Final answer:
Hydrophilic molecules are polar and generally soluble in water, as they form hydrogen bonds with water molecules. They might not easily cross cell membranes because the membrane's interior is hydrophobic, which interacts unfavorably with hydrophilic substances.
Step-by-step explanation:
Hydrophilic molecules are indeed polar and are typically soluble in water because they can form hydrogen bonds with water molecules. Hydrophilicity refers to the affinity of a molecule or substance for water, allowing it to interact readily with water and often dissolve in it. For a substance to be soluble, it must be able to disrupt the hydrogen bonds that water molecules form amongst themselves and create new interactions. Hydrophilic molecules succeed in this due to their polarity.
However, the ability of hydrophilic molecules to cross the cell membrane is limited. This is because the interior of the phospholipid bilayer that makes up the cell membrane is hydrophobic and repels polar water-loving molecules. Therefore, while hydrophilic molecules can dissolve in water, they often require special transport mechanisms to move across cell membranes.