What is the mechanism called when particles move from an area of higher solute concentration to an area of lower solute concentration?

The mechanism described, where particles move from an area of higher solute concentration to an area of lower solute concentration, is known as diffusion. This process is a fundamental concept in biology and chemistry, illustrating how substances naturally spread out in a given space over time.

In diffusion, molecules move along their concentration gradient until equilibrium is reached, which means that the concentration of the solute becomes uniform throughout the solution. This movement occurs without the need for external energy, making it a passive transport mechanism. It is crucial for various physiological processes, such as gas exchange in the lungs and the distribution of nutrients and waste products in and out of cells.

Other mechanisms described in the options serve different purposes or operate under different conditions. For instance, osmosis specifically refers to the movement of water across a selectively permeable membrane, driven by differences in solute concentration. Active transport involves the movement of substances against their concentration gradient, requiring energy, often in the form of ATP. Filtration typically involves the movement of water and solutes across a membrane due to pressure differences rather than concentration gradients. Thus, diffusion is the correct mechanism in this context as it directly pertains to the movement of solutes from high to low concentration without additional factors involved.