Human fetal haemoglobin differs from the adult haemoglobin in that it has

Options

A. higher affinity for oxygen
B. lower affinity for oxygen
C. two subunits only
D. is glycosylated

Explanation

**Step-by-Step Solution:**

1. **Understanding Hemoglobin Types**: Human hemoglobin exists in two main forms: fetal hemoglobin (HbF) and adult hemoglobin (HbA). HbF is primarily found in the fetus, while HbA is the predominant form in adults.

2. **Composition of Hemoglobin**:
- Fetal hemoglobin (HbF) is composed of two alpha chains and two gamma chains (α2γ2).
- Adult hemoglobin (HbA) consists of two alpha chains and two beta chains (α2β2).

3. **Oxygen Affinity**:
- Fetal hemoglobin has a higher affinity for oxygen compared to adult hemoglobin. This means that HbF can bind oxygen more tightly than HbA.
- This higher affinity is crucial for the fetus as it allows for effective oxygen transfer from the mother’s blood through the placenta.

4. **Physiological Importance**:
- The higher affinity of HbF for oxygen ensures that the fetus can extract sufficient oxygen from maternal blood, which is vital for its development.
- As the fetus grows and is born, the production of HbF decreases and is gradually replaced by HbA.

5. **Conclusion**: The key difference between fetal hemoglobin and adult hemoglobin is that fetal hemoglobin has a higher affinity for oxygen due to its unique composition, which is essential for fetal development.

**Final Answer**: Human fetal hemoglobin differs from adult hemoglobin in that it has a higher affinity for oxygen.

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