This is the outermost covering of the cell that separates the contents of the cell from its external environment. It is flexible and made up of organic molecules called lipids and proteins. The flexibility of the cell membrane also enables the cell to engulf in food and other material from its external environment. Such processes are known as endocytosis. Eg: Amoeba
It allows the movement of some substances into and out of the cell. It also prevents movement of some other materials. Therefore it is called a selectively permeable membrane. Movement of substances through this semi-permeable membrane can be by the process of diffusion, osmosis etc.
