Summary OCR A/AS-Level Biology 3.2.7 Transport of Oxygen and Carbon Dioxide

Transport of Oxygen
Haemoglobin
 Transported in erythrocytes (red blood cells)
 Associates with oxygen to form oxyhaemoglobin (Hb(CO₂)₄)
 Consists of 4 polypeptide chains in a quaternary structure
 Each chain consists of a non-protein haem group each containing an iron ion (Fe2+)
which attracts and holds oxygen molecules
 Haemoglobin has a high affinity for oxygen
 Oxygen dissociates and leaves haemoglobin to be released into respiring tissues



Partial Pressure of Oxygen
 Oxygen tension = oxygen concentration
 Also called partial pressure of oxygen (pO₂) and measured in kilopascals (kPa)
 Oxygen has a long diffusion distance to the haem group
 Low pO₂ = low saturation
 After one O₂ molecule binds to a haem group, a conformational change occurs in the
haemoglobin molecule
 The shape changes and the haem groups move to the outside
 Allows O₂ molecules to associate with ease
 Approaching 100% saturation, diffusion gradient decreases and oxygen struggles to
associate


After birth there is a change in environment to higher oxygen tension so adult haemoglobin is
different to foetal haemoglobin so dissociation can occur