Photosynthesis Lecture Notes

Introduction to Photosynthesis

• Definition: Use of light energy to build carbohydrates (e.g., glucose).
• Equation: 6 H2O + 6 CO2 + light → C6H12O6 + 6 O2
  • Reactants: Water (H2O), Carbon Dioxide (CO2)
  • Products: Glucose (C6H12O6), Oxygen (O2)
• Process:
  • Water enters through roots.
  • Carbon dioxide enters through stomata in leaves.
  • Oxygen is released through stomata.

Photosynthesis vs. Cellular Respiration

• Photosynthesis: Converts CO2 and H2O into glucose and O2 using light energy.
• Cellular Respiration: Converts glucose and O2 back into CO2 and H2O, releasing energy.

Chloroplasts and Chlorophyll

• Chloroplast: Organelle where photosynthesis occurs.
  • Contains thylakoids and stroma.
  • Enclosed by inner and outer membranes.
• Chlorophyll: Pigment that absorbs light (blue and red) but reflects green.
  • Located in thylakoids.
  • Forms stacks called grana.

Stages of Photosynthesis

• Light-dependent Reactions: Occur in thylakoid membranes.

  • Reactants: Water, NADP+, ADP, and phosphate.
  • Products: Oxygen gas, ATP, NADPH.
  • Processes:
    • Photosystem II oxidizes water to O2.
    • Electron transport chain creates ATP and NADPH.
  • Photosystems:
    • Photosystem II (P680) and Photosystem I (P700).

• Light-independent Reactions (Calvin Cycle): Occur in the stroma.

  • Reactants: CO2, ATP, NADPH.
  • Products: Sugars (e.g., glucose), NADP+, ADP, phosphate.
  • Processes:
    • Carbon fixation by Ribulose biphosphate (RuBP).
    • Reduction to G3P (glyceraldehyde 3-phosphate).
    • Regeneration of RuBP.

Electron Transport Chain

• Photosystem II (P680): Absorbs light, oxidizes water to O2.
• Cytochrome b6f Complex: Transfers electrons, pumps protons to create a gradient.
• Photosystem I (P700): Re-energizes electrons with light.
• NADP Reductase: Converts NADP+ to NADPH using electrons.
• ATP Synthase: Produces ATP from ADP and phosphate using proton gradient.

Calvin Cycle Details

• Steps of Calvin Cycle:
  1. Carbon Fixation: CO2 reacts with RuBP using Rubisco enzyme.
  2. Reduction: Conversion of 3-phosphoglycerate to G3P using ATP and NADPH.
  3. Regeneration: G3P used to regenerate RuBP.
• Net Result: Conversion of 3 CO2 to 1 G3P requires 9 ATP and 6 NADPH.

Summary

• Photosynthesis Comprises:
  • Light-dependent reactions: Occur in thylakoid, produce ATP and NADPH.
  • Calvin Cycle (Light-independent reactions): Occur in stroma, use ATP and NADPH to produce glucose.

This concludes the summary of photosynthesis, highlighting the critical processes and components involved. Remember the roles of chlorophyll, chloroplasts, and the differences between the light-dependent and light-independent reactions.