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The following points highlight the nineteen important functions of cell membranes.
1. The cell membranes cause compartmentalization. As plasma membranes they separate the cells from their external environment. As organelle coverings, they allow the cell organelles to maintain their identity, internal environment and functional individuality.
2. Plasma membrane protects the cell from injury.
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3. The membranes allow the flow of materials and information between different organelles of the same cell as well as between one cell and another.
4. As plasmodesmata and gap junctions, the bio membranes provide organic connections between adjacent cells.
5. Plasma membranes of the adjacent cells form various types of junctions for keeping the cells together.
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6. Plasma membranes as well as other membranes of the organelles have selective permeability, that is, they allow only selected substances to pass inwardly to selected degrees. The membranes are impermeable to others.
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7. Differential permeability and retentively of plasma membrane as well as other bio membranes control cell metabolism.
8. Plasma membrane possesses specific substances at its surface which function as recognition centers and points of attachment. Because of this, white blood corpuscles can differentiate between germ and body cells. If cells of different tissues get mixed up and allowed to join on nutrient medium, they move about and regroup to form distinct clusters of specific tissue types.
9. Substances attached to cell membrane determine antigen specificity. Glycophorins present on the surface of erythrocytes function as antigen determinants. Histocompatibility antigens signify whether a foreign cell or tissue should be incorporated or rejected.
10. Cell membrane has receptors for certain hormones. The hormone combines with its particular receptors and either changes membrane permeability or activates enzyme adenylate cyclase to produce cyclic AMP from ATP. CAMP then triggers a set of enzymes to perform a particular function.
11. Membranes have carrier proteins for active transport.
12. Cell membranes contain enzymes for performing certain reaction on their surface, e.g., ATPase (for ATP synthesis and release of energy from ATP), phosphatases, esterase’s.
13. Certain cell membranes (e.g., plasma membrane in bacteria, thylakoid membranes of chloroplasts, inner mitochondrial membrane) possess electron transport systems.
14. Membrane in-folds are used for bulk intake of materials by endocytosis.
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15. As microvilli the membrane becomes specialized for absorption of substances.
16. Secretory, excretory and waste products are thrown out by plasma membrane through exocytosis.
17. In nerve cells the cell membrane takes part in transmission of impulses.
18. Plasma lemma provides sheaths for cilia and flagella.
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19. Plasma membrane of the cell helps in movement of some cells by either developing undulations (e.g., fibroblasts) or pseudopodia (e.g., Amoeba).
