NCERT Textbook - Natural Resources Class 9 Notes | EduRev

Science Class 9

Created by: Dr Manju Sen

Class 9 : NCERT Textbook - Natural Resources Class 9 Notes | EduRev

 Page 1


Our planet, Earth is the only one on which
life, as we know it, exists. Life on Earth is
dependent on many factors. Most life-forms
we know need an ambient temperature,
water, and food. The resources available on
the Earth and the energy from the Sun are
necessary to meet the basic requirements of
all life-forms on the Earth.
What are these resources on the Earth?
These are the land, the water and the air.
The outer crust of the Earth is called the
lithosphere. Water covers 75% of the Earth’s
surface. It is also found underground. These
comprise the hydrosphere. The air that covers
the whole of the Earth like a blanket, is called
the atmosphere. Living things are found
where these three exist. This life-supporting
zone of the Earth where the atmosphere, the
hydrosphere and the lithosphere interact and
make life possible, is known as the biosphere.
Living things constitute the biotic
component of the biosphere. The air, the
water and the soil form the non-living or
abiotic component of the biosphere. Let us
study these abiotic components in detail in
order to understand their role in sustaining
life on Earth.
14.1 The Breath of Life: Air
We have already talked about the composition
of air in the first chapter. It is a mixture of
many gases like nitrogen, oxygen, carbon
dioxide and water vapour. It is interesting to
note that even the composition of air is the
result of life on Earth. In planets such as
Venus and Mars, where no life is known to
exist, the major component of the atmosphere
is found to be carbon dioxide. In fact, carbon
dioxide constitutes up to 95-97% of the
atmosphere on Venus and Mars.
Eukaryotic cells and many prokaryotic
cells, discussed in Chapter 5, need oxygen to
break down  glucose molecules and get energy
for their activities. This results in the
production of carbon dioxide. Another process
which results in the consumption of oxygen
and the concomitant production of carbon
dioxide is combustion. This includes not just
human activities, which burn fuels to get
energy, but also forest fires.
Despite this, the percentage of carbon
dioxide in our atmosphere is a mere fraction
of a percent because carbon dioxide is ‘fixed’
in two ways: (i) Green plants convert carbon
dioxide into glucose in the presence of
Sunlight and (ii) many marine animals use
carbonates dissolved in sea-water to make
their shells.
14.1.1 THE ROLE OF THE ATMOSPHERE IN
CLIMATE CONTROL
We have talked of the atmosphere covering
the Earth, like a blanket. We know that air is
a bad conductor of heat. The atmosphere
keeps the average temperature of the Earth
fairly steady during the day and even during
the course of the whole year. The atmosphere
prevents the sudden increase in temperature
during the daylight hours. And during the
night, it slows down the escape of heat into
outer space. Think of the moon, which is
about the same distance from the Sun that
the Earth is. Despite that, on the surface of
the moon, with no atmosphere, the
temperature ranges from –190º C to 110º C.
14 14
14 14 14
N N N N NATURAL ATURAL ATURAL ATURAL ATURAL R R R R RESOURCES ESOURCES ESOURCES ESOURCES ESOURCES
Chapter
Page 2


Our planet, Earth is the only one on which
life, as we know it, exists. Life on Earth is
dependent on many factors. Most life-forms
we know need an ambient temperature,
water, and food. The resources available on
the Earth and the energy from the Sun are
necessary to meet the basic requirements of
all life-forms on the Earth.
What are these resources on the Earth?
These are the land, the water and the air.
The outer crust of the Earth is called the
lithosphere. Water covers 75% of the Earth’s
surface. It is also found underground. These
comprise the hydrosphere. The air that covers
the whole of the Earth like a blanket, is called
the atmosphere. Living things are found
where these three exist. This life-supporting
zone of the Earth where the atmosphere, the
hydrosphere and the lithosphere interact and
make life possible, is known as the biosphere.
Living things constitute the biotic
component of the biosphere. The air, the
water and the soil form the non-living or
abiotic component of the biosphere. Let us
study these abiotic components in detail in
order to understand their role in sustaining
life on Earth.
14.1 The Breath of Life: Air
We have already talked about the composition
of air in the first chapter. It is a mixture of
many gases like nitrogen, oxygen, carbon
dioxide and water vapour. It is interesting to
note that even the composition of air is the
result of life on Earth. In planets such as
Venus and Mars, where no life is known to
exist, the major component of the atmosphere
is found to be carbon dioxide. In fact, carbon
dioxide constitutes up to 95-97% of the
atmosphere on Venus and Mars.
Eukaryotic cells and many prokaryotic
cells, discussed in Chapter 5, need oxygen to
break down  glucose molecules and get energy
for their activities. This results in the
production of carbon dioxide. Another process
which results in the consumption of oxygen
and the concomitant production of carbon
dioxide is combustion. This includes not just
human activities, which burn fuels to get
energy, but also forest fires.
Despite this, the percentage of carbon
dioxide in our atmosphere is a mere fraction
of a percent because carbon dioxide is ‘fixed’
in two ways: (i) Green plants convert carbon
dioxide into glucose in the presence of
Sunlight and (ii) many marine animals use
carbonates dissolved in sea-water to make
their shells.
