What is the term for the difference in concentration between two solutions?

The term that describes the difference in concentration between two solutions is known as a concentration gradient. This concept refers to the variation in the amount of a substance across a particular space, and it is fundamental in biological processes such as osmosis and diffusion.

When there is a concentration gradient, molecules tend to move from an area of higher concentration to an area of lower concentration in an attempt to reach equilibrium. This movement is driven by the tendency of substances to disperse evenly in their environment. Understanding concentration gradients is crucial in cellular processes, as they influence the way substances enter and exit cells, affecting everything from nutrient absorption to waste removal.

Osmotic pressure relates specifically to the pressure required to prevent the flow of water across a semipermeable membrane, while diffusion rate refers to how fast a substance moves across a distance. Equilibrium describes a state where the concentrations are balanced, and no net movement occurs, which is the outcome of a concentration gradient being equalized. Thus, the concentration gradient is the correct term for the difference in concentration between two solutions.