Question

Differentiate between PS-I and PS-II.

Answer 1

In plants, photosynthesis takes place in two processes, one is a light-dependent reaction and another is a carbon-assimilation reaction. PS stands for Photosystem. In both the processes energy molecules are liberated.

Complete answer:
The main differences between Photosystem I and II are:

The outer surface of the thylakoid membrane is the location for PS-I and the outer surface is the location for PS-II towards the stroma. The center for PS-I is P700 and the center for PS-II is P680. The centers are named according to the wavelength of light they absorb. PS-I absorbs a longer wavelength of light of 700nm whereas PS-II absorbs 680nm which is a shorter wavelength of light.
Photosystem I use light to convert NADP+ to NADPH2 in the presence of chlorophyll and other pigments. Photosystem II absorbs light and transfers electrons from water to plastoquinone. This dissociates the water molecules and produces hydrogen proton (H+) and oxygen (O2).Thus, the main function of Photosystem I is to synthesize NADPH whereas in Photosystem II hydrolysis of water takes place. Photosystem II synthesizes ATP molecules.
Photosystem I involve both cyclic and non-cyclic phosphorylation. In Photosystem II, only non-cyclic phosphorylation is observed.
The two subunits of Photosystem I are psaA and psaB. The two subunits of Photosystem II are D1 and D2.
The process of photolysis occurs only in Photosystem II and not in Photosystem I. In the Photosystem-II molecular oxygen is evolved and photolysis of water takes place.

Note:
ATP and NADPH are energy molecules produced by PS-II and PS-I respectively.In Photosystem I process, molecular oxygen is not involved. Photosystem I and II produce energy that is used in the Calvin cycle.