Explanation

Non-cyclic photophosphorylation includes both photo system II and I. The process requires an external electron donor. The electrons released during photolysis of water are picked up by photocentre of PS-II called$P_{680}$. The flow of electrons is unidirectional. Electrons are not cycled back and are used in the reduction of NADP to$NADPH_{2}$. In this, high energy electrons released from ‘$P_{680}$’ do not return to ‘$P_{680}$’ but pass through phaeophytin, plastoquinone, cytochrome-$b_{6} - f$ complex, plastocyanion and then enter$P_{700}$. In transfer of electrons from PQ to Cytochrome-$b_{6} - f$ complex, ATP is synthesised.