Green Science and Environment 7 Final (2076)

UNIT Life Processes

17

Weighting Distribution (Approximate) Teaching periods : 10 Marks (in %): 2

Before You Begin

Living beings perform various activities like respiration, digestion,
excretion, etc. for survival. These activities are called life processes.
No. organism can survive without life processes. Life is the result
of various metabolic activities that occur continuously in living
organisms. Life processes are simple in primitive organisms. All life
processes occur within a single cell in unicellular organisms. But
there are different organs and systems in developed organisms to
perform various life processes. In this unit, we will study some life
processes like respiration, digestion and excretion that occur in plants
and animals.

Learning Objectives Syllabus

After completing the study of this unit, students will be able to: • Introduction to life processes
i. introduce life processes with examples. • Respiration
• Respiration in animals (skin,
ii. introduce respiration and explain various breathing
organs of organisms (skin, gills, trachea, spiracles, trachea, gills, lungs)
lungs and stomata) • Respiration in human body
• Respiration in plants
iii. explain breathing in plants and animals. • Human digestive system
• Process of digestion
iv. introduce digestive system in human body and • Excretion in living beings
explain the process of digestion. • Excretion in plants
• Excretion in animals
v. introduce excretion and explain the excretion in plants • Excretion in human body
and animals in brief.

Glossary: A dictionary of scientific/technical terms

respiration : the process of releasing energy by breaking down food in the presence of
oxygen
breathing
diffuse : the process in which oxygen is inhaled and carbon dioxide is exhaled
pulmonary : to mix slowly a substance
excretion : related to the lungs
: the process of removing waste materials from the body.

GREEN Science and Environment Book-7 201

Life Processes

Respiration

We need energy to live and to do

work. We get energy from the food

that we eat. So, we cannot do any Nose
work for a long time without having

food. Therefore, we eat food to Wind pipe

obtain energy. After digestion, the Lung
food is absorbed by our body and

the absorbed food is transported to

each and every cell of our body. The

food gets oxidized in mitochondria

of the cell in the presence of oxygen. Fig.

As a result, energy is released. This

process is called respiration. So

the process of releasing energy by 17.1

breaking down food in the presence Respiratory system of human

of oxygen in mitochondria is called beings

respiration. Oxygen gas is essential in atmosphere while breathing in.

While breathing, living beings take oxygen in and the oxygen reacts with
glucose or carbohydrate in mitochondria releasing energy, water and carbon
dioxide gas. Living beings perform life processes from the energy obtained
during respiration.

Respiration occurs in two ways. They are external respiration and internal
respiration.

External respiration or breathing is the process of inhaling air rich in oxygen
and exhaling air rich in carbon dioxide. No energy is released in external
respiration.

Internal respiration is the process of oxidation of food in mitochondria of cells.
In this process, oxygen reacts with digested food and releases energy along
with water and carbon dioxide. The chemical reaction of internal respiration
is given below:

Glucose + Oxygen Enzyme Energy + Water + Carbon dioxide

C6 H12O6 + 6O2 Enzyme Energy + 6H2O + 6CO2

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Internal respiration is also called cellular respiration as it occurs in cells.
Animals and plants breathe by different ways. They have a variety of organs
for breathing. Plants breathe through stomata and animals breathe through
body surface, trachea, gills, skin or lungs.

Breathing in Animals

In aquatic unicellular animals, breathing takes place through the body surface.
Similarly, simple multicellular animals like sponges, coelenterates (hydra, sea
anemone, etc.) flatworms (tapeworm, liver fluke, etc.) breathe through their
general body surface. In these organisms, exchange of gases take place through
simple diffusion. They do not have special organs for breathing.

Carbon dioxide Carbon dioxide
(out) (out)

Oxygen Oxygen (in)
(in)

Fig. Fig.17.2 Sponge
Amoeba

Developed multicellular animals have a variety of organs for exchange of
gases. They are as follows:

1. Skin

Multicellular animals like earthworm, leech, frog, toad, etc. have moist skin.
These animals breathe through the moist skin.

17.3
Animals that breathe through moist skin

GREEN Science and Environment Book-7 203

Fig. Fig. Fig.2. Trachea

Insects like cockroach, grasshopper, butterfly, moth, etc. breathe through
trachea or air tubes. These trachea open on the outer surface of the body which
are called spiracles. Insects take oxygen and release carbon dioxide through
these spiracles.

17.4
Animals that breathe through spiracles

3. Gills

Aquatic animals like prawn, fish, tadpoles of frog, octopus, etc. breathe
through gills

Do You Know

Tadpoles of frog breathe through gills in
water. But adult frogs breathe through skin
in water and through lungs on land.

17.5
Fish breathes through gills

4. Lungs

Animals like frog, reptiles (snake, lizard, crocodile, tortoise, etc.), birds and
mammals breathe through lungs. These animals inhale oxygen and exhale
carbon dioxide with the help of lungs.

17.6
Animals that breathe through lungs

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Breathing in Human Beings

Human beings have well developed

system for breathing and respiration.

This system is called respiratory

system. This system consists of

various organs like nose, pharynx,

windpipe and lungs. While

breathing, air reaches lungs through

nose, pharynx and wind pipe. Lungs

contain numerous air sacs called

alveoli. The walls of alveoli contain

blood capillaries. Oxygen diffuses

from the thin walls of capillaries
Fig.
Fig.into the blood and combines with

red blood cells. Red blood cells 17.7
supply oxygen to each and every
cell of the body. In mitochondria of Respiratory system in human
the cell, oxygen reacts with digested body

food. As a result, energy is released along with water and carbon dioxide. At

the same time, carbon dioxide is collected back to the lungs and is exhaled

through the nose. In this way, respiration occurs in the human body.

Breathing in Plants

Unlike animals, plants do not have well developed respiratory system. Plants
breathe through stomata present on upper and lower surface of leaf, outer
stem and general surface of roots. Stomata are very small openings which
remain surrounded by guard cells. Stomata open and close due to movement
of guard cells. These stomata help in exchange of gases while breathing.

17.8 Stomata (closed)
Stomata (open)
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Human Digestive System Fig. Mouth
Tongue
We need to eat food to get Phargnx
energy. The food that we eat
should be digested before it is Food pipe
supplied to different parts of
the body. The complex food Liver
is broken down into simple Stomach
absorbable form by a group Duodenum
of organs. This process is Small
called digestion. The system intestine
formed by digestive tract Large
and digestive glands which intestine
is responsible for digestion Rectum
of food is called digestive Anus
system. Human digestive system

Human digestive system can
be divided into two parts,
viz. alimentary canal and 17.9
digestive glands.

i. Alimentary canal

Alimentary canal begins from mouth and end in anus. It consists of mouth,
food pipe, stomach, small intestine, large intestine and anus. The diameter of
alimentary canal differs from organ to organ.

ii. Digestive gland

Various chemicals are required for digestion of food. These chemicals are
called enzymes. Different glands produce different types of enzymes. The
glands involved in digestive system are salivary glands liver (gall bladder),
pancreas and intestinal glands.

Process of Digestion

Food is taken into mouth and chewed with the help of teeth. Salivary glands
secrete saliva which softens the food in mouth. The saliva contains an enzyme

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called salivary amylase. This enzyme acts on starch and converts it into
maltose. After chewing, the food is swallowed into the pharynx which finally
reaches the stomach through a food pipe (oesophagus).
The wall of stomach secretes gastric juice which contains hydrochloric acid
and two enzymes, viz. pepsin and renin. The hydrochloric acid kills microbes
present in the food. In stomach, pepsin acts on proteins and converts them into
peptones (smaller protein molecules) renin acts on milk protein (casein) and
changes into insoluble curd.

