Final answer:
Both alcohol fermentation and lactic acid fermentation function to regenerate NAD+ from NADH, enabling glycolysis to continue and allowing cells to produce a small amount of ATP anaerobically.
Step-by-step explanation:
One function of both alcohol fermentation and lactic acid fermentation is to regenerate NAD+ from NADH so that glycolysis can continue in the absence of oxygen. Neither fermentation process is involved in oxidative phosphorylation to produce ATP; instead, both types facilitate the continuation of ATP production through glycolysis, yielding a modest amount of energy for the cell. Alcoholic fermentation produces ethanol and carbon dioxide, while lactic acid fermentation produces lactate (or lactic acid) as byproducts; neither process converts glucose to glycogen nor are they responsible for producing water and carbon dioxide as a primary function.
Fermentation is an anaerobic process that allows cells to produce ATP by recycling the electron carrier NAD+ from NADH, enabling glycolysis to sustain the energy yield of 2 ATP molecules per glucose molecule broken down. This is crucial because, without this regeneration of NAD+, glycolysis would halt, and the cell would be unable to extract energy from glucose. Fermentation processes like these are fundamental not only in single-celled organisms but also in multi-celled organisms including humans, where lactic acid fermentation can occur in muscle cells under conditions of strenuous exercise when oxygen is in short supply.