Light Dependant Reaction

• • Light dependant reaction occurs on the thylakoid membrane.
  • Chlorophyll absorbs light energy and is used with water to produce reduced NADP, and ATP from ADP + Pi.
• Light Dependant Reaction P1:

  • Light energy is absorbed by 2 chlorophyll molecules/ photosystems.
  • This boosts the energy level of electrons, raising them to a higher energy level.
  • Chlorophyll loses electrons so becomes positively charged. This process is called photoionisation.
• Light Dependant Reaction P2:

  • The electrons from photosystem 2 pass along an electron carrier chain.
  • As they move between carriers in redox reaction, energy is released which is used to transport protons from the stroma into the thylakoid.
  • This creates a proton gradient and the protons diffuse back into the stroma through ATP synthase.
• Light Dependant Reaction P3:

  • ATP synthase combines 2ADP with 2Pi producing 2ATP.
  • The electrons are then used to balance those lost from photosystem 1.
  • Light energy also causes photolysis - the splitting of water into 2 electrons, 2 protons and 1/2 O2.
• Light Dependant Reaction P4:

  • The hydrogen from water and the electrons from photosystem 1 are used to reduced NADP to NADPH.
  • The electrons from water are used to balance those lost from photosystem 2.
  • Oxygen is released as a waste product.