of photosynthesis. In photosynthesis, carbon dioxide and
water make oxygen and glucose. But, in respiration, oxygen and glucose make carbon
dioxide and water. During the daytime, green plants perform photosynthesis and
take in more carbon dioxide. But, during the night time, they usually take in oxygen
for respiration.

Modern Concept Science and Environment - 7 229

Open stomata Close stomata

FACT WITH REASON

Respiration in plant is known as stomatal respiration. Why?
Respiration in plant is known as stomatal respiration because the exchange of gases occurs
through the stomata.

ACTIVITY 1

OBJECTIVE : Toshowthatgerminatingseedrespiresandreleasescarbondioxideduringrespiration.

REQUIREMENT : Two conical flasks, cotton, gram seeds, two test tubes, lime water, two corks

PROCEDURE :
1. Keep some fresh and well soaked gram seeds on wet cotton in a conical flask.
2. Do the same for the other flask but use boiled gram seeds in this flask.
3. Make the flasks airtight using wooden or rubber corks at their mouth.
4. Keep the flasks in well lit room with proper temperature, for a few days.
5. After the germination of seeds in the first flask, transfer the air of this flask to a test tube

and add some lime water to it.
6. Do the same process: transfer the air of the second flask to another test tube and add some

lime water.

OBSERVATION : It is observed that the air from the flask containing the well soaked seeds turns
lime water into milky colour. But, the air from the second flask which contains the boiled seeds
does not turn lime water into milky colour.

CONCLUSION : Well soaked gram seeds germinate and produce carbon dioxide which turn
lime water into milky colour.

CONCLUSION : Germinating seeds respire and give out carbon dioxide gas.

230 Life Processes

18.4 The Human Digestive System

Food provides energy to our body. But, all the food MEMORY PLUS
we eat does not convert into energy. The food that
we eat is in complex form. It cannot be used by 1. The approximate surface area of
our body cells. So, this complex food gets broken the small intestine is 2,700 square
down into simpler substances for our body cells feet which is over half the size of a
to absorb them. This process is called digestion. basketball court.
Digestion is a process of breaking down of complex
substances in the food into simpler and absorbable 2. Salivary glands produce 1 to 3 litres
forms. Digested food is absorbed by our body and of saliva in a day.
undigested materials are excreted out.
3. The whole digestive tract is over 29
feet long, starting at the mouth and
ending at the anus.

4. The large intestine is approximately
5 feet in length.

In digestion, there are two main processes. They are
mechanical process and chemical process. Mechanical process involves the grinding
of food materials into smaller pieces with the help of different sets of teeth. Chemical
process involves the chemical break down of food due to the action of various digestive
enzymes. Those organs which secrete enzymes are called glands. Different glands
help in the digestion of different substances present in food.

The human digestive system is made up of two main parts: alimentary canal and
digestive glands.

Alimentary Canal (Digestive Tract)

The passage along which food passes through the Oral cavity Salivary gland
body from the mouth to the anus during digestion Tongue Pharynx
process is called alimentary canal or digestive tract. Teeth
Alimentary canal of human being is composed of
mouth, pharynx, oesophagus (food pipe), stomach, Oesophagus
small intestine, large intestine, rectum and anus.
While passing through different organs of alimentary Liver
canal, food comes in contact with different digestive
enzymes. Gall bladder Stomach
Small intestine
There are also some accessory organs that help in the Duodenum
process of digestion. The food may not pass through Pancreas
all these organs but they are important for digestion
process. They include teeth, tongue, salivary glands, Rectum Large intestine
liver, gallbladder and pancreas.
Anus

Digestive system

Modern Concept Science and Environment - 7 231

Digestive glands

Digestive glands are the organs that secrete enzymes for the digestion of food. Similarly,
enzymes are the special chemical proteins that act as catalysts in various biochemical
processes. In digestion, enzymes perform chemical breakdown of the food so that
food is absorbable by body cells. Salivary gland, gastric gland, liver, pancreas and
intestinal glands secrete specific substances or enzymes to act on specific substance
in food.

FACT WITH REASON

Salivary gland is known as digestive gland, why?
Salivary gland is known as digestive gland because it secretes saliva that helps in digestion
of carbohydrates.

Process of Digestion of Food

Ingestion means the intake of food through the mouth. The tongue, teeth and the
salivary glands help in digestion of food in mouth. Teeth grind the food into smaller
pieces. Salivary glands secrete saliva that moistens the food and begins the digestion
of starch. The saliva contains an enzyme called salivary amylase (ptyalin) which
converts starch into maltose. Taste buds in the tongue taste food. The tongue helps to
lubricate the food and push it into the pharynx for swallowing.

