Fluid mosaic model was given by Singer and Nicholson. According to this theory the phospholipid molecules are arranged to form a continuous bimolecular layer of vlipid molecules. The two layers are arranged in such a way that the polar heads of the lipid molecules face the outside while the hydrophobic tails of the lipid are on the inner sides. esides lipids the cell membrane also has proteins, cholesterol and carbohydrates attached to it.
Receptor molecules are specific proteins in the cell's plasma membrane that receive chemical signals from outside the cell. When such chemical signals bind to a receptor, they cause some form of cellular response.