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Nitrogen cycle

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Nitrogen is an essential element in the chemical compounds that make up living things. When plants and animals die, these nitrogen compounds get deposited into the soil. Micro-organisms are involved in this process because they decompose the dead plants and animals and allow the organic nitrogen to be deposited in the soil.
Once the organic nitrogen is in the soil, there are bacteria that can convert it into ammonium (NH4). This is important because ammonium can be used by some plant species. Some plants absorb ammonium so that they can get the nitrogen they need.
The bacteria that convert the organic nitrogen in the soil from dead plants and animals into ammonium are called nitrogen fixing bacteria.
Once ammonium is in the soil, other bacteria called nitrifying bacteria convert the ammonium into nitrates that plants can use. These bacteria are very special type of bacteria that can make their own food from chemicals. In this case, they use ammonium and convert it into nitrates. This process benefits the bacteria because that's how it makes its food. But it also benefits the plants because they can absorb the nitrates and use them as a source of nitrogen.

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Carbon Cycle

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The carbon cycle involves many things, some of which we have talked about in class. But there is one part of it that particularly relies on micro-organisms. This is the process of dead plants and animals decomposing. When plants and animals die, saprophytic bacteria and fungi obtain their nutrition from these dead organisms by feeding on them. As they do this, they carry out respiration to get energy from their food. As a by-product of respiration they produce carbon dioxide. They excrete the carbon dioxide and it goes back into the atmosphere.