Photosynthesis

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Photosynthesis

Light Dependent Reaction

  • In Grana
  • PSII absorbs light energy
  • 2 electrons in chlorophyll are excited to a higher energy level and move along the electron transport chain
  • These are replaced by photolysis of water to produce electrons, protons and oxygen
  • As the electrons move along the chain, they lose energy
  • This energy is used to pump protons into the thylakoid membrane to create a concentration gradient of protons
  • Protons move from stroma into the thylakoid via ATP Synthase
  • ATP is also synthesised
  • PSI absorbs light energy so electrons are boosted to even higher energy level
  • Eventually NADP accepts the electrons so is reduced to NADPH

Light Independent Reaction

  • In the stroma
  • Carbon dioxide diffuses in through the stomata
  • Combines with RuBP (5C) to form unstable 6C compound
  • This breaks down into 2 x GP (3C)
  • GP is broken down into TP, so there are now 2 x TP (3C)
  • In breaking down GP to TP, ATP from LDR is broken down into ADP+Pi and NADPH is oxidised to NADP.
  • TP can be used to make useful organic molecules
  • But five out of six TP molecules generated are used to regenerate RuBP
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