Which of the following statements is true about facilitated diffusion?

• A. Facilitated diffusion involves the movement of molecules against their concentration gradient.
• B. Facilitated diffusion is a type of active transport.
• C. Facilitated diffusion requires energy input from the cell.
• D. Facilitated diffusion requires the assistance of membrane proteins to transport molecules across the cell membrane.

Answer: (D)

Verified step by step guidance

1. Facilitated diffusion is a process that allows molecules to move across the cell membrane with the help of membrane proteins.
2. Unlike active transport, facilitated diffusion does not require energy input from the cell because it occurs along the concentration gradient, from high to low concentration.
3. Membrane proteins, such as channel proteins and carrier proteins, assist in the transport of specific molecules that cannot easily pass through the lipid bilayer.
4. Facilitated diffusion is a type of passive transport, meaning it does not require cellular energy (ATP) to occur.
5. The key characteristic of facilitated diffusion is the involvement of membrane proteins to aid the movement of molecules across the cell membrane without energy expenditure.