Question

Which of the following has the greatest effect on the ability of blood to transport O2 (oxygen)?

• A. Capacity of the blood to dissolve O2
• B. Amount of haemoglobin in the blood
• C. CO2 (Carbon dioxide) content of RBCs
• D. pH of plasma

Hint:

Oxygen Carrying Capacity: $> 98.5\%$ of blood $\text{O}_2$ is bound to Hemoglobin. Total oxygen content is directly proportional to Hemoglobin concentration ($[\text{Hb}]$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Total arterial oxygen content ($ ext{CaO}_2$) is overwhelmingly determined by chemically bound oxygen to hemoglobin rather than dissolved plasma oxygen.
Key Formula or Approach:
\[ \text{CaO}_2 = ([ ext{Hb}] \times 1.34 \times S_{\text{aO}_2}) + (0.003 \times P_{\text{aO}_2}) \]

Step 2: Detailed Explanation:
In blood oxygen carrying capacity:
- Oxygen is transported in two forms:
1. Chemically Bound to Hemoglobin: $1\text{ g of Hb}$ carries $1.34\text{ mL of } \text{O}_2$. At normal $[\text{Hb}] = 15\text{ g/dL}$, bound $\text{O}_2 \approx 20.1\text{ mL/dL}$ (representing $> 98.5\%$ of total blood oxygen).
2. Physically Dissolved in Plasma: Only $0.003\text{ mL } \text{O}_2 / \text{dL / mmHg}$ ($0.3\text{ mL/dL}$ at $100\text{ mmHg}$, representing $< 1.5\%$).
Therefore, the total amount of hemoglobin in the blood has by far the greatest quantitative effect on blood oxygen transport capacity.

Step 3: Final Answer:
Thus, the Amount of haemoglobin in the blood has the greatest effect, matching option (B).