Why must reduced electron carriers be re-oxidized before entering glycolysis and the citric acid cycle again?

• A. To reset carriers to accept electrons
• B. To generate more CO2
• C. To produce pigments
• D. To store energy as fat

Answer: (A)

Redox carriers must be reset to keep metabolism moving. In glycolysis and the citric acid cycle, oxidized forms like NAD+ and FAD accept electrons and become NADH and FADH2. To continue these pathways, there must be enough oxidized carriers to accept more electrons in the next rounds. Re-oxidation—primarily in the electron transport chain where NADH is converted back to NAD+—restores the pool of carriers that can accept electrons again and also helps generate ATP. If these carriers aren’t regenerated, NAD+ and FAD become scarce, the dehydrogenase reactions stall, and glycolysis and the citric acid cycle slow or stop. The other options don’t address the need to recycle electron carriers to keep the pathways functioning.