Question

what type of molecule requires a protein channel or pump to make it through the cell membrane?
tiny molecules
large molecules
small molecules

Explanation:

The cell membrane is selectively permeable. Tiny (like gases, water) and small molecules (like some ions) can pass through via simple diffusion or facilitated diffusion (with channels for some small charged molecules), but large molecules (e.g., proteins, polysaccharides) are too big to pass through the lipid bilayer directly and need protein channels or pumps (or other mechanisms like endocytosis/exocytosis, but for the options here, large molecules require protein - mediated transport to cross the membrane as they can't diffuse through the membrane's lipid part easily. Tiny and small molecules can often cross without or with simpler channel - mediated for some small ones, but large ones need specific protein - based transport.

Answer:

B. large molecules