Biology 9700 · AS & A Level · Transport of oxygen and carbon dioxide
Transport of oxygen and carbon dioxide — practice question
Red blood cells are kept in plasma, and this plasma has a concentration equal to a 0.9\% sodium chloride (NaCl) solution. A student investigated the changes to red blood cells when they were placed in sodium chloride solutions of different concentrations. A small drop of blood was added to $10\text{ cm}^3$ of each sodium chloride solution. Samples were then taken from each mixture and viewed under the microscope. The number of red blood cells still present in each sample was worked out as a percentage of the number in the 0.9\% solution. The results are shown in Fig. 3.1.
(a)[3]
Using Fig. 3.1, outline the student’s findings.
(b)[5]
Explain the outcomes shown in Fig. 3.1, Table 3.1 and Fig. 3.2 in terms of water potential.
for the $0\%$ NaCl solution
for the $0.7\%$ NaCl solution
for the $1.5\%$ NaCl solution
(c)[4]
Describe the role of haemoglobin in transporting:
i. oxygen
ii. carbon dioxide
(d(i))[2]
Calculate the percentage increase in the number of red blood cells per $\text{mm}^3$ after three weeks at $5000\,\text{m}$. Show your working.
(d(ii))[3]
Explain why the haematocrit rises at altitude.
Worked solution & mark scheme
This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Valid comparison of rate, for example faster” …