Simple diffusion and facilitated diffusion across a membrane both ___________________:

• A. Move molecules against their concentration gradient.
• B. Move molecules with their concentration gradient.
• C. Require ATP.
• D. Use a protein transporter.
• E. Transport charged molecules from low to high concentration.
• F. Transport large, charged molecules from high to low concentration.
• G. Both b and f are true.

Answer: (B)

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, following their concentration gradient.
2. Differentiate between simple diffusion and facilitated diffusion: Simple diffusion does not require any assistance from proteins, while facilitated diffusion involves the use of protein transporters to help move molecules across the membrane.
3. Identify the role of ATP: Neither simple diffusion nor facilitated diffusion requires ATP, as both processes move molecules with their concentration gradient.
4. Recognize the types of molecules involved: Simple diffusion typically involves small, nonpolar molecules, whereas facilitated diffusion can transport larger or charged molecules using protein transporters.
5. Evaluate the options: Both simple and facilitated diffusion move molecules with their concentration gradient, and facilitated diffusion uses a protein transporter. Therefore, option 'b' (Move molecules with their concentration gradient) and option 'f' (Use a protein transporter) are true for facilitated diffusion.