What is the process called that involves the movement of particles from regions of higher density to regions of lower density?

The process of moving particles from regions of higher density to regions of lower density is known as diffusion. This phenomenon occurs as particles naturally spread out to achieve an even concentration throughout a given area. In diffusion, no energy is required; instead, particles move due to their kinetic energy, which causes them to collide and spread apart. This process is vital in many biological and physical systems, such as the exchange of gases in the lungs or the mixing of substances in solutions.

Osmosis specifically describes the movement of water molecules through a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration, which is a subset of diffusion but does not encompass the broader definition of particle movement referred to in the question.

Active transport, on the other hand, involves the movement of particles against their concentration gradient, which requires energy input, typically in the form of ATP. This process is different from diffusion as it is not driven by the natural tendency to move from high to low concentration.

Filtration is distinct as it involves the passage of fluids and solutes through a filter or membrane driven by pressure differences, which is a different mechanism than the spontaneous dispersion of particles characteristic of diffusion.

Thus, diffusion is the process that