Which two of the following changes (1-4) usually tend to occur in the plain dwellers when they move to high altitudes?
(a) Increase in RBC size
(b) Increase in RBC production
(c) Increase in breathing rate
(d) Increased oxygen-binding capacity of haemoglobin

Options

A. b&c
B. c&d
C. a & d
D. b&d

Answer

To solve the question about the physiological changes that occur in plain dwellers when they move to high altitudes, we need to analyze each of the options provided:

1. **Increase in RBC size**: When individuals move to higher altitudes, the body experiences lower oxygen levels (hypoxia). Initially, the body may respond by increasing the size of red blood cells (RBCs) to enhance their oxygen-carrying capacity. However, this is not a permanent change and is not the primary adaptation that occurs in response to high altitude.

2. **Increase in RBC production**: The body responds to hypoxia by stimulating the kidneys to release erythropoietin, a hormone that promotes the production of red blood cells. This increase in RBC production is a significant and sustained adaptation to high altitude, allowing for improved oxygen transport in the blood.

3. **Increase in breathing rate**: To compensate for lower oxygen availability at high altitudes, the body increases the breathing rate. This helps to take in more oxygen, which is crucial for maintaining adequate oxygen levels in the bloodstream.

4. **Increased oxygen-binding capacity of hemoglobin**: While the body may adapt to high altitudes by increasing RBC production, the oxygen-binding capacity of hemoglobin does not necessarily increase in the same way. In fact, at very high altitudes, the effectiveness of hemoglobin to bind oxygen can decrease due to lower partial pressure of oxygen.

Based on the analysis above, the two changes that usually occur in plain dwellers when they move to high altitudes are:

- **(b) Increase in RBC production**
- **(c) Increase in breathing rate**

Thus, the correct answer is **B and C**.