1. F211: Exchange & transport
1.2.2 Transport in animals (oxygen & carbon dioxide transport, dissociation curves & Bohr effect)
By Mr. Wilson

2. Transport of oxygen By haemoglobin in the reversible reaction:
Hb + 4O2 >< HbO8
Haemoglobin has a high affinity for oxygen.
pO2 or partial pressure of oxygen is a measure of oxygen concentration. The greater the concentration of dissolved oxygen in cells the greater the pO2.

3. Transport of oxygen
When pO2 is high oxygen loads onto haemoglobin to form oxyhaemoglobin.
When pO2 decreases oxyhaemoglobin starts to unload it’s oxygen.
In alveoli pO2 is high so Hb loads oxygen.
At respiring tissues pO2 is low so Hb unloads it’s oxygen to the cells of the tissue.
Why do athletes train at high altitudes?

4. Transport of oxygen
The classic S shaped (SIGMOIDIAL) oxygen dissociation curve for ADULT haemoglobin.
100% saturation = all Hb molecules fully loaded with oxygen.
0% saturation = no Hb molecules are loaded with oxygen.

5. Transport of oxygen Why is the graph S shaped?
The first oxygen to load onto any Hb molecule makes it easier for subsequent oxygen molecules to bind.
As it becomes fully saturated it becomes harder for oxygen molecules to bind; not a lot of room for any more.
Describe what’s happening at the shallow ends & steep middle section on the graph.

6. Foetal haemoglobin
Foetal Hb loads and unloads oxygen at lower pO2. The curve is to the left of adult haemoglobin, showing that foetal haemoglobin has a HIGHER affinity for oxygen.
This is important in transferring oxygen from maternal Hb to foetal Hb.

7. Transport of carbon dioxide
In summary:
Converted to carbonic acid in RBCs, which dissociates into H+ and HCO3- ions.
Oxyhaemoglobin unloads O2 & binds H+ ions to counteract the increased acid pH.
HCO3- ions diffuse out into plasma & Cl- ions diffuse in.
At lungs low pCO2 causes the ions to recombine as CO2, which diffuses into the alveoli & is breathed out.

8. The Bohr effect
The oxygen dissociation curve shifts more and more to the right as pCO2 increases because this causes lowering of pH (becoming more acidic).
Detail on previous slide.

9. Home study Graphs sheet – describe & explain each. Exam question.
Read through the end section of the practical skills course book.
Revision – Past paper, text book questions, exam café CD Rom, internet past papers questions etc..