Difference Between Photosystem I and Photosystem II

Photosystem I is also written as P700. Its main function is to form a molecule of NADPH. The primary electron acceptor of Photosystem I is Plastocyanin.

The main function of the Photosystem is to perform hydrolysis of water along with ATP synthesis. The primary electron acceptor of the same is Plastoquinone, and the three major electron acceptors of Photosystem II are – Unknown Q, Plastoquinone, Cytochrome b559.

Comparison Table Between Photosystem I and Photosystem II

Parameters of ComparisonPhotosystem IPhotosystem II
Present In Photosystem is present in the granum and stroma thylakoid.Photosystem II is present in the granum thylakoid only.
Wavelength Absorb It absorbs a wavelength of about 700nm.It absorbs a wavelength of about 680nm.
Number of Electron Carriers It has six in total electron carriers.It has three electron carriers in total.
Electron AcceptorPlastocyaninPlastoquinone
Formation of NADPHThe end product is NADPH.There is no formation of NADPH.
Reaction CentreP700 nmP680 nm
Photolysis of WaterPhotosystem I is not used in the photolysis of water.Photosystem II is used in photolysis.
Content of ChlorophyllThe content of chlorophyll a is more compared to the chlorophyll b content.The content of chlorophyll b is more than chlorophyll a.

What is Photosystem I?

Photosystem I is present in both granum thylakoid as well as stroma thylakoid of green plants and algae. Photosystem I contain two components – Photosynthetic Unit and Electron Carrier.

Photosystem I is made up of two protein-rich subunits, which are – psaA and psaB. It absorbs a wavelength of about 700nm.

The function played by the Photosystem is that it helps in the formation of NADPH and ATP in the light reaction.

What is Photosystem II?

Photosystem II is present in granum thylakoid only in the green plants and algae. It also contains two components like Photosystem I, which are – Photosynthetic Unit and Electron Carrier.

The reaction center consists of chlorophyll, a molecule that absorbs the wavelength of 680nm, while the light-harvesting complex has 200 molecules of chlorophyll a and b.

The core composition of the photosystem is said to be made up of two subunits named D1 and D2. It is known as a membrane-embedded protein complex that has 20 subunits and more than 50 cofactors.

The major role performed by Photosystem II is that it helps in the hydrolysis of water and ATP synthesis in the mitochondria.

Main Differences Between Photosystem I and Photosystem II

  1. The location of the presence of Photosystem I is that it is present in the stroma and granum thylakoid, while Photosystem II is present only in the granum thylakoid. 
  2. The wavelength at which Photosystem I is 700nm while the wavelength at which Photosystem II is 680nm.


Plants produce energy via making food with the help of two types of reactions named Light Reactions and Dark Reactions. The light reactions involve both cyclic and non-cyclic photophosphorylation.

Both the photosystems have different absorbing wavelengths as the first absorbs at a higher wavelength of about 700nm while the second absorbs the sunlight at a lower wavelength of 680nm.

The core component of both the photosystems are also different, but one same thing is that both are made up of in two subunits which is psaA and psaB for Photosystem I and D1 and D2 is said to be the two subunits for Photosystem II.

Photosystem I is a major part of non-cyclic photophosphorylation, generally known as Hills Reaction, while Photosystem II plays a major role in non-cyclic photophosphorylation.


  1. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1399-3054.1992.tb01328.x
  2. https://onlinelibrary.wiley.com/doi/full/10.1002/anie.201303671
  3. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1751-1097.1987.tb08413.x
  4. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1399-3054.1991.tb05101.x

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