Question

The majority of carbon dioxide produced by our body cells is transported to the lungs :

• A. Dissolved in the blood
• B. As bicarbonates
• C. As carbonates
• D. Attached to hemoglobin

Answer 1

The Correct Option is B

To understand how the majority of carbon dioxide (CO₂) produced in body cells is transported to the lungs, we need to comprehend the various mechanisms involved in CO₂ transportation in the blood.

Transportation Methods of Carbon Dioxide:

1. Dissolved in Plasma: A small percentage (around 5-10%) of CO₂ is transported dissolved directly in the blood plasma.
2. Carbamino Compounds: About 20-30% of CO₂ combines with hemoglobin and other proteins to form carbamino compounds, but this is not the predominant method.
3. Bicarbonates: The majority (approximately 60-70%) of CO₂ in the blood is transported in the form of bicarbonate ions (HCO₃^-). This conversion occurs inside red blood cells where CO₂ reacts with water under the influence of the enzyme carbonic anhydrase, forming carbonic acid, which quickly dissociates into bicarbonate and hydrogen ions.

The reaction that occurs is:

CO_2 + H_2O \leftrightarrow H_2CO_3 \leftrightarrow HCO_3^- + H^+

Conclusion:

The transport of carbon dioxide as bicarbonate ions is the most significant and effective mechanism. This is because it allows for significant amounts of CO₂ to be transported in the blood without significantly altering blood pH. Therefore, the correct answer is As bicarbonates.

Eliminating Other Options:

• Dissolved in the Blood: While CO₂ does dissolve in the blood, it is not the major route compared to bicarbonate transport.
• As Carbonates: Carbonates are not typically formed in the blood; the main ionic form is bicarbonate.
• Attached to Hemoglobin: Though some CO₂ is carried by hemoglobin, it is not the primary transportation route.

Hence, the majority of CO₂ is transported as bicarbonate ions.