Complex sentence: In 1935, Davson and Danielli proposed that biological membranes are made up of lipid bilayers that are coated on both sides with thin sheets of protein and they simplified their model into the "pauci-molecular" theory.
Split into simpler sentences: In 1935, Davson and Danielli proposed that biological membranes are made up of lipid bilayers which are coated on both sides with thin sheets of protein. They simplified their model into the "pauci-molecular" theory.