EVERYDAY SCIENCE

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: -In the absence of oxygen, NAD+ may not be regenerated via the electron transport chain (which depends on oxygen as the terminal electron acceptor). Fermentation allows NAD+ to be regenerated in the absence of oxygen via lactic acid fermentation or alcohol fermentation.

Detailed explanation-3: -Fermentation can occur in the absence and presence of oxygen both. In the presence of oxygen, it is called aerobic fermentation.

Detailed explanation-4: -Fermentation happens in the absence of oxygen. Only the two ATP from glycolysis are produced under anaerobic conditions. Alcoholic fermentation and lactic acid fermentation are the two types of fermentation.