nitrogen cycle.notebook November 21, 2011

Nitrogen Cycle

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Nitrogen is present in the environment in a wide variety of + chemical forms including organic nitrogen, ammonium (NH4 ), ­ ­ nitrite (NO2 ), nitrate (NO3 ), nitrous oxide (N2O), nitric oxide (NO) or inorganic nitrogen gas (N2). Organic nitrogen may be in the form of a living organism, humus or in the intermediate products of organic matter decomposition. The processes of the nitrogen cycle transform nitrogen from one form to another

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Many of those processes are carried out by microbes, either in their effort to harvest energy or to accumulate nitrogen in a form needed for their growth.

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Nitrogen Fixing Bacteria Atmospheric nitrogen must be processed, or "fixed" nitrogen fixation), to be used by plants. Some fixation occurs in lightning strikes, but most fixation is done by free­living or symbiotic bacteria. These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia, which is then further converted by the bacteria to make their own organic compounds.

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Plants take nitrogen from the soil, by absorption through their roots in the form of either nitrate ions or ammonium ions. All nitrogen obtained by animals can be traced back to the eating of plants at some stage of the food chain.

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Ammonification When a plant or animal dies, or an animal expels waste, the initial form of nitrogen is organic. Bacteria, or fungi in some cases, convert + the organic nitrogen within the remains back into ammonium (NH4 ), a process called ammonification.

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Nitrification Main article: Nitrification The conversion of ammonium to nitrate is performed primarily by soil­living bacteria and other nitrifying bacteria. In the primary stage + of nitrification, the oxidation of ammonium (NH4 ) is performed by bacteria such as the Nitrosomonas species, which converts ammonia to ­ nitrites (NO2 ). Other bacterial species, such as the Nitrobacter, are ­ responsible for the oxidation of the nitrites into nitrates (NO3 ). It is important for the nitrites to be converted to nitrates because accumulated nitrites are toxic to plant life.

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Denitrification Denitrification is the reduction of nitrates back into the largely inert nitrogen gas (N2), completing the nitrogen cycle.

Nov 21­8:38 AM 8 nitrogen cycle.notebook November 21, 2011 What is nitrogen used for? Nitrogen is a component of many organic molecules. It forms an essential part of amino acids (which make up proteins) and DNA. Nitrogen is essential for all living cells. What is the nitrogen cycle? Nitrogen is the major component of earth's atmosphere. It enters the food chain by means of nitrogen­fixing bacteria and algae in the soil. This nitrogen which has been 'fixed' is now available for plants to absorb. These types of bacteria form a symbiotic relationship with legumes­­these types of plants are very useful because the nitrogen fixation enriches the soil and acts as a 'natural' fertilizer. The nitrogen­fixing bacteria form nitrates out of the atmospheric nitrogen which can be taken up and dissolved in soil water by the roots of plants. When organisms excrete wastes, nitrogen is released into the environment. Also, whenever an organism dies, decomposers break down the corpse into nitrogen in the form of ammonia. This nitrogen can then be used again by nitrifying bacteria to fix nitrogen for the plants.

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