Green Science and Environment 6 Final (2076)

2. Dicotyledonous plants

The plants having two cotyledons in a seed are called dicotyledonous plants.
Mustard, bean, grams, soyabean, orange, apple mango, rose, sunflower,
etc. are examples of dicotyledonous plants. The major characteristics of
dicotyledonous plants are as follows.

i. They have two cotyledons in each seed.

ii. Tap root system is present.

iii. Leaves are broad having reticulate venation.

Fig.

12.26 Tap root Leaf of papaya
Dicot seed

Differences between monocotyledonous and dicotyledonous plants

Monocotyledonous plants Dicotyledonous plants

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

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

3. They have elongated leaves. 3. They have broad leaves.

4. Their leaves have parallel 4. Their leaves have reticulate
venation. venation.

Activity 6
Observe any five monocots and any five dicots from your locality.
Study the morphology of these plants one by one.
Compare the roots, stem and leaves of monocots and dicots.
Differentiate between them on the basis of your observation.

GREEN Science and Environment Book-6 151

Key Concepts

1. The things having life are called living beings.
2. Animals and plants are found in different habitat and climatic conditions.

They have different structures and characteristics according to their
habitat.
3. Different types of animals like fish, hydra, octopus, starfish, shark,
dolphin, etc. live in water. These animals are called aquatic animals.
4. The animals that live on land are called terrestrial animals.

5. The animals that live in cold places have thick and long hair in their
bodies to prevent them from cold.

6. The animals that live in air are called aerial animals. Different types of
birds like pigeon, parrot, crow, lophosphorus, eagle, peacock, etc. are
examples of aerial animals.

7. The animals that live in burrows are called burrowing animals. Snake,
rat, rabbit, python, mole, etc. are examples of burrowing animals.

8. The animals that live on trees, cliffs or walls are called arboreal animals.
9. The plants that live (grow) in water are called aquatic plants.
10. The plants that live (grow) on land are called terrestrial plants.

11. The plants that live for only one year or one season are called annual
plants.

12. The plants that live for two years are called biennial plants.

13. The plants that live for many years are called perennial plants.
14. The plants having only one cotyledon in their seeds are called

monocotyledonous plants.
15. The plants having two cotyledons in a seed are called dicotyledonous

plants.

Exercise

1. Tick (µ) the correct statement and cross (X) the incorrect one.

a. Most plants prepare their own food by photosynthesis.

b. Most aquatic animals breathe through lungs.

152 GREEN Science and Environment Book-6

c. Cow and buffalo have sharp and pointed canines.
d. Aquatic plants have hollow stem.
e. Maize and paddy are dicotyledonous plants.

2. Fill in the blanks using appropriate words.
a. The animals that live on land are called ................................
b. Camel has a ................................ on its back to store food.
c. Rabbit, rat and mole are ................................ animals.
d. The body of ............................. plants is covered with waxy substance.
e. ................................ plants have two cotyledons in their seeds.

3. Tick (µ) the best answer from the given alternatives.
a. The animals that live on trees and cliffs are called .................... animals.

aquatic aerial arborial desert

b. Which of the following is a desert animal?

cow zebra camel cow

c. Which of the given animals has a layer of fat under the skin?

tiger elephant yak rhinoceros

d. Which of the given plants is not a xerophyte?

cactus lotus opuntia Aloe vera

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

maize mustard bamboo onion

4. Answer the following questions.
a. Define aquatic animals with any three examples.
b. Write any three characteristics of aquatic animals.
c. What are terrestrial animals ? Give any five examples.
d. Write any four characteristics of terrestrial animals?
e. What are aerial animals? Write any four examples.

GREEN Science and Environment Book-6 153

f. Write any three characteristics of aerial animals.
g. Define arboreal animals with any three examples.
h. Write any two characteristics of desert animals.
i. What are aquatic plants? Give any two examples.
j. Write any three characteristics of aquatic plants.
k. What are xerophytes? Give any three examples.
l. Write any three characteristics of xerophytes.
m. Define annual, biennial and perennial plants with any three examples

of each.
n. Define monocots and dicots with any three examples of each.
5. Write down the major characteristics of given organisms.
a. b. c.

d. e. f.

6. Write any three characteristics of the animals that live in burrows.
7. Write any three characteristics of the plants that grow in desert.

154 GREEN Science and Environment Book-6

UNIT Invertebrates

15

Weighting Distribution (Approximate) Teaching periods : 6 Marks (in %): 1

Before You Begin

We have seen butterfly, snail, grasshopper, earthworm, slug, ant,
honeybee, mosquito, leech, etc. in our locality. These animals
are called invertebrates. They do not have backbone or vertebral
coloumn. The animals which do not have a backbone or vertebral
column are called invertebrates. These animals may be unicellular
or multicellular. Some invertebrates like amoeba, paramecium,
euglena, etc. are unicellular and microscopic. Invertebrate may be
aquatic or terrestrial. In this unit, we will study about different
types of invertebrates and their features.

Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce invertebrates with examples. • Introduction to invertebrates
ii. describe the characteristics of invertebrates. • Characteristics of invertebrates
iii. classify invertebrates upto the phylum. • Classification of invertebrates
• Nine phyla of invertebrates

Glossary: A dictionary of scientific/technical terms

primitive : very simple in structure, less developed
unicellular : having only one cell in the body
multicellular : having many cells in the body
marine : found in sea, connected with the sea
hermaphrodite : having male and female reproductive organs in the same body
cephalic : in or related to the head

GREEN Science and Environment Book-6 155

Invertebrates

Animals like earthworm, mosquito, grasshopper, butterfly, dragonfly,
honeybee, cockroach, leech, snail, slug, etc. do not have backbone or vertebral
column. These animals are called invertebrates. They are primitive animals
having less developed organs and systems. Invertebrates are those animals
which do not have backbone or vertebral column. Examples: Amoeba, sponge,
hydra, tapeworm, roundworm, earthworm, butterfly, snail, starfish, etc.

Fig.

15.1 Butterfly Earthworm Starfish
Mosquito

Characteristics of Invertebrates

1. Invertebrates do not have backbone or vertebral column.
2. Some of them are unicellular and the rests are multicellular.
3. Their organs and systems are less developed.
4. Their body may have a hard protective covering.
5. They are found in water, land and air.

Classification of Invertebrates

On the basis of structure and development, invertebrates are classified into
nine phyla (groups). They are as follows:

1. Protozoa 2. Porifera
3. Coelenterata 4. Platyhelminthes
5. Aschelminthes 6. Annelida
7. Arthropoda 8. Mollusca
9. Echinodermata

1. Phylum Protozoa

Phylum Protozoa consists of unicellular and microscopic animals.

156 GREEN Science and Environment Book-6

Habitat

Protozoans are commonly found Do You Know

in water and moist places. Some of Protozoans cannot be seen with
them are found inside the body of
our naked eyes. So, they are called

other animals as parasites. microscopic animals. However, they
can be seen through compound

Salient features microscope.
The method of reproduction in which

a. Protozoans are unicellular and an organism divides into two or more

microscopic animals. daughter organisms is called fission.

b. They breathe through general
body surface.

c. They reproduce by fission, i.e. binary fission or multiple fission.

d. All life processes of protozoans occur in the single cell.

