The important natural resources
available on Earth are land, water
and air. The region of Earth where
the atmosphere, hydrosphere and
lithosphere interact and support life
is called biosphere.
Living organisms constitute the
biotic component of the biosphere.
Air, water and soil constitute the
abiotic component of the
Air is a mixture of gases like
nitrogen, oxygen and carbon
Plants and animals use oxygen for respiration. The
combustion of fossil fuels also requires oxygen.
Marine animals absorb
dioxide and form
carbonic acid. These
carbonate ions are used
by marine animals to
Plants use co2 for
The ways by which CO2 is fixed by living organisms
On the planets Venus and Mars
carbon dioxide forms the major
component constituting up to
95-97% of the atmosphere. On
the contrary the major
component of the earth’s
atmosphere is air which
consists of nitrogen, oxygen,
carbon dioxide, argon, water
vapour and trace components.
Moreover, unlike Venus and
Mars earth has life on it.
Its composition is 95% CO2, 3% N2, 2% Ar and less than 1% O2.
How is our atmosphere different from the
atmosphere on Venus and Mars
• The mass or body of gases that surrounds the earth or any heavenly
body is called atmosphere.
• Earth’s atmosphere extends from the surface to a height of more
than 1000 km, beyond which it merges gradually with solar
atmosphere. Air is a bad conductor of heat and so, earth’s
atmosphere acts as a protective blanket.
• It keeps the average temperature of the earth fairly steady during the
day and the whole year.
• The atmosphere prevents the sudden increase in temperature during
daytime and also helps in retaining heat of the earth by slowing
down the escape of heat during night.
How does the atmosphere act as a blanket?
What causes winds?
• The movement of air from
one region to another
creates winds An
uneven heating of the
causes winds. On
air becomes lighter
and rises up. As a
result, a region of low
pressure is created.
Then, air from a high
moves to a low
Air is a bad conductor of heat.
• Take an empty long test tube. Hold the test
tube tilted with its mouth downwards. Heat
the tube at its bottom on the flame of a
candle. It is noticed that the fingers do not
feel warm. This shows that th air trapped in
test tube does not conduct heat from the
heated bottom of the test tub to the fingers.
This proves that air is a bad conductor of
The movement of air (Winds)
• When air gets heated, it rises up and produces
low pressure and cool air moves in to take its
place. The movement of air causes winds.
• During the day the land gets heated faster
than the sea. So the hot air above the land
rises up and cool air from the sea moves
towards the land.
• During the night sea cools down slowly than
the land. So the hot air above the sea rises up
and cool air from the land moves towards the
Wind develops as a result of spatial differences in atmospheric
pressure. Generally, these differences occur because of uneven
absorption of solar radiation at the Earth's surface
Air pollution & its effects
• The increase in the content of
harmful substances in the air is
called air pollution.
• 1. Fossil fuels like coal and
petroleum contain small
amounts of nitrogen and
sulphur. When these fuels are
burnt, it release oxides of
sulphur and nitrogen. These
oxides dissolve in rain and
causes acid rain.
2 Burning of fossil fuels
also release unburnt
carbon particles which
During cold weather
along with condensed
water it forms smog.
City without smog
City with smog
Water bodies get
heated during the
day and evaporate
into the air. As the
vapour rises, it
cools. This causes
the vapour to
condense into tiny
which fall down as
Organisms need water because it plays a vital
role in the reactions taking place within
organism’s cells and body.
Water acts as a universal solvent, providing a
medium for the chemical reactions to occur.
Substances are also transported from one part of
the body to the other in the dissolved state.
Therefore, it is necessary for the organisms to
maintain a certain level of water within their
bodies in order to stay alive.
Importance of water in living organisms
•The dissolved fertilizers, chemicals,
pesticides percolated with rain
water from the fields
• wastes from industries
•Breeding of decomposers (micro-
organisms) in water are the major
sources or causes
• Soil is formed by breaking down of rocks
at or near the surface of the Earth
through various physical, chemical, and
biological processes by various factors
such as the sun, water, wind, and living
During day time, the rocks are heated.
This causes the rocks to expand. During
night time, these rocks cool down and
contract. Since all parts of the rock do
not undergo expansion and contraction
at the same rate, this causes the
formation of cracks in these rocks.
These cracks lead to the breaking up of
huge rocks into smaller pieces.
Water catalyses the process of formation
of soil in two ways.
(a) Water goes into the cracks and
crevices formed in the rocks. When this
water freezes, its volume increases. As a
result, the size of the cracks also
increases. This helps in the weathering
• 3 Running water wears away hard rocks
over long periods of time. Water moving
in fast speed carries big and small
particles of rock downstream. These rocks
rub against each other, resulting in
breaking down of rocks. These smaller
particles are carried away by running water
and deposited down its path.
Strong winds carry away rocks, which
causes rubbing of rocks. This results in
the breaking down of rocks into smaller
and smaller particles.
Some living organisms like lichens help in
the formation of soil. Lichens also grow
on rocks. During their growth, lichens
release certain substances, which cause
the rock surface to powder down forming a
thin layer of soil. On this thin layer of soil,
some small plants like moss also grow.
They further cause the breaking down of
the rock particles
• (iv) Living organisms:
Some living organisms like
lichens help in the
formation of soil. Lichens
also grow on rocks. During
their growth, lichens
substances, which cause
the rock surface to powder
down forming a thin layer
of soil. On this thin layer of
soil, some small plants like
moss also grow. They
further cause the breaking
down of the rock particles
Living organisms depend on soil
• The top surface layer of earth capable of supporting plant life is called
soil. Soil is a complex mixture, comprising of minerals (45%), organic
matter (5%), water (25%), air (25%) and living organisms. It is an
important resource that determines the diversity of life in an area.
