Which of the following variables affects the rate of diffusion across a membrane?

• A. Temperature
• B. Color of the molecules
• C. Molecular size
• D. Concentration gradient

Answer: (D)

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. It does not require energy and is influenced by several factors.
2. Analyze the role of temperature: Higher temperatures increase the kinetic energy of molecules, causing them to move faster and diffuse more quickly across the membrane. Conversely, lower temperatures slow down molecular movement and diffusion.
3. Examine molecular size: Smaller molecules diffuse more easily and quickly across a membrane compared to larger molecules, which may encounter resistance or require specialized transport mechanisms.
4. Evaluate the concentration gradient: The rate of diffusion is directly proportional to the steepness of the concentration gradient. A larger difference in concentration between two areas results in faster diffusion.
5. Exclude irrelevant factors: The color of molecules does not affect the rate of diffusion, as diffusion is a physical process influenced by molecular properties and environmental conditions, not visual characteristics.