Question

Anaerobic respiration is less efficient than aerobic respiration for which of the following reasons?

Answer 1

Because the terminal electron acceptor is not O2, so less free energy is released per electron transferred. Oxygen has a very high reduction potential, so reducing O2 yields a large ΔE and a large ΔG that can be harvested to pump protons and make ATP. Common anaerobic acceptors (NO3−, SO42−, CO2 or organic molecules in fermentation) have lower reduction potentials, so the electron transport chain pumps fewer protons and yields fewer ATP. In addition, many anaerobic pathways (fermentation) bypass the ETC entirely and rely only on substrate‑level phosphorylation, leaving much of the original glucose energy in reduced end products (lactate, ethanol), so ATP yield per glucose is much lower (≈2 ATP vs. ~30–38 ATP in aerobic respiration).