Cell membranes contain and protect the contents of the cell. They are active in signaling other cells, and proteins embedded in their matrix regulate the cell's chemistry by selectively absorbing and secreting chemicals. Many single-celled organisms, such as amoebae, use their flexible membranes for locomotion and food gathering.
Cell membranes are extremely flexible structures that play many roles in the life of a cell. They are the only structures found in all cells, regardless of species, and serve as the attachment point for many intracellular structures such as cell walls and cytoskeletons, as well as extracellular structures such as cilia.