Carbon dioxide production: In aerobic glucose catabolism, CO2 is produced primarily during which stage?

Introduction / Context:
Tracking where CO2 emerges clarifies which steps fully oxidize carbon. While several stages handle electrons, only specific reactions release carbon dioxide during aerobic metabolism of glucose.

Given Data / Assumptions:

• Glucose is fully oxidized to CO2 and H2O under aerobic conditions.
• Pyruvate dehydrogenase and the Krebs cycle decarboxylate carbon.
• ETC does not release CO2; it reduces O2 to H2O.

Concept / Approach:
After glycolysis generates pyruvate, pyruvate is converted to acetyl-CoA (releasing CO2). Inside the Krebs cycle, two decarboxylation steps per acetyl-CoA release two CO2. Across one glucose (two acetyl-CoA), four CO2 are produced in the Krebs cycle, with an additional two from pyruvate oxidation.

Step-by-Step Solution:
Glycolysis: no net CO2 release.Pyruvate → acetyl-CoA: decarboxylation releases CO2 (link step).Krebs cycle: two decarboxylations per turn produce CO2.ETC: consumes O2 to form H2O; no CO2 production.

Verification / Alternative check:
Textbook stoichiometry for glucose oxidation confirms CO2 generation coupled to pyruvate dehydrogenase and Krebs cycle decarboxylations.

Why Other Options Are Wrong:

• Glycolysis: occurs in cytosol with no CO2 output.
• ETC: redox-driven proton pumping and water formation, not decarboxylation.
• Lactate fermentation: reduces pyruvate to lactate without CO2.

Common Pitfalls:
Overlooking the pyruvate dehydrogenase step; although not listed, the majority of CO2 per glucose is tied to mitochondrial oxidative decarboxylations.

Final Answer:
Krebs cycle (citric acid cycle)