This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Basic function of hemoglobin is 
Select and explain. 
A. Increased O2 delivery in lung and uptake at tissue, B. Increased O2 delivery at tissue and uptake in lung, C. Increased CO2 delivery at tissue and uptake in lung, D. None of the above
B: Increased O2 delivery at tissue and uptake in lung
Answer: B: Increased O2 delivery at tissue and uptake in lung 
Explanation: The red, oxygen-carrying pigment in the red blood cells of veebrates is hemoglobinEach of the four iron atoms in hemoglobin can reversibly bind one O2 moleculeIt takes up O2 from lungs due to increase in pO2 and released in tissues where pO2 is lessIn this way, 250 mL of O2 per minute is transpoed from the blood to the tissues at rest.Ref: Ganong's Review of Medical Physiology Twenty-Third Edition Page No: 610