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CAIE A-Level Biology AS 8.2 Transport of Oxygen and Carbon Dioxide Questions

Practise CAIE AS Biology gas transport by tracing carbon dioxide through red cells and plasma, then linking oxygen partial pressure and pH to haemoglobin loading and release.

Syllabus
2028–2030
Course
Biology 9700
Level
AS

Exam points

  • Trace how carbonic anhydrase converts CO2 to HCO3- and H+ in red cells.
  • Distinguish H+ binding as haemoglobinic acid from CO2 binding as carbaminohaemoglobin.
  • Explain the chloride shift as HCO3- leaves red cells in exchange for Cl-, balancing charge.
  • Explain plasma carriage of dissolved CO2 and HCO3-, distinguishing both from red-cell carbaminohaemoglobin.
  • Interpret adult haemoglobin dissociation graphs, estimating saturation or pO2 from plotted data.
  • Use lung and tissue pO2 values to explain haemoglobin loading and oxygen release in respiring tissues.
  • Explain how higher CO2 and lower pH shift the curve right and release more O2 in active tissues.

Covered syllabus points

8.2.1—Red blood cell roles in O2 and CO2 transport8.2.2—Chloride shift and its importance8.2.3—Plasma role in CO2 transport8.2.4—Oxygen dissociation curve8.2.5—Partial pressures and oxygen loading8.2.6—Bohr shift and its importance

Question 1

[Maximum number: 1]

Which reactions will be taking place in blood in a capillary that is next to an alveolus?

1Hb+4O2→HbO8 key 2H2O+CO2→H2CO3Hb= haemoglobin 3H2CO3→H++HCO3−\begin{array}{lll} 1 & \mathrm{Hb}+4 \mathrm{O}_{2} \rightarrow \mathrm{HbO}_{8} & \text { key } \\ 2 & \mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \rightarrow \mathrm{H}_{2} \mathrm{CO}_{3} & \mathrm{Hb}=\text { haemoglobin } \\ 3 & \mathrm{H}_{2} \mathrm{CO}_{3} \rightarrow \mathrm{H}^{+}+\mathrm{HCO}_{3}^{-} & \end{array}
A

1 and 2

B

1 only

C

2 and 3

D

2 only

Question 2

[Maximum number: 1]

What happens when carbon dioxide is transported by red blood cells?

A

Hydrogencarbonate ions move into the red blood cells and chloride ions move into the plasma.

B

Chloride ions move into the red blood cells and bind to haemoglobin.

C

Chloride ions move into the red blood cells and hydrogen ions move into the plasma.

D

Chloride ions move into the red blood cells and hydrogencarbonate ions move into the plasma.

Question 3

[Maximum number: 1]

How is most carbon dioxide transported in the blood?

A

as carbaminohaemoglobin

B

as carbonic acid

C

as hydrogencarbonate ions

D

in solution in cytoplasm

Question 4

[Maximum number: 1]

The graph shows how changes in oxygen concentration affect the percentage oxygen saturation of human haemoglobin and cat haemoglobin under normal physiological conditions. The partial pressure of carbon dioxide was kept constant at 5.0 kPa and the temperature was kept constant at 37∘C37^{\circ} \mathrm{C}.

Figure for Question 4 — CAIE A-Level Biology AS

Which conclusion is supported by the graph?

A

The affinity of cat haemoglobin for oxygen is greater than the affinity of human haemoglobin for oxygen.

B

At high partial pressures of oxygen, cat haemoglobin picks up oxygen more easily than human haemoglobin picks up oxygen.

C

At low partial pressures of oxygen, oxygen is released more easily from cat haemoglobin than from human haemoglobin.

D

The shift in the oxygen dissociation curve caused by the Bohr effect is larger for cat haemoglobin than for human haemoglobin.

Question 5

[Maximum number: 1]

The partial pressure of oxygen in blood vessels in different parts of the body affects the percentage saturation of each haemoglobin molecule with oxygen.

Table for Question 5 — CAIE A-Level Biology AS

Which statement explains the difference in saturation between a resting and an active muscle?

A

A small decrease in partial pressure causes two atoms of oxygen to leave each haemoglobin molecule because the oxygen dissociation curve is sigmoid shaped.

B

A small decrease in partial pressure between 4 kPa and 7 kPa causes two molecules of oxygen to leave each haemoglobin molecule because the oxygen dissociation curve is steep.

C

Loading of oxygen is slower between 4 kPa and 7 kPa due to binding of one oxygen molecule to each haemoglobin molecule making the next one harder to bind.

D

Loading of oxygen is faster between 4 kPa and 7 kPa due to binding of one oxygen molecule to each haemoglobin molecule making the next one easier to bind.

Question 6

[Maximum number: 1]

The diagram shows the effect of three different concentrations of carbon dioxide on the oxygen dissociation curve for human haemoglobin.

Figure for Question 6 — CAIE A-Level Biology AS

Which effect does increasing carbon dioxide concentration have on haemoglobin?

A

It makes haemoglobin less efficient at taking up oxygen and less efficient at releasing oxygen.

B

It makes haemoglobin less efficient at taking up oxygen and more efficient at releasing oxygen.

C

It makes haemoglobin more efficient at taking up oxygen and less efficient at releasing oxygen.

D

It makes haemoglobin more efficient at taking up oxygen and more efficient at releasing oxygen.

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