Which of the following is NOT a factor affecting the rate of diffusion?

• A. Temperature
• B. Concentration gradient
• C. Surface area of the membrane
• D. Color of the molecule

Answer: (D)

Diffusion rate is controlled by factors that affect how quickly molecules move and how easily they cross the membrane. Warmth increases molecular motion, so higher temperature speeds diffusion. A larger concentration difference provides a stronger drive from where there are more particles to where there are fewer, increasing the rate. More membrane surface area offers more space for molecules to pass through, also speeding diffusion. The color of a molecule has no effect on its kinetic energy, its movement, or its ability to cross the membrane, so it doesn’t influence diffusion rate. Thus, color of the molecule is not a factor.