Carbohydrate Polymers may attach to parts of the membrane, forming Glycolipids when attach to Phospholipid Molecules and Glycoproteins when they attach to proteins. Both Glycolipids and Glycoproteins can act as Cell Receptor Sites. Hormones may bind to them, as may drugs, to instigate a response within the cell. They may also be involved in Cell Signalling in the Immune System.