Why are membrane more permeable to non-polar molecules than to most polar and ionized molecules?

Answer 1

Because the permeation through a membrane depends on the diffusivity (size of the permeate molecules) and the solubility (briefly the interaction equilibrium) of the permeate in the membrane. Considering permeate mixtures, membranes can be size-selective and sorption-selective depending on which relative term (ratio of diffusivities or ratio of solubilities) dominates. Most known membrane separation processes involve size-selectivity, i.e., the "smaller" the permeate molecule, the faster it gets through the membrane. More sophisticated membrane separation processes are sorption selective, where it is possible that the "bigger" molecules exhibit a higher permeation flux than the "smaller" ones.

Answer 2

it's simply because the lipid bi layer is nonpolar, and like substances dissolve other like substances. polar molecules don't interact with non-polar and that is why the cell membrane does not allow polar molecules to diffuse right through.

Answer 3

Membranes are composed of a phospholipid bilayer which has a hydrophobic core. Non-polar molecules can easily pass through this hydrophobic region via simple diffusion. In contrast, polar and ionized molecules face difficulty passing through due to their interactions with the hydrophilic head groups of the phospholipids.

Answer 4

b/c the cell membrane is made out of phospholipids! thus lipis diffuse readily

Answer 5

Because the membranes are made up of phospholipid bilayers

Answer 6

Non-polar molecules are generally smaller than polar and ionized ones. The non-polar tails of the phospholipids repel ionic molecules and don't allow them to pass.

Answer 7

Because the phospholipids of the plasma membrane are lipid, and a lipid soluable such as cholesterols can pass through the membrane.

Answer 8

parce que c'est dommage