The variety of life:
Haemoglobin
By the end of the lesson you should be able to:
1. What haemoglobin is and how it is different in different
living things
2. What an oxygen dissociation curve is
3. The impact of different adaptations on oxygen dissociation
Blood
Haemoglobins
•
•
•
•
A family of molecules
Protein
Function: Oxygen transport
Spelling haemoglobin (UK),
hemoglobin (US)
Structure of haemoglobin
Primary:
Secondary:
Tertiary:
Quaternary:
Transport of Oxygen
• Haemoglobins
• Haem group combines with
oxygen
• 4 O2 per molecule of
haemoglobin
Oxygen + Haemoglobin
↔
Oxyhaemoglobin
4O2
↔
HbO8
+
Hb
Oxygen + Haemoglobin ↔ Oxyhaemoglobin
• Haemoglobin has a high affinity for oxygen in
oxygen-rich situations and becomes saturated:
haemoglobin is loaded with oxygen in the
lungs.
• Oxyhaemoglobin dissociates in oxygen-poor
situations: Oxygen Is unloaded in tissues.
Oxygen + Haemoglobin ↔ Oxyhaemoglobin
• The amount (%) of haemoglobin that is saturated
with oxygen depends on the concentration
(partial pressure) of oxygen in the environment.
• What is partial pressure? See ‘Hint’ box on page
152
Standard oxygen dissociation curve
Haemoglobin dissociation curve
A small drop in oxygen (being used
more in respiration) brings about a
large decrease in % saturation
Therefore, more oxygen available to
tissues for respiration
Different types of haemoglobin
• Different organisms in different environments
have different haemoglobins
• Some haemoglobins have a high affinity for
oxygen: They take up oxygen more easily but
release it less readily (e.g. organisms which live
in a low oxygen environment)
• Some haemoglobins have a low affinity for
oxygen: They take up oxygen less easily but
release it quickly (e.g. organisms with a fast rate
of respiration)
Effect of carbon dioxide on curve
If you are exercising you
need more oxygen for
aerobic respiration. You want
the haemoglobin to
dissociate (give up its
oxygen) at higher partial
pressures / more readily
This shift is known as the
Bohr shift
Due to acidity of carbon
dioxide
So, more exercise leads to
Bohr shift
Some creatures need to grab hold
of more oxygen…
Hb becomes saturated at
lower partial pressures of
oxygen.
Summary
Example Questions
The graph shows the oxygen haemoglobin dissociation curves for three
species of fish.
Species A lives in water containing a low partial pressure of oxygen.
Species C lives in water with a high partial pressure of oxygen.
(a) Explain the advantage to species A of
having haemoglobin with a curve in
this position.
(3 marks)
Hb (in A) has greater affinity
for O2;
becomes saturated at low(er)
ppO2 / more saturated at
same ppO2 / unsaturated at
very low ppO2;
able to supply enough O2 to
its tissues;
Species A and B live in
the same place but B is
more active. Suggest an
advantage to B of having
an oxygen haemoglobin
dissociation curve to the
right of that for A.
(2 marks)
fish B has a greater rate of respiration (accept more O2 needed for
respiration);
Hb dissociates more readily (than A);
more O2 supplied;
Shrews are small mammals.
Their tissues have a much
higher respiration rate than
human tissues. The graph
shows the position of the oxygen
haemoglobin dissociation curves
for a shrew and a human.
Explain the advantage to the shrew of the
position of the curve being different from
that of a human. (2 marks)
high respiration rate means high demand for oxygen;
shrew haemoglobin has lower affinity for oxygen / gives up O2 more
readily;
shrew Hb lower saturation rate than human Hb at same partial
pressure / more O2 released at same pp;
Deer mice are small mammals which live in North America. One
population lives at high altitude and another at low altitude. Less oxygen
is available at high altitude. The graph shows the oxygen haemoglobin
dissociation curves for the two populations of deer mice.
(a) Explain the advantage for mice
living at high altitude in having a
dissociation curve which is to the left of
the curve for mice living at low altitude.
(2 marks)
(b) Suggest why it would be a
disadvantage for the curve to be much
further to the
left. (1 mark)
(a)
 high altitudes have a low partial pressure of O2;
high saturation/affinity of Hb with O2 (at low partial pressure O2);
sufficient/enough O2 supplied to cells / tissues; 2 max
(b) difficult to unload/dissociate O2 (at tissues); 1 mark