What is the role of carbohydrates in the plasma membrane?

Carbohydrates covalently linked to proteins (glycoproteins) or lipids (glycolipids) are also a part of cell membranes, and function as adhesion and address loci for cells. The Fluid Mosaic Model describes membranes as a fluid lipid bilayer with floating proteins and carbohydrates.

Where are they though?

I’m not exactly sure what your trying to ask, but if it’s how an organelle is similar to a body system or a part a nucleus is like a in function. but i don’t fully understand what you’re trying to ask