Syllabus Edition

First teaching 2023

First exams 2025

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Transport of Oxygen & Carbon Dioxide (CIE AS Biology)

Exam Questions

3 hours44 questions
1a
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4 marks

Describe and explain two ways in which red blood cells are adapted to oxygen transport.

1b
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2 marks

Haemoglobin is a globular protein made of two alpha polypeptides and two beta polypeptides. Each alpha polypeptide consists of 141 amino acids and each beta polypeptide consists of 146 amino acids.

Calculate the difference in the number of amino acids and DNA bases required for a single alpha polypeptide vs a single beta polypeptide.

1c
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2 marks

A scientist is looking at a red blood cell under an electron microscope and takes an electron micrograph. The actual diameter of the red blood cell is 7µm but in the micrograph image it measures 5cm. This is shown in Fig. 1.

alveolus

Fig. 1

Calculate the magnification used by the scientist in Fig 1. Give your answer to the nearest 100.

1d
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1 mark

Mammals that live at different altitudes often have different haemoglobin.

Suggest how a mammal's haemoglobin might be adapted to live at higher altitudes.

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2a
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2 marks

Describe what is meant by the chloride shift.

2b
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3 marks

Hydrogen carbonate ions are formed in a two step process

(i)

Give the two equations that represent this two step process.

[2]

(ii)

Identify the name of the enzyme involved in these reactions. 

[1]

2c
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1 mark

Describe the importance of the chloride shift for red blood cells. 

2d
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3 marks

The chloride shift can be compared to the Bohr shift. 

Use a tick (✓) or cross (X) to assign the statements to either the chloride shift or the Bohr shift. You may choose more than one statement for each shift.

  Bohr Shift Chloride Shift
Transport of oxygen out of red blood cells    
Transport of hydrogen carbonate ions out of red blood cells    
Transport of chloride ions into red blood cells    

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3a
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3 marks

With reference to the different partial pressures of oxygen (ppO2) throughout the body explain how haemoglobin supplies oxygen to different areas of the human body.

3b
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2 marks

The oxyhaemoglobin dissociation curves for adult haemoglobin (HbA) and foetal haemoglobin (HbF) are shown in Fig. 1 below.

hb-graph

Fig. 1

Explain the steep gradient seen in the curve seen for HbA in Fig. 1

3c
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1 mark

State what can be concluded from Figure 1 about the difference between HbF and HbA.

3d
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2 marks

Haemoglobin is a quaternary protein that is broken down in the liver.

Predict what haemoglobin will be broken down into and suggest one function of this breakdown product in the body.

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4a
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4 marks

Carbon dioxide produced during respiration diffuses from cells into the blood. 

Describe the role of plasma and red blood cells in the transport of carbon dioxide.

4b
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2 marks

Red blood cells contain an enzyme that catalyses a reaction to aid the transport of carbon dioxide in blood plasma. 

(i) State the name of this enzyme. 

[1]

(ii) Describe the role of the enzyme. 

[1]

4c
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2 marks

Haemoglobinic acid is an important by-product in the transport of carbon dioxide. 

Describe how haemoglobinic acid is formed. 

4d
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2 marks

Explain the importance of the haemoglobinic acid.

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5a
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3 marks

Fig. 1 shows an oxygen dissociation curve at different partial pressures of oxygen (mmHg).

oxygen-dissociation-curve-mcq

Fig. 1

Explain the importance of the oxygen dissociation curve at the partial pressures of oxygen found in the lungs. 

5b
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3 marks

Explain the effect of partial pressure of 20 mmHg on the oxygen saturation of haemoglobin. 

5c
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1 mark

Suggest where in the body a partial pressure of 20 mmHg might be found. 

5d
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1 mark

Identify the % saturation of haemoglobin at 50 mmHg. 

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1a3 marks

Figure 1 shows the structure of haemoglobin.

8-2-fig-1-1Fig. 1

Explain how the structure of haemoglobin relates to its function.

1b3 marks

Figure 2 shows the oxygen dissociation curve for haemoglobin.

8-2-fig-1-2
Fig. 2

Explain what Figure 2 shows about the relationship between the partial pressure of oxygen (pO2) and the affinity of haemoglobin for oxygen.

1c
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2 marks

Calculate the difference in percentage saturation of haemoglobin with oxygen between a pO2 of 2 kPa and a pO2 of 8 kPa in Fig. 2.

1d3 marks

Anaemia is a condition in which an individual's blood contains less haemoglobin than usual. Individuals with anaemia can produce chemicals in their blood which influence the haemoglobin dissociation curve, as shown in Figure 3.

2

Fig. 3

Suggest the advantage to an anaemic individual of producing chemicals that have the effect shown in Figure 3.

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2a3 marks

Figure 1 shows the oxygen dissociation curve for haemoglobin.

8-2-fig-4-1
Fig. 1

Use Figure 1 to complete the table below

Location Partial pressure of oxygen / kPa Percentage saturation of haemoglobin / %

Rate of oxyhaemoglobin dissociation

(slow / fast) 

Capillaries branching from pulmonary artery 0.6    
Capillaries in respiring tissue   45  
Capillaries leading to pulmonary vein   98  

2b4 marks

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

Explain why this is the case.

2c2 marks

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

8-2-fig-4-2
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 altitudes.

2d2 marks

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.

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3a
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5 marks

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.

[2]
3b
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3 marks

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

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

fig6-1-qp-octnov-2018-9700-21

Fig. 1

i)

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

Use Figure 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 Figure 1, explain the advantage to llamas of having an oxygen dissociation curve positioned to the left of the curve for humans.

