In facilitated diffusion, which protein type is described as not picky?

• A. Enzymes
• B. Receptors
• C. Protein carriers
• D. Protein channels

Answer: (D)

Facilitated diffusion relies on transport proteins to move substances down their concentration gradient without using energy. Channel proteins form pores that allow ions or small molecules to pass when a gate is open, providing a passage that doesn’t require the solute to bind a specific site. Because they let through a range of ions or small molecules that fit the pore and meet charge requirements, they’re less selective—“not picky”—than carrier proteins, which must bind a specific solute and undergo a conformational change to shuttle it across the membrane. Enzymes aren’t transporters, and receptors bind signaling molecules rather than transporting substances. Carrier proteins are more selective and thus more picky than channels. So, the best fit for not picky in facilitated diffusion is the channel protein.