Nearly after two hours of meal, the food proceeds towards duodenum in the
form of a thick paste, i.e. chime. In duodenum, bile juice from the liver (gall
bladder) and pancreatic juice from the pancreas mix with the food. Bile juice
does not contain any enzyme but it helps to digest fat. The pancreatic juice
contains three enzymes. They are trypsin, amylase and lipase. Trypsin acts on
proteins and converts them into peptones, amylase acts on starch and changes
it into maltose and lipase acts on fats and changes them into fatty acid and
glycerol.

After digestion in duodenum, the food slowly moves to the ileum where it is
acted upon by four enzymes; viz. erepsin, maltase, lactase and sucrase, produced
by intestinal glands. Erepsin acts on peptones and peptides and converts
them into amino acids. Maltase acts on maltose and converts it into glucose.
Sucrase acts on sucrose and changes it into glucose and fructose. Lactase acts
on lactose and changes it into glucose and galactose. In this way, proteins, fats
and carbohydrates are digested in the small intestine with the help of various
enzymes. The digested food is absorbed by the thin walls of small intestine and
mixed into blood stream. This process is called absorption. After absorption,
digested food is supplied to various cells through blood circulation.

After digestion in small intestine, food proceeds towards large intestine where
absorption of water occurs. The undigested solid particles of food form faeces
which moves towards rectum and is passed away through the anus. This
process is called digestion.
In this way, digestion of food takes place in the human body.

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The digestion of food that occurs in different parts of alimentary canal is given
below:

Part of Digestive Secretion Enzyme Food acted Food
alimentary glands upon changed
Saliva Salivary
canal amylase into
Gastric Pepsin
1. Mouth Salivary juice Starch Maltose
glands Renin

Gastric Protein Peptones
2. Stomach glands
Milk Insoluble
protein curd
(casein)

Liver Bile juice No Helps to digest fat
enzyme

Trypsin Proteins Peptides
and
3. Small Pancreas Pancreatic Amylase peptones Maltose
intestine juice Starch
Fatty
Lipase Fats acid and
glycerol
Intestinal Intestinal Erepsin Peptides
glands juice Maltase Maltose Amino
acids
Lactase Lactose
Glucose
Sucrase Sucrose
Glucose
and
galactose

Glucose
and
fructose

Excretion in living Beings

A variety of waste materials are formed in the bodies of plants and animals
while performing metabolic activities. These waste products may be toxic
or poisonous when accumulated inside the body for a line time. Therefore,
these wastes should be removed from the body. So, excretion is the process
of removing waste materials from the body. The system which excretes waste
products from the body is called excretory system. This system consists of
kidneys, lungs and skin. Carbon dioxide, salts, urea, uric acid, ammonia,

208 GREEN Science and Environment Book-7

Fig.etc. are the waste products produced by animals. Different organisms have
different organs for excretion.

Excretion in plants

Plants use carbon dioxide and throw oxygen during photosynthesis. Similarly,
they use oxygen and throw carbon dioxide during respiration. Plants throw
excess water through stomata. This process is called transpiration. Plants
also produce waste products like resin, gum, latex, etc. However, these waste
products do not harm plants.

Excretion in Animal

Different animals have different organs for excretion. Unicellular animals
like amoeba, paramecium, etc. excrete through general body surface with the
help of contractile vacuole. Similarly, some multicellular animals also breathe
through the body surface. Developed animals have special organs like, skin,
nose, mouth, lungs, large intestine, liver, kidney, etc. for excretion.

Hydra excretes through its mouth. Animals like earthworm, leech, insects, etc.
excrete through anus. Fishes release carbon dioxide through gills. Frogs release
carbon dioxide through skin and lungs. Higher invertebrates and vertebrates
have digestive system and excretory system to remove waste materials from the
body. They remove waste materials through anus, urethra, skin, mouth and nose.

Excretion in Human Body

Human beings have well developed excretory system for removal of various
water materials. The major organs in human body that help in excretion are
given below:

Lungs

Lungs help in removal of carbon dioxide
gas produced during cellular oxidation
or internal respiration.

17.10
Human lungs

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Skin

Skin helps in removal of urea, uric acid,
salts and excess water in the form of
sweat.

17.11Fig. Fig. Fig. Human skin

Kidneys

Kidneys help in removal of urea, uric
acid, salt, excess water, etc. in the form
of urine.

17.12
Human urinary system

Liver

Liver helps in removal of urea, ammonia,
etc. The waste materials produced by
liver reach the kidneys through blood
circulation and are excreted in the from
of urine.

17.13

Human Liver

Large intestine Fig.

The undigested solid particles are Human large intestine
removed by large intestine through the
rectum and anus.
In this way, excretion takes place in
human body by means of various organs.

17.14

210 GREEN Science and Environment Book-7

Key Concepts

1. Life is the result of various metabolic activities that occur continuously
in living organisms.

2. The process of releasing energy by breaking down food in the presence
of oxygen in mitochondria is called respiration.

3. Living beings perform life processes from the energy obtained during
respiration.

4. External respiration or breathing is the process of inhaling air rich in
oxygen and exhaling air rich in carbon dioxide.

5. Internal respiration is the process of oxidation of food in mitochondria
of cells. In this process, oxygen reacts with digested food and releases
energy along with water and carbon dioxide.

6. Human beings have well developed system for breathing and respiration.
This system is called respiratory system.

7. In mitochondria of the cell, oxygen reacts with digested food. As a result,
energy is released along with water and carbon dioxide.

8. Plants breathe through stomata present on upper and lower surface of
leaf, outer stem and general surface of roots.

9. The system formed by digestive tract and digestive glands which is
responsible for digestion of food is called digestive system.

10. After absorption, digested food is supplied to various cells through blood
circulation.

11. Excretion is the process of removing waste materials from the body. The
system which excretes waste products from the body is called excretory
system.

12. Plants throw excess water through stomata. This process is called
transpiration.

13. Developed animals have special organs like, skin, nose, mouth, lungs,
large intestine, liver, kidney, etc. for excretion.

14. Human beings have well developed excretory system for removal of
various water materials.

Exercise

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

a. Respiration, digestion, and excretion are examples of life

processes.

b. While breathing, we take carbon dioxide and release oxygen.

GREEN Science and Environment Book-7 211

c. Plants breathe through stomata.
d. Salivary amylase is found in gastric juice.
e. Maltase acts on maltose and changes it into glucose.
f. Resin, gums, latex, etc. are the excretory products of plants.

2. Fill in the blanks using appropriate words.

a. ........................ gas is essential for respiration.

b. Most insects breathe through ........................ .

c. ........................ remain surrounded by guard cells.

d. Two enzymes found in gastric juice are ........................ and ........................
.

e. The process of removal of waste materials from the body is called
........................

3. Tick (√) the best answer from the given alternatives.
a. Which of the given animals breathes through general body surface?

fish amoeba frog snake

b. The gas essential for photosynthesis is ………………

oxygen nitrogen carbon dioxide air

c. Which of the given glands are found in the wall of stomach?

salivary gastric liver intestinal

d. Which of the given enzymes is found in gastric juice?

pepsin trypsin amylase lipase

e. The excretory organs of plants are ………………

lungs stomata kidneys gills

4. Answer the following questions.
a. What are life processes? Give any three examples.
b. What is respiration? Differentiate between external and internal
respiration.

212 GREEN Science and Environment Book-7

c. How does breathing take place in primitive animals?
d. Name any two animals that breathe through gills.
e. Name any four organisms that breathe trough lungs.
f. How does breathing occur in plants?
g. What is a digestive system? Name any three parts of alimentary canal.
h. Name any three glands that help in digestion of food.
i. How does digestion of food occur in stomach and small intestine?
j. What is excretion? Name any three excretory organs of human beings.
k. How does excretion occur in primitive animals ? Write.
l. How does excretion occur in human beings?

5. Differentiate between :
a. External respiration and Internal respiration
b. Respiration and Photosynthesis
c. Respiration and Digestion

6. Draw a neat and labelled figure showing human digestive system.

7. Draw a neat figure showing urinary system of human beings.

8. Write down the role of following organs in excretion.

– Liver – Kidney – Gills

– Lungs – Skin

9. Draw a chart showing various digestive glands of human body, their
secretion, enzymes produced and functions of these enzymes.

