What is the net gain of ATP molecules from each molecule of glucose during fermentation?

During fermentation, the net gain of ATP molecules from each molecule of glucose is indeed 2. This process occurs in the absence of oxygen and involves glycolysis followed by either alcoholic or lactic acid fermentation.

In glycolysis, which is the first step of both aerobic and anaerobic respiration, one glucose molecule is converted into two molecules of pyruvate. This pathway yields 2 ATP molecules through substrate-level phosphorylation. In fermentation, the pyruvate is further metabolized to produce either ethanol and carbon dioxide or lactic acid, depending on the organism and conditions.

It's important to note that fermentation does not produce additional ATP beyond what is generated during glycolysis; it primarily serves to regenerate NAD+, allowing glycolysis to continue. Therefore, the overall yield remains as only the 2 ATP produced during glycolysis. This understanding highlights why the correct answer specifies a net gain of 2 ATP molecules from each glucose molecule during fermentation.