Biology · Breathing and Exchange of Gases · NEET
No. These are often confused but are totally different. Carbamino-haemoglobin is CO2 (carbon dioxide) bound to haemoglobin, and it is a normal, reversible part of CO2 transport (about 20-25% of CO2). Carboxyhaemoglobin is CO (carbon monoxide) bound to haemoglobin, which is a poisonous, almost irreversible binding that blocks oxygen carriage. NCERT deals only with carbamino-haemoglobin here, but NEET options may plant carboxyhaemoglobin as a trap.
No. Oxygen binds to the iron (Fe) of the haem group to form oxyhaemoglobin. CO2 binds to the amino (globin/protein) part of haemoglobin, not to iron, to form carbamino-haemoglobin. Because they use different sites, blood can carry oxygen and some CO2 on the same haemoglobin molecule at the same time. This is why pO2 (not just pCO2) influences CO2 binding.
About 20-25% of CO2 is carried as carbamino-haemoglobin (bound to haemoglobin in RBCs). Remember the full NCERT split of total CO2 transport: about 70% as bicarbonate (HCO3-), about 20-25% as carbamino-haemoglobin, and about 7% dissolved in plasma. Bicarbonate is the major form; carbamino-haemoglobin is second.
CO2 binding to haemoglobin depends on pCO2. At the alveoli pCO2 is low and pO2 is high, so the reaction reverses: CO2 dissociates from carbamino-haemoglobin and is released to be breathed out. At the tissues pCO2 is high and pO2 is low, so CO2 binds. So the same partial-pressure gradient that loads CO2 at tissues unloads it at the lungs.
Bicarbonate carries far more. Bicarbonate (HCO3-) accounts for about 70% of CO2 transport and is formed with the help of the enzyme carbonic anhydrase inside RBCs. Carbamino-haemoglobin carries only about 20-25%. A common NEET mistake is to call carbamino-haemoglobin the main form of CO2 transport; the main form is bicarbonate.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the compound formed when carbon dioxide binds to the amino (globin) part of haemoglobin. In this form haemoglobin carries about 20-25% of the CO2 in blood.
About 20-25% of total CO2. The rest is about 70% as bicarbonate and about 7% dissolved in plasma.
The partial pressure of CO2 (pCO2) is the main control, and pO2 is also a major factor. High pCO2 and low pO2 (as at tissues) favour binding; low pCO2 and high pO2 (as at alveoli) cause CO2 to be released.
No. Carbamino-haemoglobin is CO2 bound to haemoglobin and is normal. Carboxyhaemoglobin is carbon monoxide (CO) bound to haemoglobin and is toxic. NEET often uses this pair as a trap.
Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO2 to the alveoli, per NCERT.