The pharynx passes the chewed food from the mouth to the food pipe or the oesophagus.
The oesophagus is a muscular tube connecting the pharynx to the stomach. It carries
the swallowed mass of chewed food along its length and drop into the stomach.

The stomach is a muscular sac that stores food for digestion. It secretes a gastric juice
which contains chemicals called pepsin and renin. It also produces hydrochloric acid.
The rhythmic contraction of stomach crushes the food and mixes it with gastric juice
and hydrochloric acid. In stomach,

i. Pepsin acts on proteins and convert them into peptones.

ii. Renin acts on milk protein (casein) and converts it into insoluble curd (paracasein).

iii. Hydrochloric acid kills microorganisms in the food and provides an acidic
environment for pepsin to work.

After 2-3 hours of digestion, the food passes from the stomach to the small intestine
in the form of thick paste called chyme. The small intestine is a long, thin tube about
1 inch in diameter and about 10 feet long. The internal surface of the small intestine
is full of many ridges and folds. These folds are used to maximize the digestion of
food and absorption of nutrients. Small intestine is divided into 3 parts: the upper
duodenum, the middle jejunum and the lower ileum.

232 Life Processes

In duodenum, liver secretes bile juice which converts large fat globules into tiny fat
droplets and makes food alkaline. This process is called emulsification of fat. Pancreas
also secretes pancreatic juice that contains enzymes called trypsin, amylase and lipase.

i. Trypsin converts proteins into peptides

ii. Amylase converts starch into maltose

iii. Lipase converts fats into fatty acids and glycerol.

The food then passes from duodenum to ileum. In ileum, intestinal juice secreted by
intestinal glands act on it. Intestinal juice contains four enzymes: Erepsin, Maltase,
Lactase and Sucrase.

i. Erepsin digests peptides and converts them into amino acids.

ii. Maltase digests maltose and converts it to glucose.

iii. Lactase digests lactose and converts it into glucose and galactose.

iv. Sucrase digests sucrose and converts it into glucose and fructose.

In this way, carbohydrates (starch), protein and fats get digested into simpler soluble
substances in the small intestine.

The inner wall of the small intestine is densely folded to

maximize the surface area that comes in contact with digested

food. Small projections called villi are present in the inner wall

of the small intestine. Villi help to absorb the nutrients present in

the digested food. Small blood and lymphatic vessels connected

with the villi absorb digested food molecules and transport them

throughout the body through the blood stream. This process is

called absorption. Structure of villi
The undigested food material then passes to the large intestine.

The large intestine absorbs most of the water from the undigested food. Finally, the

remaining substances move to the rectum and are excreted out from the body through

the anus. This process is called egestion.

In this way, digestion process completes in human through a series of ingestion,
secretion, mixing and movement, digestion, absorption and egestion.

FACT WITH REASON

Why is amylase called digestive enzyme?
Amylase is called digestive enzyme because it changes starch into maltose.

Modern Concept Science and Environment - 7 233

18.5 Excretion

While conducting various metabolic processes, our body produces various useful as
well as harmful substances. Our body uses the useful substances while eliminates
the unwanted and harmful substances. Harmful substances include carbon dioxide,
excess minerals and salts, uric acid, urea, ammonia, faecal waste, etc. The process
of throwing out unwanted and harmful substances from the body through various
organs is called excretion. Living organisms have various excretory organs or system
to excrete metabolic wastes.

Differences between excretion and digestion

S.N. Excretion S.N. Digestion

1 The process of throwing out 1 Digestion is a process of breaking

unwanted and harmful substances down of complex substances in the

from the body through the various food into simpler and absorbable

organs is called excretion. forms.

2 Organs like lungs, kidney, skin, 2 Organs like mouth, liver, stomach,

etc. help in excretion. intestine, etc. help in digestion.

18.6 Excretion in Animals

Life processes in animals is more advanced than in plants. The body of animals
produces various metabolic wastes. These wastes are eliminated by the different
organs and systems.

Unicellular animals like amoeba, paramecium, Euglena, etc. remove waste materials
through the general cell surface. For example: amoeba uses contractile vacuole to
release waste in water. Similarly, multicellular animals like hydra, sycon, spongilla,
etc. also release their metabolic wastes directly into water through their body surface.

Similarly, animals like tapeworm, roundworm, liver-fluke, etc. have flame cells for
excretion. Earthworm has specialized organ called nephridia for excretion. Likewise,
insects like butterfly, mosquito, cockroach, grasshopper, etc. eliminate wastes through
malpighian tubules.