Examples: Amoeba, Paramecium, Euglena, Plasmodium, etc.

Fig.

15.2 Paramecium Euglena Plasmodium
Amoeba

2. Phylum Porifera

Phylum Porifera consists of primitive multicellular animals having numerous
pores in their bodies. They are commonly known as sponges.

Habitat

Sponges are commonly found in water, i.e. fresh water and marine water.
Their body remains attached to the substratum with the help of basal disc.

Salient features
a. They have numerous pores on their bodies.
b. They are multicellular animals.
c. Their body remains attatched to the surface of rocks, woods, etc. with the

help of basal disc.
d. They don’t have head, eyes and legs.
Examples: Sycon, Spongilla, Euspongia, etc.

GREEN Science and Environment Book-6 157

Fig. Fig.15.3 Spongilla Euspongia
Sycon

3. Phylum Coelenterata

Phylum Coelenterata consists of aquatic invertebrates having hollow body
cavity called coelenteron.

Habitat
Coelenterates are found in fresh water and marine water.

Salient features
a. Coelenterates have a coelenteron, i.e. hollow body cavity.
b. Mouth is present but anus is absent.
c. Mouth remains surrounded by tentacles.
d. Breathing takes place through general body surface.
e. They reproduce by budding or regeneration.
Examples: Hydra, Sea anemone, Coral, etc.

15.4 Sea anemone Coral
Hydra

4. Phylum Platyhelminthes

Phylum Platyhelminthes consists of invertebrates having flat body. These
animals are commonly known as flatworms.

158 GREEN Science and Environment Book-6

Habitat Do You Know

Flatworms live as parasites of Parasites are organisms that take food
animals. They are found in the and shelter from their hosts, e.g. tape

intestine or liver of cow, buffalo, pig, worm, liver fluke, mosquito, etc.

human, dog, etc. The animals having male and female

reproductive organs in the same body

Salient features are called bisexual animals, e.g. tape
worm, liver fluke, etc.
a. Their body is flat which may be Host is an organism which provides

leaf-like, ribbon-like or tape-like. food and shelter to a parasite.

b. Their body may be segmented (e.g.
tape worm) or unsegmented (e.g. Liver fluke).

c. They are bisexual animals.

d. They suck blood from their hosts.

Examples: Tapeworm, Liver fluke, Planaria, etc.

Fig.

15.5 Liver fluke Planaria
Tape worm

5. Phylum Aschelminthes or Nemathelminthes

Phylum Aschelminthes consists of invertebrates having round and
unsegmented body. They are commonly known as roundworms.

Habitat

Most of the roundworms live as parasites. They are found in the intestine
of animals. They suck blood of their host. However, some roundworms are
found in soil.

Salient features Do You Know
a. The body is round, cylindrical
The organism having only one type of sex
and unsegmented. organs (male or female) in its body is called
unisexual organism, e.g. round worm.
b. Mouth and anus both are
present.

c. Both the ends of their body are pointed.

d. They are unisexual animals.

GREEN Science and Environment Book-6 159

Examples: Roundowrm, Hookworm, Pinworm, etc.

Fig. Fig.15.6 Hookworm Pinworm
Roundworm (Ascaris)

6. Phylum Annelida

Phylum Annelida consists of invertebrates having many segmented rings in
their bodies. They are commonly known as annelids.

Habitat

They are found in water, soil and sand. Some of them are parasites (e.g. leech)
and others are free-living (e.g. earthworm).

Salient features

a. Their body consists of numerous Do You Know

segmented rings. Leech sucks the blood of vertebrates

b. Their body is elongated, like human, cow, goat, etc. So, it is

cylindrical and segmented. called a parasite of vertebrates.

Earthworm is found in soil. It is a free

c. Their body is covered with soft living animal.

and moist skin (cuticle).

d. These animals may be unisexual or bisexual.
Examples: Earthworm, Leech, Sandworm, etc.

15.7 Leech Sandworm
Earthworm

160 GREEN Science and Environment Book-6

7. Phylum Arthropoda

Phylum Arthropoda consists of invertebrates having jointed legs. They are
commonly known as arthropods.

Habitats Do You Know

Arthropods are found on land, air Thorax is the middle part of an insect's body
and water. to which the wings and legs are attached.

Salient features
a. Arthropods have jointed legs.
b. Their body can be divided into head, thorax and abdomen.
c. They have wings and legs for movement.
d. Their body is protected with a hard cover.
Examples: Crab, Butterfly, Prawn, Grasshopper, Ant, Honeybee, Moth, Spider,
Scorpion, etc.

Fig.

15.8 Prawn Butterfly Centipede
Crab

8. Phylum Mollusca

Phylum Mollusca consists of invertebrate animals having soft and unsegmented
body. They are commonly called molluscs.

Habitat
Molluscs are found in water and moist soil.

Salient features
a. Mollusca have soft and unsegmented body.
b. Their body is generally covered with one or two hard shells.
c. They breathe through gills or lungs.
d. They have a distinct head which contains tentacles, eyes and mouth.
Examples: Snail, Slug, Unio, Octopus, etc.

GREEN Science and Environment Book-6 161

Fig. Fig.15.9

Snail Slug Unio Octopus

9. Phylum Echinodermata

Phylum Echinodermata consists of marine invertebrates having spiny skin.
They are commonly known as echinoderms.

Habitat
Echinoderms are found only in marine water.

Salient features
a. Echinoderms have spiny skin.
b. Their body may be star-shaped (e.g. Starfish), globular (e.g. Sea urchin) or

cylindrical (e.g. Sea cucumber).
c. Distinct head is absent.
d. They move with the help of tube feet.
Examples: Starfish, Sea cucumber, Sea urchin, Brittle star, etc.

15.10 Sea cucumber Sea urchin Brittle star
Starfish

Activity 1

Observe the invertebrate animals like earthworm, leech, butterfly, snail,
dragonfly, slug, cockroach, mosquito, honey bee, spider, grasshopper,
moth, etc. in your locality.

Study their structure carefully.
Draw a neat and labelled figure of each.
Write any three salient features of each.

162 GREEN Science and Environment Book-6

Key concepts

1. Invertebrates are those animals which do not have backbone or vertebral
column.

2. Protozoans cannot be seen with our naked eyes. So, they are called
microscopic animals.

3. Phylum Porifera consists of primitive multicellular animals having
numerous pores in their bodies.

4. Flatworms live as parasites of animals. They are found in the intestine or
liver of cow, buffalo, pig, human, dog, etc.

5. Phylum Mollusca consists of invertebrate animals having soft and
unsegmented body.

6. Phylum echinodermata consists of marine invertebrates having spiny skin.

Exercise

1. Tick (√) the best answer from the given alternatives.
a. Which of the following animals belongs to Phylum Protozoa?

snail amoeba

hydra tapeworm

b. Sea anemone belongs to Phylum ................

Coelenterata Mollusca

Protozoa Arthropoda

c. Which of the following animals lives as a parasite?

hydra tapeworm

earthworm butterfly

d. Which of the following animals have jointed legs?

snail mosquito
starfish octopus

GREEN Science and Environment Book-6 163

e. Which of the given animals moves with the help of tube feet?

slug sea anemone

leech sea urchin

2. Tick (√) the correct statement and cross (×) the incorrect one.
a. Paramecium belongs to Phylum Protozoa.
b. Coelenterates have numerous pores in their bodies.
c. Roundworm is found in the intestine of animals.
d. Cockroach is kept in Phylum Arthropoda.
e. Starfish has tentacles for movement.

