In glycolysis, how many net ATP are produced from one molecule of glucose before entering the mitochondria?

• A. 4 ATP
• B. 2 ATP
• C. 38 ATP
• D. 0 ATP

Answer: (B)

In glycolysis, glucose is activated by using two ATP at the start. Later in the pathway, two ATP are produced by substrate-level phosphorylation as the sugar is split and processed to pyruvate. When you subtract the two ATP consumed from the two ATP produced, the net gain is two ATP per glucose. Since the question specifies ATP produced before entering the mitochondria, we don’t include any ATP that would be generated later by oxidative phosphorylation in the mitochondria. So the best answer is two ATP. The other numbers come from counting either all ATP produced (without subtracting the ones used to activate glucose) or the total yield from full aerobic respiration, which isn’t applicable here.