14.1.1 THE ROLE OF THE ATMOSPHERE IN
CLIMATE CONTROL
We have talked of the atmosphere covering
the Earth, like a blanket. We know that air is
a bad conductor of heat. The atmosphere
keeps the average temperature of the Earth
fairly steady during the day and even during
the course of the whole year. The atmosphere
prevents the sudden increase in temperature
during the daylight hours. And during the
night, it slows down the escape of heat into
outer space. Think of the moon, which is
about the same distance from the Sun that
the Earth is. Despite that, on the surface of
the moon, with no atmosphere, the
temperature ranges from –190º C to 110º C.
14 14
14 14 14
N N N N NATURAL ATURAL ATURAL ATURAL ATURAL R R R R RESOURCES ESOURCES ESOURCES ESOURCES ESOURCES
Chapter
SCIENCE 190
the heating of water bodies and the activities
of living organisms. The atmosphere can be
heated from below by the radiation that is
reflected back or re-radiated by the land or
water bodies. On being heated, convection
currents are set up in the air. In order to gain
some understanding of the nature of
convection currents, let us perform the
following activity:
Activity _____________14.2
• Place a candle in a beaker or wide-
mouthed bottle and light it. Light an
incense stick and take it to the mouth
of the above bottle (Figure 14.1).
• Which way does the smoke flow when
the incense stick is kept near the edge
of the mouth?
• Which way does the smoke flow when
the incense stick is kept a little above
the candle?
• Which way does the smoke flow when
the incense stick is kept in other
regions?
Activity _____________14.1
• Measure the temperature of the
following :
Take (i) a beaker full of water, (ii) a
beaker full of soil/sand and (iii) a closed
bottle containing a thermometer. Keep
them in bright Sunlight for three hours.
Now measure the temperature of all 3
vessels. Also, take the temperature
reading in shade at the same time.
Now answer
1. Is the temperature reading more in
activity (i) or (ii)?
2. Based on the above finding, which
would become hot faster – the land or
the sea?
3. Is the thermometer reading of the
temperature of air (in shade) the same
as the temperature of sand or water?
What do you think is the reason for
this? And why does the temperature
have to be measured in the shade?
4. Is the temperature of air in the closed
glass vessel/bottle the same as the
temperature taken in open air? (i) What
do you think is the reason for this?
(ii) Do we ever come across this
phenomenon in daily life?
As we have seen above, sand and water
do not heat up at the same rate. What do you
think will be their rates of cooling? Can we
think of an experiment to test the prediction?
14.1.2 THE MOVEMENT OF AIR: WINDS
We have all felt the relief brought by cool
evening breezes after a hot day. And
sometimes, we are lucky enough to get rains
after some days of really hot weather. What
causes the movement of air, and what decides
whether this movement will be in the form of
a gentle breeze, a strong wind or a terrible
storm? What brings us the welcome rains?
All these phenomena are the result of
changes that take place in our atmosphere
due to the heating of air and the formation of
water vapour. Water vapour is formed due to
Fig. 14.1: Air currents being caused by the uneven
heating of air .
The patterns revealed by the smoke show
us the directions in which hot and cold air
move. In a similar manner, when air is heated
by radiation from the heated land or water, it
rises. But since land gets heated faster than
water, the air over land would also be heated
faster than the air over water bodies.
So, if we look at the situation in coastal
regions during the day, the air above the land
Page 3


Our planet, Earth is the only one on which
life, as we know it, exists. Life on Earth is
dependent on many factors. Most life-forms
we know need an ambient temperature,
water, and food. The resources available on
the Earth and the energy from the Sun are
necessary to meet the basic requirements of
all life-forms on the Earth.
What are these resources on the Earth?
These are the land, the water and the air.
The outer crust of the Earth is called the
lithosphere. Water covers 75% of the Earth’s
surface. It is also found underground. These
comprise the hydrosphere. The air that covers
the whole of the Earth like a blanket, is called
the atmosphere. Living things are found
where these three exist. This life-supporting
zone of the Earth where the atmosphere, the
hydrosphere and the lithosphere interact and
make life possible, is known as the biosphere.
Living things constitute the biotic
component of the biosphere. The air, the
water and the soil form the non-living or
abiotic component of the biosphere. Let us
study these abiotic components in detail in
order to understand their role in sustaining
life on Earth.
14.1 The Breath of Life: Air
We have already talked about the composition
of air in the first chapter. It is a mixture of
many gases like nitrogen, oxygen, carbon
dioxide and water vapour. It is interesting to
note that even the composition of air is the
result of life on Earth. In planets such as
Venus and Mars, where no life is known to
exist, the major component of the atmosphere
is found to be carbon dioxide. In fact, carbon
dioxide constitutes up to 95-97% of the
atmosphere on Venus and Mars.
Eukaryotic cells and many prokaryotic
cells, discussed in Chapter 5, need oxygen to
break down  glucose molecules and get energy
for their activities. This results in the
production of carbon dioxide. Another process
which results in the consumption of oxygen
and the concomitant production of carbon
dioxide is combustion. This includes not just
human activities, which burn fuels to get
energy, but also forest fires.
