Humans are not able to survive for long periods at very high altitudes primarily because:
1. The oxygen content is very low with respect of that found at sea level.
2. The carbon dioxide is much more than that found at sea level.
3. The partial pressure of oxygen is very low than that found at sea level.
4. The atmospheric pressure is much higher than that found at sea level, which makes the amount of oxygen available one-fourth that found at sea level.

The chloride shift is also known as Hamburger phenomenon and it
1. occurs primarily in pulmonary capillaries.
2. occurs when Cl- replace HCO3- within red blood cells.
3. decreases the formation of bicarbonate ions.
4. decreases the number of hydrogen ions.

The haemoglobin of a human foetus
1. has a lower affinity for oxygen than that of the adult
2. has the same affinity for oxygen as that of an adult
3. has only 2 protein subunits instead of 4
4. has a higher affinity for oxygen than that of an adult

When a man inhales air containing normal concentration of O₂ as well as CO he suffers from suffocation because
1. CO reacts with ${\mathrm{O}}_2$, reducing its percentage in air
2. haemoglobin combines with CO instead of ${\mathrm{O}}_2$ and forms carboxyhaemoglobin
3. CO affects diaphragm and intercostal muscles
4. CO affects the nerves of the lungs

Assertion: Nitric oxide transport by hemoglobin to peripheral tissues is hypothesized to assist oxygen transport in tissues.
Reason: Nitric oxide can also be transported by hemoglobin bound to specific thiol groups in the globin protein.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.