Light dependant (1)

• What are the light dependant products?

  • ATP
  • NADPH
  • Oxygen
• Photolysis


  • Light energy breaks down water into protons, electrons and oxygen
• NADPH production


  • Protons combine with electrons from transport chain and NADP to make NADPH
• What are the 5 light-dependant steps?

  • Photoionisation
  • Electron transport chain
  • Photolysis of water
  • Chemiosmosis
  • ATP and NADPH production
• Photoionisation

  • Light energy excites electrons in pigment
• Electron transport chain


  • Electrons leave pigment
  • Electrons are passed down the thylakoid membrane by redox reactions
  • Releases energy
• ATP production

  • Energy from electron transport chain actively transports protons across thylakoid membrane
  • High concentration of protons
  • Protons diffuse back through ATP synthase channel proteins
  • Chemiosmosis, facilitated diffusion
  • ADP+Pi->ATP by oxidative phosphorylation
• How to test for Light-dependant reaction?

  • Isolate chloroplasts in buffer
  • Add DCPIP
  • Electrons from transport chain reduce DCPIP
  • Reduced DCPIP changes colourless to blue
  • Faster colour change faster photosynthesis 
• What happens in the light dependant reaction? 

  • Light energy excites electrons in photosystems
  • Electrons move down membrane by a series of redox reactions releasing energy
  • Photolysis of water, broken down into protons, electrons and oxygen
  • Protons diffuse through the membrane by chemiosmosis
  • Protons diffuse back through the ATP synthase channel protein to help form ATP
  • NADP combines with protons and electrons to form NADPH