In passive transport, how does increasing a cell's surface area (while keeping the concentration gradient and diffusion distance constant) affect the rate of diffusion across its membrane?

• A. It has no effect on the rate because diffusion depends only on the concentration gradient.
• B. It increases the rate because more membrane area is available for molecules to cross per unit time.
• C. It decreases the rate because molecules must spread out over a larger area before crossing.
• D. It increases the rate only for water (osmosis) but not for solutes.

Answer: (B)