How many ATP molecules are produced per glucose molecule in the described anaerobic pathway?

• A. 0 ATP
• B. 2 ATP
• C. 4 ATP
• D. 36 ATP

Answer: (B)

In anaerobic conditions, glucose is broken down by glycolysis in the cytoplasm, and the energy gained comes mainly from substrate-level phosphorylation. This process yields a net amount of 2 ATP per glucose molecule. At the same time, NADH is produced and must be regenerated to NAD+ to keep glycolysis running; in the absence of oxygen, pyruvate is converted to lactate, which regenerates NAD+ but does not generate extra ATP. So the overall ATP produced per glucose in this anaerobic pathway is 2. The other numbers don’t fit: 0 would mean no ATP is produced, which isn’t true because glycolysis makes ATP; 4 would be the gross production sometimes cited for glycolysis, but the net gain is 2; 36 is the yield from full aerobic respiration, not applicable without oxygen.