Question

carbon dioxide is carried in the blood, mainly as

Answer 1

it is carried as a bicarbonate ion.

Answer 2

Carbon dioxide (CO₂) is carried in the blood mainly in the form of bicarbonate (HCO₃⁻) ions.

Explanation:

There are three ways by which CO₂ is carried in the blood.

1. As bicarbonate ions (85%)

2. Dissolved in plasma (5%)

3. Bound to plasma proteins and haemoglobin (10%)

Bicarbonate ions.

1. When CO₂ diffuses into RBCs, the enzyme carbonic anhydrase converts it into carbonic acid (H₂CO₃).
2. This is immediately broken down to bicarbonate (HCO₃⁻) and hydrogen (H⁺) ions.
3. The Chloride shift: While the H⁺ ion binds to hemoglobin in the RBCs, bicarbonate ions move out of the red cells to the plasma and are replaced with chloride (Cl⁻) ions. This is called the chloride shift.
4. As the blood reaches the lungs, the reverse reactions occur.

• Bicarbonates enter RBCs replacing the Cl⁻ ions.
• H⁺ ions dissociate from hemoglobin and react with bicarbonates to form carbonic acid.
• The same carbonic anhydrase enzyme then mediates the conversion of carbonic acid back into carbon dioxide and water.

Finally, during exhalation, the carbon dioxide moves out of the lungs.