Facilitated diffusion involves which?

• A. Lipids moving through
• B. Proteins to carry substances across the cell membrane
• C. ATP energy required for transport
• D. Vesicles enclosing substances

Answer: (B)

Facilitated diffusion uses membrane proteins to move specific substances across the cell membrane down their concentration gradient without using cellular energy. Channel and carrier proteins provide a passageway for solutes that cannot diffuse directly through the lipid bilayer, making the process passive and highly specific. This differs from diffusion of lipids through the membrane, which doesn’t rely on these proteins, and from active transport, which requires ATP. It also doesn’t involve vesicles enclosing substances, which is a different transport mechanism. Examples include glucose transporters and ion channels that allow particular ions to pass as gradients drive the flow.