What is the main function of the cell membrane?

The main function of the cell membrane is to regulate the entry and exit of substances. This selectively permeable barrier controls what can enter the cell and what must remain outside, providing a necessary mechanism for maintaining the cell's internal environment, or homeostasis. It allows essential nutrients to enter, waste products to be expelled, and ions to be balanced, all of which are crucial for normal cellular function.

The composition of the cell membrane, primarily made up of a phospholipid bilayer with embedded proteins, facilitates these functions. Proteins in the membrane can act as channels or transporters to assist in the movement of specific molecules, while some receptors can signal the cell in response to external stimuli.

While the cell membrane does contribute to the overall structure of the cell, as it defines its boundaries, its primary role is much more focused on regulating what substances can move in and out, thus supporting the cell's metabolic processes. This function is critical for allowing the cell to adapt to changes in its environment and maintain vital processes necessary for survival.