10. Name the excretory organ of following organisms.

– fish – frog – bird – human – plants

GREEN Science and Environment Book-7 213

Geology and Astronomy

UNIT Structure of the Earth

18

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

Before You Begin

The earth is the common habitat for all living beings. The surface
of the earth is made of rocks, soil and water. Rocks are the solid
and hard substances found on the earth's surface. More than
three-fourth parts of the earth remain covered with water and
the rest with soil. If we dig a layer of soil to a certain depth, bed
rocks can be seen from the ancient time. Rocks are being used
by human beings for various purposes. Rocks are widely used
in construction of buildings, houses, roads, pavements, bridges,
dams, walls, canals, etc. Similarly, different types of minerals are
also obtained from the rocks.

Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce rocks and describe their physical properties. • Rocks: Introduction
• Physical properties of rocks
ii. state different types of rocks and explain their features • Types of rocks
and uses. - Igneous rocks
- Sedimentary rocks
iii. give a brief account of important rocks of Nepal. - Metamorphic rocks
• Some important rocks of
iv. state the uses of rocks.
Nepal
• Uses of rocks

Glossary: A dictionary of scientific/technical terms

rocks : the hard and solid structures on the surface of the earth
minerals
igneous : a substance that is naturally formed under the ground

magma : formed by solidification of magma, formed when hot, liquid rock cools
and becomes hard
sedimentary
: molten rock material within the earth from which igneous rock results by
cooling

: formed by or from deposits of sediment

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The Structure of the Earth Fig.

Rocks

Rocks are hard solid substances that
from the surface of the earth. The earth's
crust is made of rocks. They are found
everywhere in our surroundings. They
form cliffs, hills and mountains. Rocks
form the bed of the sea. Rocks are also
found below the layer of soil, on the
banks of rivers, streams, etc. Rocks
are made of fine grains of minerals.
Different types of metals and non-
metals are found in rocks. Over a period 18.1
of time, rocks undergo weathering
which results in the formation of soil.

Physical Properties of Rocks

1. Generally, rocks are hard but some soft rocks are also found in nature.

2. They have different colours. The colour of a particular rock is due to the type of
minerals present in it. Rocks may be white, red, yellow, brown, green, gray, etc.

3. Surface of the rock may be rough or smooth. The rocks that contain big grains
of minerals appear rough and the rocks that contain small grains of minerals
appear smooth.

4. Rocks contain different types of metallic and non-metallic minerals.

5. Rocks exist in solid state. Do You Know

6. Most rocks have high density, i.e. Rocks are hard and solid substances having
they are heavy. metallic and non-metallic minerals.

Classification of Rocks

There are three types of rocks on the
basis of method of formation and origin of rocks. They are as follows:

1. Igneous rocks 2. Sedimentary rocks 3. Metamorphic rocks

1. Igneous Rocks

The rocks formed by solidification of magma are called igneous rocks.
Examples: basalt, pumice, granite, dunite, etc. During volcanic eruption, hot

GREEN Science and Environment Book-7 215

molten magma comes out through the cracks on the surface of the earth. The
magma which comes out on the surface of the earth is called lava. The lava
cools down slowly and becomes solid resulting in the formation of rocks.
Sometimes, the magma cannot come out on the surface and cools down just
below the surface of the earth, which also forms igneous rocks. On the basis
of formation, igneous rocks are of two types, viz. (i) volcanic rocks and (ii)
plutonic rocks.

The igneous rocks which are formed by solidification of magma on the surface
of the earth are called volcanic rocks. Basalt, pumice, obsidian, etc. are the
examples of volcanic rocks.

Fig. Fig.18.2

Obsidian rock Basalt rock Pumice rock

Volcanic rocks are made of small granules. Some of them may be porous or

glassy in appearance.

The igneous rocks which are formed just below the surface of the earth by
solidification of magma are called plutonic rocks. Graphite, dunite, gabbro,
etc. are examples of plutonic rocks.

18.3

Graphite rock Dunite rock Gabbro rock

Plutonic rocks contain big crystals. They are the hardest rocks and hence are

suitable for construction works.

Some useful Igneous rocks

Granite

Granite is a black or grey plutonic igneous rock having large garnules. It is rich
in quartz and felspar. It is a hard and strong igneous rock. It is widely used in
construction works.

216 GREEN Science and Environment Book-7

Pumice

Pumice is a light and porous volcanic igneous rock. It is formed by solidification
of lava having gas. It has different colours like pale, white, black, blue-grey,
green, brown, etc. Pumice is used to make cosmetic items, toothpastes, polishes,
pencils, erasers, light concrete, etc.

Obsidian rock

Obsidian is a glass-like volcanic rock. It is a dark coloured weak rock formed
by rapidly cooling lava. Due to its glass-like appearance, obsidian is also called
volcanic glass. It is used for making gemstones, arrowheads, cutting tools,
spear points, knives, etc.

2. Sedimentary Rocks
The rocks formed by the sedimented substances under high temperature
and pressure are called sedimentary rocks. Limestone, sandstone, coal, shale,
conglomerates, etc. are examples of sedimentary rocks. During the process of
soil erosion, many organic as well as inorganic substances are carried away
by water, air, etc. and these substances get deposited in some other places.
In this way, hundreds of layers are formed over a period of time. Under high
temperature and pressure, the sedimented materials become hard resulting
in the formation of rocks which are known as sedimentary rocks. These rocks
contain many layers and are soft in nature. Since sedimentary rocks may
contain fossils and hence, help to know about evolution of organisms.

Limestone Sandstone Shale

Fig.

18.4 Dolostone
Conlomerates
GREEN Science and Environment Book-7 217

Some Important Sedimentary Rocks

Limestone
Limestone is a very useful sedimentary rock having fine granules. It consists
of calcium carbonate. Limestone is formed from the skeleton of marine
organisms. It may be red, green, white, blue, black, gray, etc. It is widely used
in construction works. Limestone finally changes into marble after a long time
under the earth crust.

Sand stone
Sandstone is a sedimentary rock having sand-sized granules. It consists of
minerals like quartz, felspar and organic matter. Its colour may be red, white,
black, yellow, grey, pink, etc. It is used in construction works.

Conglomerate
The sedimentary rock having round granules is called conglomerate. It is
made of silica, quartz and granules. Conglomerate is formed by combination
of sand particles with silica or quartz. The conglomerate having silica is used
in construction works.

Shale
The sedimentary rock having clay and silt is called shale. Its colour may be
grey or black. Clay is the collection of very small granules whereas silt is
the collection of granules which are smaller than sand. It is used in artwork,
pottery and in architecture.

3. Metamorphic Rocks

The rocks which are formed by the modification of igneous and sedimentary
rocks due to high temperature and pressure under the earth's surface are
called metamorphic rocks. These rocks are formed over a long period of time
due to metamorphosis of both igneous and sedimentary rocks. Marble, state,
gnesis, schist, quartzite etc. are examples of metamorphic rocks. The physical
and chemical properties of metamorphic rocks are different from that of their
original forms.

Marble Slate Gnesis

218 GREEN Science and Environment Book-7

18.5 Fig. Fig.Quarzite
SchistFig.

Following table shows some metamorphic rocks and their previous forms
before metamorphosis.

Igneous/sedimentary rocks Metamorphic rocks
1. Shale Slate
2. Shale Schist
3. Sandstone Quarzite
4. Granite Gnesis
5. Limestone Marble

Activity 1
Study the features of the rocks that are found in your locality.
Classify these rocks into igneous, sedimentary and metamorphic rocks.
Also, write down their characteristics and uses.

