Science 8

1. Blood is a liquid connective tissue which keeps on circulating
throughout the body.

2. Plasma is the liquid portion of blood which transports digested foods, excretory
products, hormones, etc throughout the body.

3. Red blood cells are disc-shaped cells which contain haemoglobin.
4. Leucocytes are larger cells which fight with disease germs.
5. Platelets are fragments of larger cells which help for the clotting of blood.
6. Blood vessels are network of tube-like structures that carry blood to various parts.
7. Arteries are blood vessels that carry blood to different parts from the heart.
8. Veins are blue coloured blood vessels that collect blood from various parts to the

heart.
9. Capillaries are very thin hair-like blood vessels which supply blood to every cell.
10. Heart is a conical shaped organ which pumps blood to various parts of the body.

Exercise

A. Answer these questions in short.
1. What is internal transport?
2. What is blood? What are its component?
3. What is plasma? Mention its functions.
4. What are various types of blood cells? Mention their main functions.
5. What is haemoglobin? Mention its function.
6. What is blood vessel? Explain various types of blood vessels.
7. What is heart? What are its various chambers?
8. What is pericardium? What is its function?
9. What is anaemia?
10. What is venule? Which part is formed by joining venules?
11. What is ventricle? Name the ventricles present in the heart.
12. What is auricle? Name the auricles present in the heart.
13. What is venacava? How is it formed?
14. Draw a diagram of heart and label its important parts.
15. Explain blood circulation in human body in brief.

247 Times' Crucial Science & Environment Book - 8

B. Differentiate between:
i. Veins and arteries
ii. Auricles and ventricle
iii. WBC and RBC
E. Give reasons:
i. A person suffering from anaemia feels tired in a short walk.
ii Walls of arteries are thicker than that of veins.
iii. Veins have valves but arteries do not have.
iv. All arteries except pulmonary artery carry pure blood.
F. Diagrammatic questions:
i. Label parts A, B, C, D and E.
ii. Mention functions of each of A, B, C, D and E.

A
B

C

E
D

Take a heart of goat and cut its wall carefully through vertical section. Observe
its four chambers, aorta, pulmonary artery, pulmonary veins and other parts.
Draw a diagram and write about these parts.

Times' Crucial Science & Environment Book - 8 248

19.C Photosynthesis

All living things need foods to survive. Green plants prepare their food
themselves by using carbon dioxide, water and minerals in the presence of
sunlight. This process is called photosynthesis.
Thus, photosynthesis is the process in which green plants prepare their food
by using water, carbon dioxide and minerals in the presence of sunlight.
Green plants contain chlorophyll in the chloroplasts of cells. Chlorophyll traps
sunlight. Carbon dioxide is taken by the green plants from atmosphere through
stomata. Water and minerals are absorbed by the roots. Carbon dioxide and
water react in the chloroplast in the presence of sunlight to produce food which
is mainly glucose. Oxygen gas is produced as by-product in the process. The
process can be shown by the following equation:

Carbon dioxide + Water Sunlight Glucose + Oxygen
chlorophyll

CO2 + 6H2O Sunlight C6H12O6 + 6O2
chlorophyll
Glucose

The plants prepare food mainly in the form of glucose. The food prepared by
the plants are the food for animals too. Animals depend upon the food prepared
by the plants.

Essential raw materials and conditions required for photosynthesis
Photosynthesis requires the following four raw materials and conditions:

249 Times' Crucial Science & Environment Book - 8

1. Carbon dioxide (CO2)

It is the main raw material of photosynthesis. It is taken by the plants from
atmosphere through stomata. bCyOo2rggaasniissmpsredsuernitnginreasbpuinradtainont amount in
the atmosphere. It is released process. It
is also released during combustion of fuels.

2. Water (H2O)

It is another important raw material of photosynthesis. It is absorbed
from the soil by the roots and sent to the leaves by xylem. Minerals are
also supplied with water in dissolved form.

3. Sunlight

Sunlight is the natural source of energy for photosynthesis. However,
VRPH RWKHU DUWLÀFLDO VRXUFHV DUH DOVR FDSDEOH RI SURYLGLQJ OLJKW IRU
photosynthesis. The sunlight is trapped by the chlorophyll of green
plants.

4. Chlorophyll

Chlorophyll is the green pigment present in plants which trap sunlight
for photosynthesis. Chlorophyll is present in the chloroplasts of cells.
In chloroplasts, carbon dioxide and water react to produce glucose.
Thus, chlorophyll is the photosynthetic chemical and chloroplast is
photosynthetic organelle.

ĐƟǀŝƚLJ ϭϵ͘ ͘ϭ To demonstrate that starch is produced in green leaves by

photosynthesis.
Materials required:
Green leaf, alcohol, beaker, forceps, petridish, dropper, iodine solution, etc.
Procedure:
1. Pluck a fresh green leaf from a plant and keep it in water of the beaker.
2. Boil the water for few minutes then keep the same leaf in alcohol and

boil it until the leaf gets decolourized.
3. Take out the decolorized leaf from the beaker with the help of a forceps

and keep it in a petridish or white tile.
4. Put few drops of iodine to the leaf. What happens? Observe.

Ethanol

Times' Crucial Science & Environment Book - 8 250

Observation:
The decolourized leaf converts into blue black colour.
Explanation:
The changing of the leaf to blue black colour is due to action of iodine on the
starch.
Conclusion:
Starch or glucose is produced in green plants during photosynthesis.
This test is called starch test.

ĐƟǀŝƚLJ ϭϵ͘ ͘Ϯ To demonstrate that carbon dioxide is needed for

photosynthesis.

Materials required:

Potted plant, polythene bag, potassium hydroxide,
materials for starch test.

Procedure:

1. Take a potted plant and keep it in a dark
place for three days.

2. Take a polythene bag and keep a little
potassium hydroxide in the plant pot.

3. Wrap the whole plant with the polythene
bag and tie its mouth tightly so that no air
enters inside the polythene bag. WůĂƐƟĐ Potash
bag
ůĂƐƟĐ
4. Keep the plant in the sunlight for few hours. band

5. Pluck two leaves; one leaf from the bag and
another from outside plant.

6. Now, carry out starch test for both leaves. What do you observe?

Observation:

The leaf inside the bag shows negative result in starch test whereas the outside
leaf shows positive result in starch test.

Explanation:

The leaf inside the polythene bag cannot come in contact with carbon dioxide
because it is absorbed by KOH. Due to absence obfaCgOs2h, opwhsotnoseygnatthiveesirsecsaunltniont
take place. Thus, the leaf inside the polythene
starch test.

Conclusion:

Photosynthesis cannot take place in the absence of CO2 gas.

251 Times' Crucial Science & Environment Book - 8

ĐƟǀŝƚLJ ϭϵ͘ ͘ϯ To show that oxygen gas is evolved during photosynthesis.

Materials required:

Beaker, test tube, funnel, hydrilla plant or any other aquatic plant, etc.

Procedure:

1. Take a beaker and put a hydrilla or Ensure no
any other plant inside it. air tapped
Test tube
2. Invert a funnel over the plant.
3. Pour water into the beaker so that Dilute sodium
bicarborate (provides
the stem of the funnel remains CO2Ϳ ƐŽůƵƟŽŶ
inside the water.
4. Fill a test tube with water. Invert Filter funnel
the test tube over the stem of the
funnel keeping its mouth closed Hydrilla
ZLWK D ÀQJHU Wooden support

5HPRYH \RXU ÀQJHU DQG NHHS WKH DSSDUDWXV LQ WKH VXQOLJKW IRU IHZ KRXUV
What do you observe?

Observation:

Gas bubbles get evolved from the plants and get collected in the test tube by
displacing the water downwards.

When a burning matchstick is brought near the gas, the stick burns more
brighter. This shows that the gas is oxygen.

Conclusion:

Oxygen gas is evolved during the process of photosynthesis.

ĐƟǀŝƚLJ ϭϵ͘ ͘ϰ To demonstrate that sunlight is necessary for paper clip

photosynthesis.

Materials required: black paper

A potted plant with broad leaves, black paper,
cellotape, materials needed for starch test, etc.

Procedure:

1. Take a potted plant with broad leaves and parts exposed to sunlight
keep it in a dark room for
two days to make the leaves starch free.

2. Cover a part of a leaf with a black paper at both sides by using cello tape.

3. Keep the plant in the sunlight for few hours.

4. Pluck the leaf from the plant and carry out starch test on it. What do you
observe?

Times' Crucial Science & Environment Book - 8 252

Observation:
The part of the leaf which is covered by black paper shows negative result in
starch test whereas the remaining part shows positive result in starch test.
Explanation:
The part of the leaf covered by the black paper cannot come in contact with
sunlight. Therefore, photosynthesis does not take place in that part.
Conclusion:
Sunlight is necessary for photosynthesis.

byproduct : extra product
ĐŽŵďƵƐƟŽŶ : burning process
hydrilla ͗ ĂŶ ĂƋƵĂƟĐ ƉůĂŶƚ

1. Photosynthesis is a process in which green plants prepare their foods by using
water, carbon dioxide, and minerals in the presence of sunlight.

2. Starch is produced during photosynthesis.
3. Oxygen gas is produced as by-product during photosynthesis.
4. Carbon dioxide, water, chlorophyll and sunlight are required for photosynthesis.

Exercise

$ 6WDWH 7UXH RU )DOVH DQG FRUUHFW WKH IDOVH VWDWHPHQWV LI DQ\
1. Plants prepare their foods by respiration.
2. Photosynthesis takes place in mitochondria.
3. Carbon dioxide is absorbed by plants through stomata.
4. The changing of leaf into blue colour during starch test is due to
action of alcohol to the starch.
5. Carbon dioxide gas is evolved during photosynthesis.

B. Answer these questions in short.
1. What is photosynthesis? Do all plants carry out photosynthesis?
2. Where does photosynthesis take place in plants? Mention the
chemical reaction of photosynthesis.

253 Times' Crucial Science & Environment Book - 8

3. What are various essential materials required for photosynthesis?
4. Why is photosynthesis important for animals?
C. Answer these questions.
1. How can you prove that starch is produced during photosynthesis?

Explain with diagram.
2. Describe an experiment which shows that oxygen gas is evolved

during photosynthesis.
3. Describe an activity which shows that carbon dioxide is necessary

for photosynthesis.
4. Describe an activity which shows that sunlight is required for

photosynthesis.

Collect the required materials and chemicals. Then carry out the experiment
to demonstrate that oxygen is evolved during photosynthesis. Write materials
required, procedure, observation and conclusion. Provide explanation for your
observation.

