nitrogen fixation(redirected from Nitrogen-fixation)
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process in which atmospheric nitrogen is converted to ammonia.
1. The conversion of atmospheric nitrogen into compounds, such as ammonia, by natural agencies or various industrial processes.
2. The conversion by certain soil microorganisms, such as rhizobia, of atmospheric nitrogen into compounds that plants and other organisms can assimilate.
ni′tro·gen-fix′er (-fĭk′sər) n.
the process by which free nitrogen in the atmosphere is converted by biological or chemical means to ammonia and to other forms usable by plants and animals. Biological nitrogen fixation is the more important process and is accomplished by microorganisms in the soil, either free living or in close association with root nodules of certain plants. In contrast, chemical nitrogen fixation, as is used in industry, requires extremely high temperatures and pressures.
nitrogen fixationthe utilization of atmospheric nitrogen in the synthesis of AMINO ACIDS by some bacteria. Such bacteria can be free-living (e.g. Azotobacter, an aerobe; Clostridium, an obligate anaerobe) while others (e.g. Rhizobium) live in association with plants, occupying swellings in the root called root nodules. The latter relationship is one of SYMBIOSIS, in that the plant gains nutrients and thus can live in nitrogen-poor soils, while the nitrogen-fixer obtains a supply of carbohydrates from the plant. The nitrogen is reduced to ammonia in the microbes by action of the enzyme nitrogenase: N2 + 3 H2 → 2 NH3, the ammonia then reacting with keto acids to form amino acids.
a chemical element, atomic number 7, atomic weight 14.007, symbol N. See Table 6. It is a gas constituting about four-fifths of common air; chemically it is almost inert. It is not poisonous but is fatal if breathed alone because of oxygen deprivation. Nitrogen occurs in proteins and amino acids and is thus present in all living cells.
the state of the body in regard to the rate of protein intake and protein utilization. When protein is metabolized, about 90% of the protein nitrogen is excreted in the urine in the form of urea, uric acid, creatinine and other nitrogen end products. The remaining 10% of the nitrogen is eliminated in the feces.
A negative nitrogen balance occurs when more protein is utilized by the body than is taken in. A positive nitrogen balance implies a net gain of protein in the body. Negative nitrogen balance can be caused by such factors as malnutrition, debilitating diseases, blood loss and glucocorticoids. A positive balance can be caused by exercise, growth hormone and testosterone.
blood urea nitrogen (BUN)
see urea nitrogen.
see nitric oxide.
conversion of atmospheric nitrogen into organic nitrogenous compounds by bacteria which may be symbiotic, e.g. Rhizopus spp., which grow on the roots of legumes and put those plants in an advantageous position with respect to nonlegumes.
nitrogen-free extract (NFE)
consists of carbohydrates, sugars, starches, and a major portion of the hemicellulose in feeds. Calculated when crude protein, fat, water, ash, and the fiber are added and the sum is subtracted from 100.
a group of toxic, blistering alkylating agents homologous to dichlorodiethyl sulfide (mustard gas), some of which have been used as antineoplastics. The group includes mustine hydrochloride, cyclophosphamide, thiotepa, chlorambucil and melphalan.
nonprotein nitrogen (NPN)
1. the nitrogenous constituents of the blood exclusive of the protein bodies, consisting of the nitrogen of urea, uric acid, creatine, creatinine, amino acids, polypeptides, and an undetermined part known as rest nitrogen.
Measurement of nonprotein nitrogen is used as a test of renal function, but has been largely replaced by measurement of specific substances, e.g. urea and creatinine.
2. also used in relation to feeds and refers to those nitrogen-containing constituents which are not proteins, e.g. nucleic acids, amino sugars, urea, etc.
see agene process.
nitrogen washout test
measures the rate at which the nitrogen concentration in the expired air is reduced when the horse is made to breathe pure oxygen. The rate is less in incompetent lungs, e.g. those affected by emphysema.