The structure separating an animal cell from its environment or a plant cell from its cell wall. The cell membrane is a complex system that allows nutrients to enter the cell and waste products to leave, usually through osmosis.
The thin membrane that forms the outer surface of the protoplasm of a cell and regulates the passage of materials in and out of the cell. It is made up of proteins and lipids and often contains molecular receptors. The membranes of organelles within the cell are made of the same basic material as the cell membrane. In plant cells, the cell membrane is surrounded by a rigid cell wall. Also called plasma membrane. Compare cell wall. See more at cell.