Transport of O₂ and CO₂ in Blood — NEET Biology
📚 Practice ConceptOxygen is transported mainly as oxyhaemoglobin. In the alveoli where pO₂ is higher, O₂ gets bound to haemoglobin which is easily dissociated at the tissues where pO₂ is low and pCO₂ and H⁺ concentration are high. Nearly 70 per cent of carbon dioxide is transported as bicarbonate (HCO₃⁻) with the help of the enzyme carbonic anhydrase. 20-25 per cent of carbon dioxide is carried by haemoglobin as carbamino-haemoglobin. In the tissues where pCO₂ is high, it gets bound to blood whereas in the alveoli where pCO₂ is low and pO₂ is high, it gets removed from the blood.
Which of the above statements are correct? S1: Approximately 70% of carbon dioxide is transported from tissues to alveoli in the form of bicarbonate ions, primarily generated in the plasma. S2: Carbonic anhydrase is an enzyme found in high concentration in RBCs and also in minute quantities in the plasma. S3: At the tissue site, high pCO2 and low pO2 favor the formation of carbamino-haemoglobin. S4: The reaction CO2 + H2O → H2CO3 occurs spontaneously in tissues without enzymatic catalysis at a significant rate. S5: Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO2 to the alveoli.
View solution & NCERT explanation
Correct answer: B — S2, S3 and S5 are correct
The question concerns the transport mechanisms of carbon dioxide in the blood, focusing on bicarbonate formation, enzyme involvement, and factors affecting transport. S1: Approximately 70% of CO2 is carried as bicarbonate. However, the formation of bicarbonate (HCO3-) primarily occurs within the Red Blood Cells (RBCs) due to the high concentration of carbonic anhydrase, not primarily in the plasma. From RBCs, HCO3- diffuses into the plasma. Therefore, S1 is incorrect. S2: Carbonic anhydrase is indeed present in very high concentration within RBCs, and minute quantities of the same enzyme are also found in the plasma. This statement is directly in line with NCERT text. Therefore, S2 is correct. S3: At the tissue site, metabolic activities lead to high pCO2 and low pO2. These conditions are favorable for the binding of carbon dioxide with haemoglobin to form carbamino-haemoglobin. Therefore, S3 is correct. S4: The reaction CO2 + H2O ⇌ H2CO3 is facilitated by the enzyme carbonic anhydrase. Without this enzyme, the reaction would occur at a much slower rate, not at a significant rate spontaneously. Therefore, S4 is incorrect. S5: The NCERT text explicitly states that every 100 ml of deoxygenated blood delivers approximately 4 ml of CO2 to the alveoli. Therefore, S5 is correct. Based on the analysis, statements S2, S3, and S5 are correct. Final Answer: Option B is the correct answer as it includes all the correct statements (S2, S3, S5) and excludes the incorrect ones (S1, S4).
What does NCERT say about Oxygen transported mainly as?
Has this concept appeared in NEET?
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