Which property of a molecule most strongly predicts its ability to cross the intestinal epithelial cell membrane by passive diffusion?

• A. Ability to form covalent bonds with membrane phospholipids and thereby be carried across.
• B. Lipid solubility (nonpolarity) and small molecular size.
• C. Presence of multiple hydroxyl groups that create extensive hydrogen bonding with the interior of the lipid bilayer.
• D. High molecular weight and strong ionic charge that enhances attraction to membrane lipids.

Answer: (B)