Despite this, the percentage of carbon
dioxide in our atmosphere is a mere fraction
of a percent because carbon dioxide is ‘fixed’
in two ways: (i) Green plants convert carbon
dioxide into glucose in the presence of
Sunlight and (ii) many marine animals use
carbonates dissolved in sea-water to make
their shells.
14.1.1 THE ROLE OF THE ATMOSPHERE IN
CLIMATE CONTROL
We have talked of the atmosphere covering
the Earth, like a blanket. We know that air is
a bad conductor of heat. The atmosphere
keeps the average temperature of the Earth
fairly steady during the day and even during
the course of the whole year. The atmosphere
prevents the sudden increase in temperature
during the daylight hours. And during the
night, it slows down the escape of heat into
outer space. Think of the moon, which is
about the same distance from the Sun that
the Earth is. Despite that, on the surface of
the moon, with no atmosphere, the
temperature ranges from –190º C to 110º C.
14 14
14 14 14
N N N N NATURAL ATURAL ATURAL ATURAL ATURAL R R R R RESOURCES ESOURCES ESOURCES ESOURCES ESOURCES
Chapter
SCIENCE 190
the heating of water bodies and the activities
of living organisms. The atmosphere can be
heated from below by the radiation that is
reflected back or re-radiated by the land or
water bodies. On being heated, convection
currents are set up in the air. In order to gain
some understanding of the nature of
convection currents, let us perform the
following activity:
Activity _____________14.2
• Place a candle in a beaker or wide-
mouthed bottle and light it. Light an
incense stick and take it to the mouth
of the above bottle (Figure 14.1).
• Which way does the smoke flow when
the incense stick is kept near the edge
of the mouth?
• Which way does the smoke flow when
the incense stick is kept a little above
the candle?
• Which way does the smoke flow when
the incense stick is kept in other
regions?
Activity _____________14.1
• Measure the temperature of the
following :
Take (i) a beaker full of water, (ii) a
beaker full of soil/sand and (iii) a closed
bottle containing a thermometer. Keep
them in bright Sunlight for three hours.
Now measure the temperature of all 3
vessels. Also, take the temperature
reading in shade at the same time.
Now answer
1. Is the temperature reading more in
activity (i) or (ii)?
2. Based on the above finding, which
would become hot faster – the land or
the sea?
3. Is the thermometer reading of the
temperature of air (in shade) the same
as the temperature of sand or water?
What do you think is the reason for
this? And why does the temperature
have to be measured in the shade?
4. Is the temperature of air in the closed
glass vessel/bottle the same as the
temperature taken in open air? (i) What
do you think is the reason for this?
(ii) Do we ever come across this
phenomenon in daily life?
As we have seen above, sand and water
do not heat up at the same rate. What do you
think will be their rates of cooling? Can we
think of an experiment to test the prediction?
14.1.2 THE MOVEMENT OF AIR: WINDS
We have all felt the relief brought by cool
evening breezes after a hot day. And
sometimes, we are lucky enough to get rains
after some days of really hot weather. What
causes the movement of air, and what decides
whether this movement will be in the form of
a gentle breeze, a strong wind or a terrible
storm? What brings us the welcome rains?
All these phenomena are the result of
changes that take place in our atmosphere
due to the heating of air and the formation of
water vapour. Water vapour is formed due to
Fig. 14.1: Air currents being caused by the uneven
heating of air .
The patterns revealed by the smoke show
us the directions in which hot and cold air
move. In a similar manner, when air is heated
by radiation from the heated land or water, it
rises. But since land gets heated faster than
water, the air over land would also be heated
faster than the air over water bodies.
So, if we look at the situation in coastal
regions during the day, the air above the land
NATURAL RESOURCES 191
gets heated faster and starts rising. As this
air rises, a region of low pressure is created
and air over the sea moves into this area of
low pressure. The movement of air from one
region to the other creates winds. During the
day, the direction of the wind would be from
the sea to the land.
At night, both land and sea start to cool.
Since water cools down slower than the land,
the air above water would be warmer than
the air above land.
On the basis of the above discussion, what
can you say about:
1. the appearance of areas of low and
high pressure in coastal areas at night?
2. the direction in which air would flow
at night in coastal areas?
Similarly, all the movements of air
resulting in diverse atmospheric phenomena
are caused by the uneven heating of the
atmosphere in different regions of the Earth.
But various other factors also influence these
winds – the rotation of the Earth and the
presence of mountain ranges in the paths of
the wind are a couple of these factors. We
will not go into these factors in detail in this
chapter, but think about this: how do the
presence of the Himalayas change the flow of
a wind blowing from Allahabad towards the
north?
14.1.3 RAIN
Let us go back now to the question of how
clouds are formed and bring us rain. We could
start by doing a simple experiment which
demonstrates some of the factors influencing
these climatic changes.
Activity _____________14.3
• Take an empty bottle of the sort in
which bottled water is sold. Pour about
5-10 mL of water into it and close the
bottle tightly. Shake it well or leave it
out in the Sun for ten minutes. This
causes the air in the bottle to be
saturated with water vapour.
