InterviewSolution
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InterviewSolution
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Question : Decribe Z scheme of light reaction |
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Answer» Solution :In photosystem II the REACTION centre chlorophyll-a absorbs 680 nm wavelenght of RED light causing electrons to become excited and jump into an orbit farther from theatomic nucleus. These electrons are PICKED up by an ELECTRON acceptor which passes them to an electrons transport system. This movement of electrons is downhill, in terms of an oxidation - reduction or redox potential scale. The electrons are not used up as they pass through the electron transport chain, but are passed on to the pigments of photosystem PS-I. Simultaneously, electrons in the reaction centre of PS-I are also excited when they receive red light of wavelenght 700 nm and are transferred to another acceptor molecule, that has a greater redox potential. These electrons then are moved downhill again, this time to a molecule of energy rich `NADP^(+)`.The addition of these electrons reduces `NADP^(+)` to `NADPH+ H^(+)`. This is a whole scheme of transfer of electrons, starting from the PS-II, uphill to the acceptor, down the electron transport chain to PS-I, excitation of electrons transfer to another acceptor, and finally down hill to `NADP^(+)` causing it to be reduced to NADPH `+ H^(+)` This is called Z scheme due to its characteristic shape, (see : figure) This shape is formed when all the carries are placed in a sequence on a redox potential scale. 
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