39.2 The carbon cycle Living things are made up of organic compounds. Organic compounds contain carbon. Carbon is constantly moved from living organisms into the environment and back again, so it never runs out. This is called the carbon cycle.
Organic
compound A compound that contains carbon.
Fig. 3 The carbon cycle
1. Carbon dioxide is removed from the atmosphere by green plants during photosynthesis. Plants store carbon.
2. 3. 4.
Plants are eaten by animals. The carbon in the plant is absorbed by the animal. Plants and animals respire. This releases carbon dioxide into the atmosphere.
Animals produce waste. Waste is broken down by decomposers in the soil. This releases carbon dioxide into the atmosphere.
5. When plants and animals die, their remains are broken down by decomposers. This releases carbon dioxide into the atmosphere.
6. 7.
If dead plants and animals are not completely broken down they may eventually (after millions of years) form fossil fuels. When fossil fuels are burned they release carbon dioxide into the atmosphere. Types of fossil fuels include coal, peat, oil and natural gas.
Oceans absorb and store carbon dioxide. Movement of the ocean releases carbon dioxide back into the atmosphere.
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Photosynthesis Chemical reaction in a green plant that uses light energy, carbon dioxide and water to produce glucose and oxygen.
