Which of the following best describes the process of facilitated diffusion?

• A. Movement of molecules across a membrane against their concentration gradient using energy
• B. Movement of molecules across a membrane through transport proteins without energy input
• C. Movement of water molecules through a selectively permeable membrane
• D. Random movement of molecules from an area of higher concentration to an area of lower concentration

Answer: (B)

Verified step by step guidance

1. Facilitated diffusion is a type of passive transport, meaning it does not require energy input from the cell.
2. In facilitated diffusion, molecules move across the cell membrane through transport proteins.
3. These transport proteins help molecules that cannot directly pass through the lipid bilayer due to size, polarity, or charge.
4. Facilitated diffusion occurs along the concentration gradient, from an area of higher concentration to an area of lower concentration.
5. Unlike active transport, facilitated diffusion does not move molecules against their concentration gradient and does not use ATP.