Science book class 8

Modern Concept Science and Environment – 8 293

19.6 Soil Conservation

We cannot live without food. Food comes from the plants that grow in soil. Formation of soil
takes millions of years. Soil is a main natural resource. So, it is necessary to conserve it. We can
conserve the soil by following conservation methods.
a) We should discourage deforestation and should encourage afforestation.
b) We should practise terrace farming in the slopes.
c) We should practise contour ploughing in the slopes.
d) Impervious surfaces should be reduced which decreases speed of water flow.
e) Overgrazing should be controlled.
f) Plants which have strong roots like bamboo should be planted on the river sides.
g) Rain barrel should be made to conserve water and soil.
h) We should construct embankment in the rivers.
i) Explosion should be stopped while constructing roads, building, industries, etc. in the

hilly regions.
j) Planting buffer strips along the stream banks should be done.
k) Windbreaks should be planted which reduce wind erosion.
l) Crop rotation should be done to conserve the fertility of soil.

Contour farming Windbreaks of trees Embankment in river

ACTIVITY 2

1. With the help of elders name the minerals found in your locality. Write down their uses in your day
to day life.

2. How is soil being eroded in your locality? Ask to your elders about it and prepare a short report
and submit to your science teacher.

ANSWER WRITING SKILL

1. Name the main minerals found in Nepal.

Ans: The main minerals found in Nepal are iron, copper, lead, zinc, limestone, graphite, etc.

2. Write down the uses of minerals.

Ans: The uses of minerals are:
i) Minerals are the major sources of metals.
ii) Many minerals are used for making jewelleries and decorative items.
iii) They are used for making fuels. Examples: coal, petrol, natural gas, etc.
iv) Calcite minerals are used for making construction materials, medicine and toothpaste.
v) Silica is used for manufacturing glass, semiconductors, electronic devices, etc.

294 Structure of the Earth

3. How is soil formed? Write down in very short.

Ans: Soil is formed by the weathering of parent rocks by various methods. The sun, wind, water, glaciers,
etc. are responsible for weathering of rocks into soil. Formation of soil is very slow process. It takes
millions of years.

4. What is soil erosion and deposition?

Ans: The removal of top fertile soil by various agents like air, water, wind, river, glaciers, hurricane,
cyclone, etc. is called soil erosion. After soil erosion, it is necessary to sediment the eroded soil away
from the site of erosion. It is called soil deposition. So, soil deposition is a process of accumulation
of the eroded soil away from the place of erosion.

5. Write any two differences between metallic minerals and non-metallic minerals.

Ans: Differences between metallic minerals and non-metallic minerals are:

S.N. Metallic mineral S.N. Non-metallic mineral

1 The minerals that contain significant 1 The minerals that do not contain

amount of metals are called metallic significant amount of metals are called

minerals. non-metallic minerals.

2 Metallic minerals are simply metallic 2 Most of the non-metallic minerals are

compounds. metallic compounds while some are

also non-metallic compounds.

6. Which materials are present in soil? What is soil profile? Draw a diagram to show the soil profile.

Ans: Soil is composed of organic materials, inorganic materials, air and water. An ideal soil is supposed
to be composed of 45% minerals, 25% water, 25% air, and 5% organic matter. In reality, the
percentage of these four components varies from place to place. The vertical arrangement of
various layers of soil down from the surface of the soil is called soil profile. A soil profile contains
various layers like top-soil, sub-soil and bed rocks.

Vegetation
Top soil (Horizon A)

Sub-soil (Horizon B)

Horizon C

Bed rock

7. What are effects of soil erosion and soil deposition? Write down any five points.
Ans: The effects of soil erosion and soil deposition are:

i) After soil erosion, the soil becomes infertile and hence production of crops decreases.
ii) After soil erosion, the soil does not support vegetation for longer time.
iii) Soil erosion causes landslides and flood.

Modern Concept Science and Environment – 8 295

iv) Deposition of soil into reservoir decreases the life of the reservoir.
v) Deposition of soil, silt, sand, etc. destroys crops and vegetation.
8. Write down any five methods to conserve the soil.
Ans: Soil conservation can be done by following methods.
i) We should discourage deforestation and should encourage afforestation.
ii) We should practise terrace farming in the slopes.
iii) We should practise contour ploughing in the slopes.
iv) Crop rotation should be done to protect the fertility of the land.
v) Overgrazing should be controlled.

STEPS EXERCISE

STEP 1

1. Fill in the blanks with appropriate words.
a) We can extract metals from ………..... minerals.
b) Coal is an example of ……… mineral.
c) ……… is found in Ganesh Himal.
d) Soil is formed by ……………. of rocks.
e) ………… is a main ore of iron.
f) Erosion and deposition occur……….

2. Write True for the correct and False for the incorrect statements.
a) Rust is a metallic mineral.
b) Argentite is an ore of iron.
c) Graphite is found in Chhovar of Kathmandu.
d) Soil profile shows different layers of the soil.
e) Rainfall and flood is the major natural cause of soil erosion.
f) Crop rotation does not conserve soil.

STEP 2

3. Answer the following questions in one word.
a) Write the name of rock that contains large amount of metal in it?
b) What percentage of the earth is covered with land?
c) Where is iron mainly found in Nepal?
d) What is name of the process in which rock breaks into small pieces?
e) Name the matter that makes top soil black coloured.

4. Write any two differences between:
a) Mineral and ore
b) Metallic mineral and non-metallic mineral
c) Erosion and deposition

296 Structure of the Earth

d) Iron and graphite
5. Give reasons.

a) Rust is a mineral but magnetite is an ore.
b) Coal is a fuel mineral.
c) Graphite is a non-metallic mineral.
d) Deforestation is a cause of soil erosion.
e) Soil in Terai region is fertile.
6. Write down the name of following land forms and mention one example of each.

A

B

C

D

STEP 3

7. Answer the following questions
a) What is mineral? List any four uses of minerals.
b) Define metallic mineral, non-metallic mineral and fuel minerals.
c) Explain how plants cause weathering of rocks.
d) Define soil and soil profile.
e) What is the composition of soil?
f) Define erosion and deposition.
g) What are the main agents of erosion and deposition of soil?
h) What is soil erosion?
i) List out any four ways of soil conservation.
j) Describe an experiment to show soil is composed of different substances.
k) Define humus and soil horizon.
l) Name the ores, two major places of occurrence and one important use of the
following minerals.

i) Iron ii) Copper iii) Lead
iv) Zinc v) Limestone vii) Graphite

8. Draw a diagram to show different layers of soil.

UNIT Estimated teaching periods Theory MPordaecrtnicCaolncept Science and Environment – 8 297
5 1
20
Weather and Climate

Syllabus issued by CDC Cloudy day

 Introduction to weather and climate
 Factors affecting climate: Distance from the equator,Altitude, Distance from the sea
 Climate of Nepal
 Monsoon and its formation
 Effects of monsoon

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 introduce climate and explain the factors affecting climate.
 give general introduction to climate of Nepal.
 introduce monsoon, its formation and monsoon of Nepal.
 describe the effects of monsoon.

Key terms and terminologies of the unit

1. Weather : Weather is the state of atmospheric condition at any place at any time.
2. Climate : The average atmospheric condition of a place over a long period of time is called climate.

3. Equator : The imaginary line on the earth surface, equidistant from the north and south poles
which divides the earth into northern and southern Hemispheres is called equator.

4. Latitude : The angular distance from equator to the north and south poles of the earth is called
5. Altitude latitude.

: The height from the sea level is called altitude.

6. Monsoon : The large scale seasonal wind that determines the climate of a large region is called
monsoon.

7. Summer monsoon : The moisture bearing wind which blows from sea to land during summer that causes
heavy rainfall is called summer monsoon.

8. Winter monsoon : The wind which blows from land to sea during winter that causes very less rainfall is
called winter monsoon.

20.1 Weather

In our daily life we feel that some days are hot, some days are cold, some days are shiny,
some days are windy, some days are cloudy and some days are rainy. Sometimes we may feel
various changes even in a single day. These changes are due to the change in atmospheric
conditions of a place. The atmospheric condition of a place refers to the state of sunshine,
wind, clouds, temperature, rainfall, etc.

298 Weather and Climate

Weather is the state of atmospheric condition at any place at any time. It varies from place
to place and time to time. Even within a day, there is different weather in morning, day and
evening. Weather describes the short-term state of the atmospheric condition. Rainy, windy,
dry, cold, hot, etc. are the different types of weather conditions. Daily changes in the weather
are due to winds and storms. Similarly, seasonal changes are due to the revolution of the earth
around the sun.

Sunny weather Cloudy weather Windy weather Rainy weather

20.2 Climate

The average atmospheric condition of a place over a long period of time is called is called
climate. Climate is different from weather. But, it is the average pattern of weather for a
particular region over a long period of time. For example, most of the time of the year, the
Terai region of Nepal is hot. Therefore, we can say Terai has a hot climate. The climate is
different in different places. For example, the climate of Nepal is different from the climate of
Canada. Even the climate of Pokhara is different from the climate of Biratnagar.

On the basis of Koppen system of classification, the climate Memory Tips
of the word is divided into three major types. They are
tropical climate, temperate climate and cold climate. These Equatorial belt of the earth has hot
three types of climates are further divided into sub-types. but wet climate.

Differences between climate and weather.

SN Climate SN Weather

1 The average atmospheric condition of 1 Weather is the state of atmospheric

a place over a long period of time is condition at any place at any time.

called climate.

2 Climate covers a wide region. 2 Weather covers a small region.

Factors affecting climate

There are many factors which affect climate. For example, distance from the equator, height
from the sea level, slope, distance from ocean, ocean current, vegetation, lakes, local climate,
human activities, etc. Among them, the most important three natural factors are given below.

a) Distance from the equator (Latitude)

The imaginary line on the earth surface, equidistant from the north and south poles
which divides the earth into northern and southern hemispheres is called equator.
Similarly, the angular distance from equator to the north and south poles of the earth

Modern Concept Science and Environment – 8 299

is called latitude. The distance from the equator affects climate of a region. In the

equator, the sunlight falls perpendicularly providing more heat energy. Similarly, at

the poles, the sunlight falls obliquely Toward the poles, the sun’s rays
providing less heat energy. At the poles, hit Earth at an oblique angle
the sunlight also passes through a thicker and are spread over a large area
diffusing their energy.

layer of atmosphere than at the equator. It

means that the sun rays are more intense

in equatorial region than at poles. So, the At and near
climate of the equator region is warmer the Equator,
than at poles. sunlight hits
Earth directly,
delivering more
heat and light at
any given spot.

FACT WITH REASON Difference in sunlight intensity in equator and poles

Why is the equatorial region of the earth hotter than poles?

In the equator, the sunlight falls perpendicularly providing more heat energy. Similarly, at the poles,
the sunlight falls obliquely providing less heat energy. So, equatorial region of the earth is hotter than
poles.

Cold polar wind does not affect Nepal, why?

Cold polar wind does not affect Nepal because most of the polar wind does not reach Nepal. Nepal is
far from pole and there is mountain range at northern borders.

b) Altitude and topography

The height from the sea level is called

altitude. At higher altitude, there is

less temperature and at lower altitude

there is more temperature. Thus, the

areas at higher altitude have low Windward slope Leeward slope

temperature. Temperature usually

decreases by about 6.5°C for every

1000 metres increase in altitude. Due Windward and leeward effect, attitudinal effect
to this reason, the climate is cool in

the hills than the plains. Topography of the surface also affects the climate. South

facing slope of Nepal receives more sunlight than the north facing slope. So, south

facing slopes are warmer and support much vegetation than north facing slopes.

Similarly, the windward hill sides experience more rainfall than leeward sides.

c) Distance from sea

Oceans heat up and cool down much more slowly than land. It means that coastal areas
tend to be cooler in summer and warmer in winter compare to other places. During
winter, warm air flows from ocean to coastal area and similarly in summer,cold air
flows from ocean to coastal area. That is why; there is mild climate in coastal areas.

300 Weather and Climate

The climate of the places that remain far away from the sea is more extreme, i.e. very
hot in day and very cold at night.

Warm air warm air

Cold sea breeze Cool
land breeze

day land warmer Sea cooler night land cooler Sea warmer

Sea breeze Land breeze

FACT WITH REASON

Coastal areas always have almost same climate all over the year. Why?

Due to land breeze (movement of cold air from land to sea) in the night time and sea breeze (movement
of cold air from sea to land) in the day time, the coastal areas always have the same climate all over
the year.

20.3 Climate of Nepal

Nepal covers latitudinal gradients between 26°N to 30°N and therefore lies in mid-latitude
region of the earth. Despite its location out of the tropical zone, some part of Nepal shows
tropical climate. It is because more than latitude, topography and altitude influence climate
of Nepal.

