What is the primary role of the cell membrane?

The primary role of the cell membrane is to regulate what enters and exits the cell. This semipermeable barrier is crucial for maintaining homeostasis within the cell, allowing essential substances, such as nutrients and ions, to enter while keeping out harmful materials. The cell membrane is composed of a phospholipid bilayer with embedded proteins that facilitate the selective transport of molecules. This selective permeability is vital for the cell's ability to maintain its internal environment, respond to external signals, and engage in communication with surrounding cells.

In contrast to energy production, which primarily occurs in organelles like mitochondria; protein synthesis, which takes place at ribosomes in the cytoplasm; and the storage of genetic information, which is confined to the nucleus, the regulation of cellular transport is a fundamental function of the cell membrane that supports all other cellular processes.