Cyclic photophosphorylation is performed by PS-I only. In this process, an electron expelled by the excited photocentre, ie, P700 is returned to it after passing through a series of electron carriers. PS-I is located on both the non-appressed part of grana thylakoids as well as stroma thylakoids, while PS-II is located in the appressed part of grana thylakoids only, stroma thylakoids lack PS-II.