[Campbell Biology P.249] According to Figure 10.17, which of the following steps directly or... | Practice Question

According to Figure 10.17, which of the following steps directly or indirectly contribute to increasing the H+ concentration in the thylakoid space or decreasing it in the stroma, thereby establishing the proton gradient across the thylakoid membrane? Select all that apply.

  • A: Step 1: Energy from light excites an electron from chlorophyll.
  • B: Step 2: Water is split in the thylakoid space, releasing H+.
  • C: Step 3: Electrons travel down the transport chain, pumping H+ into the thylakoid space.
  • D: Step 4: H+ diffuses from the thylakoid space to the stroma through ATP synthase.
  • E: Step 5: NADPH formation removes H+ from the stroma.

Explanation

The H+ gradient across the thylakoid membrane is established by three main mechanisms: the splitting of water photolysis within the thylakoid space Step 2 , the pumping of protons from the stroma into the thylakoid space by the electron transport chain Step 3 , and the removal of H+ from the stroma for NADPH formation Step 5 , which maintains a low H+ concentration in the stroma.