LDS of photosynthesis

• 5.1 PHOTOSYNTHESIS- LDS

  • The LDS occurs in the thylakoid membranes and uses light energy
  • The end products are ATP, reduced NADP and O2
  • During the LDS a process called phosphorylation occurs
  • There are 2 types of photophosphorylation- cyclic and non cyclic
  • Cyclic only produces ATP and only uses PS1. There is no photolysis of water required because the electrons are recycled because they are not used to reduce NADP
  • Non cyclic produces ATP, reduced NADP and oxygen. Photolysis (splitting) of water is what replaces the photoionised electrons AND the hydrogen needed to produce reduced NADPH AND is what produces the O2 for the next stage
• 5.1 PHOTOSYNTHESIS- LDS CYCLIC PHOSPHORYLATION

  • Only PS1 involved
  • Produces ATP
  • NO PHOTOLYSIS OF WATER
  • Electrons in chlorophyll are photoionised
  • The excited electrons move down the ETC to PS1and lose energy as they move
  • The energy is used to move proteins into the thylakoid to create a gradient- higher conc in thylakoid
  • The proteins then diffuse out into the stroma via ATP synthase which phosphorylates ADP to make ATP in the process
  • The electrons are recycled and continoudly flow through PS1 instead of being used to reduce NADP
• 5.1 PHOTOSYNTHESIS- LDS NON-CYCLIC PHOSPHORYLATION

  • Uses PSII mostly
  • Produces ATP, O2 AND REDUCED NADP
  • Involves photolysis of water
  • Electrons in chlorophyll are photoionised
  • Electrons have energy now so move down to PSII first through the ETC
  • Photolysis of water ( water is split by light energy) produces H ions, O2 and electrons to replace the other electrons as they move down the ETC
  • Energy from the excited electrons creates ATP. This is bc the energy from the electrons actively transports proteins into the thylakoids so the conc is higher than in the stroma. Then the proteins diffuse out of the thylakoid back into the stroma using ATP synthase as a catalyst. This phosphorylates ADP into ATP
  • Now there is ATP, O2 and hydrogen ions left. PSI absorbs more light energy to excite the electrons again. The electrons along with the H ions combine with NADP tp produce reduced NADP
  • Now you have ATP, O2 and reduced NADP to be used in the Calvin cycle/ light independent stage