AS & A Level Biology - 9700 Paper 5 2011 Summer Zone 1

A student investigated the storage tissue in potato tubers of different ages
• a newly formed tuber
• an old tuber that was just beginning to form new shoots.
In one investigation, the water potential of different parts of the tubers was estimated using discs of potato tissue and sucrose solutions of different concentrations.
Fig. 1.1 shows
• the appearance of the tubers
• the places from where the tissues were removed.

The results of the investigation are shown in Fig. 1.2.

(a) Describe a procedure by which the student could have obtained the results in Fig. 1.2.
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(b) (i) State how the percentage change in mass is calculated.
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(ii) Explain why the student used percentage change in mass rather than actual mass.
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The student looked at the graphs in Fig. 1.3 and estimated the water potential from where there was no change in mass.
The student decided to find out if the difference in the water potential between the central region of the old tuber and the central region of the newly formed tuber was significant.
• 20 samples of tissue were taken from the central region of each tuber.
• The change in mass was measured separately for each sample using the same procedure as in the original investigation.
(c) (i) Give one reason why the \( t \)-test is a suitable statistical test for this investigation.
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(ii) Explain how the student should use the value for \( t \) to find out if the difference in water potential between the tubers is significant.
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From the readings in Fig. 1.3 the student concluded that
• the tissue in the old tuber close to the growing shoot has the lowest water potential.
• in the old tuber close to a growing shoot, starch reserves were being converted to sugar.
• in the old tuber central region, starch was being converted to sugar.
• in the newly formed tuber all the sugar had been converted to starch.
(d) With reference to Fig. 1.3, state the evidence that supports these conclusions and the evidence that does not support these conclusions.
evidence to support these conclusions
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evidence that does not support these conclusions
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(e) Suggest what further investigations the student could do to provide more support for the conclusions about starch and sugar in the storage tissue.
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(f) The student found that newly formed tubers do not form shoots until a period of dormancy lasting several months has occurred.
The student investigated tissues taken from tubers of different ages to test the hypothesis
Dormancy in tubers is caused by an inhibitory growth regulator.
Suggest what results would be obtained if this hypothesis was valid.
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(a) Outline how the white blood cells may have been treated so that the chromosomes could be observed.
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(b) (i) Identify the independent and dependent variables in the investigation.

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(ii) Identify the control for this investigation.
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(iii) Use the grid and the data in Table 2.1 to plot a line graph showing the frequency of normal mitosis at each concentration of the organo-mercury compound.

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(c) (i) Suggest an explanation for the effect of organo-mercury compounds on mitosis.
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(ii) The data in this investigation was considered to be reliable.
Suggest one reason why this is so.
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