The component of cell membrane which has contact with outer aqueous environment but not with the cytoplasmic aqueous substance.

In the cell membrane the carbohydrates component as oligosaccharides are associated with proteins (Glycoproteins) and Lipids (Glycolipids) only at the outer surface exposed the aqueous environment. They are not exposed to aqueous region of cytoplasm as they are absent on the inner surface of cytoplasmic face of plasma membrane.