Lecture Notes: Chapter 10 - Photosynthesis

Overview

• Photosynthesis converts solar energy into chemical energy in chloroplasts.
• It supports nearly all life by producing energy and oxygen.
• Autotrophs (self-feeders) conduct photosynthesis and produce organic molecules from CO2 and inorganic substances.
• Heterotrophs (other-feeders) consume these organic molecules to sustain themselves.

Types of Photosynthesizers

• Plants and Algae:
  • Eukaryotic photosynthesizers include multicellular algae and unicellular organisms like euglena.
• Bacteria:
  • Prokaryotic photosynthesizers include cyanobacteria and purple sulfur bacteria.

Structure of Chloroplasts and Leaves

• Chloroplasts, located mainly in mesophyll cells of leaves, carry out photosynthesis.
• Key Structures:
  • Stomata: Pores on the underside of leaves for gas exchange.
  • Chloroplast Anatomy:
    • Outer and inner membranes.
    • Thylakoids: Membranous sacs stacked into grana.
    • Stroma: Fluid surrounding the thylakoids.

Photosynthesis Equation

• Chemical Equation:
  • Reactants: Light energy, CO2, and water.
  • Products: Glucose and oxygen.
• Photosynthesis is the reverse of cellular respiration.

Importance of Photosynthesis

• Produces oxygen for aerobic organisms.
• Generates glucose, the primary energy source for heterotrophs.
• Regulates atmospheric CO2, helping mitigate climate change.

Photosynthesis Process

Light Reactions

• Location: Thylakoid membranes.
• Reactants: Light and water.
• Products: ATP, NADPH, and oxygen.
• Mechanism:
  • Chlorophyll absorbs sunlight, energizing electrons.
  • Water is split, releasing oxygen and providing electrons.
  • ATP and NADPH are produced for the Calvin cycle.

Calvin Cycle

• Location: Stroma.
• Process:
  • CO2 is fixed into organic molecules.
  • ATP and NADPH are used to convert CO2 into glucose.
• Phases:
  1. Carbon Fixation
  2. Reduction
  3. Regeneration of RuBP

Energetics of Light

• Electromagnetic Spectrum:
  • Visible light ranges from 380 to 740 nm.
  • Shorter wavelengths (e.g., gamma rays) have higher energy.
• Plant Pigments:
  • Chlorophyll a and b, and carotenoids capture light energy.
  • Green light is reflected, not absorbed, making plants appear green.

Role of Photosystems

• Photosystem II: Captures light energy to energize electrons.
• Photosystem I: Further energizes electrons for NADPH production.
• Electron Transport Chain: Transfers electrons, pumps protons to create a gradient for ATP synthase.

Differences in Electron Flow

• Linear Electron Flow: Produces ATP, NADPH, and oxygen.
• Cyclic Electron Flow: Only produces ATP, allowing for adjustments in energy needs.

Chloroplast and Mitochondrion Comparisons

• Both organelles have electron transport chains and ATP synthesis mechanisms.
• They share similarities in proton concentration gradients and locations of ATP synthesis.

Key Takeaways

• Photosynthesis is vital for life; it provides energy and oxygen to ecosystems.
• Understanding the mechanisms of light reactions and the Calvin cycle is essential for grasping photosynthesis.
• Photosynthesis and cellular respiration are interdependent processes, balancing energy and matter in ecosystems.

End of Chapter 10

These notes provide a comprehensive summary of the photosynthesis process as discussed in the lecture.