Breathing and Exchange of Gases

People living at sea level have around 5 million RBC per cubic millimetre of their blood whereas those living at an altitude of 5400 metres have around 8 million. This is because at high altitude

1. people eat more nutritive food, therefore more RBCs are formed
2. people get pollution-free air to breathe and more oxygen is available
3. atmospheric O2 level is less and hence more RBCs are needed to absorb the required amount of O2 to survive
4. there is more UV radiation which enhances RBC production.

Answer

(3) atmospheric O2 level is less and hence more RBCs are needed to absorb the required amount of O2 to survive

Solution

At high altitude the atmospheric pressure, and hence the partial pressure of O2, is low.

Less O2 binds to haemoglobin; the kidneys release erythropoietin, which stimulates the bone marrow to form more RBCs.

More RBCs (more haemoglobin) are needed to absorb the required amount of O2.

Answer: (3)