Can you describe the process and the circumstances under which fermentation occurs?
Anaerobic respiration occurs when oxygen is not available. Under normal conditions, when oxygen is available, oxygen acts as the final electron acceptor after the Electron Transport Chain in cellular respiration. Without oxygen, something else needs to accept the electron. During fermentation, NADH accepts the electron to become NAD+. The NAD+ then goes back to glycolysis. This turns up a lot less ATP can aerobic respiration, but it works. One example of when this may occur is if during exercise, when oxygen levels are short, but your body still needs to undergo this process, it will undergo anaerobic respiration temporarily instead.
I hope this helps!
This can also include some organisms that use sulfur as their final electron acceptor! They do not do fermentation; they use the ETC and therefore still get a lot of ATP.