• Now, take a lighted incense stick. Open
the cap of the bottle and allow some of
the smoke from the incense stick to
enter the bottle. Quickly close the bottle
once more. Make sure that the cap is
fitting tightly. Press the bottle hard
between your hands and crush it as
much as possible. Wait for a few
seconds and release the bottle. Again
press the bottle as hard as you can.
Now answer
1. When did you observe that the air
inside seemed to become ‘foggy’?
2. When does this fog disappear?
3. When is the pressure inside the bottle
higher?
4. Is the ‘fog’ observed when the pressure
in the bottle is high or when it is low?
5. What is the need for smoke particles
inside the bottle for this experiment?
6. What might happen if you do the
experiment without the smoke from the
incense stick? Now try it and check if
the prediction was correct. What might
be happening in the above experiment
in the absence of smoke particles?
The above experiment replicates, on a very
small scale, what happens when air with a
very high content of water vapour goes from
a region of high pressure to a region of low
pressure or vice versa.
When water bodies are heated during the
day, a large amount of water evaporates and
goes into the air. Some amount of water
vapour also get into the atmosphere because
of various biological activities. This air also
gets heated. The hot air rises up carrying the
water vapour with it. As the air rises, it
expands and cools. This cooling causes the
water vapour in the air to condense in the
form of tiny droplets. This condensation of
water is facilitated if some particles could act
as the ‘nucleus’ for these drops to form
around. Normally dust and other suspended
particles in the air perform this function.
Once the water droplets are formed, they
grow bigger by the ‘condensation’ of these
water droplets. When the drops have grown
big and heavy, they fall down in the form of
rain. Sometimes, when the temperature of air
Page 4


Our planet, Earth is the only one on which
life, as we know it, exists. Life on Earth is
dependent on many factors. Most life-forms
we know need an ambient temperature,
water, and food. The resources available on
the Earth and the energy from the Sun are
necessary to meet the basic requirements of
all life-forms on the Earth.
What are these resources on the Earth?
These are the land, the water and the air.
The outer crust of the Earth is called the
lithosphere. Water covers 75% of the Earth’s
surface. It is also found underground. These
comprise the hydrosphere. The air that covers
the whole of the Earth like a blanket, is called
the atmosphere. Living things are found
where these three exist. This life-supporting
zone of the Earth where the atmosphere, the
hydrosphere and the lithosphere interact and
make life possible, is known as the biosphere.
Living things constitute the biotic
component of the biosphere. The air, the
water and the soil form the non-living or
abiotic component of the biosphere. Let us
study these abiotic components in detail in
order to understand their role in sustaining
life on Earth.
14.1 The Breath of Life: Air
We have already talked about the composition
of air in the first chapter. It is a mixture of
many gases like nitrogen, oxygen, carbon
dioxide and water vapour. It is interesting to
note that even the composition of air is the
result of life on Earth. In planets such as
Venus and Mars, where no life is known to
exist, the major component of the atmosphere
is found to be carbon dioxide. In fact, carbon
dioxide constitutes up to 95-97% of the
atmosphere on Venus and Mars.
Eukaryotic cells and many prokaryotic
cells, discussed in Chapter 5, need oxygen to
break down  glucose molecules and get energy
for their activities. This results in the
production of carbon dioxide. Another process
which results in the consumption of oxygen
and the concomitant production of carbon
dioxide is combustion. This includes not just
human activities, which burn fuels to get
energy, but also forest fires.
Despite this, the percentage of carbon
dioxide in our atmosphere is a mere fraction
of a percent because carbon dioxide is ‘fixed’
in two ways: (i) Green plants convert carbon
dioxide into glucose in the presence of
Sunlight and (ii) many marine animals use
carbonates dissolved in sea-water to make
their shells.
14.1.1 THE ROLE OF THE ATMOSPHERE IN
CLIMATE CONTROL
We have talked of the atmosphere covering
the Earth, like a blanket. We know that air is
a bad conductor of heat. The atmosphere
keeps the average temperature of the Earth
fairly steady during the day and even during
the course of the whole year. The atmosphere
prevents the sudden increase in temperature
during the daylight hours. And during the
night, it slows down the escape of heat into
outer space. Think of the moon, which is
about the same distance from the Sun that
the Earth is. Despite that, on the surface of
the moon, with no atmosphere, the
temperature ranges from –190º C to 110º C.
14 14
14 14 14
N N N N NATURAL ATURAL ATURAL ATURAL ATURAL R R R R RESOURCES ESOURCES ESOURCES ESOURCES ESOURCES
Chapter
SCIENCE 190
the heating of water bodies and the activities
of living organisms. The atmosphere can be
heated from below by the radiation that is
reflected back or re-radiated by the land or
water bodies. On being heated, convection
currents are set up in the air. In order to gain
some understanding of the nature of
convection currents, let us perform the
following activity:
Activity _____________14.2
• Place a candle in a beaker or wide-
mouthed bottle and light it. Light an
incense stick and take it to the mouth
of the above bottle (Figure 14.1).
• Which way does the smoke flow when
the incense stick is kept near the edge
of the mouth?
• Which way does the smoke flow when
the incense stick is kept a little above
the candle?
