Final answer:
The ability of a carrier molecule to transport only one specific molecule or a group of closely related molecules is known as selective permeability. This is part of passive transport mechanisms like facilitated diffusion, which allows specific substances to cross the cell membrane along their concentration gradient without energy input.
Step-by-step explanation:
The ability of a carrier molecule to transport only one specific molecule or a group of closely related molecules is called selective permeability. This particular characteristic is crucial to the functioning of the cell membrane, which controls the movement of substances in and out of the cell. Passive transport, including diffusion, osmosis, and facilitated diffusion, involves the movement of substances across the cell membrane without the need for cellular energy. Facilitated diffusion, in particular, involves specific protein channels that allow molecules such as glucose or amino acids, which cannot readily pass through the lipid bilayer, to move down their concentration gradient into the cell.
Active transport, on the other hand, requires energy to move molecules against their concentration gradient, reflecting one of the key differences between passive and active transport mechanisms. The specificity of transport proteins during facilitated diffusion is a hallmark of selective permeability, which is essential for maintaining cellular homeostasis and function.