[Campbell Biology P.217] In the electron transport chain, electrons fall down an energy grad... | Practice Question

In the electron transport chain, electrons fall down an energy gradient. What is the primary reason oxygen O2 serves as the 'terminal electron acceptor' and drives this 'downhill' flow?

  • A: It is the most abundant molecule in the mitochondria.
  • B: It has the lowest reduction potential among all carriers.
  • C: It has a very great affinity for electrons, making it a highly electronegative atom.
  • D: It is required to oxidize NADH back to NAD+ at the start of the chain.

Explanation

The text explicitly states: 'Each “downhill” carrier has a greater affinity for electrons than, and is thus capable of accepting electrons from oxidizing , its “uphill” neighbor, with O2 at the bottom of the chain. Therefore, the electrons transferred from glucose to NAD+, reducing it to NADH, fall down an energy gradient in the electron transport chain to a far more stable location in an electronegative oxygen atom from O2.' This highlights O2's high affinity for electrons and electronegativity as the driving force.