Which statement best describes carrier proteins?

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Carrier proteins help polar molecules cross the cell membrane by binding the molecule on one side, changing shape, and releasing it on the other side. This transport is driven by the concentration gradient, so the same carrier can move substances in either direction depending on which side has the higher concentration. Nonpolar molecules don’t need carriers because they can diffuse through the lipid bilayer. While some carrier-mediated transport can move against a gradient when energy is involved, the general idea is that carrier proteins handle polar molecules and can operate in both directions as the gradient dictates.