Questions: Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.

The answer is the third one: Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.

Explanation for each option:

1. "Diffusion is the movement of molecules from an area of low concentration to an area of high concentration." - This statement is incorrect. Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration, not the other way around.

2. "Diffusion requires ATP to function." - This statement is incorrect. Diffusion is a passive process that does not require energy (ATP). It occurs naturally due to the random movement of molecules.

3. "Diffusion is the movement of molecules from an area of high concentration to an area of low concentration." - This statement is correct. It accurately describes the process of diffusion, where molecules move down their concentration gradient.

4. "Diffusion is the movement of molecules across a plasma membrane, regardless of concentration gradient." - This statement is incorrect. While diffusion can occur across a plasma membrane, it specifically involves movement down a concentration gradient, from high to low concentration.

In summary, the correct statement about diffusion is that it involves the movement of molecules from an area of high concentration to an area of low concentration.