WHAT IS THE DIFFERENCE BETWEEN SINGLE MEMBRANE AND UNIT MEMBRANE ?

Single membrane means that the cell is having only one membrane in which there is two layer is of lipid and it have protein molecules  between the lipids which shows that ice berg are floating in a sea where protein are the ice berg and lipid is like sea, where as unit membrane  was a concept or model of cell membrane given by Robertson in 1959 in which there is a bilayer of phospholipid and outside it has a strip of  beta protein layer. This model was rejected later.