Photosynthesis Lecture Notes

Introduction to Photosynthesis

Photosynthesis Definition: Process using light energy to build carbohydrates.
Equation: 6H2O + 6CO2 + light → C6H12O6 + O2
- Reactants: Water (H2O) and Carbon Dioxide (CO2)
- Products: Glucose (C6H12O6) and Oxygen (O2)
Process Summary:
- Water is absorbed via roots.
- Carbon dioxide enters through stomata.
- Oxygen is released through stomata.

Chloroplast: Site of photosynthesis
- Contains chlorophyll (pigment that absorbs blue and red light)
- Reflects green light (why plants are green)
- Structure: Contains thylakoids (site of light-dependent reactions)
Mitochondria: Responsible for cellular respiration (opposite of photosynthesis)
- Converts glucose and oxygen back to CO2 and water

Occur in the thylakoid membranes
Convert light energy into chemical energy (ATP and NADPH)
Key Reactions:
- Water is oxidized to oxygen gas
- NADP+ is reduced to NADPH
- ATP is generated from ADP and phosphate via ATP synthase
Photosystems:
- Photosystem II (P680): Absorbs light at 680 nm, oxidizes water
- Photosystem I (P700): Absorbs light at 700 nm, re-energizes electrons

Occur in the stroma
Use ATP and NADPH from light-dependent reactions to reduce CO2 into G3P (glyceraldehyde-3-phosphate)
Steps:
- Carbon Fixation: CO2 is fixed by reacting with RuBP (ribulose biphosphate) catalyzed by rubisco, forming 3-phosphoglycerate (PGA)
- Reduction Phase: 3-phosphoglycerate is phosphorylated by ATP and reduced by NADPH to form G3P
- Regeneration of RuBP: G3P is used to regenerate RuBP, continuing the cycle
Outputs: For every 3 CO2, one G3P is produced

Overall Photosynthesis Process: Involves both light-dependent and light-independent reactions
- Light-dependent reactions produce ATP and NADPH
- Calvin cycle utilizes these to fix carbon into glucose
Energy Requirement: Requires 18 ATP and 12 NADPH to produce one glucose molecule

Conclusion: Photosynthesis is a complex but essential process converting light energy into chemical energy, forming the basis of the food chain.