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Chapter: 4th Science : Term 3 Unit 3 : Air We Breathe

Air We Breathe

After the completion of this unit students will be able to • know that air is a mixture • understand the composition and components of air • explain air pollution and its effects

Unit 3



Learning Objectives

After the completion of this unit students will be able to

• know that air is a mixture

• understand the composition and components of air

• explain air pollution and its effects



Our earth is made of land, water, and air. All three components are very much important for the survival of all living creatures. Air is present all around us and is very important for our lives. It is very important to cause rain and for the growth of crops. It is needed for the respiration of plants and animals.


Take a squeezable bottle. Make a hole on the lid and close the bottle tightly. Bring the bottle near your face and press the bottle. What do you feel?


Importance of Air in Our Daily Life 

1. Oxygen present in air is needed for respiration.

2. We can speak and hear the sound only when there is air around.

3. Air helps in the dispersal of seeds for plant reproduction.

4. Monsoon and rain occurs due to the wind action.

5. Air regulates the atmospheric temperature.

Let us do

Tick the objects which have air in them.


Air is a Mixture

The air we breathe consists of a mixture of gases. It contains solid and liquid particles too. Air can be separated into its constituents such as oxygen, nitrogen etc. Water vapour mixes with air and becomes a part of it. Air also contains dust and smoke. Air shows the properties of all the gases present in it. E.g. Air supports combustion because of oxygen present in it. While cooking using firewood, fanning air helps in burning of fire wood.

Do you Know?

How do we get cool water from a clay water pot on hot sunny days?

Clay pot has thousands of tiny pores through which water seeps out. This causes cooling effect.

Let us do

Tick the object which gives out water vapour.

Do you Know?

The nathaswaram and the flute are some of the examples for wind instrument.


Composition and components of air

The composition of air is not constant. It varies from place to place and over time.

Air is not a single element; it is made up of different substances.


Write the percentage of the gases present in air.


The amount of Nitrogen present in air is about 78%.

It is used to fill up food packages to extend their shelf life.

Liquid nitrogen is used to store living cells.

Plants need nitrogen for their growth. We can see root nodules containing nitrogen in some plants.

Nowadays people use nitrogen gas to fill the tyres of their vehicles. Some compounds of nitrogen are used as explosives also.

Do you Know?

In 1772, the Scottish chemist, Daniel Rutherford, reported “noxious air,” which now we call “Nitrogen”.


You might have seen some huge colourful balloons flying high in malls. Those balloons are filled with nitrogen gas. Write the reason for filling nitrogen gas in balloons.

Nitrogen is an inert gas. It is similar to air but it is slightly lighter than air. So when there is no necessity to lift the balloon very high, we use nitrogen gas.


It is one of the main components of air. The amount of Oxygen present in air is about 21%. All the creatures cannot live without oxygen. It can be tested with a piece of glowing splint, which relights in oxygen.

Uses of oxygen

1. All living things use oxygen for breathing.

2. Oxygen is essential for burning.

3. Oxygen cylinders are used in hospitals to enable the patients to breathe when they cannot breathe normally.

 4. Oxygen is used in gas welding.

Do you Know?

Mountaineers carry oxygen cylinders at high altitudes.

 Deep sea divers also carry oxygen cylinders along with them while diving deep into the sea.

Carbon dioxide

The amount of carbon dioxide present in air is only 0.03%. Though it is less in percentage its uses are more and essential. It can be tested with lime water. The lime water changes from colourless to milky.

Uses of carbon dioxide:

1. Carbon dioxide helps plants in photosynthesis.

2. It is used in fire extinguishers.

3. It is used in refrigerators as dry ice for cooling purposes.

4. It is used to make plastics and polymers.

Do you Know?

The Scottish chemist Joseph Black discovered that carbon dioxide is present in air.

Air has other gases like hydrogen, helium, argon etc. in small proportion. Air also contains water vapour which varies according to the environment. When we breathe, we take oxygen from air and release carbon dioxide and water vapour to air.


Classify the following.

( Dog, cat, coconut tree, monkey, brinjal plant, papaya plant)

Do you Know?

A grown up tree intakes 1/3 of carbon dioxide exhaled by one person and it gives out the same amount of oxygen required by a person. Hence, three trees are needed to fulfill the required oxygen for a man to survive.


Air pollution

The atmospheric balance is disturbed by human activities. This leads to environmental problems like air contamination and global warming. The air carries soot, smoke, and other particles from car exhaust and power plants. These are the major contributors to air pollution.


Look at the path of light rays entering through window of your home/school. You can see lot of tiny particles suspended and moving in the air. These are dust particles. You can also test the same with the help of a torch light in darkness.

Do you Know?

Covering our mouth and nose while sneezing or coughing prevents spreading of germs through air to people around us.

Adverse effects of air pollution


Tick the causes of global warming

Effects of air pollution on human beings

Air pollution has bad impact on human health. When the pollutants increase in air, they cause irritation in the eyes, nose and throat. Air pollution can also produce wheezing, coughing and breathing problems in humans.

Some of the major effects of air pollution on human beings are:

1. Respiratory diseases. E.g. Flu, Tuberculosis

2. Cardiovascular damage.

3. Fatigue, headaches and anxiety.

4. Nervous system damage.


 Go by walk or use a bicycle to nearby places.

 Plant more trees.

Steps to check air pollution

Air pollution can be reduced by the following steps.

1. Alternative source of energy (E.g. Solar energy) should be used.

2. Air filters should be used to prevent harmful gases mixing with air.

3. Smoke emission test and certification of motor vehicles must be enforced.

4. More trees should be planted to absorb carbon dioxide.

Do you Know?

Alternative source of energy are Solar Power, Nuclear Power, Hydroelectric Energy, Wave Energy, Biofuels, Natural Gas, Geothermal Power, Wind Energy, Biomass Energy, Tidal Energy and Hydrogen Gas


Write slogans on harmful effects of air pollution in a chart and stick it on the display board

1. Polluted air, harms our heir.

2. Pollution kills, brings all ills

3. Smoke and fog like rabid dog.

4. Bike race thrills but pollution kills.

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