An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. Facultative anaerobes grow and survive in an oxygenated environment and so do aerotolerant anaerobes.
- Obligate aerobes require oxygen for aerobic cellular respiration. In a process known as cellular respiration, these organisms use oxygen to oxidize substrates (for example sugars and fats) in order to obtain energy.
- Microaerophiles are organisms that may use oxygen, but only at low concentrations.
- Aerotolerant organisms can survive in the presence of oxygen, but they are anaerobic because they do not use it as a terminal electron acceptor.
Oxygen is used during the oxidation of glucose and water is produced.
Yeast is an example of a facultative anaerobe, which can develop in the presence of oxygen but does not require it. 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.
See also 
- Aerobic digestion
- Anaerobic digestion
- Facultative anaerobic organism
- Fermentation (biochemistry)