8.2 Transport of Oxygen & Carbon Dioxide

Fig. 1 shows the oxygen dissociaton curve for the haemoglobin of adults (HbA), as well as for a special type of haemoglobin produced by the cells of foetuses prior to birth; this second type of haemoglobin is known as foetal haemoglobin (HbF).

Fig. 1

Describe and explain the shape of the curve for HbA shown in Fig.1.

Use Fig.1 to determine the percentage saturation of the following with oxygen at a partial pressure of oxygen of 4kPa:

• • HbA
  • HbF

Sickle cell disease is a genetic condition in which a mutation in the gene coding for part of the haemoglobin molecule causes red blood cells to take on a sickled, or crescent, shape. This influences the ability of the red blood cells to pass easily through the capillaries.

An experimental treatment for sickle cell disease involves gene therapy to increase the expression of the gene that codes for HbF, a gene that is normally switched off in adults.

[1]

[2]

Another form of oxygen-binding protein that exists in the tissues of humans is myoglobin. Myoglobin is present in the muscles where it functions as an oxygen store. It has a higher affinity for oxygen than both HbA and HbF.

Sketch a suggested dissociation curve for myoglobin on Fig.1.

Fig. 1 below shows an oxyhaemoglobin dissociation curve. 

Fig. 1

Using Fig. 1 and your own knowledge describe the structure of haemoglobin and explain how it transports oxygen around the body.

Fig. 2 shows the oxygen dissociation curves for myoglobin, M, and haemoglobin, H. 

Fig. 2

Using Fig. 2,

State the percentage saturation of myoglobin and haemoglobin when the partial pressure of oxygen is 1 kPa.

[1]

Explain the significance of the difference in percentage saturation that you have identified in part (i).

[3]

The structure of myoglobin is shown in Fig. 3.

Fig. 3

Compare the structure of myoglobin with the structure of haemoglobin. 

[2]

Using Fig. 3, explain the shape of the oxygen dissociation curve for myoglobin in Fig. 2. 

[2]

Fig.1 shows the oxygen dissociation curve for haemoglobin.

Fig. 1

Use Fig.1 to complete the table below

During exercise, oxygen is released from haemoglobin more readily than is shown in Fig.1.

Explain why this is the case.

Fig. 2 shows the oxygen dissociation curves for the haemoglobin of three different mammal species; X, Y, and Z. 

Fig. 2

Species Z lives at sea level while species X lives at high altitude where the atmospheric partial pressure of oxygen is lower.

Suggest how the haemoglobin of species X enables it to survive at high altitude.

Species Y lives at the same altitude as species X but is more metabolically active.

Suggest how the haemoglobin of species Y enables it to be more metabolically active.

Haemoglobin is a globular protein which is able to transport oxygen and is soluble in water.

(i)

Explain how the structure of a haemoglobin molecule makes it able to transport oxygen efficiently.

[3]

(ii)

Explain how the structure of a haemoglobin molecule allows it to be soluble in water.

Llamas are mammals that are adapted to live at high altitudes.

Fig.1 shows oxygen dissociation curves for haemoglobin of llamas and humans.

Fig. 1

i)

The partial pressure of oxygen in the lungs of mammals at 3500 m is 6.4 kPa.

Use Fig.1 to state the percentage saturation of haemoglobin of llamas and humans at an oxygen partial pressure of 6.4 kPa.

[1]

ii)

With reference to Fig.1, explain the advantage to llamas of having an oxygen dissociation curve positioned to the left of the curve for humans.

[2]