The cytochromes of the electron transport chain are

  • A. lipids that store electrons
  • B. carbohydrates that carry oxygen
  • C. iron containing proteins that pass electrons along by changing valency
  • D. enzymes that fix carbon dioxide

Explanation

Each cytochrome carries a haem group whose iron alternates between Fe2+ and Fe3+ as it accepts and passes electrons, releasing energy in steps. They are proteins, not lipids or carbohydrates, and they carry electrons rather than oxygen.

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