<P> In the light - dependent reactions ( mainly three vital reaction steps : ( I ) Hill and Bendall 's Z - scheme of cyclic and non-cyclic reactions , ( II ) Mitchell 's chemi - osmosis for ATP synthesis and ( III ) Dolai 's S - state diagrams in water - splitting ) , one molecule of the pigment chlorophyll absorbs one photon and loses one electron . This electron is passed to a modified form of chlorophyll called pheophytin , which passes the electron to a quinone molecule , starting the flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP to NADPH . In addition , this creates a proton gradient ( energy gradient ) across the chloroplast membrane , which is used by ATP synthase in the synthesis of ATP . The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis , which releases a dioxygen ( O ) molecule as a waste product . </P>
what is the first basic process in the light reaction of photosynthesis
one molecule of the pigment chlorophyll absorbs one photon and loses one electron