What is a concentration gradient?

A concentration gradient refers to the difference in concentration of a particular substance across a space or between two areas. This concept is fundamental to understanding processes such as diffusion and osmosis in biology. When there is a concentration gradient present, molecules tend to move from an area of higher concentration to an area of lower concentration in an effort to achieve equilibrium.

This movement occurs because particles are in constant motion and tend to spread out to areas with less concentration over time. The steeper the gradient, the more significant the driving force for diffusion, leading to a faster rate of movement. It is a key concept in various biological processes, including nutrient absorption, gas exchange in respiration, and signaling in neurons.

Other options do not accurately describe a concentration gradient as they focus on different aspects. While one suggests a measurement of solute, another refers to the force exerted by solute particles, which is unrelated. The last choice talks about the movement of solute from low to high concentration, which actually describes active transport rather than the concentration gradient itself. Therefore, choice C most accurately captures the essence of what a concentration gradient signifies in biological contexts.