Photosystems comprise a reaction center and an antenna complex. Typically, there are two photosystems categorised on the basis of the different absorption wavelengths of the chlorophyll. The two photosystems are Photosystem I and Photosystem II.
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Both these photosystems PS I and PS II are multi-subunit membrane-protein complexes participating in oxygenic photosynthesis. The pigment that is mainly involved in trapping light energy is chlorophyll. Thus, it is called a pigment system or photosystem. While the pigment system 1 comprises chlorophyll A-695, chlorophyll A-670, chlorophyll A-680, chlorophyll A-700, chlorophyll B, and carotenoids, pigment system 2, on the other hand, comprises chlorophyll A-670, chlorophyll A-660, chlorophyll A-695, chlorophyll A-680, chlorophyll A-700, chlorophyll B, phycobilins and xanthophylls.
The key difference between both the photosystems – Photosystem I and photosystem II is that PS I tends to absorb light of longer wavelengths > 680nm, whereas PS II absorbs light of shorter wavelengths <680 nm.
Key Differences between Photosystem 1 and Photosystem 2
The table below depicts the differences between Photosystem 1 and Photosystem 2.
|These use light energy to convert NADP+ to NADPH2
|These are protein complexes absorbing light energy. They function in the dissociation of water molecules.
|Seen at the outer surface of the grana thylakoid membrane
|Seen at the inner surface of the grana thylakoid membrane
|Approximately 700 nm
|A comparatively fewer number of proteins (about 15 subunits)
|A multisubunit complex (about 25-30 subunits)
|Iron-sulphur type reaction centre
|Quinone type reaction centre
|Chlorophyll a is more compared to chlorophyll b
|Chlorophyll b is more compared to chlorophyll a
|Cyclic and non-cyclic photophosphorylation
|Non-cyclic photophosphorylation only
|Comprises chlorophyll A-695, chlorophyll A-670, chlorophyll A-680, chlorophyll A-700, chlorophyll B, and carotenoids.
|Comprises chlorophyll A-670, chlorophyll A-660, chlorophyll A-695, chlorophyll A-680, chlorophyll A-700, chlorophyll B, phycobilins and xanthophylls.
|In Cyclic photophosphorylation – ATP synthesis
In non-cyclic photophosphorylation – NADPH synthesis
|Hydrolysis of water and ATP synthesis
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