Most living things, such as human beings, need oxygen, because they have to oxidize and decompose the food they eat, release a lot of energy to maintain the normal life activities of living things and keep their body temperature.

Anaerobic organisms decompose sugar, protein and other organic substances under anaerobic conditions, but release little energy, so anaerobic organisms are generally small.

Anaerobic is everywhere in biology. All living things that can breathe aerobic can breathe anaerobic. People can survive for a short time under anaerobic conditions, such as diving without a respirator, but because anaerobic breathing releases less energy, people can't persist underwater for long.

From a biological point of view: aerobic respiration is carried out step by step, and the first step is anaerobic respiration.

For example, the first step of glucose decomposition:

Glucose pyruvate

(Anaerobic respiration) This process does not need oxygen, and it is carried out by anaerobic and aerobic organisms.