yt

• Photosynthesis


  The process by which plants convert sunlight, carbon dioxide and water into glucose and oxygen
• Photosynthesis was developed 450 million years ago
• Photosynthesis is complicated, inefficient and confusing
• Reactions in photosynthesis


  • Light dependent reactions
  • Light independent reactions (Calvin cycle)
• Light dependent reactions


  Reactions that require light energy
• Light independent reactions (Calvin cycle)


  Reactions that do not require direct light energy
• Photosynthesis is basically respiration in reverse
• Requirements for photosynthesis


  • Water
  • Carbon dioxide
  • Sunlight
• How plants obtain requirements for photosynthesis

  1. Roots absorb water and transport it to leaves

  2. Carbon dioxide enters and oxygen exits through stomata in leaves

  3. Chlorophyll in leaves absorbs sunlight
• Chloroplast


  • Contains thylakoid membranes with chlorophyll
  • Contains stroma outside thylakoids
• Light dependent reactions


  1. Chlorophyll absorbs photon

  2. Electron in chlorophyll becomes excited

  3. Electron transported through electron transport chain

  4. Energy used to pump protons into thylakoid lumen

  5. ATP synthase uses proton gradient to produce ATP

  6. Electrons used to produce NADPH
• Oxygen is a byproduct of the light dependent reactions
• Calvin cycle (light independent reactions)

  1. Carbon dioxide fixed to RuBP by RuBisCO enzyme

  2. RuBP split into 3-phosphoglycerate

  3. 3-phosphoglycerate converted to glyceraldehyde 3-phosphate (G3P) using ATP and NADPH

  4. Some G3P used to regenerate RuBP, remainder is used to produce carbohydrates
• RuBisCO


  Enzyme that fixes carbon dioxide to RuBP in the Calvin cycle
• RuBisCO is the most abundant protein on Earth
• RuBisCO is not very efficient, often reacting with oxygen instead of carbon dioxide
• G3P is the ultimate product of photosynthesis, which can be used to produce various carbohydrates