Which of the following best describes the role of a concentration gradient in the process of diffusion?

• A. Molecules move randomly with no regard to concentration differences.
• B. Molecules move from an area of lower concentration to an area of higher concentration.
• C. Molecules only move when there is no concentration gradient present.
• D. Molecules move from an area of higher concentration to an area of lower concentration.

Answer: (D)

Verified step by step guidance

1. Understand the concept of diffusion: Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient, until equilibrium is reached.
2. Clarify the role of the concentration gradient: A concentration gradient is the difference in the concentration of molecules across a space. It acts as the driving force for diffusion, causing molecules to move down the gradient (from high to low concentration).
3. Eliminate incorrect options: Analyze each option provided in the problem. For example, 'Molecules move randomly with no regard to concentration differences' is incorrect because diffusion is influenced by the concentration gradient.
4. Focus on the correct description: The correct answer is 'Molecules move from an area of higher concentration to an area of lower concentration,' which aligns with the definition of diffusion and the role of the concentration gradient.
5. Summarize the process: Diffusion occurs due to the natural tendency of molecules to spread out evenly in a space, and the concentration gradient is essential for this movement to occur passively without the need for energy input.