• Created by: Catr08
  • Created on: 27-03-21 12:26

Stages of photosynthesis:

Light-dependent stage occurs in the thylakoids and converts light energy into chemical energy (ATP+NADH)

Light-independent stage occurs in the stroma and uses the chemical energy to produce carbon compounds

1. Light-dependent stage 

1.1 Non-cyclic phosphorylation

  • Chlorophyll in photosystems I and II (PSI and PSII) absorbs light which triggers the release of energised electrons (photoactivation) --> electrons are excited 
  • Electrons from PSI reduce NADP to form NADPH
  • Electrons from PSII pass through the electron transport chain before replacing electrons from PSI
  • The transport chain produces ATP (photophosphorylation
    • PSII electrons pass through the electron chain, lose energy, translocates H+ ions to thylakoid
    • this creates an electrochemical gradient or proton motive force 
    • Chemiosmosis: H+ ions return to the stroma via ATP synthase 
    • This catalyzes ATP 
  • Electrons lost by PSII are replaced by water (photolysis)
    • H2O --> 2H++2e-+1/2O2

1.2 Cyclic phosphorylation

  • Only chlorophyll in Photosystem I are activated by light
  • The electrons move through an electron transport chain before returning to their original location (i.e. cyclic)
  • The transport chain


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