[Campbell Biology P.249] Which of the following processes directly leads to the highest conc... | Practice Question

Which of the following processes directly leads to the highest concentration of H+ in the thylakoid space during the light reactions, as depicted in the figure?

  • A: The excitation of electrons in Photosystem II.
  • B: The splitting of water molecules (photolysis) in the thylakoid space.
  • C: The pumping of protons by the electron transport chain (cytochrome complex) into the thylakoid space.
  • D: The formation of NADPH by NADP+ reductase.

Explanation

While water splitting Step 2 does contribute H+ to the thylakoid space, the electron transport chain cytochrome complex actively pumps a larger quantity of H+ 4 H+ per electron pair shown in Step 3 into the thylakoid space from the stroma. This active pumping is a primary driver for establishing and maintaining the very high H+ concentration within the thylakoid space.