Photosynthesis Study Notes

Concept 8.1: Photosynthesis Overview

  • Photosynthesis converts light energy into chemical energy, enabling organic compound synthesis.
  • Photosynthetic processes originated from photosynthetic bacteria; chloroplasts evolved from these prokaryotes (endosymbiotic theory).

Chloroplast Structure

  • Major sites of photosynthesis are the chloroplasts, primarily located in leaf mesophyll cells.
  • Chloroplasts contain:
    • A double membrane envelope
    • Stroma: dense fluid inside the chloroplast
    • Thylakoids: membrane sacs where chlorophyll is embedded, forming stacks called grana.

Photosynthesis Equation

  • Simplified overall equation: 6CO<em>2+6H</em>2O+light→C<em>6H</em>12O<em>6+6O</em>26 CO<em>2 + 6 H</em>2O + light \rightarrow C<em>6H</em>{12}O<em>6 + 6 O</em>2
  • Water is split to provide O2, and carbon is fixed into glucose.

Tracking Atoms in Photosynthesis

  • Experimental evidence shows O2 released comes from H2O, not CO2 (C.B. van Niel's research).
  • Photosynthesis is a redox process; water is oxidized and CO2 is reduced.

Light Reactions

  • Convert solar energy into chemical energy (ATP and NADPH).
  • Occur in the thylakoid membranes where water is split, releasing O2 and transferring electrons to form NADPH and ATP.

The Calvin Cycle

  • Takes place in the stroma; uses NADPH and ATP from light reactions to convert CO2 into carbohydrates (sugar synthesis).
  • Carbon fixation occurs, followed by reduction of carbon to carbohydrates.

Light Properties and Photosynthetic Pigments

  • Light is electromagnetic radiation; visible light is the portion driving photosynthesis (380-750 nm).
  • Chlorophyll absorbs primarily violet-blue and red light, reflecting green.

Photosystem Function

  • Photosystems (PS I and PS II) are complexes of chlorophyll and other pigments that capture light energy.
  • Linear electron flow energizes electrons through these systems, producing ATP and NADPH for the Calvin cycle.

Chemiosmosis Mechanism

  • Similar to mitochondria; protons (H+) are pumped across membranes to generate ATP via ATP synthase as they diffuse back across the membrane.

Summary of Light Reactions

  • Light reactions generate ATP and NADPH, with O2 released as a by-product. Products are utilized in the Calvin cycle for sugar synthesis.