Oxygen is carried round the body by haemoglobin.
1. Red blood cells contain haemoglobin.
2. It's a large protein with a quaternary structure - it's made up of four polypeptide chains.
3. Each chain has a haem group which contains iron and gives haemoglobin its red colour.
4. It has a high affinity for oxygen - each molecule can carry four oxygen molecules.
5. in the lungs, it joins to oxygen to form oxyhaemoglobin.
6. This is a reversible reaction - oxygen dissociates from it near the body cells and turns it back to haemoglobin.
The partial pressure (pp) of oxygen is a measure of concentration.
The greater the concentration if dissolved oxygen in cells, the higher the pp.
Haemoglobins affinity for oxygen varies depending on the pp of oxygen.
Oxygen loads onto haemoglobin where there's a high pp.
Oxyhaeomoglobin unloads its oxygen where there's a low pp.
The lungs have a high pp of oxygen.
Respiring tissues have a low pp of oxygen.
The concentration of carbon dioxide affects oxygen unloading.
haemoglobin gives up its oxygen more readily at higher pressures of carbon dioxide.
1. When cells respire, they give off carbon dioxide.
2. This increases the rate of oxygen unloading - so the dissociation curve 'shifts' down. The saturation of blood with oxygen is lower, meaning that more oxygen is being released.
3. This is called the Bohr effect.
Different organisms haave different types of haemoglobin with different oxygen transporting capacities.
Organisms that live in evnironments with low concentrations of oxygen have haemoglobin with a higher affinity for oxygen - the dissociation curve is to the left of ours.
Organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen - the dissociation curve is to the right of ours.
Good luck on your exams!