Some Important Rocks Found in Nepal

1. Marble

Marble is a very useful metamorphic rock formed
by modification of limestone. It has many layers
and different colours. A large deposit of marble
is located in Godawari, Lalitpur. Marble is widely
used in construction and for decorative purposes. 18.6

2. Limestone

Limestone is a sedimentary rock formed by
calcium carbonate. It is used for making cement

and lime. It is also used in construction works.

It has different colours. Limestone is found in

different parts of Nepal like Chobar, Godawari,

Udaypur, Jogimara, Bhaise, Ghorahi, etc. 18.7

GREEN Science and Environment Book-7 219

Fig. Fig.3. Slate
Slate is a metamorphic rock having fine granules
and various layers. It is formed by modification
of schist. It is used for making writing boards
and roofing of houses, temples, etc. A large
deposit of slate is located in Bandipur.

18.8

4. Silica
Silica is formed by weathering of rocks. It is
made of silica and oxygen. It is found on the
bank of rivers. It is used in construction works.

5. Conglomerate
It is a sedimentary rock having round granules. 18.9
It consists of silica, quartz and granules connected together. It is found on the
banks of rivers. It is used in construction works.

6. Sandstone
It is a sedimentary rock having sand-sized granules of different colours. It
consists of quartz, felspar and organic matter. It is found on the banks of rivers
in Nepal. It is also used in construction works.

Uses of Rocks

1. Rocks are widely used in construction of houses, temples, buildings, bridges,
walls, dams, road, monuments, columns, palaces, etc.

2. Rocks like marble, limestone, slate, etc. are used in decoration of walls,
temples, floors, etc.

3. Rocks are used for extraction of minerals.

4. Rocks are used for extraction of metals.

5. Rocks like slate are used for roofing of houses and temples.

6. Rocks are used for making gemstones and decorative items.

Key Concepts

1. Rocks contain different types of metallic and non-metallic minerals.

2. The rocks formed by solidification of magma are called igneous rocks.

3. The igneous rocks which are formed by solidification of magma on the
surface of the earth are called volcanic rocks.

220 GREEN Science and Environment Book-7

4. The igneous rocks which are formed just below the surface of the earth by
solidification of magma are called plutonic rocks.

5. The rocks which are formed by the modification of igneous and sedimentary
rocks due to high temperature and pressure under the earth's surface are
called metamorphic rocks.

6. Rocks are widely used in construction of houses, temples, buildings, bridges,
walls, dams, road, monuments, columns, palaces, etc.

Exercise

1. Tick (√) the correct statement and cross (×) the incorrect one.
a. Rocks are hard and solid substances found on the earth.

b. Igneous rocks contain fossils.

c. Granite is an example of sedimentary rocks.

d. Marble is formed by modification of limestone.

e. Sandstone contains quartz and felspar.

2. Fill in the blanks using appropriate words.
a. The rocks that contain big granules appear ..........................
b. .......................... rocks are formed by solidification of magma.
c. Granite and dunite are the examples of .......................... rocks.
d. Quartzite is formed by modification of ..........................
e. A large deposit of .......................... is located in Godawari, Lalitpur.

3. Answer the following questions.
a. What are rocks? What are they made of?
b. Where are rocks found?
c. Name three types of rocks.
d. What are igneous rocks? Give any three examples.
e. What are volcanic and plutonic rocks? Give any two examples of each.

GREEN Science and Environment Book-7 221

f. What are sedimentary rocks? How are they formed?
g. Give any three examples of sedimentaty rocks.
h. What are metamorphic rocks? Give any three examples.
i. Where is marble found in Nepal?

4. Give reason.
a. Fossils are found in sedimentary rocks.
b. Igneous rocks are widely used in construction works.
c. Marble is called a metamorphic rock.

5. Differentiate between:
a. Sedimentary rocks and Igneous rocks
b. Volcanic rocks and Plutonic rocks
c. Limestone and Marble

6. Give a brief account of the rocks found in Nepal.

7. Identify the rocks given below. c.
a. b.

8. Write down the major uses of rocks.

222 GREEN Science and Environment Book-7

UNIT Weather and Climate

19

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

Before You Begin

Most days are sunny, some are cloudy and other may be rainy or
foggy. Similarly, some days are hot and other days are cold. It may be
sunny in the morning, cloudy in the noon and rainy in the evening.
Weather and climate both refer to the condition of the atmosphere in
a certain place. The condition of the atmosphere at a particular place
and time is called weather. Sunny, cloudy, foggy, rainy, hot, cold, etc.
are some states of weather. The weather of a place keeps on changing
from time to time. Similarly, the weather varies from place to place.
Climate is the average atmospheric condition over a long peroid of
time. The totality of existing temperature, atmospheric pressure,
humidity, rainfall, etc. is called climate.

Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce weather and climate. • Introduction to weather and
climate.
ii. describe in brief about cloud, rain, snow and dew.
• Cloud, rain, snow and dew
iii. introduce various layers of air with their features.
• Atmosphere and its layers
iv. describe the cause of movement of air.
• Wind and movement of air
v. Introduce the equipment of measuring the factors
affecting weather. • Equipment for measuring the
factors affecting weather
vi. state the ways of weather forecasting and explain its
importance. • Weather forecasting

Glossary: A dictionary of scientific/technical terms

weather : the condition of the atmosphere at a particular time and place
climate : the average atmospheric condition of place over a long period of time
dew : the water in the form of droplets that appears on leaves in the morning
atmosphere : the thick layer of air that surrounds the earth's crust
forecast : to predict something such as weather

GREEN Science and Environment Book-7 223

Weather and Climate

Weather can be defined as the specific atmospheric condition of a particular
place at a particular time. Weather varies from place to place and time to time.
The weather may be sunny, windy, cloudy, rainy, etc. On the same day, the
weather in the morning, at noon and in the evening may be different.

Fig.19.1Cloudy weatherRainy weather
Fig. Sunny weather

Climate can be defined as the average atmospheric condition of a place over a
long period of time. It is the average weather pattern of a place throughout the
year. The climate of some places may be hot and wet and in other places it may
not be hot and dry. Similarly, it may be cold and humid in some other places.

The earth has been divided into three main climate regions. They are (i) tropical,
(ii) sub-tropical and (iii) cold or tundra. These climate regions are further
divided into many sub-regions. These sub-regions are called climate belts. The
natural vegetation, animals and mode of human life and their activities are
determined by the climate of their habitat.

Clouds

When the sky is not clear, we can see different
types of clouds. Clouds that we see in the
sky have different shape, size, colour and
appearance. Clouds give us idea about the
changing weather. Have you seen clouds in
the sky? What are clouds made of? Have you
ever wondered? Water exists in three different 19.2
forms in nature, viz. solid, liquid and gas. In
solid state, water is found in the Himalayas and in liquid state, it is found in
river, lake, ponds, oceans, etc. Similarly, in gaseous state, water is found in the
form of vapour in the atmosphere. When the water vapour changes back into
water droplets, cloud is formed. So, cloud can be defined as a grey or white
mass of very small drops of water that float in the sky.

224 GREEN Science and Environment Book-7

Formation of Cloud Do You Know

The water present in the rivers, lakes, The droplets of water in clouds are so small
ponds, oceans, etc. gets converted that millions of them combine to form a
into vapour due to the heat of the single drop of rain.
Sun. The water vapour rises up in

the atmosphere and gets mixed with

dust particles. Then the mixture of

water vapour and dust particles undergoes condensation on cooling. As a

result, cloud is formed. Cloud is very light, so it floats in the atmosphere.

Rain Fig. Fig. Fig.

The water present in ocean, river, pond, lake,
etc. gets converted into vapour due to the heat
of the Sun. Then the water vapour rises up in
the sky. When the water vapour reaches high
up in the sky, it cools down and changes into
clouds. The clouds further cool down in the
sky. As a result, rainfall occurs on the earth.
High hills and forest play a great role in the 19.3
formation of rain. In Nepal, heavy rainfall
occurs in the months of Asar and Shrawan.

