How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
Neutral solutes may move across the membrane by the process of simple diffusion along the concentration gradient. The polar molecules cannot pass through the non-polar lipid bilayer, they require a carrier protein to facilitate their transport across the membrane. A few ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to the higher concentration. Such a transport is an energy dependent process, in which ATP is utilized and is called active transport.