The primary component of the cell membrane is phospholipids. These molecules form a bilayer that creates a semi-permeable barrier, allowing selective passage of substances in and out of the cell. Each phospholipid consists of a hydrophilic (water-attracting) "head" and two hydrophobic (water-repelling) "tails." This configuration enables the formation of a membrane that is flexible yet protective. In addition to phospholipids, cell membranes also contain proteins, cholesterol, and carbohydrates, which contribute to their functionality, including signaling, transport, and structural integrity.