Difference Between Photosystem I and Photosystem II

Main Difference

A photosystem is a process in plants and other organisms to absorb sunlight and use it as a source of energy; this system enables plants to convert light energy into chemical energy. There are two photosystems in the thylakoid membrane of chloroplasts of leaves in plants. These are Photosystem I and Photosystem II. Photosystem I is the system that absorbs light photons of the wavelength of 700nm, whereas photosystem II absorbs the photons of the wavelength of 680nm. Photosystem I is so named because it was discovered first and photosystem II was discovered later. But if we see their function, photosystem II comes before photosystem I. The only major difference between photosystem I and photosystem II is of the wavelength of light that is absorbed by it. However, both are having equal importance in the process of photosynthesis.

Comparison Chart

Photosystem IPhotosystem II
LightPhotosystem I absorbs light of 700nm wavelengths.Photosystem II absorbs light of 680nm wavelengths.
Active CenterPhotosystem I has active center P700.Photosystem II has active center P680.
PhotophosphorylationPhotosystem I is involved in cyclic and non-cyclic photophosphorylation.Photosystem II is involved only in non-cyclic photophosphorylation.
Main FunctionThe main function of photosystem I is the synthesis of ATP.The main function of photosystem II is a synthesis of ATP and photolysis of water.
Located atPhotosystem I is located at the outer surface of grana of thylakoid.Photosystem II is located in at the inner surface of grana of thylakoid.
Binding ProteinsPhotosystem I has larger binding proteins.Photosystem II has smaller binding proteins.

What is Photosystem I?

Photosystem I is one of the systems of photosystems involved in photosynthesis. Photosystem I is so named because it was discovered first and photosystem II was discovered later.

Photosystem I is located at the outer surface of grana of thylakoid. Photosystem I is a complex of collections of proteins. It is sensitive to light, and it absorbs light of about 700nm. Its pigments absorb light and use it as a source of energy. And it is not associated with photolysis of water. Here light energy is converted into chemical energy and finally used in the process of photosynthesis. The main function of photosystemI is synthesizing of ATP. Photosystem I is involved in cyclic and non-cyclic photophosphorylation. Photosystem I includes following pigments:

  1. Chlorophyll -a 670
  2. Chlorophyll -a 680
  3. Chlorophyll -a 695.
  4. Chlorophyll -a 700.
  5. Chlorophyll b

What is Photosystem II?

Photosystem II is one of a system of photosystems involved in photosynthesis. Photosystem II was discovered later. But if we see their function, photosystem II comes before photosystem I. Photosystem II is located in at the inner surface of grana of thylakoid. Photosystem II has a smaller binding protein as compare to photosystem I that has MW of 110,000. It absorbs light of about 680nm. Its pigments absorb light and use it as a source of energy. And it is associated with photolysis of water. Here light energy is converted into chemical energy and finally used in the process of photosynthesis. The main function of photosystem II is the synthesizing of ATP and photolysis of water. Photosystem II is involved only in non-cyclic photophosphorylation.

Photosystem II includes following pigments:

  1. Chlorophyll -a 660
  2. Chlorophyll -a 670
  3. Chlorophyll -a 680.
  4. Chlorophyll -a 695.
  5. Chlorophyll -a 700.
  6. Chlorophyll

Photosystem I vs. Photosystem II

  • Photosystem I absorbs light of 700nm wavelengths, whereas photosystem II absorbs light of 680nm wavelengths.
  • Photosystem I has active center P700 while photosystem II has active center
  • Photosystem I is involved in cyclic and non-cyclic photophosphorylation, whereas photosystem II is involved only in non-cyclic photophosphorylation.
  • The main function of photosystem I is synthesizing of ATP, on the other hand, the main function of photosystem II is synthesizing of ATP and photolysis of water.
  • Photosystem I is located at the outer surface of grana of thylakoid while, photosystem II is located in at the inner surface of grana of thylakoid.
  • Photosystem I has larger binding proteins, whereas photosystem II, has smaller binding proteins.

Comparison Video

YouTube video
Janet White

Janet White is a writer and blogger for Difference Wiki since 2015. She has a master's degree in science and medical journalism from Boston University. Apart from work, she enjoys exercising, reading, and spending time with her friends and family. Connect with her on Twitter @Janet__White

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