The picture below diagrams the redox potential of oxygenic photosynthesis, which
ID: 209952 • Letter: T
Question
The picture below diagrams the redox potential of oxygenic photosynthesis, which occurs in cyanobacteria and eukaryotic phototrophs. All other phototrophic bacteria perform anoxygenic photosynthesis using only photosystem I (labeled P700 in the diagram). These bacteria generate a proton gradient by relying on the cyclic electron transport system because they do not contain photosystem II (P680). Examine the redox potentials to explain why organisms that rely only on PSI must be anoxygenic?
Copyright © McGraw-Hill Education. Permission required for reproduction or display P* 700 Reaction center 0.8 P680 FeS 0.6 Fd Pheo.a Pyridine nucleotide reductase (FAD) -0.4 NADP+ 0.2 Cyt b 563 PS I NADPH+H PQA 0.0 ADP+P 2 photons PQB ATP Cyt be FeS CytfPC 2e +0.2 PS II +0.4 Antenna P700 (Noncyclic) 2 photons +0.6 OEC +0.8 P680 2022HExplanation / Answer
In oxygenic photosynthesis, water is used as an electron donor that evolves oxygen through PSII that has high electropositive reduction potential.PSII functions in ATP synthesis.PS I on the other hand being at a lower reduction potential than P680 , is therefore reduced by the final electron carrier from PS II i.e plastocyanin. Since PSII is missing in all other phototropic bacteria, they cannot synthesize ATP,they therefore solely rely on cyclic electron transport system to generate a proton gradient.
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