Photosystem I vs Photosystem II: Difference and Comparison

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Key Takeaways

  1. Photosystem I is responsible for the production of NADPH, while photosystem II produces ATP.
  2. Photosystem I is associated with photosystem II in the electron transport chain, while photosystem II works independently.
  3. Photosystem II is sensitive to herbicides, while photosystem I am not.

Photosystem I vs. Photosystem II 

Photosystem I (PS I) is the second protein complex in the light-dependent reactions of photosynthesis. It is located in the thylakoid membrane. Photosystem II (PS II) is the first protein complex in the light-dependent reactions of photosynthesis. It is located in the thylakoid membrane and is responsible for the initial capture of light energy.

Photosystem I vs Photosystem II

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

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


Science Quiz

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Comparison Table

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 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 the granum thylakoid and stroma thylakoid of green plants and algae. Photosystem I contain two components – Photosynthetic Unit and Electron Carrier.

Photosystem I comprises 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 green plants and algae. It also contains two components, Photosystem I: 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 a membrane-embedded protein complex with 20 subunits and more than 50 cofactors.

The primary 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 at which Photosystem II is 680nm.



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