Glucose oxidation cannot occur in one step, needs a series of steps controlled by enzymes.

• A. It occurs in one step
• B. It cannot occur at all
• C. It occurs only during fermentation
• D. It occurs in a series of enzyme-controlled steps

Answer: (D)

Glucose oxidation is a stepwise, enzyme-controlled process that lets cells harvest energy efficiently. Glucose is a relatively stable molecule, and releasing all its energy in one rapid reaction would be dangerous for the cell and would waste energy that could be captured as ATP and other carriers. Instead, the body routes glucose through a series of tightly regulated reactions: glycolysis in the cytoplasm breaks glucose into pyruvate with a small ATP/NADH payoff; pyruvate is then converted to acetyl-CoA; the acetyl group enters the citric acid cycle to produce additional NADH and FADH2; and these carriers power the electron transport chain to generate most of the ATP by oxidative phosphorylation. This staged process also allows the cell to regulate energy production based on needs and oxygen availability. So glucose oxidation is best described as occurring in a series of enzyme-controlled steps. Fermentation, by contrast, is a separate, anaerobic pathway that partially oxidizes glucose and yields less ATP.