Photosystem I [PSI] :

Location : It is present in the membrane of stroma thylakoids and non-appressed parts of grana thylakoids.

Pigment molecules : In PS I the reaction centre chlorophyll a which has an absorption peak at P₇₀₀. 

Reducing agents : The PS I has following reducing agents viz. ferrodoxin, plastoquinone, cytochrome complex, n-plastocyanin.

Function of PS I : In PS I cyclic photophos-phorylation occurs.

Photosystem II [PS II] :

Location : It is present in appressed part of grana thylakoids.

Pigment molecules : It has in the centre special type of chlorophyll ‘a’ molecules called P_680.

Reducing agents : PS II has quencher, plastoquinone, cytochrome complex and plastocyanin reducing agents.

Function : In PS II non-cyclic photophosphorylation occurs, alongwith photolysis of water.