1. Air and atmosphere :

(i) The invisible thin layer of air surrounding the Earth is known as the atmosphere.

(ii) Air is a mixture of nearly $78 %$ nitrogen, $21 %$ oxygen, $0.9 %$ argon, $0.04 %$ water vapour, $0.03 %$ carbon dioxide and the remaining $0.03 %$ are inert gases.

2. What is air made up of :

(i) Human beings and animals take in oxygen and release carbon dioxide during breathing.

(ii) Organisms that live in soil (termites and earthworms) use the air trapped between the soil particles for respiration.

(iii) Oxygen present in atmosphere is supporter of combustion.

(iv) On burning plant and animal matter, carbon dioxide is released in the atmosphere along with other gases.

(v) Water is present as water vapour in the atmosphere. The gaseous form of water is called water vapour. Presence of water vapour in air is necessary for the water cycle.

(vi) Air also consists of dust and smoke. These are released in the air mainly due to burning of fuel and also due to other activities.

3. How is the oxygen in the atmosphere replaced?

(i) In the presence of sunlight and chlorophyll, plants prepare their own food from water and carbon dioxide through a process called photosynthesis.

(ii) During photosynthesis, plants take in carbon dioxide and give out oxygen. This is how the volume of oxygen is maintained in the atmosphere.

(iii) Moving air is called wind.

(iv) Weather cock shows the direction of air in which it is moving.

(v) Windmills are used for pumping groundwater, producing electricity or helping people sail boat.

4. Air pollution :

(i) An undesirable change in the natural quality of air is known as air pollution.

(ii) Greenhouse gases have the property of absorbing infrared radiations and prevent the escape of heat from the earth.

Some instruments are played by blowing air into them. Observe the picture below and write the name of the instrument. Use the help box for writing down the name.

Important Questions on Air

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