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Science

Food chains and cycles

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The carbon cycle

The carbon cycle shows how carbon moves from the atmosphere, through various animals and plants, then back into the atmosphere again.

All cells contain carbon compounds such as proteins, fats and carbohydrates. Carbon is passed from the atmosphere, as carbon dioxide, to living things. It is passed from one organism to the next in complex molecules, and returned to the atmosphere as carbon dioxide again.

Removing carbon dioxide from the atmosphere

Green plants and algae remove carbon dioxide from the atmosphere by photosynthesis [photosynthesis: The chemical change that occurs in the leaves of green plants. It uses light energy to convert carbon dioxide and water into glucose. Oxygen is produced as a by-product of photosynthesis. ]. The carbon becomes part of complex molecules such as proteins, fats and carbohydrates in the plants and algae.

Returning carbon dioxide to the atmosphere

Organisms return carbon dioxide to the atmosphere by respiration [respiration: Chemical change that takes place inside living cells, which uses glucose and oxygen to produce the energy organisms need to live. Carbon dioxide is a by-product of respiration ]. It is not just animals that respire. Plants, algae and microorganisms do too.

Carbon dioxide is also released into the atmosphere when fossil fuels such as coal and oil, and wood, are burned.

Passing carbon from one organism to the next

When an animal eats a plant, carbon from the plant becomes part of the fats and proteins in the animal. Microorganisms and some animals feed on waste material from animals, and the remains of dead animals and plants. The carbon then becomes part of these microorganisms and detritus feeders.

This slideshow should help you to understand how the cycle works:

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