3. Fill in the blanks using appropriate words.

a. Amoeba belongs to Phylum ..........................................
b. Tapeworm is found in .......................................... of animals.
c. Leech sucks .......................................... of vertebrates.
d. Cockroach has jointed .......................................... for movement.
e. Snail is grouped in Phylum ..........................................

4. Match the following. Phylum Arthropoda
a. Amoeba Phylum Protozoa
b. Roundworm Phylum Aschelminthes
c. Coral Phylum Annelida
d. Honeybee Phylum Coelenterata
e. Octopus Phylum Mollusca


5. Answer the following questions.
a. Define invertebrates with any five examples.
b. State any two features of invertebrates.

164 GREEN Science and Environment Book-6

c. Define coelenterates and flatworms with any three examples of each.
d. Write any three salient features of the animals that belong to Phylum

Aschelminthes.
e. Define arthropods with any four examples.
f. Write any three salient features of the animals belonging to Phylum

Mollusca.
g. Why is octopus kept in Phylum Mollusca?
h. Define echinoderms with any two examples.
6. Differentiate between:
a. Tapeworm and Liverfluke
b. Roundworm and Tapeworm
c. Earthworm and Roundworm
7. Identify the given animals. Write their phylum with any two salient
features.
a. b. c. d.

8. Give suitable reason.
a. Spongilla is called invertebrate.
b. Tapeworm is called a parasite.
c. Leech is grouped in Phylum Annelida.
d. Sea cucumber is kept in Phylum Echinodermata.

GREEN Science and Environment Book-6 165

UNIT Structure of a Cell

16

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

Before You Begin

The bodies of living organisms are made of very small units.
These small units are called cells. The bodies of all plants and
animals are made of cell. Cells act as the building blocks of life.
Some animals like amoeba, paramecium, euglena, etc. are made
of only one cell. These organisms are called unicellular organisms.
Many plants and animals contain so many cells in their bodies.
These organisms are called multicellular organisms. In this unit,
we will study cell, structure and functions of different parts of a
cell in brief.

Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce cell and describe the structure of a cell. • Introduction to cell

ii. differentiate between plant cell and animal cell. • Structure of cell

iii. describe the functions of cell, cell organelles and • Study of plant cell and animal
inclusions. cell

• Structure and functions of
parts of a cell

• Differences between plant cell
and animal cell

• Functions of a cell

Glossary: A dictionary of scientific/technical terms

cell : the basic, structural and functional unit of life
microscopic : extremely small and difficult or impossible to see without a microscope
microscope : an instrument used to see microscopic things
cell organelles : the living bodies present in a cell, e.g. mitochondria, nucleus, etc.
inclusions : the non-living structures present in a cell, e.g. vacuoles
membrane : a very thin layer
cytoplasm : a jelly-like substance found in cells
cellulose : non-living substance that forms cell wall

166 GREEN Science and Environment Book-6

Structure of a cell

The bodies of living beings are made of tiny

units called cells. Different types of plants

and animals are found around us. Some of

them are made of only one cell, whereas

most of the plants and animals are made of

many cells. The cells in living beings can be

compared with the bricks in a building. Fig.

Cells are very small in size and cannot be

seen with our naked eyes. Therefore, we 16.1

use compound microscope to see the Compound Microscope

detailed structure of cells. The basic,

structural and functional unit of life is called cell. Various activities like growth,

reproduction, respiration, excretion, etc. occur inside the cell.

Plants and animals differ greatly in Do You Know
their shapes and sizes. Similarly,

cells also differ in their shapes. They Cell was discovered by an English
may be rectangular, hexagonal, oval, scientist Robert Hooke in 1665 AD.
spherical, polygonal, etc. Most of the
cells are microscopic. They are very Most of the cells are microscopic and
cannot be seen with our naked eyes.

small in size. However, some plant

cells and animal cells can be seen with our naked eyes.

Activity 1

Go to the science laboratory along with your science teacher.
Observe the slides of plant cell and animal cell under the compound

microscope.
Draw neat and labelled figure of each.

Though cells are very small in size, they are made of various parts such as
cell wall, cell membrane, mitochondria, vacuoles, plastids, centrosome,
endoplasmic reticulum, ribosomes, etc. A brief description of various parts of
a cell is given below:

GREEN Science and Environment Book-6 167

1. Cell wall Fig. Fig. Cell wall Cytoplasm
Cell membrane
The outermost covering layer Rough ER
of plant cells is formed by cell Vacuole Smooth ER
wall. It is a hard and rigid Nucleus Ribosomes
structure made of a non-living Nucleolus Golgi body
substance called cellulose.
Chloroplast
Functions
(i) Cell wall provides a fixed 16.2 Mitochondrion
Chromatin
shape to the plant cell.
Plant cell

(ii) It also protects the internal parts of plant cells.

(iii) Cell wall allows all substances to enter or leave the cell.

2. Cell membrane Lysosome Golgi apparatus
Mitochondrion

Cell membrane forms the Golgi vesicles Nucleolus
outermost covering layer of Rough ER

animal cells. It is a thin, living

and elastic membrane. Cell Smooth ER Nucleus
membrane is found just inside Cell membrane
the cell wall in plant cells. Microtubules
Centrioles Cytoplasm
Ribosome
Functions 16.3

(i) It provides an outer Animal cell

boundary to an animal cell and protects internal parts of the cell.

(ii) Cell membrane allows only selected substances to enter or leave the cell.

3. Cytoplasm Do You Know

The jelly-like substance found in a The living bodies present inside the cell
cell is called cytoplasm. It is made are called cell organelles, e.g. nucleus,
of water, carbohydrate, protein, fat mitochondria, plastids, etc.
droplets, etc. Cytoplasm is enclosed
by cell membrane and surrounds the The non-lving bodies present in a cell
nucleus. The cytoplasm consists of are called inclusions, e.g. vacuoles, fat
cell organelles and inclusions. droplets, etc.

168 GREEN Science and Environment Book-6

Function
(i) Cytoplasm provides space for various cell organelles and inclusions.

4. Nucleus Nucleolus Nuclear
membrane
Nucleus is the most important cell
organelle present in the cytoplasm. It is Nuclear
round or spherical in shape. It is made pores
of nuclear membrane, nucleoplasm,
nucleolus and chromosomes. Fig.
Fig.
The nucleus is found nearly at the centre 16.4 Chromosomes Chromatin
in animal cells but it is slightly shifted

towards the side in plant cells. Nucleus

Functions Do You Know

(i) Nucleus controls various Chromosomes are thread-like structures
activities of a cell. present in the nucleus of a cell.

(ii) It takes part in cell division. Nucleus is called the director or
controller of a cell.

5. Endoplasmic recticulum

The space between cell membrane and Rough endoplasmic Nuclear membrane
nuclear membrane is occupied by an reticulum Nucleus

irregular network of channels which

is called endoplasmic reticulum. It is

of two types, i.e. smooth endoplasmic Ribosomes
reticulum and rough endoplasmic
reticulum. Ribosomes are attached 16.5 Smooth endoplasmic
to the surface of rough endoplasmic reticulum

Endoplasmic reticulum

reticulum.

