Final answer:
The reactant of lactic acid fermentation in muscle tissue is pyruvic acid, and the product that builds up during intense exercise is lactic acid. A buildup of lactic acid can lead to muscle fatigue.
Step-by-step explanation:
The reactant of lactic acid fermentation in muscle tissue is pyruvic acid, and the product that builds up during intense exercise is lactic acid.
During intense exercise, the oxygen supply to muscle cells may become insufficient to continue aerobic respiration. In this situation, muscle cells undergo lactic acid fermentation as an alternative metabolic pathway to produce ATP. Pyruvic acid, which is produced by the breakdown of glucose through glycolysis, is converted into lactic acid.
A buildup of lactic acid can lead to muscle fatigue, although recent research disputes the hypothesis that it causes muscle stiffness and soreness. Lactic acid accumulated in muscle tissue is transported to the liver, where it can be further catabolized for energy.