(N/A) The plasma membrane is the outermost covering of the cell that separates it from the environment. It regulates the movement of substances into and out of the cell. It allows the entry of only some substances and prevents the movement of others.
Hence,the membrane is selectively permeable.
Movement of neutral solutes: Neutral molecules move across the plasma membrane by simple passive diffusion. Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration.
Movement of polar molecules: The cell membrane is made up of a phospholipid bilayer and proteins. The movement of polar molecules across the non-polar lipid bilayer requires carrier proteins. Carrier proteins are integral protein particles having a specific affinity for certain solutes. As a result,they facilitate the transport of these molecules across the membrane.