What is the main function of the cell membrane?

The main function of the cell membrane is to control the movement of substances in and out of the cell. It acts as a selective barrier, allowing certain molecules to enter or exit while restricting others. This selective permeability is crucial for maintaining the proper internal environment of the cell, known as homeostasis. The cell membrane is made up of a phospholipid bilayer embedded with proteins, which play key roles in transporting materials across the membrane, receiving signals from the environment, and facilitating communication between cells. By regulating what enters and leaves, the cell membrane helps to maintain essential processes such as nutrient uptake, waste removal, and the overall functionality of the cell.