∞ generated and posted on 2016.01.09 ∞
Presence of molecular oxygen.
Presence separately refers to both the availability of oxygen (O2) within environments and its utilization of by aerobic organisms. Aerobic organisms thus can utilize oxygen (O2) when those organisms are present within aerobic environments.
Molecular oxygen (O2), in the most familiar form of cellular respiration, is used to accept electrons at the end of electron transport chains, a process otherwise known as aerobic respiration as well as oxidative phosphorylation.
The oxygen itself is generated during the light reaction of photosynthesis and is present wherever air can reach, though to only limited extents in wet environments that lack both oxygen-generating photosynthetic organisms along with substantial environmental mixing, e.g., mud. Such environments tend to be anaerobic instead.