Final answer:
The cell membrane is a lipid bilayer with proteins that separates the cell interior from the extracellular space. It regulates material passage, acts as a protective barrier, and ensures semipermeability. Its composition consists of phospholipids, cholesterol, and proteins.
Step-by-step explanation:
The cell membrane, also known as the plasma membrane, is a lipid bilayer with proteins dispersed in it that separates the cell interior from the extracellular space. It provides a protective barrier around the cell, regulates what materials can pass in or out, and ensures the cell is semipermeable. The cell membrane is primarily composed of back-to-back phospholipids, cholesterol, and various proteins.