Páginas: 3 (528 palabras) Publicado: 15 de agosto de 2012
Biogeochemical cycles
The biogeochemical cycle is the movement chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartmentsof Earth. There are several biogeochemical cycles, some of the most important are water cycle, carbon cycle, nitrogen cycle, phosphorus cycle, sulfur cycle and oxygen cycle among others.
Water cycleThe water cycle, also known as hydrological cycle, is the constant movement of water on, above and below earth surface.
First the sun heats water, it causes water to evaporate into the air. Thereis also water evaporated from plants this is called transpiration. The vapor condenses due to cooler temperatures in the atmosphere. Then the condensed vapor precipitates.
Carbon cycle
The carboncycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, hydrosphere, and atmosphere of the Earth.
Carbon is all around the atmosphere, but it enters to biotic world throughthe autotrophs like plants, so then it passes to animals when they eat plants and so on. Then the carbon returns to the atmosphere through respiration, burning and decay.
Nitrogen cycle
Nitrogencycle is the process by which nitrogen is converted between its various chemical forms. Four processes participate in the cycling of nitrogen through the biosphere:
Nitrogen fixation: is the process bywhich atmospheric nitrogen is converted into ammonia. The process can be done by lightning, being under a great pressure and by some bacteria and archaea.
Decay: Consists in the breakdown of themolecules in excretions and dead organisms by decay microorganisms into ammonia.
Nitrification: is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitritesinto nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification.
Denitrification: The three processes above remove nitrogen from the atmosphere and pass it...
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