Answer:
The answer is Pulmonary alveoli
Step-by-step explanation:
Pulmonary alveoli are the primary gas exchange site. The alveoli are in intimate contact with the surrounding capillaries, removing the CO2 from the blood and passing the oxygen through a pressure gradient. This barrier between air and blood has a thickness of approximately one micron. To maintain this exchange gradient to the lungs, between 5 and 8 L of air per minute must enter.