Times' Crucial Science & Environment Book - 8 254

20CHAPTER Structure of
The Earth

Christiaan Huygens,

&KULVWLDDQ +X\JHQV ZDV D SURPLQHQW 'XWFK PDWKHPDWLFLDQ DQG VFLHQWLVW +H
LV NQRZQ SDUWLFXODUO\ DV DQ DVWURQRPHU SK\VLFLVW SUREDELOLVW DQG KRURORJLVW

+X\JHQV ZDV D OHDGLQJ VFLHQWLVW RI KLV WLPH

Estimated Periods : 7
Objectives: At the end of the chapter, the students will be able to:

GHILQH PLQHUDOV
WHOO IHDWXUHV DQG XVHV RI PLQHUDOV
LQWURGXFH WKH PDLQ PLQHUDOV IRXQG LQ 1HSDO
WHOO WKH W\SHV RI VRLO DQG WKH PHWKRG RI IRUPDWLRQ RI VRLO
H[SODLQ VRLO SURILOH
H[SODLQ WKH SURFHVV RI VRLO HURVLRQ DQG GHSRVLWLRQ
WHOO WKH ZD\V WR FRQVHUYH VRLO

Can you tell some minerals and their uses?
How is soil formed? Are soil and rocks related?
What is soil erosion? Is it a good process?
How can soil be conserved? Discuss with your friends.

Introduction

Our earth’s crust is made of various types of substances. They are mainly
soil, rocks, minerals, etc. Minerals are natural substances either elements or
compounds which remain together in soil and rocks or found in free state. One
piece of rock or a handful of soil contains various types of minerals. Minerals are
formed from natural substances after millions or billions of years. Minerals are
obtained from inorganic substances. Talc, ruby, emerald, diamond, graphite,
topaz, nickel, iron, gold, copper, silver, etc are some minerals.
Minerals are chemical substances either elements or compounds which are
found naturally on the earth’s crust.
0LQHUDOV FDQ QHLWKHU EH SUHSDUHG DUWLÀFLDOO\ QRU EH H[WUDFWHG IURP WKH OLYLQJ
things. They are formed naturally.

255 Times' Crucial Science & Environment Book - 8

Types of minerals

The minerals can be categorized into two types. They are metallic minerals
and non-metallic minerals.
1. Metallic minerals

The minerals which contain metal are called metallic minerals. The
metallic minerals are the compounds of metal mixed with some impurities.
7KH PLQHUDOV IURP ZKLFK PHWDOV FDQ EH H[WUDFWHG SURÀWDEO\ DUH FDOOHG
ores. Hence, all ores are minerals but all minerals may not be ores. For
example, bauxite is the ore of aluminium, haematite is the ore of iron,
chalcopyrite is the ore of copper, etc.
2. Non-metallic minerals
The minerals from which metals are not obtained are called non-metallic
minerals. Although these minerals may contain some metals such as
VRGLXP SRWDVVLXP DQG FDOFLXP WKH PHWDOV FDQQRW EH H[WUDFWHG SURÀWDEO\
These minerals are used to make chemical fertilizers, cement, etc. They
are also used to make road, bridge, house, chemicals, etc. Some of these
minerals are used as precious stones in ornaments and in making idols.
The fossil fuels such as petrol, diesel, kerosene, coal, etc are also the non-
metallic minerals. These minerals are used as fuel in vehicles, factories,
household use, etc.
Some of the features of minerals are as follows:
i) They are solid and crystalline in shape.
ii) They are either elements or compounds.
iii) They are naturally formed on the earth’s crust.
iv) They are obtained from inorganic source not from living things.
v) Minerals are found in soil and rocks mixed with other substances.
Uses
1. Minerals like iron, copper, aluminium, etc are used to make utensils,

rods for buildings, body of vehicles, wires, etc.
2. Minerals like gold, silver, ruby, topaz, etc are used to make

jewelleries and ornaments.
3. Minerals like limestone, marble, gypsum, etc are used for the

construction of buildings.
4. Living things need various minerals like iron, sodium, calcium,

magnesium, etc to get various types of nutrients.

Times' Crucial Science & Environment Book - 8 256

Occurrence of minerals in Nepal

About 300 types of minerals are found on the surface of the earth but only 100
types of minerals are common and useful to us.
Our country, Nepal is also rich in various types of minerals. Some of the
important minerals found in our country are as follows:

61 Minerals Places of occurrence

1. Iron Phulchoki (Lalitpur), Thosey (Ramechhap), Chitwan, Pyuthan

2. Magnesite Dolakha, Hetauda, Chovar

3. Lead Phulchoki, Baglung, Rasuwa, Ganesh Himal

4. Zinc Ganesh Himal, Phulchoki

5. Mica Sundarijal, Lamjung, Bajhang

6. Limestone Hetauda, Chovar, Palpa, Surkhet

7. Copper Tamakhani, Kulekhani, Bandipur

8. Gold Kaligandaki, Sunkoshi river

9. Marble Godavari, Mahabharat range

Even though our country is rich in various types of minerals, we are not able
to extract and use them. This is due to the lack of advanced technology, skilled
manpower and poor economic condition of the country.

Rocks

Rocks are hard solid parts of the earth’s crust. They consist of one or more
minerals combined with other substances. Rocks are also natural substances.
The rocks differ in their hardness and origin. On the basis of their origin, they
DUH FODVVLÀHG DV igneous rocks, sedimentary rocks and metamorphic rocks.
6RLO LV ÀQH DQG HURGHG SDUWLFOH RI WKH URFN 7KH URFN JHWV HURGHG E\ YDULRXV
weathering processes like chemical and physical processes.

Differences between rocks and minerals

Rocks Minerals

1. Rocks are hard parts of the earth’s 1. Minerals are chemical substances
crust. either elements or compounds found
on the earth’s crust.

2. Rocks are impure substances which 2. Minerals are pure substances.
consist of one or more minerals
combined with other materials.

3. Rocks may be organic or inorganic. 3. Minerals are inorganic.

4. Same type of rocks obtained from 4. Same types of minerals obtained
different places may have different from different places have the same
properties. properties.

257 Times' Crucial Science & Environment Book - 8

Soil

Crust of the earth is composed of rocks and soil. Soil is the weathered form of
rocks. It is made from tiny particles found on the earth’s crust.

The soil is very important component of the earth. It provides shelters for
various types of animals. Plants grow on the soil. It contains various minerals
and nutrients which are used by plants for the preparation of food. We
grow crops on the soil. It consists of various types of organic and inorganic
substances. Thus, it is a renewable source of mineral and various types of
organic and inorganic substances.

Types of soil

Soil of the earth’s crust differs from place to place. It is different in colour,
composition or texture 2Q WKH EDVLV RI FRPSRVLWLRQ DQG WH[WXUH VRLO LV FODVVLÀHG
into the following three types:

a) Loam soil b) Clay soil c) Sandy soil

a) Loam soil

In this soil, particles are coarse. It
consists of sand, clay and humus
in right proportion. Humus is the
remaining of dead and decayed
matters. Due to the presence of
humus, loamy soil is fertile. It can
DEVRUE DQG KROG VXIÀFLHQW DPRXQW
of water. It is the best soil for
cultivation.

b) Clay soil

,Q WKLV W\SH RI VRLO WKH SDUWLFOHV DUH YHU\ ÀQH DQG DUH WLJKWO\ SDFNHG
Water does not percolate through this soil easily. The soil does not get
dry easily. There is no any air space between the particles. Thus, it is not
good for cultivation.

c) Sandy soil

In this type of soil, the particles are bigger. It contains mainly sand and less
proportions of other particles. It absorbs water but cannot retain or hold it.
It is found in desert. It lacks humus. It is not good for cultivation. But, some
plants like cactus, pumpkin, watermelon, etc grow on this type of soil.

Soil formation

Soil is formed by breaking down of the rocks. This process is called weathering.

Times' Crucial Science & Environment Book - 8 258

The weathering may be physical, chemical or biological. It takes thousands of
years to form soil from the rocks.

The rivers or glaciers sweep away rocks, small stones, sands, dead bodies of
plants or animals. These substances collide with each other on their way and
break into small particles. This process continues and soil is formed.

During day time, rocks get heated and expanded. At night, the rocks get cooled
and contracted. Continuous expansion and contraction causes the breaking of
rocks into smaller particles.

The two processes explained above are the examples of physical weathering.
Rocks break into smaller particles by chemical changes. During rainy season,
acid rain occurs. The acid decomposes the rocks into smaller particles.

Sometimes, water enters into the small crevices of the rocks. When the
temperature becomes too low, the water freezes and converts into ice. The ice
occupies more space causing the rocks to break. Thus, smaller particles are
formed from rocks.

Roots of the plants may grow into narrow cracks of rocks. The roots grow further
and break the rocks into smaller particles. It is a way of biological weathering.

When rocks break into smaller particles, they get mixed with water, humus,
minerals and other various substances. Thus, soil is formed.

6RLO SURÀOH

When we observe vertical section of land of a particular place, we see different
OD\HUV RI WKH VRLO IURP WRS WR ERWWRP ,W LV FDOOHG VRLO SURÀOH

6RLO SURÀOH RI GLIIHUHQW SODFHV LV GLIIHUHQW *HQHUDOO\ VRLO SURÀOH KDV WKH
following layers:

A-Horizon

,W LV WKH WRSPRVW OD\HU RI WKH VRLO ,W FRQVLVWV RI ÀQH ŚŽƌŝnjŽŶ
particles. It is rich in humus and thus black in colour.
It can absorb and hold water. It is fertile and suitable
for cultivation. Many micro organisms are seen in
this layer. Plants absorb food from this layer.

B-Horizon ŚŽƌŝnjŽŶ
Below the top-soil, there is a layer of the sub-soil ŚŽƌŝnjŽŶ
which is rich in minerals with little or no humus. The
VRLO SDUWLFOHV DUH ÀQH DQG FRPSDFWO\ SDFNHG ,W LV less Bed rock
fertile and is not good for cultivation. Only few plants
have roots long enough to reach the sub-soil.

259 Times' Crucial Science & Environment Book - 8

C-Horizon
Below the sub-soil, there is a layer of weathered pieces of rocks. It is called
C-Horizon. It contains pebbles but does not contain organic matter. It contains
various types of minerals.

Bed rock

,W LV WKH ORZHUPRVW OD\HU RI WKH VRLO SURÀOH ,W FRQVLVWV RI SDUHQW URFN 7KH EHG
rock undergoes weathering and soil is formed.

ĐƟǀŝƚLJ ϮϬ͘ϭ 7R REVHUYH WKH VRLO SURÀOH

Materials required:

A beaker, soil from garden, water, a glass rod, etc. Humus

Procedure: Water

1. Take a beaker and put some soil from your Sand
garden. Gravel

2. Put water to the soil so that water level is little
more than the soil level.

3. Stir the soil with a rod and leave the beaker undisturbed for two hours
2EVHUYH DIWHU WZR KRXUV :KDW GR \RX ÀQG"

Observation:

Different layers of soil are seen. The lower most layer consists of gravels or
pebbles. Above that, there is a layer of sand. Above the layer of sand, there is
a layer of silt then the layer of clay. At the topmost part above the water, there
DUH GHDG DQG GHFD\HG RUJDQLF SDUWLFOHV FDOOHG KXPXV ZKLFK UHPDLQ ÁRDWLQJ
on water.

