Energy yields — Compared with complete aerobic metabolism of glucose, the amount of energy (calories per mole) obtained by a cell from glucose via fermentation is:

Introduction / Context:
Cells extract energy from glucose through pathways that differ dramatically in ATP yield: aerobic respiration (glycolysis + pyruvate oxidation + TCA + electron transport chain) and fermentation (glycolysis followed by redox-balancing end steps). Knowing which strategy yields more energy is essential for microbiology, biochemistry, and industrial fermentation design.

Given Data / Assumptions:

• Aerobic respiration allows complete oxidation of glucose to CO2, transferring electrons to O2.
• Fermentation ends with partially oxidized products (e.g., lactate, ethanol) and no electron transport chain is used.
• ATP yield correlates with how completely electrons are transferred to a high-potential acceptor (like O2).

Concept / Approach:
Aerobic respiration yields the highest ATP because the electron transport chain and oxidative phosphorylation convert redox energy into a proton gradient that drives ATP synthase. Fermentation regenerates NAD+ by transferring electrons to organic intermediates without an external terminal electron acceptor. This yields only the substrate-level phosphorylation ATP from glycolysis (typically 2 ATP per glucose), far below the ~28–32 ATP per glucose often cited for aerobic conditions in eukaryotes (bacteria may vary but remain far higher than fermentation). Therefore, energy per mole from fermentation is less than from aerobic metabolism.

Step-by-Step Solution:

Verification / Alternative check:
Redox balance: fermentation products retain substantial potential energy (not fully oxidized), demonstrating why energy recovery is lower than when O2 is the acceptor.

Why Other Options Are Wrong:

• Greater/equal: contradict the fundamental role of the ETC and full oxidation in maximizing ATP.
• None of the above: incorrect because “less than aerobic” is accurate.

Common Pitfalls:
Equating rapid growth in some fermenters with high ATP yield; growth rate also depends on flux and regulation, not ATP per mole alone.

Final Answer:
less than aerobic metabolism