The curve obtained when percentage saturation of Hb with `O_2` is plotted against `pO_2` is

Options

A. J shaped
B. Rectangular hyperbola
C. Linear curve
D. Sigmoid curve

Answer

To solve the question regarding the curve obtained when the percentage saturation of hemoglobin (Hb) with oxygen (O2) is plotted against the partial pressure of O2 (pO2), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Variables**:
- The x-axis will represent the partial pressure of oxygen (pO2).
- The y-axis will represent the percentage saturation of hemoglobin with oxygen.

2. **Concept of Hemoglobin Saturation**:
- Hemoglobin can bind to oxygen, and its saturation level indicates how much oxygen is bound to hemoglobin at various pressures of oxygen.

3. **Plotting the Graph**:
- As the partial pressure of O2 increases, the percentage saturation of hemoglobin also increases. Initially, at low pO2, the increase in saturation is slow.

4. **Identify the Shape of the Curve**:
- At low pO2, the curve rises slowly (low saturation).
- As pO2 increases, the curve steepens (high saturation).
- Eventually, as pO2 continues to rise, the curve levels off, indicating that hemoglobin is becoming fully saturated with oxygen.

5. **Conclusion on the Type of Curve**:
- The overall shape of the graph is sigmoidal (S-shaped). This is characteristic of cooperative binding, where the binding of one oxygen molecule increases the likelihood of additional oxygen molecules binding to hemoglobin.

6. **Final Answer**:
- The curve obtained when the percentage saturation of Hb with O2 is plotted against pO2 is a **sigmoid curve**.