Transport of carbon dioxide

• how can carbon dioxide be transported in the body?

  • dissolved in plasma
  • combined with haemoglobin to form carbaminohaemoglobin
  • converted into hydrogen carbonate ions
• how do hydrogencarbonate ions form?

  • carbon dioxide produced during respiration combines with water to form carbonic acid, catalysed by enzyme carbonic anhydrase
  • carbonic acid dissociates into hydrogen ions and hydrogen carbonate ions
• what are the steps for forming hydrogencarbonate ions?

  • CO2 diffuses from body cells to erythrocytes
  • enzyme in erythrocytes combine CO2 and H2O
  • carbonic acid dissociates
  • hydrogencarbonate ions diffuse out of erythrocytes
  • Cl- chloride shift to maintain charge in erythrocytes
  • oxyhaemoglobin dissociates under influence of H+ ions
  • haemoglobinic acid formed (haemoglobin acts as a pH buffer)
  • oxygen released into blood plasma
• why is carbon dioxide important?

  is essential to the release of oxygen from oxyhaemoglobin to tissue
• what doe the Bohr effect explain?

  • the differing behaviour of haemoglobin in different regions of the body, depending on the levels of carbon dioxide
  • in the presence of carbon dioxide, haemoglobin has a reduced affinity for oxygen
  • is important during exercise because as more CO2 is produced, the more readily O2 is supplied for haemoglobin
• why does the formation of haemoglobinic acid help the dissociation of oxygen?


  • changes 3D tertiary shape which will release oxygen from haem groups
  • due to charges and hydrogen bonding which are slightly altered by H+ ions
  • H+ ions bind to haemoglobin to form haemoglobinic acid
• what is meant by a pH buffer?

  keeps the pH constant by maintaining a constant free concentration of H+ ions
• at actively respiring tissues there is more CO2 produced so there is a higher pCO2 meaning more carbonic acid is produced which increases levels of H+ causing haemoglobin to have a lower affinity for O2 meaning more oxyhaemoglobin dissociates
• what is the advantage of the effects of lactic acid?

  • lactic acid produced by anerobic respiration meaning lack of oxygen
  • this decreases haemoglobins affinity for oxygen so oxyhaemoglobin dissociates
  • the cell that hasn't got enough oxygen receives a greater oxygen supply
• why is carbon monoxide so poisonous?

  • will more readily bind to haemoglobin than oxygen
  • carboxyhaemoglobin is stable so doesn't readily dissociate
  • this reduces oxyhaemoglobin levels preventing cells getting enough oxygen
  • treatment is breathing a higher concentration of oxygen