cell membrane (plasmalemma, plasma membrane, protoplast) A sheet-like membrane, 7.5–10 nm thick, that forms a selectively permeable barrier enclosing and delimiting the protoplasm of a cell. It is a living structure consisting of lipid molecules in a fluid bi-layer, and associated protein. Water molecules can pass freely through this structure, but the passage of most other molecules can be controlled. It may also have other functions, as in prokaryotic cells, where it is associated with oxidative metabolism and cell division.

cell membrane (plasmalemma, plasma membrane) The sheet-like membrane, 7.5–10 nm thick, that encloses and delimits the contents of a cell. It is a living structure consisting of lipid molecules forming a fluid bi-layer and associated protein. Water molecules can pass freely through this structure, but the passage of most other molecules can be controlled (i.e. it is selectively permeable). The cell membrane may also have other functions, as in prokaryotic cells, where it is associated with oxidative metabolism and cell division.

cell membrane Any membrane that is found in a living cell, especially the plasma membrane, which forms the cell boundary. Other cell membranes include the nuclear envelope; the tonoplast, which encloses the vacuole of plant cells; and the membranes of the various cell organelles, such as the endoplasmic reticulum, Golgi apparatus, mitochondria, chloroplasts, and lysosomes.