Functions
(i) Endoplasmic reticulum forms the supporting framework of the cell.
(ii) It provides mechanical support to the cytoplasm.

GREEN Science and Environment Book-6 169

6. Mitochondria Fig.

Mitochondria are spherical, oval or Mitochondrion
thread-like cell organelles present in
the cytoplasm. They have an outer
membrane and an inner membrane.
Mitochondria are the sites of energy
production and storage. Therefore,
they are called the power houses of a 16.6
cell.

Functions
(i) Mitochondria produce energy required for the cell.
(ii) They store energy.

7. Vacuoles

Vacuoles are non-living, fluid-filled structures found in the cytoplasm. In
animal cells, vacuoles are smaller but more in number, whereas they are larger
but less in number in plant cells. Vacuoles are filled with water, waste materials,
carbohydrates, minerals, etc.

Functions
(i) Vacuoles help in excretion.
(ii) They help in the growth of the cell.

8. Ribosomes Do You Know

Ribosomes are very small round Chlorophyll traps the solar energy and
or spherical structures present in helps the green plants in photosynthesis.
the cytoplasm. They are also found
attached to the tubes of rough The process of making food by
endoplasmic retciculum. green plants in their leaves is called
photosynthesis.

Function

(i) Ribosomes help is protein synthesis.

170 GREEN Science and Environment Book-6

9. Plastids

Plastids are spherical, oval or disc-shaped structures found in plants cells.
They are located in the cytoplasm. In plant cells, plastids are of three types.
They are:

(i) Chloroplast Outer membrane
(ii) Chromoplast and Inner membrane

(iii) Leucoplast

Chloroplasts include green pigment Fig. Plastids
Fig.
called chlorophyll. The leaves and
young stem of plants appear green 16.7

due to the presence of chlorophyll.

Chromoplasts are found in petals of flowers and pericarp of fruits. They
contain colourful pigments.

Leucoplasts are found in underground parts of the plants such as roots. They
contain colourless pigments.

Functions
(i) Chloroplasts trap the solar energy and help in photosynthesis.
(ii) Chromoplasts give colour to petals and fruits.
(iii) Leucoplasts store food.

10. Centrosome

Centrosome is a very small protoplasmic

structure present near the nucleus in the

cytoplasm. It is found only in animal

cells.

16.8

Function Centrosome

(i) It helps in cell division of animals cells.

GREEN Science and Environment Book-6 171

Activity 2
Take a cardboard paper. Collect materials like thread, bits of bead, paper,

glue, grains, pulses, etc.

Use these materials and prepare models of plant cell and animal cell.

Label various parts of these cells and submit to your science teacher.

Plant cell Animal cell

1. Cell wall is present. 1. Cell wall is absent.
2. Plastids are present. 2. Plastids are absent.

3. Centrosome is absent. 3. Centrosome is present.

4. Vacuoles are less but larger is size. 4. Vacuoles are more but smaller in
size.

5. The shape may be rectangular or 5. The shape may be round or oval.
hexagonal.

Key concepts

1. The bodies of living beings are made of tiny units called cells.

2. The cells in living beings can be compared with the bricks in a building.

3. The basic, structural and functional unit of life is called cell.
4. The outermost covering layer of plant cells is formed by cell wall.
5. Cell membrane forms the outermost covering layer of animal cells. It is a

thin, living and elastic membrane.
6. The jelly-like substance found in a cell is called cytoplasm.
7. Nucleus is the most important cell organelle present in the cytoplasm. It

is round or spherical in shape.

8. The space between cell membrane and nuclear membrane is occupied by
an irregular network of channels which is called endoplasmic reticulum.

9. Mitochondria are the sites of energy production and storage.
10. Vacuoles are non-living, fluid-filled structures found in the cytoplasm.
11. Ribosomes are very small round or spherical structures present in the

cytoplasm.

172 GREEN Science and Environment Book-6

Exercise

1. Tick (√) the best answer from the given alternatives.
a. ........................ controls the various activities of a cell.

vacuole nucleus

centrosome plastid

b. The outermost covering layer of animal cell is called ........................

nucleus cell membrane

cell wall cytoplasm

c. Which of the following cell organelle helps in photosynthesis?

plastid mitochondrion

centrosome nucleus

d. The cell organellele which is found only in plant cell is ........................

centrosome plastid

mitochondrion ribosome

2. Tick (√) the correct statement and cross (×) the incorrect one.
a. Cell is the fundamental unit of life.
b. Cell wall is the outermost covering layer of plant cells.
c. Mitochondrion controls various activities of a cell.
d. Plastids help in photosynthesis.
e. Nucleus is found only in animal cells.

GREEN Science and Environment Book-6 173

3. Fill in the blanks using appropriate words.
a. The structural and functional unit of life are called .........................
b. Cell wall is made of .........................
c. Chloroplasts help in .........................
d. Mitochondria are also called ......................... of a cell.
e. Chromoplasts are found in ......................... of flowers.

4. Match the following. Vacuole
a. Controls various activities of a cell Cell wall
b. Helps in photosynthesis Centrosome
c. Helps in protein synthesis Plastid
d. Provides shape to a cell Nucleus
e. Helps in excretion Ribosome


5. Answer the following questions.
a. Define cell. Why is cell called fundamental unit of life?
b. Name the instrument which is used to see the details of a cell.
c. Name the scientist who discovered the cell.
d. What is cell wall? Write down its functions.
e. Name the outermost covering layer of animal cells.
f. What is cytoplasm? Write its functions.
g. What is nucleus? Write its two functions.
h. What is endoplasmic reticulum? Write its functions.
i. What are plastids? Where are they found?
j. Name three types of plastids. Also, write down the functions of each.

174 GREEN Science and Environment Book-6

k. What are ribsomes? Write down their function.
l. What is a centrosome? Write down its function.
6. Write any four differences between plant cell and animal cell.
7. Draw a neat and labelled figure showing the detailed structure of a
(i) Plant cell
(ii) Animal cell
8. Name the parts of A to F shown in each of the given figures.

A
B
C
D
E
F

9. Give suitable reason.
a. Cell is called the basic unit of life.
b. Nucleus is called the controller of the cell.
c. Mitochondria are called the power house of a cell.

GREEN Science and Environment Book-6 175

UNIT Life Processes

17

Weighting Distribution (Approximate) Teaching periods : 9 Marks (in %): 1

Before You Begin

Living beings take food. They breathe. They excrete. They
reproduce. They transport various substances from one part of
body to another. These activities are called life processes. Those
activities which are performed by living beings to survive are
called life processes. For example, growth, nutrition, respiration,
excretion, internal transport, sensitivity, reproduction, etc.

