Question

Which one of the following events does NOT contribute to formation of the proton gradient in the chloroplast?

a. reduction of plastoquinone (PQ)
b. oxidation of plastoquinol (PQH₂)
c. splitting of water in the lumen
d. oxidation of NADPH
e. oxidation of P680

Answer 1

The oxidation of NADPH does not contribute to the formation of the proton gradient in the chloroplast; this event is part of the Calvin cycle and is separate from the electron transport chain which establishes the proton gradient.

Step-by-step explanation:

The event that does NOT contribute to the formation of the proton gradient in the chloroplast is the oxidation of NADPH. In the light-dependent reactions of photosynthesis, the proton gradient is established by several processes: the splitting of water in the lumen, the oxidation of plastoquinol (PQH₂), and the reduction of plastoquinone (PQ). When water is split, protons are added to the thylakoid lumen and electrons are provided to PSII. The oxidation of plastoquinol (PQH₂) also pumps protons into the lumen, further establishing the gradient. Conversely, the oxidation of NADPH occurs in the Calvin cycle, which is separate from the electron transport chain and does not contribute to creating a proton gradient across the thylakoid membrane.