[2]

3c
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1 mark

Fetal haemoglobin in mammals causes a shift in the oxygen dissociation curve to the left. 

Suggest the percentage saturation of haemoglobin for fetal llama haemoglobin at an oxygen partial pressure of 4 kPa.

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4a
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3 marks

Transportation of hydrogen carbonate ions out of red blood cells results in a positive charge within the cell.

Describe the mechanism of red blood cells to prevent this electrical imbalance. 

4b
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3 marks

Fig. 1 shows a red blood cell at a respiring tissue. 

Identify labels A -C on the diagram. cie-ial-8-2-m-q4b

Fig. 1

4c
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4 marks

Table 1 shows the difference in ion concentrations in arterial and venous blood. 

Table 1

Venous blood (mmol) Arterial blood (mmol)
Na+ 137.0 Na+ 137.0
K+ 4.0 K+ 4.0
Cl- 101.2 Cl- 104.8
HCO3- 25.2 HCO3- 22.7

Calculate the percentage change in chloride ions and suggest a reason for this difference. 

Give your answer to 3 significant figures. 

4d
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1 mark

Red blood cells transport ions through a carrier protein.

Give the method of transport that this is this an example of.

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5a
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3 marks

Table 1 shows the partial pressure of oxygen at different saturations of haemoglobin. 

Table 1

Animal Partial pressure of oxygen at 25% haemoglobin saturation (mmHg)  Partial pressure of oxygen at 50% haemoglobin saturation (mmHg)   Partial pressure of oxygen at 90% haemoglobin saturation (mmHg)  
Elephant 12 22 44
Mouse 38 52 98

Plot the haemoglobin saturation data from Table 1 and use these points to sketch the full oxyhaemoglobin dissociation curves for an elephant and a mouse.

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5b
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3 marks

Explain why the dissociation curve for the mouse is different to the dissociation curve for the elephant. 

5c
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4 marks

Haemoglobin in the respiring tissues has a lower affinity for oxygen. 

Explain why. 

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1a2 marks

Red blood cells are a type of specialised cell with a limited life span of around 120 days; at this point, their function has declined and they are destroyed by white blood cells. During their lifespan, red blood cells are exposed to high levels of physical stress, as well as undergoing the loss of structure of proteins both within the cell and within their cell surface membranes.

Use this information and your knowledge of red blood cells to suggest and explain one special feature of red blood cells that contributes to their short-lived nature.

1b3 marks

Figure 1 shows some of the events taking place in and around a red blood cell as it travels through actively respiring tissues.

8-2-fig-2-1Fig. 1

(i)
Write a word equation to show the process taking place at P.

[1]

(ii)
Explain what is happening at points Q and S. 

[2]

1c2 marks

The process marked R in Fig. 1 is involved in generating the Bohr shift. The Bohr shift occurs when carbon dioxide levels are increased from low to high, as shown in Fig. 2.

8-2-fig-2-2
Fig. 2

Explain the connection between process R in Fig. 1 and the Bohr shift shown in Fig. 2.

1d2 marks

Explain the importance of the Bohr shift to metabolically active tissues.

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2a5 marks

Figure 1 shows the oxygen dissociation 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).

m-q1

Fig. 1

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

2b1 mark

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

  • HbA
  • HbF

2c3 marks

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.

(i)
Suggest how an increase in the expression of HbF could help to treat sickle cell disease.

[1]

(ii)
Suggest why HbF may not be a perfect replacement for HbA.

[2]

2d2 marks

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 Figure 1.

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3a
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6 marks

Figure 1 below shows an oxyhaemoglobin dissociation curve. 

oxyhaemoglobin-dissociation-curve-sq

Fig. 1

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

3b
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4 marks

Figure 2 shows the oxygen dissociation curves for myoglobin, M, and haemoglobin, H. myoglobin-dissociation-curve

Fig. 2

Using Figure 2

(i)

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

[1]

(ii)

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

[3]

3c
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4 marks

The structure of myoglobin is shown in Figure 3.myoglobin-sq

Fig. 3

(i)

Compare the structure of myoglobin with the structure of haemoglobin. 

[2]

(ii)

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

[2]

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4a
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3 marks

The dissociation and binding of oxygen to and from haemoglobin in red blood cells produces a sigmoid curve. 

Explain the property of haemoglobin that causes this shaped curve. 

4b
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1 mark

Fig. 1 below shows oxygen dissociation curves of haemoglobin at two different carbon dioxide concentrations. 

cie-ial-8-2-h-q4b

Fig. 1

The partial pressure of oxygen in the lungs is 100 mmHg and the partial pressure in metabolically active tissue is 40 mmHg. 

Identify the percentage saturation of haemoglobin with oxygen in the lungs and in metabolically active tissue. 

4c
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4 marks

Figure 2 shows how changes in the partial pressure of oxygen (PO2) influence oxygen (O2) binding to, and dissociation from, haemoglobin alongside the oxygen content of whole blood.  

The human body contains approximately 5 litres of blood. The concentration of haemoglobin is 15 g per 100 ml of blood, when fully saturated there is 1.34 cm3 oxygen per gram of haemoglobin.

100 mmHg partial pressure of oxygen in found in arterial blood and 40 mmHg partial pressure of oxygen is found in venous blood.

cie-ial-8-2-h-q4c

Fig. 2

(i)
Calculate the percentage change in ml of oxygen in blood from arterial to venous blood in a human body. 

 [2]

(ii)
Calculate how much oxygen is carried in venous blood in a human body. 
[2]

4d
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1 mark

A scientist comments that "venous blood is not deoxygenated". 

Use the information and your answers in part (b) to explain this.

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