Learning Objectives Syllabus

After completing the study of this unit, students will be able to: • Introduction to life processes
introduce life processes with examples.
• Structure of a flowering plant
ii. describe the structure of a flowering plant.
• Structure and functions of
iii. describe the structure of root, stem and leaf of root, stem and leaves of
flowering plants. flowering plants

iv. introduce absorption, transport and transpiration that • Absorption in plants
occurs in plants.
• Transport in plants
v. demonstrate absorption, transport and transpiration
that occurs in plants. • Transpiration in plants

Glossary: A dictionary of scientific/technical terms

life processes : those activities which are performed by living beings to survive, e.g.
growth, respiration, transport, etc.
shoot
trunk : the part of a plant above the ground
lateral
vascular : the thick stem of a plant from which branches grow

transpiration : connected with the side of something

: of or containing veins or tubes that carry liquids around the bodies of
plants and animals

: the process of losing water in the form of vapour through stomata of
leaves

176 GREEN Science and Environment Book-6

Life Processes

Life processes are essential for survival of living beings. Living beings take
food. They breathe. They excrete. They transport materials from one part of
body to another. Similarly, they reproduce their own kinds. These activities are
known as life processes. Growth, nutrition, respiration, digestion, excretion,
internal transport, sensitivity, reproduction, etc. are the life processes that occur
in living organisms. Life processes are those activities which are performed by
living organisms for survival. In this unit, we will study some common life
processes like nutrition, respiration, internal transport, excretion, reproduction
and interrelation between livings beings and environment.

Structure of Flowering Plant

Different types of non-flowering and flowering plants are found in our

surroundings. The plants that bear flowers, fruits and seeds are called flowering

plants. Sunflower, lotus, rose, marigold, pea, bean, mustard, mango, apple,

etc. are some common examples

of flowering plants. A flowering Flower
plant consists of various parts like

root, stem, branches, leaves, buds,

flowers and fruits. These parts Fruit

perform specific functions.

A flowering plant can be divided Leaf
into two parts, viz. root system Stem
and shoot system. Root system is
the part of a plant below the soil
whereas shoot system is the part
of the plant above the soil. Stem,
branches, leaves, flowers and fruits
are the parts of the shoot system.

Flowering plants produce flowers Fig. Root
of various colours like red, pink,
purple, orange, yellow, white, blue, A flowering plant
etc. They have green leaves and
brown or white roots. The leaves of 17.1
the plants appear green due to the
presence of chlorophyll.

GREEN Science and Environment Book-6 177

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 root system. Flowering plants have
two types of root system, viz. (i) tap root system and (ii) fibrous root system.

The root system having primary root, its

branches and sub-branches is called tap root

system. The branches of primary root are

called secondary roots and the branches of

secondary roots are called tertiary roots. Tap
Fig.
Fig.
root system is found in dicot plants like bean,

pea, mustard, apple, mango, rose, soyabean, 17.2

orange, etc. Tap root system

17.3 The root system having cluster of roots of the
Fibrous root system same size and thickness is called fibrous root
system. Fibrous 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.

178 GREEN Science and Environment Book-6

Stem

The part of a flowering plant that grows Fig. Fig. Fig. Stem of mango
upwards from the soil is called 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 17.4
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.

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

The flat and green part of a plant that sprouts Vein

from a node is called leaf. Flowering plants Lamina

have leaves of various shapes and sizes. Mid rib
Petiole
Lamina, petiole and leaf base are the three
Leaf
main parts of a leaf. Lamina or leaf blade is

the flat and wide green portion of the leaf. 17.5
Green plants prepare food in the lamina

as it has chlorophyll, i.e. green pigment.

Chlorophyll traps solar energy and helps

plants in photosynthesis.

Petiole is a narrow, short stalk of a leaf which
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 17.6

Parallel venation

GREEN Science and Environment Book-6 179

gives branches and sub-branches that form a network in the leaf. The network
is formed by veins and veinlets which distribute water, minerals and prepared
food to the lamina.

Flowering plants have two types of venations Fig.
in their leaves. They are parallel venation and
reticulate venation. The arrangement of veins Reticulate venation
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, 17.7
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.

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

Visit a nearby garden and uproot a few plants like onion, pea, bean ,
garlic, mustard, wheat, radish, carrot, etc.

Wash the roots of these plants and study their structure.
Compare these roots and identify fibrous roots and tap roots.
Draw a neat and labelled figure of each root system.

Activity 3

Take a plate and keep some moist cotton on it.
Keep some soaked seeds of maize and bean in moist cotton and leave it

in a warm place and wait until those seeds germinate.
Compare the roots of maize and mustard. Study their structure and

identify fibrous roots and tap root.
Observe the growth of these roots every day. Measure the length of these

roots every day and keep the record.
Draw a neat and labelled figure of roots of maize and bean.
Demonstrate those roots to your friends in the classroom.

180 GREEN Science and Environment Book-6

Activity 4

Take a marigold plant and cut the stem at the base.
Take a beaker with some water. Put a few drops of pink ink in water and

stir.
Immerse the stem of the plant in the beaker and leave it for one day.
Remove the plant from the beaker and cut the stem above 3 cm obliquely

from the base. You can see pink lines in the stem.
Where did these pink lines come from? How did pink water rise through

the stem to reach the leaves?
This activity shows that stem conducts water from root to the leaves.

Activity 5

Collect leaves of different plants from your surroundings.
Observe the shape, size and venation of these leaves one by one.
Identify the types of the leaf.

Experiment: 1

Iodine-starch test
To test the presence of starch in green leaf

Requirements
Iodine solution, beaker, burner, a fresh green leaf, petridish, alcohol, test tube,
foreceps, stand, water

Beaker Test tube

Stand Leaf
Burner Alcohol
Leaf Water

Fig.17.8 Iodine
solution

Leaf

Petridish

Procedure
Go to a sunny place and pluck a fresh green leaf from a plant.

GREEN Science and Environment Book-6 181

Take a test tube and put some alcohol in it. Now, immerse the leaf in
alcohol.

Place the test tube in a beaker containing water.
Heat the water in the beaker with a burner till the alcohol in the test tube

boils.
As the alcohol boils, the chlorophyll dissolves in alcohol and the leaf

becomes pale.
Remove the leaf from the test tube and wash it with warm water.
Now, put the leaf in a petri dish and put a few drops of iodine and observe

the change in colour.

Observation
In iodine solution, the leaf changes into blue-black due to the presence of
starch.

Conclusion
This experiment proves that starch is produced in green leaves during
photosynthesis.

Absorption and Transport in Plants

The roots of plants fix the plant Carbon dioxide Oxygen
body to the soil. Roots have
branches, sub-branches and Oxygen Carbon Light
root hairs. The roots of plants dioxide
form a network to the soil. The
root hairs of plants absorb water
and minerals from the soil. This
process is called absorption.

Green plants prepare food

in leaves by using water and

carbon dioxide in the presence

of sunlight. So, the water

absorbed by roots should be

transported to the leaves. Xylem Fig.

tissue transports water from

roots to the leaves. Similarly, Water and Water
phloem tissue transports 17.9 minerals

prepared food from leaves to different parts of plants.

Green plants have transport system to transport water, minerals and prepared
food from one part to another. The system which is responsible for distribution

182 GREEN Science and Environment Book-6

of water, minerals and food to different parts of the plant is called transport
system. This system is also called vascular system. In plants, vascular system
contains two types of tissues. They are xylem tissue and phloem tissue.

Transpiration

Transpiration is the process of losing water in the form of vapour through
stomata. Green plants absorb a large amount of water by the roots. But all water
is not used during photosynthesis. So they lose excess water through stomata
in the form of vapour. If the rate of transpiration is more than the absorption,
the leaves, stem and flowers droop. This process is called wilting. Green plants
expel a large amount of water during transpiration which increases humidity.
The rate of transpiration increases in bright light and at high temperature.

