The primary role of phospholipids is to form cell membranes. Phospholipids are a type of lipid molecule that consists of a hydrophilic head and a hydrophobic tail. In the cell membrane, the hydrophilic head faces the aqueous environment, while the hydrophobic tail is oriented towards the interior of the membrane. This creates a selectively permeable barrier that allows certain molecules to pass through the membrane while preventing others from doing so. Phospholipids play a crucial role in maintaining the structure and function of cell membranes.