3 A small molecule, such as a drug or a nutrient, cannot pass the cell membrane and must be transported via an integral or transmembrane protein because: 6 Due to the polar nature of the interior of the membrane, nonpolar molecules cannot exist in the membrane. 9 None of these 12 These molecules require the presence of water, so the must be actively transported by water into the cell. 15 Due to the nonpolar nature of the interior of the membrane, polar molecules cannot exist in the membrane. 18 Hydrophobic molecules, such as these drugs, cannot exist in the hydrophilic nature of the cell membrane