Question

The graph shows the oxygen dissociation curves of haemoglobin from two species of mammals, S and T.

Which statements could explain the difference in the oxygen dissociation curves of species S and species T?
I. Species T has a higher haemoglobin concentration in its red blood cells than species S.
II. The haemoglobin in species T has a lower affinity for oxygen than the haemoglobin in species S.
III. Species T may be living at a higher altitudes than species S.

• A. I, and III only
• B. II and III only
• C. I, II, and III
• D. III only

Answer 1

Answer: (C)

The oxy-haemoglobin dissociation curve provides information about the relation between the partial pressure of oxygen and the oxygen saturation. Haemoglobin's affinity for oxygen increases as more molecules of oxygen bind to it. Thus, a higher number of molecules bind as the oxygen partial pressure increases until the maximum amount that can be bound is reached. The curve on the right (T) indicates that there is an easy dissociation of oxyhaemoglobin. This occurs when there is a lower affinity between oxygen and haemoglobin. Some conditions which decrease affinity are low partial pressure of oxygen, the high partial pressure of carbon dioxide, low pH, high temperature and high altitudes.
In acute mountain syndrome (AMS), the following changes take place in the individual: the number of RBC increases (polycythemia), the affinity of hemoglobin to oxygen decreases, etc.