Most of the carbon dioxide in the blood is carried in the form of

Options

A. carbonic acid
B. bicarbonates
C. carbaminohaemoglobin
D. dissolved `CO_2`

Answer

**Step-by-Step Solution:**

1. **Understanding Carbon Dioxide Transport**: Carbon dioxide (CO2) is a waste product produced by cells during metabolism. It needs to be transported from the tissues to the lungs for exhalation.

2. **Forms of Carbon Dioxide in Blood**: CO2 can be carried in the blood in three main forms:
- Dissolved in plasma
- As bicarbonate ions (HCO3-)
- Bound to hemoglobin as carbamino compounds

3. **Analyzing the Options**:
- **Carbonic Acid**: While CO2 can react with water to form carbonic acid (H2CO3), this is not the primary form in which CO2 is transported in the blood.
- **Bicarbonate**: Most of the CO2 (about 70%) is converted into bicarbonate ions (HCO3-) in the red blood cells. This process involves the enzyme carbonic anhydrase, which facilitates the reaction between CO2 and water.
- **Carbamino-Hemoglobin**: CO2 can bind to hemoglobin to form carbamino compounds, but this accounts for a smaller percentage of CO2 transport.
- **Dissolved CO2**: A small amount of CO2 is transported dissolved in plasma, but this is not the predominant form.

4. **Conclusion**: The majority of carbon dioxide in the blood is carried in the form of bicarbonate ions (HCO3-).

5. **Final Answer**: Most of the carbon dioxide in the blood is carried in the form of bicarbonate (HCO3-).

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