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

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?

Quizplus · Accepted Answer

DCMU blocks electron transport between Photosystem II and Photosystem I, which prevents the creation of a proton gradient across the thylakoid membrane. Without a proton gradient, ATP synthase cannot produce ATP from ADP and inorganic phosphate, even though light-dependent reactions have occurred. Thus, choice C is the correct answer. Choices A, B, and D are incorrect because they are dependent on the Calvin cycle, which occurs in the stroma and depends on ATP and NADPH produced by the light-dependent reactions.

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