Soil erosion and deposition

You must have seen the sweeping away of soil from one place to another by
water or wind. Rain water, streams, rivers, waterfalls, wind, etc make the soil
loose and sweep away the soil. This process is called erosion.

Thus, erosion is the process of taking away soil or rock particles from one place
to another by the agents like wind, water, glaciers, etc.

When the soil erosion occurs, the eroded soil gets collected at a particular
place. It is called deposition. After erosion, deposition is a must. Therefore,
erosion and deposition take place side by side.

Erosion by wind

The forcefully (fast) blowing air is called wind. Wind removes and sweeps
away loose soil particles from naked hills and barren sandy land. The wind
carrying soil particles can wear away the upper surface of the rock. Thus, wind

Times' Crucial Science & Environment Book - 8 260

is an important agent for erosion of soil and rocks.

Erosion by water

Water is one of the important agents for erosion of soil. Rain water causes the
upper surface of the land and rocks to wear away gradually. The stream water
ÁRZV ZLWK KLJK VSHHG FDUU\LQJ VWRQHV DQG SHEEOHV 7KH\ FROOLGH ZLWK RWKHU
ELJJHU URFNV DQG FDXVH HURVLRQ RI URFNV :DWHU ÁRZLQJ ZLWK VSHHG erodes the
soil and other materials and washes them away to the lower land or banks.
Glaciers collide with earth’s surface and stones causing erosion of rocks and
soil. Tidal currents also cause the erosion of sand and soil of the seashore.

Effects of erosion and deposition

a. Erosion sweeps away fertile soil from cultivable land.
b. Erosion can cause landslide.
c. Erosion forms plains, plateaus and residual mountains.
d. Deposition forms plains and plateaus.
e. Deposition increases or decreases the fertility of soil.

Soil conservation

Soil is very important for living things. Plants grow on the soil. They get all
nutrients from it. We grow crops on the soil. Soil provides shelters to various
DQLPDOV (DUWKZRUP PLFH VQDNHV LQVHFWV HWF ÀQG WKHLU VKHOWHUV XQGHU WKH
soil. Soil contains various types of minerals such as iron, aluminium, ruby,
topaz, gold, copper, etc which are very useful for human beings. Thus, soil is
very important and it is to be conserved. Soil conservation is the process of
preserving or conserving the soil.
Following activities should be done for soil conservation:

a. Afforestation
Plantation of saplings is called afforestation. Roots of plants capture soil
particles tightly. Soil particles cannot be washed away by the agents like
wind, rainfall, stream water, etc if plantation is done. Thus, afforestation
in naked and barren land is one of the important ways of soil conservation.

ĐƟǀŝƚLJ ϮϬ͘Ϯ To show that soil erosion is more in bare lands.

Materials required:
Two wooden frames, two tubs, wooden block, soil, soil with plants, and sprinkler.
Procedure
i) Take two wooden frames and adjust them inclined with equal angles as

VKRZQ LQ WKH ÀJXUH

261 Times' Crucial Science & Environment Book - 8

ii) Put a tub at the lower end of each wooden frame.
iii) Put soil from garden in a wooden frame and

put soil with plant grown in the another frame.
iv) Put water to both soil with equal force from a

sprinkler. What do you observe?
Observation
The soil is eroded more in the area where there are
no plant.
Conclusion
Soil erosion is minimized by tree plantation or
afforestation

b. Terrace farming
In hilly or mountain region, the land is
sloppy. In sloppy land, the land is cut
into large plain steps called terraces.
Farming is done in such terraces. Such
farming is called terrace farming.
Terrace farming reduces the speed of
ÁRZLQJ ZDWHU DQG PLQLPL]HV WKH VRLO
erosion.

c. Reduction of the use of various chemicals
Use of chemicals like chemical fertilizers, pesticides, insecticides, etc
should be minimized. Excessive and improper use of chemical fertilizers
FKDQJHV WKH QDWXUDO FRPSRVLWLRQ RI WKH VRLO DQG PDNHV LW XQÀW IRU
FXOWLYDWLRQ ,QVHFWLFLGHV PDNH WKH VRLO SROOXWHG DQG XQÀW IRU WKH RUJDQLVPV
to survive.

d. Treatment of chemicals from industries and hospitals
Chemicals produced from industries and hospitals should be treated
before mixing to the soil. If they are mixed without proper treatment,
many problems arise in the land.

e. Recycle and reuse of the non-biodegradable wastes
The non-biodegradable substances are the substances which do not
decay. Glass, plastic, metal pieces, etc are non-biodegradable wastes.
These wastes should not be thrown to the land. These wastes should be
reused or recycled.

Times' Crucial Science & Environment Book - 8 262

talc ͗ Ă ǁŚŝƚĞ ŐƌĞLJ ƐŽŌ ŵŝŶĞƌĂů
ruby : a precious stone
emerald : a bright green precious stone
ƚŽƉĂnj : a precious stone typically pale blue coloured
crevices : narrow opening

1. Minerals are chemical substances either elements or compounds which are found
naturally on the earth’s crust.

2. Minerals like iron, copper, aluminium, etc are used to make utensils, rods for
buildings, body of vehicles etc.

3. Iron, magnesite, zinc, mica, limestone, copper, marble, etc are the main minerals
found in our country.

4. Rocks are hard solid part of the earth’s crust.

5. Soil is the weathered form of rocks.

7. Loam is a type of soil in which particles are coarse and is composed of sand, humus
and clay in proper amount.

8. Clay is a type of soil in which particles are very fine and are tightly packed.

9. Sandy soil is the soil in which particles are bigger and is composed of sand.

10. Weathering is the process of breaking down of rocks into smaller particles.

11. Physical weathering, chemical weathering and biological weathering are the various
types of weathering.

12. Soil profile includes various layers of soil observed when land of a particular place
is cut vertically.

13. Top soil is the topmost layer of the soil profile which contains humus.

14. Sub-soil is the layer of the soil which lies below the top-soil and is

composed of fine particles with little or no humus.

15. C-Horizon is the layer of the soil which consists of weathered pieces of rocks.

16. Bed rock is the lowermost layer of the soil profile which contains parent rock.

17. Erosion is the process of taking away soil or rock particles from one place to
another place.

18. Deposition is the process of collection of eroded soil particles at a particular place.

19. Soil or rock erosion is carried out by wind or water.

20. Soil conservation is the process of preserving or conserving the soil.

21. Afforestation, terrace farming, reduction in the use of chemicals, treatment of
chemicals from factories, reuse and recycle of the non-biodegradable wastes are
some activities to be done for soil conservation.

263 Times' Crucial Science & Environment Book - 8

Exercise

$ 6WDWH 7UXH RU )DOVH DQG FRUUHFW WKH IDOVH VWDWHPHQWV
0LQHUDOV DUH SUHSDUHG DUWLÀFLDOO\ E\ KXPDQ EHLQJV
,URQ PDJQHVLXP JROG FRSSHU JUDSKLWH IUXLWV ÁRZHUV HWF DUH
minerals.
3. Minerals are used to make buildings, statues, etc.
4. Rocks are composed of various types of minerals.
5. All rocks are formed from organic substances.
6. C-horizon soil is good for cultivation.
&OD\ FRQWDLQV ÀQH SDUWLFOHV ZKLFK DUH WLJKWO\ SDFNHG
8. Soil is eroded by wind and water from one place to another.

B. Answer these questions in brief.
1. What is mineral? Give some examples.
2. Mention some features of minerals.
3. Explain uses of minerals.
4. What is soil? Mention various types of soil.
5. Which soil is the best soil for cultivation? Why?
:KDW LV VRLO SURÀOH" 0HQWLRQ YDULRXV OD\HUV RI VRLO SURÀOH 6KRZ
them in a diagram.
7. What is erosion? What are the various effects of soil erosion?
8. What is soil conservation? What are the various activities for soil
conservation?

C. Give reasons:
1. Soil is another form of rock.
2. Loamy soil is the best for cultivation.
3. Erosion and deposition go side by side.
4. Soil erosion can be controlled by afforestation.
5. Terrace farming is done in hilly and mountainous regions.

Times' Crucial Science & Environment Book - 8 264

D. Differentiate between:
1. Minerals and rocks
2. Loam and clay
3. Top soil and sub soil
4. Erosion and deposition

E. Answer these questions.
1. Explain various types of minerals present in Nepal. Where are they
located?
2. Explain the soil formation process.
3. Explain the soil erosion process.
4. Explain the soil conservation methods.

Visit a landslide affected area and carefully observe the different layers of soil.
<RX FDQ VWXG\ VRLO SURÀOH ZLWK WKH KHOS RI WKDW DUHD

265 Times' Crucial Science & Environment Book - 8

21CHAPTER Weather and
Climate

Edmond Halley,

(GPRQG +DOOH\ ZDV DQ (QJOLVK DVWURQRPHU JHRSK\VLFLVW
mathematician, meteorologist, and physicist who is best known
IRU FRPSXWLQJ WKH RUELW RI +DOOH\
V &RPHW +H ZDV WKH VHFRQG

$VWURQRPHU 5R\DO LQ %ULWDLQ VXFFHHGLQJ -RKQ )ODPVWHHG

Estimated Periods : 7
Objectives: At the end of the chapter, the students will be able to:

GHILQH ZHDWKHU DQG H[SODLQ LWV IDFWRUV
GHVFULEH WKH DYHUDJH FOLPDWLF FRQGLWLRQV RI 1HSDO
H[SODLQ WKH SURFHVV RI PRQVRRQ LWV DUULYDO LQ 1HSDO DQG HIIHFWV RI PRQVRRQ

What is weather?
How is weather different from climate?
What factors affect the climate of a place?
How does rainfall occur? Discuss.

Weather

Weather is the sum of all processes occurring in a particular area at a
particular time. In general, weather refers to a day-to-day temperature,
rainfall, humidity, sunshine, etc. The weather occurs due to the differences
in temperature and moisture of different places. The weather includes wind,
cloud, rain, snow, frost, etc.

Climate

The average atmospheric conditions of a particular place over a long period
of time is called climate. For the climatic average, a minimum period of 35
years is needed. The climate of a particular place is determined with the help
of systematic observation, recording and analysis of various factors such as
temperature, rainfall, wind, cloud, sunshine, humidity, atmospheric pressure,
etc.
There are separate branches of science to study the weather and climate.
Meteorology is the branch of science that deals with weather whereas
climatology is the branch of science that deals with climate.

Times' Crucial Science & Environment Book - 8 266

Determining factors of climate

A bigger area of land which has more or less similar type of hotness, coldness,
precipitation, atmospheric pressure, wind, etc is called a climatic region. There
are different climatic regions in the world because different factors determine
the type of climate in different places.

Hence, we do not experience similar type of climate at the same time in
different parts of the world. The major factors that affect the climate of a place
are:

1. Altitude of a place from the sea level

The density of air is higher at the 1°C

lower altitude as it contains carbon Atmospheric Temperature 5°C
dioxide, dust particles, nitrogen in winter
oxides, water vapour, etc. Due to 9°C
these factors, the atmosphere at
lower altitude absorbs more heat. Temperature inside the crust
Sea

17°C 21°C 25°C

The atmosphere at higher altitude
is thinner and absorbs less heat. Hence, the land area at lower altitude
is hotter than that at higher altitude. It is the reason why it is hotter in
the Terai than in hilly region.

