Transport of Carbon Dioxide (A-level Biology)

Transport of Carbon Dioxide


  • Myoglobin is a substances that can act as another respiratory pigment. As it is found in muscle, it does not travel in the blood.
  • It has more of an affinity for oxygen than haemoglobin. Because of this, it only releases oxygen at a very low partial pressure.
  • Myoglobin only has one polypeptide chain and is often found in animals living in aerobic mud.
  • Its function is to act as a store of oxygen. This acts to prevent aerobic respiration occurring. The process is outlined below:
  1. Carbon dioxide diffuses into erythrocytes from the tissues
  2. The carbon dioxide then reacts with water, producing carbonic acid. This reaction is catalysed by carbonic anhydrase, an enzyme in the cell.
    • Carbonic acid ionises into H+ and HCO3
    • Haemoglobin combines with H+ ions to form haemoglobinic acid (very weak)
    • Carbonic acid ions diffuse into blood plasma where it is able to be transported to the lungs
    • Chlorine ions diffuse into the red blood cell from the plasma, counteracting the build up of positive charge from the H+ ions. This is called the chloride shift.
    • This whole process reverses once the blood reaches the lungs.
    • Whilst most of the CO2 in the blood is carried this way, a small amount can be combined with haemoglobin to be carried as carbaminohaemoglobin.

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