Carbon Cycle

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The cyclic changes that carbon undergoes in nature is referred to as the Carbon cycle. Carbon in the form of carbon dioxide gets added to the air and gets removed from the air constantly. This addition and subtraction is so well balanced that the percentage of carbon dioxide remains remarkable steady at 0.03 to 0.04 (Fig.11.16).

Addition of carbon dioxide to air

1. By the respiration of living organisms.

2. By the combustion of carbon present in carbon compounds, such as wood, coal, coke, petroleum oil, vegetable oil, alcohol etc.

3. By the decay of organic matter, like the dead bodies of animals and plants.

4. From chemical industry such as, heating of limestone, fermentation of molasses to form alcohol, in beer and wine making processes etc.

Removal of carbon dioxide from air

By photosynthesis

Green plants take in carbon dioxide to synthesize carbohydrates.

The carbohydrates formed are consumed by animals, digested, absorbed and used in respiration. During respiration, the carbohydrate is oxidised to carbon dioxide, which is released into the air.

By dissolution

Carbon dioxide of the air dissolves in water, forming a very dilute solution of carbonic acid.

This reaction is an unstable one and depends upon water temperature. If water gets warmer, some of the dissolved carbon dioxide gets released into the air.