• Which way does the smoke flow when
the incense stick is kept in other
regions?
Activity _____________14.1
• Measure the temperature of the
following :
Take (i) a beaker full of water, (ii) a
beaker full of soil/sand and (iii) a closed
bottle containing a thermometer. Keep
them in bright Sunlight for three hours.
Now measure the temperature of all 3
vessels. Also, take the temperature
reading in shade at the same time.
Now answer
1. Is the temperature reading more in
activity (i) or (ii)?
2. Based on the above finding, which
would become hot faster – the land or
the sea?
3. Is the thermometer reading of the
temperature of air (in shade) the same
as the temperature of sand or water?
What do you think is the reason for
this? And why does the temperature
have to be measured in the shade?
4. Is the temperature of air in the closed
glass vessel/bottle the same as the
temperature taken in open air? (i) What
do you think is the reason for this?
(ii) Do we ever come across this
phenomenon in daily life?
As we have seen above, sand and water
do not heat up at the same rate. What do you
think will be their rates of cooling? Can we
think of an experiment to test the prediction?
14.1.2 THE MOVEMENT OF AIR: WINDS
We have all felt the relief brought by cool
evening breezes after a hot day. And
sometimes, we are lucky enough to get rains
after some days of really hot weather. What
causes the movement of air, and what decides
whether this movement will be in the form of
a gentle breeze, a strong wind or a terrible
storm? What brings us the welcome rains?
All these phenomena are the result of
changes that take place in our atmosphere
due to the heating of air and the formation of
water vapour. Water vapour is formed due to
Fig. 14.1: Air currents being caused by the uneven
heating of air .
The patterns revealed by the smoke show
us the directions in which hot and cold air
move. In a similar manner, when air is heated
by radiation from the heated land or water, it
rises. But since land gets heated faster than
water, the air over land would also be heated
faster than the air over water bodies.
So, if we look at the situation in coastal
regions during the day, the air above the land
NATURAL RESOURCES 191
gets heated faster and starts rising. As this
air rises, a region of low pressure is created
and air over the sea moves into this area of
low pressure. The movement of air from one
region to the other creates winds. During the
day, the direction of the wind would be from
the sea to the land.
At night, both land and sea start to cool.
Since water cools down slower than the land,
the air above water would be warmer than
the air above land.
On the basis of the above discussion, what
can you say about:
1. the appearance of areas of low and
high pressure in coastal areas at night?
2. the direction in which air would flow
at night in coastal areas?
Similarly, all the movements of air
resulting in diverse atmospheric phenomena
are caused by the uneven heating of the
atmosphere in different regions of the Earth.
But various other factors also influence these
winds – the rotation of the Earth and the
presence of mountain ranges in the paths of
the wind are a couple of these factors. We
will not go into these factors in detail in this
chapter, but think about this: how do the
presence of the Himalayas change the flow of
a wind blowing from Allahabad towards the
north?
14.1.3 RAIN
Let us go back now to the question of how
clouds are formed and bring us rain. We could
start by doing a simple experiment which
demonstrates some of the factors influencing
these climatic changes.
Activity _____________14.3
• Take an empty bottle of the sort in
which bottled water is sold. Pour about
5-10 mL of water into it and close the
bottle tightly. Shake it well or leave it
out in the Sun for ten minutes. This
causes the air in the bottle to be
saturated with water vapour.
• Now, take a lighted incense stick. Open
the cap of the bottle and allow some of
the smoke from the incense stick to
enter the bottle. Quickly close the bottle
once more. Make sure that the cap is
fitting tightly. Press the bottle hard
between your hands and crush it as
much as possible. Wait for a few
seconds and release the bottle. Again
press the bottle as hard as you can.
Now answer
1. When did you observe that the air
inside seemed to become ‘foggy’?
2. When does this fog disappear?
3. When is the pressure inside the bottle
higher?
4. Is the ‘fog’ observed when the pressure
in the bottle is high or when it is low?
5. What is the need for smoke particles
inside the bottle for this experiment?
6. What might happen if you do the
experiment without the smoke from the
incense stick? Now try it and check if
the prediction was correct. What might
be happening in the above experiment
in the absence of smoke particles?
The above experiment replicates, on a very
small scale, what happens when air with a
very high content of water vapour goes from
a region of high pressure to a region of low
pressure or vice versa.
When water bodies are heated during the
day, a large amount of water evaporates and
goes into the air. Some amount of water
vapour also get into the atmosphere because
of various biological activities. This air also
gets heated. The hot air rises up carrying the
water vapour with it. As the air rises, it
expands and cools. This cooling causes the
water vapour in the air to condense in the
form of tiny droplets. This condensation of
water is facilitated if some particles could act
as the ‘nucleus’ for these drops to form
around. Normally dust and other suspended
particles in the air perform this function.
Once the water droplets are formed, they
grow bigger by the ‘condensation’ of these
water droplets. When the drops have grown
big and heavy, they fall down in the form of
rain. Sometimes, when the temperature of air
SCIENCE 192
14.1.4 AIR POLLUTION
We keep hearing of the increasing levels of
oxides of nitrogen and sulphur in the news.
