respiration



respiration defined in 1951 year

respiration - respiration;
respiration - (1) Breathing, e.g. pumping air in and out of lungs, or water over gills. (2) Taking oxygen from the environment and giving off carbon dioxide, (1) and (2) are sometimes referred to as external respiration in contrast to (3) internal, tissue or cell respiration, i.e. the chemical reactions from which an organism derives energy. In most organisms internal respiration is accompanied by consumption of free oxygen and production of carbon dioxide (the external manifestation of which is (2); in some organisms (2) being facilitated by (1)). This kind of respiration is called aerobic. If glucose, for instance, is being used as basis for aerobic respiration, it is oxidized to carbon dioxide and water, and the same amount of energy is liberated as if that glucose were burnt in air. In the organism a complicated chain of oxidation-reduction reactions is involved, various substances being alternately oxidized and reduced under the influence of various enzyme systems (See also: Cytochrome, Dehydrogenase, Oxidase). Energy can be liberated by the break-down of substances without molecular oxygen being concerned in the reaction; this is known as anaerobic respiration, e.g. breakdown of glycogen to lactic acid in vertebrate muscle; or of glucose to ethyl alcohol and carbon dioxide by yeast. Such processes do not liberate as much energy as does aerobic respiration. Many organisms (or parts of them) respire anaerobically for some time when their supply of oxygen is insufficient for aerobic respiration, in which case they may acquire an oxygen debt. A few bacteria are strictly anaerobic, i.e. they do not use free oxygen at all.

near respiration in Knolik


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respiratory enzyme

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