If the appropriate final electron acceptor is not present the pyruvate that was formed at the end of glycolysis is reduced.?

If the final electron acceptor is not present, pyruvate undergoes fermentation instead of entering the aerobic respiration pathway. This process involves the reduction of pyruvate to lactate in animals or to ethanol and carbon dioxide in yeast. This conversion regenerates NAD+, allowing glycolysis to continue producing ATP even in the absence of oxygen. Thus, while less efficient than aerobic respiration, fermentation provides a way to sustain energy production when oxygen is scarce.