In the context of passive transport across the plasma membrane, how do simple diffusion and facilitated diffusion differ?

• A. Simple diffusion can transport ions efficiently across the membrane, whereas facilitated diffusion cannot transport ions.
• B. Simple diffusion requires ATP hydrolysis, whereas facilitated diffusion does not require energy input.
• C. Facilitated diffusion requires specific membrane proteins (channels or carriers), whereas simple diffusion occurs directly through the lipid bilayer without transport proteins.
• D. Facilitated diffusion moves solutes against their concentration gradient, whereas simple diffusion moves solutes down their concentration gradient.

Answer: (C)