In passive transport, how does increasing the distance a molecule must travel (diffusion path length) affect the rate of diffusion across a medium when all other factors remain constant?

• A. It decreases the diffusion rate because a longer path length slows net movement down the concentration gradient.
• B. It has no effect on diffusion rate because diffusion depends only on concentration gradient, not distance.
• C. It increases the diffusion rate because molecules gain more kinetic energy over a longer distance.
• D. It reverses the direction of diffusion so molecules move from low to high concentration.

Answer: (A)