anaerobic

Not requiring oxygen for the release of energy from food molecules such as glucose. An organism is described as anaerobic if it does not require oxygen in order to survive. Instead, anaerobic organisms use anaerobic respiration to obtain energy from food. Most anaerobic organisms are micro-organisms such as bacteria, yeasts, and internal parasites that live in places where there is never much oxygen, such as in the mud at the bottom of a lake or pond, or in the alimentary canal. Anaerobic organisms release much less of the available energy from their food than do aerobic organisms.

Obligate anaerobes, such as certain primitive bacteria, cannot function in the presence of oxygen, but facultative anaerobes, such as the fermenting yeasts and most bacteria, can function with or without oxygen.

In some bacteria, instead of oxygen, an inorganic compound, such as sulphate (SO4), is the final acceptor of electrons stripped from food molecules during their breakdown.

In fermentation (as practised by yeasts) the final acceptor is an intermediate product of the glucose molecule being degraded.