What is the difference between photosystem I and photosystem II?
Photosynthesis takes place in both light stage and dark stages. The reaction normally takes place in the grana of the chloroplast. The chlorophyll absorbs the light energy to foster photosynthesis. The chlorophyll is what is known as the photosystem. There are different types of chlorophyll and they absorb different types of light wavelength.
The common types of chlorophyll are photosystem I and photosystem II. The discussion provides a detailed insight into the core difference between photosystem I and photosystem II in a tabular form.
What Is Photosystem I?
Photosystem I refers to the collection of the green pigment that occurs on the outer surface of the thylakoid membrane. These pigments mostly absorb the wavelength of about 70nm. It is responsible for facilitating the final stage of light reaction. The core of PSI is made up of psaA and psaB subunits.
What Is Photosystem II?
Photosystem II refers to the collection of chlorophyll pigment that occurs in the inner grana of the thylakoid membrane. These pigments mostly absorb the wavelength of about 680nm. It is responsible for catalyzing the first stage of light reaction. The core of PSII consists of D1 and D2 subunits.
Comparison Chart: Photosystem I vs Photosystem II
| Basic Terms | Photosystem I | Photosystem II |
| Location | The outer surface of the thylakoid membrane | The inner surface of grana of the thylakoid membrane |
| Photocenter | P700 | P680 |
| Absorbing Wavelength | Pigments absorb longer wavelengths of light | Pigments absorb shorter wavelengths of light |
| Photophosphorylation | Occur in both cyclic and non-cyclic photophosphorylation | Occur in cyclic photophosphorylation. |
| Photolysis | Do not happen | Tend to occur |
| Core Function | Synthesis of NADPH | Hydrolysis of water and synthesis of ATP |
| Electron Replacement | Released high energy electrons are replaced by the releasing energy of photolysis. | Released high energy electrons are replaced by the electrons released from photosystem II. |
| Pigments | Consists of chlorophyll B, chlorophyll A-670, Chlorophyll A-680, chlorophyll A-695, chlorophyll A-700 and carotenoids. | Consists of chlorophyll B, chlorophyll A-660, chlorophyll A-670, chlorophyll A-680, chlorophyll A-695, chlorophyll A-700, phycobilins and xanthophylls. |
| Composition of the Core | Compose of psaA and psaB subunits | Compose of D1 and D2 subunits. |
| The ratio of the chlorophyll carotenoid pigments | 20-30:1. | 3-7:1. |
Core Difference Between Photosystem I and Photosystem II
- Photosystem I has pigment system 1 while photosystem II has pigment system 2
- PS1 is located on the outer surface of the thylakoid membrane while PS2 in the grana of the thylakoid membrane
- The light wavelength of PS1 is 700nm while that of PS2 is 680nm
- The core of PS1 contains psaA and psaB subunits while that of PS2 is D1 and D2 subunits.
- PS1 is responsible for the synthesis of NADPH while PS2 for the synthesis of ATP and hydrolysis of water
- PS1 does not experience photolysis of water while PS2 experience photolysis of water
- PS2 involve in cyclic photophosphorylation whereas PS1 involved in both cyclic and non-cyclic photophosphorylation.
- PS1 absorbs longer wavelength whereas PS2 absorb the shorter wavelength
- PS1 result in more reducing agent whereas PS2 generate more oxidizing agent
- PS1 has a photo center of P700 while PS2 has a photo center of P680
Read More: Difference between Oviparous and Viviparous Animals
Comparison Video
Summary
The core difference between photosystem I and photosystem II is that photosystem I occur on the outer surface of the thylakoid membrane while photosystem II occurs in the grana of the thylakoid membrane.