The chemical 3-(3,4-dichloro-phenyl)-1,1-dimethylurea (DCMU) blocks the movement of electrons at the point indicated by the black, downward-pointing arrow in the figure below. Which of the following would be an immediate effect of treating a chloroplast with this drug?

Question

Quizplus · Accepted Answer

DCMU is an inhibitor of photosystem II, and it blocks electron flow from the primary electron acceptor to plastoquinone. This causes a decrease in the amount of ATP and NADPH produced in the light reactions, as well as a decrease in the rate of water splitting. Without electron flow, a proton gradient cannot be created, so ATP cannot be made. Therefore, choice C is the correct answer.

The Chemical 3-(3,4-Dichloro-Phenyl)-1,1-Dimethylurea (DCMU) Blocks the Movement of Electrons at the Point