Which of the following statements is not true ?

Options

A. The partial pressure of oxygen in oxygenated blood is 95 mm Hg
B. The partial pressure of oxygen in the alveolar air is 104 mm Hg
C. The partial pressure of carbon dioxide in the alveolar air is 40mm Hg
D. The partial pressure of carbon dioxide in deoxygenated blood is 95 mm Hg

Answer

To determine which of the following statements is not true, we will analyze each statement regarding the partial pressures of oxygen and carbon dioxide in blood and alveolar air.

1. **Statement 1**: The partial pressure of oxygen in oxygenated blood is 95 millimeters of mercury (mmHg).
- This statement is true. The normal partial pressure of oxygen in oxygenated blood is approximately 95 mmHg.

2. **Statement 2**: The partial pressure of oxygen in the alveolar air is 104 millimeters of mercury (mmHg).
- This statement is also true. The partial pressure of oxygen in the alveolar air is typically around 104 mmHg.

3. **Statement 3**: The partial pressure of carbon dioxide in the alveolar air is 40 millimeters of mercury (mmHg).
- This statement is true as well. The normal partial pressure of carbon dioxide in the alveolar air is about 40 mmHg.

4. **Statement 4**: The partial pressure of carbon dioxide in deoxygenated blood is 95 millimeters of mercury (mmHg).
- This statement is not true. The partial pressure of carbon dioxide in deoxygenated blood is approximately 45 mmHg, not 95 mmHg.

Based on the analysis, the statement that is not true is:

**Answer**: The partial pressure of carbon dioxide in deoxygenated blood is 95 millimeters of mercury.