Question

Q42.) Assume we add a chemical blocks the reduction of NADP+ to NADPH at the end of the electron transport chain in the light dependent reactions of photosynthesis. What would happen to thesize of the H+ gradient in the light dependent reactions. Explain your reasoning.

Answer 1

photos excite electrons from the PSII, these electrons are carried by plastoquinone to cytochrome b6f, then electrons from cytochrome b6f is transferred to plastocyanin, which carries electrons to PSI, from there ferredoxin carries electron to FNR which reduces NADP+ to NADPH.

during the electron transport chain, H+ from the stroma is pumped to thylakoid lumen, so concentration of H+ in the thylakoid lumen increases and creates an H+ gradient which is used to synthesize ATP by the ATP synthase.

if chemical blocks the reduction of NADP+ to NADPH at the end of the electron transport chain in the light dependent reactions of photosynthesis, all the proteins and complexes till ferredoxin remains reduced so electron transport chain stops, so H+ cannot be pumped to thylakoid lumen so size of the H+ gradient in the light dependent reactions decreases.