Plasma membrane or cell membrane is the outer most boundary of the animal cells and inner to cell wall in plant cells. Cell membrane is chemically composed of lipids (20-40%) and proteins (60-80%). In addition there is small quantity of carbohydrates present. Many biologists contributed to establish the structural organization of cell membrane. The modern technology has revealed that lipid bilayer is not sandwiched between.two protein layers. In 1972, Singer and Nicholson proposed a most acceptable model for membranes Called Flutd Mosale Model. This model is in agreement with photograph of cell membrane by electron microscope. This model explains that "the membrane is like a sea ot lipids in which protein are floating"
