Photosynthesis Lecture Notes

Overview of Photosynthesis

• Photosynthesis is vital for life; transforms sunlight, CO2, and water into glucose and oxygen.
• Developed 450 million years ago; complex and inefficient but crucial.
• Consists of two main reactions:
  • Light-dependent reactions
  • Light-independent reactions (Calvin Cycle)

Requirements for Photosynthesis

• Water: Absorbed by plant roots and transported via xylem.
• Carbon Dioxide: Enters through stomata in leaves.
• Sunlight: Absorbed by chlorophyll in chloroplasts.

Structure of Chloroplasts

• Unique to plant cells; contain plastids.
• Thylakoids: Membranous sacs with chlorophyll.
• Grana: Stacks of thylakoids.
• Lumen: Inside thylakoid.
• Stroma: Space outside thylakoid but inside chloroplast.

Light-Dependent Reactions

• Initiated by photons exciting electrons in chlorophyll.
• Takes place in thylakoid membranes.
• Photosystem II (PSII):
  • First protein complex; contains chlorophyll.
  • Splits water (H2O) to replace lost electrons, releasing oxygen.
  • Energized electrons transferred to electron transport chain.
• Cytochrome Complex: Transfers electrons, pumps protons into thylakoid.
• ATP Synthase:
  • Protons exit through ATP Synthase, creating ATP from ADP.
• Photosystem I (PSI):
  • Re-energizes electrons to form NADPH.
• Outcomes: Production of ATP, NADPH, and oxygen.

Calvin Cycle (Light-Independent Reactions)

• Occurs in the stroma.
• Carbon Fixation:
  • CO2 attached to RuBP by enzyme RuBisCo.
  • Forms unstable six-carbon compound split into 3-Phosphoglycerate.
• Reduction Phase:
  • Uses ATP and NADPH to convert 3-Phosphoglycerate into G3P (Glyceraldehyde 3-Phosphate).
  • G3P converted into glucose and other carbohydrates.
• Regeneration of RuBP:
  • 5 G3Ps regenerate 3 RuBP, needing ATP and NADPH.
• Ultimate product: 1 G3P leaves cycle for carbohydrate synthesis.

Conclusion

• Photosynthesis transforms sunlight, water, and CO2 into carbohydrates and oxygen, supporting life on Earth.
• For further understanding, review and re-watch materials as needed.

Note: References and further readings can enhance comprehension.