Final answer:
B) 3 A hemoglobin molecule can carry four oxygen molecules. At 75% saturation, three of the four heme units are bound to oxygen, so a 75% saturated hemoglobin molecule has three oxygen atoms bound to it.
Step-by-step explanation:
The question is how many oxygen atoms would be bound to a hemoglobin molecule that is 75% saturated. Each hemoglobin molecule can bind up to four oxygen molecules.
Therefore, at 100% saturation, a hemoglobin molecule would have all four of its heme units bound to oxygen. At 75% saturation, three out of four heme units would be occupied with oxygen, as the saturation percentage can be seen as a direct indicator of the proportion of bound oxygen molecules.
Hence, the correct answer is B) 3 oxygen atoms bound to a hemoglobin molecule that is 75% saturated.