Vertebrates have well developed excretory organs and system to release metabolic
wastes. Excretory organs like skin, gills, lungs, liver, kidney, large intestine, etc. found
in vertebrates are responsible for eliminating various wastes.

Excretion in Human Body

A number of waste materials are produced in the human body. Some of these wastes
are: carbon dioxide, urea, uric acid, excess minerals and salts, undigested faecal
matter, excess water, etc. The excretory system of the human body removes these

234 Life Processes

wastes with the help of various organs. The organs that help in excretion are called
excretory organs. Excretory organs include skin, kidney, lungs, liver, large intestine,
etc. Some of the excretory organs are briefly explained below:

a) Kidneys

Kidneys are bean shaped organs present on the either
side of the abdomen. They consist of millions of filtration
units called nephrons. The main function of nephrons is
to filter waste fluid from the blood. The filtration process
removes wastes like urea, uric acid, excess mineral salts,
water, etc. These wastes excreted by the kidneys get
collected in the urinary bladder. Now, they are expelled out from the body in the
form of urine through urethra.

MEMORY PLUS

1. Each individual kidney consists of at least 1 million to 2 million nephrons. Nephrons are the structural and
functional unit of kidneys.

2. The entire blood in the human body gets filtered about 400 times in a day through the kidneys.

FACT WITH REASON

Kidneys are the major excretory organs of human body. Give reason
Kidneys are the major excretory organs of human body because they filter blood about 400 times
a day and remove waste materials. The collection of even small amount of waste in the blood for
a long time is harmful to us.

Lungs

Lungs are the pair of spongy respiratory organs that are situated
inside the rib cage. There are two lungs in human beings. They
consist of millions of air sacs called alveoli. Alveoli are supplied
with blood rich capillaries. Exchange of oxygen and carbon
dioxide takes place in the alveoli of the lungs. Lungs take in
oxygen and release carbon dioxide in the alveoli. The carbon
dioxide is a waste for human body which is then excreted out
from the body through the nose. Without lungs, all the cells of the body die including
the cells of heart, brain, muscles, etc.

Liver

Liver is the vital organ of the human body. It is a reddish
brown multi lobed organ found at the upper right part
of the abdominal cavity. Liver has an important role in

Modern Concept Science and Environment - 7 235

excretion process. It stores harmful substances like urea, metals, ammonia, etc. and
releases them in the bloodstream. Blood is then filtered by kidneys. Liver also gets rid
of the medicines and other toxic wastes present in the blood.

Large Intestine

All the food that we eat is not digested by the body. The large intestine absorbs water
from undigested matter and passes it to the rectum. Undigested matter is then excreted
out through the anus.

Skin

Skin excretes the extra water, minerals, fats and salts through
the small pores in them. The blood capillaries pass wastes like
excess salt and water to sweat producing glands. These waste
materials are then excreted out through the pores in the skin in
the form of sweat.

18.7 Excretion in Plants

Two major wastes that the plants produce are carbon dioxide CO2 Water + O2
and water. Plants release carbon dioxide and water vapour
into the atmosphere through the stomata present in the
leaves. Stomata are the tiny pores found in the upper and
lower surface of the leaves. The excretion of excess water by
the plants in the form of water vapour is called transpiration.
Some inorganic wastes are also produced in the plants which
are converted into harmless substances and are deposited in
the bark of plants. Some plants release their wastes in the
form of latex, resin, oil, tannin, etc.

STEPS EXERCISE

STEP 1

1. Fill in the blanks with appropriate words.
a) The ………... of food takes place in mitochondria to release energy.
b) Energy is not produced in ………... respiration.
c) Internal respiration takes place in………...
d) Gills are the specialized organs to absorb dissolved ………...
e) Amylase converts...............into.............
f) Insects eliminate wastes through ............. tubules.

236 Life Processes

2. Write True for the correct and False for the incorrect statements.
a) Respiration is the process of oxidation of food.
b) Earthworm can breathe through its moist skin.
c) Lungs contain millions of air sacs called alveoli.
d) Amylase digests protein.
e) Exchange of gases takes place in skin in human beings.
f) Latex is the most useful substance for plants.

STEP 2

3. Answer the following questions in one word.
a) What is the term for oxidation of glucose in mitochondria of cell?
b) Which organ is involved in cutaneous respiration?
c) What are the filtration units of kidneys called?
d) Which parts of plants involve in transpiration?
e) What is the length of a digestive tract of human beings?

4. Write any two differences between:
a) Respiration and digestion
b) Internal respiration and external respiration
c) Digestion and excretion

5. Give reasons.
a) Respiration is essential to living beings.
b) Respiration in plant is known as stomatal respiration.
c) Salivary gland is known as digestive gland.
d) Amylase is called digestive enzyme.
e) Kidneys are the major excretory organs in human body.

