Photosynthesis Lecture Notes

Introduction

• Topic: Photosynthesis
• Focus: Light phase and Dark phase

Photosynthesis Equation

• Components Required:
  • Carbon dioxide
  • Water
• Additional Requirements:
  • Sunlight (not a material, but energy)
  • Chlorophyll (not absorbed but essential)
• Products:
  • Glucose
  • Oxygen

Chloroplast Structure

• Key Components:
  • Thylakoids: Site of the light phase
  • Stroma: Site of the Dark phase

Light phase Reactions

• Location: Thylakoids
• Process:
  • Occurs during the day
  • Photolysis: Splitting of water into hydrogen and oxygen
  • Oxygen is released as a gas
  • Hydrogen is captured by NADP to form NADPH
  • Electron from hydrogen used for photophosphorylation to convert ADP to ATP
• Key Products:
  • NADPH (carries hydrogen)
  • ATP (energy carrier)

Dark phase Reactions

• Location: Stroma
• Process:
  • Occurs at night or low light
  • Start with ribulose biphosphate (RUBP, 5 carbons)
  • Carbon dioxide combines with RUBP to form an unstable 6-carbon compound
  • Breaks into two pyruvic acid molecules (3 carbons each)
  • Using ATP and NADPH from light phase to convert PGA to PGAL
  • PGAL can become glucose or reform RUBP
• Products:
  • Glucose
  • Regeneration of ADP and NADP

Cycle Continuity

• ADP and NADP return to the light-dependent phase to be re-energized
• Importance of photoperiod for the process

Terminology Recap

• Photolysis: Splitting water with light
• Photophosphorylation: Using light to add a phosphate to ADP forming ATP
• RUBP: Ribulose biphosphate, a 5-carbon molecule
• PGA/PGAL: Intermediates in the Calvin cycle; PGAL can become glucose or reform RUBP

Conclusion

• Continuous process between light-dependent and independent phases
• Importance of understanding the cycle for energy production and storage in plants

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