The plasma membrane, also known as the cell membrane, is a thin barrier that surrounds and protects the cell. It is primarily composed of a double layer of phospholipids, which helps regulate what enters and exits the cell. This selective permeability is crucial for maintaining the cell's internal environment and supporting its functions. In addition to phospholipids, the plasma membrane contains proteins, cholesterol, and carbohydrates. These components play various roles, such as facilitating communication between cells and transporting substances. The plasma membrane is essential for the overall health and functionality of all living cells, including those in plants and animals.