The temperature decreases when we go higher from the sea level. In an
average, the temperature decreases by 1°C for every 165m above from
the sea level.

2. Distance of a place from the equator

An imaginary circular line
that divides the earth into two
equal halves is called equator.
The equator of the earth lies at
the shortest distance from the
sun. The rays from the sun fall
vertically on the equator but fall
slanting in the areas towards the
poles. The vertically falling rays
have to heat small area only but the slanting rays have to heat greater
area through wide atmosphere. Some heat of the slanting rays is lost
in the atmosphere before reaching the earth’s surface. Hence, the areas
near the equator are hotter than those away from the equator.

The climate of a place is also affected by the distance of the place from
the sea, features of topography, slope of the land, local factors (such as
river, lake and valley), etc.

267 Times' Crucial Science & Environment Book - 8

3. Distance of a place from sea

The climate of a place is also affected by its distance from the sea. It is
due to the difference in VSHFLÀF KHDW FDSDFLW\ of water and land. Land
gets heated faster and cools down faster. On the other hand, water gets
heated slowly and cools down slowly. Due to this difference, the sea water
is still hot when the land turns cold. Similarly, the sea is still cold when
the land is hot due to solar heat.

In the coastal regions, hot air from sea blows toward land during winter
and cold air from sea blows toward land during summer. Therefore, these
regions have temperate and pleasant climate round the year. As the air of
such region contains a lot of water vapour, it rains frequently in these regions.

As we go away from the sea level especially toward the inner parts of
FRQWLQHQWV PRUH ÁXFWXDWLRQ LQ FOLPDWH LV REVHUYHG ,Q WKHVH DUHDV LW
is very hot in summer and very cold in winter. Such climate is called
extreme climate.

Climatic conditions of Nepal

Climate of a place is determined on the basis of statistics of temperature,
humidity, atmospheric pressure, rainfall, wind, etc over a long period of time.
The climate of a place is affected by its latitude, altitude, terrain, nearby water
bodies and their currents.

Despite being a small country, Nepal has all kinds of climatic conditions. The
climate of our country varies with its altitude and topography. It ranges from
tropical climate to tundra climate. An approximate account of the climate
found in the different parts of our country is given below:

Terai and inner terai : Tropical climate

Hilly region : Sub-tropical and temperate climate

Himalayan region : Apline climate

The low-land plains of the Terai have a tropical climate. The atmosphere of
this area remains hot and humid for most time of the year. The maximum
temperature can rise up to 45°C during the hot summer days.

The mid-land hilly regions have a pleasant sub-tropical and temperate climate.
The temperate climate means neither too hot nor too cold. It is also called
moderate climate. The days have favourable climate almost round the year but
the winter nights are chilly cold. The northern Himalayan (mountain) region
has an alpine climate. The climate is cold almost round the year. The high
mountains are covered with snow. There is less rainfall and more snowfall in
these areas. The upper Himalayas have tundra and Tiga vegetation. But the
lower slopes of Himalayas consist of coniferous plants.

Times' Crucial Science & Environment Book - 8 268

Process of monsoon

The word monsoon has been derived from an Arabic word mausam which
means the change in climatic conditions. 7KH PRQVRRQ LV GHÀQHG DV D VHDVRQDO
wind of the Indian Ocean in the southern part whose direction of movement is
reversed in regular period of time.
In summer, the rays from the sun fall perpendicularly on the northern
hemisphere of the earth. Nepal also lies in the northern hemisphere. The
direct sun rays heat up the surface of the earth. Thus, the air near the earth’s
surface becomes hot and rises up. This decreases the atmospheric pressure
near the hot area. But, the atmosphere above the sea is cold and its pressure
is high. Hence, the moist air containing water vapour from the high pressure
zone moves towards the low pressure zone in the form of wind. This wind is
saturated with water vapour. The wind at higher altitude becomes colder and
condenses to form clouds. When these clouds come across the high mountains,
they get cooled further and condense to form rainfall. This rain is called
monsoon rain.

Arrival of monsoon in Nepal

The monsoon enters from the south-east of Nepal in the summer season. This
monsoon is originated from the Bay of Bengal. During the summer, the water
YDSRXU ULVLQJ IURP WKH %D\ RI %HQJDO HQWHUV 1HSDO DQG ÁRZV WRZDUGV WKH
north and west. When the vapour reaches the northern hills and mountains, it
is blocked to a large extent and is condensed. This causes rainfall. The vapour
WKDW ÁRZV WRZDUGV WKH ZHVW RI 1HSDO FRQGHQVHV VORZO\ DQG FDXVHV UDLQIDOO LQ
different parts of the country. The eastern part of Nepal receives more rainfall
than the western in the summer.
During winter, Asia as well as Nepal receives less heat because the sun rays
fall slanted in this area during this season. Hence, the atmosphere of Nepal is
cold and has higher pressure. But the atmospheric pressure above the warmer
seas is less. This difference in atmospheric pressure causes the blow of air from
ODQG WRZDUGV VHD 6LQFH WKH DLU WKDW ÁRZV IURP ODQG WR VHD GRHV QRW FRQWDLQ
much water vapour, it causes less rainfall.

Effects of monsoon

Monsoon causes a lot of rainfall in Nepal. More than 80% of the annual rainfall
occurs within the period of monsoon, i.e. June to September in Nepal. The
monsoon is the major rainfall event upon which most of the agriculture and
agro-industries are based in Nepal.
Major crops like paddy, sugarcane, vegetables, fruits, etc are grown during
this season.

269 Times' Crucial Science & Environment Book - 8

Paddy Apple Sugarcane

The heavy rainfall during the monsoon also brings serious problems of ÁRRGV
and landsides in Nepal. The heavy rainfall increases the volume of water in
the rivers. The swollen rivers can enter the settlement areas in the form of
ÁRRG DQG FDXVH KHDY\ ORVV RI OLIH DQG SURSHUW\ 7KH ÁRRG LQ WKH .RVKL ULYHU KDV
destroyed life and property in large amount. It has taken lives of hundreds of
people and destroyed the fertile lands, cattle,
houses, crops, and other property of people. The
landslides take the lives of several people and
destroy their property during every monsoon in
Nepal.

The rainfall accompanied by a storm is more īĞĐƚ ŽĨ ƐƚŽƌŵ
destructive. It can break the electric poles,
branches of trees or even uproot the trees. They
can destroy the life and property of the people.

Sea breeze and land breeze

A soft and gentle wind that blows mainly in seashore is called breeze. The
breeze can be categorized into two types on the basis of its origin. They are
land breeze and sea breeze.

^ĞĂ ďƌĞĞnjĞ ;Ăƚ ĚĂLJͿ >ĂŶĚ ďƌĞĞnjĞ ;Ăƚ ŶŝŐŚƚͿ

During day time, the land gets heated faster than water. The heated land
heats up the air near it. The heated air being lighter moves up and a partial

Times' Crucial Science & Environment Book - 8 270

empty space (vacuum) is created. But, the sea water surface is still cold and
the cold air from the sea blows towards the land to occupy the empty space.
This blow of soft and gentle air from sea to land is called sea breeze. The sea
breeze occurs at day.
At night, the land cools faster than the sea water. But the sea water is still
hot. So, it heats up the air nearby it and a partial vacuum is created. Hence,
the cold air from the land blows towards the sea. This is called land breeze.
The land breeze occurs at night.

humidity : amount of water vapour in air

topography : arrangement of natural feature of an area

Bay of Bangal : north eastern part of Indian Ocean

1. Weather is the sum of all atmospheric processes occuring in a particular area at a
particular time

2. The average atmospheric conditions of a particular place over a long period of time
is called climate.

3. The branch of science that deals with weather is called meteorology.

4. The branch of science that deals with climate is called climatology.

5. The climate of a place is determined on the basis of statistics of temperature,
humidity, atmospheric pressure, rainfall, wind, etc. over a long period of time.

6. The climate of Nepal varies with its altitude and topography.

7. An area at lower altitude is hotter than that at higher altitude.

8. The monsoon is defined as the seasonal wind of Indian Ocean in the southern part
whose direction of motion is reversed in regular period of time.

9. The rainfall which is caused by monsoon wind is called monsoon rain.

10. The monsoon enters from south-east of Nepal in the summer season.

Exercise

A. Answer these questions in very short.
1. What is weather ?
2. What affects the climate of a place ?
3. What is the climate of hilly region of Nepal?
4. What is a climatic region?

271 Times' Crucial Science & Environment Book - 8

5. How does temperature decrease for every 165m above from the sea
level?

6. What is monsoon ?
7. Where does monsoon enter Nepal from ?

B. Write down differences between:
1. Weather and climate
2. Sea breeze and land breeze
3. Summer rainfall and winter rainfall

C. Give reasons:
1. Monsoon rainfall is useful as well as dangerous.
2. Eastern part of Nepal receives more rainfall than the western
during monsoon.
3. The atmosphere is hotter at less altitude from the sea level.
4. It is hot at the equator.

D. Answer these questions.
1. Explain the climatic conditions of Nepal.
2. State and explain the major factors that affect the climate of a
place.
3. How does monsoon bring rainfall in summer?
4. Explain the devastating effects of monsoon.

Organize a tour to visit different parts, i.e. Terai, Hill and Mountain regions
of our country. Observe the weather and climatic conditions of each part and
prepare a brief report.

Times' Crucial Science & Environment Book - 8 272

22CHAPTER The Earth
and Space

Sir Harold Jeffreys

6LU +DUROG -HIIUH\V ZDV DQ (QJOLVK PDWKHPDWLFLDQ VWDWLVWLFLDQ
JHRSK\VLFLVW DQG DVWURQRPHU +LV ERRN 7KHRU\ RI 3UREDELOLW\
ZKLFK ÀUVW DSSHDUHG LQ SOD\HG DQ LPSRUWDQW UROH LQ WKH
UHYLYDO RI WKH %D\HVLDQ YLHZ RI SUREDELOLW\

Estimated Periods : 7
Objectives: At the end of the chapter, the students will be able to:

H[SODLQ WKH K\SRWKHVLV DERXW WKH RULJLQ RI WKH HDUWK
WHOO WKH UHDVRQV IRU HYROXWLRQ RI OLIH RQ WKH HDUWK
H[SODLQ WKH SRVLWLRQV RI WKH HDUWK DQG WKH VXQ LQ YDULRXV VHDVRQV
WHOO WKH PHDQLQJ RI SKDVHV RI WKH PRRQ
WHOO WKH SRVLWLRQV RI WKH PRRQ LQ GLIIHUHQW SKDVHV RI WKH PRRQ

Can you say how our earth is evolved?
How is life possible on the earth?
Why does season change?
Have you seen the change in the shape of the moon every night? Discuss with
friends.

