Permeability is the condition of
being capable of having materials flow into and out of a membrane. The
permeability of a cell membrane is determined by how easily a molecule can diffuse across the membrane. Usually,
only molecules that are fat-soluble can permeate across a cell membrane. This
is because the layer that is exposed on the linings of the cell membrane is
nonpolar and can therefore allow the fat-soluble molecule to pass through.
