Biology 9700 · AS & A Level · Transport of oxygen and carbon dioxide
Transport of oxygen and carbon dioxide — practice question
Fig. 6.1 illustrates several of the changes that happen as a red blood cell passes through a capillary in the lungs. The diagram shows the reactions $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+$ and $X + \text{O}_2 \rightarrow \text{HbO}_2 + \text{H}^+$, and the movement of $\text{HCO}_3^-$ and $\text{Cl}^-$ between the red blood cell and plasma.
(a)[1]
State why transport proteins are present in red blood cell membranes to permit the movement of hydrogencarbonate ions ($\text{HCO}_3^-$) and chloride ions ($\text{Cl}^-$).
(b)[1]
Fig. 6.1 shows chloride ions leaving the red blood cells. Explain why this movement is needed as red blood cells pass through capillaries in the lungs.
(c)[1]
State the reason carbon dioxide molecules move from the red blood cells into the plasma.
(d)[1]
State the name of the compound represented by $X$.
Worked solution & mark scheme
This 4-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Ions cannot cross the phospholipid bilayer” …