[Campbell Biology P.11] If a chemical compound selectively inhibits the function of the cyt... | Practice Question

If a chemical compound selectively inhibits the function of the cytochrome complex within the electron transport chain of the light reactions, which of the following would be the most direct consequence?

  • A: Photosystem II would be unable to absorb light energy.
  • B: Water molecules would no longer be split.
  • C: The proton gradient across the thylakoid membrane would not be established, reducing ATP synthesis.
  • D: NADP+ would be directly reduced to NADPH by electrons from Photosystem I.

Explanation

The cytochrome complex specifically cytochrome b6f complex plays a crucial role in the electron transport chain between Photosystem II and Photosystem I. As electrons pass through this complex, it pumps protons from the stroma into the thylakoid lumen, establishing a proton gradient. This proton gradient is then used by ATP synthase to generate ATP. Therefore, inhibiting the cytochrome complex would directly prevent the establishment of this gradient and thus inhibit ATP synthesis.