What is selecticely permeable?
Selective permeability usually refers to the ability of a membrane to regulate the movement of materials. An intervening membrane can physically prevent a solute from diffusing down its concentration gradient. This allows cells, for example, to maintain a cytoplasm with a different composition than the extra-cellular fluid. A membrane may contain protein channels for the passive diffusion of a specific substance, actively acquire or discharge others, and have no channels to facilitate the movement of another. Thus, the membrane is selectively permeable for different solutes, usually depending on the needs of the cell.
