ATP yield comparison: Relative to complete aerobic respiration of glucose, the amount of ATP produced by fermentation is generally…

Introduction / Context:
Cells harvest energy by oxidizing substrates such as glucose. The total ATP yield depends on whether electrons are transferred to oxygen via respiration or to organic acceptors via fermentation. Understanding the difference is fundamental to microbial physiology and industrial bioprocessing.

Given Data / Assumptions:

• Aerobic respiration includes glycolysis, pyruvate oxidation, TCA cycle, and oxidative phosphorylation.
• Fermentation includes glycolysis followed by reduction of organic molecules to reoxidize NADH to NAD+.
• Typical bacterial aerobic yields greatly exceed the ~2 ATP per glucose from glycolysis alone.

Concept / Approach:
Fermentation yields ATP primarily by substrate-level phosphorylation during glycolysis (net 2 ATP per glucose). Aerobic respiration captures additional energy via the electron transport chain and ATP synthase, often yielding an order of magnitude more ATP per glucose depending on organism and conditions.

Step-by-Step Solution:
Recognize fermentation lacks an external terminal electron acceptor like oxygen. Acknowledge that without oxidative phosphorylation, ATP comes mainly from glycolysis. Conclude fermentation yields less ATP than aerobic respiration.

Verification / Alternative check:
Empirical measurements of ATP yield or growth yield (g cell per g glucose) consistently show higher values for aerobic conditions compared with fermentative growth.

Why Other Options Are Wrong:

• Greater / Equal: Contradicted by the absence of oxidative phosphorylation in fermentation.
• Indistinguishable / Zero: Incorrect; mechanisms and yields differ, and fermentation does produce some ATP.

Common Pitfalls:
Confusing anaerobic respiration (non-oxygen electron acceptors) with fermentation; anaerobic respiration can yield more ATP than fermentation but typically less than aerobic.

Final Answer:
Lesser than by aerobic metabolism.