Light Dependent Reaction

• LDR

  OCCURS IN THE THYLAKOID MEMBRANE
• PSII - P680


  loses electrons which are produced by the photolysis of water
• PSI - P700


  is of a higher energy level compared to PSII
• What are the light dependent reactions in photosynthesis responsible for producing?

  ATP and reduced NADP
• Where do the light dependent reactions take place?

  On the thylakoid membranes
• What is produced as a byproduct of the light dependent reactions?

  Oxygen
• What are the two types of photo phosphorylation involved in the light dependent reactions?

  Non-cyclic and cyclic photo phosphorylation
• What is the role of photosystems in the light dependent reactions?

  To absorb light energy
• What happens to the electrons after they are excited in photosystem 2?

  They pass through an electron transport chain
• How is ATP produced during the light dependent reactions?

  By chemiosmosis
• What happens to the electrons after they pass through the electron transport chain from photosystem 1?

  They are added to NADP in the stroma
• What is the process called when water is split to replace lost electrons in photosystem 2?

  Photolysis
• What does photolysis produce besides electrons?

  Oxygen
• Under what conditions does cyclic photo phosphorylation occur?

  When the chloroplast requires an increased amount of ATP
• What is the role of the proton gradient in ATP production?

  It drives protons through ATP synthase to generate ATP
• What is the enzyme that synthesizes ATP found on the thylakoid membrane?

  ATP synthase
• What is the process called when protons diffuse down their gradient through ATP synthase?

  Chemiosmosis
• What are the key steps involved in non-cyclic photo phosphorylation?

  • Light energy absorbed by photosystem 2
  • Electrons excited and passed through an electron transport chain
  • ATP produced by chemiosmosis
  • Electrons transferred to photosystem 1
  • Electrons excited again and passed through another electron transport chain
  • Electrons added to NADP to form reduced NADP
• What are the key steps involved in cyclic photo phosphorylation?

  • Light energy absorbed by photosystem 1
  • Electrons excited and passed through an electron transport chain
  • ATP produced by chemiosmosis
  • Electrons return to photosystem 1
• How does the proton gradient enhance ATP production during photosynthesis?

  • Protons are pumped into the thylakoid interior
  • The gradient drives protons through ATP synthase
  • ATP is generated from ADP and Pi
• What are the two processes that enhance the proton gradient during non-cyclic photo phosphorylation?

  1. Protons removed from the stroma to form reduced NADP
  2. Protons produced from water during photolysis
• What is the significance of the thylakoid membrane being impermeable to protons?

  • It maintains a higher concentration of protons in the thylakoid interior
  • It allows for the establishment of an electrochemical gradient
• Photolysis of water


  • to replace electrons lost in PSII
  • provides protons for producing reduced NADPH
  • 2H2O → O2 + 4e- + 4H+
• Overall products

  • ATP
  • reduced NADP
  • oxygen (photolysis)