Photosynthesis

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THE LIGHT DEPENDENT STAGE

The passage of electrons:

  • PS1 absorbs photons of light, which excites electrons in its reaction centre. These are emitted are picked up by an electron acceptor.
  • The electrons are transported via a series of electron carrier molecules via redox reactions. The energy released is used to phosphorylation ADP into ATP.
  • The electrons are returned to PS1.
  • This is called cyclic phosphorylation.
  • Electrons do not always return to PS1, leaving it with a positive charge. Instead, they are transferred to oxidised NADP+ in the stroma where they reduce it, along with protons from the photolysis of water.
  • In order to neutralise the positive charge of PS1, PS2 absorbs photons of light, exciting its electrons at the reaction centre. They are emitted, picked up by an electron acceptor and transported down the ETC to PS1. The energy released is used to phosphorylate ADP into ATP.
  • PS2 is left with a positive charge.
  • Electrons from the photolysis of water neutralise this.
  • This is…

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