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PHOTOSYNTHESIS

CHLOROPHYLL IN THE CHLOROPLAST

  • Pigment molecules are located on the thylakoid membranes.
  • The pigment molecules are arranged in an antenna complex.
  • Light strikes the antenna complex and it is channelled towards the reaction centre
  • The electrons are excited by the light energy in the reaction centre.
  • The electrons are picked up by electron acceptors
    (1 photon of light = 1 electron released).
  • The electrons that are lost are replaced by splitting water.

2H2O 4H+ + 4e- + O2

  • So 1 molecule of oxygen released requires 4 photons of light.
  • Two types of pigment systems have been found
     
    PHOTOSYSTEM I Mainly chlorophyll a
    PHOTOSYSTEM II Chlorophyll b, some chlorophyll a
    plus other pigments
  • These photosystems bring about three reactions:
  1. Photolysis of water to provide electrons (e-) and protons (H+)
  2. Photophosphorylation to produce ATP from coupled redox reactions in an electron transport chain.
  3. Reduction of NADP to NADPH + H+ (NADP is therefore the final electron acceptor).

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© Paul Billiet 2012