Question

what molecules are constituents of cell membranes?
phospholipids and proteins
phospholipids and carbohydrates
phospholipids, carbohydrates, and proteins
phospholipids, proteins, carbohydrates, and cholesterol

Explanation:

Cell membranes are composed of a phospholipid - bilayer. Proteins are embedded in or associated with this bilayer, carbohydrates are attached to proteins (glycoproteins) or lipids (glycolipids) on the outer surface, and cholesterol is also present to regulate membrane fluidity.

Answer:

Phospholipids, proteins, carbohydrates, and cholesterol