6. Identify the following organs or parts and write any two functions of each.

CO2 Water + O2

a) b) c) d)

Modern Concept Science and Environment - 7 237

STEP 3

7. Answer the following questions
a) What do you mean by internal respiration? Explain respiration in human
beings.
b) What is digestion? Explain in short about digestion in stomach.
c) What are digestive glands? Give any two examples.
d) Describe digestion in human beings.
e) List the name of waste products excreted by plants.
f) Write down the functions of enzymes given below. Also, name the organs
which produce them.
i) Amylase ii) Pepsin
iii) Trypsin
g) Write short note on:
i) liver ii) kidneys
iii) Skin
h) Name the excretory organs of the following animals:
i) Human beings ii) Hydra
i) Name the respiratory organs of the following animals:
i) Tadpole ii) Butterfly
iii) Fish iv) Human beings
j) Draw a well labelled diagram of kidneys.

8. Describe an experiment:
a) to show digestive system in human body.
b) to show respiratory system in human body.

2U38NITS t r u c t uEsrtiemoatfedt hteaecEhaingr tpehriods Theory Practical
5 1

19 Structure of the Earth

Syllabus issued by CDC Earth

 Introduction to rocks
 Structure of rocks
 Physical properties of rocks
 Types of rocks (igneous rock, sedimentary rock and metamorphic rock)
 Uses of rocks
 Some important rocks of Nepal

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 define rocks and explain their structures and physical properties.
 introduce different types of rocks and explain their importance and uses.
 identify some important rocks found in Nepal.

Key terms and terminologies of the unit

1. Lithosphere: The solid portion of the earth’s crust is called lithosphere.

2. Hydrosphere: The watery portion of the earth that includes the seas and the
oceans is called hydrosphere.

3. Rock: Rocks are the solid aggregates of one or more minerals.

4. Minerals: Minerals are inorganic substances that have specific chemical
composition and characteristics.

5. Cleavage: Cleavage is the plane through which the rock or a mineral in the
rock breaks out.

6. Sedimentary rock: The rocks that are formed by the accumulation and cementing of
deposited sediments are called sedimentary rocks.

7. Igneous rock: The rocks that are formed by the solidification of magma are called
igneous rocks.

8. Plutonic rock: The igneous rocks that are formed by gradual solidification of
magma below the earth’s surface are called plutonic rocks. They
are also known as intrusive rocks.

Modern Concept Science and Environment - 7 239

9. Volcanic rock: The igneous rocks that are formed after the
solidification of lava are called volcanic rocks.
They are also known as extrusive igneous rocks.

10. Metamorphic rock: The rocks that are formed by the modification of
pre-existing rocks as a result of heat, pressure and
chemical processes are called metamorphic rocks.

11. Metamorphism: The process of modification of sedimentary, igneous
or metamorphic rocks is called metamorphism.

12. Foliated metamorphic rocks: The metamorphic rocks that have a layered or
banded appearance are called foliated rocks.

13. Non-foliated metamorphic rocks: The metamorphic rocks that do not have layered or
banded appearance are called non-foliated rocks.

19.1 Introduction

Our earth is made up of 92 different natural elements and their compounds. All these
elements and their compounds exist in three major forms: solid, liquid and gas. The
solid portion of the earth’s crust is called Lithosphere. The watery portion of the
earth that includes the seas and the oceans is called hydrosphere. Oxygen, silicon,
aluminium and iron are the major elements that are found in lithosphere. Lithosphere
is made up of rocks. The upper thin part of the lithosphere is covered by weathered
rocks and is called soil. Soil is unconsolidated materials of the earth’s surface. Rocks
are consolidated materials that form the lithosphere.

Rocks MEMORY PLUS
Ocean crust is made of denser
Rocks are the solid aggregates of one or more minerals than continental crust.
minerals. Minerals are inorganic substances

that have specific chemical composition and

characteristics. Talc, gypsum, calcite, apatite, topaz,

diamond, etc. are some of the examples of minerals.

Rocks are made up of various mineral crystals

that differ in shape, size and appearance. Breaking

of rocks due to the effect of various physical and

chemical activities is called weathering of rocks. It

takes hundreds of years to weather rocks. Weathered

rocks form pebbles, gravel, sand, silt and clay. In Rocks

simple words, soil forms due to the weathering of rocks.

240 Structure of the Earth

FACT WITH REASON

Rock are important natural resources, why?
Rock is important natural resource because it can be used in construction, making of idols,
decoration, etc.