We know that Nepal is a landlocked country. So, there is no sea and ocean in Nepal. Around
the border of Nepal, China is present in the north and India is present in the east, west and
south. Nepal is located in the northern hemisphere between the latitudes of about 26°N and
30°N. The equatorial line is the line of 0°. Generally, the region from the equator to 30° of both
hemispheres shows a tropical climate. But being within the range of the tropical region, Nepal
has variable climates. It is due to the effect of different altitude. The altitude of Nepal ranges
between 60 m to 8,848 m from the sea level. Thus, there is different climate in different parts
of Nepal. The major climates of Nepal are briefly described below:

a) Tropical climate : In Nepal, tropical climate is found below the altitude of 1200m. This
climate is generally found in Terai and Doon valleys of Nepal. Most of the time in year,
this zone experiences hot climate but it is very cold in winter. In winter cold waves
move in Terai. It is called Seetlahar. In summer,the temperature of this zone becomes
more than 40°C and similarly in winter,the temperature falls below 6°C. Evergreen
forest is found in this climate.

b) Sub-tropical climate : Sub-tropical climate is found between 1200 meters to 2100
meters from the sea level. Lower hills and mid hills of Nepal lie in this zone. This zone
experiences summer for less than 4 months in a year. The maximum temperature of this

Modern Concept Science and Environment – 8 301

zone reaches upto 30°C in summer and the minimum temperature becomes less than
0°C in winter. Generally, deciduous vegetation is found in this region. Plants of this
vegetation shed leaves during winter.

c) Temperate climate : Temperate climate is found between 2100 meters to 3300 meters
from the sea level. High hills of Nepal lie in this climatic zone. This zone experiences
summer for about less than 3 months. The maximum temperature of this zone is about
20°C in summer and less than freezing temperature in winter. Coniferous forests are
found in this region.

d) Sub-alpine climate : Sub-alpine climate is found between 3300 meters to 5000 meters
from the sea level. Lower Himalayan region of Nepal shows this type of climate. This
zone experiences summer for about 2 months only. The maximum temperature of this
zone is 15°C in summer and less than freezing temperature in winter. Very less spiny
shrubs are found in this region. The plants of this vegetation complete their life cycle
within a few months.

e) Alpine climate : This type of climate is found above 5000 meters from the sea level. It is
also called tundra region. The temperature of this zone remains below freezing point.
No vegetation exists in this region.

FACT WITH REASON

The region above 5000 meters is called tundra region, why?
The temperature above 5000 meters remains below freezing point throughout the year. Due to extreme
cold, there is no vegetation in this region. So, it is called tundra region.

The climate of Nepal is also influenced by other factors. During winter, cold polar wind from
Siberia tries to enter into Nepal from its northern region. Due to the presence of mountain
range, this cold wind is blocked and cannot enter into Nepal. This prevents us from the deadly
polar wind. During summer, hot wind enters into Nepal from India, Arabian Desert and the
Thar Desert through the western region of our country. So, the western Terai region of our
country has a hot climate.

Western part of Nepal around Pokhara valley allows moisture bearing wind to enter through
it. But its mountains at the north part block the way of wind. Due to this we get more rainfall
at Lumle of Pokhara. Lumle lies in windward direction. Similarly, Mustang and Manang that
lie in Leeward directions get very less rainfall.

Higher Himalayas borders the northern boundary of our country. These Himalayas prevent
us from cold polar winds that travel from regions of north pole.

FACT WITH REASON

Western part of Nepal is comparatively hotter than eastern part, why?
During summer, hot wind enters into Nepal from India, Arabian Desert and the Thar Desert through
the western region of our country. So, the western Terai region of Nepal has a hotter climate than
eastern region.

302 Weather and Climate

20.4 Monsoon

The large scale seasonal wind that determines the climate Memory Tips

of a large region is called monsoon. Monsoon is a result of 1. Monsoon is also the lifeline
asymmetric heating of the land and sea (ocean). Usually, of people in South East Asia
monsoon means rainy season as it brings heavy rainfall. because it brings rainfall for
As monsoon causes rainfall, it is also known as the lifeline agriculture.
of South Asia. Monsoon occurs in different regions of the
world but it almost always refers to the Asian monsoon. 2. Nepal gets most of its rain from
Asian monsoon covers a large region extending from water of Indian Ocean that rises
India to Southeast Asia. Monsoon is of two types. They are through Bay of Bengal.

summer monsoon and winter monsoon. 3. In Nepal monsoon, activates

during June and ends on
During summer, the land areas are quickly heated than September.
water in the ocean. Warm air rises up and creates low

pressure in land and high pressure in ocean. Due to this, moisture bearing wind from ocean

blows towards the land. This causes heavy rainfall in the land areas. This monsoon has two

origins. They are Bay of Bengal and Arabian Sea. As the direction of wind flow is south-west,

it is also called south-west monsoon. The south-west wind gets activated in summer so it is

called summer monsoon. The moisture bearing wind which blows from sea to land during

summer that causes heavy rainfall is called summer monsoon.

The monsoon occurring in Nepal is called South Asian Monsoon. It provides rainfall for south
Asian region. In average, Nepal receives more than 80% of its total annual rainfall due to summer
monsoon. The summer monsoon wind which brings rainfall in Nepal during summer comes
from the Bay of Bengal. It causes rainfall from June to September. Summer monsoon enters from
eastern region and moves to western region of our country. It takes about a week to flow from
eastern to far western. So, eastern areas of Nepal get more rainfall than western areas.

FACT WITH REASON

Why Lumle receives the highest rainfall while the same region Mustang and Manang receive lowest
rainfall?
Lumle lies in the south of the mountain range (windward slope) which receives heavy rainfall. But
mustang and Manang receive the lowest rainfall because these districts are beyond the mountain
range (leeward side) which blocks the moisture bearing wind.
Winter crops grow more in the southern part of Nepal, why?
During winter, the winter monsoon enters from the southern part of Nepal causing rainfall. So, winter
crops grow more in the southern part of Nepal.
Paddy cultivation is more in Jhapa district, why?
Paddy is a summer crop. It grows in summer monsoon. In Nepal, summer monsoon enters from the
eastern part of Nepal. Since Jhapa lies in the eastern part of Nepal, rice grows more in Jhapa district.
There is more flood and landslide in eastern hilly part of Nepal, why?
In Nepal, summer monsoon enters from the eastern part of Nepal. It becomes weak as it goes towards
the west. So, due to strong summer monsoon, eastern part of Nepal suffers heavy rainfall that causes
landslide and flood.

Modern Concept Science and Environment – 8 303

During winter, the land areas are cooler and water bodies are warmer. This causes low

pressure near coastal and ocean areas and high pressure in land area. Due to this, cold wind

with less moisture flows from land areas to coastal and ocean areas. As, the wind is dry, it

causes very less rainfall. It is called winter monsoon. Winter monsoon moves from north to

east, so it is also called north-east monsoon. The wind which blows from land to sea during

winter that causes very less rainfall is called winter monsoon. Winter monsoon gets activated

from China and Mongolia. Himalaya range prevents most of the winter monsoon to enter into

Nepal and other countries. The moisture of the winter monsoon also freezes and falls as snow

in mountains. Memory Tips

On the basis of activity of monsoon wind, seasons of Nepal Monsoon is a periodic wind. For
are divided into:
about 6 months it moves towards
i) Pre-monsoon season (March to May) the land and for about 6 months, it

ii) Monsoon (June to September) moves towards the sea.

iii) Post monsoon (October and November)

iv) Winter (December to February)

Differences between summer monsoon and winter monsoon.

SN Summer monsoon SN Winter monsoon

1 The moisture bearing wind which 1 The wind which blows from land to

blows from sea to land during summer sea during winter that causes very less

that causes heavy rainfall is called rainfall is called winter monsoon.

summer monsoon.

2 Summer monsoon has two origins. 2 Winter monsoon activates from China

They are Bay of Bengal and Arabian and Mongolia.

Sea.

Effects of monsoon

The average rainfall of Nepal is about 1600mm. More than 80% of this total amount covers by
monsoon alone. During monsoon, wind from Arabian Sea meets with the wind coming from
Bay of Bengal. It causes strong rainfall in Nepal. Therefore, monsoon has a lot of positive and
negative effects.

Flood Landslide Urban flood

Positive effects of monsoon
i) Due to diverse topography, our country is depended more upon rain fed
agriculture system.

ii) Monsoon is the major source of water for irrigation in hilly region of Nepal.

304 Weather and Climate

iii) Himalaya of Nepal also stores huge amount of monsoon rain as snow. This snow
cap melts in dry season and maintains continuous flow of water round the year.
This water is used for drinking, irrigating lands, producing hydro-electric, etc.

iv) Monsoon increases the water level of the earth. This water can be taken out form
well, tube well, etc. for drinking purpose.

v) It increases water level in the rivers that helps in irrigation, producing hydro-
electricity, etc.

vi) It moderates the hot climate.

vii) Monsoon also controls destructive fires occurring in dry season.

Negative effects of monsoon

Monsoon has some negative effects too. Yearly, Nepal bears damage of lives and
properties due to various water induced disasters. Mountains and hilly terrain of Nepal
suffer from massive flood and landslides. Terai and low lying regions of Nepal suffer
from floods everywhere. Soil erosion is also one of the main effects due to monsoon rain.

Preventive measures of landslide and flood

The negative effects of monsoon can be prevented or controlled by discouraging haphazard
deforestation, adopting bioengineering technologies, increasing afforestation in bare hills and
open land, constructing embankments, etc. It can be reduced by terrace farming in hilly region.

ANSWER WRITING SKILL

1. What is weather? Write down the elements of weather.
Ans: The atmospheric condition of a particular place at a particular time is called weather. The elements

of weather are temperature, humidity, cloudiness, wind, precipitation, pressure, etc.
2. Describe the climatic condition depending upon the distance from the equator.
Ans: Climate also depends upon the distance from the equator. The sunlight falls perpendicularly on the

equator, so it has warmer climate but as we go far from the equator the sunlight falls slanted. The
heat is disturbed thinly over a large area. So, it is comparatively cooler.
3. Floods and landslides are more in eastern hilly region of Nepal, why?
Ans: Floods and landslides are more in eastern hilly region of Nepal because summer monsoon comes
from Bay of Bengal which is nearer to the eastern hilly region of Nepal. This monsoon causes heavy
rainfall causing landslides and floods.
4. Paddy production is higher in Jhapa, why?
Ans: Paddy production is higher in Jhapa because Jhapa lies in east-south region of Nepal which is near
from Bay of Bengal. The summer monsoon enters from here. So, annual rainfall is more in Jhapa
that is profitable for paddy production.
5. How does monsoon bring rainfall in summer?
Ans: Monsoon is a wind that blows from Bay of Bengal towards the land of southern Asia. Since it comes
from ocean, it brings lot of water vapour with it. This water vapour condenses into cloud and brings
rain.

Modern Concept Science and Environment – 8 305

6. Explain the phenomenon of sea breeze and land breeze.
Ans: During the day time, land becomes hotter causing air above it hot. Hot air rises up creating a low

pressure zone in land. But comparatively, ocean is colder with high pressure zone. So, air blows
from ocean to land. It is called sea breeze. Similarly, during the night time, land cools faster
resulting high density of air. But comparatively ocean is hotter than land. At this condition, air
above the ocean has low pressure. So, air moves from land to ocean. It is called land breeze.
7. How does altitude affect climate of a place?
Ans: Climate of a place greatly depends upon the altitude of a place from the sea level due to decrease
in temperature. As altitude increases the density of air also decreases. Due to this, amount of air,
carbon dioxide, nitrogen, water vapour, dust particles, etc. is less at higher level. It traps less heat.
But the lower level has more amount of carbon dioxide, water vapour, etc. which traps more heat
and increases the temperature.
8. Write down any three disadvantages of monsoon in Nepal.
Ans: Disadvantages of monsoon in Nepal are:
i) Monsoon brings lot of rainfall. It causes floods.
ii) Monsoon may cause landslide and loss of life and property.
iii) Storm may damage building, crops, electric poles, etc.

STEPS EXERCISE

STEP 1

1. Fill in the blanks with appropriate words.
a) The sunlight is perpendicular in………….. of the earth.
b) …………………. climate is found in the equatorial region of the earth.
c) ……………… region of Nepal shows tropical climate.
d) Nepal receives monsoon rain from ……………………
e) The average monsoon rainfall of Nepal is about ………………

2. Write True for the correct and False for the incorrect statements.
a) Climate denotes the change in weather components for at least 1 year.
b) The places in the earth at low latitudes have hot climate.
c) Sub-tropical climate is found in Terai region of Nepal.
d) Monsoon activates in September and ends in December.
e) Flood and landslide are the main effects of monsoon rain in Nepal.

STEP 2

3. Answer the following questions in one word.
a) What it the term used for the movement of air from sea to land?
b) What is the term for scientific study of weather and climate?
c) Where does monsoon rain come from in Nepal?
d) Name the rain that is useful for agriculture in Nepal.
e) Is it true that air blows from low pressure zone to high pressure zone?

306 Weather and Climate

4. Write any two differences between:
a) Climate and weather
b) Summer monsoon and winter monsoon
c) Alpine climate and temperate climate
d) Windward and Leeward side

5. Give reasons.
a) Equatorial regions are hotter than polar.
b) Cold polar wind does not affect Nepal.
c) Lumle receives the highest while the same region Mustang and Manang receive
the lowest rainfall.
d) There is more flood and landslide in the eastern hilly region of Nepal.
e) Paddy production is more in Jhapa.

