Which of the following does NOT affect the rate of diffusion across a membrane?

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

Answer: (A)

Verified step by step guidance

1. Understand the concept of diffusion: Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient, without requiring energy input.
2. Identify the factors that influence the rate of diffusion: These include the concentration gradient, surface area of the membrane, temperature, and the size or nature of the diffusing molecule.
3. Analyze the options: The color of the diffusing molecule is not a physical or chemical property that affects diffusion. Factors like surface area, concentration gradient, and temperature directly influence the kinetic energy and movement of molecules.
4. Relate the factors to the process: A larger surface area increases the space available for diffusion, a steeper concentration gradient increases the driving force, and higher temperature increases molecular motion, all of which enhance diffusion.
5. Conclude that the color of the diffusing molecule does NOT affect the rate of diffusion, as it is unrelated to the physical or chemical properties that govern molecular movement.