Lactic acid is a by-product of glycolysis.

• A. True
• B. False
• C. Only during aerobic metabolism
• D. Only in the liver

Answer: (A)

During glycolysis, glucose is split to form pyruvate, ATP, and NADH. When oxygen is limited or energy demand is high, cells regenerate NAD+ by converting pyruvate to lactate (the form commonly called lactic acid in everyday language) using the enzyme lactate dehydrogenase. This step allows glycolysis to continue producing ATP even without aerobic respiration. So the statement is true: lactate is produced as a by-product of glycolysis under anaerobic conditions, helping sustain energy production. The liver can later convert lactate back to glucose (the Cori cycle), and lactate production also occurs in other tissues like red blood cells and resting muscles, not just in the liver or only during aerobic metabolism.