anaerobic respiration

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.