Light Dependent Reaction

• Where does the light dependent reaction take place?

  • Within the chloroplast on the thylakoid membrane / Grana
• What are the reactants and products of the LDR?

  Reactants:

  • Light energy
  • Water

  Products:

  • ATP
  • Reduced NADP
• 4 key stages of the LDR:

  1. Photoionisation of chlorophyll
  2. Photolysis
  3. Chemiosmosis
  4. Production of ATP and NADP
• Describe the PHOTOIONISATION stage

  • Light energy is absorbed by chlorophyll
  • Electrons become excited raises up an energy level to leave chlorophyll
  • Chlorophyll has been ionised (e-)
• Describe the PHOTOLYSIS of water

  • Light energy is absorbed by chlorophyll and splits water into O2 , H+ and , e-
  • H+ is picked up by NADP to form NADPH (LIR)
  • e- are passed along a chain of carrier proteins
  • O2 is used for respiration or diffuses out the leaf through the stomata
• Describe the CHEMIOSMOSIS stage

  • e- are transported by an electron transfer chain releasing energy
  • Energy is used to pump H+ across the membrane into the lumen by active transport
  • So high concentration of H+ in the lumen (electrochemical gradient)
  • H+ diffuses through the enzyme ATP synthases catalysing the production of ATP

  Chemiosmosis:

  • Some H+ combine with co-enzyme NADP to become reduced NADP as protons move from high to low concentration gradient