Final answer:
Concentration gradient is the term given to the difference in concentration between two adjacent areas, dictating the movement of substances via diffusion, such as in osmosis where water moves across a semipermeable membrane until equilibrium is reached.
Step-by-step explanation:
Differences in concentration between two adjacent areas is known as a concentration gradient. This gradient is a crucial aspect of diffusion processes, where molecules move from an area of high concentration to one of low concentration until the concentration is equal on both sides of a membrane, reaching equilibrium. In the special case of osmosis, water moves from an area where it is more concentrated to where it is less concentrated across a semipermeable membrane.
The concentration gradient plays a significant role, given that it is the principal force driving the movement in diffusion. The gradient becomes less steep as the substance diffuses, and the rate of diffusion decreases until equilibrium is reached. In biological systems, molecules move down their concentration gradient to facilitate various cellular processes without the expenditure of additional energy.