The fine, thin, elastic and permeable membrane that surrounds the protoplasm is called the plasma membrane. It is composed of lipids and proteins. It is called cytoplasmic membrane, cytomembrane, cell membrane, plasmalemma, biomembrane etc. It is called biomembrane as it exists in plant and animal body i.e. in all living cells. Chemically it consists of three layers: protein-lipid-protein. Carl Nageli and Cramer (1855) first discovered the cell membrane and named it plasma membrane. J. Q. Plower (1931) called it plasmalemma.