In respiration, the coenzymes NAD and FAD function as carriers of

  • A. hydrogen atoms and electrons removed from the substrate
  • B. carbon dioxide released by the Krebs cycle
  • C. oxygen from haemoglobin
  • D. phosphate groups for ATP synthesis

Explanation

Dehydrogenase enzymes strip hydrogen from intermediates and hand it to NAD or FAD, which carry the electrons to the electron transport chain. They do not carry gases or phosphates, so their role is purely that of a reusable shuttle.

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