Oxygen Dissociation Curves

Different Positions of the Oxygen Dissociation Curve:

• The further to the left the curve, the greater the affinity of haemaglobin for oxygen (takes up oxygen easily, releases it less easily) Organisms with environments of lower O2 have haemaglobin with a higher affinity for O2. This is because they need to extract as much O2 as possible from their environment.
• The further to the right the curve, the lower the affinity of haemaglobin for oxygen (takes up O2 less easily, releases it more easily) Organisms with environments of higher O2 or are very active have a lower affinity for O2. This is because they already have plentiful O2 in their environment so need it to be released easily to their respiring tissues.

Loading, Transport and Unloading of Oxygen:

• At the gas exchange surface (lungs) CO2 is constantly being removed.
• This increases the pH (due to lack of CO2)
• At this increased pH, haemoglobin changes its shape so O2 can be loaded more readily. 
• Because the affinity for O2 also increases, O2 is not released whilst being transported in the blood.
• CO2 is being released by respiring tissues.
• This increase in CO2 lowers the pH.
• This changes the shape of haemoglobin to have a lower affinity for O2.
• Therefore O2 is released into respiring tissues.