What is the process of simple diffusion?

Simple diffusion refers to the process where particles move from an area of high concentration to an area of low concentration. This movement occurs as a result of the natural kinetic energy of the molecules, which causes them to spread out in an attempt to achieve equilibrium within the environment.

This process is passive, meaning it does not require energy input from the cell or organism. Simple diffusion is a fundamental concept in cellular biology, as it explains how substances like oxygen and carbon dioxide pass through cell membranes and how nutrients can move in and out of cells. Understanding this concept is crucial for grasping how molecules interact within biological systems and how concentration gradients drive many processes essential for life.

The other options describe different processes that do not align with the definition of simple diffusion. For instance, active transport involves energy usage to move substances against their concentration gradient, while the movement of particles from low to high concentration is characteristic of that process. The diffusion of water through a semi-permeable membrane is a specific case known as osmosis, rather than simple diffusion, which pertains more broadly to substances in general.