Light Dependent Reaction

• What is the first stage of photosynthesis called?

  Light dependent reactions
• What are the two stages of photosynthesis?

  Light dependent reactions and light independent reactions
• Where do the light dependent reactions occur?

  In the thylakoid membranes of the chloroplast
• What is the significance of light in the light dependent reactions?

  Light provides energy needed to split water and produce ATP and reduced NADP
• What are the four key reactions in the light dependent reactions?


  1. Photoionization of chlorophyll
  2. Photolysis of water
  3. ATP production
  4. Reduced NADP production
• What does photolysis of water refer to?

  Light energy splitting water into oxygen, electrons, and protons
• What is the word equation for photolysis of water?

  Water → Oxygen + Electrons + Protons
• What happens to the protons produced during photolysis of water?

  They are picked up by NADP to form reduced NADP (NADPH)
• What is the role of electrons in the light dependent reactions?

  Electrons are passed along a chain of protein carriers, releasing energy
• What is the waste product of photosynthesis?

  Oxygen
• What does photoionization of chlorophyll involve?

  Light energy causing electrons to be lost from chlorophyll
• How does the process of chemiosmosis contribute to ATP production?

  Protons move down their electrochemical gradient through ATP synthase, catalyzing ATP formation
• What is the process of chemiosmosis in the light dependent reactions?

  • Electrons move down the electron transfer chain
  • Energy from electrons pumps protons into the thylakoid lumen
  • Creates an electrochemical gradient
  • Protons diffuse back into the stroma through ATP synthase
  • ATP is produced from ADP and inorganic phosphate
• What is the role of ATP synthase in the light dependent reactions?

  It catalyzes the reaction of ADP and inorganic phosphate to produce ATP
• How is reduced NADP formed in the light dependent reactions?

  By NADP picking up protons and electrons at the end of the electron transfer chain
• What are the main outcomes of the light dependent reactions?

  • Production of ATP
  • Formation of reduced NADP (NADPH)
  • Release of oxygen as a waste product
• What is the electrochemical gradient created during the light dependent reactions?

  A difference in proton concentration across the thylakoid membrane
• Why is the oxygen produced during photosynthesis considered a waste product?

  It is not used in the photosynthesis process itself
• How do the light dependent reactions prepare for the light independent reactions?

  By producing ATP and reduced NADP, which are needed in the light independent stage