The light dependent stage

• What are the two stages of photosynthesis?

  Light-dependent and light-independent stages
• Where does the light-dependent stage of photosynthesis occur?

  In the thylakoids
• What is produced during the photolysis of water in the light-dependent stage?

  Hydrogen ions, electrons, and oxygen
• What causes the formation of a proton gradient in the thylakoid lumen?

  Photolysis of water
• What happens to electrons during the light-dependent stage?

  They travel through an electron transport chain
• What is produced when hydrogen ions and electrons combine with NADP?

  Reduced NADP (NADPH)
• What is the process called that produces ATP during the light-dependent stage?

  Photophosphorylation
• What is the difference between cyclic and non-cyclic photophosphorylation?

  Cyclic involves only PSI; non-cyclic involves both PSI and PSII
• How is ATP synthesized during chemiosmosis?

  Protons flow back into the stroma through ATP synthase
• What is the equation for the photolysis of water?

  H₂O → 2H⁺ + 2e⁻ + ½O₂
• What replaces the electrons lost from Photosystem II?

  Electrons from the photolysis of water
• What happens to the excited electrons from Photosystem I?

  They pass along an electron transport chain
• What do the excited electrons from Photosystem I combine with to form reduced NADP?

  Hydrogen ions and NADP
• What is produced in non-cyclic photophosphorylation?

  ATP, oxygen, and reduced NADP
• What are the key differences between cyclic and non-cyclic photophosphorylation?

  • Cyclic involves only Photosystem I
  • Non-cyclic involves both Photosystem I and II
  • Cyclic does not produce reduced NADP
  • Non-cyclic produces ATP, oxygen, and reduced NADP
• What are the steps involved in cyclic photophosphorylation?

  1. Light absorbed by Photosystem I (P700)
  2. Electrons excited and emitted (photoactivation)
  3. Electrons captured by electron acceptor
  4. Electrons passed through electron transport chain
  5. Electrons returned to Photosystem I
  6. Protons pumped into thylakoid lumen
  7. ATP synthesized via chemiosmosis
• What are the steps involved in non-cyclic photophosphorylation?

  1. Light absorbed by Photosystem II (P680)
  2. Water photolysis occurs
  3. Electrons excited and emitted (photoionisation)
  4. Electrons passed through electron transport chain to Photosystem I
  5. Protons pumped into thylakoid lumen
  6. ATP synthesized via chemiosmosis
  7. Electrons from Photosystem I combine with NADP to form reduced NADP
• What are the products of cyclic and non-cyclic photophosphorylation?

  Cyclic:

  • ATP

  
  

  Non-cyclic:

  • ATP
  • Oxygen
  • Reduced NADP
• What is the role of the electron transport chain in photosynthesis?

  • Transfers electrons from photosystems
  • Provides energy for proton pumping
  • Drives ATP synthesis via chemiosmosis
• What is the significance of the proton gradient in the thylakoid lumen?

  • Drives ATP synthesis
  • Maintains energy balance in chloroplasts
  • Facilitates chemiosmosis
• How does reduced NADP contribute to photosynthesis?

  • Acts as an electron carrier
  • Used in light-independent reactions for carbohydrate synthesis