An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.
A good example would be the oxidation of glucose (a monosaccharide) in aerobic respiration.
Notice that oxygen is used during the oxidation of glucose and water is produced.
This equation is a summary of what actually happens in three series of biochemical reactions: glycolysis, the Krebs cycle, and oxidative phosphorylation.
Almost all animals, most fungi, and several bacteria are obligate aerobes. Most anaerobic organisms are bacteria. Being an obligate aerobe, although advantageous from the energetical point of view, also means obligatory exposure to high levels of oxidative stress.
Yeast is an example of a facultative anaerobe. Individual human cells are also facultative anaerobes: they switch to lactic acid fermentation if oxygen is not available. However, for the whole organism this cannot be sustained for long, and humans are therefore obligate aerobes.
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