Final answer:
Carbohydrates in the membrane are either bound to proteins as glycoproteins or to lipids as glycolipids on the exterior surface of cells, forming specialized sites for cell recognition.
Step-by-step explanation:
Carbohydrates are the third major component of plasma membranes. They are always found on the exterior surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids). These carbohydrate chains may consist of 2-60 monosaccharide units and may be either straight or branched. Along with peripheral proteins, carbohydrates form specialized sites on the cell surface that allow cells to recognize each other.