Photosynthesis Lecture Notes

Introduction to Photosynthesis

• Photosynthesis: Process plants, some bacteria, and protistans use sunlight to produce glucose from CO2 and water.
• Glucose can be converted into pyruvate, releasing ATP via cellular respiration.
• Oxygen is also a by-product.
• Summary Equation:
  • Carbon dioxide + water → glucose + oxygen
• Involves chlorophyll, a green pigment converting sunlight into chemical energy.

Chlorophyll

• Complex molecule with variations among photosynthetic organisms.
• Chlorophyll a: Primary pigment, absorbs violet-blue and reddish-orange-red wavelengths.
• Accessory pigments: Include chlorophyll b, xanthophylls, and carotenoids.
• Structure:
  • Lipid-soluble hydrocarbon tail
  • Flat hydrophilic head with magnesium ion
  • Tail and head connected by ester bond

Leaf Structure and Function

• Leaves: Main photosynthetic organs in plants.
• Water enters via roots, transported through xylem vessels.
• Stomata: Specialized structures for gas exchange; guard cells control opening.
• Water loss through stomata, especially in heat (e.g., cottonwood trees).

Chloroplast and Photosynthetic Membranes

• Thylakoid: Structural unit of photosynthesis, found in both prokaryotes and eukaryotes.
• Eukaryotic chloroplast: Has three membrane systems, forming thylakoid stacks (grana) and stroma.

Stages of Photosynthesis

Light-dependent Reactions

• Occur in grana, require light to create energy-carrier molecules for the next stage.
• Key processes:
  • Photophosphorylation: Light energy used to make ATP
  • Photolysis: Water split into oxygen, hydrogen ions, and electrons
  • Electrons reduce NADP+ to NADPH

Light-independent Reactions (Calvin Cycle)

• Occur in the stroma.
• Use ATP and NADPH to convert CO2 into carbohydrates (carbon fixation).
• Steps:
  • CO2 combines with RuBP, forming an unstable 6-carbon sugar.
  • Breaks down into glycerate 3-phosphate (GP).
  • GP converted to glyceraldehyde 3-phosphate (GALP) via phosphorylation and reduction.
  • Some GALP converted into glucose; others regenerate RuBP.

Photosystems and Electron Transfer

• Photosystems: PSII (P680) occurs before PSI (P700).
• Z scheme: Electron transfer process that enables ATP production, involves photophosphorylation and redox reactions.
• Chemiosmosis: Proton pump creates electrochemical gradient, driving ATP synthesis.

Cyclic and Non-Cyclic Phosphorylation

• Non-cyclic: Electrons from water to NADP+, producing ATP and NADPH.
• Cyclic: Involves PSI, generates ATP but not NADPH.

Factors Affecting Photosynthesis

• Limiting factors: Light intensity, CO2 concentration, and temperature.
• Light intensity: Affects rate of light-dependent reactions.
• CO2 concentration: Influences carbon fixation rate.
• Temperature: Enzyme activity dependent, affects rate of reactions.

Review

• Understand the stages and mechanisms of photosynthesis.
• Recognize factors that affect photosynthesis efficiency.

For more in-depth details, refer to the original resource or textbook material.