Correct option is B
Explanation-
At low pH (more acidic, e.g., due to higher CO₂), hemoglobin's affinity for O₂ decreases, so the oxygen dissociation curve shifts to the right — promoting O₂ unloading in tissues.
At high pH (more basic, less CO₂), hemoglobin's affinity for O₂ increases, so the curve shifts to the left — promoting O₂ binding in lungs.
Curve Analysis:
Curve A – Shifted Left (Higher O₂ Affinity)
Position: Left of curve B.
Hemoglobin has a higher affinity for oxygen — it binds O₂ more readily and releases it less easily to the tissues.
Caused by: ↑ pH (alkaline), ↓ CO₂ (less carbonic acid → higher pH), ↓ Temperature, ↓ 2,3-BPG (2,3-bisphosphoglycerate)
Curve B – Standard (Physiological Condition)
Position: Reference (middle) curve.
Oxygen binding at normal pH (7.4) and normal CO₂ concentration. This is the baseline curve, and changes in pH, CO₂, temperature, or 2,3-BPG will shift the curve left or right. It represents normal O₂ binding and release.
Curve C – Shifted Right (Lower O₂ Affinity)
Position: Right of curve B.
Hemoglobin has lower affinity for O₂ — it releases O₂ more readily. It represents oxygen unloading in tissues.
Caused by: ↓ pH (acidic), ↑ CO₂ (Bohr effect), ↑ Temperature, ↑ 2,3-BPG
Curve D – Abnormal (Very Low Saturation)
Position: Flat and very low across all pO₂ values.
Hemoglobin fails to bind oxygen effectively. It represents non-functional oxygen transport.
Could be due to: Defective hemoglobin (e.g., methemoglobinemia), carbon monoxide poisoning (CO binds irreversibly to Hb), severe anemia or structural abnormality
An increase in pH shifts the curve to the left → matches Curve A.
Final answer : Option b - Curve A
