NCERT Class 11 Science — Chapter 4: Breathing and Exchange of Gases

Correct Option

The correct option is Low pCO2 and high pO2

Explanation

Carbamino-haemoglobin is the compound formed when carbon dioxide binds to the amino group of the globin chain in haemoglobin. Approximately 20-25% of carbon dioxide is transported in the blood in this form. The binding and dissociation of carbon dioxide are primarily regulated by the partial pressures of carbon dioxide (pCO₂) and oxygen (pO₂).

Analysis of Conditions

The dissociation of carbamino-haemoglobin (release of CO₂) occurs at the alveoli to facilitate exhalation. The factors influencing this are:

• Partial Pressure of Oxygen (pO₂): In the alveoli, pO₂ is high. High pO₂ favors the binding of oxygen to haemoglobin to form oxyhaemoglobin. The formation of oxyhaemoglobin promotes the release of carbon dioxide from carbamino-haemoglobin (Haldane Effect).
• Partial Pressure of Carbon Dioxide (pCO₂): In the alveoli, pCO₂ is lower compared to the deoxygenated blood arriving from the tissues. This gradient encourages the dissociation of CO₂ from haemoglobin and its diffusion into the alveoli.

Conversely, in the tissues, low pO₂ and high pCO₂ favor the binding of carbon dioxide to haemoglobin.

Conclusion: The combination of low pCO₂ and high pO₂ is the specific physiological condition at the alveoli that favors the dissociation of carbamino-haemoglobin.

Key Takeaway: High pO₂ and low pCO₂ at the alveolar surface facilitate the dissociation of CO₂ from carbamino-haemoglobin, whereas low pO₂ and high pCO₂ at the tissue level favor its formation.