Plasma membrane or Cell membrane:
The plasma membrane is the border between the cell and its surroundings. It regulates what enters and exits the cell. Just beneath the cell wall there is a soft living membrane adjoining the whole protoplasm. This is called cytoplasmic membrane or cell membrane.
Structure: The plasma membrane is composed of a phospholipid bilayer, which are two layers of phospholipids back-to-back. Plasma membrane is bi-layered. Under electron microscope there revealed a light layer between two dark layers. In the cell membrane of some epithelial cell there found some finger like out growth-these are called Microvilli (Singular: Microvillus). They enlarge the absorption exterior of the cell. The membrane between two adjacent cells modified in various forms to make the connection between two cells rigid. They also make the movement of different substances between the cells easier. In many cells spaces in the cell membrane may be broader.
Functions of Cell membrane:
(a) Transportation of different materials inside and outside the cell,
(b) Absorption of different substances (mainly nutrients) from outside the cell,
(c) Protection of the cell body and giving the cell a definite shape.
(d) It separates the contents of the cell from its outside environment and it regulates what enters and exits the cell.
(e) It plays a vital role in protecting the integrity of the interior of the cell by allowing only selected substances into the cell and keeping other substances out.