Number of RBCs per unit volume of blood is likey to be higher in person living at high altitudes , because

Options

A. air clean and unpolluted
B. more sunshine is available
C. air is less dense
D. vegetation gives out more `O_(2)`

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks why the number of red blood cells (RBCs) per unit volume of blood is likely to be higher in individuals living at high altitudes.

2. **Analyzing the Options**:
- **Option 1: Air clean and unpolluted**: This option is incorrect because the cleanliness of the air does not directly affect the number of RBCs.
- **Option 2: More sunshine is available**: This option is also incorrect as sunshine does not influence the production of RBCs.
- **Option 3: Air is less dense**: This option is correct. At high altitudes, the air pressure is lower, which means there is less oxygen available in the air.
- **Option 4: Vegetation gives out more oxygen**: This option is incorrect because while vegetation does produce oxygen, it does not significantly affect the RBC count in high-altitude environments.

3. **Explaining the Correct Answer**:
- At high altitudes, the atmospheric pressure decreases, leading to a lower partial pressure of oxygen. This means that there is less oxygen available for breathing.
- In response to the lower oxygen availability, the body compensates by producing more red blood cells to enhance oxygen transport in the blood. This physiological adaptation helps individuals living at high altitudes to maintain adequate oxygen levels in their tissues.

4. **Conclusion**: Therefore, the number of RBCs per unit volume of blood is higher in individuals living at high altitudes primarily because the air is less dense, resulting in lower oxygen levels, which stimulates increased RBC production.

**Final Answer**: The number of RBCs per unit volume of blood is likely to be higher in a person living at high altitudes because the air is less dense, leading to lower oxygen availability and a compensatory increase in RBC production.

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