Question

What do you mean by permeability of membranes?

Answer 1

By varying the glycocalyx proteins or lipid-associated sugar molecules on the outside of the cell, or the membrane Cell - Transport across the membrane: the higher the permeability of the membrane to that particular substance. 

Answer 2

it means that membranes are porous but they give permission of passing through it to only certain materials. For example , in plant cells permeable membrane allows movement of water through it but blocks the way for materials.

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