6. Write down the name of natural phenomena shown in the diagrams given below.

Warm air

warm air

Cold sea breeze Cool
land breeze

day land warmer Sea cooler night land cooler Sea warmer

a) b)

STEP 3

7. Answer the following questions

a) What is weather? Write the major components of weather.

b) What is climate? Name the major types of climates of the world.

c) How does distance from equator affect the climate of a place?

d) How does distance for the sea influence the climate of the place?

e) What is monsoon? How does monsoon originate in summer season?

f) Name the climates zones of Nepal along with their altitude and maximum and

minimum temperature.

g) Define sub-tropical climate.

h) List any two advantages and two disadvantages of monsoon.

i) Write short noteon:

i) Tropical climate ii) Sub-tropical climate

iii) Temperate climate iv) Alpine climate

v) Sub-alpine climate X

8. Study the given diagram and answer the following questions.

a) Why is the part A hotter?

b) Why is the part X colder? A

X

UNIT Estimated teaching periods Theory MPoradecrtnicCaolncept Science and Environment – 8 307
5 2
21
Earth and Space

Syllabus issued by CDC Milky Way Galaxy

 Some hypotheses about the origin of the earth
 Change in the position of the earth and the sun
 Change in season
 Phases of the moon

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 explain some hypotheses about the origin of the earth.
 explain the change in the position of the earth in different seasons.
 explain the phases of the moon.

Key terms and terminologies of the unit

1. Nebula : A nebula is a vast interstellar cloud of gas and dust.

2. Rotation of the earth : Rotation refers to the anti-clockwise spinning of the earth on its axis. It is also
called diurnal motion of the earth.

3. Revolution of the earth: The orbiting of the earth around the sun is called revolution. It is also called annual
motion of the earth.

4. Day and night : The time duration during which the earth faces the sun while rotating on its axis is
called day and the time duration during which the earth faces away from the sun
is called night.

5. Perihelion : The point in the earth’s orbit nearest to the sun is called perihelion.

6. Aphelion : The point in the earth’s orbit farthest from the sun is called aphelion.

7. Solstice : A solstice is an astronomical event that occurs twice each year (on June 21 and
December 22) when the tilt of the earth’s axis is most oriented towards or away
from the sun. It is marked by the longest day and the shortest day.

8. Equinox : The astronomical event that occurs twice each year (on March 21 and September
23), when the earth’s axis is tilted neither towards nor away from the sun, making
day and night of approximately equal duration is called equinox.

9. Sidereal month : The time taken by the moon to complete one revolution around the earth is called
sidereal month. It is of 27.3 days.

10. Synodic month : The time interval between two successive full moon days or two new moon days
is called synodic month. It is of about 29.5 days.

11. Phases of the moon : The different shapes of the illuminated portion of the moon as seen by an observer on the
earth are called phases of the moon. They change cyclically as the moon orbits the earth.

308 Earth and Space

12. New moon : A phase of the moon when the reflected light from its surface does not reach on the
earth and hence moon is not visible is called new moon.

13. Full moon : A phase of the moon when the reflected light from its full face reach the earth and hence
moon is completely visible is called full moon.

14. Waxing crescent : The phase of the moon in increasing order of brightness from new moon, when less
than half of its face gets illuminated is called waxing crescent.

15. Waxing gibbous : The phase of the moon in increasing order of brightness from new moon, when more
than half of its face gets illuminated is called waxing gibbous.

16. Waning gibbous : The phase of the moon in decreasing order of brightness from full moon, when less
than half of its face gets darkened is called waning gibbous.

17. Waning crescent : The phase of the moon in decreasing order of brightness from full moon, when more
than half of its face gets darkened is called waning crescent.

21.1 Introduction

Space is the vast region that lies beyond the atmosphere of the earth including all the celestial
bodies. Even scientists are unable to define the limit of the space. In this space, uncountable
number of celestial bodies are present. These celestial bodies form the clusters of different
shapes and sizes called galaxies. Our solar system is a small portion of the Milky Way galaxy.
In the solar system there are eight planets and their satellites, comets, meteors, meteorites,
asteroids, etc. In the solar system, life exists only on the the earth. Scientists always wondered to
understand the formation of the solar system and the earth. They proposed various hypotheses
regarding the formation of the earth. But none of the hypothesis has been universally accepted
yet. However, the age of the earth is estimated to be 4.5 billion years.

Some hypothesis about the origin of the earth

a) Planetisimal hypothesis: This hypothesis was proposed by a French scientist George
Buffon in 1749 AD. According to this hypothesis, a rapidly spinning large star
approached to the sun and hit it. Due to this, the sun broke down into many fragments.
The unbroken larger part continued as the sun and other smaller parts cooled down to
form planets and other heavenly bodies.

b) Nebular hypothesis : This hypothesis was proposed Nebular hypothesis
by a German philosopher Kant in about 1755 AD.
It was modified by a French mathematician known
as Laplace in 1796. According to this hypothesis,
the earth, along with other planets and the sun
originated from a Nebula. A nebula is a vast
interstellar cloud of gas and dust. It was rotating
in the space slowly. During its rotation, it started
to cool and contract slowly due to its own gravity.
While rotating, an outer ring was detached from
the central core, which started to revolve round
the central core. The large mass present in the ring

Modern Concept Science and Environment – 8 309

broken down into many smaller masses. These smaller masses began to revolve around
the central mass called the sun. On repetition of the process all other planets originated.

c) Tidal theory : Jeans and Jeffrey proposed the tidal hypothesis in 1925. This hypothesis
explains that a large revolving star came near to the sun. Due to the gravitational pull
of the star, a gaseous tide was ejected out on the surface of the sun. This gaseous tide
detached from the sun and moved away. The shape of the tide was like a spindle. It
has been broken down into many pieces. Later these pieces cooled to form planets,
satellites, meteors etc. of the solar system.

d) Solar system from milky way : This theory

explains that the sun, its planets, satellites and

other celestial bodies of the solar system are

originated from the Milky Way galaxy. According

to this hypothesis, gas, dust and cloud of the Milky

Way galaxy gradually combined to form the sun,

planets, satellites, comets, meteors, asteroids, etc. Solar system from Milky Way

21.2 Causes of Evolution of Life on the Earth

The earth is the only planet in the solar system with life. The conditions for the existence of life
on the earth were not suitable 4.5 billion years ago. In the beginning, the earth was a hot mass
of gases and dust. It started to cool and contract slowly causing the heavy rainfall. This heavy
rainfall made large water bodies where different types of chemical substances dissolved in
it. Gradually, different kinds of unicellular and multicellular organisms evolved in the water
bodies. The development of photosynthetic bacteria and blue green algae increased the
concentration of oxygen in water and atmosphere. So, the major reasons for evolution of life
on the earth can be listed below:

i) The earth has suitable amount of oxygen, carbon dioxide, nitrogen, etc.
ii) It has sufficient amount of water.
iii) It has suitable temperature.
iv) Its atmosphere has suitable amount of greenhouse gases (carbon dioxide,

methane, water vapour) which maintain the suitable temperature.
v) It has ozone layer that prevents harmful ultraviolet rays reaching to the earth.
vi) It has a large amount of soil mass.

FACT WITH REASON

Why is the earth called a living planet?

The earth is called a living planet because it has suitable conditions of temperature, atmosphere,
water, etc. for evolution and development of living organisms.

Evolution of life was not possible along with the formation of the earth, why?

At the beginning, the earth was very hot and the climatic conditions of the earth were not suitable for
the evolution and development of the life on the earth. So, evolution of life was not possible along with
the formation of the earth.

310 Earth and Space

21.3 Position of the Earth with Respect to the Sun

The earth shows two types of motions. They are rotation and revolution. Earth rotates on its
axis and revolves on an orbit. Axis of the earth is an imaginary straight line perpendicular to
its equatorial plane and passing through centre. The earth’s orbit around the sun is not
completely circular, but it is an oval or elliptical. Thus, orbit of the earth is an elliptical path on
which it revolves around the sun.

Rotation refers to the anti- Earth revolve around the sun
clockwise spinning of the
earth on its axis. It is also
called diurnal motion.
One rotation takes about
twenty four hours and is
called a mean solar day.
The orbiting of the earth
around the sun is called
revolution. It is also called
annual motion of the earth.
One revolution of the earth
takes 365.25 days.

The orbital plane is a two-dimensional flat surface on which the earth revolves around the
sun. The earth’s axis is not perpendicular to the orbital plane of the earth. It makes an angle of
66.50 with the orbital plane of the earth. This tilting causes variation in intensity and duration
of the sunlight reaching to the earth. The most prominent effects of tilting of the earth are
given below:

a) The four seasons in a year are caused by the tilt of the earth’s axis as it orbits the sun.

b) Tilting of the earth causes different climate in the different places of the earth.

c) Due to tilting of the earth, the duration of days and nights are not always equal except
in equatorial areas.

d) Due to tilting of the earth, the point and time of the sun rise and sun set is different.

e) Variation in the solar altitude (height of the sun from the earth at noon) is due to the
tilting of the earth’s axis.

Differences between orbital plane of the earth and axis of the earth

SN Orbital plane of the earth SN Axis of the earth

1 The orbital plane of the earth is a two- 1 Axis of the earth is an imaginary line

dimensional flat surface on which it perpendicular to its equatorial plane and

revolves around the sun. passing through centre.

2 It is a thin elliptical disk shaped. 2 It is a straight line.

Modern Concept Science and Environment – 8 311

21.4 Days and Nights

The sun is a major source of light on the earth. As, the earth spins
continuously in its axis, at any time half of the surface of the earth
faces towards the sun and half of its surface faces away from the sun.
The time duration during which the earth faces the sun while rotating
on its axis is called day and the time duration during which the earth
faces away from the sun is called night. As the earth takes 24 hours to
complete a rotation, a complete day is of nearly 12 hours day time and
12 hours night time. But, the days and nights are not equal due to tilting
of the earth. Thus, the continuous rotation of the earth on its axis is the
cause of day and night on the earth.

FACT WITH REASON Day and night

Why does variation occur in day time and night time throughout a year?

The earth’s axis is not perpendicular to the orbital plane of the earth. It makes an angle of 66.5° with
the orbital plane of the earth. This tilting causes variation in the duration of the light received by the
earth. So, variation occurs in day time and night time throughout a year.

21.5 Change in Seasons

The earth revolves around the sun in an elliptical orbit. Earth's orbit around the sun D Northern spring

While revolving around the sun in an elliptical orbit, Southern fall
the earth reaches at different distance from the sun.
The point in the earth’s orbit nearest to the sun is called Northern summer 21 March equinox Northern winter
perihelion. At this point, the earth is about 147.3 million
km away from the sun. It occurs on January 3. The point A Southern summer C
farthest from the sun is called aphelion. At this point,
Southern winter 22 December solstice
21 June solstice

Northern fall

B Southern spring
23 September equinox

the earth is about 152.1 million km away from the sun. It occurs on July 4.

The elliptical orbit causes variation of the earth’s distance from the sun. Yet, this phenomenon
is not responsible for the seasons on the earth. The tilting of the earth’s axis is the major cause
of change in season. Seasons are of four major types. They are:

a) Summer season: In the Northern Hemisphere, summer season officially begins on June
21 and ends on September 23.

b) Autumn season: In the Northern Hemisphere, autumnal season officially begins on
September 23 and ends on December 22.

c) Winter season: In the Northern Hemisphere, winter season officially begins on
December 22 and ends on March 21.

d) spring season: In the Northern Hemisphere, spring season officially begins on March 21
and ends on June 21.

The seasons in the Southern Hemisphere are the opposite of those in the Northern Hemisphere.
That is, the autumnal season in the Northern Hemisphere is the spring season in the Southern

312 Earth and Space

Hemisphere and the summer season in the Northern Hemisphere is the winter season in
the Southern Hemisphere. The change in season in the Northern Hemisphere and Southern
Hemisphere is described below in solstice and equinox.

Solistice

The Northern Hemisphere is tilted toward the sun in June and away from the sun in December.
Due to this reason, the sun heats up more to the Northern Hemisphere in June and Southern
Hemisphere in December. Nepal lies in the Northern Hemisphere. So, in the Northern
Hemisphere, it is summer in June and winter in December. A solstice is an astronomical event
that occurs twice each year (on June 21 and December 22) when the tilt of the earth’s axis is most
oriented towards or away from the sun. It is marked by the longest day and the shortest day.

a) Summer solstice/ beginning of summer season: In Northern Hemisphere, summer
solstice occurs when the earth’s axis tilts towards the sun, or the Northern Hemisphere,
is most inclined toward the sun. Thus, on June 21 (around Ashar 8), the Northern
hemisphere is most inclined towards the sun and receives solar radiations for maximum
duration. This is called summer solstice in the Northern Hemisphere. On this day there
is longest day and shortest night in the Northern Hemisphere. On summer solstice, the
sun’s rays perpendicularly strike
the Tropic of Cancer (23.5o north of
the Equator). Summer solstice is
often referred to as Midsummer.
But it is just opposite in case of the
Southern Hemisphere. There is
winter solstice, or the shortest day
and longest night on June 21 in the
Southern Hemisphere.

b) Winter solstice/ beginning of winter season: In Northern Hemisphere, winter solstice
occurs when the earth’s axis tilts away from the sun, or the Northern Hemisphere
is most inclined away from the sun. Thus, on December 22 (around Poush 7), the
Northern hemisphere is most inclined away from the sun and receives solar radiations
for minimum duration. This is called winter solstice in the Northern Hemisphere. On
this day there is shortest day and longest night in the Northern Hemisphere. On winter
solstice, the sun’s rays perpendicularly strike the Tropic of Capricorn (23.5o south of the
Equator). Winter solstice is often referred to as Midwinter. But it is just opposite in case
of the Southern Hemisphere. There is summer solstice, or the longest day and shortest
night on December 22 in the Southern Hemisphere.

