During the exchange of gases in the human respiratory system ,Carbon dioxide is transported from tissues to respiratory surface by only

Options

A. plasma and erythrocytes
B. plasma
C. erythrocytes
D. erythrocytes and leucocytes

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: The question asks how carbon dioxide (CO2) is transported from tissues to the respiratory surface in the human body. It's important to know that CO2 is produced as a waste product during cellular respiration in tissues.

2. **Identifying the Source of CO2**: During metabolic reactions in tissues, glucose is oxidized, resulting in the production of carbon dioxide. This leads to a higher partial pressure of CO2 in the tissues compared to the blood.

3. **Role of Hemoglobin**: Red blood cells (RBCs) contain hemoglobin, which can bind to gases. The binding of hemoglobin to CO2 occurs when the partial pressure of CO2 is high, resulting in the formation of carbaminohemoglobin.

4. **Transport Mechanisms**: Carbon dioxide is transported in three main ways:
- **Dissolved in Plasma**: About 7% of CO2 is transported dissolved in the plasma.
- **Bound to Hemoglobin**: Approximately 23% of CO2 binds to hemoglobin to form carbaminohemoglobin.
- **As Bicarbonate Ions**: The majority, about 70%, is converted to bicarbonate ions (HCO3-) in the blood.

5. **Conclusion**: The question specifically asks how CO2 is transported from tissues to the respiratory surface. The correct answer is that it is transported by both plasma and red blood cells (RBCs). Therefore, the option that states "both plasma and erythrocytes" is correct.

**Final Answer**: Carbon dioxide is transported from tissues to the respiratory surface by both plasma and red blood cells (RBCs).

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