CO₂ Transport and Bicarbonate Formation — NEET Biology
📚 Practice ConceptAt the tissue site where partial pressure of CO₂ is high due to catabolism, CO₂ diffuses into blood (RBCs and plasma) and forms HCO₃⁻ and H⁺. At the alveolar site where pCO₂ is low, the reaction proceeds in the opposite direction leading to the formation of CO₂ and H₂O. Thus, CO₂ trapped as bicarbonate at the tissue level and transported to the alveoli is released out as CO₂. Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO₂ to the alveoli.
Which of the following statements are correct regarding carbon dioxide transport from systemic tissues? S1: At the tissue site, where partial pressure of CO₂ (pCO₂) is high due to catabolism, CO₂ diffuses into blood (RBCs and plasma). S2: The enzyme carbonic anhydrase, which facilitates the conversion of CO₂ and H₂O, is present only in minute quantities in the plasma and is absent in RBCs. S3: The binding of CO₂ to hemoglobin to form carbamino-haemoglobin is mainly promoted by low pCO₂ and high pO₂ conditions. S4: Most of the bicarbonate ions (HCO₃⁻) formed from CO₂ within the RBCs largely remain inside the RBCs, contributing to their osmotic balance. S5: Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO₂ to the alveoli.
View solution & NCERT explanation
Correct answer: A — S1 and S5 are correct
Let's evaluate each statement regarding carbon dioxide transport from systemic tissues: S1: At the tissue site, due to high metabolic activity, the pCO₂ is high. This creates a pressure gradient, causing CO₂ to diffuse from the tissues into the blood (both RBCs and plasma). This statement is correct. S2: RBCs contain a very high concentration of the enzyme carbonic anhydrase, and minute quantities of the same are present in the plasma too. Therefore, the statement that it is present only in minute quantities in plasma and absent in RBCs is incorrect. S3: The binding of CO₂ to hemoglobin as carbamino-haemoglobin is favored when pCO₂ is high and pO₂ is low (as in the tissues), not by low pCO₂ and high pO₂. This statement is incorrect. S4: At the tissue site, CO₂ diffuses into RBCs and forms HCO₃⁻ and H⁺. A significant portion of HCO₃⁻ then moves into the plasma (chloride shift), it does not largely remain within the RBCs. This statement is incorrect. S5: Under normal physiological conditions, every 100 ml of deoxygenated blood delivers approximately 4 ml of CO₂ to the alveoli. This statement is correct. Therefore, statements S1 and S5 are correct.
What does NCERT say about At tissue site where?
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