How is hemoglobin's affinity for oxygen affected by the presence or absence of oxygen?

• A. Hemoglobin's affinity for oxygen decreases as more oxygen molecules bind to it.
• B. Hemoglobin's affinity for oxygen is not influenced by oxygen binding but by carbon dioxide levels.
• C. Hemoglobin's affinity for oxygen increases as more oxygen molecules bind to it.
• D. Hemoglobin's affinity for oxygen remains constant regardless of oxygen binding.

Answer: (C)

Verified step by step guidance

1. Understand the concept of hemoglobin's affinity for oxygen, which refers to how readily hemoglobin binds to oxygen molecules.
2. Recognize that hemoglobin exhibits cooperative binding, meaning that the binding of one oxygen molecule increases the affinity for subsequent oxygen molecules.
3. Identify the correct statement: Hemoglobin's affinity for oxygen increases as more oxygen molecules bind to it, due to the cooperative nature of hemoglobin.
4. Consider the physiological significance of this property, which allows hemoglobin to efficiently load oxygen in the lungs and release it in tissues where it is needed.
5. Review the Bohr effect, which describes how factors like pH and carbon dioxide levels can also influence hemoglobin's oxygen affinity, but the primary focus here is on the cooperative binding mechanism.