Answer:
Regeneration of NAD+
Explanation:
Glycolysis is an inefficient process to produce ATP, but it has been crucial for survival of different kind of cells, and is a step previous in aerobic respiration, where carbohydrates are completely oxidized producing much more ATP molecules.
Both alcoholic and lactic acid fermentations, generate ATP from glycolysis. NADH is also produced in glycolysis, and is used to reduce piruvic acid (glycolysis end product) direct or indirectly in these fermentations. Directly, piruvic acid is reduced by NADH to produce lactic acid in lactic acid fermentation. Indirectly, reducing acetaldehyde (product of previous piruvic acid decarboxilation) into ethanol, in alcohol fermentation.
In both fermentations NAD+ is regenerated, to be used in another round of glycolysis
