What is the primary role of the cell membrane?

The cell membrane's primary role is to control the movement of substances in and out of the cell, which is essential for maintaining homeostasis within the cell. This semi-permeable barrier allows certain molecules to pass while restricting others, thus regulating the internal environment of the cell. It achieves this through various mechanisms including passive transport, active transport, and facilitated diffusion.

Additionally, the cell membrane is involved in cell signaling and communication, allowing the cell to respond to external stimuli. This selective permeability is crucial as it enables the cell to take in necessary substances such as nutrients and eliminate waste. Overall, the ability of the cell membrane to control the movement of ions, nutrients, and other molecules is vital for the cell's survival and function.