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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. ...read more.


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 known as decomposers will break down the dead organic material using enzymes and absorb the carbon compounds by diffusion. Carbon is returned to the atmosphere in the form of carbon dioxide when organisms respire. This can also happen through the combustion of fossil fuels. If the dead organic matter ends up in a place where there arent any decomposers, e.g the bottom of the ocean, the carbon compounds can be turned into fossil fuels by heat and pressure. ...read more.


This cycle happens twice for every molecule of glucose. Finally, the light independent reaction in photosynthesis is known as the calvin cycle. This cycle takes place in the stroma of the chloroplasts and is used to make triose phosphate from carbon ddioxide and ribulose biosphosphate. In the first stage of the cycle carbon dioxide is combined with RuBP to form a six carbon compound called glycerate-3-phosphate(GP). This rection is catalysed by rubisco. Then ATP from the light dependant reaction provides energy to turn GP into triose phosphate (TP). This reaction also requires a hydrogen ion which comes from reduced NADP. TP is then used to help produce useful organic compounds for the body such as glucose. However, Five out of every six molecules of TP formed are used to regenerate RuBP and start the cycle again. ...read more.

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