4. Many organisms can withstand periods of oxygen debt (anaerobic conditions). Yeast undergoing oxygen debt converts pyruvic acid to ethanol and carbon dioxide. Animals undergoing oxygen debt convert pyruvic acid to lactic acid. Pyruvic acid is fairly nontoxic in even high concentrations. Both ethanol and lactic acid are toxic in even moderate concentrations. Explain why this conversion occurs in organisms.

The anaerobic respiration that is respiration which is involved in producing energy molecules like ATP without oxygen evolved earlier than aerobic respiration.

The anaerobic respiration undergoes glycolysis which produces pyruvic acid form lactic acid, ethanol, and very low amount of ATP. This anaerobic respiration is known as fermentation.

The fermentation produces a very low amount of ATP that is only 2 molecules but the amount is sufficient for the simple organisms to survive therefore the fermentation is still performed by the organisms.