Equinox

In March and September, earth’s Northern and Southern Hemispheres receive the sun’s rays
almost equally and the length of night and day are nearly equal. The astronomical event that
occurs twice each year (on March 21 and September 23), when the earth’s axis is tilted neither
towards nor away from the sun, making day and night of approximately equal duration is
called equinox.

Modern Concept Science and Environment – 8 313

i) Autumn equinox: On September 23 (around Ashwin 7), the sun’s rays perpendicularly
strike the Equator. On this day night and day are of approximately equal length all
over the earth. This is called autumn equinox in the Northern Hemisphere. But there
is spring equinox in the Southern Hemisphere on September 23. In autumn season the
weather is neither so cold as in winter, nor so hot as in summer.

ii) Spring equinox (Vernal equinox): On March 21 (around Chaitra 8), the sun’s rays
perpendicularly strike the Equator. On this day night and day are of approximately
equal length all over the earth. This is called spring equinox in the Northern Hemisphere.
But there is autumn equinox in the Southern Hemisphere on March 21. In spring season
the weather is neither so cold as in winter, nor so hot as in summer.

Earth's orbit around the sun D
Northern spring

Southern fall

Northern summer 21 March equinox Northern winter

A Southern summer C

Southern winter 22 December solstice
21 June solstice

Northern fall

B Southern spring
23 September equinox

Change in season

FACT WITH REASON

Why do seasons change on the earth?
Change in seasons takes place on the earth due to its tilted axis and revolution around the sun.

21.6 Phase of Moon

The moon is only natural satellite of the earth. It is a non-luminous body. It looks bright
because it reflects sunlight towards the earth. We see the portion of the moon that reflects
sunlight towards the observers on the earth. Moon revolves around the earth in its orbit. The
time taken by the moon to complete one revolution around the earth is called sidereal month.
It is of 27.3 days.

As moon revolves around the earth, the earth is also revolving around the sun. Due to this
reason, the sunlight falls on the moon at different angles. This creates different shapes of the
moon while observing from the earth. Thus, the different shapes of the illuminated portion
of the moon as seen by an observer on the earth are called phases of the moon. They change
cyclically as the moon orbits the earth. Four major phases of the moon are first quarter, full
moon, last quarter and half-moon. The moon takes 29.5 days to come in the same phase after
complete revolution. This is called synodic month. Therefore, the time interval between two
successive full moon days or two new moon days is called synodic month. It is of about 29.5
days. The difference between sidereal and synodic months causes delay in the rising of the
moon everyday by 50 minutes. Different phases of the moon are described below:

314 Earth and Space

Memory Tips

1. Earth’s moon is the fifth largest
satellite of the solar system.

Phase of moon 2. The moon orbits the Earth
once every 27.322 days. It
takes approximately 27 days
to rotate once on its axis. Thus,
we always see the same face
of the moon as it rotates on its
axis at nearly the same time as
it revolves around the earth.

a) New moon: As the time of rising of the moon delays 50 minutes per day, after 15 days,
the rising time of both the sun and the moon becomes the same. That is, the moon and
the earth both come in the same side from the earth. In other words, the moon comes in
between the sun and the earth. The sunlight falling on the moon reflects away from the
earth. People on the earth do not receive the reflected light from the moon. At this time, we
cannot see the moon from the earth. A phase of the moon when the reflected light from its
surface does not reach on the earth and hence moon is not visible is called new moon

b) Waxing crescent: The order of brightness gradually increases after new moon. The
phase of the moon in increasing order of brightness from new moon, when less than
half of its face gets illuminated is called waxing crescent.

c) First quater: When the moon is perpendicular to the earth and the sun, the sunlight from
half of its part reflects towards the earth. The phase of the moon in increasing order of
brightness from new moon, when half of its face gets illuminated is called first quarter.

d) Waxing ggibbous: When the moon moves further on its orbit we see more than half
bright part of the moon. The phase of the moon in increasing order of brightness from
new moon, when more than half of its face gets illuminated is called waxing gibbous.

e) Full moon: Almost after 15 days from the new moon, the moon rises just after the sun
set. That is the sun and the moon come in opposite side of the earth. The sunlight falling
on the moon reflects towards the earth. People on the earth receive the reflected light
from the moon. At this time, we can see the moon. A phase of the moon when the
reflected light from its full face reach the earth and hence moon is completely visible is
called full moon.

f) Wanning gibbous: After full moon, the bright face of the moon goes on decreasing in
the coming days. The phase of the moon in decreasing order of brightness from full
moon, when less than half of its face gets darkened is called waning gibbous.

g) Third quater: After waning gibbous, the moon becomes perpendicular to the sun and
the earth. At this condition, the bright part decreased to half. The phase of the moon in
decreasing order of brightness from full moon, when half of its face gets darkened is
called third quarter.

h) Waning crescent: The phase of the moon in decreasing order of brightness from full
moon, when more than half of its face gets darkened is called waning crescent.

Modern Concept Science and Environment – 8 315

Finally, the moon comes in between the sun and the earth again and the moon becomes
totally dark. It is again called new moon. In this way, the phases of the moon change
cyclically within a synodic month as the moon orbits the earth. The duration of increasing
order of brightness of the moon after new moon to the full moon is called bright half
(Shukla Pakshya). While the duration of decreasing order of brightness of the moon
after full moon to the new moon is called dark half (Krishna Pakshya).

FACT WITH REASON

How is sidereal month different from synodic month?
Sidereal month is the duration of revolution of the moon. However, as the moon revolves around the
earth, the earth also moves ahead in its own orbit around the sun. So, some extra time is required for
the moon to come in its own phase. So, there is difference between the synodic and sidereal month.

Differences between new moon and full moon.

SN New moon SN Full moon

1 During new moon, the moon is not 1 During full moon, the bright face of the

seen at all. moon is seen completely.

2 Solar eclipse occurs in a new moon day. 2 Lunar eclipse occurs in a full moon day.

FACT WITH REASON

Why can’t we see moon in a new moon day?
We cannot see moon in a new moon day because moon does not reflect sunlight toward the earth
during new moon.

ANSWER WRITING SKILL

1. What is Jeans and Jeffrey (tidal) hypothesis regarding the origin of the solar system?
Ans: Jeans and Jeffrey proposed the tidal hypothesis in 1925. This hypothesis explains that a large

revolving star came near to the sun. Due to the gravitational pull of the star, a gaseous tide was
ejected out from the surface of the sun. This tide detached and broken down into many pieces.
Later these pieces cooled to form planets, satellites, meteors etc. of solar system.
2. Write down any five major reasons to support evolution of life on the earth.
Ans: The major reasons for evolution of life on the earth can be listed below:
i) The earth has suitable amount of oxygen, carbon dioxide, nitrogen, etc.
ii) It has sufficient amount of water.
iii) It has suitable temperature.
iv) Its atmosphere has suitable amount of greenhouse gases.
v) The earth is covered by ozone layer to protect from the harmful solar radiations.
3. What are major effects of tilting of the earth by 66.5 degrees?

316 Earth and Space

Ans: The most prominent effects of tilting of the earth are given below:
i) Tilting of the earth causes occurrence of four seasons in a year.
ii) Tilting of the earth causes different climate in the different places of the earth.
iii) Due to tilting of the earth, the days and nights are not always equal except in equatorial areas.

4. What are the phases of the moon? Write down the major phases of the moon.

Ans: The different shapes of the illuminated portion of the moon as seen by an observer on the earth are
called phases of the moon. Four major phases of the moon are new moon, first quarter, full moon,
and last quarter.

5. Differences between bright half and dark half.

Ans: Differences between bright half and dark half are:

S.N. Bright half S.N. Dark half

1 The time take by the moon from new 1 The time take by the moon from full

moon to full moon is called bright half. moon to new moon is called dark half.

2 In this condition the brighter face of 2 In this condition the brighter face of the

the moon goes on increasing. moon goes on decreasing.

6. Differences between summer season and winter season.

Ans: Differences between summer season and winter seasons are:

S.N. Summer season S.N. Winter season

1 Summer season is characterized by 1 Winter season is characterized by the

the long days and short night. long night and short days.

2 In this season, we feel hot. 2 In this season, we feel cold.

STEPS EXERCISE

STEP 1

1. Fill in the blanks with appropriate words.
a) The hypothesis of Jeans and Jeffrey is known as ……………. tidal hypothesis.
b) Availability of ……………. gas is the major feature of the earth so that it can
sustain living beings on it.
c) …………. of the earth is responsible for the change in season.
d) The days and nights are equal on ……………. and ………………..
e) The synodic month has duration …………… days and sidereal month has
………… days.

2. Write True for the correct and False for the incorrect statements.
a) Tidal hypothesis was formulated by Kant.
b) Oxygen is a life supporting gas.
c) Tilting of the earth is responsible for difference in duration of days and nights.
d) June 21 is the winter solstice in southern hemisphere.
e) The next phase of the moon after waning crescent is full moon.

Modern Concept Science and Environment – 8 317

STEP 2

3. Answer the following questions in one word.
a) Write down the name of the planet with life on it.
b) Which day is the longest day in the Northern Hemisphere?
c) Name the nearest heavenly body to the earth.
d) How long is the bright half?
e) What causes day and night?

4. Write any two differences between:
a) Dark half and bright half
b) Summer solstice and winter solstice
c) Synodic month and sidereal month
d) Waxing gibbous and waning gibbous

5. Give reasons.

a) We cannot see moon in a new moon day.

b) There is a difference between the synodic and sidereal month of the moon.

c) Season changes in the earth. b c
d
d) Days and nights are not always of equal duration.

6. Observe the figure and name the phases of the moon. a

STEP 3 e

7. Answer the following questions. h f
g

a) Write in short about tidal hypothesis, planetesimial hypothesis, nebular

hypothesis, and Milky Way hypothesis.

b) What is axis of the earth? Write the effects of tilting of axis of the earth.

c) What is orbital plane? Explain how do seasons change on the earth.

d) Explain the phases of the moon with a labelled diagram.

e) When do the following occur in the Northern Hemisphere?

i) Vernal equinox ii) Winter solstice

iii) Autumnal equinox iv) Summer solstice

8. Study the given diagram and answer the following:

A

B

a) Which type of motion of the earth is shown in the diagram?
b) Write one effect of such motion.
c) Write the name of season A and B in the Northern Hemisphere.

3U18NITEnvironmEesntitmaanteddittesaBcahlinagnpceeriods Theory Practical
12 3

22 Environment and its Balance

Syllabus issued by CDC Environment

 Natural resources and human dependency
 Brief introduction to national parks,wildlife reserves, conservation areas and hunting reserve of Nepal.
 Status of forest resources in Nepal
 Need and importance of forests in Nepal
 Status of fauna in Nepal
 Some endangered species of Nepal

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 explain the dependency of human beings on food, habitat, medicinal plants and other natural

resources.
 list and introduce national parks, wildlife reserves and conservation areas of Nepal.
 describe the need and importance of forest resources of Nepal with its present status.
 list the timbers and important medicinal herbs and introduce them.
 describe the need and importance of fauna and list the endangered species of Nepal.
 introduce some conserved fauna of Nepal.

Key terms and terminologies of the unit

1. Protected area : The public areas of natural, historical or cultural values that are protected from the
influence of human activities are called protected areas.

2. National park : National parks are the large areas of public land that are provided special protection
due to their scenic, recreational, scientific or historical importance.

3. Wild life reserve : The area of the public land that is preserved and managed to protect the particular
flora and fauna in their natural habitat is called wildlife reserve.

4. Conservation area : A conservation area is the part of land that is separated for the protection of natural,
historical and cultural resources along with their sustainable use for the development
of people in and around them.

5. Hunting reserve : A reserved area where wildlife are conserved in their natural habitat with the occasional
hunting of a particular species of the animals is called hunting reserve.

6. Shelter : place that protects living organisms from weather and enemies is called shelter.

7. Medicinal plants : The plants and their parts that can be used for making medicines are called medicinal
plants.

8. Forest : An area with a lot of trees and bushes is called forest.

9. Wildlife : Different species of organisms that live in their natural habitat are called wildlife.

Modern Concept Science and Environment – 8 319

10. Endangered species : Those organisms which are less in number and are in threat of being extinct are
called endangered species.

11. Extinct species : Those organisms that lived in the past but exist no more in the present are called
extinct species.

12. Timber plant : Those plants from which wood can be extracted are called timber plants.

22.1 Introduction

The earth is composed of various biotic and abiotic components. Abiotic components include
air, water, rocks, soil, sunlight, minerals, etc. Similarly, biotic components include all living
organisms from simple cyanobacteria to large complex animals and plants. From human point
of view, all these abiotic and biotic components are the gift of nature for mankind. Water, air,
sunlight, soil, rocks, plants and animals that are the gift of nature are called natural resources.

Absence in one of these resources can have significant impact in human development as
well as their survival. Human beings use these natural resources directly or indirectly. Many
small scale methods to large scale industrial processes have been developed by humans for
harnessing and consuming these resources. The continuous and overexploitation of natural
resources has degraded the environment and its components. In long run, it will affect humans
in several ways.

22.2 Natural Resources and Human Dependency

Everything that comes from the nature are natural resources. Natural resources are the sources
of food, water, fibre and shelter for human beings.

