Light-dependent reactions Transitional Reasoning Download PDF

Questions

1. 1.

   In an experiment investigating the light-dependent reactions of photosynthesis, intact thylakoids isolated from spinach leaves are suspended in an illuminated buffer containing ADP, inorganic phosphate, and $\text{NADP}^+$. When a chemical ionophore that selectively allows protons to diffuse freely across the thylakoid membrane is added to the suspension, the transmembrane proton gradient immediately collapses. Under these conditions, which of the following outcomes would most directly be observed regarding the light-dependent reactions?

   • A) Both ATP synthesis and oxygen evolution completely cease due to the immediate inactivation of photosystem II complexes.
   • B) ATP synthesis accelerates because protons cross the membrane more rapidly, whereas the reduction of $\text{NADP}^+$ is inhibited.
   • C) Oxygen evolution stops because photosystem II cannot extract electrons from water molecules in the absence of a lumenal proton pool.
   • D) ATP synthesis ceases while electron transport, oxygen evolution, and the reduction of $\text{NADP}^+$ continue.