The Lactic Acid System (anaerobic glycolysis) yields how many ATP per glucose?

• A. 4 ATP
• B. 1 ATP
• C. 0 ATP
• D. 2 ATP

Answer: (D)

Under anaerobic conditions the Lactic Acid System relies on glycolysis to make ATP. Glucose is split into two pyruvate molecules, and glycolysis produces four ATP in the payoff steps, but consumes two ATP in the early steps, giving a net gain of two ATP per glucose. Because there’s no oxygen to accept electrons, pyruvate is converted to lactate by lactate dehydrogenase, which also regenerates NAD+ needed for glycolysis to continue. This keeps ATP flowing but at a lower rate and total yield than aerobic metabolism, which can make about 30–32 ATP per glucose. So the lactic acid system yields two ATP per glucose.