Functions of cell membrane :
(a) The proteins and enzymes present in the cell membrane helps in the transport of certain substances like sugar, sodium and other ions etc. across the cell membrane. (b) Cell membrane protects the internal structures of the cell and different organelles of the cytoplasm. (c) It maintains the shape of the cell. (d) It acts as a selective permeable membrane because it allows to pass certain substances while others are not, hence it helps in the transport of selective materials from and to the cells. (e) The membranes on the cytoplasmic organelles and nucleus most probably formed from the plasma membrane. (f) Other important functions of cell membrane of the cells are endocytosis and exocytosis. Endocytosis is the process by which materials are transported into the cells by the formation of vesicles. It includes two processes-phagocytosis (cell eating) and pinocytosis (cell drinking). The reverse process of endocytosis is exocytosis. During this process the cytoplasmic vesicle fuses with the plasma membrane and ultimately releases its contents out of the cell.
Difference between cell membrane and cell wall:-
Cell membrane-
1. Present both in plant and animal cells.
2. Present outside the protoplasm of all living cells.
3. Living material made up of lipid and protein.
4. The membrane is thin and elastic.
5. Semi permeable membrane.
6. Shows no pattern of ornamentation.
7. Made up of three consecutive layers like protein, lipid and protein.
Cell wall-
1. Present only in plant cells.
2. Present outside of the cell membrane of a plant cell.
3. Non living material made up of cellulose and protein.
4. The wall is thick and rigid.
5. Permeable membrane.
6. Shows different patterns of ornamentation.
7. Made up of middle lamella, primary wall and secondary wall.
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