Final answer:
Hydrophobic molecules can easily pass through the plasma membrane, while hydrophilic molecules require help.
Step-by-step explanation:
Molecules that are hydrophobic can easily pass through the plasma membrane, if they are small enough, because they are water-hating like the interior of the membrane. Molecules that are hydrophilic, on the other hand, cannot pass through the plasma membrane at least not without help-because they are water-loving like the exterior of the membrane, and are therefore excluded from the interior of the membrane.