Light Harvesting Complex (LHC)

  • Captures light.
  • Made of proteins and pigments.
  • Transfers energy to photosystems.
Feature Photosystem I (PSI) Photosystem II (PSII)
Location in Chloroplast Thylakoid membranes, primarily in stroma lamellae Thylakoid membranes, primarily in grana
Core Reaction Center Pigment P700 P680
Primary Function Absorbs light to energize electrons, reduces NADP+ to NADPH Absorbs light to energize electrons, splits water to replace lost electrons
Light Absorption Peak Around 700 nm Around 680 nm
Electron Source From PSII through the electron transport chain Water molecules (H₂O)
Oxygen Production No Yes, as a byproduct of water splitting
Role in Electron Transport Chain End point for electron transfer, reduces NADP+ Starting point for electron transfer
Associated Complexes Light-harvesting complex I, ferredoxin, NADP+ reductase Light-harvesting complex II, oxygen-evolving complex

Photosynthetic Electron Transport Chain

  • Involves Photosystem II (PSII), cytochrome b6f, Photosystem I (PSI).
  • Transfers electrons, produces ATP and NADPH.
  • Splits water, releases oxygen.

Process Summary

  1. LHC absorbs light, transfers energy to photosystems.
  2. PSII: Light excites electrons, splits water for electrons, releases O₂.
  3. Electrons move to cytochrome b6f, create proton gradient.
  4. PSI: Boosts electron energy, reduces NADP+ to NADPH.
  5. ATP synthase uses gradient to make ATP.
Feature Non-Cyclic Photophosphorylation Cyclic Photophosphorylation
Photosystems Involved Photosystem I and II Photosystem I only
Electron Source Water Photosystem I (recycled electrons)
Products ATP, NADPH, Oxygen ATP only
Oxygen Production Yes (from water splitting) No
NADPH Production Yes No
Role in Photosynthesis Primary pathway, supports the Calvin cycle and oxygen production Supplementary, mainly ATP production


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