Final answer:
Hydrophilic substances can't permeate cell membranes by passive diffusion due to the hydrophobic interior of the lipid bilayer, which repels water-soluble materials.
Step-by-step explanation:
The type of substances that can't permeate membranes by passive diffusion are hydrophilic substances. These substances include polar molecules and ions, such as glucose, amino acids, and electrolytes. The plasma membrane's lipid bilayer has a hydrophobic interior that repels water-soluble materials, making it difficult for them to pass through without assistance. On the other hand, lipid-soluble substances, non-ionized materials, and hydrophobic molecules can pass through the membrane more easily, as they are compatible with the hydrophobic interior of the bilayer.
A hydrophilic molecule or portion of a molecule is one whose interactions with water and other polar substances are more thermodynamically favorable than their interactions with oil or other hydrophobic solvents.
They are typically charge-polarized and capable of hydrogen bonding. This makes these molecules soluble not only in water but also in other polar solvents.