Which stage of cellular respiration uses pyruvate to release carbon dioxide and generate energy carriers in a cycle?

• A. Glycolysis
• B. Krebs Cycle
• C. Electron Transport Chain
• D. Fermentation

Answer: (B)

The Krebs cycle is the stage where acetyl groups derived from pyruvate are oxidized in a cyclic pathway, releasing carbon dioxide and producing energy carriers. After glycolysis, pyruvate is transported into the mitochondria and converted to acetyl-CoA, releasing CO2 and generating NADH in a preparatory step. The acetyl group then enters the citric acid cycle, where it is fully oxidized: carbon dioxide is released, and high-energy carriers NADH and FADH2 are produced along with a small amount of ATP (as GTP in some organisms). These carriers go on to fuel the electron transport chain, driving most of the ATP synthesis. Glycolysis happens in the cytosol and does not form a cycle that releases CO2, while the electron transport chain uses the carriers to make ATP but does not release CO2 itself; fermentation regenerates NAD+ without producing the same cyclic oxidation and energy-carrier production.