What Are The Differences Between Photosystem 1 And Photosystem 2?

Photosystems can be difficult to understand for Biology students. In this article we will explain what photosystems are, describe their components, and then distinguishes the things that make them different from each other. 

What Are Photosystems?

There are two multicomponent complex organometallic membrane systems (or Photosystems) that accept light with wavelengths of 700 nm and 680 nm, respectively.

  • Each photosystem is replenished by the electrons lost as a result of the secondary electron deficiency of an electron, but the source of the electrons is different for the PS II that obtains its electrons from the PS I by an electron transport chain, while the PS I, in turn, acquires its electrons from water.
  • Photosystems are required to take part in photosynthesis, and have roles in chlorophyll-containing thylakoid membranes of algae, cyanobacteria, and plants in particular. Everyone knows that plant and photosynthetic cells absorb sunlight, which is carried via chlorophyll molecules.
  • Energy received from light is first converted to chemical energy during the stage of photosynthesis. This process follows a series of chemical reactions, known as light-dependent reactions.
  • Phytochemicals like chlorophyll a, chlorophyll b and carotenoids are found in the thylakoid membranes of the photosynthetic chlorplast. The photosynthesis system consists of light chlorophylls, proteins, and other pigments.
  • Photosynthesis excites these pigments after absorbing light, then an electron is promoted to a higher-energy orbital.
  • Excited pigment passes its energy to other pigment by the resonance energy transfer, and this is the actual transfer of electromagnetic interactions. Further, in turn, the neighbouring pigment transfers energy to pigment and the process is repeated many times.
  • To these pigment molecules, all the light’s energy enters into the core region of the photosystem known as a reaction center.
  • The Photosystem I or PSI protein is situated inside the thylakoid membrane and is itself composed of multiple subunits. The initial stage of the photo-driven electron transport process is the capture of the solar energy needed by the mitochondria.


What’s The Difference Between Photosystem 1 and 2

Photosystem 1 Photosystem 2
Have the ability to absorb wavelength of 700nm. Have the ability to absorb wavelength of 680nm.
Carries 6 electrons. carries 3 electrons only.
Exist in Stroma Thylakoid and granum. exist only in granum thylakoid only.
The ultimate product it produces is NADPH. No NADPH is produced as an ultimate product.
psaA and psaB are the 2 subunits it has. D1 and D2 are 2 subunits it has.
There is no occurrence of photolysis. Occurrence of photolysis exists.

Photosystem 1

PS I is the system where the chlorophyll and other pigments are gathered and absorb the wavelength of light at 700 nanometers. It is the series of reactions, and its reaction center comprises chlorophyll a-700, with the two subunits namely psaA and psaB.

The subunits of PSI is larger than those of P-SII. This system also contains (the chlorophyll a -670, chlorophyll a -680, chlorophyll a -695, chlorophyll b, and carotenoids). Startups absorbed the old wavelengths as they passed into the photosystem II reaction center. Eventually, photons become high-energy electrons and release a number of electron carriers before undergoing a series of electron carriers and finally arising from NADP reductase to NADPH, which becomes involved in the Calvin cycle.

As such, the major objective of this integral membrane protein complex is to use light energy to generate ATP and NADPH. Plastocyanin-ferredoxin oxidoreductase also used as title for Photosystem I.


Photosystem 2

The protein complex consisting of more than 20 subunits and around 100 cofactors is a part of the light-receiving antenna. In the reaction center, light is absorbed with chlorophyll, carotenoids, and phycobilin becoming excited. The parts that are responsible for the absorption of light and chlorophyll, along with other pigments, are located at the core of chloroplasts.

As previously stated, the light transmitted through the left side of the PS II container is absorbed by P680. In this high-energy state of the electron, P680 donates an electron, which in turn becomes the primary acceptor.

When the P680 loses an electron and gains positive charge, it takes an electron for replenishment which is carried out by splitting waterpeices. Bacteria that oxidize manganese eightfold produce an oxygen molecule and two tackles (hydrogen ions).

The opposing mechanism is opposite in nature to the water-dissociated constituent of the photosystem II process in PS II, but water is utilized to synthesize NADPH and ATP. The Photosystem II is the same as water-plastoquinone dioxidase, and is also called the first protein complex in the light reaction.

Major Differences Between Photosystems

  • Photosystem I is located on the outside of the thylakoid membrane and is paired to the special photo-resynthesis center called P700, whereas PS II is located on the inside of the thylakoid membrane and the reaction center called P680.
  • Phtosynthetase 1 acquires the hues light which is a profoundly highlighted array, while the photosynthetase 2 converts hues that are progressively watered down.
  • The cyclic photophosphorylation that takes place in polypeptide syntheses is carried out by PS I, and the non-cyclic photophosphorylation that takes place in polypeptide syntheses is carried out by PS II.
  • The primary function of this system is the synthesis of NADPH from PS II, where it receives electrons from PS II. The PS II organ performs the hydrolysis of water as well as the ATP synthesis process.
  • The core part of the PSI are composed of the psaA and psaB subunits, and PS II is made up of the D1 and D2 subunits.
  • Photosystem I or PS I and Photosystem II or PS II are the major protein-mediated complex, whose main purpose is to produce energy (ATP and NADPH2), which is used in the Calvin cycle.
  • It begins with P700, chlorophyll, and other pigments; PS II is the reaction that absorbs light energy, involving P680, chlorophyll, and other accessory pigments; and water, which is broken down into protons (H ) and oxygen molecules through the dissociation of water molecules.


We can say that in plants, photosynthesis involves two major processes: the light-dependent reactions and the carbon assimilation reaction that is given misleadingly the moniker of dark reactions. In the light reactions, the photosynthetic pigments and chlorophyll absorb light and turn into adenosine triphosphate (ATP) and NADPH.

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