Oxygen crosses tiny air sacs into blood, rides on hemoglobin's iron, and is burned in mitochondria to release energy.
How it works, step by step
Air reaches ~480 million alveoli.
Oxygen diffuses into capillaries.
Hemoglobin's iron carries it to tissues.
Mitochondria use it to make ATP; CO₂ returns to be exhaled.
Evidence & sources
Hemoglobin, an iron-containing protein in red blood cells, carries oxygen from the lungs to tissues. Evidence: established. Known: Foundational physiology. Unknown: — Source: NIH Office of Dietary Supplements, Iron — Health Professional Fact Sheet (Current revision).