Snow

Snow is a soft, white and fluffy crystalline
water. It falls from clouds. It is a granular
material and found in the form of flakes.
The Himalayas remain covered with snow
throughout the year. In Nepal, snowfall
occurs in most of the tall peaks during winter.

19.4

Dew

During winter season, the water vapour

present in atmosphere undergoes condesation

and changes into water droplets which is

called dew. So, dew is the water in the form

of droplets that can be seen on leaves. We can

observe dew on leaves and other objects in

the morning during winter season. 19.5

GREEN Science and Environment Book-7 225

Air

The mixture of various gases like nitrogen, oxygen, carbon dioxide, argon,
etc. is called air. The air is made of 78% nitrogen, 21% oxygen, 0.03% carbon
dioxide by volume. The surface of the earth is surrounded by thick layer of air.

Atmosphere

Atmosphere is the thick layer of air Exosphere
that surrounds the surface of the Thermosphere
earth. Various gases like nitrogen,
oxygen, carbon dioxide, argon, water Mesosphere
vapour, etc. and dust particles are
found in the atmosphere. On the basis
of height and features, atmosphere is
divided into five layers.

1. Troposphere Stratosphere

2. Stratosphere Troposphere

3. Mesosphere

4. Thermosphere Fig.

5. Exosphere

1. Troposphere 19.6

Troposphere is the lowermost layer of atmosphere which extends upto 16
km from the surface of the earth. Different heavy gases like nitrogen, oxygen,
carbon dioxide, etc. are found in this layer. The temperature of this layer
decreases as the height increases. Weather-related activities like rainfall,
snowfall, lightning, thunder, hailstones, etc. occur in this layer. Therefore,
troposphere is very important for meteorologists to study weather.

2. Stratosphere

Stratosphere is the layer of atmosphere which is located between troposphere
and mesosphere. It extends between 16 km to 50 km from the surface of the
earth. This layer is very important for living beings because upper part of this
layer contains ozone which shields the harmful UV-radiations and protects
the living beings on the earth. The temperature of stratosphere increases as it
increases in height.

226 GREEN Science and Environment Book-7

3. Mesosphere

Mesosphere is the layer of atmosphere which is located between troposphere
and thermosphere. It extends between 50 km to 80 km from the surface of
the earth. In mesosphere, strong wind blows. The temperature of this layer
decreases when the height increases.

4. Thermosphere

Thermosphere is a very hot layer of atmosphere which is located between
mesosphere and exosphere. It extends between 80 – 720 km from the surface
of the earth. In this layer, temperature increases with the increasing height.
This layer has less amount of air.

5. Exosphere

It is the uppermost layer of atmosphere located above 720 km from the surface
of the earth. This layer consists of very less air. It is also called fringe region.

Wind

In the months of Fagun, Chaitra, Baisakh and Jestha, strong wind blows in
Nepal. It carries dust particles, waste papers, plastics, dried leaves and many
other light objects in its way. Some times, it blows away roofs made of tins and
uproot trees which may destroy life and property. Similarly, wind breaks the
branches of trees and it damages crops and fruits.

Fig.

19.7 Tree broken due to wind
Windy day

The fast blowing air is called wind. Air is a mixture of different gases in which
molecules are loosely bound together. Due to the heat of the Sun, the air
becomes light and rises up as hot air is light. Now, cold air rushes down to
occupy the empty space. When hot masses of air move up and cold masses of
air move down rapidly, wind blows. Such types of movement of air is called
convection.

GREEN Science and Environment Book-7 227

Fig. Fig.Movement of Air (Land breeze and Sea breeze)

During day time, land gets heated faster than water. So the air above land
surface gets heated faster than the air above the sea. So the air above the
land surface that gets heated due to heat of the Sun during day time rises up.
Then the cold air from the sea moves towards the land to occupy the empty
space. As a result, cold air blows towards the land from the sea. Such type of
movement of air is called sea breeze.

Do You Know

The movement of cold air towards land from
the sea during the day is called sea breeze.

19.8
Sea breeze

The surface of land cools down faster at night than the water in the sea. Due
to this, the air above the land surface cools down faster than the water in the
sea. So the air above sea rises up as it remains hot. As a result, cold air moves
towards the sea from the land at night. Such type of movement of air is called
land breeze.

Do You Know

The movement of cold air towards the sea
from the land at night is called land breeze.

19.9
Land breeze

Information Regarding the Weather

Today's era is the era of science and technology. Scientists have developed
many equipment to gather information regarding weather. Various means
of information and communication like radio, television, newspaper, smart
phones, etc. disseminate information regarding weather and change in weather.

228 GREEN Science and Environment Book-7

Meteorologists forecast weather by studying the factors that affect weather
such as humidity, direction of air, temperature, types of clouds, movement of
clouds, rain, etc. Now-a-days, various equipment like rain-guaze, barometer,
anemometer, hygrometer, maximum-minimum thermometer, etc. are used by
meteorologists to study weather and factors affecting weather.

Equipment for Measuring Used for Weather Forecasting

1. Rain-guaze

The equipment which is used to measure the amount of rainfall in a certain
place and time is called rain-guaze. The amount of rainfall is measured in mm
(millimetre). In Nepal, maximum rainfall occurs in Pokhara.

Do You KnowFig.
Fig.
The amount of rainfall in Biratnager is 60
mm means that if all rain remains in the
same place where it falls, it would be 60 mm
high from the ground.

19.10
Rain-guaze

2. Barometer

The equipment which is used for measuring atmospheric pressure is called
barometer. Generally, two types of barometers are used to measure atmospheric
pressure. They are mercury barometer and aneroid barometer.

Do You Know

Atmospheric pressure determines the
weather of a place. When atmospheric
pressure increases, weather remains clear
but day becomes windy and cloudy when
atmospheric pressure decreases.

19.11

Barometer

GREEN Science and Environment Book-7 229

3. Anemometer

The speed of direction of air keep changing from time to time. So, meteorologists
have developed an equipment to measure the speed and direction of air. This
equipment is called anemometer. So, the equipment which is used to measure
the speed and direction of air is called anemometer.

Do You Know

In mountains of Nepal, strong wind blows in
the evening. Similarly, the speed of air is less
in the morning and more in the noon.

19.12

Anemometer

4. Hygrometer

Hygrometer is the equipment which is used for measuring humidity. When
the temperature of air increases, humidity decreases and vice-versa.
Fig.
Do You Know
Fig.
Fig. Relative humidity is the amount of vapour
in air. When the relative humidity increases,
the possibility of rainfall increases.

19.13

Hygrometer

5. Maximum-minimum Thermometer

Theequipmentwhichisusedtomeasurethemaximum
and minimum temperature of a day in a certain place
is called maximum-minimum thermometer.

Weather forecasting 19.14

Before booking a flight ticket, we check the forecast Maximum-minimum
Thermometer
of weather for that day. Similarly, farmers listen

230 GREEN Science and Environment Book-7

to the weather forecasting in the radio before harvesting crops. It is done to
be aware of forthcoming weather. The process of predicting the forthcoming
weather of a particular region is called weather forecasting.

Fig.
Fig. Fig.
19.15

Weather forecasting is done by collecting data about current atmospheric
condition. In this process, scientific understanding of atmospheric condition
is used. It helps to forecast how the atmospheric condition will change in
the near future. Now-a-days, weather forecasting is done by observing the
situation and the speed of cloud in the sky and studying the pictures received
from artificial satellites. Such forecasting is reliable to a large extent.

19.16 19.17

Artificial satellite for weather Satellite picture of weather

forecasting forecasting

A scientist who helps in weather forecasting after studying the data received
from artificial satellites is called a meteorologist. Metorologists try to give
complete and accurate picture of weather conditions before hand. It helps
people to be aware of forthcoming weather and take necessary precautions. In
Nepal, there are meteorological laboratories in different parts of the country to
study weather and the factors responsible for change in weather.

