Which of these statements describes what occurs in facilitated diffusion?

• A. Molecules are engulfed by the cell membrane in vesicles.
• B. Molecules move against their concentration gradient using ATP.
• C. Molecules move directly through the phospholipid bilayer without assistance.
• D. Molecules move across the cell membrane through protein channels without the use of energy.

Answer: (D)

Verified step by step guidance

1. Facilitated diffusion is a type of passive transport, which means it does not require energy input from the cell.
2. In facilitated diffusion, molecules move down their concentration gradient, from an area of higher concentration to an area of lower concentration.
3. Unlike simple diffusion, facilitated diffusion requires the assistance of specific transport proteins embedded in the cell membrane.
4. These transport proteins form channels or carriers that help specific molecules or ions to pass through the cell membrane.
5. The key characteristic of facilitated diffusion is that it does not involve the use of cellular energy (ATP), distinguishing it from active transport processes.