Final answer:
During lactic acid fermentation, pyruvate is converted to lactic acid. The lactic acid produced needs to be removed from the muscles and transported to the liver for further metabolism.
Step-by-step explanation:
In lactic acid fermentation, pyruvate from glycolysis is converted to lactic acid by the enzyme lactate dehydrogenase. This process occurs in muscles that have an insufficient oxygen supply, such as during strenuous exercise. The lactic acid produced needs to be recycled or reused by our bodies, so it is removed from the muscles and circulated to the liver. In the liver, the lactic acid can be converted back into pyruvic acid and further metabolized for energy.