Air is present all around us. We cannot see the air around us but we can feel its presence when the leaves rustle or branches sway.
Fig: Composition of Air
Air is a mixture of gases, water vapour and dust particles. Some of the gases; present in air; are discussed below.
Nitrogen: Nitrogen is the largest component of air. Nitrogen makes up 79% of air around us. Nitrogen is used by plants to make protein. Plants cannot take nitrogen directly from the air. Some nitrogen fixing bacteria live in soil. They help in nitrogen fixation in soil. Thus, plants are able to take nitrogenous compounds from the soil.
Oxygen: Oxygen is the second largest component of air. Oxygen makes up 21% of the air around us. Oxygen is used by living beings for respiration. After respiration, the living beings produce carbon dioxide.
Carbon dioxide: The remaining 1% of air is composed of carbon dioxide, many other gases, water vapour and dust particles. Carbon dioxide is also important for living beings. Plant need carbon dioxide to make food during photosynthesis. During photosynthesis, plants take in carbon dioxide and release oxygen. Thus, green plants help in maintaining the balance of carbon dioxide and oxygen in atmosphere.
Air in water: Air is also present in water. Aquatic animals breathe the air which remains dissolved in water. When water is boiled, air bubbles can be seen coming up from the bottom of the pan. This simple activity shows that air is present in water.
For this, take a candle, a glass tumbler and a pan which is filled with some water. Keep the candle upright in the pan and light the candle. Now cover the candle with the glass tumbler. It is observed that the candle extinguishes after some time.
This happens because oxygen in the air inside the glass tumbler is utilised in burning the candle. All the oxygen gets converted into carbon dioxide. Carbon dioxide does not support burning and hence candle stops burning.
Once the candle stops burning, some amount of water is sucked inside the tumbler. This happens because the volume of cabron dioxide is less than the volume of oxygen which was displaced.
It is also seen that a lot of air is still inside the tumbler. A major portion of this air is nothing but nitrogen. Nitrogen too does not support burning.
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