1. Oxygen Dissociation Curves
Text p.152

2. Objectives What is an oxygen dissociation curve?
What is the effect of carbon dioxide concentration on the curve and why?

3. What is an oxygen dissociation curve?
Why don’t we just use oxygen concentration?

4. How is oxygen concentration measured?
Oxygen binds to haemoglobin when oxygen is at a high concentration, and dissociates from haemoglobin when oxygen is at a low concentration.
The concentration of a gas in a mixture of gases can be quantified in terms of its partial pressure. This is the amount of pressure exerted by the gas relative to the total pressure exerted by all the gases in the mixture.
Partial pressure is measured in kilopascals (kPa) and is written as P(O2) or pO2, P(CO2), etc.
Write down pp definition from blue box
Photo credit: Jupiterimages Corporation
Teacher notes
When a gas is dissolved in a liquid, as is the case with gas transport in blood, the partial pressure is slightly more complex. In this case, the liquid is treated as if it were in equilibrium with a gas phase, and the partial pressures are those that would be exerted by the gases in that phase.

5. The oxygen dissociation curve

7. Oxygen dissociation curves
Using your diagram of adult human oxygen dissociation curve:
Add the title
Annotate the axes so you really understand what is on each of the x and y
What does it show?
Why isn’t it a straight line?
What is the name for this shape of curve?
What 2 facts are important to remember about dissociation curves?

8. A schematic visual model of oxygen binding process, showing all four monomers and haems, and protein chains.
Oxygen is not shown in this model, but it binds to the iron (red sphere) in the flat haem.
This causes the iron atom to move backward into the haem which holds it, tugging the histidine residue (modeled as a red pentagon on the right of the iron) closer, as it does. This, in turn, pulls on the protein chain holding the histidine.

9. Factors affecting oxygen dissociation

10. Effects of carbon dioxide concentration – the Bohr effect.
Using your diagram of the effect of carbon dioxide concentration on the oxygen dissociation curve:
Add the title
Describe to your partner:
what effect carbon dioxide has on oxygen dissociation and
how this influences what haemoglobin does in different parts of the body (lungs/respiring tissues)

11. Effects of carbon dioxide concentration – the Bohr effect.
Haemoglobin has a reduced … for oxygen in the presence of carbon dioxide.
In the lungs carbon dioxide concentration is…, so haemoglobin has a higher affinity for oxygen (curve to the…). Together with the … concentration of oxygen this means oxygen readily combines with haemoglobin to make oxyhaemoglobin
In respiring tissues carbon dioxide is … so haemoglobin has a lower affinity for oxygen (curve to …). Together with the … concentration of oxygen this means oxyhaemoglobin will readily dissociate into oxygen and haemoglobin, releasing the oxygen the tissues require.
Missing words - Left right affinity low low high high

12. Answer -Effects of carbon dioxide concentration – the Bohr effect.
Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.
In the lungs P(CO2) is low, so haemoglobin has a higher affinity for oxygen (curve to the left). Together with the high P(O2) this means oxygen readily combines with haemoglobin to make oxyhaemoglobin
In respiring tissues P(CO2) is high so haemoglobin has a lower affinity for oxygen (curve to right). Together with the low P(O2) this means oxyhaemoglobin will readily dissociate into oxygen and haemoglobin, releasing the oxygen the tissues require.

13. Why does the Bohr effect occur
Why does the Bohr effect occur? Order the cards into 2 sets, check and copy
In lungs
Carbon dioxide is removed so is low
pH higher as carbon dioxide is low
Haemoglobin is a shape that can load oxygen readily
Oxygen binds haemoglobin
Haemoglobin becomes ‘loaded’ with oxygen
In respiring tissues
Carbon dioxide is produced so is high
pH lower as carbon dioxide dissolves to give a weak acid
Haemoglobin changes shape into one with a lower affinity for oxygen
Haemoglobin releases oxygen into the respiring tissues.
Haemoglobin becomes ‘unloaded’ with oxygen

15. Loading, transport and unloading of oxygen (fig 3 p.153)
Why is it that the more active a tissue is, the more oxygen is unloaded?
In humans haemoglobin leaving the lungs is saturated. What does this mean?
What is haemoglobin like after passing through an inactive tissue?
What is haemoglobin carrying after passing through a very active tissue?

16. Plenary - Understanding oxygen transport