gce biology by2 oxygen dissociation curves gce biology by2 adaptations for transport next

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Adaptations for Transport

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Click on the magnifying glass to enlarge this

image of the haemoglobin molecule

Click on the magnifying glass to enlarge this

image of the haemoglobin molecule

The haem part of the molecule contains iron.

Each molecule has four haem groups and each one of these can bind with an oxygen molecule.

Hb + 4O2 HbO8 NextNext

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Oxygen Dissociation Curve

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Partial Pressure of Oxygen/ kPa

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The red blood cells collect oxygen in the capillaries surrounding the lungs. The red blood cells collect oxygen in the capillaries surrounding the lungs.

The partial pressure of oxygen is high and the haemoglobin reaches saturation.

The partial pressure of oxygen is high and the haemoglobin reaches saturation.

The red blood cells transport the oxygen to respiring tissues. The partial pressure of oxygen in these tissues is low, as the oxygen is being used for respiration.

The red blood cells transport the oxygen to respiring tissues. The partial pressure of oxygen in these tissues is low, as the oxygen is being used for respiration.

Under conditions of a lack of oxygen (low partial pressure of oxygen), the haemoglobin yields its oxygen to the respiring cells – we refer to this as dissociation.

Under conditions of a lack of oxygen (low partial pressure of oxygen), the haemoglobin yields its oxygen to the respiring cells – we refer to this as dissociation.

Haemoglobin’s properties allow it to bind with a lot of oxygen at a high partial pressure of oxygen, but at low partial pressure, only a limited amount binds to it.

Haemoglobin’s properties allow it to bind with a lot of oxygen at a high partial pressure of oxygen, but at low partial pressure, only a limited amount binds to it.

Click the numbered sections on the graph for an explanation of what happens at each stage

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haemoglobin

The molecule is now saturated.

Haemoglobin

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This diagram shows how a model of haemoglobin reaches saturation with oxygen.

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HIGHER PRESSURE

(kPa)

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The oxygen partial pressure (pO2) is a measure of oxygen concentration.

The higher the concentration of dissolved oxygen, the higher the pressure.

Click on the above boxes to see movement of the molecules. Click on the above boxes to see movement of the molecules.

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Oxygen Dissociation Curve

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Samples of haemoglobin can be placed in different partial pressures of oxygen, before estimating how much of it becomes bound to the oxygen.

We can plot the percentage saturation against the partial pressure to get an oxygen dissociation curve.

Samples of haemoglobin can be placed in different partial pressures of oxygen, before estimating how much of it becomes bound to the oxygen.

We can plot the percentage saturation against the partial pressure to get an oxygen dissociation curve.

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CorrectIncorrect

The haemoglobin is almost saturated at a high partial

pressure of oxygen

Oxyhaemoglobin dissociates at a low partial pressure of

oxygen

Respiring tissues have a high partial pressure of oxygen

A molecule of haemoglobin can carry seven molecules of

oxygen at most

The group haem contains iron

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Why is an Oxygen Dissociation Curve S-shaped?

Note that each haemoglobin

molecule contains four haem groups

Note that each haemoglobin

molecule contains four haem groups

Hint

Answer

When the first oxygen molecules binds to the first haem group, the haemoglobin molecule loses its shape. This makes it easier for the three other molecules to combine with the remaining haem groups.

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The Effect of CO2 on the Oxygen Dissociation Curve

CO2

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How much oxygen is transported by a molecule of haemoglobin also depends on partial pressure of carbon dioxide.

From the graph we see that at high partial pressures of carbon dioxide, the oxygen dissociation curve shifts to the right.

This is called Bohr’s shift.

Higher partial pressure of carbon dioxide increases the dissociation of oxyhaemoglobin.

From the graph we see that at high partial pressures of carbon dioxide, the oxygen dissociation curve shifts to the right.

This is called Bohr’s shift.

Higher partial pressure of carbon dioxide increases the dissociation of oxyhaemoglobin.

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CO2

What is the significance of this in the body?

When oxyhaemoglobin reaches the tissues, the high partial pressure of carbon dioxide from respiration causes oxyhaemoglobin to release its oxygen more easily. So oxygen is released where it’s needed.

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The Effect of CO2 on the Oxygen Dissociation Curve

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Show/ hide the CO2 curve

pHCO2

Show/ hide the pH curve

The Effect of pH on the Oxygen Dissociation Curve

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Explain what you see here(Keep in mind what you’ve already seen)

HINTS

What has happened to the level of oxygen in the water?

What happens to the level of CO2 in the water?

What has happened to reduce the pH of the water?

What does the pH meter show?

pH

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Discuss each image in turn – what do they have to do with oxygen dissociation?

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The Oxygen Dissociation Curve of an Athlete in Training

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The further the oxygen dissociation curve shifts to the right, the easier it is for the haemoglobin to give up its oxygen.

The further the oxygen dissociation curve shifts to the right, the easier it is for the haemoglobin to give up its oxygen.

The further left the curve shifts, the easier it is for haemoglobin to pick up oxygen.

The further left the curve shifts, the easier it is for haemoglobin to pick up oxygen.

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Haemoglobin Myoglobin

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1. Found in the blood.

2. It joins to 4 molecules of oxygen at its maximum saturation but low affinity compared to myoglobin.

3. The haemoglobin never

reaches 100% oxygen saturation

1. Found in tissues.

2. It binds to only one molecule of oxygen but there is greater affinity to oxygen.

3. The myoglobin can reach 100% oxygen saturation.

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Oxygen Dissociation Curve for MYOGLOBIN

Myoglobin is a molecule in muscles that combines with oxygen. The oxygen dissociation curve for myoglobin is far to the left of haemoglobin.

What does this mean?

When is a person likely to obtain oxygen from the dissociation of oxyhaemoglobin?

Myoglobin is a molecule in muscles that combines with oxygen. The oxygen dissociation curve for myoglobin is far to the left of haemoglobin.

What does this mean?

When is a person likely to obtain oxygen from the dissociation of oxyhaemoglobin?

MyoglobinMyoglobin

HaemoglobinHaemoglobin

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Foetus

placenta

What is the function of the placenta?

Answer

The blood of the foetus and the mother flows closely together, but never mixes. This allows substances like oxygen to diffuse into the blood of the developing foetus. NextNext

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Oxygen Dissociation Curve for a Foetus

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We see form this graph of oxygen dissociation that foetus haemoglobin binds more easily to oxygen than the mother’s haemoglobin.

Why is this higher affinity advantageous to the foetus?

Is there a disadvantage to the mother?

We see form this graph of oxygen dissociation that foetus haemoglobin binds more easily to oxygen than the mother’s haemoglobin.

Why is this higher affinity advantageous to the foetus?

Is there a disadvantage to the mother?

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Foetal haemoglobin

Mother’s haemoglobin