Final answer:
In humans, concurrent gas exchange occurs in flexible lungs, whereas in birds, countercurrent gas exchange occurs in minimally expandable lungs. This reflects the adaptation of bird respiration for efficient oxygen uptake required for flight.
Step-by-step explanation:
In humans, concurrent gas exchange occurs in flexible lungs, while in birds, countercurrent gas exchange occurs in minimally expandable lungs. The bird respiratory system is highly efficient due to unidirectional airflow, which pairs with a counter-current exchange system to maximize oxygen absorption—especially vital for the high metabolic demands of flight. In contrast, human lungs feature a bidirectional flow of air through branching bronchi and alveoli, fostering gas exchange that uses pressure differences to move oxygen into the blood and carbon dioxide out. Understanding these differences gives insight into how diverse respiratory systems have adapted to meet the oxygen demands of various organisms.