People often bemoan the fact that the quality
of air has gone down since their childhood.
How is the quality of air affected and how
does this change in quality affect us and other
life forms?
The fossil fuels like coal and petroleum
contain small amounts of nitrogen and
sulphur. When these fuels are burnt, nitrogen
and sulphur too are burnt and this produces
different oxides of nitrogen and sulphur. Not
only is the inhalation of these gases
dangerous, they also dissolve in rain to give
rise to acid rain. The combustion of fossil fuels
also increases the amount of suspended
particles in air. These suspended particles
could be unburnt carbon particles or
substances called hydrocarbons. Presence of
high levels of all these pollutants cause
visibility to be lowered, especially in cold
weather when water also condenses out of
air. This is known as smog and is a visible
indication of air pollution.  Studies have
shown that regularly breathing air that
contains any of these substances increases
the incidence of allergies, cancer and heart
diseases. An increase in the content of these
harmful substances in air is called air
pollution.
is low enough, precipitation may occur in the
form of snow, sleet or hail.
Rainfall patterns are decided by the
prevailing wind patterns. In large parts of
India, rains are mostly brought by the south-
west or north-east monsoons. We have also
heard weather reports that say ‘depressions’
in the Bay of Bengal have caused rains in
some areas (Figure 14.2).
Activity _____________14.4
• Collect information from newspapers
or weather reports on television about
rainfall patterns across the country.
Also find out how to construct a rain-
gauge and make one. What precautions
are necessary in order to get reliable
data from this rain-gauge? Now answer
the following questions :
• In which month did your city/town/
village get the maximum rainfall?
• In which month did your state/union
territory get the maximum rainfall?
• Is rain always accompanied by thunder
and lightning? If not, in which season
do you get more of thunder and
lightning with the rain?
Activity _____________14.5
• Find out more about monsoons and
cyclones from the library. Try and find
out the rainfall pattern of any other
country. Is the monsoon responsible for
rains the world over?
Fig. 14.2: Satellite picture showing clouds over India.
Fig. 14.3: Lichen
Page 5


Our planet, Earth is the only one on which
life, as we know it, exists. Life on Earth is
dependent on many factors. Most life-forms
we know need an ambient temperature,
water, and food. The resources available on
the Earth and the energy from the Sun are
necessary to meet the basic requirements of
all life-forms on the Earth.
What are these resources on the Earth?
These are the land, the water and the air.
The outer crust of the Earth is called the
lithosphere. Water covers 75% of the Earth’s
surface. It is also found underground. These
comprise the hydrosphere. The air that covers
the whole of the Earth like a blanket, is called
the atmosphere. Living things are found
where these three exist. This life-supporting
zone of the Earth where the atmosphere, the
hydrosphere and the lithosphere interact and
make life possible, is known as the biosphere.
Living things constitute the biotic
component of the biosphere. The air, the
water and the soil form the non-living or
abiotic component of the biosphere. Let us
study these abiotic components in detail in
order to understand their role in sustaining
life on Earth.
14.1 The Breath of Life: Air
We have already talked about the composition
of air in the first chapter. It is a mixture of
many gases like nitrogen, oxygen, carbon
dioxide and water vapour. It is interesting to
note that even the composition of air is the
result of life on Earth. In planets such as
Venus and Mars, where no life is known to
exist, the major component of the atmosphere
is found to be carbon dioxide. In fact, carbon
dioxide constitutes up to 95-97% of the
atmosphere on Venus and Mars.
Eukaryotic cells and many prokaryotic
cells, discussed in Chapter 5, need oxygen to
break down  glucose molecules and get energy
for their activities. This results in the
production of carbon dioxide. Another process
which results in the consumption of oxygen
and the concomitant production of carbon
dioxide is combustion. This includes not just
human activities, which burn fuels to get
energy, but also forest fires.
Despite this, the percentage of carbon
dioxide in our atmosphere is a mere fraction
of a percent because carbon dioxide is ‘fixed’
in two ways: (i) Green plants convert carbon
dioxide into glucose in the presence of
Sunlight and (ii) many marine animals use
carbonates dissolved in sea-water to make
their shells.
14.1.1 THE ROLE OF THE ATMOSPHERE IN
CLIMATE CONTROL
We have talked of the atmosphere covering
the Earth, like a blanket. We know that air is
a bad conductor of heat. The atmosphere
keeps the average temperature of the Earth
fairly steady during the day and even during
the course of the whole year. The atmosphere
prevents the sudden increase in temperature
during the daylight hours. And during the
night, it slows down the escape of heat into
outer space. Think of the moon, which is
about the same distance from the Sun that
the Earth is. Despite that, on the surface of
the moon, with no atmosphere, the
temperature ranges from –190º C to 110º C.
14 14
14 14 14
N N N N NATURAL ATURAL ATURAL ATURAL ATURAL R R R R RESOURCES ESOURCES ESOURCES ESOURCES ESOURCES
Chapter
SCIENCE 190
the heating of water bodies and the activities
of living organisms. The atmosphere can be
heated from below by the radiation that is
reflected back or re-radiated by the land or
water bodies. On being heated, convection
currents are set up in the air. In order to gain
some understanding of the nature of
convection currents, let us perform the
following activity:
Activity _____________14.2
• Place a candle in a beaker or wide-
mouthed bottle and light it. Light an
incense stick and take it to the mouth
of the above bottle (Figure 14.1).
