When a concentration gradient exists, dissolved substances move from an area of _____ concentration to an area of _____ concentration. This movement is known as what?

The movement of dissolved substances along a concentration gradient occurs when these substances move from an area of higher concentration to an area of lower concentration. This process is known as diffusion. In diffusion, molecules naturally move to achieve an equilibrium, where their concentrations become evenly distributed across a space.

Understanding diffusion is fundamental to the study of animal physiology, as this process plays a vital role in many physiological functions, including gas exchange in the lungs and the movement of nutrients and waste products across cell membranes. In biological systems, substances tend to move toward areas where they are less concentrated to balance out concentration differences, demonstrating the principle of spontaneous movement governed by concentration gradients.