The main function of the cell membrane is to regulate the passage of substances into and out of the cell. This is crucial for the cell to maintain its internal environment, which is essential for its proper functioning.

Here's a breakdown of its key roles:

* Selectively permeable barrier: The membrane acts as a gatekeeper, controlling which molecules can enter or exit the cell. This is vital for maintaining the cell's internal environment and for carrying out essential processes like nutrient uptake, waste removal, and signaling.

* Maintains cell shape and structure: The membrane provides structural support for the cell, helping to maintain its shape and integrity.

* Cell communication: The membrane is involved in cell-to-cell communication, allowing cells to interact with their environment and with each other. This is achieved through various receptors and signaling molecules embedded in the membrane.

* Protection: The membrane acts as a barrier against harmful substances and pathogens.

In essence, the cell membrane is essential for life, ensuring that the cell can function properly and interact with its environment.