Yes, eukaryotic cells possess a plasma membrane that separates the cellular contents from the external environment. The plasma membrane is a semi-permeable, phospholipid bilayer composed mainly of lipids, proteins and carbohydrates. It is a 3-layered structure with a thickness of about 6 nm to 10 nm. The lipid layer lies in between an outer and an inner protein layer. The plasma membrane performs several vital functions. Its main role is regulating the passage of substances in and out of the cell to maintain optimum internal conditions.