Human beings completely depend on natural resources for development and survival. They
get air to breathe, water to drink and land to cultivate. The major aspects in which human
beings are dependent upon natural resources are briefly discussed below:

a) Food

People depend on plants and animals for their food. Plants and animals are living natural
resources. People cultivate land and practice agriculture. Agriculture yields food crops from
which we get food. Wheat, maize, rice, potato, vegetables, fruits etc. are the major food crops.
Apart from plants, people also rear animals to get food. Dairy products like cheese, yoghurt,
ghee, cream, ice-cream, curd etc. are derived from the milk of animals like cow, buffalo, sheep,
goat, etc. People get meat from animals like goat, hen, pig, fish etc. People also consume
various sea animals and plants as food products.

b) Habitat

People depend on land for habitat. Land is one of the natural resources. People build houses,
colonies and societies on land. People obtain all the necessary raw materials for building
houses from land. Forest, which provides timber, also grows on land. Rocks, gravel, sand and
other construction materials are found on land. Bricks, cement, iron etc. are also made from
minerals of the land. Thus, human beings depend fully on natural resources for their habitat.

320 Environment and its Balance

c) Medicinal Plants

The people of rural areas depend mostly on medicinal plants for the treatment of injury and
curing of diseases. So, plants are also useful for their medicinal values. We use medicinal
plants for making ointments, gel, capsules, tonic, etc. Yarsagumba, Panchaunle, Sarpagandha,
Sugandhakokil, Kutki, Bikh, Harro, Barro, Talispatra, Timur, etc. are the examples of medicinal
plants. Resin of Simal is used to treat diarrhoea and dysentery. Powder of Yarsagumba and
powder of root of Panchaunle act as a tonic when used with cow milk and honey. Paste of
Talispatra is used to treat inflammation. Root juice of Sarpagandha is used to cure fever.
Similarly, Sugandhawal is used to get relieved from cold, cough, headache, tonsillitis, eye
ache, conjunctivitis and infected wound.

d) Air

Living organisms need fresh air to breathe. We breathe oxygen and release carbon dioxide
during respiration. Air is also needed for combustion. Nitrogen, which is the most abundant
gas in the air, helps to create stable atmosphere to humans. People also use air for various
works like sailing boats, inflating tubes of vehicles, drying clothes and agricultural crops etc.
The amount of pollution in the air is increasing day by day. Breathing polluted air may
cause various diseases like pneumonia, asthma, COPD, etc. Therefore, we should control air
pollution in order to ensure clean air for breathing.

e) Water

Water is also one of the most important natural resources. Water comprises about 60-70% of
the total volume of human body. It is primarily used for drinking and sanitation. But, it is also
used for other purposes like agriculture, transportation, irrigation, hydropower, recreation
etc. Most of the ancient civilizations and even the modern cities were developed near the
water sources. Human life is impossible without water. The water that is so much important
to us is being polluted on a daily basis. People are throwing wastes into the water sources
directly. If we drink polluted water, we might suffer from various diseases like diarrhoea,
cholera, jaundice, typhoid, dysentery, hepatitis etc.

f) Land

Land or soil is another important natural resource. Land provides food to the people. People
cultivate land to grow and harvest food crops. Crops like vegetables, fruits, cereals, pulses etc.
are grown on land. People tame and rear animals on land. They also extract minerals from the
land. Houses are also built on land. Land is the basis of almost all the human activities.

22.3 Brief Description on National Park, Reserves and Conservation Areas

Nepal has established protected areas of different categories in different parts. National parks,
wildlife reserves, conservation areas and buffer zones are the protected areas of Nepal. The
protected areas of Nepal are discussed below:

Modern Concept Science and Environment – 8 321

Api Nampa CA Shey-phoksundo NP

Rara NP Annapurna CA

Khaptad NP

Suklaphanta NP Manaslu CA
Bardia NP

Blackbuck CA Banke NP Dhorpatan HR Langtang NP
Chitwan NP
Shivapuri Sagarmatha NP
Nagarjun NP Makalu-Barun NP

National Park (NP)

Buffer Zone Gaurishankar CA Kanchanjunga CA
Conservation Area (CA) Parsa NP
Wildlife Reserve (WR)
Koshi Tappu WR

Hunting Reserve (HR)

Protected areas of Nepal

A. National Park Memory Tips

National parks are the large areas of public land that are 1. Rara N.P. is the smallest and
provided special protection due to their scenic, recreational, Shey-Phoksundo N. P. is the
scientific, or historical importance. In Nepal, there are twelve largest national park.
national parks out of which two national parks (Chitwan 2. Chitwan N. P. is the oldest.
N.P. and Sagarmatha N.P.) are enlisted by the United
Nations Educational, Scientific and Cultural Organization 3. Chitwan N. P. and Sagarmatha
(UNESCO) as world heritages. By taking permission from N.P. are world heritage sites
enlisted by the UNESCO.
the concerned authorities, people can visit national parks

for recreation, scientific researches and tourism. But, they should not disturb or destroy the

plants, wildlife, landscape etc. present in those areas.

National Parks of Nepal b) Sagarmatha National Park

a) Chitwan National Park

c) Lantang National Park d) Rara National Park

e) Bardia National Park f) SheyPhoksundo National Park

g) Khaptad National Park h) Makalu Barun National Park

i) ShivapuriNagarjun National Park j Banke National Park

k) Shuklaphanta National Park l) Parsa National Park

a) Chitwan National Park

Chitwan national park is the oldest national park of our country. It was established
in 2030 B.S. (1973 A.D.) It is enlisted by the UNESCO as a world heritage site in 2041

322 Environment and its Balance

B.S. (1984 A.D.). Chitwan N.P. is located in the inner Terai region of central Nepal. It
extends over Chitwan, Parsa and Makwanpur districts, covering an area of 932 square
kilometres (km2).

Chitwan National Park is famous for One-horned rhinoceros, Royal Bengal tiger and
Gharial. Other important animals of the park are sloth bear, gaur, wild elephant,
pangolin, antelope, Asiatic python etc. The major birds of Chitwan National park are
Bengal florican, lesser florican, giant hornbill, black stork, white stork etc. Trees like Sal,
Sisso, Khair, Simal and elephant grasses are the major vegetation found in this park.

b) Sagarmatha National Park

Sagarmatha National Park is the second national park of the country which was established
in 2032 B.S. (1976 A.D.). It was the first national park of the country enlisted by the UNESCO
(2039 B.S. / 1979 A.D) as a world heritage. It is located in the northern part of eastern Nepal
and extends over Solukhumbu district, covering an area of 1,148 km2.

Mountain peaks like Lhotse, Nuptse, Ama Dablam, Cho Oyu etc. including the highest
peak of the world, Sagarmatha (Mt. Everest) also lies in this national park. This park
is well known for animals like snow leopard, musk deer, red panda, Himalayan tahr,
Himalayan mouse hare (Pika), black bear etc. It is also the habitat of birds like Impeyan
pheasant, snowcock, blood pheasant, red billed chough etc. Rhododendron, Gobre
Salla, Thigre Salla, Birch, Juniper etc., are the major vegetation of this park.

c) Lantang National Park

Lantang National Park was established in 2032 B.S. (1976 A.D.). It is located in the
northern part of central Nepal and extends over Rasuwa, Nuwakot and Sindhupalchowk
districts, covering an area of 1,710 km2.

Langtang, Yala Peak etc. are some of the famous mountains in this park. The holy lake
and Ramsar listed wetland “Gosainkunda” is also located in this park. The national
park is well known for its population of red panda, snow leopard, Himalayan black
bear, wild boar, ghoral, serow etc. like wild animals. Different species of birds including
Impeyan pheasant are found in this national park. Rhododendron, Chir pine, silver fir,
Hemlock, Oak, etc. are the major vegetation of this park.

d) Rara National Park

Rara National Park was established in 2032 B.S. (1976 A.D.). It is located in the northern
part of mid-western Nepal and extends over Mugu and Jumla district covering an area
of 106 km2. It is the smallest national park of the country.

Rara Lake, which is the biggest lake of Nepal, is located in this park. The lake is the
habitat for endemic fishes like snow trout. This park is a home for wildlife like musk
deer, Himalayan black bear, leopard, Himalayan tahr, yellow throated marten, red
panda and other animals. Birds like coot, snow cock, grebe, mallard, common teal, red-
crested pochard, gulls and other pheasants including large numbers of migratory birds

Modern Concept Science and Environment – 8 323

are found in this park. Birds from Siberia and Mansarobar migrate in this national park
before the winter arrives. Vegetation like pine, fir, oak, rhododendron, hemlock, etc. are
found in this park.

e) Bardia National Park

Bardia National Park was established in 2045 B.S. (1988 A.D.). It is located in the southern
part of mid-western Nepal and extends over Bardia district covering an area of 968 Km2.

This park is inhabited by wildlife like royal Bengal tiger, one-horned rhinoceros, wild
elephant, swamp deer, black buck, etc. Rivers in this park are the habitat for gharial,
marsh mugger crocodile, Gangetic dolphin etc. Bird species found in this park includes
Bengal florican, lesser florican and Sarus crane and other several species of migratory
birds. The Sal trees dominate the forest in this national park. It also has a number of
grasslands with several species of snakes and lizards.

f) Shey-Phoksundo National Park

Shey-Phoksundo National Park was established in 2040 B.S. (1984 A.D.). It is located
in the northern part of mid-western Nepal and extends over Mugu and Dolpa districts
covering an area of 3,555 Km2. It is the largest national park of the country.

Shey Monastery and Phoksundo Lake are the famous religious and natural heritage of
this national park. This park is the home for a large number of wildlife including snow
leopard, grey wolf, musk deer, blue sheep, ghoral, great Tibetan sheep, Himalayan
tahr, leopard, jackal, Himalayan black bear and yellow-throated marten. The major
birds found in this park are Tibetan partridge, wood snipe, white-throated tit, wood
accentor, and crimson-eared rose finch, Impeyan pheasant, Chir pheasant etc. Major
vegetation found in this park are blue pine, spruce, hemlock, cedar, silver fir, poplar,
rhododendron, Juniper and white Himalayan birch.

g) Khaptad National Park

Khaptad National Park was established in 2040 B.S. (1984 A.D.). It is located in hilly
region of far-western Nepal and extends over Accham, Bhajhang, Bajura and Doti
districts covering an area of 225 km2.

This national park got its named from “Khaptad Baba”, a famous religious sage of
that region. Ramaroshan Lake is the famous lake in that park. The park is inhabited
by wildlife like barking deer, wild boar, ghoral, Himalayan black bear, Yellow-
throated Marten, Rhesus and Langur monkey, leopard, wild dogs, jackal, musk deer
etc. Common birds in this park are Impeyan pheasant, flycatchers, partridge, bulbuls,
cuckoos, eagles etc. The park consists of trees like sal, pine, fir, spruce, hemlock, oak,
birch and rhododendron. Grasslands in this park are beautified by wild flowers like
primulas, buttercups, wild berries.

h) Makalu Barun National Park

Makalu Barun National Park was established in 2049 B.S. (1992 A.D.). It is located in
the northern part of eastern Nepal and extends over Sankhuwasabha and Solukhumbu
districts covering an area of 2,330 km2.

324 Environment and its Balance

This national park got its name from Mount Makalu and Barun valley. It is home for a
number of wildlife including snow leopard, clouded leopard, wild boar, Tibetan hare,
red panda, musk deer, barking deer, etc. Different species of birds including Wren
babbler, ground babbler, etc. are recorded in this place. This national park is famous for
its diverse and rare vegetation. Many species of rhododendron and orchids are found
in this park. Bhojpatra, champ, wild rose, pine and phirphire are the major vegetation
of this park.

i) Shivapuri- Nagarjun National Park

Shivapuri-Nagarjun National Park was established in 2058 B.S. (2002 A.D.). It is located
in the northern part of central Nepal and extends over the hills of Kathmandu, Nuwakot,
Dhading and Sindhupalchowk districts, covering an area of 159 km2.

Major wildlife in this park are leopard, jungle cat, Himalayan black bear, barking deer,
wild boar, golden jackal, Rhesus monkey, pika, squirrel, etc. Various species of birds
like golden throated barbet, eagle, owl, Flycatcher, Cuckoo etc. are also found. The park
has different types of forests in which trees like pine, oak and rhododendron etc. are
present. This park is also well known for its diversity in mushroom and butterfly.

j) Banke National Park

Banke National Park was established in 2067 B.S. (2010 A.D.). It is located in the southern
part (Terai and Churia hills) of mid-western Nepal and extends over Banke districts,
covering an area of 550 km2.

Wildlife like tiger, stripped hyena, four-horned antelope, Asiatic elephant, wild bear,
leopard etc. are found in this park. Birds like giant hornbill, black stork, Sarus crane,
Bengal florican, and lesser florican are common birds of this park. As it consists of flood
plains with grasslands and forest, reptiles like gharial crocodile and python along with
numbers of fish species are found here. Sal, Khayer, Sissoo, Karma etc. are the major tree
species found in the forest of this park.

k) Shuklaphanta National Park

Shuklaphanta National Park was established as a Wildlife Reserve in 2032 B.S. (1973
A.D.). In 2017, the status of the protected area was changed to a national park. It is
located in the southern plain of Far-western development region of Nepal and extends
over the Kanchanpur district covering an area of 305 km2.

