Final answer:
Whether pyruvic acid undergoes lactic acid or alcoholic fermentation is determined by the organism involved and the environmental conditions, with specific enzymes leading to the two distinct fermentation processes.
Step-by-step explanation:
What determines whether pyruvic acid will undergo lactic acid fermentation or alcoholic fermentation depends primarily on the type of organism and the conditions under which fermentation is taking place. In lactic acid fermentation, pyruvate from glycolysis is reduced to lactic acid by the enzyme lactate dehydrogenase, and this process does not produce carbon dioxide.
This type of fermentation is carried out by certain bacteria and by our muscle cells during intense activity. On the other hand, alcoholic fermentation involves the conversion of pyruvate to ethanol and carbon dioxide, a process carried out by yeasts and some bacteria using the enzymes pyruvate decarboxylase and alcohol dehydrogenase. The conditions that promote one type of fermentation over the other include the presence or absence of oxygen and the specific enzymes that are present in the organism.