GREEN Science and Environment Book-7 231

Some common ways of weather forecasting

1. Heavy rainfall may occur if the sky is suddenly covered with dark clouds.

2. If the day is partially cloudy from the morning, it may not rain throughout
the day.

3. The possibility of rain increases with a sudden hot sunshine.

4. In the rainy season, if the day begins with very hot sunshine, it may rain in the
afternoon.

5. In context of Nepal, if the clouds move towards the end of the rainy season,
rain stops after some days.

Key Concepts

1. Weather can be defined as the specific atmospheric condition of a particular
place at a particular time.

2. Climate can be defined as the average atmospheric condition of a place over
a long period of time.

3. The earth has been divided into three main climate regions. They are (i)
tropical, (ii) sub-tropical and (iii) cold or tundra.

4. Clouds can be defined as a grey or white mass of very small drops of water
that float in the sky.

5. High hills and forest play a great role in the formation of rain. In Nepal,
heavy rainfall occurs in the months of Asar and Shrawan.

6. The mixture of various gases like nitrogen, oxygen, carbon dioxide, argon,
etc. is called air.

7. Atmosphere is the thick layer of air that surrounds the surface of the earth.
8. Troposphere is the lowermost layer of atmosphere which extends upto 16

km from the surface of the earth.
9. Weather-related activities like rainfall, snowfall, lightning, thunder,

hailstones, etc. occur in this layer. Therefore, troposphere is very important
for meteorologists to study weather.
10. Mesosphere is the layer of atmosphere which is located between troposphere
and thermosphere.
11. Thermosphere is a very hot layer of atmosphere which is located between
mesosphere and exosphere.
12. The movement of cold air towards land from the sea during the day is called
sea breeze.
13. The movement of cold air towards sea from the land at night is called land
breeze.

232 GREEN Science and Environment Book-7

14. Meteorologists forecast weather by studying the factors that affect the
weather such as humidity, direction of air, temperature, types of clouds,
movement of clouds, rain, etc.

15. The equipment which is used to measure the amount of rainfall in a certain
place and time is called rain-guaze.

16. The equipment which is used for measuring atmospheric pressure is called
barometer.

17. The equipment which is used to measure the speed and direction of air is
called anemometer.

18. Hygrometer is the equipment which is used for measuring humidity.

19. The process of predicting the forthcoming weather of a particular region is
called weather forecasting.

20. A scientist who helps in weather forecasting after studying the data received
from artificial satellites is called a meteorologist.

Exercise

1. Tick (√) the correct statement and cross (×) the incorrect one.
a. The weather of a place always remains unchanged.

b. Clouds have different shape, size and colour.

c. About 21% of nitrogen is found in the atmosphere.

d. Ozone layer is present in mesosphere.

e. Hygrometer is used for measuring humidity.

2. Fill in the blanks using appropriate words.

a. ...................... is the average condition of atmosphere over a long time.

b. ...................... is a soft white and fluffy crystalline water.

c. Troposhere extends upto ......................km from the surface of the earth.

d. The movement of cold air towards land from the sea is called

......................

GREEN Science and Environment Book-7 233

e. ...................... is used to measure the speed and direction of air.

3. Tick (√) the best answer from the given alternatives.
a. ...................... is the mixture of various gases.

cloud air snow rain

b. ...................... is the uppermost layer of atmosphere.

atmosphere mesosphere

exosphere stratosphere
c. Ozone layer is found in ...................... thermosphere
mesosphere

troposhere stratosphere

d. ...................... is used for measuring atmospheric pressure.

hygometer barometer

anemometer rain guaze

4. Answer the following questions.

a. What is a weather?

b. What is meant by climate?

c. What is cloud? Describe in brief the method of formation of cloud.

d. Define rain, snow and dew.

e. What is air? Write down the percentage of oxygen gas in air.

f. Define atmosphere. Draw a neat figure showing various layers of
atmosphere.

g. What is stratosphere? Write down the importance of this layer for
living beings.

h. Write any three features of each troposhere, mesosphere and
thermosphere.

i. What is meant by land breeze and sea breeze?

234 GREEN Science and Environment Book-7

j. What is rain-guaze? Write down the use of anemometer.
k. Name any four equipment that are used in weather forecasting.
l. What is weather forecasting? Write down its importance.
5. Write any two differences between snow and cloud.
6. Write any two differences between troposphere and exosphere.
7. Name the equipment shown in the given figures. Also, write down the
use of each.
a. b. c.

8. Mention any three ways of weather forecasting.

GREEN Science and Environment Book-7 235

UNIT The Earth and Space

20

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

Before You Begin

The earth is our home planet. All planets and animals live on the
earth. The earth revolves around the sun in an elliptical orbit.
The earth is a member of solar system. The family of the Sun that
includes the Sun, eight planets, natural satellites, comets, astroids,
meteors, meteorites, etc. is called the solar system. Similarly,
planets are heavenly bodies that revolve around the Sun. In
this unit, we will study about solar system, planets, stars and
constellations in brief.

Learning Objectives Syllabus

After completing the study of this unit, students will be able to: • Introduction to solar system,
i. introduce solar system and planets. the Sun and planets.

ii. explain the features of eight planets of the solar • Description of eight planets of
system. the solar system.

iii. introduce stars and differentiate between planets and • Stars- Introduction and
stars. features

iv. introduce constellations with examples. • Differences between planets
and stars

• Constellations and methods of
identification of constellations

Glossary: A dictionary of scientific/technical terms

solar : related to or of the sun
planets : the heavenly bodies that revolve around the Sun
satellites : the heavenly bodies that revolve around the planets
stars : the bright twinkling objects having their own source of light
constellations : a small group of brilliant stars which seems to form the pattern or shape

of some objects

236 GREEN Science and Environment Book-7

The Earth and Space

The Sun

The Sun is the brightest heavenly object. It is a medium sized star close to
the earth. The Sun is extremely hot. It is a huge ball of burning gas. So it is
extremely hot. It releases a large amount of heat and light energy. All the
plants, animals and human beings use the solar energy. Life would not exist
on the earth in the absence of the Sun.

Solar system

Solar system is the family

of the Sun which consists

of eight planets and their

satellites, comets, asteroids,

meteors, meteorites, etc. The Fig.

Sun occupies the central

position of the solar system.

All the planets and other 20.1

members of the solar system Solar System

revolve around the Sun in fixed paths called orbits.

Project work Do You Know

Take a chart paper and draw a The Sun is the brightest heavenly body
neat and labelled figure of the that we see from the earth.
solar system.
Animals and plants cannot survive on the
Put suitable colour on the picture earth in the absence of the Sun.
and demonstrate in your classroom

Planets

We know that the earth revolves around the Sun in its own orbit. So, it is called
a planet. Planets are heavenly bodies that revolve around the Sun in elliptical
paths called orbits. Planets do not have their own source of light for shining.
So they are called non-luminous bodies. However, planets appear bright in
the sky as they reflect the light coming from the Sun. The Sun holds all planets
together with its strong force of attraction which is called gravitation.

There are eight planets in the solar system. The eight planets of the solar system
in the order of their increasing distance from the Sun are given below:

(i) Mercury (ii) Venus

GREEN Science and Environment Book-7 237

(iii) Earth (iv) Mars

(v) Jupiter (vi) Saturn

(vii) Uranus (viii) Neptune

A brief description of all the planets of the solar system is given below:

1. Mercury

Out of the eight planets, mercury is the closest

planet to the sun. It is the smallest planet

of the solar system. Life cannot exist on the

mercury as it has no atmosphere. The part of Fig. Fig.

the mercury that faces the sun is extremely hot

and the other part is extremely cold. Mercury

has no satellites. 20.2

Mercury

Activity 1 Do You Know

Mercury can be seen just before the Mercury is the smallest planet of the solar
sunrise in September and October. system.
It can also be seen just after the
sunset in March and April. Venus is the hottest and brightest planet of
the solar system.
Observe the mercury in the sky
and write its three features after
your observation

2. Venus

Venus is the nearest planet to the earth. It is

the brightest and hottest planet of the solar Venus
system. Life cannot exist on the venus. The
atmosphere of the venus consists of carbon
dioxide. This planet also has no statellites. 20.3

Activity 2

Venus can be seen just before the Do You Know
sunrise and just after the sunset.
Mars is called a red planet.

