Photosynthesis Lecture Notes

Introduction

• Presenter: Dr. Demi
• Chapter: A-Level Biology, Chapter 13: Photosynthesis
• Purpose of the Video: Revision and pre-exposure to Photosynthesis
• Video Structure: Split into 2 parts; today's focus is on the process, structure of chloroplasts, and light-dependent and light-independent reactions

Key Themes

• Photosynthesis: Essential process for plant biology, often considered challenging by students
• Structure of Videos: Designed for both revision and foundational understanding

Structure of Chloroplasts

• Chloroplasts: Biconvex disk-shaped, 3-10 micrometers in diameter, site of photosynthesis
• Double Membrane Organelles: Both mitochondria and chloroplasts have double membranes, linked to the endosymbiont theory
• **Internal Structures: Grana: Stacks of thylakoids, site of light-dependent reactions
  • Stroma: Fluid inside chloroplasts, site of light-independent reactions**

Thylakoid and Photosystem

• Thylakoids: Contain photosystems for harvesting light
• Photosystem: Funnel-like structure that traps light and passes it through pigments (chlorophyll a, chlorophyll b, and accessory pigments)

Light-Dependent Reactions

• Stages: Two stages - Light-Dependent and Light-Independent
• Photosystems I and II: Harvest light differently
  • Photosystem I (P700): Releases electrons, leading to ATP production
  • Photosystem II (P680): Splits water (photolysis), produces O2, and releases electrons
• ATP and NADPH Production: Produced during light-dependent reactions and carried over to light-independent reactions

Light-Independent Reactions (Calvin Cycle)

• Overview: Takes place in the stroma, does not require light
• Key Steps:
  1. Carbon Fixation: CO2 combines with ribulose bisphosphate (RuBP) catalyzed by Rubisco enzyme
  2. Formation of Intermediate: Produces glycerate 3-phosphate (3-carbon compound)
  3. Use of ATP and NADPH: Converts glycerate 3-phosphate to glucose
  4. Regeneration of RuBP: Cycle continues

Essential Points

• Photosynthesis Reaction: CO2 + H2O + light → C6H12O6 + O2
• Importance of Photosynthesis: Balancing environmental O2 and CO2 levels
• Types of Reactions: Cyclic and non-cyclic phosphorylation

Important Terminologies

• Photolysis: Splitting of water using light
• Phosphorylation: Production of ATP
• Chemiosmosis: Process driving ATP production

Summary

• Photosynthesis: Involves both light-dependent and light-independent reactions, interconnected by ATP and NADPH
• Importance: Crucial for the survival of plant cells and overall ecosystem balance
• Upcoming Topics: Factors affecting photosynthesis, C4 plants