Photosynthesis

The light-dependent and independent reactions

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Light dependent reactions

In the thylakoid membranes of the chloroplast:

  • light energy is absorbed by a chlorophyll molecule
  • electrons are excited to a higher energy level
  • these electrons are passed along an electron transport chain
  • this releases energy which is used to reform ATP from ADP +Pi (oxidative phosphorylation)
  • photolysis of water into H+, electrons and oxygen
  • H+ goes to NADP converting it to NADP with addition of electrons from the electron transport chain
  • electrons replace those lost by chlorophyll and Oxygen is released as gas through stomata
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Light Independent reactions

In the STROMA:

  • Ribulose Bisphosphate combines with CO2 to from two molecules of Glycerate-3-phosphate
  • GP is reduced to TP- addition of hydrogen from reduced NADP and energy released from hydrolysis of ATP to ADP + Pi
  • TP gives one carbon to the build up of organic molecules such as glucose for growth
  • TP is then phosphorylated back to RuBP, so the cycle continues
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