`CO_(2)` is carried in blood as

Options

A. sodium bicarbonate
B. sodium carbonate
C. potassium carboate
D. magnesium carbonate

Answer

To answer the question "CO₂ is carried in blood as," we need to analyze the different forms in which carbon dioxide is transported in the blood. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Forms of CO₂ Transport
Carbon dioxide (CO₂) is transported in the blood in three main forms:
1. Dissolved in plasma
2. Bound to hemoglobin
3. In the form of bicarbonate ions (HCO₃⁻)

### Step 2: Analyze Each Form
1. **Dissolved in Plasma**: Approximately 7% of CO₂ is transported in this form. This is a minor pathway for CO₂ transport.

2. **Bound to Hemoglobin**: About 20-25% of CO₂ binds to hemoglobin to form carbaminohemoglobin. This is another significant pathway but not the major one.

3. **In the Form of Bicarbonate**: The majority of CO₂, around 70%, is transported in the form of bicarbonate ions. This process occurs primarily in red blood cells (RBCs) where the enzyme carbonic anhydrase catalyzes the reaction between CO₂ and water (H₂O) to form carbonic acid (H₂CO₃), which quickly dissociates into bicarbonate ions (HCO₃⁻) and protons (H⁺).

### Step 3: Identify the Correct Answer
Given the options:
- Sodium bicarbonate
- Sodium carbonate
- Potassium carbonate
- Magnesium carbonate

The correct answer is **sodium bicarbonate**, as this is the form in which the majority of CO₂ is transported in the blood.

### Conclusion
Thus, CO₂ is primarily carried in the blood as sodium bicarbonate.

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