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Question #46321
The Question
During placental gas exchange, fetal hemoglobin (HbF) exhibits a left-shifted oxygen dissociation curve compared to maternal adult hemoglobin (HbA). Which of the following accurately describes the structural basis and physiological consequence of this shift?
Options
- A.
The gamma-chains of HbF have a lower affinity for 2,3-BPG compared to the beta-chains of HbA, preventing the stabilization of the T-state and ensuring O2 loading at lower pO2.
- B.
HbF exhibits an exaggerated Bohr effect, allowing it to bind oxygen more tightly in the presence of the high pCO2 levels found in the placental environment.
- C.
The replacement of alpha-chains with gamma-chains in HbF eliminates the allosteric binding site for CO2, making fetal blood immune to the Haldane effect.
- D.
Fetal erythrocytes secrete high levels of 2,3-BPG into the placental villi, which shifts the maternal oxygen dissociation curve to the right, forcing O2 release.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Haldane_Effect|Oxyhemoglobin_Dissociation_Curve|Nucleic_Acid_Structural_Stability
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'HbF has a higher O2 affinity' (left shift) but fail to connect it to the structural mismatch (reduced 2,3-BPG binding) rather than an inherent increase in O2 binding capability.
Furthermore, distractors exploit common misconceptions about the Bohr effect (confusing triggers for loading vs. unloading) and the exact polypeptide chain substitutions in fetal hemoglobin.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Breathing and Exchange of Gases - Class 11 |
| Concept | Haldane Effect vs. Bohr Effect |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |