Moves air in and out so oxygen can enter the blood and carbon dioxide can leave.
Path of air
Nose and mouth → throat → trachea → bronchi → bronchioles → about 480 million tiny air sacs (alveoli).
Control
Breathing rate is driven mainly by carbon dioxide levels in the blood, not oxygen.
Evidence & sources
In the lungs' tiny air sacs (alveoli), oxygen moves into the blood and carbon dioxide moves out. Evidence: established. Known: Basic physiology. Unknown: — Source: NIH National Heart, Lung, and Blood Institute, How the Lungs Work (Current revision).