alleryStart learning →How does fetal haemoglobin differ from adult haemoglobin?
AIt has six subunits and binds oxygen weakly
BTwo subunits differ, raising its oxygen affinity
CIt has two subunits and no iron in the heme
DAll four subunits differ, lowering its affinity
Answer & Solution
Correct answer: B. Two subunits differ, raising its oxygen affinity
1. Both fetal and adult haemoglobin are built from four subunits, so subunit count is not the difference.
2. Two of the four subunits of fetal haemoglobin have a different structure.
3. That structural difference gives fetal haemoglobin a greater affinity for oxygen than adult haemoglobin.
4. The higher affinity is what lets the fetus extract oxygen despite a small gradient at the placenta.
5. So the second option is correct.
6. The fourth option gets the direction of affinity backwards, which would leave the fetus unable to load oxygen at all.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 22 "The Respiratory System", section 22.5 Transport of Gases_
Keep practising The Respiratory System
Browse all The Respiratory System questions for NEET PG, or explore more Physiology topics.
Related questions
Why is survival low for a baby born before 26 weeks?By how much has surfactant therapy reduced death from respiratory distress syndrome?What proportions of preterm infants are quoted as developing respiratory distress syndromeWhat happens to the fluid left in the lungs after delivery?How soon after birth does the first inhalation occur?What does the fetus move in and out during fetal breathing movements?Around which week do fetal breathing movements begin?When does a full complement of functional alveoli appear?