Question

please give mi answer of this question

Answer 1

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Answer 2

Non- Cyclic photophosphorylation involves both Photosystem I and Photosystem II. These two photosystems work in series, first PS II and then PS I. The two photosystems are connected through an electron transport chain. Both ATP and NADPH + H⁺ are synthesized by this kind of electron flow.

First in PS II, the P₆₈₀ molecule absorbs 680 nm wavelength of red light causing electrons to become excited and jump into an orbit which is farther from the atomic nucleus.

These electrons are picked up by an electron acceptor which passes them to an electron transport system of cytochromes. This movement of electrons is downhill on redox potential scale. The electrons are then passed onto the pigments of PS I, without being used as they pass through the electron transport chain. Simultaneously, electrons in the reaction centre of PS I (P₇₀₀) are excited when they receive light of wavelength 700 nm and these electrons are transferred to another acceptor molecule that has greater redox potential. These electrons are then moved downhill again to a molecule of NADP⁺. The addition of these electrons reduces NADP⁺ to NADPH + H⁺.

The whole scheme of transfer of electrons , starting from PS II, uphill to the acceptor, down the electron transport chain to PS I, excitation of electrons, transfer to another acceptor and finally downhill to NADP⁺ causing it to be reduced to NADPH + H⁺ is called Z-scheme. This shape is formed when all the carriers are placed in sequence on a redox potential scale.