Page 305 - Biology_F5

Biology for Advanced Level Secondary Schools

Therefore, most haemoglobin molecules are saturated with oxygen. This situation is
likely to occur in the lungs, where oxygen concentration is high.

100
% saturation of haemoglobin with oxygen
FOR ONLINE READING ONLY
80

60

40

20

0
0 5 10 15
Partial pressure of oxygen/ KPa

Figure 6.4: The oxygen dissociation curve of haemoglobin

The effect of carbon dioxide in the dissociation curves when less carbon
transport of oxygen in blood dioxide is present and when more carbon
Increased concentration of carbon dioxide dioxide is present in the blood.
can affect oxygen transport in the blood.
This is because haemoglobin can combine The Bohr Effect
with carbon dioxide (although to a lesser The Bohr Effect describes how an increase
extent) to form carbaminohaemoglobin. in carbon dioxide partial pressure of the
The presence of carbon dioxide lowers blood or decrease in blood pH results
the affinity of haemoglobin to oxygen into a lower affinity of haemoglobin to
and causes the release of oxygen from oxygen. It is manifested by right-ward
haemoglobin. Therefore, an increase in shifting of oxygen dissociation curve,
carbon dioxide in the tissues causes faster resulting from enhanced unloading of
release of oxygen from haemoglobin and oxygen by haemoglobin. The relationship
this is known as the Bohr Effect which is between carbon dioxide partial pressure
the result of shifting of dissociation curves and blood pH is mediated by carbonic
to the right in areas with increased partial anhydrase, which catalyses conversion of
pressure of carbon dioxide (Figure 6.5). carbon dioxide to carbonic acid, that in
The effect of carbon dioxide concentration turn releases a free hydrogen ion, hence
on oxygen transport by haemoglobin can reducing the local pH of blood.
be revealed by comparing the oxygen

Form Five Student’s Book
298