In cellular biology, diffusion is primarily characterized by which of the following?

Diffusion is a fundamental process in cellular biology characterized by the movement of molecules from an area of high concentration to an area of low concentration. This concept is rooted in the tendency of substances to distribute themselves evenly in a given space. As molecules move down their concentration gradient, they achieve equilibrium, minimizing concentration differences across the membrane or within a solution.

This process is passive, meaning it does not require energy input; instead, it is driven by the kinetic energy of the molecules themselves. The movement continues until there is no longer a concentration gradient, at which point the molecules are evenly distributed. This mechanism is essential for various biological functions, such as gas exchange in the lungs and the uptake of nutrients by cells.

Other mechanisms, such as facilitated diffusion (which involves assisted movement through protein channels), active transport (which does require energy), and considerations around isotonic solutions, all describe different processes in cellular transport but do not define diffusion itself.