Observe the venus and write its Jupiter is the largest planet of the solar
three salient features. system.

238 GREEN Science and Environment Book-7

3. Earth

The earth is our home planet. It is the third
nearest planet from the Sun. The earth has

plenty of water, suitable temperature and life

supporting gases. Therefore, life can exist on

the earth. The earth is the only planet having

all the requirements for the existence of life. Fig. Fig. Fig. Fig.

The earth takes 24 hours to complete one

rotation in its own axis. Similarly, the earth 20.4
takes 365.25 days to complete one revolution
The earth
around the earth. The revolution of the earth

around the Sun causes the change in seasons and the rotation of the earth

causes day and night. The earth has only one satellite, i.e. the moon.

4. Mars

Mars is commonly known as a red planet. It

is the fourth distant planet from the Sun. It is

nearly half the size of the earth. The mars can

be seen with our naked eyes and it looks like a

bright orange red star. The atmosphere of the

mars mainly consists of nitrogen gas. It has 20.5

two satellites.

5. Jupiter Mars
Jupiter
Jupiter is the largest planet of the solar system. Saturn

It looks like a bright star with our naked eyes.

Jupiter is the third brightest object in the night

sky after the moon and the venus. The jupiter

consists of bands of clouds and a big red spot.

This planet has 63 known satellites. 20.6

6. Saturn

Saturn is the second largest planet of the solar

system. It is the third farthest planet from

the sun. The saturn is surrounded by rings

of dust and rocks. This planet has 60 known

satellites. Titan is the largtest satellite of the

saturn. 20.7

GREEN Science and Environment Book-7 239

7. Uranus Fig. Fig. Uranus

Uranus is the second farthest planet from
the Sun. It is a very cold planet. It has rings
around it like the saturn. This planet has 27
known satellites.

20.8

8. Neptune

Neptune is the coldest planet of the solar
system. It cannot be seen with our naked eyes.
This is the farthest planet of the solar system.
Neptune has 13 known satellites.

20.9
Neptune

Stars

Stars are extremely large burning balls of

gases. We can observe millions of stars when

we see at a dark and clear night sky. Stars

twinkle at night. The extremely large and hot

balls of gases that twinkle at night are called Fig.

stars. Stars have their own source of light for

shining. So they are called luminous bodies.

Stars are the extremely large masses of gases. 20.10 Stars
But they appear very small from the earth

since they are very far from the earth. The sun is a medium-sized yellow star.

Some of the stars are thousands times larger than the Sun whereas some stars

are smaller than the Sun. The Sun is the star nearest to the earth. So it appears

very large and bright in comparison to other stars. Stars are extremely large in

size as compared to the size of the planets of the solar system.

Activity 3
Look at a dark and clear night sky.
Observe numerous stars, planets, moon, etc.

240 GREEN Science and Environment Book-7

Motion of stars

Stars keep on changing their relative position in space. It means that one star
is in a state of motion with respect to another.

Brilliance of Stars

Stars have different levels of brilliance which varies according to size, distance
from the earth, surface temperature, etc. The nearby small stars may appear
brighter than the distant large stars.

Structure of stars

Stars are very large heavenly bodies made of hydrogen and helium gases. The
heat and light energy of stars is due to nuclear fusion reaction that takes place
in the stars.

Distance of Stars

Stars are situated very far away from the earth. For example, the Sun is located
about 15 crore kilometers far away from the earth. Such extremely large
distance in space is measured in some other units like light year, astronomical
unit, per sec, etc.

The total distance covered by light in one year is called a light year. One light
year is equal to 9.5 × 1015m.

One light year = One year × Speed of light

= 365 days × 3 × 105 km/s

= 365 × 24 × 60 × 60 s × 3 × 105 km/s

= 9.5 × 1012 km

= 9.5 × 1012 × 103 m

= 9.5 × 1015 m

\ One light year = 9.5 × 1015 m

Similarly, the distance between the Sun and the earth, i.e. 15 crore kilometers
is called 1 Astronomical Unit (AU).

Colours of Stars

Different stars have different colours. The colour of a star depends on its
temperature. The colour of a star may be blue, white, yellow, orange, red,
etc. The stars having relatively high temperature appear blue whereas those
having relatively low temperature appear red.

GREEN Science and Environment Book-7 241

Temperature 25000° C 11000° C 6000° C 4000° C 3000° C
Colours of stars
Blue White Yellow Orange Red

Differences Between Planets and Stars

Planets Stars

1. Planets are non-luminous objects. 1. Stars are luminous objects.
They are relatively large.
2. They are relatively small. 2. Their surface temperature is
relatively high.
3. Their surface temperature is 3. They do not revolve around the
relatively low. Sun.

4. They revolve around the Sun. 4.

Constellations

A constellation is a small group of brilliant stars that seems to form a shape or
pattern of some objects. Virgo, Sagittarius, Ursa major, Ursa minor, Big dipper,
etc. are some examples of constellations. The total number of constellations is
88. Among them, 12 constellations are called zodiac.

Fig.

20.11

Methods of Identification of Constellations

In a clear night sky, we can see different groups of stars. Since Nepal lies in
the northern hemisphere, we can observe the constellations of the northern
hemisphere only. To identify constellations, first of all we should observe the
position of two famous constellations of the north pole, viz. Ursa major and
Ursa minor which can easily be identified. Ursa major has seven bright stars
arranged in the form of a ladle. Other constellations are identified by using sky
map. The earth revolves around the sun. Therefore, the constellations seen in
one season are not seen in another.

242 GREEN Science and Environment Book-7

Some famous constellations

1. Ursa major

Ursa major is a very famous
constellation which can be seen in
the summer season in the northern

sky. It can be easily recognized. It

consists of a group of seven bright

stars arranged in the form of a ladle Fig. Fig. Fig.

or question mark. This group of

stars is called saptarishi or the great 20.12

bear.

2. Ursa minor

Ursa minor is another ladle-shaped

constellation. It is also a group of

seven stars but the stars are less

brighter and nearer than that in

Ursa major. It is also called little

bears. Ursa minor is seen in the

northern hemisphere. 20.13

3. Orion

Orion is a constellation having
many stars arranged in the shape
of a hunter. It can be seen in the
northern hemisphere in winter
season.

4. Cassiopeia
Cassiopeia is a constellation having 20.14
five stars arranged in the shape of 'W'. It can be seen in the northern hemisphere
in no moon night. This constellation got its name after a mythological Ethiopian
queen Cassiopeia.

Activity 4

Take a chart paper and draw the picture of the solar system.

Observe the bright stars in the clear night sky and try to identify pole
star, ursa major, ursa minor, etc.

GREEN Science and Environment Book-7 243

Key Concepts

1. The sun is the brightest heavenly object. It is a medium sized star closed to
the earth.

2. All the plants, animals and human beings use the solar energy. Life would
not exist on the earth in the absence of the Sun.

3. Solar system is the family of the Sun which consists of eight planets and
their satellites, comets, asteroids, meteors, meteorites, etc.

4. Planets do not have their own source of light for shining. So they are called
non-luminous bodies.

5. The earth is the only planet having all the requirements for the existence of
life.

6. The revolution of the earth around the Sun causes the change in seasons and
the rotation of the earth causes day and night.

