Photosynthesis Light Dependent Reactions and Calvin Cycle

Light Dependent Reactions

• Occur in thylakoid membranes of chloroplasts
• Light energy excites electrons, which are passed along a series of electron carriers
• Water is split into oxygen and hydrogen ions (H+)
• ATP and NADPH are produced
• Two stages:
  • Light-harvesting complex: absorbs light energy
  • Reaction center: converts light energy into ATP and NADPH

Calvin Cycle

• Occurs in stroma of chloroplasts
• Uses ATP and NADPH produced in light-dependent reactions
• CO2 is fixed into organic molecules (glucose)
• Regeneration of RuBP (ribulose-1,5-bisphosphate) for continuous CO2 fixation
• Three stages:
  • Carbon fixation: CO2 is fixed into 3-phosphoglycerate (3-PGA)
  • Reduction: 3-PGA is reduced to form glyceraldehyde 3-phosphate (G3P)
  • Regeneration: G3P is used to regenerate RuBP

Electron Transport Chain

• Series of electron carriers in thylakoid membranes
• Electrons passed from high-energy state to low-energy state, releasing energy
• Energy used to pump protons (H+) across thylakoid membrane
• Proton gradient used to produce ATP
• Cyclic and non-cyclic pathways:
  • Cyclic: electrons return to reaction center, producing ATP only
  • Non-cyclic: electrons reduce NADP+, producing NADPH and ATP

Light Dependent Reactions

• Light energy excites electrons in thylakoid membranes, passing them along a series of electron carriers
• Water is split into oxygen and hydrogen ions (H+), producing ATP and NADPH
• The process involves two stages: light-harvesting complex, which absorbs light energy, and reaction center, which converts light energy into ATP and NADPH

Calvin Cycle

• Occurs in the stroma of chloroplasts, using ATP and NADPH produced in light-dependent reactions
• CO2 is fixed into organic molecules (glucose) through a three-stage process
• The stages involve carbon fixation, where CO2 is fixed into 3-phosphoglycerate (3-PGA), reduction, where 3-PGA is reduced to form glyceraldehyde 3-phosphate (G3P), and regeneration, where G3P is used to regenerate RuBP (ribulose-1,5-bisphosphate) for continuous CO2 fixation

Electron Transport Chain

• A series of electron carriers in thylakoid membranes, where electrons are passed from high-energy state to low-energy state, releasing energy
• Energy is used to pump protons (H+) across the thylakoid membrane, creating a proton gradient used to produce ATP
• The process involves both cyclic and non-cyclic pathways, with cyclic pathways producing ATP only, and non-cyclic pathways producing NADPH and ATP