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
- LHC absorbs light, transfers energy to photosystems.
- PSII: Light excites electrons, splits water for electrons, releases O₂.
- Electrons move to cytochrome b6f, create proton gradient.
- PSI: Boosts electron energy, reduces NADP+ to NADPH.
- 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 |
