Energy conservation in fermentation: the acquisition of ATP during glucose fermentation occurs primarily via which mechanism?

Introduction / Context:
Fermentation enables ATP production without external electron acceptors. Recognizing how ATP is generated in fermentation is key to distinguishing it from respiration.

Given Data / Assumptions:

• No functional electron transport chain is used to conserve energy in classic fermentation.
• NADH produced in glycolysis is reoxidized by internal organic acceptors.
• ATP yield is modest compared to respiration.

Concept / Approach:
Fermentative pathways generate ATP directly by substrate-level phosphorylation, where a high-energy phosphate from a metabolic intermediate is transferred to ADP. Electron transport phosphorylation (oxidative phosphorylation) requires an external terminal acceptor and a membrane-linked chain, which fermentation lacks.

Step-by-Step Solution:

Verification / Alternative check:
Measured fermentation yields (e.g., 2 ATP per glucose in lactic fermentation) match substrate-level phosphorylation accounting.

Why Other Options Are Wrong:
Electron transport from NADH: Defines respiration, not classical fermentation. Fatty acid oxidation: Catabolic but not the basis of fermentative ATP gain. Formic-hydrogen lyase: Enzyme present in some bacteria for redox balance, not the ATP-conserving step.

Common Pitfalls:
Assuming any NADH reoxidation implies electron transport; in fermentation, reoxidation is substrate-linked.

Final Answer:
substrate-level phosphorylation