5.7

• Photosynthesis


  1. Light-dependent reaction

  2. Light-independent reaction (Calvin Cycle)
• Light-dependent reaction


  • Electrons are excited to a higher energy level by the energy trapped by chlorophyll molecules in the thylakoid membranes, electrons are then passed down the electron transport chain from one electron carrier to the next, generating ATP from ADP and inorganic phosphate in a process called photophosphorylation, reduced NADP is also generated
• Cyclic Phosphorylation


  Photon hits chlorophyll, electrons are excited, taken up by an electron acceptor, passed along an electron transport chain, energy is released and ATP is synthesised, electron returns to Photosystem I chlorophyll
• Non-Cyclic Phosphorylation


  Photon hits chlorophyll in Photosystem II, electrons are excited and taken up by an electron acceptor, passed along an electron transport chain to Photosystem I chlorophyll, energy is released and ATP is synthesised, photolysis occurs where water dissociates into hydrogen and hydroxide ions, electrons are excited in Photosystem I and taken up by an electron acceptor, passed along an electron transport chain to NADP, NADP takes up an H+ ion and forms reduced NADP, hydroxide ions react together to form water and oxygen
• Light-independent reaction (Calvin Cycle)


  RuBP is combined with carbon dioxide in a reaction called carbon fixation, catalysed by RUBISCO, RuBP is converted into two glycerate 3-phosphate (GP) molecules, reduced NADP and ATP are used to convert GP to GALP, some GALP molecules are used to make glucose which is then converted to essential organic compounds, remaining GALP molecules are used to reform RuBP with the help of ATP