Effects of breathing nitrogen under increased pressure. In divers breathing compressed air, nitrogen saturates the nervous system, causing an intoxicating light-headed, numb feeling, then slowed reasoning and dexterity, and then emotional instability and irrationality. Severe cases progress to convulsions and blackout. Susceptibility varies, and severity increases with depth, but there are no aftereffects. Physical function remains normal, and divers may be unaware of the growing irrationality that can cause them to rise too fast (see decompression sickness) or let their air supply run out. Helium, which dissolves less easily in body tissues, is substituted for nitrogen for deep dives.
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Any natural or industrial process that causes free nitrogen in the air to combine chemically with other elements to form more reactive nitrogen compounds such as ammonia, nitrates, or nitrites. Soil microorganisms (e.g., Rhizobium bacteria living in root nodules of legumes) are responsible for more than 90percnt of all nitrogen fixation. Though nitrogen is part of all proteins and essential in both plant and animal metabolism, plants and animals cannot use elemental nitrogen such as the nitrogen gas (N2) that forms 80percnt of the atmosphere. Symbiotic nitrogen-fixing bacteria invade the root hairs of host plants, where they multiply and stimulate the formation of root nodules, enlargements of plant cells and bacteria in close association. Within the nodules the bacteria convert free nitrogen to nitrates, which the host plant uses for its development. Nitrogen fixation by bacteria associated with legumes is of prime importance in agriculture. Before the use of synthetic fertilizers in the industrial countries, usable nitrogen was supplied as manure and by crop rotation that included a legume crop.
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Circulation of nitrogen in various forms throughout nature. Nitrogen is essential to life, but in the atmosphere it is in a form (the diatomic molecule N2) unavailable to most organisms. Nitrogen fixation by microbes turns this nitrogen into nitrates and other compounds, which plants or algae assimilate into their tissues. Animals that eat plants in turn incorporate the compounds into their own tissues. Microbes decompose the remains and waste of all living things into ammonia (ammonification); the ammonia may leave the soil through vaporization into the air or leaching into water. Ammonia remaining in soil may be transformed by bacteria into nitrates (nitrification), which then can be reassimilated into living organisms, or into free nitrogen (denitrification), which reenters the atmosphere. Hence, once fixed from air, some nitrogen goes through the cycle repeatedly without returning to the gaseous state.
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Gaseous chemical element, chemical symbol N, atomic number 7. A colourless, odourless, tasteless gas, it makes up 78percnt of Earth's atmosphere and is a constituent of all living matter. As the nearly unreactive diatomic molecule N2, it is useful as an inert atmosphere or to dilute other gases. Nitrogen is commercially produced by distillation of liquefied air. Nitrogen fixation, achieved naturally by soil microbes and industrially by the Haber-Bosch process, converts it to water-soluble compounds (including ammonia and nitrates). Industrially, ammonia is the starting material for most other nitrogen compounds (especially nitrates and nitrites), whose main uses are in agricultural fertilizers and explosives. In compounds, nitrogen usually has valence 3 or 5. It forms several oxides including nitrous oxide (N2O; laughing gas), nitric oxide (NO), nitrogen dioxide (NO2), and other forms (such as N2O3 and N2O5). Some of the nitrogen oxides, often referred to generically as NOmath.x, are notorious as contributors to urban air pollution. Other compounds include the nitrides, exceptionally hard materials made from nitrogen and a metal; cyanides; azides, used in detonators and percussion caps; and thousands of organic compounds containing nitrogen in functional groups or in a linear or ring structure (see heterocyclic compound). Seealso nitrogen cycle.
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