Transport of 02 by haemoglobin

• Oxygen dissociation curve


  Graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen
• Explanation for the shape of the oxygen dissociation curve

  1. Haemoglobin molecule makes it difficult for the first oxygen molecule to bind

  2. Binding of first oxygen molecule changes the quaternary structure of haemoglobin

  3. Binding of second oxygen molecule is easier

  4. Binding of third and fourth oxygen molecules becomes harder
• There are different types of haemoglobin molecules in different species, each with a different shape and hence a different affinity for oxygen
• The shape of any one type of haemoglobin molecule can change under different conditions
• Oxygen dissociation curve position


  • The further to the left, the greater the affinity of haemoglobin for oxygen
  • The further to the right, the lower the affinity of haemoglobin for oxygen
• Higher carbon dioxide concentration

  Haemoglobin has reduced affinity for oxygen (Bohr effect)
• At gas-exchange surface (e.g. lungs)

  Carbon dioxide concentration is low, affinity of haemoglobin for oxygen is increased, oxygen is loaded
• In rapidly respiring tissues (e.g. muscles)


  Carbon dioxide concentration is high, affinity of haemoglobin for oxygen is reduced, oxygen is readily unloaded
• Dissolved carbon dioxide is acidic and the low pH causes haemoglobin to change shape
• Loading, transport and unloading of oxygen


  1. At gas-exchange surface, carbon dioxide is removed, pH is slightly raised, haemoglobin shape changes to enable oxygen loading

  2. In tissues, carbon dioxide is produced, pH is lowered, haemoglobin shape changes to enable oxygen unloading
• The higher the rate of respiration, the more carbon dioxide the tissues produce, the lower the pH, the greater the haemoglobin shape change, the more readily oxygen is unloaded, the more oxygen is available for respiration
• Different species


  • Lugworm
  • Llama
• Lugworm haemoglobin has a higher affinity for oxygen than human haemoglobin, allowing it to extract more oxygen from low oxygen environments
• Llama haemoglobin has a higher affinity for oxygen than human haemoglobin, allowing it to load oxygen at the lower partial pressures found at high altitudes