• Which way does the smoke flow when
the incense stick is kept near the edge
of the mouth?
• Which way does the smoke flow when
the incense stick is kept a little above
the candle?
• Which way does the smoke flow when
the incense stick is kept in other
regions?
Activity _____________14.1
• Measure the temperature of the
following :
Take (i) a beaker full of water, (ii) a
beaker full of soil/sand and (iii) a closed
bottle containing a thermometer. Keep
them in bright Sunlight for three hours.
Now measure the temperature of all 3
vessels. Also, take the temperature
reading in shade at the same time.
Now answer
1. Is the temperature reading more in
activity (i) or (ii)?
2. Based on the above finding, which
would become hot faster – the land or
the sea?
3. Is the thermometer reading of the
temperature of air (in shade) the same
as the temperature of sand or water?
What do you think is the reason for
this? And why does the temperature
have to be measured in the shade?
4. Is the temperature of air in the closed
glass vessel/bottle the same as the
temperature taken in open air? (i) What
do you think is the reason for this?
(ii) Do we ever come across this
phenomenon in daily life?
As we have seen above, sand and water
do not heat up at the same rate. What do you
think will be their rates of cooling? Can we
think of an experiment to test the prediction?
14.1.2 THE MOVEMENT OF AIR: WINDS
We have all felt the relief brought by cool
evening breezes after a hot day. And
sometimes, we are lucky enough to get rains
after some days of really hot weather. What
causes the movement of air, and what decides
whether this movement will be in the form of
a gentle breeze, a strong wind or a terrible
storm? What brings us the welcome rains?
All these phenomena are the result of
changes that take place in our atmosphere
due to the heating of air and the formation of
water vapour. Water vapour is formed due to
Fig. 14.1: Air currents being caused by the uneven
heating of air .
The patterns revealed by the smoke show
us the directions in which hot and cold air
move. In a similar manner, when air is heated
by radiation from the heated land or water, it
rises. But since land gets heated faster than
water, the air over land would also be heated
faster than the air over water bodies.
So, if we look at the situation in coastal
regions during the day, the air above the land
NATURAL RESOURCES 191
gets heated faster and starts rising. As this
air rises, a region of low pressure is created
and air over the sea moves into this area of
low pressure. The movement of air from one
region to the other creates winds. During the
day, the direction of the wind would be from
the sea to the land.
At night, both land and sea start to cool.
Since water cools down slower than the land,
the air above water would be warmer than
the air above land.
On the basis of the above discussion, what
can you say about:
1. the appearance of areas of low and
high pressure in coastal areas at night?
2. the direction in which air would flow
at night in coastal areas?
Similarly, all the movements of air
resulting in diverse atmospheric phenomena
are caused by the uneven heating of the
atmosphere in different regions of the Earth.
But various other factors also influence these
winds – the rotation of the Earth and the
presence of mountain ranges in the paths of
the wind are a couple of these factors. We
will not go into these factors in detail in this
chapter, but think about this: how do the
presence of the Himalayas change the flow of
a wind blowing from Allahabad towards the
north?
14.1.3 RAIN
Let us go back now to the question of how
clouds are formed and bring us rain. We could
start by doing a simple experiment which
demonstrates some of the factors influencing
these climatic changes.
Activity _____________14.3
• Take an empty bottle of the sort in
which bottled water is sold. Pour about
5-10 mL of water into it and close the
bottle tightly. Shake it well or leave it
out in the Sun for ten minutes. This
causes the air in the bottle to be
saturated with water vapour.
• Now, take a lighted incense stick. Open
the cap of the bottle and allow some of
the smoke from the incense stick to
enter the bottle. Quickly close the bottle
once more. Make sure that the cap is
fitting tightly. Press the bottle hard
between your hands and crush it as
much as possible. Wait for a few
seconds and release the bottle. Again
press the bottle as hard as you can.
Now answer
1. When did you observe that the air
inside seemed to become ‘foggy’?
2. When does this fog disappear?
3. When is the pressure inside the bottle
higher?
4. Is the ‘fog’ observed when the pressure
in the bottle is high or when it is low?
5. What is the need for smoke particles
inside the bottle for this experiment?
6. What might happen if you do the
experiment without the smoke from the
incense stick? Now try it and check if
the prediction was correct. What might
be happening in the above experiment
in the absence of smoke particles?
The above experiment replicates, on a very
small scale, what happens when air with a
very high content of water vapour goes from
a region of high pressure to a region of low
pressure or vice versa.
When water bodies are heated during the
day, a large amount of water evaporates and
goes into the air. Some amount of water
vapour also get into the atmosphere because
of various biological activities. This air also
gets heated. The hot air rises up carrying the
water vapour with it. As the air rises, it
expands and cools. This cooling causes the
water vapour in the air to condense in the
form of tiny droplets. This condensation of
water is facilitated if some particles could act
as the ‘nucleus’ for these drops to form
around. Normally dust and other suspended
particles in the air perform this function.
