Membrane Permeability.
Plasma membrane is selectively permeable.
lmpermeable membrane membrane though which nothing can pass.
Freely permeable membrane any substance can pass through it.
selectively permeable membrane permits free passage of some materials and restricts passage of others.
Distinction may be based size, electrical charge, molecular shape, lipid solubility.
Cells differ in their permeabilities, depending on what lipids and proteins are present in the membrane how these components are arranged.