Question

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

Explanation:

In facilitated diffusion, protein channels are integral membrane proteins that form pores or channels. Large or polar molecules (like glucose, ions) that can't pass through the lipid bilayer of the cell membrane directly use these channels. The option "block all molecules" is incorrect as channels facilitate transport. "Help molecules expand" is also incorrect as channels don't change molecule size. The correct function is to help large (or specific) molecules cross the cell membrane.

Answer:

A. help large molecules cross the cell membrane