Question

Refute the argument that membranes resemble an inert plastic bag.

Answer 1

Cell mrmbranes are not inert 'plastic bags' but rather dynamic, interconvertible, fluid structures of lipid and proteins with different features in different cell types. Different substances has to cross various membranes in order to enter and move through the body. For example, in lungs a substance must cross the membranes that separates the air present in alveolus from the blood in the adjacent capillary. To reach a particular organ, the substance must pass through a capillary wall into interstitial space and then into the contact of the membrane of the target organ cell. Cell membrane allows the transport of the molecules across it. The membrane is selectively permeable to some molecules and impermeable to others. Some substances pass mainly through membrane pores or channels while others are transported via transporter molecules and some remain in the membrane bound to receptors on the cell surface. Transportation via pores or channels does not require energy and takes place by simple diffusion along the concentration gradient i.e, from higher to lower concentration. Active transport involves the uphill transport of materials across the membrane against their concentration gradient via transporter molecules with the aid of energy obtained from ATP. In addition, chemicals may target membranes and cause injury by lipid peroxidation and alteration of membrane fluidity. The cell membrane fluidity of lipid molecules can be demonstrated by the lateral movement of protein molecules.

Hence all these evidences suggest that cell membranes does not resemble an inert plastic bag.