“ a Cycle Is a Biological Pathway or Process in Which the End Product of One Cycle Becomes the Starting Point for the Next. Write an Essay About Cycles in Biology.”

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“ A cycle is a biological pathway or process in which the end product of one cycle becomes the starting point for the next. Write an essay about cycles in biology.” Plants and animals need nitrogen to synthesise proteins and nucleic acids. The nitrogen cycle is how nitrogen is converted into a useable form and then passed on between different living organisms and the non-living environment. The first stage of the nitrogen cycle is nitrogen fixation where the nitrogen gas from the environment is turned into ammonia by bacteria called Rhizobium, which are found in the root nodules of leguminous plants. They form a mutualistic relationship with the plants, they provide the plant with nitrogen and the plants provide them with carbohydrates. The second stage is ammonification where nitrogen sources in dead organisms are turned into ammonium compounds by decomposers. The third stage of the nitrogen cycle is nitrification. Nitrifying bacteria convert ammonium compounds to nitrites, and then other nitrifying bacteria convert these to nitrates. The last stage is denitrification where nitrates in the soil are converted into nitrogen gas by denitrifying bacteria that use the nitrates in the soil to carry out respiration and produce nitrogen gas. This happens in anaerobic conditions. Another ecological cycle is the carbon cycle - all organisms need carbon to make essential compounds. Plants absorb carbon in the form of CO2 during photosynthesis and this carbon becomes part of the plant biomass in their tissues. Carbon is passed onto the primary consumers when they eat the plant, secondary and tertiary consumers obtain the carbon source when they eat other consumers. When the living organisms die, saprobiotic bacteria feed on the dead organic matter. Carbon returns to the atmosphere when all living organisms, including the bacteria, respire, as this produces CO2. If dead

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