Lecture Notes on Photosynthesis

Introduction

• Speaker: Dr. Sammy, Entomologist
• Topic: Photosynthesis
  • Essential for most life on Earth.
  • Converts solar energy into physical matter.

Photosynthesis Basics

• Common misunderstanding: "Plants make sugar from light."
• Light:
  • Not a substance, but a form of energy.
  • Energy: Capacity to do work.
• Etymology of 'Photosynthesis':
  • Greek origins: "Photo" (light) + "synthesis" (to put together).
  • Using light to drive reactions combining ingredients into new products.

The Process

• Ingredients:
  • Carbon dioxide (CO2)
  • Water (H2O)
• Products:
  • Carbohydrate (e.g., glucose)
  • Oxygen (O2) as a byproduct
• Analogy:
  • Like baking a cake using heat to combine ingredients.

Chemical Reaction

• Photosynthesis Equation:
  • 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2
• Energy Storage:
  • Carbohydrates store more chemical energy than CO2 and H2O.
  • Reactions that store energy: Endergonic reactions.
• Chloroplast:
  • Organelles in plant cells where photosynthesis occurs.
  • Contains chlorophyll (green pigment).

Process Segmentation

• Two Main Steps:
  1. Charging Step (Light-dependent reactions):
     • Location: Thylakoid
     • Process: Converts solar energy into ATP (Adenosine Triphosphate).
     • ATP: Energy currency of the cell.
     • Creates NADPH (electron carrier).
  2. Synthesis Step (Light-independent reactions/Calvin Cycle):
     • Location: Stroma
     • Function: Fixates CO2 into organic carbon (e.g., glucose).
     • Uses ATP and NADPH.

Detailed Mechanism

• Light-dependent Reactions:

  • Occur in thylakoid membrane.
  • Photons excite chlorophyll, creating an energy imbalance.
  • ATP is formed by adding a phosphate to ADP.
  • NADP+ is converted to NADPH.
  • Oxygen is released as a byproduct.

• Light-independent Reactions (Calvin Cycle):

  • Occur in chloroplast stroma.
  • Use ATP and NADPH to fixate carbon and form glucose.
  • Byproducts (ADP and NADP+) are recycled.

Importance of Photosynthesis

• Converts solar energy to chemical energy.
• Provides energy for plants and animals.
• Plants fill the atmosphere with oxygen.

Conclusion

• Photosynthesis is crucial for life on Earth.
• Carbon in living organisms originates from atmospheric CO2.
• Plants play a vital role in converting inorganic carbon to organic matter and maintaining atmospheric oxygen.

Takeaway: Appreciate plants for their essential role in sustaining life.