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Decomposition and the carbon cycle
Decomposition is carried out by bacteria and fungi. When animals and plants die they are decomposed by soil bacteria. This happens most in warm moist conditions where there are decomposers (bacteria and fungi) and there is lots of oxygen and the organic material is cut up into little bits.
Plants take the CO2 in the air and turn it into fats carbohydrates and proteins. These are then used for respiration in the plant (by which they are turned into CO2 ). The fats, proteins and carbohydrates can then either decay when the plant dies, be turned into products by humans or be eaten by animals.
If they are eaten then some of the carbon compounds are used in respiration by the animal which has eaten the plant (which gives off carbon dioxide). The rest are then brought into the soil when the animal dies, and the CO2 is released by microbes and fungi when the animal decomposes. Sometimes however, this carbon dioxide is not released and fossil fuels are formed
If they are turned into a product this product is then burnt which releases carbon dioxide, and if the tree dies the carbon dioxide is created by decomposers.
The nitrogen cycle
Nitrates are taken out of the soil by plants, they are washed out of the soil (leaching) and de-nitrifying bacteria turn nitrates back into nitrogen gas. This happens mostly in anaerobic conditions, e.g. waterlogged marshes.
Nitrogen fixing bacteria are bacteria which are in the roots of legumes, and are used in crop rotation because they are very useful for turning nitrogen in the air.
Also See
Here are the other comprehensive GCSE Biology notes by Prometheus:
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