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(a) (i) Identify the independent and dependent variables in this investigation.
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(a) (ii) Identify two variables that the student has controlled in this investigation as shown in Fig. 1.2.
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(a) (iii) There are other variables that the student could have controlled in this investigation. Describe how two other variables could have been controlled.
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(b) (i) The student used solid sodium nitrate to prepare the highest concentration of sodium nitrate solution shown in Fig. 1.2 (25 mmol $ ext{dm}^{-3}$). This concentration was then used to prepare all the other concentrations. Describe the procedure that the student used to prepare the concentrations shown in Fig. 1.2. Your description should be sufficiently detailed so that another person can easily follow your procedure. The molar mass of sodium nitrate is 85 g mol$^{-1}$.
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(b) (ii) The student also prepared another flask to use as a control.
Suggest a suitable solution to use as a control for this investigation.
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(c) (i) State how the mean percentage increase in number of cells was calculated.
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(c) (ii) Suggest why the student calculated the mean percentage increase in numbers of Chlorella.
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(d) State what conclusions can be drawn from the results in Table 1.1 about the effect of different concentrations of nitrate on the growth of Chlorella.
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(e) Suggest how the student’s investigation should be modified to find the optimum nitrate concentration for the growth of this Chlorella.
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(f) Sewage lagoons also contain high concentrations of phosphate. In another investigation, the student used sodium phosphate instead of sodium nitrate to find out the effect of different phosphate concentrations on the growth of Chlorella.
Suggest a prediction that the student could make about the effect of the different concentrations of phosphate on the growth of Chlorella.
Show your answer as a sketch graph on the axes below.
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(a) Tests are carried out on each patient receiving CAPD to find out if the treatment is effective. One of these tests uses strips that change colour to indicate the urea concentration.
Outline how test strips could be used to find the effectiveness of CAPD in removing urea.
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One effect of kidney failure is anaemia which can be treated by injecting a hormone that stimulates red blood cell production. This treatment can cause a lack of iron used for the synthesis of haemoglobin. Iron supplements are usually taken by mouth.
Ten male and four female patients with a mean age of 63, all using dialysis and being treated for anaemia, took part in a study into a different way of giving iron supplements.
Test A was carried out on samples of blood from the patients at the start. Measurements were made of:
• haemoglobin content
• iron content
• ferritin, a plasma protein for transporting iron.
The patients were supplied with an iron supplement which they took by mouth for three months. At the end of this time test B was carried out on samples of blood from the patients by measuring the same three substances as before.
In the next part of the study the patients’ iron supplements were replaced by an iron-dextran complex that was injected into their muscles once a week for three months. Test C was carried out on samples of blood from the patients in the same way as in tests A and B.
Table 2.1 shows the results of this study.
(b) (i) State what $S_M$ shows about the data.
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(ii) A number of t-tests were carried out to determine if the treatments with iron supplements had a significant effect on the concentrations of the substances tested. The results of test A were used as a comparison for both test B and test C. State why the t-test is a suitable statistical test to use for the data.
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(iii) State evidence in Table 2.1 that suggests the results of these t-tests might be significant.
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(c) The researchers who carried out this study concluded that providing iron supplement by injection was more effective than providing iron by mouth.
(i) State the evidence from Table 2.1 for this conclusion.
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(ii) Suggest limitations of this study.
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