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Carbon Cycle
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Carbon is a very important part of living things. It is used to make proteins, fats
and carbohydrates.
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About 0.04% of the air is CO2. When plants photosynthesize some carbon
dioxide is used up and carbon atoms from CO2 become part of glucose and starch
molecules.
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Some glucose is broken down by plants in respiration. The carbon molecules
used in photosynthesis again become part of atmospheric CO2.
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Some carbon-containing compounds are eaten by animals, who then also
respire.
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Decomposers also feed on waste materials and use carbon nutrients from
them. They respire and release some in the air as CO2.
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Decomposers may not break up all dead animals. Instead, these become
buried in layers. Over very long periods of time they become fossil fuels in the form of
coal, oil and natural gas.
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These fossil fuels are burnt in air and undergo combustion. A word can also
come by. They form carbon dioxide, which is released to the air again.