7. In the figure, the three curves represent hemoglobin oxygen binding at three different pH values, pH 7.2, pH 7.4, and pH 7.6. What conclusion can be drawn from these data about the oxygen binding of hemoglobin at different pH values? 

A) Low pH favors the high affinity oxygen binding state.

B) Low pH favors the low affinity oxygen binding state.

C) Oxygen affinity is independent of pH.

D) Oxygen binding is non-cooperative at low pH.

Answer Analysis

The correct answer is B.

Rationale: This is a data-based statistical reasoning question that again draws on your knowledge of protein structure and function. You are asked to explain the oxygen binding property of hemoglobin using the graph provided. You must evaluate and compare the hemoglobin oxygen binding data, or percent saturation of blood with O2, for each pH value to determine the relationship between pH and hemoglobin oxygen affinity. This approach will allow you to conclude that the lower the pH, the lower the affinity of hemoglobin for oxygen.

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