Biology – Energy, Enzymes, Cellular Respiration, Photosynthesis, And Metabolic Pathways Practice Test

Fermentation yields far less ATP than respiration because it relies only on glycolysis and does not use oxidative phosphorylation via the electron transport chain. In glycolysis, you start with one glucose and net 2 ATP. Without an electron transport chain to harvest more energy, the electrons from NADH are returned to NAD+ by transferring them to the end product of fermentation (pyruvate or a related molecule). This regeneration of NAD+ lets glycolysis continue in the absence of oxygen, but it doesn’t drive additional ATP production beyond the initial 2 ATP from glycolysis. In contrast, aerobic respiration uses glycolysis plus pyruvate processing, the citric acid cycle, and the electron transport chain, pulling much more energy out of each glucose molecule—roughly 30–32 ATP in many cells. So the statement that fermentation yields less ATP than respiration and does not use the electron transport chain best captures the key difference. The other ideas aren’t accurate for fermentation in general: it doesn’t require oxygen to proceed, and while CO2 can be produced in some fermentation pathways (for example, during alcoholic fermentation), CO2 is not the final electron acceptor in fermentation.