What is the primary function of the cell membrane?

The primary function of the cell membrane is to regulate what enters and exits the cell. This selective permeability is crucial for maintaining homeostasis within the cell, allowing it to control its internal environment by permitting certain substances to pass while excluding others. The cell membrane is composed of a phospholipid bilayer with embedded proteins that facilitate various transport processes, including passive and active transport, signaling, and cell communication. By carefully managing the movement of ions, nutrients, and waste products, the cell membrane plays a vital role in the overall functioning and survival of the cell.

In contrast, while transporting nutrients throughout the cell and providing structural support are important cellular functions, they are not the primary roles of the cell membrane itself. Additionally, synthesizing proteins is a function carried out by ribosomes and the endoplasmic reticulum, not the cell membrane. Therefore, the regulation of entry and exit is the fundamental role of the cell membrane, ensuring that the cell can adapt and respond to changes in its environment.