Final answer:
During anaerobic breakdown of glucose, pyruvic acid is converted to lactic acid in the absence of oxygen.
Step-by-step explanation:
During the anaerobic phase of the breakdown of glucose, pyruvic acid is converted to lactic acid in the absence of oxygen. This conversion occurs through a process called fermentation, which helps regenerate the enzyme NAD* needed for glycolysis to continue. Lactic acid production is important during high-intensity exercise when oxygen cannot be delivered to the muscles efficiently.