Air is transparent and colourless, occupies space, and surrounds us. The thin blanket of air surrounding the Earth's surface is called the atmosphere. The atmosphere is divided into five distinct layers based on temperature variations, which change with increasing altitude. As we ascend, the air becomes thinner.

2. Air is Everywhere
Our earth is surrounded by a thin layer of air.
We cannot see air, but we can feel its presence in many
ways.
Leaves of the trees rustle and the branches sway in the
wind.
The clothes hanging on a clothesline swing because of the
presence of air.
This layer extends up to many kilometres above the
surface of the earth and is called the atmosphere.

3. Colour of Air
Air has no colour and one can see through it. It is transparent.
Air as a Mixture
Air is a mixture of different gases and particles; oxygen, water
vapour, nitrogen, carbon dioxide, dust and smoke.
Atmosphere
The layer of air that covers the Earth extends up to some
kilometres in space, this is the atmosphere.
Moving Air
Moving air can be termed as the wind. We can feel the wind as it
sways leaves on a tree or during storms the wind blows at a very
high speed even uprooting trees in their way.

4. What is the Composition of Air?
Air is present all around us. We can feel the presence
of air but cannot see the air around us. Air is a mixture
of gases. The different components of air includes –
78% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon
dioxide, and remaining water vapour. Air plays an
important role in breathing and burning. The
existence of life on the planet earth is mainly because
of the presence of air.

5. Water vapour
Water vapour is present in the air as a gaseous form of water and is responsible for
humidity.
Dust and smoke
The minor particles that are present in the air. The high amount of these particles in the air
can cause pollution.
Breathing in Humans
Both animals and humans breathe by inhaling oxygen and exhaling carbon dioxide. this
process is termed as respiration.
Breathing in Plants
Plants respire through the process of photosynthesis. In this process, they take in carbon
dioxide and give out oxygen as a waste, which we breathe in.

6. Air is present in the Soil
Take a lump of dry soil in a beaker or a glass.
Add water to it and note what happens. We can
see bubbles coming out from soil. These bubbles
indicate the presence of air in the soil.

7. Fire( oxygen)
Fire requires oxygen for sustenance.
NITROGEN
This gas does not support burning ,but it is a major component in making fertilizers.
Carbon dioxide
It is used to fill fire extinguishers.

8. AIR SUPPORTS BURNING
Take a small burning candle. Cover the burning
candle with a glass jar. After few minutes the candle
is extinguished. As the supply of air is stopped due
to glass jar the burning of candle is also stopped.
This experiment proves that air supports burning
Air is Dissolved in water
Take some water in a glass vessel or beaker. Heat it
slowly on a tripod stand. Before the water begins to
boil, look carefully at the inner surface of the vessel.
You will see tiny bubbles on the inside. On heating,
air dissolved in water escapes in the form of these
bubbles.

9. We inhale air when we breathe through our nostrils.
Fine hair and mucus are present inside the nose to
prevent dust particles from getting into the
respiratory system. Since our mouth does not
contain mucus and fine hair, so if we breathe
through it, dust particles may enter in our
respiratory tract. That is why breathing through
mouth is not suggested.

10. Breathing in Fish
Oxygen dissolved in water is used by fishes to breathe.
Symbiotic Cycle
Organisms usually come together where each benefits from the
other.
We get oxygen and other products from plants and they get not
only carbon dioxide but other advantages from us.
This is in the form of a cycle. Respiration and photosynthesis lead
to recycling of oxygen and carbon dioxide in the environment.

11. How is the oxygen replaced in the atmosphere?
As we all know, air contains only 21% oxygen. All living organisms
including the plants require oxygen for breathing. Plants play an
important role in the balance of oxygen and carbon dioxide in the
atmosphere and are maintained through the process of
photosynthesis.
Photosynthesis is a biological process in which all green plants
synthesize their food in the presence of sunlight, water, and carbon
dioxide. Oxygen gas is the most important by-products of this
process.

12. WIND ENERGY
Moving air is called wind. Wind possesses kinetic
energy. The kinetic energy possessed by wind is
called wind energy.
Uses of Wind Energy are
(i) Wind energy is used to pump the ground water.
(ii) Wind energy is used to generate electricity with
the help of windmills