Which photosystem is involved in cyclic photophosphorylation?
a)	PS-II	b)	PS-I
c)	Xanthophyll and PS-II	d)	Xanthophyll and PS-I

(b)

ATP is synthesised by cells (in mitochondria and chloroplast) and the process is named as phosphorylation. Photophosphorylation is the synthesis of ATP from ADP and inorganic phosphate in the presence of light. When the two photosystems work in a series, first PS-II and then the PS-I, a process called non-cyclic photophosphorylation occurs. The two photosystem are connected through an electron transport chain, as seen earlier- in the Z scheme. Both ATP and NADPH +  are synthesised by this kind of electron flow. When only PS-I is functional, the electron is circulated within the photosystem and the phosphorylation occurs due to the cyclic flow of electrons