Photosynthesis Notes

Overview

• Photosynthesis is the process used by plants, some bacteria, and protists to convert sunlight into glucose from carbon dioxide and water.

• Byproduct of photosynthesis: Oxygen.

• Basic Equation:

  • Carbon Dioxide + Water → Glucose + Oxygen

Role of Chlorophyll

• Chlorophyll converts sunlight energy into chemical energy.

• Types of Chlorophyll:

  • Chlorophyll a (all photosynthetic organisms)

  • Accessory pigments (chlorophyll b, xanthophylls, carotenoids)

• Chlorophyll a absorbs light primarily from violet-blue and reddish orange-red wavelengths.

Leaf Structure

• Leaves are solar collectors filled with photosynthetic cells.

• Water enters through roots and is transported via xylem.

• Stomata regulate gas exchange; carbon dioxide enters and oxygen exits.

• Water loss occurs through stomata during gas exchange.

Chloroplast Structure

• Thylakoids are flattened sacs containing photosynthetic components.

• Stacks of thylakoids are referred to as grana.

• The stroma is the area between grana.

• Chloroplasts have three membrane systems.

Stages of Photosynthesis

Light-Dependent Reactions

• Occurs in grana; uses light to produce ATP and NADPH.

• Key Processes:

  • Photoactivation of chlorophyll leads to electron excitement and transfer.

  • Water is split (photolysis) into oxygen and electrons.

• Inputs: Light, Water, NADP+

• Outputs: ATP, NADPH, Oxygen

Light-Independent Reactions (Calvin Cycle)

• Occurs in the stroma; uses ATP and NADPH to convert carbon dioxide into carbohydrates.

• Key Processes:

  • Carbon fixation (combining CO2 with RuBP to form GP).

  • Reduction of GP to GALP using ATP and NADPH.

  • GALP can form glucose and regenerate RuBP for the cycle.

Components of Light-Dependent Reactions

• Photosystem II (PSII) and Photosystem I (PSI) absorb light.

  • PSII passes electrons to the electron transport chain.

  • PSI generates NADPH from excited electrons.

• Chemiosmosis:

  • H+ ions move to produce ATP via ATP synthase.

Factors Affecting Photosynthesis Rate

• Limiting Factors: Light intensity, CO2 concentration, temperature.

• Increased light enhances photosynthesis until limited by other factors.

• Optimal temperature increases enzymatic activity; too high decreases rate.

• Specific wavelengths of light are more effective (PSI at 700 nm, PSII at 680 nm).

Conclusion

• Photosynthesis is essential for converting solar energy into chemical energy stored as glucose, facilitating life on Earth.