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What are Photosystem? Definition and Summary of PS I and PS II

What are Photosystems antenna molecule complex?
The light harvesting complexes (LHC) formed by photosynthetic pigments are located on the thylakoid membrane of the chloroplast in two pigment systems called as Photosystem I and Photosystem II.

Definition: Each photosystem consists of collection of chlorophyll-a molecules, accessory pigments and associated proteins present on the surface of the thylakoid membrane of the chloroplast.
Each photosystems consists of two closely linked components namely reaction centre and antenna molecules.
Photosystems antenna molecule complex
Reaction centre molecules are the primary pigment which is chl-a molecules in green plants. Accessory pigments that surround the reaction centre forms the antenna complex. Accessory pigments include chl-b, carotenes and xanthophylls.

The antenna molecules made up of accessory pigments of photosystems absorb photons (light energy) get excited and transfer the excitation energy to the adjacent accessory pigment and finally reaching the reaction centre by resonance transfer.

Photosystem I (PS I): Reaction centre chl molecule has light absorption peak at 700 nm (P700). PS I occurs mostly on the inter-granal lamellae of the chloroplast. PSI uses light energy to convert NADP+ to NADPH + H+


Photosystem II (PS II): Reaction centre chl molecule has light absorption peak at 680 nm (P680). PS II occurs mostly on the granal lamellae of the chloroplast. PS II uses light energy for photolysis of H2O molecules, or oxidizing H2O molecules producing electrons, protons (H+) and O2.
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