Atrazine is an herbicide that is commonly used to control weeds in corn, sorghum

Question

Atrazine is an herbicide that is commonly used to control weeds in corn, sorghum, and sugar cane fields. It binds at the Q_B site of the D2 subunit, blocking electron flow from Q_A to A_B. (It competes with A_B for the binding site on D2.) Which of the following can you infer from this information? Atrazine directly interferes with photosystem I function. Atrazine inhibits the splitting of water. Atrazine directly interferes with photosystem II function. Atrazine can interfere with the formation or availability of ATP. Atrazine prevents the reduction of pheophytin.

Explanation / Answer

Answer: C

Atrazine directly interferes with photosystem II function. In the light reactions of photosynthesis,excited photosystem II (P680) transfers electrons to pheophytin which are then transferred to special quinones QA and QB. Atrazine blocks electron flow from QA to QB thereby interfering with PSII function.  

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