If the thylakoid membrane becomes leaky to ions, what happens?

• A. It would stop ATP production, NADPH production, and the oxidation of H2O.
• B. It would increase ATP production.
• C. It would have no effect on photosynthesis.
• D. It would only affect NADPH production.

Answer: (A)

The key idea is that the thylakoid membrane must keep a proton gradient intact to power ATP synthesis. Light energy pumps protons into the thylakoid lumen, creating a proton motive force. ATP synthase uses that gradient to convert ADP and Pi into ATP. If the membrane becomes leaky to ions, protons leak back into the stroma, the gradient collapses, and ATP production stops.

Because the light reactions rely on a continuous flow of electrons and the associated proton pumping to drive the entire process, a leak also disrupts the overall electron transport that feeds NADP+ to form NADPH. With the gradient dissipated, the chain can’t operate effectively, so NADPH production is halted or greatly reduced, and the downstream reaction that depends on receiving electrons from water oxidation is impeded as well. In practice, the system cannot sustain water splitting for long, so the oxidation of water would stop as the light reactions collapse.

So, a leaky thylakoid membrane defeats the proton-driven energy supply needed for ATP synthase, and this disruption cascades to stopping NADPH formation and the continued water oxidation.