Photolysis of water 0.0 / 5 ? BiologyCellular processesA2/A-levelWJEC Created by: sophiee96Created on: 13-08-13 09:48 What happens when light strikes a molecule at the reaction centre of photosystem II? An electron is raised to a higher energy level and leaves the chlorophyll molecule short of electrons 1 of 21 What must happen if the chlorophyll molecule is to continue absorbing light energy? It needs to replace the lost electrons 2 of 21 The replacement of electrons are provided from what? Water molecules that are split using light energy 3 of 21 What do the protons do? Combine wih electrons from photosystem I and NADP to give reduced NADP 4 of 21 How can the photolysis of water be demonstrated? Using the Hill reaction 5 of 21 Robert Hill used isolated chloroplasts to demonstrate what? That they have the reducing power to evolve oxygen from water in the presence of an oxidising agent 6 of 21 It is possible to repeat this using the blue dye DCPIP which acts as a substitute for what? The plants NADP 7 of 21 What happens to the DCPIP when reduced? It becomes colourless 8 of 21 Cyclic photophosphorylation involves which photosystem? Photosystem I 9 of 21 Light energy is absorbed by PSI, then what happens? It is passed to chlorophyll a at the reaction centre 10 of 21 What happens to the electrons? They are passed to a higher energy level where they are received by the second electron centre 11 of 21 What happens to the electrons that aren't used up in the production of reduced NADP? They pass along a chain of electron carriers before being returned to PSI 12 of 21 What happens as the electron passes along the chain of carriers? Sufficient energy is generated to make ATP 13 of 21 Is any reduced NADP produced in this process? No 14 of 21 Where do the reactions of the light-dependent stage of photosynthesis take place? In the thylakoid membranes of the chloroplast 15 of 21 Electrons flow along the chain of electron carriers from where to where? PSII to PSI 16 of 21 What does this flow of electrons provide the energy for? To pump hydrogen ions from the stroma, across the thylakoid membrane and into the thylakoid space 17 of 21 What does this result in? An electrochemical gradient 18 of 21 Why? Because there are more hydrogen ions inside the thylakoid space than outside the stroma 19 of 21 What do hydrogen ions then do? Flow along this gradient across the thylakoid membrane through the protein channels 20 of 21 This produces energy for what? The formation of ATP by ATP synthetase 21 of 21
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