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.
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 PS 1 comprises chlorophyll A-695, chlorophyll A-670, chlorophyll A-680, chlorophyll A-700, chlorophyll B, and carotenoids, PS 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.
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These use light energy to convert NADP+ to NADPH2 |
These are protein complexes absorbing light energy. They function in the dissociation of water molecules. |
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Seen at the outer surface of the grana thylakoid membrane |
Seen at the inner surface of the grana thylakoid membrane |
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P700 |
P680 |
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Approximately 700 nm |
Approximately 680nm |
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A comparatively fewer number of proteins (about 15 subunits) |
A multisubunit complex (about 25-30 subunits) |
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Iron-sulphur type reaction centre |
Quinone type reaction centre |
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Chlorophyll a is more compared to chlorophyll b |
Chlorophyll b is more compared to chlorophyll a |
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No |
Yes |
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Cyclic and non-cyclic photophosphorylation |
Non-cyclic photophosphorylation only |
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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. |
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In Cyclic photophosphorylation – ATP synthesis In non-cyclic photophosphorylation – NADPH synthesis |
Hydrolysis of water and ATP synthesis |
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