Which of the following best describes the process of facilitated diffusion across a cell membrane?

• A. Movement of molecules directly through the phospholipid bilayer without the use of proteins.
• B. Movement of water molecules through a selectively permeable membrane.
• C. Movement of molecules from an area of higher concentration to an area of lower concentration with the help of transport proteins.
• D. Movement of molecules from an area of lower concentration to an area of higher concentration using energy.

Answer: (C)

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 from an area of higher concentration to an area of lower concentration, following the concentration gradient.
3. This process involves the use of transport proteins embedded in the cell membrane, which help specific molecules to pass through the membrane.
4. Transport proteins can be channel proteins, which form pores in the membrane, or carrier proteins, which change shape to move molecules across.
5. Facilitated diffusion is distinct from simple diffusion, where molecules pass directly through the phospholipid bilayer without the aid of proteins.