Facilitated diffusion moves substances across a membrane via specific transport proteins. Is facilitated diffusion an active or passive transport process?

• A. Active, because it always uses ATP to move molecules across the membrane
• B. Active, because it moves molecules against their concentration gradient using a carrier protein
• C. Passive, because it moves molecules down their concentration gradient without requiring ATP
• D. Neither passive nor active, because it occurs only through the phospholipid bilayer without proteins

Answer: (C)