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: -When yeast cells are kept in an anaerobic environment (i.e., without oxygen), they switch to alcoholic fermentation to generate usable energy from food. Like lactic acid fermentation, alcoholic fermentation generates NAD+ so that glycolysis can continue to produce ATP.

Detailed explanation-3: -In the presence of oxygen, yeast undergo aerobic respiration and convert carbohydrates (sugar source) into carbon dioxide and water. In the absence of oxygen, yeasts undergo fermentation and convert carbohydrates into carbon dioxide and alcohol (Figure 2).