O2-Binding Physiology — What do the oxygen-binding curves of hemoglobin and myoglobin collectively achieve, and what structural feature of hemoglobin underlies the difference?

Introduction:
Hemoglobin and myoglobin exhibit distinct oxygen-binding behaviors that together optimize oxygen uptake in lungs and release in tissues. Understanding these curves connects biochemistry to physiological oxygen delivery.

Given Data / Assumptions:

• Myoglobin behaves as a single-site binder with a hyperbolic curve.
• Hemoglobin is a tetramer with cooperative binding, producing a sigmoidal curve.
• Efficient oxygen transfer requires high loading in lungs and unloading in tissues.

Concept / Approach:
Relate curve shapes to function. Hemoglobin's quaternary structure enables cooperative transitions between lower- and higher-affinity states, whereas myoglobin's single-site binding yields high affinity for storage within muscle.

Step-by-Step Solution:

Verification / Alternative check:
Classic Hill analysis shows hemoglobin's Hill coefficient >1 (cooperative), whereas myoglobin's is approximately 1 (noncooperative), confirming differing curve shapes.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming high affinity always improves delivery; in fact, controlled affinity changes in hemoglobin are essential for release in tissues.

Final Answer:
Both (a) and (b).