Biological Cycles

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One of the main biological cycles is the nitrogen cycle, in which nitrogen is used and regenerated in four stages. Nitrogen fixation is when nitrogen gas in the atmosphere is turned into ammonia by Rhizobium bacteria and this ammonia can then be used by plants. The bacteria are found on root nodules of legimous plants, and the two form a mutualistic realationship. In return for the bacteria supplying the plant with ammonia, the plant supplies carbohydrates for the bacteria. The next stage is ammonification where nitrogen compounds from dead organisms and also animal waste is turned into ammonium compounds by decomposers such as saprobiotic bacteria. The third stage is Nitrification where ammonium compounds in the soil are changed into nitrogen compounds that can then be used by plants. First nitrifying bacteria change ammonium into nitrites, then other nitrifying bacteria called Nitrobacter turn nitriles into nitrates. Denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria, During this process the bacteria use nitrates in the soil to carry out respiration and produce nitrogen gas which then goes back into the air. This only happens under anaerobic conditions e.g in waterlogged soils.

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Another crucial biological cycle is the carbon cycle. All organisms need carbon to make essential compounds, therefore it is important that it is continuously used and returned back to the atmosphere. The cycle itself can be summarised in several stages. Firstly, plants absorb carbon dioxide from the atmosphere or areas of water for photosynthesis. The carbon-containing products of photosynthesis become incorporated into the tissues of these plants. The carbon is then passed on to other organisms if the plant is eaten by a primary consumer, then to a secondry consumer and so on. Once a plant or animal dies, microorganisms ...

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