Which of the following describes diffusion best?

Diffusion is best described as a passive process that moves solutes from an area of high concentration to an area of low concentration. This movement occurs due to the natural kinetic energy of the particles, which causes them to spread out until they are evenly distributed. The essence of diffusion is its reliance on concentration gradients; substances naturally migrate from crowded regions (high concentration) to less crowded regions (low concentration) without the need for additional energy input. This characteristic defines diffusion as a passive transport mechanism, differentiating it from active transport processes that do require energy to move substances against their concentration gradient.

Other responses highlight either a misunderstanding or a misrepresentation of the principles of diffusion. For example, movement from low to high concentration does not align with the fundamental concept of diffusion, as it contradicts the directionality of how particles behave in a gradient. While it is true that some proteins facilitate the movement of substances across cell membranes, this pertains to facilitated diffusion and does not encompass the broader definition of diffusion itself.