7. Jupiter is the largest planet of the solar system. It looks like a bright star
with our naked eyes.

8. The extremely large and hot balls of gases that twinkle at night are called
stars.

9. Stars are extremely large in size as compared to the size of the planets of the
solar system.

10. The Sun is located about 15 crore kilometers far away from the earth.
11. The total distance covered by light in one year is called a light year. One

light year is equal to 9.5 × 1015m.
12. The stars having relatively high temperature appear blue whereas those

having relatively low temperature appear red.
13. A constellation is a small group of brilliant stars that seems to form a shape

or pattern of some objects.
14. Cassiopeia is a constellation having five stars arranged in the shape of 'W'.

Exercise

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

a. There are eight planets in the solar system.

b. The distance between the Sun and the earth is about 15 crore
meters.

c. Jupiter is the largest planet of the solar system.

244 GREEN Science and Environment Book-7

d. Stars are luminous bodies.

e. We can see the constellations of the southern hemisphere from
Nepal.

2. Fill in the blanks using appropriate words.
a. ...................... occupies the central portion of the solar system.
b. The nearest planet from the Sun is ......................
c. ...................... is the coldest planet of the solar system.
d. ...................... are the luminous objects that twinkle at night.
e. Ursa major consists of ...................... bright stars arranged in the shape
of a ladle.

3. Tick (√) the best answer from the given alternatives.
a. Solar system does not include the .......................

Sun stars planets comets

b. The smallest planet of the solar system is the .......................

earth mercury jupiter urnus

c. The colour of the coldest star is ......................

orange red yellow blue

d. The constellation that appears like a hunter is .......................

Ursa major Orion Ursa minor Cassiopiea

4. Answer the following questions.
a. What is the solar system? Write any three features of the Sun.
b. What are planets? Name the eight planets of the solar system.
c. Write any two features of each mercury, earth, mars, jupiter and saturn.
d. Name the largest and smallest planet of the solar system.
e. Name the coldest and hottest planet of the solar system.
f. Name the nearest and farthest planet of the solar system.
g. Define stars and write any three features of stars.

GREEN Science and Environment Book-7 245

h. The colours of stars guide their temperature, why?
i. Write in brief about brilliance and motion of stars.
j. What are constellations? Give any three examples.

5. Write any three differences between planets and stars.

6. Write any two differences between planets and satellites.

7. Write in brief about Ursa major, Orion and Cassiopeia.

8. Draw a neat figure showing solar system and Cassiopeia constellation.

9. Identify the given heavenly bodies. c.
a. b.

10. Write down the method of identifying the constellations.

246 GREEN Science and Environment Book-7

Environment Science

UNIT Environment and Its

21 Balance

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

Before You Begin

The natural world around us is environment. It includes booth living beings
and non-living things. Different types of plants and animals are found in the
environment. Similarly, soil, water, air, sunlight, temperature, rainfall, etc.
are the non-living things of the environment. In this sense, the totality of all
living beings and non-living things is called environment. There is a close
relationship between living beings and non-living things in the environment.
The proper interaction between living beings and non-living things of the
environment is called balance in environment. But various human activities
are responsible to create imbalance in the natural environment.

Learning Objectives Syllabus

After completing the study of this unit, students will be able to: • Natural Resources and
Kinds of natural Resources
i. introduce environment and balance in environment. (Perpetual, Renewable and
ii. define natural resources and classify natural resources non-renewable)

with their introduction. • Importance of natural
iii. tell the importance of natural resources with examples. resources
iv. explain the ways of conserving natural resources.
v. introduce water resources with its importance and • Natural Resource
Conservation
necessity.
vi. tell the ways of conserving water resources. • Water resource, its importance
vii. define watershed and explain its importance. and necessity
viii. introduce wetlands, explain its importance and tell
• Conservation of water
the ways of conserving wetlands. resources
ix. name the various elements of environment with their
• Water shed, its importance
brief introduction. and conservation
x. explain the role of human beings in environment
• Wetlands, its importance and
balance. conservation
xi. describe the role of human beings on environment
• Elements of environment (Air,
conservation. water, land, plants, animals,
living, community, producer,
consumer and decomposer

• Role of human beings in
environment balance (Man
and environment, impact
of manmade environment
degradation on human beings

• Role of human beings on
environment conservation

Glossary: A dictionary of scientific/technical terms

environment : the natural world around us where plants and animals live
perpetual : everlasting or continuing forever
conservation : the protection of animals, plants and natural resources

GREEN Science and Environment Book-7 247

Environment and Its Balance

Natural Resources

Natural resources refer to the resources that are available in natural
environment. These resources are water, air, land, forest, minerals, animals,
plants, sunlight, etc. These resources are naturally created in the environment.
Both living beings and non-living things are natural resources. Living beings
include all types of plants and animals, whereas air, water, soil, minerals,
etc. are non-living things. Natural resources provide suitable environment
for all living beings for their life in the environment. All living beings in the
environment get food and habitat from natural resources. Thus, natural
resources are very important for living beings.

Kinds of Natural Resources

Natural resources are classified into perpetual, renewable and non-renewable
on the basis of their properties and utility. The brief description of each type of
natural resource is provided below:

a. Perpetual Resources
The natural resources like solar energy, wind energy, tidal energy, etc. have
never-ending supply. These are perpetual natural resources. In this case, the
natural resources which do not get exhausted after large exploitation are
called perpetual resources of energy. They have never ending supply of energy
and do not get depleted due to their continuous use. Perpetual resources are
unlimited in nature.

Fig.

21.1 Tides of sea
Sun

b. Renewable Resources

The natural resources like water, air, forests, soil, etc. can be used again and
again by producing them are renewable resources. They never get exhausted

248 GREEN Science and Environment Book-7

from the environment and can be maintained repeatedly for our use. The
natural resources that can be used repeatedly by creating them again and again
and do not deplete from the environment are called renewable resources.

c. Non-renewable resources

Some natural resources like

petroleum products, minerals,

natural gas, etc. are limited in
nature and get exhausted after
their use. They cannot be obtained
and produced again and again in a

short period of time. Such types of Fig.

natural resource are non-renewable

resources. Non-renewable natural Burning coal
resources refer to the resources that 21.2
cannot be used again and again and

get exhausted after their use. Some examples of non-renewable resources are

petrol, diesel, coal, kerosene, minerals, etc. They are found in specific places of

the earth and their store gets finished after their use.

Activity 1

Make a list of any 15 natural resources available in your locality. Classify them
under the headings perpetual, renewable and non-renewable by making a
table.

Importance of Natural Resources

There is a close relationship between living beings and non-living things in
nature. The life of organisms is not possible in the absence of non-living things.
Various natural resources available in nature have their own importance. For
example, living beings cannot survive in the absence of food, water, air, etc.
The importance of natural resources can be explained in the following points.

a. Sources of Food

Various natural resources found in nature are the sources of food for living
beings. Green plants prepare their food by using water and carbon dioxide
in the presence of sunlight. Human beings grow various crops in soil to get
their food. Herbivores feed on plants and carnivores feed on various creatures.
Thus, living beings or non-living things found in the form of natural resources
are the sources of food for living beings.

GREEN Science and Environment Book-7 249

b. Habitat
Land, water, forest, etc. are the habitats of various kinds of living beings.
For example, human beings build houses on land by using various natural
resources like soil, water, wood, etc. Aquatic animals live in water and wild
animals live in forest. Various types of plants grow in water and on land. Thus,
natural resources are habitat of both plants and animals.

c. Fresh Air and Water
Air and water are vital components essential for survival of living beings. Both
animals and plants need air and water for their survival and these natural
resources are available in nature.

d. Beauty
Natural resources are the sources of beauty of the place where they are
available. For example, forest, wildlife, water bodies, mountains, falls, valleys,
etc. have their own beauty in nature.

Fig.21.3Falls
Fig. Rara lake

e. Tourism

Human beings are attracted towards
natural beauty. Natural beauty is
the result of natural resources and

it is the major source of attraction of

tourists. The flow of tourists results

in flourishing of tourism. Thus,

natural resources are important for

tourism. 21.4

250 GREEN Science and Environment Book-7