The correct option is 5 mL.
Explanation
Oxygen transport in the blood is primarily facilitated by hemoglobin, an iron-containing pigment in red blood cells. The efficiency of oxygen delivery is determined by the oxygen-carrying capacity of hemoglobin and the physiological demand of the tissues.
Detailed Analysis
- Hemoglobin Content: Under normal conditions, 100 mL of blood contains approximately 15 grams of hemoglobin.
- Oxygen Binding Capacity: Each gram of hemoglobin can bind with approximately 1.34 mL of oxygen. Therefore, 100 mL of oxygenated blood carries roughly 20 mL of oxygen ($15 \text{ g} \times 1.34 \text{ mL/g}$).
- Oxygen Delivery: As blood passes through the systemic capillaries, tissues extract oxygen for metabolic activities. Under normal resting physiological conditions, the blood does not release its entire oxygen load.
- Venous Reserve: The deoxygenated blood returning to the heart retains approximately 15 mL of oxygen per 100 mL.
- Conclusion: The amount of oxygen actually delivered to the tissues is the difference between the arterial and venous oxygen content, which is approximately 5 mL per 100 mL of blood ($20 \text{ mL} - 15 \text{ mL}$).
Key Takeaway: While 100 mL of oxygenated blood carries about 20 mL of oxygen, it delivers only about 5 mL to tissues under normal resting conditions. During strenuous exercise, this delivery can increase significantly.