Final answer:
Polar and charged molecules can pass through cell membranes, but they usually require transport proteins to do so, since the hydrophobic interior of the membrane impedes their direct passage.
Step-by-step explanation:
The statement that polar and charged molecules cannot pass through membranes because they have a hydrophobic interior is partially true. While it is accurate that the hydrophobic interior of cell membranes impedes the passive diffusion of polar and charged molecules, there are mechanisms that facilitate their transport. The cell membrane's structure, known as a phospholipid bilayer, presents a barrier to these molecules due to its hydrophobic interior. However, transport proteins and channels allow for the selective passage of these molecules, which cannot pass through solely by simple diffusion.
Transport proteins provide a means for polar and charged molecules to traverse the membrane through facilitated diffusion or active transport. For example, ions such as calcium (Ca2+) and glucose, a polar molecule, require specific transport proteins to enter or exit the cell. While small nonpolar molecules like oxygen (O2) and carbon dioxide (CO2) can diffuse freely due to their hydrophobic nature and smaller size, larger polar molecules and ions are generally excluded by the lipid barrier.
Therefore, it is not entirely true to say that polar and charged molecules cannot pass through cell membranes; rather, they typically require specialized transport mechanisms to do so.