1. Module 2 Exchange and transport
Carriage of oxygen

2. Concept question: How does haemoglobin know where to deliver its oxygen?

3. Learning Objectives Success Criteria
To understand the role of haemoglobin in carrying oxygen
To be able to compare fetal and adult haemoglobin curves
Explain the meaning of the term affinity
(Grade E - D)
Describe the role of haemoglobin in carrying oxygen
(Grade C –B)
Explain the significance of the different affinities for oxygen of foetal haemoglobin & adult haemoglobin
(Grade B – A)

4. Haemoglobin
Haemoglobin has a quaternary structure, made up of 4 polypeptide chains.
Each polypeptide chain has a haem group
A haem group has an iron ion (Fe2+)
Each Fe2+ can join to an Oxygen molecule (O2)
Total = 4 O2 molecules can be carried by 1 haemoglobin molecule in humans
Hb O Hb08
Haemoglobin + oxygen Oxyhaemoglobin
Students to make sure it can demonstrate loading and unloading
loading
unloading

5. The Role of Haemoglobin
Main role: to transport oxygen
It must:
Readily associate (loads) with oxygen at the gas exchange surface eg. lungs
Readily dissociate (unloading) from oxygen at the tissues that require it
How does it manage this?
The shape of haemoglobin changes under different conditions e.g. when CO2 is present: haemoglobin’s shape makes it bind more loosely to O2, so it loses the oxygen
It binds more readily at high partial pressures of oxygen

6. Affinity of haemoglobin for O2
Explain the meaning of the term affinity
(Grade E - D)
Affinity of haemoglobin for O2
Copy and complete the table
Region of body
Oxygen Concentration
CO2 concentration
Affinity of haemoglobin for O2
Result – what happens to oxygen?
Gas exchange surface
High
Low
Oxygen is attached
Respiring Tissues
Oxygen is released
Words to use:
High, Low, Oxygen is attached, Oxygen is released

7. The oxygen dissociation curve
Shows how much oxygen is combined with haemoglobin at different oxygen concentrations
100 % - every haemoglobin molecule is carrying the max of 4 molecules of oxygen
Partial pressure – measure of oxygen concentration in a mixture of gases (greater the concentration of dissolved oxygen in cells the higher the partial pressure)
Atmospheric pressure at sea level is 100KPa, so at sea level what is the partial pressure of oxygen?
0 % saturation = none of the haemoglobin molecules are carrying any oxygen

8. Oxygen Dissociation Curves
Why are oxygen dissociation curves S shape.
At low oxygen tension: the 4 chains in the haemoglobin are very closely united, making it difficult to load the first oxygen molecule
When the oxygen tension rises, the diffusion gradient into the haemoglobin molecule steeply rises. Once loaded, the oxygen causes the shape to alter known as a conformational change so the chains can load the other oxygen molecules easier
However as Hb becomes saturated it gets harder for more oxygen to join. It is difficult to reach 100% even at high oxygen pressure, so the curve levels off again.
The steep part of the curve are where its easy for oxygen to join and the shallow bits at the end show where it gets harder.
The graph of this is called the oxygen dissociation curve

9. Oxygen Dissociation Curves
Other 3 oxygen molecules bind easily
Small decrease in partial pressure of O2 leads to a lot of dissociation
First oxygen molecule is difficult to bind

10. Oxygen Dissociation Curves
Describe the role of haemoglobin in carrying oxygen (Grade C –B)
Oxygen Dissociation Curves
May be different for different haemoglobins (in different organisms), but will have a similar shape
Will be in a different place on the graph:
Further to the left: Greater affinity for O2
Further to the right: Lower affinity for O2
Adult and fetal haemoglobin have different affinities for oxygen. Fetal haemoglobin has a higher affinity for oxygen in lower partial pressures of oxygen (better at absorbing oxygen than it’s mothers blood), this is important as the fetus gets oxygen from its mother’s blood across the placenta.
Task – Complete worksheet – page 64 help

11. Plenary Role play the action of haemoglobin and foetal haemoglobin
Fetal haemoglobin curve is shifted to the left
Explain the significance of the different affinities for oxygen of foetal haemoglobin & adult haemoglobin
(Grade B – A)