What term refers to the movement of substances from a high concentration to a low concentration?

The term that describes the movement of substances from a high concentration to a low concentration is diffusion. This process occurs naturally as particles move in an attempt to reach a state of equilibrium, where concentrations are balanced across an area. Diffusion does not require energy input; it relies on the kinetic energy of the molecules involved.

For example, when a drop of dye is placed in water, the dye molecules move from an area of high concentration (the drop) to areas of lower concentration (the surrounding water) until they are evenly distributed. This principle is fundamental not only in biological systems, where it is vital for processes such as gas exchange in cells, but also in various agricultural applications, including nutrient absorption in plants.

In contrast, osmosis specifically refers to the diffusion of water across a semipermeable membrane, making it a narrower term than diffusion. Filtration involves moving substances through a filter based on size or pressure rather than concentration gradients, while transportation typically refers to mechanisms that move materials across various pathways but may involve energy or active processes rather than simply relying on concentration gradients.