The Cell Surface Membrane B io F actsheet September 1997 Number 8 1 The cell surface membrane (formerly called the plasma membrane) surrounds the cytoplasm of eukaryotic cells. The membrane forms a selectively permeable barrier, controlling the substances that enter and leave the cell and therefore enables the cell to regulate its internal environment. 2. Glycolipids - which make up 5% of membrane lipids. Glycolipids occur on the external surface of the cell surface membrane and the carbohydrate portion of the glycolipid extends into the intercellular space and is called a glycocalyx. These are important in cell-to-cell recognition. 3. Cholesterol - a steroid which makes up 20% of lipids in animal membranes but is rarely found in plant cell membranes.