During anaerobic metabolism, which compound tends to accumulate in tissues?

• A. Pyruvic acid
• B. Lactic acid
• C. Acetyl-CoA
• D. Glucose

Answer: (B)

In low-oxygen conditions, cells keep making ATP mainly through glycolysis. But glycolysis needs NAD+ to continue, and with limited oxygen, the mitochondria can’t recycle NADH back to NAD+ fast enough. To solve this, pyruvate is converted to lactate by lactate dehydrogenase, which regenerates NAD+ so glycolysis can keep going. This causes lactate to accumulate in tissues (and can spill over into the bloodstream), leading to acidosis if it builds up a lot. Pyruvate isn’t accumulating because it’s being pushed toward lactate to sustain ATP production; acetyl-CoA formation from pyruvate requires oxygen and is reduced under anaerobic conditions; glucose serves as the substrate being consumed, not stored.