Question

In man percentage of CO${}_2$, transported as bicarbonates is

• A. 5% to 10%
• B. 70% to 80%
• C. 90% to 95%
• D. 50% to 65%

Answer 1

The correct option is B 70% to 80%

The majority of carbon dioxide molecules (85 percent) are carried as part of the bicarbonate buffer system. In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H${}_2$CO${}_3$). Carbonic acid is an unstable, intermediate molecule that immediately dissociates into bicarbonate ions (HCO${}_{3-}$) and hydrogen (H+) ions. Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood, down its concentration gradient. It also results in the production of H+ ions. If too much H+ is produced, it can alter blood pH. However, hemoglobin binds to the free H+ ions, limiting shifts in pH. The newly-synthesized bicarbonate ion is transported out of the red blood cell into the liquid component of the blood in exchange for a chloride ion (Cl-). This is called the chloride shift.

Therefore, the correct answer is option B.