5.1.2

Photoionisation of Chlorophyll

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Photoionisation of Chlorophyll

The first step of the light-dependent reaction is the absorption of light energy by chlorophyll. This causes photoionisation, which is the release of electrons.

Light absorption

Light absorption

  • Light energy is absorbed by chlorophyll in the photosystems. This is the first step in photosynthesis.
  • Absorbing light energy excites the electrons within the photosystem.
  • The electrons are now in a more excited state. This causes them to be released from the chlorophyll.
  • Chlorophyll is now considered to be photoionised.
Energy from photoionisation

Energy from photoionisation

  • The photoionisation of chlorophyll also results in a release of energy.
  • This energy is used in photosynthesis to drive three reactions:
    • Photophosphorylation - production of ATP from ADP and inorganic phosphate.
    • Reduction - production of reduced NADPH from NADP.
    • Photolysis - splitting of water into protons, electrons and oxygen.
  • These three reactions are necessary for photosynthesis to take place.
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