Summary of Light Reactions in Photosynthesis

PHOTOSYNTHESIS SUMMARY

Overview

  • Photosynthesis is a multi-step process, not a single chemical reaction.

  • General Equation: 6CO2(g)+6H2O(l)+extsolarenergy<br>ightarrow6O2(g)+C6H12O6(aq)6CO₂(g) + 6H₂O(l) + ext{solar energy} <br>ightarrow 6O₂(g) + C₆H₁₂O₆(aq).

Light Reactions (Light-Dependent Reactions)

  • Occur in thylakoid discs.

  • Main products: ATP and NADPH.

  • Water (H₂O) is oxidized; oxygen is released as waste.

Structure of Thylakoid Disc

  • Contains photosystems (clusters of pigments).

  • Primary pigment: Chlorophyll (a), which reflects green light, absorbs blue/red light.

  • Photosystem II and I are connected by an electron transport chain.

Key Processes

  • Photolysis: Reaction utilizing light to split water into rac12O2+2H++2e−rac{1}{2} O₂ + 2 H^+ + 2 e^-.

  • Electron Transport Chain (ETC):
      - Excited electrons are transported, losing energy to synthesize ATP.
      - Energy loss from electrons is harnessed to pump H+ ions into the thylakoid space.
      - Chemiosmosis drives ATP production via ATP synthase as H+ ions flow back to the stroma.