Difference between Photosystem 1 and Photosystem 2

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.

Photosystem 1

Photosystem 2

What are they?

These use light energy to convert NADP+ to NADPH2

These are protein complexes absorbing light energy. They function in the dissociation of water molecules.

Where is it found?

Seen at the outer surface of the grana thylakoid membrane

Seen at the inner surface of the grana thylakoid membrane

Reaction centre

P700

P680

Wavelength pigments absorbs

Approximately 700 nm

Approximately 680nm

Composition of its core complex

A comparatively fewer number of proteins (about 15 subunits)

A multisubunit complex (about 25-30 subunits)

Type of reaction centre

Iron-sulphur type reaction centre

Quinone type reaction centre

Pigment richly supplied with

Chlorophyll a is more compared to chlorophyll b

Chlorophyll b is more compared to chlorophyll a

Involved in the photolysis of water

No

Yes

Participates in which type of photophosphorylation

Cyclic and non-cyclic photophosphorylation

Non-cyclic photophosphorylation only

Pigments involved

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.

Important function

In Cyclic photophosphorylation – ATP synthesis

In non-cyclic photophosphorylation – NADPH synthesis

Hydrolysis of water and ATP synthesis

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