Functions of the Cell Membrane

(1) Transport

The concentration gradient: osmosis. A membrane which allows the passage of a solvent but not of a solute is called a semi permeable membrane. A membrane which permits one substance to pass through more easily than another is said to be selectively permeable. A selectively permeable membrane allows the passage of both solvent and solute. Cell membranes are selectively permeable rather than semi permeable.



Transport of metabolites of across biomembranes takes place in at least four ways:
Passive Transport –     (i) Simple diffusion
            _____________(ii) Facilitated discussion
Active transport –     (i) Simple active transport
           __________ (ii) Group translocation

(2) Cell recognition and adhesion

Mammalian leucocytes recognize foreign cells like bacteria and engulf them by phagocytes, but leave other cell types in the blood alone. Similarly macrophages of the spleen can differentiate between healthy and worn our erythrocytes and destroy the latter by phagocytosis.

(3) Antigen specificity

The glycoproteins on the surface of the cell membrane determine the antigen specificities of the cell. The different blood group systems are all based on the antigenic properties of erythrocytic cell membranes. The antigen determinants on the surface of erythrocytes are mainly glycolipids.

(4) Hormone receptors

It is known the hormones control the metabolism of cells. The cell membrane contains receptors which recognize specific hormones and convey the information in the latter to the interior of the cell. This stimulates of change in the metabolism of the cell. Hormones receptors are most commonly located in the plasma membrane, possibly on the outer surface of the membrane.

(5) Secretion

Polypeptide chains are synthesized by ribosome and released into the lumen of ER cisternae. Secretory protein in next transported to the Golgi complex where it may undergo modification.

(6) Oxidative phosphorylation

The inner membrane of the mitochondria and the plasma membrane of bacteria contain the electron transport chain which plays an important part in cell respiration. This chain consists of a series of components which can transfer electrons.

(7) Endocytosis and exocytosis

Endocytosis is the process by which material is transported into cells by formation of vesicles. The term includes two essentially similar processes, phagocytes and pincocytosis.

(8) Chemoreception

Molecules associated with the cell membrane respond to a variety of stimuli. Chemoreception or the response to chemical stimuli is shown by a variety of organism ranging from bacteria to mammals.

(9) Transmission

The transmission of nerve impulse takes place at the surface membrane of nerve cells.


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