Dissociation Curves

• What do dissociation curves show?

  Shows how sturated the haemoglobin is with oxygen at any given partial pressure
• What does 100% saturation mean?

  Every haemoglobin molecule is carrying the maximum of 4 molecules of oxygen
• What does 0% saturation mean?

  none of the Hb molecules are carrying any oxygen
• Where is pO2 high?

  eg in the lungs
• Where is pO2 low?

  eg in respiring tissues
• What happens where pO2 is high?

  Hb has a high affinity for oxygen - (i.e. it will readily combine with oxygen) so it has a high saturation of oxygen
• What happens where pO2 is low?

  Haemoglobin has a low affinity for oxygen- this means it releases oxygen rather than combines with it

  • That is why it has a low saturation of oxygen
• Why is the graph S-shaped?


  when haemoglobin combines with the first O2 molecule, its shape alters in a way that makes it easier for other molecules to join too
• What happens on the graph as the Hb starts to become saturated?

  It gets harder for O2 molecule to join = the curve has a steep part in the middle where it is really easy for O2 molecules to join, and SHALLOW bits at each end where it is harder
• What happens when the curve is steep?

  A small change in pO2 causes a big change in the amount of O2 carried by the Hb