What role do proteins play in facilitated diffusion?

What role do proteins play in facilitated diffusion?

• A. They form channels or carriers to move substances along gradient without energy
• B. They hydrolyze ATP to pump ions against gradient
• C. They create vesicles for bulk transport
• D. They restructure membrane lipids to allow diffusion

Answer: (A)

The key idea is that facilitated diffusion uses membrane proteins to help substances cross the lipid bilayer down their concentration gradient without using energy. Proteins act as channels or carriers that provide a specific passage for ions or polar molecules that can’t diffuse easily on their own. Channels form pores that allow rapid movement of ions, while carriers bind the solute and undergo a shape change to shuttle it across, still moving with the gradient. The other mechanisms involve energy use or different transport modes: actively pumping substances against the gradient requires ATP, bulk transport uses vesicles, and changing lipid organization isn’t how facilitated diffusion operates.

The key idea is that facilitated diffusion uses membrane proteins to help substances cross the lipid bilayer down their concentration gradient without using energy. Proteins act as channels or carriers that provide a specific passage for ions or polar molecules that can’t diffuse easily on their own. Channels form pores that allow rapid movement of ions, while carriers bind the solute and undergo a shape change to shuttle it across, still moving with the gradient. The other mechanisms involve energy use or different transport modes: actively pumping substances against the gradient requires ATP, bulk transport uses vesicles, and changing lipid organization isn’t how facilitated diffusion operates.