2

• what is stage 1 of non-cyclic photophosphorylation? 


  • light energy excited electrons in the chlorophyll
  • light energy absorbed by PS II
  • light energy excites the electrons in chlorophyll
  • the electrons move to a higher energy level
  • the high energy electrons are released from chlorophyll and move down the electron transport chain to PS I
• what is stage 2 of non-cyclic photophosphorylation?


  • photolysis of water --> protons, electrons and oxygen
  • as excited electrons from the chlorophyll leave the PS II to move down the electron transport chain, they must be replaced
  • light energy splits water into protons (H+), electrons and oxygen.
  • this is photolysis
  • H2O --> 2H+ + 1/2 O2
• what is stage 3 of non-cyclic photophosphorylation?


  • excited electrons lose energy as they move down the electron transport chain
  • this energy is used to transport protons into the thylakoid, so thylakoid has higher conc of protons than the stroma
  • this forms a proton gradient across the thylakoid membrane
  • protons move down the conc gradient, into the stroma, via ATP synthase (enzyme) this is embedded in thylakoid membrane
  • energy from this movement combines ADP with an inorganic phosphate to form ATP
• what is stage 4 of non-cyclic photophosphorylation?


  • light energy is absorbed by PS I, this excited the electrons again to an even higher energy level
  • finally, the electrons are transferred to NADP along with a proton (H+) ion from the stroma to form reduced NADP
• what is chemiosmosis?


  the process of electrons flowing down the electron transport chain and creating a proton gradient across the memrbane