PSII (680nm)

• this stage occurs in the thylakoids membranes
• 1. the arrangement of many accessory pigments in an antenna complex ensures that if enough light is available, enough energy can pass to the reaction centre allowing electrons in chlorophyll a to become excited in the process of photoactivation
• 2. if enough energy is available, the electrons in chlorophyll a are emitted and taken up by an electron acceptor, chlorophyll a becomes the electron acceptor
• 3. the emitted electrons are accepted by electron acceptors arranged at the start of an electron carrier chain, with cytochromes forming the carriers in the chain itself
• 4. carriers are progressively reduced and oxidised in a series of redox reactions as they take up and pass on electrons 
• 5. each new carrier is at a slightly lower energy level than the previous one, so the electrons lose energy as they pass along the chain 
• 6. at certain stages in the electron transport chain, there is sufficient energy available to make ATP from ADP + Pi, called photophosphorylation
• 7. it is necessary to replace the electrons that are lost from the reaction centre in the antenna complex, which comes from photolysis
• 8. when photolysis occurs, the hydrogen dissociates into hydrogen ions (protons) and electrons 
• 9. the electrons replace the electrons lost during photo activation and the hydrogen ions are used in the light independent reaction
• 10. Oxygen is emitted as a waste product