Introduction

The earth is a member of solar system. It is only the planet where life is
possible. It contains suitable conditions such as presence of oxygen, water,
suitable temperature, air pressure, etc for the survival of life. Thus, life is
possible on the earth.
There are many undiscovered questions about the origin of the earth. Many
scientists have put forward their views about the origin of the earth. But, no
universal theory of the origin of the earth has been put forward yet. Some of
the main hypotheses about the origin of the earth are as follows:

1 Planetesimal hypothesis

Old Planetesimal hypothesis was put forward by a French scientist
George Wofan in 1749 A.D. According to this hypothesis, the earth along

273 Times' Crucial Science & Environment Book - 8

with other planets and satellites was formed when the revolving comet
collided with the sun and materials got
separated from the sun in the thread-like
arms. The materials cooled and formed
solid particles called planetesimals. From
those planetesimals, the planets along
with the earth were formed.

2. Nebular hypothesis Comet

German philosopher Immanuel Kant put forward a hypothesis named
QHEXODU K\SRWKHVLV LQ $ ' ,W ZDV PRGLÀHG ODWHU E\ D )UHQFK
astronomer Laplace in 1796 A. D. According to this theory, the earth and
other heavenly bodies were originated from nebula. The nebula is the big
mass of the dust, cloud and gases.

According to this theory, nebula attracted more dust particles, clouds
and gases. When its mass increased, its gravity also increased but its
size decreased. When it became smaller, it started to spin faster. As the
surface got cooled by the radiation, a ring of matter was formed around
the surface. The ring escaped from the surface of the main body and
planets were formed. The main core mass is the sun.

3. Tidal hypothesis

English astronomers Sir James Jeans and Sir Harold Jeffrey proposed
Tidal hypothesis in 1917 A. D. According to this theory, a big star passed
QHDUE\ WKH VXQ $ ORQJ ÀODPHQW RI JDVHV ZDV GUDZQ IURP WKH VXQ E\ WKH
KXJH JUDYLW\ RI WKH ELJ VWDU 7KH RXWHU SDUW RI WKH ÀODPHQW HVFDSHG LQ WKH
space and inner part came back to the sun. But the middle part of the
ÀODPHQW GHWDFKHG WR D VHULHV RI URXQG VWUXFWXUHV RI GLIIHUHQW VL]HV 7KH\
were planets. In this way, the earth along with the other planets were
originated.

4. Formation of solar system from Milky Way

According to this hypothesis, the sun was formed due to the attraction
and collection of dust particles from the Milky Way galaxy. In the same
way, other planets and satellites were formed from the dust and started
to revolve the sun in their elliptical orbits.

Scientists argued that the earth was originated about 4.5 billion years
ago. Scientists calculated the age of the earth by studying the rocks
and fossils of pre-historic time. Radioactivity of the rocks and fossils
ZHUH VWXGLHG WR ÀQG WKH VWUXFWXUH DQG DJH RI GLIIHUHQW W\SHV RI URFN DQG
organisms on the earth. It is called radioactive dating.

Times' Crucial Science & Environment Book - 8 274

6RPH VWDWLVWLFDO GDWD UHODWHG WR WKH HDUWK

1. Estimated age 4.5 billion years

2. Total Surface area 5, 09, 700, 000 km2

3. Area of land 14840000 km2

4. Area of water covered surface 3,61,300,00 km

5. Diameter 12,756 km

6. Mass 6 × 1024 kg

7. Number of satellite 1 moon

8. Average temperature 20°C

Evolution of life on the earth

There were no favourable conditions for the existence of life when the earth was
originated. There was no free oxygen in the beginning. Oxygen was in combined form
with other chemicals in rocks. When rocks of the interior part of the earth melted,
oxygen was produced and freed to the atmosphere. Water was also produced due to
the chemical reaction occurred in the interior of the earth. When oxygen and water
were produced, the conditions on the earth became favourable for the life.

The atmosphere became rich in water, carbon dioxide and methane. The
wIRaUPte rS(UHRW2HOL)Q, carbon LdV ioWKxiHd eED(VCLOF 2F)RaPnSdRQmHeQtWh aRIn eOLY(CLQHJ 4)WKcLoQmJbV i n7eKdXtVo gWeKtHh eÀrUtVoW
ZKLFK
protein containing body prokaryotic cells were developed. Prokaryotes are the
unicellular living things having poorly developed nucleus.

Gradually the conditions of the earth became favourable for other types of
organisms too. After prokaryotes, cyanobacteria and bacteria were evolved.

About 540 million years ago, there occurred change in the environmental
condition of the earth which set favourable conditions for the existence of
invertebrates such as trilobites and branchiopods. Early plants and insects
were also evolved at this period.

About 250 million years ago, drastic climatic changes occurred. Very big
animals and plants appeared. Dinosaurs and giant fern plants appeared at this
SHULRG 9DULRXV W\SHV RI ÁRZHULQJ SODQWV VXFK DV FRQLIHUV DQG J\PQRVSHUPV
also appeared in this period.

About 65 million years ago, again there occurred drastic change in the
environmental conditions such as fragmentation of rocks, change in atmosphere,
etc. Consequently, many organisms like dinosaurs became extinct and various
types of animals like mammals and aves were evolved.

Thus, various types of organisms appeared from the time of origin of the earth
till now. Some of them became extinct and turned into fossils. Some of them
DUH SUHVHQW WRGD\ WRR %XW WKH ÀUVW RUJDQLVPV ZHUH SURNDU\RWHV

275 Times' Crucial Science & Environment Book - 8

Motion of the earth Axis
ƐƵŶΖƐ ƌĂLJƐ
The earth moves around the sun and round on its
own axis, too. The movement of the earth around ŝƌĞĐƟŽŶ ŽĨ ĂƌƚŚΖƐ ƐƉŝŶ
WKH VXQ LQ D À[HG SDWK LV FDOOHG revolution or annual
motion. The movement of the earth around its own
axis is called rotation or diurnal motion. The earth
takes about 24 hours to complete one rotation. The
rotation of the earth causes day and night. The earth
takes around 365 days to complete one revolution
around the sun. The evolution of the earth has direct
effect on the change in the seasons and variation in
the length of day and night.

Day and night

When the earth moves around its axis, only a part of its surface faces towards
the sun and experiences the day. The other portion remains hidden from the
sun and experiences the night. Thus, day and night is the effect of diurnal
motion of the earth.

Earth tilt
Polar day

DAY SUN RAYS
EQUATOR
NIGHT

Polar night

ĐƟǀŝƚLJ ϮϮ͘ϭ To observe the day and night.

Materials required:
A candle, a globe, etc.
Procedure:
1. Take a globe in a dark room.
2. Light a candle and place it about

4-5 feet away from the globe. What
do you observe?

Times' Crucial Science & Environment Book - 8 276

Observation:
The part of the globe which faces to the candle is bright. It represents the day.
Another portion which is hidden from the candle is dark. It represents the
night.

Revolution of the earth and its effects

The earth moves around the sun in an elliptical path called orbit. The earth
takes 365.25 days to make one complete revolution. But 365 days time is
considered as 1 year and extra one day is added in every 4 years. Thus, after
every 4 years, extra 1 day is available for that year. Hence, in an interval of
every 4 years, the duration of the year becomes 366 days. It is called leap year.
The axis of the earth is tilted by 66.5° to the plane of its orbit. Due to it, there
occurs change in seasons and variation in the length of day and night.

Following diagram illustrates the change in the seasons and variation in the
length of day and night.

When the earth is in 21st June 21st March
position A, the northern A D 22nd December
hemisphere is tilted
towards the sun whereas C
the southern hemisphere B
is tilted away from the
sun. In this condition, the 23rd September
sun rays directly fall to the ŚĂŶŐĞ ŝŶ ƐĞĂƐŽŶ ĚƵĞ ƚŽ ƌĞǀŽůƵƟŽŶ ŽĨ ƚŚĞ ĞĂƌƚŚ
northern hemisphere and
there is summer in northern
hemisphere. The northern
hemisphere has the longest
day and the shortest night.
It is called summer solstice.
This day is June 21st.

When the earth is in position C, the southern hemisphere is tilted towards
the sun whereas the northern hemisphere is tilted away from the sun. In this
condition, the sun rays directly fall to the southern hemisphere and there is
summer in the southern hemisphere. The southern hemisphere has the longest
day and shortest night. It is called winter solstice. This day is December 22nd.

When the earth is in positions B and D, both hemispheres receive equal amount
of sunlight and the days and nights are equally longer in both hemispheres.
When earth is in position B, it is 23rd September. It is called autumn equinox.
When the earth is in position D, it is 21st March. It is called spring equinox.

From 21st June to 22nd December, the days in the northern hemisphere become

277 Times' Crucial Science & Environment Book - 8

shorter and nights longer. Whereas, the days become longer and the nights
shorter in the northern hemisphere from 22nd December to 21st June.

Around the north pole, i.e. Artic circle and the south pole, i.e. Antartic circle,
there is six month’s day and six month’s night.

There is no effect of tiltation of the axis of the earth for the equator. The days
and nights are always equal at the equator.

Phases of the moon

:KHQ ZH REVHUYH WKH VN\ IRU VRPH QLJKWV ZH ÀQG WKH FKDQJH LQ VKDSH RI WKH
moon every night. Different shapes of the moon in the sky are called phases
of moon.

The causes for the change in the shape of the moon every night are as follows:

a. The moon does not have its own light.

b. The moon moves around the earth in an elliptical path.

When the moon in position mpo1s, itthioenm, tohoen makes an angle of 0° with the orbital
plane of the earth. In this part of the moon, on which sunlight
falls, faces to the sun. Whereas, the dark part faces towards the earth and no
any part of the moon can be seen from the earth. It is called New moon. After
1 day, the moon moves little and makes an angle of 18° with the plane of orbit.
In this pcroessitcieonnt.(Amf2t)e,rathliimtstls3etabgreig, hthtepbarritghist seen from the earth. It is called
waxing part of the moon increases.

m4 m2

First Qu arter

Waxing CWraesxcinegnt
Gi bbous
m5 Full Moon EARTH m1 SUN

New Moon

Waning CWraesncinegnt
Gi bbous Last Quarter

m6 m8

m7

Phases of the moon

When the moon remains at an angle of 90° with the orbital plane, half part of
the moon seems bright. It is called ÀUVW TXDUWHU P3). The moon moves forward

Times' Crucial Science & Environment Book - 8 278

and when tchoims epsotsoittihoen,pvoseirtyiolnit(tmle4)p, aitrtmoafktehseanmaonongleseoefm16s8d°awrikt.hItthiesocrablilteadl
plane. In
waxing gibbous. When itthriseapcohseitsioton,ththeepomsiotoinonsmee5m, ist makes an angle of 180°
to the orbital plan. In completely round. It is
called full moon.
After full moon, the moon further moves and makes an angle of 192°. In this
pImnoosotihtniioscnopm(omseis6t)i,toolnit,ptohlesailtpfiaohrnetm(smeise7)pm,hsietrdmearaokkf .etsIhteainsmcaoanolnglelesdeoewfma2ns7i0bn°rgitgohgittb.hbIeotuoirssb. ciWtaalhlleepdnlaltanhseet.
quarter. The moon further moves and comes to position (tmhe8)m. Ionotnhcisancobnedisteieonn.,
the moon makes an angle of 348° and very little part of
It is called wanning crescent. After this the moon comes to the position m1. It
is again new moon.
Thus, when the moon completes one revolution around the earth, it passes
through different stages. The time period in which the moon makes one
complete revolution around the earth is lunar month. The period in which
the bright part of the moon increases is called bright half or Sukla Paksha.
The period in which the dark part of the moon increases is called dark half or
Krishna Paksha.

