The Bohr Shift (CIE A Level Biology)

• Changes in the oxygen dissociation curve as a result of carbon dioxide levels are known as the Bohr effect, or Bohr shift
• When the partial pressure of carbon dioxide in the blood is high, haemoglobin’s affinity for oxygen is reduced
  • This is the case in respiring tissues, where cells are producing carbon dioxide as a waste product of respiration
  • This occurs because CO₂ lowers the pH of the blood
    • CO₂ combines with water to form carbonic acid
    • Carbonic acid dissociates into hydrogen carbonate ions and hydrogen ions
    • Hydrogen ions bind to haemoglobin, causing the release of oxygen
• This is a helpful change because it means that haemoglobin gives up its oxygen more readily in the respiring tissues where it is needed
• On a graph showing the dissociation curve, the curve shifts to the right when CO₂ levels increase
  • This means that at any given partial pressure of oxygen, the percentage saturation of haemoglobin is lower at higher levels of CO₂

The dissociation curve shifts to the right as a result of the Bohr effect. This means that any given partial pressure of oxygen, the percentage saturation of haemoglobin is lower at higher CO₂ levels.