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(a) A student investigated the effect of these enzymes on the hydrolysis of starch by incubating a 2% starch suspension separately with each of the enzymes.
The mixtures were incubated for 60 minutes to allow all the reactions to be completed.
- Each mixture of enzyme and starch was incubated at 35°C and at the optimum pH of each enzyme.
- After 60 minutes, samples of each mixture were removed using a capillary tube.
- The products of hydrolysis of each mixture were separated by chromatography using the same solvent.
- The products of hydrolysis were located by spraying the chromatogram with the same specific dye.
(i) Identify the independent variable in this investigation.
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(ii) Identify three variables, other than the chromatography solvent and the specific dye, that the student has standardised in their investigation.
Describe how the student might have standardised two of these variables.
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(iii) Suggest a control that the students could use for this investigation.
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(b) Describe a method that the student could use to prepare and use chromatograms to compare the changes in the products of hydrolysis of starch by the three different amylases over time.
Your method should be detailed enough for another person to follow.
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(c) Fig. 1.2 shows the chromatograms produced from each of the starch enzyme mixtures after 60 minutes incubation.
(i) Use the information on page 2 to identify which type of amylase gave each of the results shown in chromatograms, A, B and C. Write your answers in Table 1.1.
Table 1.1
|chromatogram|A|B|C|
| --- | --- | --- | --- |
|type of amylase| | | |[1]
(ii) Explain how you decided which chromatogram showed the results of hydrolysing starch with each type of amylase.
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534
592
554
(a) (i) State the dependent variable in this investigation.
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(ii) Describe the features of the experimental design that are intended to ensure reliability.
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(b) (i) State the reason for including the plots of non-Bt maize without any treatment (NBt) in this investigation.
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(ii) Explain how the results from the plots of non-Bt maize could be used to analyse the results from the other two plots.
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Table 2.1 shows the results of the investigation.
[Table_1]
(c) In this investigation, Bt maize (Bt) or a soil insecticide (NBt + In) were used to control rootworm.
Describe the effectiveness of these two treatments as shown by the data in Table 2.1.
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(d) Statistical tests were carried out on the data obtained from each day that samples were taken and tested to find out if the effectiveness of rootworm control by using insecticide was significantly different from growing transgenic Bt maize.
Pairs of soil samples were tested from:
• Bt and non-Bt +In
• Bt and non-Bt
• non-Bt +In and non-Bt.
(i) State a null hypothesis for the test between Bt and non-Bt +In.
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(ii) Show how to calculate the number of degrees of freedom for this test.
answer ....................... degrees of freedom [2]
(e) The results of the statistical tests at $p < 0.05$ showed that:
• in both years the results on day 1 were not significant
• In year 1 the results for Bt maize and non-Bt maize +In were significant on day 6, 19 and 26 and in year 2 the results were significant on day 4 and day 19
• In year 1 the results for NBt +In maize and NBt was significant on day 14 and 19 and in year 2 on day 4.
Explain what is meant by not significant at $p < 0.05$.
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530
584
597
