During fermentation, the primary byproduct is

Core Concept

Fermentation is a metabolic process that occurs in the absence of oxygen, resulting in the production of ethanol or lactic acid as a primary byproduct. This is a key adaptation that allows cells to generate energy in low-oxygen environments. Options A, B, and D are incorrect because fermentation does not produce ATP, CO2 is a byproduct of aerobic respiration, and O2 is not produced during fermentation.