Sidereal month and synodic month

The earth moves around the sun and the moon moves around the earth in
À[HG RUELWV 7KH\ PRYH LQ DQ DQWLFORFNZLVH GLUHFWLRQ

The moon completes one revolution Earth m1
around the earth in 2713days. (27 days
7 hours 43 minutes 11.5 sec). This
period is called sidereal month.

,Q WKH JLYHQ ÀJXUH WLPH WDNHQ E\ WKH Sun
moon to move from position m1 to m2 is
sidereal month. m3

When the moon is in pmosoiotniocnommp1,leitteiss Earth m2
new moon. When the
one revlution around the earth and
comes Ftoorptohseitnioenxtmn2e,wthmeroeonistonoocncuewr,
moon. ZĞǀŽůƵƟŽŶ ŽĨ ƚŚĞ ŵŽŽŶ

the moon has to travel little orbital distance and come to pthoesittiootnalmt3i.mFeortatkheisn,
moon takes 2 days 5 hrs and 51.5 seconds more. Thus,
by the moon to come to the next new moon from the previous new moon is

m(27o1n3 tdha. y + 2 days 5 hours 51.5 seconds) 29 1 days. This period is called synodic
2

279 Times' Crucial Science & Environment Book - 8

The duration between two consecutive new moons or similar phases of the
moon is called synodic month.

6LGHUHDO 0RQWK 6\QRGLF 0RQWK

1. It is the actual time taken by the 1. It is the duration between two
moon to complete one revolution consecutive new moons or similar
around the earth. phases of the moon.

2. Its value is 2713 days. 2. Its value is 29 1 days.
2

ĞůůŝƉƟĐĂů : oval or egg shaped

pre-historic ͗ ƉĞƌŝŽĚ ďĞĨŽƌĞ ǁƌŝƩĞŶ ƌĞĐŽƌĚƐ

1. The earth is the living planet of solar system.

2. Planetesimal hypothesis was propounded by French scientist George Wofan.

3. Nebula is the big mass of dust, cloud, gases, etc.

4. The earth was originated along with other planets 4.5 billion years ago.

5. The first living things originated on the earth were prokaryotes.

6. About 65 million years ago, mammals and aves were evolved.

7. The movement of the earth around the sun is called revolution or annual motion.

8. The movement of the earth around its axis is called rotation or diurnal motion.

9. The part of the earth which faces to the sun experiences the day.

10. The part of the earth which gets hidden from the sun experiences the night.

11. In summer solstice the northern hemisphere has the longest day and the shortest
night.

12. In winter solstice, the southern hemisphere has the longest day and the shortest
night.

13. The position of the earth at which the days and nights are equal is called equinox.

14. Different shapes of the moon which can be observed when seen in the sky are
called phases of moon.

15. The period of a month in which bright part of the moon increases is called bright
half.

16. The period of a month in which the dark part of the moon increases is called dark
half.

17. The time needed for the moon to make one complete revolution around the earth is
sidereal month.

18. The duration between to consecutive new moons or similar phases of the moon is
called synodic month.

Times' Crucial Science & Environment Book - 8 280

Exercise

A. Answer these questions in short.

1. What is rotation of the earth? What are the effects of rotation?

2. What is revolution of the earth? What are the effects of revolution?

3. When do days and nights occur?

4. What is a leap year?

5. What is summer solstice?

6. When does the northern hemisphere have the shortest day and the
longest night?

7. What is equinox? What are the dates for equinox?

8. What are the phases of the moon?

9. What is new moon?

'HÀQH WKH IROORZLQJ WHUPV

i. Waning gibbous ii. Last quarter iii. Waxing crescent

11. What is dark half and bright half?

12. What is synodic month? Mention its duration.

B. Differentiate between:
1. Bright half and dark half
2. Sidereal month and synodic month
3. New moon and full moon
4. Summer solstice and winter solstice

C. Give long answers:
1. Explain the planetesimal hypothesis about the origin of the earth.
2. Explain Tidal hypothesis of the origin of the earth.
3. How did evolution of the life take place on the earth?
4. Draw revolution of the earth around the sun to show the change of season.
5. Why is synodic month longer than sidereal month?
6. Draw the phases of the moon when the moon revolves around the earth.

Observe the shapes of the moon for all 15 days of a bright half (Shuklapaksha).
Draw the shape of the moon that you see each day and describe the phases of
the moon.

281 Times' Crucial Science & Environment Book - 8

23CHAPTER Environment
and Its Balance

Charles Darwin

Charles Robert Darwin, was an English naturalist,
geologist and biologist, best known for his
FRQWULEXWLRQV WR WKH VFLHQFH RI HYROXWLRQ

Estimated Periods : 14
Objectives: At the end of the chapter, the students will be able to:

H[SODLQ WKH GHSHQGHQFH RI KXPDQ EHLQJV RQ IRRG VKHOWHU PHGLFLQDO SODQWV DQG RWKHU
QDWXUDO UHVRXUFHV

H[SODLQ WKH QHHG DQG LPSRUWDQFH RI IRUHVW
H[SODLQ WKH LPSRUWDQFH RI ZLOGOLIH DQG HQOLVW VRPH HQGDQJHUHG VSHFLHV RI DQLPDOV
HQOLVW DQG EULHIO\ H[SODLQ WKH QDWLRQDO SDUNV ZLOGOLIH UHVHUYHV DQG FRQVHUYDWLRQ DUHDV

RI 1HSDO
LQWURGXFH VRPH SURWHFWHG ZLOGOLIH RI 1HSDO

What do human beings get from the environment?
Can you name some food plants?
Can you name some medicinal plants of mountain, hill and Terai regions?
Can you name some timber trees of different regions? Discuss.

Introduction

Human beings have been dependent on the natural resources since their
appearance on the earth. Water, soil, air, minerals, sun, fossil fuels, forest,
grass, land, mountains and wildlife are the natural resources. Every natural
resource has some utility. All the organisms including human beings also
depend on natural resources for their survival, reproduction, growth and
development. Most of the natural resources are formed, used up and then
recycled in nature. For example, old grass plants and trees die during the
course of time. Then, new plants and trees grow in the same place. Similarly,
oxygen of air is utilized by organisms for breathing. This decreases the amount
of oxygen in air. But the green plants continuously release oxygen into the air
during the process of photosynthesis. This process increases the amount of
oxygen in the air. Thus, the use and production of oxygen in nature balances
its amount in the atmosphere. In the similar processes, the amount of other
natural resources is also balanced.

Times' Crucial Science & Environment Book - 8 282

The dependence of human beings on some of the natural resources is given
below:

1. Food

The plants are the main source of food for the human beings. The food
SODQWV FDQ EH FODVVLÀHG LQWR FHUHDOV OHJXPHV VSLFHV YHJHWDEOHV DQG
fruits.
The monocotyledonous plants such as rice, wheat, maize, barley, millet,
etc are known as cereals. Maize and rice are the main crops of Nepal.

ƌŝĐĞ ŵĂŝnjĞ ǁŚĞĂƚ

Legumes are the dicotyledonous plants that provide pulses. Pea, bean,
gram, soyabean, etc are some legumes. Similarly, onion, garlic, turmeric,
ginger, coriander, cumin seed, black pepper, chilli, etc are used as spices.
7KH VSLFHV DUH WKH SODQW SURGXFWV WKDW DGG WDVWH DQG ÁDYRXU WR RXU IRRG

pea gram garlic

We use different parts of plants as vegetables. For example, roots of
radish, carrot, turnip, stem of potato, arum, leaves of spinach, broad
mustard (rayo), mustard, cabbage and garden cress, fruits of cucumber,
pumpkin, capsicum, brinjal, gourds, etc are used as vegetables. The
plants like mango, apple, guava, banana, orange, pineapple, peach,

283 Times' Crucial Science & Environment Book - 8

plum, pear, etc give us fruits.

ĐƟǀŝƚLJ Ϯϯ͘ϭ Visit your locality and observe the different types of food plants.

Write down their name, draw diagram and explain them in term of season of
cultivation and importance. Show your work to your teacher.

2. Shelter

We need land (a natural resource) to build our houses and buildings. The
materials used for making house such as stones, gravel, sand, soil, etc
are also the natural resources. The bricks are made using the natural
resources, soil and water. The forest is the natural resource that provides
wood for building our houses. The metals used for making rods, pipes,
nuts, etc are also obtained from nature. Thus, we depend on nature for
our shelter.

3. Medicinal plants

The plants whose parts or whole body are used as medicine are called
medicinal plants. The parts such as root, stem, bark, leaf, rhizome, etc of
plants are useful in healing wounds, illness or infection. The geographical
distribution and varying climatic conditions have favoured the growth of
hundreds of medicinal plants in Nepal. It has been estimated that about
800 species of medicinal plants are found in Nepal. About 60 species of
medicinal plants are being exported to other countries from Nepal.

The medicines obtained from plants have no side effects if they are used
in right way. The consumption of such plants helps people to stay healthy.

A number of medicinal plants are found in different geographical regions
of Nepal. The medicinal plants such as Amala, Asuro, Harro, Barro,
Sarpagandha, Rajbriksha, etc are found in the Terai region. Similarly,
Chutro, Timur, Dhaturo, Chiraito, Bojho, Sugandhawal, etc are found in
Hilly region. Yarsagumba, Jatamashi, Panchaunle, Padamchal, Bikhma,
etc are the medicinal plants found in the Himalayan (mountain) region
of Nepal.

