LIGHT DEPENDENT REACTION

• light dependent reaction provides ATP and NADPH needed for light independent reaction
• photolysis of water is when light energy is absorbed by the chlorophyll and splits water into oxygen, H+ and e-

  • H2O -----> 1/2 O2 + 2e- + 2H+
• photoionisation of chlorophyll is when light energy is absorbed by the chlorophyll in the thylakoid and this energy excites electrons to a higher energy level to leave chlorophyl
• chemiosmosis is the movement of H+ across the membrane via ATP synthase - down their electrochemical gradient
• Photophosphorylation is the process of converting ADP + pi to ATP
• 1st part:

  1. chlorophyll in the thylakoid membrane absorb light energy exciting electrons to a higher energy level to leave chlorophyl - photoionisation
  2. These exited electrons that have left chlorophyl enter the electron transfer chain
  3. electrons release energy as they pass down chain - this energy is used to actively transport H+ ions (from photolysis) into thylakoid lumen via proton pump
• 2nd part:

  • High concentration of H+ in lumen creates a electrochemical gradient. Protons move back via facilitated diffusion of the ATP synthase enzyme - chemiosmosis
  • the change in shape of the ATP synthase enzyme provides energy to catalyse ADP + PI -----> ATP - photophosphorylation
  • left over 2H+ and 2e- from photolysis of water is used to combine with NADP to form reduced NADP or NADPH