Semipermeable

A cell membrane is a thin layer of molecules that surrounds the cell. Its function is to allow certain materials to enter the cell, yet, keep harmful materials out. In order to do this, the cell controls which substances can enter the cell through the membrane. The cell membrane is selectively permeable (or semipermeable), which means that certain molecules, such as oxygen and water, are permitted to enter the cell. Molecules that are not recognized as helpful are not able to pass through the membrane.