Final answer:
The site of gas exchange between air and blood occurs in the alveoli of the lungs, where oxygen is absorbed and carbon dioxide is expelled through the process of diffusion.
Step-by-step explanation:
The site of gas exchange between air and blood occurs in the alveoli of the lungs. These tiny sacs are surrounded by networks of pulmonary capillaries, where oxygen is picked up and carbon dioxide is released. This process, known as pulmonary gas exchange, involves the diffusion of gases across cell membranes, following the concentration gradients without the need for energy.
After inhalation, the oxygen concentration is higher in the alveoli than in the blood, causing oxygen to diffuse from the alveoli into the capillaries. Concurrently, carbon dioxide diffuses from the blood in the capillaries into the alveoli due to its higher concentration in the blood.
The efficiency of gas exchange is maximized by the anatomy of the alveoli: their walls are extremely thin, the respiratory membrane is highly permeable to gases, there is a significant surface area available, and a continuous blood flow maintains a steep concentration gradient for optimal diffusion.