Z scheme of electron transport was 1^st proposed by

Z scheme of electron transport was 1^st proposed by Hill and Bendall. It includes both the PS I and PS II photosystems.
The Z scheme is an energy diagram for electron transfer in the "light reactions" of plant photosynthesis. A mechanism to convert light energy into electrical energy, which is then converted into chemical energy in the form of reduced NADPH and ATP.
It applies equally well to photosynthesis by algae and cyanobacteria. The vertical energy scale shows each molecule's ability to transfer an electron to (i.e., to reduce) the next one from left to right.