Shuklaphanta National Park is famous for its large tropical grasslands in which grass
species like imperata (cogon grass), heteropogon, Khagra reed and saccharum are
found. Forest in this reserve are dominated by tree species like Sal, Khayer and Sissoo.
It is well known for its population of swamp deer in which more than thousand swamp
deer can be seen in a herd. Other wild animals in this park are Royal Bengal tiger, sloth
bear, elephant, hispid hare, leopard etc. Reptiles like mugger crocodile, Asiatic rock
python, cobra and krait are also found in this reserve. Common birds found in this park
are Bengal florican, swamp francolin, spot-bellied eagle-owl, oriental pied hornbill,
babbler, sarus crane, etc.

Modern Concept Science and Environment – 8 325

l) Parsa National Park

Parsa National Park was established as a Wildlife Reserve in 2040 B.S. (1984 A.D.). In
2017, the status of the protected area was changed to a national park. It is located in the
southern part of eastern development region of Nepal and extends over an area of 499
km2 covering parts of Parsa, Chitwan, Bara and Makwanpur districts.

Parsa National Park is well known for the conservation of wild Asiatic elephants. Other
animals found in this park are tiger, sloth bear, wild boar, hog deer, barking deer,
sambar, chital, jungle cat, etc. Reptiles like common cobra, common and banded Krait,
Python and King cobra are also found in this park. White breasted kingfisher, Paradise
flycatcher, greater racket-tailed drongo (bhimaraj chibe), Golden backed woodpecker,
etc., are the major birds found in this park. Sal, Khayar and sabai grass are the common
vegetation of this park.

B. Wildlife Reserve

The area of the public land that is preserved and managed to protect the particular flora and
fauna in their natural habitat is called wildlife reserve. Wildlife reserves protect endangered
or rare animals in their natural habit. These reserves are restricted from unauthorized entree,
invading and human activities. Though the government of Nepal had declared three wildlife
reserves earlier, two of their status has been changed to national park. Koshi-tappu Wildlife
Reserve is the only one Wildlife Reserve now.

Koshi-tappu Wildlife Reserve

Koshi-tappu Wildlife Reserve was established in 2032 B.S. (1973 A.D.). It is located in the
eastern Terai of Nepal and extends over an area of 176 km2 in Sunsari, Saptari and Udayapur
district. This is a wetland reserve enlisted as a Ramsar site in 2044 B.S. (1987 A.D.).

This reserve is well known for the conservation of water buffaloes. Other important animals
conserved in this reserve are spotted deer, Asiatic elephant, hog deer, wild boar, blue bull,
rock python, gharial crocodile, Gangetic dolphin etc. It is also famous for the habitat of large
number of birds including the migratory birds even from the Siberia of Russia. Some of
the major birds found in this reserve are Ibis species, shore birds, swamp partridge, Bengal
florican, water cock, fish eagle, swamp florican, etc. The reserve is rich in grassland and marshy
vegetation with forests of Khayer and Sisso.

Differences between national park and wildlife reserve

S.N. National park S.N. Wild life reserve

1 National park is an area set up for 1 Wild life reserve is an area where rare

conservation and management plants and animal exists.

of flora, fauna, landscapes and

geographical area.

2 People are allowed to visit national 2 People are not allowed to visit wild life

parks but cannot use forest products. reserve.

326 Environment and its Balance

C. Hunting reserve

A reserved area where wildlife is conserved in their natural habitat and sometimes hunting
is also allowed is called a hunting reserve. However, the hunter should take permission from
concerned authority and is liable to hunt only the particular species that are approved by the
authority. Usually, animals or birds with large and uncontrolled population are approved for
hunting. It is a source of foreign currency in the country.

Dhorpatan Hunting Reserve is the only hunting reserve in our country.It was established
in 2044 B.S. (1987 A.D.). It is located in the western hilly region and extends over the parts
of Myagdi, Baglung and Rukum district covering an area of 1,325 km2. Blue sheep is the
popular animal in this reserve. Leopard, Himalayan tahr, wild boar, barking deer, jharal etc.
are present in this reserve. Similarly, some of the major birds in this reserve are chir pheasant,
impeyan pheasant and partridge.

Differences between hunting reserve and conservation area.

S.N. Hunting reserve S.N. Conservation area

1 Hunting reserve is an area where 1 Conservation area is a large area

wildlife are protected but hunting is where wildlife and vegetations are

also allowed. protected by the committee of local

people.

2 People are allowed to hunt a 2 People are not allowed to hunt animals

particular animals in open season. and use rare plants but they can use

forest products.

D. Conservation Area

A separate large area where flora and fauna are conserved by the area authorities and local
people along with the wise use of natural resources is called a conservation area. It has no
special protection status but hunting and poaching of flora and fauna is restricted. The main
objective of establishing a conservation area is to upgrade and develop the economic status of
the local people by the proper use of natural, cultural and historical resources. There are six
conservation areas in our country. They are:

a) Annapurna Conservation Area b) Manaslu Conservation Area

c) Kanchanjunga Conservation Area d) Api-Nampa Conservation Area

e) Gauri Shankar Conservation Area f) Krishnasar Conservation Area

a) Annapurna Conservation Area

Annapurna Conservation Area is the largest and oldest conservation area of the country.
It was established in 2049 B.S. (1992 A.D.). It is located in the northern part of the western
region of Nepal and extends over the parts of Kaski, Lamjung, Myagdi, Mustang and
Manang district covering an area of 7,629 km2.

This conservation area is named after Mount Annapurna. It is rich in biological and
cultural diversity. It includes 22 different forest types with 1226 species of plants,
101 species of mammals, 474 species of birds, 39 species of reptiles and 22 species of
amphibians. Annapurna conservation area is managed by National Trust for Nature

Modern Concept Science and Environment – 8 327

Conservation (NTNC). Annapurna Circuit is the most famous trekking route in this
conservation area. NTNC collects revenue from tourists visiting this area and utilizes
that in the development of the local area and people.

b) Kanchenjunga Conservation Area

Kanchanjunga Conservation Area was established in 2054 B.S. (1997 A.D.). It is located
in the northern part of eastern Nepal. It extends over an area of 2,035 km2 in Taplejung
district. Tibet lies in its northern boundary and Sikkim in the eastern boundary.

This conservation area is named after Mount Kanchenjunga that lies in this area. It is
the habitat for various species of wildlife and plants. It is famous for its rich diversity of
rhododendron. Out of 30 species of rhododendron found in Nepal, 24 species are here
in this area. Other vegetation include pine, oak, larch, maple, fir, birch etc. Wildlife in
this area includes animals like snow leopard, Himalayan black bear, Ghoral, Wild boar,
musk deer, Nayan, red panda, blue sheep etc. Birds like snow cock, golden breasted
fulvetta (swarnabaksha fulbutta), blood pheasant, red-billed chough etc. World Wildlife
Fund (WWF) and International Centre for Integrated Mountain Development (ICIMOD)
are involved in the development of people within this conservation area.

c) Manaslu Conservation Area

Manaslu Conservation Area was established in 2055 B.S. (1998 A.D.). It is located in the
northern part of western Nepal in Gorkha district of Nepal and covers an area of 1,663
km2. Its boundary extends up to Tibet in the north and Annapurna Conservation Area
in the west.

This conservation area got its name from Mount Manaslu that lies in this area. It is a
habitat of 2000 species of plants and 11 types of forest. Among wildlife, 33 species of
mammals, 110 species of birds, 11 species of butterfly and 3 species of reptiles are found
in this area. Major wildlife includes clouded leopard, musk deer, Himalayan tahr, blue
sheep, etc. It also contains unique cultural resources.

d) Api Nampa Conservation Area

Api Nampa Conservation Area was established in 2066 B.S. (2010 A.D.). It is located in
the northern part of far western region of Nepal and extends over an area of 1,903 km2
in Darchula district. It is bounded by Mahakali River in the west and Tibet in the north.

This conservation area is named after Mount Api and Nampa which lie in this area.
Vegetation like pine, oak, fir, hemlock, juniper, rhododendron etc. are found in this
conservation area. High value endangered medicinal plants like Yarshagumba,
Jatamashi, Panchaunle, Kutki, Talispatra, Sugandhawal etc. are found here. It is the
habitat of animals like snow leopard, clouded leopard, musk deer, Ghoral, Himalayan
black bear, serow, Himalayan tahr, etc. and birds like Impeyan pheasant, Snow Cock,
Blood pheasant, Red billed chough and Yellow-billed chough.

e) Gaurishankar Conservation Area

Gaurishankar Conservation Area was established in 2066 B.S. (2010 A.D.). It is located in
the northern part of central region of the country and extends over an area of 1,179 km2
in Ramechhap, Dolakha and Sindhupalchowk district of Nepal.

328 Environment and its Balance

This conservation area is named after Mount Gaurishankar of Dolakha district. It is
also rich in biological and cultural diversity. Pine, oak, maple and rhododendron are
the common vegetation found in this conservation area. It is the habitat of wildlife like
clouded leopard, red panda, wild boar, musk deer, python etc. Impeyan pheasant,
babbler etc. are the important birds found in this area.

f) Krishnasar Conservation Area

Krishnasar Conservation Area was established in 2065 B.S. (2010 A.D.). It covers an area
of 16.95 km2 and is located in the Bardia district. It is the conservation area of Nepal that
was designated to conserve the endangered Krishnasar (black buck).

ACTIVITY 1

Visit a nearby protected area. Enlist five major plants, mammals, birds and insects found in that area
in a tabulated form.

22.4 Status of Forest in Nepal

Nepal is rich in forest resources. According to the latest

data of Department of Forest Research and Survey, forest

occupies 40.36% of the total area of the country. Out of

the total forested areas, 82.68% lies outside the protected

areas and remaining 17.32% is inside the protected areas.

In spite of deforestation, the coverage of forests in Nepal

is increasing. Success of community forest programmes

in Nepal along with other efforts have contributed to Forest of Nepal

the increase in forest coverage. But, deforestation of Sub-tropical forests found in the Terai

region is still alarming. Trees like Sal, Sisso, Khayer, Simal, Jamun etc. are found in this forest.

In Hilly region, deciduous forest are found. Such forest includes trees like Chilaune, Katus,

Salla, Uttis, Kharsu, rhododendron, etc. Similarly, coniferous forests are mainly found in the

mountain region. Trees of mountain region are Rhododendron, LauthSalla, ThigreSalla, Rani

Salla, Okhar, Talispatra etc. Upper mountain region does not have forest but sparse bushy

land and meadows. Above them is permanent snow covering.

FACT WITH REASON

Nepal is rich in forest resource. Give reason.

Nepal is rich in forest resource because Nepal has plenty of water resources and varying altitudes to
grow different kinds of plants.

Need and importance of forest

Forest is an important natural resource. It directly provides us timber, fodder, firewood, fruits,
vegetables, grasses, medicinal plants etc. It also provides most of the raw materials needed
for industries and factories to produce goods, clothes, cosmetics, medicines, paper, furniture,
oil, etc. It also conserves environment by conserving wild flora and fauna, conserving soil,
improving ground water infiltration, cleansing air etc. Some of the major needs and importance
of forest are listed below:

Modern Concept Science and Environment – 8 329

i) Forest is a source of oxygen gas needed for all living beings.
ii) Forest provides timber for wood industries.
iii) Forest is the source of fuel wood for domestic purpose.
iv) Forest conserves watersheds.
v) Forest conserves habitat of wild flora and fauna.
vi) Forest maintains soil moisture and prevents from desertification and soil erosion.
vii) Trees of the forest act as a barrier for strong winds.
viii) Forest along with river banks can control bank erosion and flood.
ix) Forest prevents small to medium scale landslides.
x) Forest yields raw materials like parts of herbs, shrubs or trees for various industries.
xii) Forest is the site of research and recreation.

FACT WITH REASON

How is there an increase in forest resources of Nepal in comparision to that in past?
Forests of Nepal have been increasing in Nepal compared to the past because of the following reasons:
1. Increase in public awareness and participation.
2. Success of community forest programmes
3. Rules and regulations against deforestation

Forest products

Forest provides various products to us. We get timber, firewood, wood, fodder, etc. from them.
We also get non-timber products like gum, latex, resin, oil, medicinal herbs, spices, fruits,
grains, fibres, etc. Forest also provides us services. It provides fresh air to breathe, maintains
moisture in soil, controls soil erosion, flood and landslides. The widely used products of forest
are timber and medicinal herbs; which are briefly discussed below:

a) Timber Trees

Timber is one of the most important forest products. It is used for making furniture and
in construction works. Building houses, ships, musical and wooden instruments need
high quality timber. Some are hard wooded trees while some are soft wooded. Hard
wooded trees are used for construction of durable materials. Soft wooded trees are used
for manufacturing of ply boards, pencils, brush, etc. Degraded wood and soft wood are
also used as firewood.

Different kinds of timber trees are found in Nepal due to the difference in climate and
topography. Timber trees found in Terai region of our country are Sal, Simal, Masala,
Sissoo, Bijayasal, Satisal, Siris, Asna, etc. Similarly, Uttis, Salla, Katus, Chilaune,
Bhojpatra, Kharsu, Banjh, Tuni, Okhar etc. are the timber trees of hilly region. Likewise,
timber trees of mountain region include Gobre Salla, Thigre Salla, Rani Salla, Talispatra,
Kharsu, Okhar etc.

b) Medicinal Plants

Some plants and their parts are used for the treatment and cure of diseases and wounds.
Such plants are called medicinal plants. These plants are processed to manufacture
homeopathic medicines, allopathic medicines, ayurvedic medicine, food and cosmetics.

