What is plotted on each axis of an oxygen dissociation curve?

The percentage saturation of the respiratory pigment with oxygen is plotted on the vertical axis against the partial pressure of oxygen on the horizontal axis.

What does it mean if one pigment's dissociation curve lies to the left of another's?

It means that pigment has a higher affinity for oxygen, because it reaches any given percentage saturation at a lower partial pressure of oxygen.

State how the dissociation curve of fetal haemoglobin compares with that of adult haemoglobin.

It lies to the left of the adult curve, so at every partial pressure of oxygen fetal haemoglobin is more highly saturated.

Suggest what would happen to a fetus whose haemoglobin had the same affinity for oxygen as its mother's.

There would be no net transfer of oxygen across the placenta at the low partial pressure found there, so the fetus would be starved of oxygen and would not develop normally.

OCR A-Level Biology B H422

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Metabolism and Exercise

Oxygen dissociation curves of different respiratory pigments

3 things to know
Components 01, 02 and 03

Overview

Recall questions on reading oxygen dissociation curves, fetal haemoglobin and its higher affinity, myoglobin's structure, hyperbolic curve and role as an oxygen store, diving mammals, the effect of a right shift, and adaptation to high altitude.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Which chains replace the beta chains of adult haemoglobin in fetal haemoglobin?

Key term

Explain why fetal haemoglobin must have a higher affinity for oxygen than the mother's.

Key term

Place adult haemoglobin, fetal haemoglobin and myoglobin in order of increasing affinity for oxygen.

Questions from this subtopic

Each one with the model answer underneath.

1
What is plotted on each axis of an oxygen dissociation curve?
Model answer
The percentage saturation of the respiratory pigment with oxygen is plotted on the vertical axis against the partial pressure of oxygen on the horizontal axis.
2
What does it mean if one pigment's dissociation curve lies to the left of another's?
Model answer
It means that pigment has a higher affinity for oxygen, because it reaches any given percentage saturation at a lower partial pressure of oxygen.
3
Which chains replace the beta chains of adult haemoglobin in fetal haemoglobin?
Model answer
Gamma chains, so fetal haemoglobin consists of two alpha and two gamma chains.
4
State how the dissociation curve of fetal haemoglobin compares with that of adult haemoglobin.
Model answer
It lies to the left of the adult curve, so at every partial pressure of oxygen fetal haemoglobin is more highly saturated.
5
Explain why fetal haemoglobin must have a higher affinity for oxygen than the mother's.
Model answer
The partial pressure of oxygen in the placenta is low, and fetal haemoglobin can only load oxygen there if its affinity is high enough to take oxygen from the maternal haemoglobin, which unloads it.
6
Suggest what would happen to a fetus whose haemoglobin had the same affinity for oxygen as its mother's.
Model answer
There would be no net transfer of oxygen across the placenta at the low partial pressure found there, so the fetus would be starved of oxygen and would not develop normally.

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