Lecture Notes: Photosynthesis and Its Role in Food Creation

Introduction

• The lecture focuses on photosynthesis and addresses the question of where the food we eat comes from.
• Initial checkpoint: "Plants only photosynthesize to process energy while animals use cellular respiration" is false.

Cellular Respiration and Photosynthesis

• Key Point: Both plants and animals need ATP.
  • Plants use cellular respiration to break down sugar for ATP, similar to animals.
• Connection: Photosynthesis and cellular respiration form a loop.
  • Photosynthesis reactants become cellular respiration products and vice versa.
• Photosynthesis: Occurs in chloroplasts with sunlight, water, and CO2 as reactants; produces glucose and oxygen.
• Cellular Respiration: Occurs in mitochondria, using glucose and oxygen to release ATP, CO2, and water.

Photosynthesis Reaction Types

• Photosynthesis: An anabolic reaction as it builds glucose (larger molecule) from smaller molecules like CO2 and water.
• Cellular Respiration: A catabolic reaction breaking down glucose into smaller molecules, releasing energy.

Photosynthetic Organisms

• Commonly known: Trees, flowering plants, ferns.
• Others include:
  • Green algae (protists)
  • Green seaweed (protists)
  • Lichens (mutualistic relationship between a fungus and an algae)

Photosynthesis Equation

• Basic equation: CO2 + water + sunlight = glucose + oxygen.
• Enzymes and pigments like chlorophyll play essential roles.
• Balance of the equation through stoichiometry.

Plant Anatomy and Photosynthesis

• Water: Absorbed through roots.
• CO2: Enters through stomata, guarded by guard cells.
• Products: Oxygen exits through stomata.

Plant Cell Structure

• Epidermis: Upper and lower surfaces without chloroplasts.
• Mesophyll: Contains chloroplasts, divided into palisade and spongy mesophyll.

Chloroplast Structure

• Chloroplasts contain granum and thylakoids.
• Chlorophyll absorbs light energy.

Photosynthesis Process

• Two Stages: Light reactions and Calvin Cycle.
  • Light reactions (dependent on light) occur in thylakoids, producing ATP and NADPH.
  • Calvin Cycle (light-independent) synthesizes glucose from CO2 in the stroma.

Electromagnetic Spectrum and Chlorophyll

• Sunlight's role in photosynthesis linked to the electromagnetic spectrum.
• Visible Light: The part used in photosynthesis.
  • Plants absorb certain wavelengths and reflect others.
  • Chlorophyll reflects green.

Pigments in Photosynthesis

• Different pigments absorb different wavelengths:
  • Carotenes reflect orange.
  • Xanthophylls reflect yellow.
  • Chlorophyll a (absorbs blue-violet and red) reflects green.

Photosynthesis Reactions

• Light Reactions: Convert solar energy to chemical energy.
  • Major reactant: Water
  • Major product: Oxygen
  • NADP+ acts as an electron carrier.

Calvin Cycle

• Converts CO2 into glucose using ATP and NADPH from light reactions.
• Steps:
  • CO2 combines with RuBP, forming 3-PGA.
  • ATP and NADPH convert 3-PGA to G3P.
  • G3P is used to regenerate RuBP and form glucose.

Conclusion

• Photosynthesis involves complex interactions between light and chemical processes.
• Critical for food production and energy transfer in ecosystems.