Which statement correctly contrasts aerobic oxidative phosphorylation with fermentation?

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During aerobic oxidative phosphorylation, the energy from electron transport is used to pump protons across a membrane, creating a proton motive force. ATP synthase then uses the flow of these protons back across the membrane to synthesize ATP from ADP, a process called chemiosmosis. This proton-gradient–driven mechanism is the hallmark that sets oxidative phosphorylation apart from fermentation.

In fermentation, there is no electron transport chain or chemiosmotic gradient, so ATP is produced only by substrate-level phosphorylation during glycolysis, yielding far less ATP per glucose. The NADH that accumulates is reoxidized by transferring electrons to pyruvate to form lactate or ethanol, regenerating NAD+ without generating additional ATP via oxidative phosphorylation.

Oxygen isn’t a coenzyme in glycolysis; it acts as the final electron acceptor in aerobic respiration, enabling the full energy harvest, but glycolysis itself does not require oxygen. Glucose is not completely transformed in cytosol during fermentation; the pathway ends with pyruvate being reduced to byproducts like lactate or ethanol, rather than fully oxidizing glucose to CO2 and water.