330 Environment and its Balance

There are various kinds of medicinal plants in Nepal. Medicinal plants like Sarpagandha,
Kutki, Rajbriksha, Simal, Amala, Harro, Barro, Neem etc. are found in Terai region and
Siwalik Hills. Jimmu, Timur, Bhojpatra, Pakhanbed, Bojho, Dhaturo, Chiraito, Chutro,
Sugandhawal, Rittha, Okhar etc. are found in mid hills. High hill and High Himal are
also rich in various medicinal herbs like Yarsagumba, Panchaunle, Jatamasi, Talispatra,
Bisjara, Bikh, Setobikh, Atis, Padamchal etc. Mountain region of our country has many
valuable medicinal plants. These medicinal plants can be commercialized in a rational
manner which acts as a source of national income. According to the Department of Plant
Resources, there are 701 species of medicinal plants in our country. Among them, 30
species are prioritized for research and 12 species are prioritized for the development
of agro-technology. At present, more than 70 species of medicinal plants are legally or
illegally exported from Nepal.

ACTIVITY 2

Name the timber trees found in your locality. Also, write their uses. An example is provided below.

S.N. Name of timber trees Major use

1 Sal Used for making door and window frame

2

3

FACT WITH REASON

Medicinal plants can be used as a source of income, how?
Medicinal plants can be used as a source of income because they can be used to manufacture
medicines in local and international market. So, after their export we can get foreign currency.

ACTIVITY 3

List the names of any five medicinal plants found in your locality. Also state their major uses.

S.N. Name of plant Plants part used Major uses in treatment/ curing disease
1 Sal
2
3

22.5 Protected Plants in Nepal

Many plant species are protected in Nepal. Panchaunle, bark of Okhar and Kutki are banned
for collection and export. Plants like Jatamasi, Sarpagandha, Sugandhakokila, Sugandhawal,
Jhyau, Talispatra, LauthSalla and Yarsagumba are banned for export without processing.
Seven timber trees of Nepal are banned for selling, transportation and export. These timber
trees are Okhar, Bijaysal, Satisal, Simal, Sal, Khayar and Champ. The above mentioned plants
are protected because these plants are found in limited parts of the world in limited number.

Modern Concept Science and Environment – 8 331

But, some of them are used in illegal international trade. If there is continuous exploitation
or illegal trading of these plants, these species may go extinct very soon. So, government of
Nepal has made legal provision to conserve them.

22.6 Animals and Birds

Present status

Nepal is rich in wildlife resources. Nepal has 185 species of mammals, 874 species of birds, 118
species of amphibians, 78 species of reptiles and 187 species of fishes. Similarly, Nepal consists
of 651 species of butterflies, 785 species of moths and 175 species of spiders. The protected
wildlife species of Nepal include 26 mammals, 9 birds and 3 reptiles. Some of the examples of
protected mammals are: Red panda, Black buck, Wild water buffalo, Asiatic Elephant, Indian
Pangolin, Himalayan musk deer, Bengal tiger, Leopard cat, Clouded leopard, Gangetic dolphin,
Asamese monkey, Swamp deer, Asian one horned rhinoceros etc. Similarly, Great pied hornbill,
Impeyan pheasant, Bengal florican, Lessor florican, Black stork, White stork, Cheer pheasant,
Crimson horned pheasant etc. are some of the protected birds of Nepal. Likewise, Gharial
crocodile, Asiatic rock python and Golden monitor lizard are the protected reptiles.

The rate of deforestation in Terai region is very high Memory Tips
compared to other regions of Nepal. Most of the protected
animals are also found in Terai region. Due to this reason, 1. Spiny Babbler is a bird found
animals and birds are losing their habitat and getting rare only in Nepal.
day by day. Some protected animals are also in the verge
of extinction. Hence, conservation of wildlife habitat is one 2. Snow trout is a fish found
of the important steps for their long term protection and only in Rara Lake of Nepal.
conservation of nature.
3. Csorba’s Mouse-eared
Need and importance
Bat and the Nepalese Field

Mouse are endemic mammals

of Nepal.

Wild animals and birds are the basic part of ecosystem. Like every other animals, they also
form an important part of the food chain. Imbalance in food chain can cause adverse effects in
the environment. Wild animals and birds are also important for natural and aesthetic beauty.
They are the sources of recreation. National parks and wildlife reserves attract domestic and
international tourists. This provides employment opportunity and also generates revenue for
the government. Numerous products of wild fauna are used as raw material in industries to
produce goods. Animals and birds are also the subject of research and development. Hence,
animals and birds are important for us and the natural environment.

FACT WITH REASON

Why is wildlife important for us?
Wild life is important for us because it is the source of food, medicine, timber, fresh air and water.

332 Environment and its Balance

Rare animals and birds in Nepal

Some animals and plants are large in number while some are less in a given geographical
area. Animals or plants whose distribution is limited and are few in number at a given
geographical area at that time are called rare animals or plants. If the rare animals and birds
are not conserved in time, they may go extinct. Nepal has many species of rare plants and
animals. They are protected in Nepal. Some of them are briefly discussed below:

a) One Horned Rhinoceros
Scientific name:Rhinoceros unicornis

Physical characteristics: One-horned rhino is

one of the protected animals of Nepal. It has

rough, thick and folded skin on its body. It is

blackish grey in colour. The average length of

a mature rhino is about 3m to 3.8m and height

extends from 1.7 to 2m. It weighs about 1800

to 2700 kg. It has one horn that grows as an One horned rhinoceros

extension of its nasal bone. The horn is 20cm to 61cm long and regrows if broken off.

The body is hairless except around the tip of tail, ears and eyelashes. It gives birth to a

single baby at a time.

Food: The staple food of rhino is grass, fruits, leaves, branches of trees, shrubs and
submerged and floating aquatic plants.

Habitat: One-horned rhino is found in the foothills of Himalaya in the Terai region of our
country. Grasslands, swamps, forest and riversides that are rich in its fodder are its habitat.

Lifespan: It has an estimated life span of about 40-50 years.

b) Bengal Tiger
Scientific name: Panthera tigris

Physical characteristics: The Bengal tiger

is known best for its yellow/light orange

and black/dark brown stripes. It has white

underbelly and white tail with black rings on

it. White spots can be seen on the back of their

ears. Male tigers are generally larger than the

female ones. A male tiger is about 3m long Bengal Tiger

while a female is just about 2.75m in length. Bengal tigers have a tail of about 0.6 m to

0.9m in length. Their body weight ranges from 130 kg (Females) to 230 kg (Males).

Food: Large mammals like deer, wild-buffalo, Nilgai etc. are its food. It also preys on
birds and reptiles.

Habitat: They live in dense grasslands and Terai forests of Nepal. They prefer habitats
in which they can mimic the surrounding.

Life span: Its life span is estimated about 15 years in wild. It can survive up to 20 years
in captivity.

Modern Concept Science and Environment – 8 333

c) Asiatic Elephant
Scientific name: Elephus maximus

Physical characteristics: An Asian elephant is one
of the largest land animals. It is blackish grey in
colour. It is about 2.5m to 3.5m in height. It weighs
about 2250 kg to 5500 kg. It has a huge head and a
long muscular trunk. It has large floppy ears, wide
thick legs and a small short tail. Its incisor teeth are
modified outward into long tusks.

Food: Grasses, roots, fruits, fodder and bark of Asiatic Elephant

trees are its major sources of food. They use their tusks to pull the bark off and dig the

roots of tress out of the ground.

Habitat: It lives in hot and humid habitat. It is found in the forest and large grasslands
of Terai region of our country.

Lifespan: Its lifespan in wild is about 50-60 years. But, it can live upto 70 years in
captivity.

d) Red Panda
Scientific name: Ailurus fulgens

Physical characteristics: Red panda is a small Red Panda
sized mammal with long fluffy tail and red-white
marking on its body. Its body is covered with
reddish brown furs with white patches around
the inner ears, eyes and nose. It is about 51cm to
66cm in length excluding the tail. The tail is about
25.4cm to 51cm long. It has a rounded head, large
pointed ears and a stumpy muzzle. The ears are
dark red on the outer surface.

Food : It is a herbivorous animal but more similar to carnivorous and omnivorous bears
in body structure and systems. Bamboo shoot is its major food. It also eats forage of
roots, fruits and grasses.

Habitat: It is found in the temperate forest at an altitude of 3000m to 3500m in higher
hills and lesser mountains of Nepal. It is mostly found in Rasuwa, Panchthar, Taplejung
and other districts of Nepal.

Lifespan: Its lifespan is about 8-10 years in wild and 15 years in captivity.

FACT WITH REASON

Why is red panda a rare mammal?

Red panda is a rare animal because its number is too few on the earth. It is found only in high altitudes
and is going to be extinct.

334 Environment and its Balance

e) Asiatic Rock Python

Scientific name: Python molurus

Physical characteristics: It is a large non-poisonous
snake. It has long body, thin and slender head and
tail while the middle portion of the body is thick
and swollen. Its body is light brown to yellowish in
colour with brown spots all over the body. Brown
spots have black or dark brown boundary. It’s about
7m to 10m in length and weighs about 85 kg to 90 kg.

Food: It preys on mammals like small lambs of Asiatic Rock Python

sheep, goat, etc. It also preys on deer, rabbit, rat, squirrel, birds and reptiles.

Habitat: It is found in dense forest of Terai region that is rich in dried leaves and dead
logs. Moist and swampy places, grasslands and riverside bushes are also its habitat.

Lifespan: Its average lifespan is about 18-20 years.

f) Giant Pied Hornbill

Scientific name: Buceros bicornis

Physical characteristics: It has a very long bill capped Giant Pied Hornbill
with a yellow rectangular and flattened casqued. It
extends over the head like hat. It is fairly large with
length ranging from 95cm to 120 cm. Its wingspan is
about 151cm to 178cm. It weighs about 3kg to 3.5 kg. Its
body, head and wings are black. While its abdomen and
neck is white.

Food: It is a frugivore and feeds on lipid rich and sugar rich fruits. But, it also eats small
mammals, birds, reptiles, and insects as well.

Habitat: It is arboreal and lives mainly in wet, tall and evergreen forest. It prefers to live
in the canopy of taller trees. It is found in Terai and Siwalik Hills of Nepal.

Lifespan: Its average lifespan is about 6 to 7 years.

ACTIVITY 4

Visit a nearby protected area. Observe different animals and birds in the area. Consult your teacher
and find at least two protected mammals and two protected birds of that park. Describe them briefly
mentioning their scientific names, body structure, food, life span and habitat with their figure.

ANSWER WRITING SKILL

1. What are natural resources?
Ans: Water, air, sunlight, soil, rocks, plants and animals that are the gift of nature are called natural resources.
2. What are National parks? How many national parks are there in Nepal?
Ans: National parks are the large areas of public land that are provided special protection due to their

scenic, recreational, scientific or historical importance. There are 12 national parks in Nepal.

Modern Concept Science and Environment – 8 335

3. Define wildlife reserve. Name the wildlife reserve in Nepal.

Ans: The area of the public land that is preserved and managed to protect the particular flora and fauna
in their natural habitat is called wildlife reserve. Koshi Tappu Wildlife Reserve is the only one
wildlife reserve in Nepal.

4. What is hunting reserve? Name the hunting reserve present in Nepal.

Ans: A reserved area where wildlife are conserved in their natural habitat with the occasional hunting
of the particular species of the animals is called hunting reserve. Dhorpatan Hunting Reserve is the
only hunting reserve in our country.

5. What do you understand by conservation area? Name the conservation areas of Nepal.

Ans: A conservation area is the part of land that is separated for the protection of natural, historical and
cultural resources along with their sustainable use for the development of people in and around
them. There are six conservation areas in Nepal. They are:

i) Annapurna Conservation Area ii) `Manaslu Conservation Area

iii) Kanchanjunga Conservation Area iv) Api-Nampa Conservation Area

v) Gauri Shankar Conservation Area vi) Krishnasar Conservation Area

6. What are medicinal plants? Write down their importance.

Ans: Some plants and their parts are used for the treatment and cure of diseases and wounds. Such plants
are called medicinal plants. These plants are processed to manufacture homeopathic medicines,
allopathic medicines, ayurvedic medicine, food and cosmetics. We can sell these plants in foreign
country to gain foreign currency.

7. Write down examples of medicinal plants found in Terai and mid hills of Nepal.

Ans: Medicinal plants like Sarpagandha, Kutki, Rajbriksha, Simal, Amala, Harro, Barro, Neem etc. are
found in Terai region and Siwalik Hills. Jimmu, Timur, Bhojpatra, Pakhanbed, Bojho, Dhaturo,
Chiraito, Chutro, Sugandhawal, Rittha, Okhar etc. are found in mid hills.

8. What are rare animals and plants? Write down examples.

Ans: Animals or plants whose distribution is limited and are few in number at a given geographical
area at that time are called rare animals or plants. Examples: One-horned rhino, Bengal tiger, Asian
elephant, Red panda, etc.

STEPS EXERCISE

STEP 1

1. Fill in the blanks with appropriate words.
a) ………………… are the resources that we get from nature.
b) The largest national park of our country is …………………national park.
c) Yarsagumba is a medicinal plant found in ………………… region of Nepal.
d) …………… conservation area is designated for the conservation of Black Buck.
e) Koshi Tappu was enlisted as a………………… site in 2044 B.S.
f) Red panda is found in …………………national park of Nepal.
g) Bijayasal is protected ………………… plant of Nepal.

