Which of the following is the most important factor that determines whether oxygen binds to or dissociates from haemoglobin?

Options

A. Partial pressure of carbon dioxide
B. pH
C. Body temperature
D. Partial pressure of oxygen

Answer

To determine the most important factor that influences whether oxygen binds to or dissociates from hemoglobin, we can analyze the given options step by step.

### Step-by-Step Solution:

1. **Understanding the Factors**:
- The options provided are:
- A) Partial pressure of carbon dioxide (pCO2)
- B) pH
- C) Body temperature
- D) Partial pressure of oxygen (pO2)

2. **Role of Each Factor**:
- **Partial Pressure of Carbon Dioxide (pCO2)**: A low pCO2 favors oxygen binding to hemoglobin. When CO2 levels are high, it promotes the release of oxygen (Bohr effect).
- **pH**: A higher pH (more alkaline) favors oxygen binding, while a lower pH (more acidic) promotes oxygen release.
- **Body Temperature**: Lower temperatures favor oxygen binding, while higher temperatures promote oxygen release.
- **Partial Pressure of Oxygen (pO2)**: This is the concentration of oxygen available. A high pO2 is crucial for oxygen to bind effectively to hemoglobin.

3. **Identifying the Most Important Factor**:
- While all the factors influence oxygen binding, the most critical factor is the **partial pressure of oxygen (pO2)**.
- If the pO2 is low, it does not matter what the levels of pCO2, pH, or temperature are; oxygen will not bind to hemoglobin effectively. Conversely, if pO2 is high, it allows the other factors to play their roles in enhancing oxygen binding.

4. **Conclusion**:
- Therefore, the most important factor that determines whether oxygen binds to or dissociates from hemoglobin is the **partial pressure of oxygen (pO2)**.

### Final Answer:
The most important factor is **D) Partial pressure of oxygen (pO2)**.

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