In plant and animal cells, a process in which energy is released from food molecules such as glucose without requiring oxygen. Some aerobic plants and animals are able to use anaerobic respiration for short periods of time. For example, during a sprint, human muscles can respire anaerobically. Unfortunately,
lactic acid is produced and accumulates until the muscles cannot continue working. Anaerobic respiration in humans is less efficient than
aerobic respiration at releasing energy, but releases energy faster (see
respiration). This explains why humans can run faster in a sprint than over longer distances. When humans stop after a sprint, they have to continue breathing more heavily for a while. This is to take in extra oxygen in order to break down the accumulated lactic acid on top of the normal breakdown of sugar in aerobic respiration. The body is paying back the
oxygen debt built up during the sprint.
Use of anaerobic respiration in industry In plants, yeasts, and bacteria, anaerobic respiration results in the production of alcohol and carbon dioxide, a process that is exploited by both the brewing and the baking industries (see
fermentation).
Origins of anaerobic respiration Although anaerobic respiration is a primitive and inefficient form of energy release, deriving from the period when oxygen was missing from the atmosphere, it can also be seen as an
adaptation. To survive in some habitats, such as the muddy bottom of a polluted river, an organism must be to a large extent independent of oxygen; such habitats are said to be
anoxic.
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