2. Write True for the correct and False for the incorrect statements.
a) Sarpagandha is a medicinal plant found in the mountain region.

336 Environment and its Balance

b) Resin of Simal is used to treat diarrhoea.
c) Chitwan national park is the youngest national park of our country.
d) Annapurna conservation area lies in the central region of Nepal.
e) GosainKunda Lake is listed as a Ramsar site.
f) Rani Salla is a timber tree of mountain region.
g) Medicinal herbs are non-timber forest products.
h) Panthera tigris is the scientific name of Bengal tiger.

STEP 2

3. Answer the following questions in one word.
a) How many national parks are there in Nepal?
b) What is the area of Chitwan national park?
c) When was Langtang national park established?
d) How many species of fishes are found in Nepal?
e) In which region of Nepal Simal is found?

4. Write any two differences between:
a) National parks and conservation areas
b) National parks and wildlife reserves
c) Wild life reserves and Hunting reserves
d) Medicinal plants and timber plants

5. Give reasons.
a) Nepal is rich in forest resources.
b) Forest areas of Nepal have been increasing day by day.
c) Red panda is a rare mammal.
d) Wildlife are important to us.

6. Write the scientific names of the following protected animals with two important
features of each:

a) b) c)

d) e) d)

Modern Concept Science and Environment – 8 337

STEP 3

7. Answer the following questions
a) What are natural resources? Enlist any six important natural resources.
b) Describe briefly about the dependence of human on natural resources.
c) What do you mean by timber products? Explain about the forest resources of Nepal.
d) What are medicinal plants? Mention the names of any four medicinal plants each
from Terai, hilly and mountain region of Nepal.
e) What are timber plants? Write the names of four timber plants each from Terai,
hilly and mountain regions of Nepal.
f) What do you mean by protected plants of Nepal? List the names of protected
trees of Nepal.
g) What is a national park? Write down the names of national parks of Nepal.
h) What is a conservation area? Write down the names of conservation areas of Nepal.
i) Write a short note on:
i) Chitwan National Park ii) Lantang National Park
iii) Sukhlaphanta National Park iv) Annapurna Conservation Area
j) What do you mean by rare plants and animals? Name any six rare animals of Nepal.
k) Define wildlife reserve and hunting reserve.
l) Give a brief introduction to the following:
i) Red panda ii) Bengal tiger iii) Great pied hornbill

8. Fill the required data in the given table:

S.N. Name Established Area coverage District coverage
1 Chitwan N.P. date (B.S) (Sq. km)

2 Sagarmatha N.P.

3 Lantang N.P.

4 Rara N.P.

5 Bardia N.P.

6 Shey-Phoksundo N.P.

7 Khaptad N.P.

8 Makalu Barun N.P

9 Shivapuri-Nagarjun N.P.

10 Banke N.P.

11 Shuklaphanta N.P.

12 Parsa N.P.

3U38NITEnvironmEesntitmaalteddegteraacdhaintgiopneraiondds itsTchoeonrsyervaPtraiocntical
61

23 Environmental degradation and its
conservation

Syllabus issued by CDC WWF

 Introduction to environmental degradation
 Effects of human activities on environment
 Environmental pollution (air pollution, water pollution and noise pollution)
 Greenhouse effect, causes and adverse effects
 Climate change and acid rain
 Disaster and disaster management
 Measures of environment conservation
 Introduction to NTNC, IUCN, WWF, UNEP and ICIMOD and their role to conserve environment

LEARNING OBJECTIVES

At the end of this unit, students will be able to:

 explain environmental pollution (air pollution, water pollution and noise pollution) and its effects.
 describe greenhouse effect and its impact on environment due to global warming.
 introduce climate change, its effects and describe local efforts to reduce climate change.
 describe acid rain, its causes and effects.
 explain measures of environment conservation.
 introduce the different natural disasters and their causes.
 explain the measures of disaster management and reduction.
 introduce and explain the role of NTNC, IUCN, WWF, UNEP and ICIMOD.

Key terms and terminologies of the unit

1. Environment : The surrounding that incluedes every living and non-living components is

called environment.

2. Environment degradation : Decrease in the quality and quantity of components of environment is called

environment degradation.

3. Deforestation : The act of cutting or burning down the trees or forests is called deforestation.

4. Pollution : The decrease in the quality and quantity of air, water, land, etc. is called pollution.

5. Pollutant : Any substance that decreases the quality or quantity of environmental factors
is called pollutant.

6. Air pollution : Decrease in the quality of air due to the mixing of industrial gases, dust etc. is
7. Water pollution called air pollution.

: Decrease in the quality of water due to the mixing of drainage, sewage, etc. so
that it is not usable is called water pollution.

8. Soil pollution : Decrease in the quality of soil due to the mixing of solid wastes, chemicals, etc.
is called soil pollution

9. Sound pollution : Sound that affects the listener by causing irritation and disturbance in any form is
called noise pollution.

Modern Concept Science and Environment – 8 339

10. Green house : A house made up of glass or plastic that can trap solar energy is called green house.

11. Greenhouse gases : Those gases which absorb and trap the solar heat in the atmosphere are called
greenhouse gases.

12. Greenhouse effect : The phenomenon of trapping of solar heat by the greenhouse gases in the atmosphere
is called greenhouse effect.

13. Global warming : The condition of increased temperature of the earth is called global warming.

14. Climate change : Climate change is defined as the change in statistical distribution of weather patterns
15. Acid rain when this change lasts for thousands to millions of years.

: The falling of rain water mixed with acids is called acid rain.

16. Industrial gases : The gases that are emitted from industries are called industrial gases.

17. Natural disasters : A sudden, violent and destructive activity caused by nature that destructs life and
property is called a natural disaster. Example: earthquake

18. Flood : The overflow of water from the river is called flood.

19. Landslide : Falling down of large masses of rocks and debris down a lower altitude is called
20. Earthquake landslide.

: An earthquake is the violent shaking of the Earth’s crust.

21. Hypocenter : The point inside the earth’s crust from where the earthquake originates is called focus
22. Epicenter or hypocentre.

: The point on the surface of the earth just above the hypocentre is called epicentre.

23. Seismograph : A scientific instrument which detects, records and measures the seismic wave is called
seismograph.

24. Seismogram : The paper on which seismic waves are recorded is called seismogram.
25. Richter scale : The unit for measuring the magnitude of an earthquake is called Richter scale.

23.1 Introduction

The natural environment is composed of physical components like air, water, rock, soil,
sunlight etc. and biological components like plants and animals. Human beings have modified
the natural environment for their comfort. They have developed cities, build industries and
factories, constructed roads and bridges and so on. All the human activities depend on
resources from the natural environment. Overexploitation of environmental resources by
human beings has caused rapid destruction of these components. The occurrence of natural
disasters like flood, landslide, forest fire, earthquake, volcano, soil erosion, etc. has also
increased. These disasters decrease the quality of environment. However, their impact is very
less in the environment in comparison to the destructive human activities.

The decrease in overall quality of environment and its resources is known as environment
degradation. Environment degradation is defined as the deterioration of environment or its
components due to the exploitation of resources by natural disasters or human activities. Air
pollution, water pollution, decrease in fertility of soil, loss of habitat of plants and animals,
desertification etc. are some of the examples of environment degradation.

340 Environmental degradation and its conservation

Effects of Human activities on Environment

Human beings use various kinds of natural resources. The use of the resources increases with
population growth. With increasing population growth, people over exploit resources like air,
water, land, minerals, forest etc. to meet their demand. The result of this exploitation is that
the environment is adversely affected and the natural capacity of environment to produce
goods and services is reduced. Human activities also have caused pollution to a larger extent.
Air pollution, water pollution and land pollution are the main kinds of pollution that is
destructing the overall health of the environment.

23.2 Environmental Pollution

The mixing of harmful substances in the natural environment that cause adverse effect in the
quality of the environment is called environmental pollution. Our environment is polluted by
various harmful substances that are produced by human activities.

Broadly, environmental pollution can be classified into following groups:

i) Air Pollution ii) Water pollution

iii) Land pollution iv) Noise pollution

Air pollution

The mixing of unwanted and harmful substances in Air pollution
the atmosphere which decreases its quality is called air
pollution. Harmful substances that pollute air can be
physical, biological or chemical substances. Substances
like dust particles, metallic dust, ashes etc. are physical
substances. Air borne germs and microorganisms are
biological substances. Similarly, carbon dioxide, carbon
monoxide, chlorofluorocarbons, oxides of nitrogen
and sulphur, ground level ozone, etc. are chemical
substances. When these substances get mixed with the
air, air becomes polluted.

Causes of air pollution

Some of the causes of air pollution are:
i) Burning of fossil fuels like coal, petroleum etc. in industries, factories and vehicles.
Burning of these substances produce carbon dioxide, carbon monoxide, sulphur
dioxide, nitrogen dioxide, nitrous oxide etc.

ii) Use of chemical insecticides, pesticides and fertilizers in agricultural field.

iii) Burning agricultural residues on land also cause land and air pollution. They
emit particulate matter and harmful chemicals into the air.

iv) Manufacturing industries release large amount of carbon monoxide, mercury,
organic compounds and other chemicals into the air. This also causes air pollution.

v) Release of dust and chemicals into the air during mining.

vi) Using firewood in household cooking emits many pollutants.

Modern Concept Science and Environment – 8 341

Effects of air pollution
i) It causes several health problems like lung diseases (asthma, lung cancer,
pneumonia, etc.), heart diseases, eye diseases, headache, etc. Children and old
aged people are mostly affected by such diseases.

ii) Air pollution causes several diseases in animals and plants too.

iii) It reduces the visibility in roads and air which might cause road accidents and
air accidents. Visibility is reduced by a thick mist of chemicals and smoke in air
called photochemical smog. Smog is the mixture of chemical smoke and fog.

iv) Air pollution causes acid rain which corrodes the historical monuments and buildings.

v) It destroys the ozone layer which protects us from the harmful UV rays.

vi) It causes climate change which can result into the extinction of species, natural
disasters, mass migration, etc.

FACT WITH REASON

Acid rain is an example of air pollution, how?
Acid rain is an example of air pollution because acids that mix with the rain water are unwanted
substances that can harm the crops and the quality of soil.

Water pollution Water pollution

Alteration in the quality of water due to the
contamination of water bodies by harmful
substances is called water pollution. Water
can be contaminated by chemical substances,
physical substances or germs. Chemical
substances include chemical wastes from
industries and factories containing chemicals
like acid, bases, heavy metals, etc. Physical
substances include dissolved solids,
suspended solids, etc. Germs and microbes
of different diseases also pollute the water.
Water pollution affects water sources and
bodies like river, lake, stream, pond, etc.

FACT WITH REASON

Water pollution can cause epidemics, how?

Water pollution can cause epidemics because polluted water contains bacteria, parasites, viruses and
other disease causing germs which can spread diseases easily.

Causes of water pollution
i) Mixing of chemical wastes from industries and factories into the water bodies.

ii) Dumping of sewage, hospital wastes, garbage etc. into the water sources.

iii) Mixing of chemical fertilizers and pesticides from the fields into the water bodies.

342 Environmental degradation and its conservation

iv) Defecating, urinating and bathing animal in or near the water sources.
v) Leakage of drinking water pipes and drainage pipes.
vi) Washing clothes and utensils, dumping wastes and discharge of faecal matters.
Effects of water pollution
i) Outbreak of water borne diseases such as cholera, diarrhoea, dysentery,

tuberculosis, jaundice, typhoid, scabies, etc.
ii) Growth of unnecessary plants in the water sources which consume most of the

oxygen of water and hinder the development of useful plants.
iii) Loss of aquatic habitat due to the harmful chemicals like heavy metals, acid, bases etc.
iv) Increase in the temperature of water due to which aquatic life that prefer low

temperatures dies.
v) Polluted water is the breeding habitat of disease spreading insects.

Differences between air pollution and water pollution.

S.N. Air pollution S.N. Water pollution

1 Decrease in the quality of air due to 1 Mixing of harmful solid or liquid wastes

the mixing of industrial gases, dust in water that decrease the quality of

etc. is called air pollution water is called water pollution.

2 Air pollution mostly causes 2 Water pollution mostly causes

respiratory diseases. gastrointestinal diseases.

Land pollution

The change in the composition and quality of soil due

to the presence of harmful substances is called land

or soil pollution. Land is polluted by substances like

solid and liquid waste, chemicals, microorganisms

and radiation. These substances degrade the quality

of land either by destroying the soil composition

and structure or hindering the growth of plants and

microorganisms in it. Land pollution

Causes of land pollution

i) Excessive use of chemicals fertilizers and pesticides in agricultural land.

ii) Haphazard dumping of industrial, agricultural and household solid wastes on land.

iii) Irrigating land using polluted water containing heavy metals, acids, bases or salts.

iv) Large scale mining activities which remove the layer of topsoil from the land.

v) Deforestation in watershed areas that washes the topsoil and deposits them in

river basins.

vi) Falling of acid rain on the soil which increases the acidity of soil.

Effects of land pollution
i) Fruits and vegetables grown with polluted water transfer water borne diseases
when eaten.
ii) Irrigation with polluted water decreases the productivity of crops.