Question

what is the function of protein channels in facilitated diffusion? help molecules expand to larger molecules block all molecules from entering the cell membranes help large molecules cross the cell membrane

Explanation:

Facilitated diffusion is a type of passive transport. Protein channels act as conduits. They allow specific large molecules (e.g., polar or charged ones that can't pass through the lipid - bilayer easily) to cross the cell membrane down their concentration gradient. They do not expand molecules (as molecules have a fixed structure in this context) and do not block all molecules (they are selective).

Answer:

help large molecules cross the cell membrane