Cycles in Biology

A cycle is defined as any complete round or series of occurrences that repeats or is repeated in the same order and at the same intervals. The natural existence of cycles is highly important without cycles resources would run out and organisms would die. The amount of carbon nitrogen and oxygen on the earth is fixed, they can exists in different forms but no more may be added. So that these don’t run out they are cycles so they may be reused. Photosynthesis and respiration are the reverse of each other, and you couldn’t have one without the other.

Carbon is an essential component of all organic substances, necessary in nucleic acids, proteins, carbohydrates. The only way that can enter ecosystems is when it’s used for photosynthesis. Carbon dioxide diffuses into the plants stomata and through the Calvin cycle is combined with other molecules to make glucose. This may then be used in lipids, carbohydrates and proteins, incorporating carbon into the plants biomass e.g. cellulose cell wall and used for respiration. When a plant respires it releases some of this carbon back into the atmosphere as carbon dioxide. Moreover if deforestation or slash and burn occurs it releases carbon dioxide into the atmosphere during the combustion process. When the primary producer is eaten by the primary consumer it passes its biomass and carbon along too. This happens through all the trophic levels. The consumers will leave detritus either urine, faeces or the carcass, or in the case of producers leaf litter. Decomposers known as Saprophytic bacteria then break down the detritus using enzymes. As they do so they respire again releasing carbon dioxide into the atmosphere. If plants or animals die in situations were there are no decomposers for instance deep oceans, the carbon in them may turn into fossil fuels over millions of years by the process of fossilisation. Alternatively vast amount of the carbon is used by marine zooplankton to make calcium carbonate shells. These are not