Physical properties of rocks

Rocks have their unique physical features that separate them from each other. Some
of the common factors that make rocks different from each other are:

a) Streak

Streak is the colour of mineral in its powdered MEMORY PLUS
form. The colour of minerals found in the The Earth's outer solid layer, the
rocks makes one rock different from the other. lithosphere, is made of rocks.

b) Crystalline structures

Crystals are the substances with definite geometrical arrangement. The shape
and size of different minerals differ from each other. Thus, rocks also differ by
crystal structure of the minerals. Smooth rocks have fine crystals in them while
rocks with rough surfaces have larger crystals.

FACT WITH REASON

Diamond is called crystalline rock. Why?

Diamond is called a crystalline rock because it is formed by repeated symmetric arrangement
of carbon atoms.

c) Cleavage

Cleavage is the plane through which the rock or a mineral in a rock breaks out.

d) Hardness

Hardness is considered as one of the important properties of mineral or rock.
The hardness is measured by Moh’s Scale in which the softest mineral is given
the value of 1 and hardest is given the value of 10. Talc is the softest mineral and
diamond is the hardest mineral.

e) Colour

Rocks are of various colours. Some of the common rock colours are brown,
grey, white, smoky white, etc. Study and observation of colour of rocks can also
provide some basis for classification of rocks.

Modern Concept Science and Environment - 7 241

Types of rocks

On the basis of formation, rocks can be divided into three major types. They are
sedimentary rocks, igneous rocks and metamorphic rocks.

1. Sedimentary Rocks MEMORY PLUS

The lithosphere of the earth is continuously 1. Sedimentary rock has layers
weathered and eroded by the action of of sediments that are arranged
heat, water, wind and ice. The fine eroded according to their density.
materials resulting from the weathering of
rocks are called sediments. These sediments 2. Sand-stone is a sedimentary
get accumulated at the bank or bottom of rock that has been used to make
lakes, seas and oceans layer by layer and get housewares since prehistoric
cemented to form rocks. The rocks that are times.
formed by the accumulation and cementing of
3. The Taj Mahal in India is made
entirely out of marble.

deposited sediments are called sedimentary rocks. Sometimes, the remains of

dead plants and animals also get trapped during the formation of sedimentary

rocks. Due to this reason, we find remains or imprints of organisms preserved

as fossils in sedimentary rocks. Sedimentary rocks with smooth face and fossils

in them are called ‘Shaligram’ in Nepali.

Some of the examples of sedimentary rocks are: Shale, conglomerate, sandstone,
limestone, dolomite, halite, gypsum, etc.

Sandstone Shale Limestone Coal

Conglomerate Dolostone

Evaporates

FACT WITH REASON

Fossils may be present in the sedimentary rocks. Give reason.

Fossils may be present in the sedimentary rocks because organic matters are trapped during
the sedimentation of sand particles, mud, etc.

242 Structure of the Earth

Some important sedimentary rocks

a) Conglomerate Conglomerate MEMORY PLUS
It is a sedimentary rock Conglomerate rocks are colourful
that contains large round and attractive; however, it is rarely
particles. The space between used as ornamental stone for
the pebbles is generally interior use because of its unreliable
filled with smaller particles physical strength and durability.

like sand and/or chemical cement that binds the rock together. Silica is the

common cementing material in such rocks.

FACT WITH REASON

Conglomerate is a sedimentary rock, why?
Conglomerate is a sedimentary rock because it is formed by deposition of pebbles, cements, etc.

b) Limestone MEMORY PLUS

It is a rock that is composed 1. Limestone turns into the
metamorphic rock marble when
mainly of calcium carbonate. subjected to high amounts of
pressure and heat.
It can form from the
2. Roughly 70% of the Earth’s
accumulation of shell, coral, Limestone surface is covered by shale.
algae and other organic
3. Roughly 55% of all sedimentary
matters. Limestone is used in many ways like rock is shale.

in the production of cement, crushed stone, etc.

c) Shale

It is a sedimentary rock that is made up of clay and silt granules.

Shale typically breaks into thin flat pieces and is the famous roofing

and paving materials. Shale
d) Sandstone

It  is a sedimentary rock that is made up of mainly sand-sized

granules. The cementing material that binds together the grains

of sand is usually composed of silica, calcium carbonate or iron

oxide. Sandstone

2. Igneous rocks

Mantle is the layer of the earth below the crust. Due to its high temperature,
rocks and minerals are found in molten form. Such mixture of molten rocks and
minerals is called magma. Rocks that are formed by the solidification of magma
are called igneous rocks. As igneous rocks are formed from molten magma, they
do not bear fossils in them. However, crystallization of magma causes them to
form grains in them. So, igneous rocks are also called granular rocks.