In passive transport by simple diffusion, how does the magnitude of the concentration gradient across a membrane affect the net rate of diffusion (all else equal)?

• A. The concentration gradient has no effect on net diffusion rate; only temperature matters.
• B. A steeper concentration gradient reverses diffusion so solutes move from low to high concentration.
• C. A steeper concentration gradient decreases the net rate of diffusion.
• D. A steeper concentration gradient increases the net rate of diffusion.

Answer: (D)