Once the water droplets are formed, they
grow bigger by the ‘condensation’ of these
water droplets. When the drops have grown
big and heavy, they fall down in the form of
rain. Sometimes, when the temperature of air
SCIENCE 192
14.1.4 AIR POLLUTION
We keep hearing of the increasing levels of
oxides of nitrogen and sulphur in the news.
People often bemoan the fact that the quality
of air has gone down since their childhood.
How is the quality of air affected and how
does this change in quality affect us and other
life forms?
The fossil fuels like coal and petroleum
contain small amounts of nitrogen and
sulphur. When these fuels are burnt, nitrogen
and sulphur too are burnt and this produces
different oxides of nitrogen and sulphur. Not
only is the inhalation of these gases
dangerous, they also dissolve in rain to give
rise to acid rain. The combustion of fossil fuels
also increases the amount of suspended
particles in air. These suspended particles
could be unburnt carbon particles or
substances called hydrocarbons. Presence of
high levels of all these pollutants cause
visibility to be lowered, especially in cold
weather when water also condenses out of
air. This is known as smog and is a visible
indication of air pollution.  Studies have
shown that regularly breathing air that
contains any of these substances increases
the incidence of allergies, cancer and heart
diseases. An increase in the content of these
harmful substances in air is called air
pollution.
is low enough, precipitation may occur in the
form of snow, sleet or hail.
Rainfall patterns are decided by the
prevailing wind patterns. In large parts of
India, rains are mostly brought by the south-
west or north-east monsoons. We have also
heard weather reports that say ‘depressions’
in the Bay of Bengal have caused rains in
some areas (Figure 14.2).
Activity _____________14.4
• Collect information from newspapers
or weather reports on television about
rainfall patterns across the country.
Also find out how to construct a rain-
gauge and make one. What precautions
are necessary in order to get reliable
data from this rain-gauge? Now answer
the following questions :
• In which month did your city/town/
village get the maximum rainfall?
• In which month did your state/union
territory get the maximum rainfall?
• Is rain always accompanied by thunder
and lightning? If not, in which season
do you get more of thunder and
lightning with the rain?
Activity _____________14.5
• Find out more about monsoons and
cyclones from the library. Try and find
out the rainfall pattern of any other
country. Is the monsoon responsible for
rains the world over?
Fig. 14.2: Satellite picture showing clouds over India.
Fig. 14.3: Lichen
NATURAL RESOURCES 193
people are forced to spend considerable
amounts of time in fetching water from far-
away sources.
Activity _____________14.7
• Many municipal corporations are trying
water-harvesting techniques to
improve the availability of water.
• Find out what these techniques are and
how they would increase the water that
is available for use.
But why is water so necessary? And do
all organisms require water? All cellular
processes take place in a water medium. All
the reactions that take place within our body
and within the cells occur between
substances that are dissolved in water.
Substances are also transported from one
part of the body to the other in a dissolved
form. Hence, organisms need to maintain the
level of water within their bodies in order to
stay alive. Terrestrial life-forms require fresh
water for this because their bodies cannot
tolerate or get rid of the high amounts of
dissolved salts in saline water. Thus, water
sources need to be easily accessible for
animals and plants to survive on land.
Activity _____________14.8
• Select a small area (say, 1 m
2
) near a
water-body, it may be a river, stream,
lake or pond. Count the number of
different animals and plants in this
area. Also, check the number of
individuals of each type or species.
• Compare this with the number of
individuals (both animals and plants)
found in an area of the same size in a
dry, rocky region.
• Is the variety of plant and animal life
the same in both these areas?
Activity _____________14.9
• Select and mark out a small area (about
1 m
2
) in some unused land in or near
your school.
• As in the above activity, count the
number of different animals and plants
in this area and the number of
individuals of each species.
Activity _____________14.6
• Organisms called lichens are found to
be very sensitive to the levels of
contaminants like sulphur dioxide in
the air. As discussed earlier in section
7.3.3, lichens can be commonly found
growing on the barks of trees as a thin
greenish-white crust. See if you can
find lichen growing on the trees in your
locality.
• Compare the lichen on trees near busy
roads and trees some distance away.
• On the trees near roads, compare the
incidence of lichen on the side facing
the road and on the side away from the
road.
What can you say about the levels of
polluting substances near roads and away
from roads on the basis of your findings
above?
uestions
1. How is our atmosphere different
from the atmospheres on Venus
and Mars?
2. How does the atmosphere act as
a blanket?
3. What causes winds?
4. How are clouds formed?
5. List any three human activities
that you think would lead to air
pollution.
14.2 Water: A Wonder Liquid
Water occupies a very large area of the Earth’s
surface and is also found underground. Some
amount of water exists in the form of water
vapour in the atmosphere. Most of the water
on Earth’s surface is found in seas and oceans
and is saline. Fresh water is found frozen in
the ice-caps at the two poles and on snow-
covered mountains. The underground water
and the water in rivers, lakes and ponds is
also fresh. However, the availability of fresh
water varies from place to place. Practically
every summer, most places have to face a
shortage of water. And in rural areas, where
water supply systems have not been installed,
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