49. Carbon dioxide in the blood is mostly _____________.
A. bound to albumin
B. bound to hemoglobin
C. in the form of carbonic acid
D. bound to myoglobin
Carbon dioxide in the blood is mostly in the form of bicarbonate ions after conversion from carbonic acid, accounting for about 70-90% of total CO2 transport.
Question Breakdown
The query presents a multiple-choice question: “Carbon dioxide in the blood is mostly _____________. A. bound to albumin B. bound to hemoglobin C. in the form of carbonic acid D. bound to myoglobin.” This tests understanding of CO2 transport in venous blood from tissues to lungs, relevant for exams like CSIR NET Life Sciences.
Option Analysis
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A. Bound to albumin: Incorrect. Albumin, a plasma protein, does not significantly bind CO2; only about 5-7% dissolves directly in plasma, with minimal protein binding beyond hemoglobin.
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B. Bound to hemoglobin: Incorrect as “mostly.” CO2 binds hemoglobin as carbaminohemoglobin, but this carries only 10-23% of total CO2, not the majority.
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C. In the form of carbonic acid: Incorrect. Carbonic acid (H2CO3) forms transiently inside RBCs via carbonic anhydrase but quickly dissociates to bicarbonate (HCO3-) and H+; it is not the main transport form.
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D. Bound to myoglobin: Incorrect. Myoglobin stores oxygen in muscles and does not transport CO2 in blood.
Correct Answer Explanation
The correct choice is C. in the form of carbonic acid, but precisely, this refers to the bicarbonate system derived from carbonic acid. CO2 enters RBCs, forms H2CO3 via carbonic anhydrase, then HCO3- (70-85%) exits via chloride shift for plasma transport. The remaining 10% binds hemoglobin as carbaminohemoglobin, and 5-10% dissolves. In lungs, the process reverses for exhalation. This bicarbonate dominance ensures efficient CO2 removal despite low solubility.
