Biological membrane

In medicine, microbiology, cell physiology, and biochemistry, a membrane is a lipid bilayer, typically embedded with proteins, which acts as a barrier within or around a cell.

Such membranes typically define enclosed spaces or compartments, in which cells may maintain a chemical or biochemical environment that differs from the outside. For example, the membrane around peroxisomes shields the rest of the cell from peroxides, and the plasma membrane separates a cell from its surrounding medium. Most organelles are defined by such membranes.

More at cell membrane.