Final answer:
Animals exchange gas with the atmosphere through respiration, a biological process where gases move across cell membranes by diffusion based on concentration gradients, primarily occurring in the lungs.
Step-by-step explanation:
The process utilized by animals to exchange gas in the atmosphere is known as respiration. During this biological process, gases are transferred across cell membranes to either enter or leave the blood. Particularly in gas exchange, oxygen diffuses from the air in the lungs into the blood, while carbon dioxide and other waste gases move from the blood into the air in the lungs. This process is driven by a concentration gradient, facilitated by diffusion, where gas molecules move from a region of higher concentration to one of lower concentration. In addition to the lungs, several parts of the respiratory system, including the nasal cavity and the bronchioles, play roles in preparing the air for this efficient gas exchange. Moreover, the large surface area provided by the alveoli in the lungs maximizes the area over which gas exchange can occur.