In the context of principles of transmembrane transport, which statement correctly distinguishes facilitated diffusion from active transport?

• A. Facilitated diffusion requires ATP hydrolysis, whereas active transport never uses cellular energy.
• B. Facilitated diffusion moves solutes down their electrochemical gradient without direct energy input, whereas active transport moves solutes against their electrochemical gradient using an energy source (e.g., ATP hydrolysis or ion gradients).
• C. Facilitated diffusion is always non-saturable, whereas active transport is never saturable.
• D. Facilitated diffusion can only occur through lipid bilayers without proteins, whereas active transport always occurs through channels.

Answer: (B)