The phenomenon that explains the exchange of gases during respiration in animals is called diffusion. In this process, oxygen from the air enters the lungs and passes into the bloodstream, while carbon dioxide moves from the blood to the lungs to be exhaled. Diffusion occurs due to the concentration gradient—oxygen moves from areas of higher concentration (inhaled air) to lower concentration (in the bloodstream) and vice versa for carbon dioxide. This process is essential for cellular respiration.