The majority of solutes that diffuse across the plasma membrane cannot move directly through the lipid bilayer. The passive move
ment of such solutes (down their concentration gradients without the input of cellular energy) requires the presence of specific transport proteins, either channels or carrier proteins. Diffusion through a transport protein in the plasma membrane is called facilitated diffusion. True or false?
The plasma membrane does not allow the charged and polar substances to cross through its inner core that is made up of non-polar fatty acid tails of the phospholipids. Therefore, membrane proteins serve as transport proteins. Some of the transport proteins allow the movement of substances down the concentration gradient without any energy input. This passive movement of substances via membrane transport proteins is called facilitated diffusion.
Carriers and channels are the membrane proteins that facilitate the diffusion of substances. Carrier proteins pick the substances from one side of the membrane and undergo a change in shape to deliver the substance on the other side. Channel proteins make a passage for the movement of substances. Examples: aquaporins, ion channels.
