How does increasing diffusion distance affect the rate of diffusion across a membrane (all else being equal)?

• A. The diffusion rate decreases because diffusion time increases with distance
• B. The diffusion rate decreases only if the diffusing molecule is charged; neutral molecules are unaffected by distance
• C. The diffusion rate increases because particles gain kinetic energy over longer distances
• D. The diffusion rate is unaffected by distance as long as the concentration gradient is constant

Answer: (A)