Plants are dependent on the soil from where they obtain various types
of minerals, water and air. All these three components are essential for
the growth of plants. Animals (herbivores) depend on plants for food.
Other animals (carnivores) depend on these herbivores. Hence, all
living organisms directly or indirectly depend on the soil.
• Aquatic organisms are not entirely independent of soil as a resource.
Microscopic decomposers (e.g. fungi, archaebacteria and bacteria)
present in the bottom sediments of water bodies decompose dead,
decaying organic matter into simple, inorganic substances (minerals).
The latter get dissolved in water and are available as nutrients for
aquatic plants and they indirectly through plants to animals. Also,
water bodies get supply of minerals from soil through rivers, spring
etc. without which minerals present in the water bodies will exhaust.
Aquatic green plants and animals get these minerals from water
Composition of soil
Soil is a mixture of rock particles, decayed
organisms called humus, living organisms,
minerals, air and water. The amount of
minerals, humus, air and water are the
factors which decides the biodiversity in that
• The addition of harmful substances which
affects the fertility of the soil and kills the
diversity of organisms living in it is called soil
• Soil pollution is caused by the excessive
use of fertilisers and pesticides. It kills the
organisms like earthworms and bacteria
which makes the soil rich in humus. The
removal of useful components and addition of
other harmful substances reduces the fertility
of soil and causes soil pollution.
The carrying away of soil from one place to the other by flowing water
and wind is called soil pollution. Large scale deforestation also causes
Soil erosion can reduced or prevented by vegetative cover on the
ground, afforestation, construction of bunds, terraces, dams etc.
Activity :- Effect of flowing water on top soil.
Take two trays of the same size and fill them with soil. Plant mustard
or green gram in one of the trays. Water both the trays for a few days till
the first tray is covered by plant growth. The tilt both the trays at the
sane angle. Pour equal amount of water gently on both the trays. More
soil is carried out of the tray which did not have plant growth. This
shows that vegetative cover reduces soil erosion.
Biogeochemical cycles :-
Biogeochemical cycles are the transfer of
matter and energy between the biotic and
abiotic components of the biosphere.
The common biogeochemical cycles are :-
i) Water cycle,
ii) Nitrogen cycle,
iii) Carbon cycle
iv) Oxygen cycle.
• When water bodies are heated
during the day, a large amount of
water evaporates and rises up. Some
water vapour also get into the
atmosphere due to biological
activities like transpiration and
• As the water vapour rises, it cools
and condenses to form tiny droplets
of water. This appears as clouds.
When the tiny droplets of water join
together to form bigger drops of
water, they fall down as rain, snow
• Some of this water enters the
ground and forms ground water.
When water flows from the land to
the seas it carries many nutrients
and minerals which are used by
• The nitrogen in the atmosphere is fixed into nitrogen
compounds in the soil by nitrogen fixing bacteria in the
root nodules of leguminous plants and also during
lightning. These nitrogen compounds are taken by plants
and used to make proteins. When animals eat plants they
also get proteins.
• When plants and animals die, bacteria convert the proteins
into nitrogen compounds like nitrites and nitrates. Other
bacteria convert these nitrogen compounds back into
nitrogen in the atmosphere.
• Nitrogen is an essential component of biological
molecules like proteins, nucleic acids and some vitamins
Carbon in the form of carbon dioxide is
used by plants to prepare glucose by the
process of photosynthesis.
The glucose is used to provide energy and
to convert into other organic compounds
When animals eat plants it enters the body
of animals. During respiration energy and
carbon dioxide are produced. The carbon
dioxide goes back into the atmosphere.
Another process which adds carbon dioxide
back into the atmosphere is the combustion
of fuels like coal and petroleum.
The organic compound in plants and
animals are also converted into carbonates,
limestone, coal, petroleum, exoskeletons
(shells) of some animals.
Carbon is an essential component of
biological molecules like carbohydrates,
fats, proteins, vitamins, nucleic acids etc.
CO2 in atmosphere
Oxygen cycle :-
Oxygen in the atmosphere is used for respiration,
combustion and formation of oxide of elements. Oxygen is
sent back into the atmosphere during photosynthesis.
Oxygen is an essential component of biological molecules
like carbohydrates, fats, and proteins.
Green house effect
• A part of the sunlight incident on the
earth is reflected back in the form of
infrared light. Some gases such as
carbon dioxide, methane,
chlorofluorocarbons (CFCs), also
known as greenhouse gases, present
in the earth’s atmosphere prevent the
escape of heat from the earth by
absorbing this infrared light which is
reflected back by the earth. An
increase in the percentage of this
greenhouse gases in the atmosphere
would cause an increase in the
average temperature world-wide and
this phenomena is known
• Thus, the heating of the atmosphere
due to the absorption of infrared
radiations by carbon dioxide
molecules and other greenhouse
gases is called the ‘Greenhouse
Oxygen & Ozone
• Oxygen is found in the atmosphere in the
• (i) A diatomic molecule having two atoms of
oxygen, with chemical formula O2.
• (ii) A tri-atomic molecule having three atoms
of oxygen, with chemical formula O3 called
Location of Ozone elayer
• Ozone is present in
the tratosphere. The
reaches 30 miles
above the Earth, and
at the very top
• it contains ozone.
Functions of Ozone layer
• The ozone layer
shields the entire
Earth from much of
that comes from the
Depletion of Ozone layer
• The main cause of this is the release of