AP BIOLOGY

Detailed explanation-1: -When oxygen is not present or if an organism is not able to undergo aerobic respiration, pyruvate will undergo a process called fermentation. Fermentation does not require oxygen and is therefore anaerobic. Fermentation will replenish NAD+ from the NADH + H+ produced in glycolysis.

Detailed explanation-2: -Fermentation is another anaerobic (non-oxygen-requiring) pathway for breaking down glucose, one that’s performed by many types of organisms and cells. In fermentation, the only energy extraction pathway is glycolysis, with one or two extra reactions tacked on at the end.

Detailed explanation-3: -Cellular respiration requires oxygen as the final electron acceptor in the mitochondrial electron chain, and generation of ATP by oxidative phosphorylation will not take place without oxygen. Without an alternative pathway for ATP synthesis, cells will soon run out of this vital energy source and die.