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(also anoxybiosis), life in the absence of free oxygen. Anaerobiosis is the usual condition of existence for the anaerobic organisms which obtain energy for vital activities from the decomposition of compound inorganic substances (for example, nitrates and sulfates) or organic substances (for example, carbohydrates).
The concept of anaerobiosis was introduced in 1861 by L. Pasteur, who showed that the microorganisms that cause lactic acid fermentation die in the presence of oxygen. In multicelled animals, anaerobiosis is often only a temporary state which provides for survival during periods when there is no oxygen, and it is accompanied by a sharp decline in metabolism and a transformation to an inactive state. Aerobic organisms also have anaerobic stages in the metabolic processes that are accompanied by the generation of energy. In the tissues of a majority of the multicelled animals, anaerobic carbohydrate conversion occurs chiefly by glycolysis. In rapidly growing embryonic cells and in tumor cells, anaerobic processes are more strongly expressed than in the normal cells of a healthy organism. The processes of anaerobic conversion (fermentation and putrefaction) are of great significance in the circulation of matter in nature.