A primary role of the cell membrane is to selectively regulate the movement of substances in and out of the cell. This semi-permeable barrier consists of a phospholipid bilayer embedded with proteins, allowing for communication and transport. The cell membrane aids in maintaining homeostasis by controlling the internal environment, facilitating nutrient uptake, and expelling waste. Additionally, it plays a role in cell signaling, enabling cells to respond to external stimuli. The integrity and functionality of the cell membrane are crucial for overall cellular health.