Carbon dioxide (CO) diffuses into blood from tissue site and passes to alveolar site in the form of

Options

A. bicarbonate: 70%
B. bicarbonate: 20-25%
C. carbamino haemoglobin: 60-70%
D. carbamino haemoglobin: 7%

Answer

To answer the question "Carbon dioxide (CO2) diffuses into blood from tissue site and passes to alveolar site in the form of," we need to understand how carbon dioxide is transported in the blood. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Understanding CO2 Diffusion**: Carbon dioxide (CO2) is produced in the tissues as a byproduct of cellular respiration. It diffuses from the tissue cells into the blood.

2. **Transport Mechanisms**: Once in the blood, CO2 is transported in three main forms:
- **Dissolved in Plasma**: A small amount of CO2 (about 7-10%) is dissolved directly in the plasma.
- **Carbamino Compounds**: About 20-25% of CO2 binds to hemoglobin and other proteins to form carbamino compounds (carbaminohemoglobin).
- **Bicarbonate Ions**: The majority of CO2 (approximately 70%) is converted into bicarbonate ions (HCO3-) in the red blood cells.

3. **Conversion to Bicarbonate**: The conversion of CO2 to bicarbonate is facilitated by the enzyme carbonic anhydrase, which catalyzes the reaction:
\[ CO2 + H2O \leftrightarrow H2CO3 \leftrightarrow H^+ + HCO3^- \]
This reaction allows CO2 to be transported efficiently in the blood.

4. **Final Transport to Alveoli**: When blood reaches the alveoli in the lungs, CO2 is released from bicarbonate and carbamino compounds, diffusing back into the alveoli to be exhaled.

5. **Conclusion**: Therefore, the primary form in which CO2 is transported from tissues to the alveolar site is as bicarbonate ions.

### Answer:
Carbon dioxide (CO2) diffuses into blood from tissue sites and passes to alveolar sites primarily in the form of bicarbonate ions (approximately 70%).

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