What does the cell membrane do?

The cell membrane is a biological membrane that encloses a cell and separates its content from the extracellular environment. Its main function is the protection of cells. However, it is selectively permeable to ions and small molecules so another function of the cell membrane is the regulation of movements of substances in and out of cells. Nontheless, their function in cell adhesion and cell signaling is important in a number of cellular processes.