An erythrocyte holding about 300 million hemoglobin molecules can transport up to how many oxygen molecules?

1. Each hemoglobin molecule carries four heme groups. 2. Each heme holds one iron ion, and each iron ion binds one oxygen molecule. 3. One hemoglobin molecule therefore transports four oxygen molecules. 4. An erythrocyte may contain about 300 million hemoglobin molecules. 5. Multiplying 300 million by four gives 1.2 billion oxygen molecules. 6. About 300 million is the hemoglobin count itself, the answer for someone who forgets the factor of four. 7. About 600 million assumes two oxygen molecules per hemoglobin, and 2.4 billion assumes eight, so both misread the number of heme groups. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.3 Erythrocytes_