Activity 6

Take a small potted plant which can be covered with a glass jar.

Take a plastic and
cover the surface of
the soil in the pot in
such a way that no
vapour escapes from
the soil in the pot.

Take a big glass jar and Water droplets
wipe its inner surface.

Cover the potted plant Glass jar
with the bell jar and
keep it on a smooth Fig.
surface in the sunny 17.10
place.

Observe the inner surface of the glass jar after 2-3 hours.

After 2-3 hours, water droplets can be observed on the inner surface of
the glass jar. These water droplets come through transpiration.

Key Concepts

1. Life processes are those activities which are performed by living
organisms for survival.

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

shoot system.

GREEN Science and Environment Book-6 183

4. The underground part of the plant is called root system.
5. The root system having primary root, its branches and sub-branches is

called tap root system.
6. Tap root system is found in dicot plants like bean, pea, mustard, apple,

mango, rose, soyabean, orange, etc.
7. The root system having cluster of roots of the same size and thickness is

called fibrous root system.
8. Fibrous root system is found in monocot plants like sugarcane, onion,

maize, bamboo, paddy, wheat, garlic, etc.
9. Shoot system is the part of the plant which is found above the ground.
10. The part of a flowering plant that grows upwards from the soil is called

stem.
11. The portion of the stem between two nodes is called internode.
12. The flat and green part of a plant that sprouts from a node is called leaf.
13. Chlorophyll traps solar energy and helps plants in photosynthesis.
14. The arrangement of veins and veinlets in a leaf is called venation.
15. Leaves prepare food by using carbon dioxide and water in the presence

of sunlight.
16. The root hairs of plants absorb water and minerals from the soil. This

process is called absorption.
17. Xylem tissue transports water from roots to the leaves. Similarly, phloem

tissue transports prepared food from leaves to different parts of plants.
18. Transpiration is the process of losing water in the form of vapour through

stomata.
19. The rate of transpiration increases in bright light and at high temperature.

Exercise

1. Tick (√) the correct statement and cross (X) the incorrect one.
a. Respiration, digestion, excretion, etc. are the examples of life
precesses.

b. The underground part of a plant is called shoot system.

c. The stem grows vertically upward from the soil.

184 GREEN Science and Environment Book-6

d. Phloem tissue transports water from root to the leaves.
e. Transpiration takes place through stomata.

2. Fill in the blanks using appropriate words.
a. A flowering plant can be divided into two parts. They are ....................
and ................................

b. ................................ system is found above the ground.

c. Leaves appear green due to the presence of ................................

d. The process of making food by green plants is called .............................

e. ................................ tissue transports prepared food from leaves to
different parts of plants.

3. Tick (√) the best answer from the given alternatives.
a. Which of the given plants contain fibrous root system?

pea bean maize mustard

b. Which part of the plant has nodes and internodes?

root stem leaf flower

c. Reticulate venation is found in the leaf of ................................

maize rose paddy bamboo

d. Transpiration takes place through ................................

buds stomata roots flowers

4. Answer the following questions.
a. Define life processes with any three examples.
b. What is root system?
c. Name two types of roots found in flowering plants.
d. Write down the major functions of roots.
e. What is shoot system? Name any two parts of stem.

GREEN Science and Environment Book-6 185

f. Write down the major functions of stem.
g. What are leaves? Draw a neat and labelled figure of a dicot leaf.
h. What is meant by venation? Name its types.
i. Where are stomata found? Write down their functions.
j. What is meant by absorption and transportation?
k. Define transpiration. Name the parts of plants that help in transpiration.
l. What happens when the rate of transpiration is more than that of

absorption?
m. Write down the function of xylem and phloem tissue.
5. Differentiate between:
a. Root system and Shoot system
b. Xylem and Phloem
c. Fibrous root and Tap root
6. Describe an activity to demonstrate starch is produced in green leaves
during photosynthesis.

186 GREEN Science and Environment Book-6

Geology and Astronomy

UNIT The structure of the
Earth
18
Weighting Distribution (Approximate) Teaching periods : 5 Marks (in %): 1

Before You Begin

The earth is our home plant. Different types of plants and animals
live on the earth. The earth revolves around the sun in an elliptical
orbit. The shape of the earth is spherical. Its diameter is about
12756km. However, the earth is not a perfect sphere. It is flat at
poles and bulging out at equator. The external surface of the earth
is made of rocks, soil and water. The outer surface of the earth is
hard and strong. It consists of plains, valleys, hills, mountains,
plateaus, rivers, lakes, ponds, oceans, etc. Similarly, the internal
part of the earth consists of crust (outer layer, mantle (middle
layer) and cone (inner layer). In this unit we will study about
external and structure of the earth in brief.

Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce the earth as the common habitat of living • Introduction to the earth

beings with its features. • External structure of the earth
(mountain, hill valley, plateau,
ii. describe the external structure of the earth. plain, sea, river, lake)

iii. describe the internal structure of the earth. • Internal structure of the earth
(crust, mantle, outer core,
inner core)

Glossary: A dictionary of scientific/technical terms

planet : the heavenly body that revolves around the sun
hydrosphere : the part of water present on the earth
lithosphere : the part of land present on the earth
plateau : the plain surface at the top of a mountain, e.g. tibetan plateau
crust : the outermost solid and hard layer of the earth.
mantle : the layer of the earth between the crust and the core

GREEN Science and Environment Book-6 187

The Structure of the Earth

External Structure of the Earth

The mass of the earth is 6 × 1024 kg
and its average density is 5.5 × 103
kg/m3. Similarly, the diameter of the
earth is 12756 km and the distance
between north pole and south pole
is 12713 km. The earth completes
one revolution around the sun in
365.25 days.
Fig.
Fig. 18.1

Plain Earth

The flat structure of the earth existing upto 200 m from the sea level is called
plain. Generally, it is formed by deposition of soil, sand, etc,. that are swept
by running water like river, streams, etc. It is also formed by deposition of
landmass due to natural disasters like soil erosion, flood, landslide, etc. The
plain is fertile land for agriculture due to the presence of large amount of
human in it. The Terai region of Nepal is plain.

Do You Know

On the basis of the distance from the sun,
the earth is the third planet of the solar
system.

The earth is the fifth largest planet of the
solar system.

18.2
Terai region (Plain)

Mountain and Hill

Steep and uneven surfaces of the earth are called mountains and hills. Generally,
they exist above 200 m from the sea level. But, there is variation in the heights of
hills and mountains. The hills exist upto 300 meter and mountains exist above
300 meter of the sea level. There are many mountains in the northern part of
Nepal. The mountains having more than 1829 m height are called Himalayas.

188 GREEN Science and Environment Book-6

The Himalayas are covered by snow through out the year. Among ten highest
mountains of the world, seven are located in Nepal. Mt. Everest (8848 m), the
highest mountain of the world, also lies in our country. The outer surfaces of
the hills and mountains are covered by soil and pebbles, where as hard rocks
are found in the inner parts of hills and mountains.

