F211: Exchange & transport
1.2.2 Transport in animals
(oxygen & carbon dioxide
transport, dissociation curves &
Bohr effect)
By Mr. Wilson
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.
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?
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.
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.
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.
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 & Clions diffuse in.
• At lungs low pCO2 causes the ions to
recombine as CO2, which diffuses into the
alveoli & is breathed out.
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.
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..