Some medicinal plants found in Terai region:

61 Local name 6FLHQWLÀF ERWDQLFDO QDPH

1. Amala (PEOLFD RIÀFLQDOLV

2. Tulasi 2VFLPXP VDQFWXP

3. Asuro $GKDWRGD YDVLFD

4. Harro 7HUPLQDOLD FKHEXOD

5. Barro 7HUPLQDOLD EHOHULFD

6. Rajbrikasha &DVVLD ÀVWXOD Ashok

Times' Crucial Science & Environment Book - 8 284

7. Sarpagandha 5DXZROÀD VHUSHQWLQD

8. Pipala 3LSHU ORQJXP

9. Ashok 6DUDFD LQGLFD

10. Neem $]DGLUDFKWD LQGLFD

Some medicinal plants found in Hilly region

61 Local name 6FLHQWLÀF ERWDQLFDO QDPH

1. Timur =DQWKR[\OXP DUPDWXP

2. Chutro %HUEHULV DULVWDWD

3. Bojho $FRUXV FDODPXV

4. Chiraito 6ZHUWLD FKLUDWD

5. Sugandhawal 9DOHULQD ZDOOLFKLL

6. Tejpat &LQQDPRPXP WDPDOD

7. Beladonna $WURSD EHOODGRQQD

8. Vyakur 'LRVFRUHD GHOWRLGHV

9. Dhaturo 'DWXUD PHWHO

10. Titepati $UWHPLVLD YXOJDULV dŝƚĞƉĂƟ

Some medicinal plants found in the Himalayan region

61 Local name 6FLHQWLÀF ERWDQLFDO QDPH

1. Atis $FRQLWXP KHWHURSK\OOXP

2. Panchaunle 2UFKLV ODWLIROLD

3. Jatamasi 1DUGRVWDFK\V MDWDPDQVL

4. Padamchal 5KHXP HPRGL

5. Bikhama $FRQLWXP SDOPDWXP

6. Yarshagumba &RUG\FHSV VLQHQVLV

4. Timber Yarshagumba

A long, heavy and strong piece of wood is called timber. It can be used
to make furniture, building, ships, boats, etc. We get timber from the
timber trees. The trees which are tall and provide surplus wood are
called timber trees.

Different timber trees are distributed in different geographical regions of
Nepal. In the Terai region, most plants provide timber. The hot climate
and fertile soil is favourable for the growth of sal (Shorea robusta), Sisau
(Dalbergia sisoo), Saj, Harro, Barro, Jamuno, Simal, Khayar, etc. In
the hilly and inner terai region, the trees like Katus, Chilaune, Banjh,
Rainch, Champ, Sadan, Tuni, etc. are found. Similarly, in the Himalayan

285 Times' Crucial Science & Environment Book - 8

UHJLRQ WKH SODQWV VXFK DV SLQH %KRMSDWUD 3DL\XQ *XUDQV GHYGDU ÀU
etc are found.
Some important timber trees in different geographical regions are listed
below:

Timber trees of the Terai region

61 Local Name 6FLHQWLÀF ERWDQLFDO QDPH

1. Sal 6KRUHD UREXVWD

2. Sisau 'DOEHUJLD VLVVRR

3. Simal %RPED[ FHLED

4. Harro 7HUPLQDOLD FKHEXOD

5. Khayar $FDFLD FDWHFKX

6. Karma $GLQD FDUGLIROLD

7. Ashma 7HUPLQDOLD WRPHQWRVD

Timber trees of Hilly region

61 Local Name 6FLHQWLÀF ERWDQLFDO QDPH

1. Katus &DVWDQRSVLV LQGLFD

2. Utis $OQXV QHSDOHQVLV

3. Chilaune 6FKLPD ZDOOLFKL

4. Rani sallo 3LQXV UR[EXUJKLL

5. Paiyun 3UXQXV FHUDVRLGHV

6. Champ 0LFKHOLD FKDPSDFD

7. Banjh 4XHUFXV LQFDQD

Timber trees of the Himalayan region

61 Local Name 6FLHQWLÀF ERWDQLFDO QDPH

1. Dhupi -XQLSHUXV FRPPXQLV

2. Devdar &HGUXV GHRGDUD

3. Laligurans 5KRGRGHQGURQ DUERUHXP

4. Bhojpatra (Birch) %HWXOD XWLOLV

5. 7DOLVSDWUD ÀU $ELHV SLQGURZ

6. Maple $FHU FDPSKHOOLL

7. Elma 8OQXV ZDOOLFKLDQD

8. Gobre sallo 3LQXV ZDOOLFKLDQD Laligurans

The timber is used for different purposes. It is used for making furniture,
building, houses, constructing boats, making suspension bridges, etc. It

Times' Crucial Science & Environment Book - 8 286

FDQ DOVR EH XVHG DV IXHO XQGHU WKH QDPH RI ÀUHZRRG ,Q WKH countryside,
the small branches and twigs of plants which have been dried by sunshine
DUH XVHG DV ÀUHZRRG (YHQ ELJJHU ORJV FDQ EH FKRSSHG ZLWK D[H WR PDNH
ÀUHZRRG

5. Ornamental plants

7KH SODQWV ZKLFK EHDU DWWUDFWLYH ÁRZHUV OHDYHV RU DSSHDUDQFH DUH
called ornamental plants. 0DULJROG VXQÁRZHU poinsettia (Lalupate),
rhododendron, asare, makhamali, carnation, chrysanthemum (godawari),
fern, etc are some decorative plants.

^ƵŶŇŽǁĞƌ WŽŝŶƐĞƫĂ;>ĂůƵƉĂƚĞͿ ZŚŽĚŽĚĞŶĚƌŽŶ ŚƌLJƐĂŶƚŚĞŵƵŵ;'ŽĚĂǁĂƌŝͿ

The ornamental plants are used for different purposes. Many of them
DUH XVHG IRU GHFRUDWLRQ 7KH ÁRZHUV RI PDULJROG DVDUH PDNKDPDOL
chrysanthemum, etc are used to make garlands. The garlands are used
in different religious, social and cultural occasions. Some plants such as
poinsettia, fern, cedrus, etc are grown in the garden or pot for decoration.
/HDYHV RI IHUQV DQG ÁRZHUV RI FDUQDWLRQ WXOLS URVH HWF DUH XVHG WR PDNH
bouquet.

Forest and its importance

Forest is one of the important natural resources. The very thick and green
forest of Nepal used to be called as ‘Nepal’s wealth’ until some decades ago.
But, the rapid growth in population has resulted in uncontrolled destruction
of the forest. So, the forest areas of Nepal are declining.
:H IXOÀOO VHYHUDO RI RXU QHHGV IURP WKH IRUHVW 7KH LPSRUWDQFH RI IRUHVW FDQ EH
summarized in the following points:

:H JHW WLPEHU ÀUHZRRG GDOH JUDVV EDPERR KHUEV FDQH HWF IURP WKH
forest.

2. Paper, plywood, furniture and matchbox industries are based on the raw
products of forest.

)UXLWV PHGLFLQHV ÁRZHUV HWF DUH REWDLQHG IURP WKH IRUHVW

4. Forest is the shelter of wild animals and birds.

287 Times' Crucial Science & Environment Book - 8

5. Forest plays important role to maintain water cycle.
6. It helps to conserve soil, water resources, wild animals, beautiful natural

scenery, etc.
)RUHVW KHOSV WR FRQWURO ÁRRG ODQG VOLGHV VRLO HURVLRQ HWF

Wild animals of Nepal

Different species of wildlife are found in Nepal. In Nepal 5059 species of
LQVHFWV VSHFLHV RI ÀVKHV VSHFLHV RI DPSKLELDQV VSHFLHV RI UHSWLOHV
867 species of birds and 208 species of mammal are found. Most of them live
in forest. Due to deforestation, their habitats are destroyed and their number
is decreasing. Musk deer, pheasant, munal, jungle fowl, wild fox, wild buffalo,
hornbill, python, etc fall under endangered species.

ůĞƉŚĂŶƚ ZŚŝŶŽĐĞƌŽƐ ƌŽǁŶ ďĞĂƌ ĞŶŐĂů ƟŐĞƌ

Black buck Musk deer Snow leopard Red panda

The wildlife are also known as fauna. Some of the common fauna found in
different geographical regions of Nepal are given below:

Terai region

Animals Birds Animals Birds
Peacock
Tiger Sloth bear Pigeon Deer Jackal Giant hornbill
Parrot
Rhinoceros Wild boar Saras Wild cat Wild dog Sparrow
Crane
Elephant Wild buffalo Black buck Lemur Crow

Leopard Langur Porcupine Fox Kalij

Gaur Monkey Crocodile Python Jungle fowl

Hilly region

Animals Birds
Kalij
Tiger Deer Dove Parrot
Eagle Pigeon
Leopard Chital Crow

Black bear Ghoral

Kalij

Times' Crucial Science & Environment Book - 8 288

Wild cat Porcupine Kokale Titra
Fox Kite
Malsapro Rabbit Vulture Nightingale
Monkey Crane
Otter Hawk

Langoor Cuckoo

Himalayan region

Animals Birds
Lophophorus
Musk Deer Blue Sheep Monal
Blood pheasant
Red Panda Snow Leopard Cheer pheasant
Kalij
Ghoral Wild Yak Hawk

Himalayan Bear Gaur

Jharal Munt Jack

Himalayan goat Panda tŝůĚ LJĂŬ

Saras crane Cuckoo Dove Gŝant hornbill

Endangered animals of Nepal

If the natural habitat of animals is destroyed or the climate is changed
adversely, some wild animals become unable to adapt themselves and die.
Thus, the number of these animals decreases or they may disappear completely
DQG ZH FDQQRW ÀQG WKHP

ŽůƉŚŝŶ tŝůĚ ďƵīĂůŽ ^ǁĂŵƉ ĚĞĞƌ 'ŚŽƌĂů

Python Pangolin Grey wolf Striped hyena

The species of animals which cannot be found in the areas where they once
lived, or in any other habitat are called extinct animals. The species of

289 Times' Crucial Science & Environment Book - 8

animals which are declining in number at very fast rate and whose existence
is threatened by the existing environmental conditions are called endangered
animals. Animals such as one-horned rhinoceros, Bengal tiger, wild buffalo,
musk deer, gangetic dolphin, swamp deer, snow leopard, blue sheep, wild
elephant, black buck, pigmy hog, wild ass, etc are in the verge of extinction
from Nepal and are regarded as endangered animals.
Several factors are responsible for the decline in the number of wildlife. The
increase in population has caused large scale destruction of forest which
has resulted in the loss of habitat by the wildlife. Similarly, climate change,
pollution, killing of animals for meat, skin, bones, etc are equally responsible
for decreasing the number of wildlife.
Some endangered species of mammals, birds and reptiles are given below:

Mammals Birds Reptiles
Asiatic wild elephant
%HQJDO ÁRULFDQ Cobra (snake)
Assamese monkey
Bengal tiger Black stork (Bhundiphor) Gharial crocodile
Black buck
Gangetic dolphin Cheer pheasant Golden monitor lizard
Grey wolf
Himalayan tahr Giant hornbill (Dhanesh) Monitor lizard (Gohoro)
Hispid hare
Leopard cat Lophophorus Mugger crocodile
Musk deer
One-horned rhinoceros Munal (Crimson-horned pheasant) Land tortoise
Pigmy hog
Pongolin (salak) Saras crane Rock Python (Azingar)
Snow leopard
Tibetan antelope White stork -
Wild yak
Wild ass Peacock -
Wild buffalo
Vultures -

Koklas -

Great egret -

Pied hornbill -

--

--

--

--

--

Importance of wildlife

Wildlife are the important biotic components of all ecosystems. They play
important role in the balance of nature.
+XPDQ EHLQJV JHW VHYHUDO EHQHÀWV IURP DQLPDOV 7KH\ JHW PHDW PLON DQG HJJV
from domestic animals. They tame horse, donkey, ass, bull, buffalo, camel,

Times' Crucial Science & Environment Book - 8 290

elephant, etc for getting help in work. People can get skins, hides, bones,
wool, meat, etc from the animals. The animals such as tiger, bear, elephant,
UKLQRFHURV EXWWHUÁLHV DQG ELUGV LQFUHDVH WKH natural beauty.

