[Campbell Biology P.250] In an experiment, isolated chloroplasts are placed in an illuminate... | Practice Question

In an experiment, isolated chloroplasts are placed in an illuminated solution with appropriate chemicals, allowing them to carry out ATP synthesis. If a compound is added to the solution that makes thylakoid membranes freely permeable to hydrogen ions, what would be the most likely effect on ATP synthesis?

  • A: ATP synthesis would increase significantly due to enhanced hydrogen ion movement.
  • B: ATP synthesis would decrease or cease because the proton gradient across the thylakoid membrane would be dissipated.
  • C: ATP synthesis would be unaffected as it primarily depends on light energy, not hydrogen ion gradients.
  • D: ATP synthesis would shift from the thylakoid membrane to the stroma.
  • E: Oxygen production would stop, leading to a halt in ATP synthesis.

Explanation

The text states that a pH gradient across the thylakoid membrane is crucial for ATP synthesis chemiosmosis and that turning off lights abolishes it. Making membranes freely permeable to hydrogen ions would dissipate this essential proton gradient, thereby preventing ATP synthase from functioning and leading to a decrease or cessation of ATP synthesis.