Light-dependent stage

• Light-dependent stage

  A) sun

  B) light-dependent stage

  C) H20

  D) ATP

  
• Light-dependent stage

  A) Light

  B) electrons

  C) hydrogen

  D) electron

  E) photolysis

  F) Stroma

  G) Thykaloid

  H) PSII

  I) PSI

  J) ATP

  K) Reduced

  L) ATP synthase

  
• Electrons lost from the reaction centre at PSII are replaced from water molecules broken down using energy from the sun - Photolysis
• 1st step of LD reaction:

  Light is absorbed by the photo stems
• 2nd step of LD reaction:

  Electrons are excited at PSII causing them to be passed along an electron transport chain and is a product of photolysis
• 3rd step of LD reaction:

  Electrons are passed along an electron transport chain
• 4th step of LD reaction:

  As electrons are being passed along an electron transport chain energy is created and is used to pump hydrogen ions from the stroma into the the thylakoid space
• 5th step of LD reaction:

  • At PSI light is absorbed causing electrons to become excited
  • Electrons from PSII pass along PSI
• 6th step of LD reaction - Photolysis:

  • Water molecules are split into hydrogen ions, electrons, and oxygen molecules using energy from the sun
  • Replace electrons lost from reaction centre of PSII - Why water is a raw material of photosynthesis
• Equation of Photolysis:

  H2O = 2H+ + 2e- + 1/2O2
• 7th step of LD reaction:

  1. Hydrogen ions from photolysis and the electron transport chain create a high concentration at the end of the membrane in the thylakoid space
  2. Hydrogen ions move through the membrane down an electrochemical gradient
  3. More ATP formation is driven - chemiosmosis
• 8th step of LD reaction:

  1. Once in the stroma Hydrogen combines with the final electron acceptor NADP and an electron from PSI that was passed along an electron carrier
  2. Reduced NADP / NADPH if formed
  3. Hydrogen ions are removed from the stroma to maintain the proton gradient across the thylakoid membranes
• Cyclic photophosphorylation:

  Alternate route for electrons that leave PSI

  1. Electrons can return to PSI (rather than forming NADPH)
  2. Cyclic photophosphorylation occurs
  3. Meaning: PSI can lead to ATP production with out an electron supply from PSII

  NADPH is not produced

  Uses light energy
• Cyclic photophosphorylation

  A) sun

  B) PSI

  C) ATP