Attempts to conserve wildlife

The increase in population has caused large-scale deforestation for the
settlement and cultivation. The forest and grassland is also destroyed by
the grazing of domestic animals. These activities damage the habitat of wild
animals. The loss of habitat, poaching and the climate change have shown
serious threat to the existence of wildlife. Hence, it is essential to protect and
conserve wildlife in their natural habitats. For this purpose, the government
of Nepal has established several national parks, wildlife reserves and wildlife
conservation areas.

National park

A national park is a separate piece of land protected for the proper management
and conservation of wildlife together with their natural environment. The
QDWLRQDO SDUNV KHOS WR FRQVHUYH WKH ÁRUD IDXQD DQG QDWXUDO VFHQHU\ RI
particular areas. Since the national parks are rich in natural beauty and
resources, they attract tourists. The important national parks of Nepal are
given below:

6 1 National Parks Location Area Year of Prominent
VT establishment animals
NP

1. Chitwan Chitwan, 952 2030 B.S. Bengal tiger, one-
National Park Makwanpur and horned rhinoceros,
Parsa districts crocodile, deer,
leopard, several
species of birds and
EXWWHUÁLHV

2. Rara National Mugu and Jumla 106 2032 B.S. Musk deer,
Park (Smallest districts Himalayan bear,
National Park) wild boar, etc. Also
includes Rara Lake

3. Sagarmatha Solukhumbu 1148 2032 B.S. Snow leopard, red
National Park district panda, musk deer,
etc.

4. Langtang Rasuwa, 1710 2032 B.S. Red pandas, musk
National Park Nuwakot and deer Himalayan
Sindhupalchowk bear, etc.
districts

291 Times' Crucial Science & Environment Book - 8

5. Shivapuri Kathmandu, 159 2032 (declared as Black bear, leopard,
Nagarjun Nuwakot and National Park in deer, jackal, fox, etc.
National Sindhupalchowk 2059 B.S.)
Park (set up districts
as Shivapuri
watershed &
wildlife reserve in
the beginning)

6. Shey-phoksundo Dolpa and Mugu 3555 2040 B.S. Himalayan bear,
National Park districts Snow leapard,
Tibetan, hare, musk
deer, etc.

7. Khaptad Bajhang, Bajura, 225 2042 B.S. Wild dog, wild cat,
National Park Doti and Achham musk deer, barking
districts deer, leopard, etc.

8. Bardiya National Bardiya district 968 2045 B.S. Tiger, black buck,
Park spotted deer,
leopard, blue bull,
etc.

9. Makalu Barun Sankhuwasabha 1500 2049 B.S. Snow leopard, black
National Park & Solukhumbu bear, deer, ghoral,
etc.

10. Banke National Banke 550 2067 B.S. Wild elephant,
Park leopard, deer, tiger,
305 2031 B.S. (as wild bear, blue bull,
11. Shuklaphanta Kanchanpur Wildlife reserve) etc.
National Park district and
2073 B.S. (as Swamp deer,
National Park) spotted deer, wild
boar, sloth bear,
627 2040 B.S. (as blue bull, tiger, wild
Wildlife reserve) elephant, leopard,
and etc.
2073 B.S. (as
12. Parsa National Chitwan, National Park) Wild elephant,
Park Makwanpur, tiger, leopard, sloth
Parsa and Bara bear, gaur, spotted
districts deer, barking deer,
stripped hyena, etc.

Wildlife reserves

Wildlife reserve is a separate reserved area for the protection and management
of endangered species of animals and plants. The species whose number is
decreasing and are disappearing rapidly from the world are called endangered
species. Tiger, rhino, pigmy hog, sloth bear, musk deer, red panda, grand pied
hornbill, etc are some species which are listed as ’endangered.’

Times' Crucial Science & Environment Book - 8 292

The wildlife reserves are guarded by security forces. In these reserves, grazing
RI GRPHVWLF DQLPDOV FXWWLQJ RI IRGGHU FXWWLQJ WLPEHU DQG ÀUHZRRG FXOWLYDWLRQ
etc are strictly prohibited. Even the tourists or visitors are not allowed to enter
the wildlife reserves. There is only one wildlife reserve in Nepal.

6 1 Wildlife Location Area Year of Main animals
1. reserve Sunsari VT NP establishment conserved
Koshi and Saptari
Tappu districts 175 2032 B.S. Wild buffalo (arna), hog
wildlife deer, wild boar, spotted
reserve dear, blue bull, Gangetic
dolphin, crocodile, etc.

Hunting reserves

It is a separate reserved area for the conservation and management of wildlife
in which permitted hunting is allowed. The tourists or hunters can hunt inside
the hunting reserve by taking permission from concerned authorities. The
hunters have to pay certain amount of money as royalty for taking permission.
After taking permission, particular animals in particular number and region
can be hunted at particular time.
Dhorpatan Hunting Reserve LV WKH ÀUVW DQG RQO\ KXQWLQJ UHVHUYH LQ RXU
conntry. It is located in Baglung district of Dhaulagiri zone and Rukum district
of Rapti zone. Its area is 1325 square kilometers. It is attracting Nepalese and
foreign hunters with blue sheep or Bharal and other game animals. The other
animals found in this reserve include Himalayan tahr, ghoral, musk deer,
wild boar, wild dog, barking deer, red panda, etc.

Wildlife conservation areas

These are the conserved areas with the participation of local people. In these
areas, the plants and animals are conserved in their natural environment.
3HRSOH FDQ REWDLQ IRGGHU ÀUHZRRG GU\ OHDYHV HWF IURP WKH FRQVHUYDWLRQ DUHD
through a consumer committee. There are four wildlife conservation areas in
Nepal.

61 Wildlife Area Year of Location
Conservation VT establishment
area NP
7629 2049 B.S. Kaski, Lamjung, Myagdi,
1. Annapurna 2054 B.S. Mustang and Manang
wildlife 2035 districts
conservation area Taplejung district

2. Kanchanjangha
wildlife
conservation area

293 Times' Crucial Science & Environment Book - 8

3. Manaslu Wildlife 1663 2055 B.S. Northern part of Gorkha
Conservation Area 2067 BS. district
2066 BS Darchula district
4. Apinampa 1903 2065 BS
Conservation Area Dolakha, Sindhupalchok
and Ramechhap districts
5. Gaurishanker 2179 Bardia district
Conservation Area

6. Krishnasar 15.95
Conservation Area

The location of different national parks, wildlife reserves, hunting reserve and
conservation areas is shown in the map of Nepal as follows:

Importance of national parks and wildlife reserves
1. These areas conserve the wildlife together with their natural environment.
2. They protect natural scenery, water resources and natural heritages.
7KHVH DUHDV KHOS WR FRQWURO VRLO HURVLRQ ÁRRG DQG ODQGVOLGHV
4. These are the best places for entertainment.
7KH\ DUH XVHIXO IRU VFLHQWLÀF VWXGLHV DQG UHVHDUFKHV
6. They provide employment to the people.
7. They help to increase the revenue of the country as the tourists spend

money while visiting these areas, etc.

Times' Crucial Science & Environment Book - 8 294

Some protected wildlife of Nepal

Bengal tiger (Panthera tigris)
Bengal tiger is found in the dense forest of the Terai
region of Nepal. It is protected in Chitwan National
Park, Bardia National Park, Parsa National Park
and Shuklaphanta National Park.
It has a big body with yellow to light orange coat.
The strips range from dark brown to black, the belly
is white and the tail is white with black rings. The
male is about 235kg in an average and the female is

about 140kg. It is strictly carnivorous animal which attacks and eats a variety
of animals such as deer, wild boar, gaur, nilgai, antelope, etc. Sometimes,
tigers enter the human settlements and kill and eat domestic animals such as
cow, goat, sheep, dog, etc.
Asiatic elephant (Elephus maximus)
It is the largest living land animal. It is found in the
Terai forest of Nepal especially between the chure
and the forest of low plain area. It is protected in
Chitwan National Park, Parsa National Park and
Shuklaphanta National Park.
The elephant is tall with the height of about 3.5
metres in an average and weighs about 4,000 to
10,500 kilograms. It eats tree leaves, grass, bamboo and crops.
One-horned rhinoceros (Rhinoceros unicornis)

It is a large mammal weighing 2,000 to 4,000
kilograms and height 1.5 - 2 metres. It is found in
siwalik and the Terai region of Nepal. It is protected
in Chitwan National Park and Bardiya National
Park.
One-horned rhinoceros has excellent sense of
hearing and smell, but relatively poor eyesight. It
eats grasses, leaves, branches of shrubs and trees,
IUXLWV DQG VXEPHUJHG DQG ÁRDWLQJ DTXDWLF SODQWV
Red panda (Ailurus fulgens)
It is one of the rare animals found in Nepal. Its
habitat is at an altitude of 3500 metres in the dense
grass and bamboo area. Its size is slightly larger
than that of a domestic cat. It weighs between 3

295 Times' Crucial Science & Environment Book - 8

to 7 kilograms. Its average life span is about 7 years. Red panda is protected
in Sagarmatha National Park, Lantang National Park and Makalu-Barun
National Park and Wildlife Reserve.
Red pand has long soft reddish brown fur on its upper parts, blackish fur on
its lower parts and a light face with tear markings. Its tail is long and bushy.
Rock python (Python molurus)

Asiatic rock python is a large non-poisonous snake
found in the dense forest of the Terai. It lives beside
logs or trees or dry leaves on the ground. It can also
live nearby the ponds and rivers. It is protected in
Bardiya National Park.
It has a length of about 7 meters and its weight is
about ninety kilograms. It is non-poisonous but can
swallow the kids of goats and fawns of deers whole.
Pythons reproduce through eggs.
The average life span of a rock python is about 19 years.
Giant pied hornbill (Buceros bicornis)
It is a big bird with a giant beak. It is found in the
forest of the Terai region of Nepal. It is protected
in Chitwan National Park, Bardiya National Park,
Koshi-Tappu Wildlife Reserve and Shuklaphanta
National Park.
Giant pied hornbill feeds on fruits, insects and small
YHUWHEUDWHV ,W LV KXQWHG IRU ÁHVK DQG ERQHV ZKLFK
are used for medicinal purposes.

recycle : convert to usable form

cereals : grains used for food

yarshagumba : a unique caterpillar - fungus fusion fond in mountains

1. Water, soil, air, minerals, sun, fossil fuels, forest, grass, land, mountains and
wildlife are the natural resources.

2. The plants are the main sources of food for human beings. They provide cereals,
spices, legumes, vegetables and fruits.

3. The plants whose parts or whole body are used as medicine are called medicinal
plants.

Times' Crucial Science & Environment Book - 8 296