Photophosphorylation- the making of ATP from ADP and Pi in the presence of light.
Non-cyclic phosphorylation: Occurs in the GRANA.
1. Light hits photosystem II, exciting a pair of electrons. They leave PSII. These electrons travel along the elctron carrier chain (made up of Ferredoxin, an Fe-S complex that carries electrons). Energy is released to produce ATP.
2. Light strikes photosystem I, exciting a pair of electrons. The electrons leave PSI, and join with NADP and the protons produced at PSII (from photolysis of water) to make reduced NADP. This is catalysed by NADP reductase.
3. The electrons produced during photolysis replace those lot from photosystem II.
4. Some protons and electrons from photophosphorylation are used in chemiosmosis in respiration to make ATP.
In cyclic photophosphorylation there is NO PHOTOLYSIS OF WATER. This means there is no reduced NADP formed. This is used in guard cells to bring in K+, lowers the water potential to increase intake of water and carbon dioxide as guard cells swell.
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