Fig. Fig.18.3Hills
Fig. Mountains

Valley and Plateau Kathmandu Valley

Valley is the bowl-shaped flat land
surrounded by hills or mountains.
Generally, valleys are formed by
drying ponds or lakes and hence
contain a large amount of humus.
Valleys are fertile land for
agriculture due to the presence of 18.4
humus. Some valleys of Nepal are
Kathmandu, Pokhara, Dang,
Surkhet, etc.

The plain land located at the top
of mountain is called plateau. The
hills and mountains that have flat
land at the top are plateaus. The
well known plateau of the world is
Pamir. It is located in Tibet and is
known as the roof of the world.

18.5

Tibetan plateau

GREEN Science and Environment Book-6 189

Stream and River

A body of small amount of moving
water confined by banks is called a

stream. The natural flow of water

between the blanks formed by

the collection of streams, springs,

glacier, etc. is called river. In the Fig. Fig. Fig.

context of Nepal, streams and

rivers ranging from small to large Koshi river
are the major water sources. The 18.6
Koshi, Gandaki, Karnali, Mahakali,

etc. are big rivers of Nepal. These are the major sources of water used for

generating hydroelectricity, irrigating agricultural land, supplying drinking

water, etc. Streams and rivers carry different types of substances like dust

particles animals and plants, dissolves salts, etc.

Pond and Lake

An inland body of standing water,

either natural or man-made is called

pond. A large landlocked stretch of

water is called a lake. The lakes and

ponds contain different impurities

like mud, soil, germs, etc. Lakes

are suitable for swimming, boating,

etc. There are many lakes in our 18.7

country, The notable lakes of Nepal Rara lake

are the Phewa lake, Rara lake, Tilicho, Shey, Phoksundo, Ghodaghodi, Jilmila,

etc. The water of lakes is not suitable for drinking purpose. It can be used for

irrigating, washing, bathing, etc.

Sea and Ocean Sea

The large water bodies are called
sea and ocean. All the oceans of
the earth are part of a single sea.
Pacific, Atlantic, Indian, Arctic and
Antarctic are five great oceans on
the earth. The sea/ocean water is
not suitable for drinking because it
contains various impurities, salts, 18.8
minerals, etc. Sea water has a great

190 GREEN Science and Environment Book-6

role to maintain water cycle on the earth. Also, oceans play great role for
transportation, aqua-tourism, fishing, etc.

Activity 1

Draw the map of Nepal and show its Terai, Hill and Mountain regions by
drawing boundary.

Internal Structure of the Earth

It is very difficult to study Crust
the internal structure of

the earth. It is studied with Inner core

the help of earthquake Outer core
and volcano. Scientists

were able to study the 1360km
inner parts of the earth

having the radius of about 2000 km
6400 km. The internal part
Fig.
of the earth is divided into 2900 km
crust, mantle, outer core Mantle
and inner core. The brief 18.9
Internal structure of earth
description of these four

layers of the internal part of the earth is presented below.

Crust

The outermost and thinest layer of the earth is crust. The average thickness of
crust ranges from 5 to 50 km with the variation of temperature from 25°C to
750C. The temperature of the crust increases with the increase in its depth. The
pressure on the surface of the crust is one atmosphere and its density is about
3gm/cm3. Generally, the crust is found in solid state. The elements found in
crust are gases, liquids and solids. The elements that cover about 90% part of
the crust are oxygen, aluminium, silicon, iron and calcium. The crust consists
of various land structures like mountains, hills, plains, valleys, etc. including
water bodies, deserts, farm lands, forests, etc.

Mantle

The thickest layer of the earth found just beneath the crust is called mantle. It
is 2 – 3 times heavier than the crust with thickness of about 2900 km. Similarly,
the average pressure of mantle is 2 – 3 times more than that of crust. The
temperature in mantle ranges from 750°C to 2500°C. The important elements

GREEN Science and Environment Book-6 191

found in mantle in molten state are iron, magnesium, silicon and oxygen. The
molten state of these elements is called magma. During volcanic eruption, this
molten magma escapes out of the earth's surface.

Outer Core

The third layer of the earth which is found between mantle and inner core
is called outer core. It is the second thickest layer of the earth with thickness
about 2100 km. Its temperature ranges from 2500°C to 3000°C. The density
of the outer core ranges from 8gm/cm3 to 10gm/cm3 with pressure about 1.5
million atmospheric pressure. The important elements found in outer core
liquid state are iron, cobalt and nickel.

Inner Core

The central layer of the earth with thickness is about 1300 km is called inner
core. It is the innermost layer of the earth with temperature ranging from
3000C to 5000C. The pressure in the inner core is about 3.5 million atmospheric
pressure and its density is about 18 gm/cm3. The substances in inner core are
found in solid state due to its high pressure. The important elements found in
inner core are iron, cobalt and nickel.

Activity 2

Draw a neat figure showing the internal structure of the earth and label the
various parts.

Key Concepts

1. The earth is an orange shaped green planet flattened at the poles with a
bulge at the equator.

2. Steep and uneven surfaces of the earth are called mountains and hills.

3. Valley is the bowl-shaped flat land surrounded by hills or mountains.
4. A body of small amount of moving water confined by banks is called a

stream.
5. An inland body of standing water, either natural or man-made is called

pond. A large landlocked stretch of water is called a lake.
6. The internal part of the earth is divided into crust, mantle, outer core and

inner core.
7. The outermost and thinest layer of the earth is crust.
8. The thickest layer of the earth found just beneath the crust is called

mantle.

192 GREEN Science and Environment Book-6

9. The third layer of the earth which is found between mantle and inner
core is called outer core.

10. The central layer of the earth with thickness about 1300 km is called inner
core.

Exercise

1. Tick (√) the correct statement and cross (×) the incorrect one.
a. The earth is orange-shaped in structure.
b. The outer surface of the earth which is covered by water is called
lithosphere.
c. Steep and uneven surfaces of the earth are called valleys and
plateaus.

d. Mantle is found just beneath the crust of the earth.

e. Inner core is the thickest layer of the earth.

2. Fill in the blanks using appropriate words.
a. The mountains with more than 1829 m height are called .......................
b. The ....................... located at the top of a mountain is called plateau.
c. The sea and oceans are the large .......................
d. The density of the crust is about .......................
e. The molten state of elements in mantle is called .......................

3. Answer the following questions.
a. What is a plain? How is it formed?
b. Define valley with any three examples.
c. What are lakes? Why are they important?
d. Name the four internal layers of the earth.
e. What is crust? Name any four important elements found in the crust.
f. Define magma? When does it escape out of the earth surface?

GREEN Science and Environment Book-6 193

g. The substances in the mantle are found in molten state, why?
h. "Plains and valleys are fertile lands for agriculture." Justify this

statement with examples.
i. Name any three elements found in the inner core.
4. Differentiate between:
a. Hydrosphere and Atmosphere
b. Valley and Plateau
c. Pond and Lake
d. Outer core and Inner core
5. Draw a well-labeled diagram of the internal structure of the earth.

194 GREEN Science and Environment Book-6

UNIT The structure of the

19 Earth

Weighting Distribution (Approximate) Teaching periods : 6 Marks (in %): 2

Before You Begin

We have experienced hot summer days to cold winter days. The
weather of a place throughout the day does not remain the same.
It changes from time to time and place to place. The weather
of a place may be sunny, cloudy, windy, rainy, foggy, etc. The
atmospheric condition of a certain place in a certain time is called
weather. It is the change in temperature, humidity, cloud, rain,
etc. of a particular place. Weather is the condition of atmosphere
of a certain place of a short period. But the average atmospheric
condition of a certain place over a very long time is called climate.
In this unit, we will study about weather, factors affecting weather
and water cycle in brief.

Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce weather and climate. • Introduction to weather and
ii. describe the factors affecting the weather. climate
iii. describe the different types of weather in brief.
iv. explain water cycle with a neat figure. • Factors affecting weather
– Temperature
– Humidity
– Rainfall
• Types of weather
– Sunny weather
– Windy weather
– Hot weather
– Cold weather
• Water cycle

Glossary: A dictionary of scientific/technical terms

weather : the atmospheric condition of a certain place for a certain period of time
meteorology : the scientific study of weather
climatology : the scientific study of climate
humidity : the amount of water vapour present in atmosphere
breeze : a light wind
hygrometer : the device which is used to measure relative humidity

GREEN Science and Environment Book-6 195

Weather

Factors Affecting Weather

Weather is affected by various factors. The major factors that affect weather are
position of the sun and sunlight, temperature, pressure, velocity of air, rain,
humidity, cloud, etc. Weather of a particular place depends upon these several
factors. The brief description of some of these factors is given below.

Rainfall

Rainfall is a major factor that affects

the weather of a particular place.

The total amount of rain that falls

in a particular area in a particular

amount of time is called rainfall.

Rainfall is occurred due to the

contact of clouds with cold air. The Fig. Fig.

clouds condense into water droplets

and they fall in combined form 19.1
resulting in rainfall. The weather
Rain guage
becomes cold due to the rainfall. A

rain guage is used to measure the amount of rainfall of a particular place.

Activity 1

Have you experienced a heavy rainfall?

Write down advantages and disadvantages of rainfall in a chart paper
and discuss in your classroom.

Temperature Thermometer

The degree of hotness or coldness
of a body is called temperature.
The heat of the sun is responsible
for increasing the temperature of
the earth. Various factors like hot,
cold, storm, wind, etc. change the
temperature of the surrounding.
Simple thermometer is used to
measure temperature. The SI unit 19.2
of temperature is Kelvin (K). There
is a variation in the temperature

196 GREEN Science and Environment Book-6

of a single day also. Maximum-minimum thermometer is used to record the
maximum and minimum temperature of a day.

Pressure

The earth is surrounded by atmosphere. The atmosphere is the totality of the air
that causes pressure on the earth surface. This pressure is called atmospheric
pressure. Pressure is one of the major factors that affects weather. It causes
air to blow from one place to another place. The blowing air is called wind.
Pressure varies from place to place and hence there is variation in weather in
different places. The instrument which is used to measure pressure is called a
barometer.

Humidity

Humidity refers to the amount

of water vapour present in the

air. Humid air contains water

vapour. Relative humidity is

measured by an instrument called

hygrometer. Humidity is measured Fig. Fig.

in percentage. Relative humidity is

helpful to forecast the weather. 19.3

Types of Weather Hygrometer

Various factors are responsible for variation in weather. Generally, there are
four types of weather. They are : (i) Hot weather, (ii) Cold weather, (iii) Sunny
weather , (iv) Windy weather.

Hot weather

Weather becomes hot due to high

temperature. Generally days

are hot during summer season

due to continuous sunshine. The

heat of the sun causes increase in

temperature. In hot weather, land

and water becomes hot and hence

surrounding air also gets heated.

The water of the surface water 19.4
bodies gets heated and evaporate

during hot weather. The water vapour is the cause of humidity.

GREEN Science and Environment Book-6 197

Cold weather

Decrease in temperature causes cold
weather. Cloudy days are colder

than sunny days. Generally, days

are cold during winter season. In

cold weather, water of the extremely

cold places freezes into ice. Animals Fig. Fig.

like snakes, frogs, birds, etc. hide

themselves to protect from cold. 19.5

Sunny weather

The day with continuous sunshine

without clouds in the sky is called

a sunny day. The weather of the

sunny day is called sunny weather.

Sunny days are brighter and sunny

weather is warmer than cold and

windy weather. 19.6

Windy weather Fig.

The earth is surrounded by
atmosphere. The air in the
atmosphere moves from one place
to another due to atmospheric
pressure. The movement of air
causes wind. The blowing of air
from one place to another slowly
is called wind. The air blowing
weather is called windy weather.
Windy weather gives us pleasant 19.7
feeling during summer season
due to breeze. If the air moves fast, it becomes storm. Storm is dangerous for
animals and plants. It covers a long distance due to its high speed. It destructs
infrastructures, kills animals, breaks and sweeps plants and other materials.
Thus, storm is destructive.

198 GREEN Science and Environment Book-6

Fig.Activity 2

Observe the weather of your locality for one week. Prepare a short report and
submit to your class teacher.

Water Cycle

The water bodies
like oceans, rivers,
streams, ponds,
lakes, etc. get
heated due to heat
of the sunlight. The
evaporated water
rises up and goes
higher in the sky
and takes the form 19.8
of clouds due to
cold in the sky. The clouds further cools down by coming in contact with cold
air and change into water droplets. The water droplets fall on the earth in
the form of rainfall. The rain water falls into water bodies like, lakes, ponds,
rivers, oceans, etc. The water of these bodies again gets heated, goes up after
evaporation, takes form of clouds in the sky, changes into water droplets and
falls on the ground. This natural phenomenon of occurring rainfall is called
water cycle. In water cycle, water changes into vapour, vapour into clouds,
clouds into water droplets and water droplets fall down on the ground in the
form of rainfall. Water cycle is very essential for the existence of both living
beings and non-living things on the earth.

Activity 3

Take a chart paper and crayons.

Draw a neat and labelled figure of water cycle and demonstrate in the
classroom.

Key Concepts

1. The major factors that affect weather are position of the sun and sunlight,
temperature, pressure, velocity of air, rain, humidity, cloud, etc.

2. The total amount of rain that falls in a particular area in a particular
amount of time is called rainfall.

3. The degree of hotness or coldness of a body is called temperature.

GREEN Science and Environment Book-6 199

4. Humidity refers to the amount of water vapour present in air.
5. Weather becomes hot due to high temperature. Generally days are hot

during summer season due to continuous sunshine.
6. The day with continuous sunshine without clouds in the sky is called a

sunny day.
7. The earth is surrounded by atmosphere. The air in the atmosphere moves

from one place to another due to atmospheric pressure.
8. In water cycle, water changes into vapour, vapour into clouds, clouds

into water droplets and water droplets fall down on the ground in the
form of rainfall.

Exercise

1. Tick (√) the correct statement and cross (×) the incorrect one.
a. Weather is affected by sunlight only.

b. Temperature is the degree of hotness or coldness of a body.

c. Atmospheric pressure is measured by hygrometer.

d. Humid air contains water vapour.

e. Water vapour changes into clouds in the sky.

2. Fill in the blanks using appropriate words.
a. The weather becomes ....................... due to rainfall.

b. Simple ....................... is used to measure temperature.

c. Pressure ....................... from place to place.

d. Sunny days are .......................

e. Storm is ....................... for living beings and non-living things.

200 GREEN Science and Environment Book-6