The difference between simple and facilitated diffusion is that facilitated diffusion:

• A. Requires a protein transporter.
• B. Moves molecules against their concentration gradient.
• C. Requires energy.
• D. Freely diffuses molecules against their concentration gradient.

Answer: (A)

Verified step by step guidance

1. Understand the concept of diffusion: Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. It is a passive process, meaning it does not require energy.
2. Differentiate between simple and facilitated diffusion: Simple diffusion occurs without the aid of any proteins, allowing molecules to pass directly through the lipid bilayer of the cell membrane.
3. Explore facilitated diffusion: Facilitated diffusion involves the use of protein transporters or channels embedded in the cell membrane to help specific molecules cross the membrane.
4. Identify the role of protein transporters: In facilitated diffusion, protein transporters assist molecules that cannot freely pass through the lipid bilayer due to size, polarity, or charge.
5. Clarify energy requirements: Facilitated diffusion does not require energy because it moves molecules along their concentration gradient, unlike active transport which requires energy to move molecules against their concentration gradient.