Chapter 11: Air Around Us

Air comprises water vapour, oxygen, nitrogen, carbon dioxide, dust and smoke.

Oxygen in the atmosphere is essential for respiration.

Place two candles of the same length on a table. Light both candles. Cover one of the candles with an inverted glass tumbler. We can observe that the candle covered with the glass tumbler got extinguished after some time, whereas the other candle continued burning. The candle gets extinguished because the air component inside of the glass tumbler, which supports burning, is limited. Most of the component is used up by the burning candle. However, the other candle is getting a continuous supply of air. This component of air, which supports burning, is known as oxygen.

Take some water in a container. Heat it slowly on a tripod stand. Before the water begins to boil, look at the inner surface of the container. We observe tiny bubbles inside. 

These bubbles come from the air dissolved in water. When you heat the water, to begin with, the air dissolved in it escapes. This experiment concludes that air is present in the water.

The lump of cotton wool shrink in water because the air inside the cotton lumps is replaced by water which makes the layer stick together.

The layer of air around the earth is known as the atmosphere.

The component of air used by green plants to make their food is carbon dioxide.

The five activities that are possible due to air are as follows:

1. Photosynthesis
2. Cloud formation
3. Respiration
4. Transpiration
5. Winnowing

During the process of respiration, animals and plants consume oxygen from the air and release carbon dioxide gas into the air. Besides, green plants also release oxygen gas by utilising carbon dioxide during the process of photosynthesis. Hence, in this way, plants and animals help each other in the exchange of gases in the atmosphere.