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1 A protein is used to hold other chemicals onto the clear plastic backing of photographic film,as shown in Fig. 1.1.

)~::; : .: .. ::: '=======:::::" ::" .. : .: .. : ====: =: : , t'~chemicals of photographic film clear plastic

held in a layer of protein backingFig.1.1

Trypsin is an enzyme which will digest the protein so that the coating on the photographicfilm is removed and the film becomes clear.Table 1.1 shows the results obtained by two students who investigated the effect of pH onthe activity of this enzyme. They made up the solutions, set up the experiment and timedhow long the enzyme took to digest the protein and clear the film.

Table 1.1

time for the protein to be digested I minspH student 1student 22.014.0.0 9.0.0 3.0.5 1.0.0 9.0

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3(a) (i) Plot the results obtained by student 2 in the form of a suitable graph.

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(ii) Describe and explain the effect of pH on the activity of the enzyme.

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3(a) (i) Plot the results obtained by student 2 in the form of a suitable graph.

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[5]

(ii) Describe and explain the effect of pH on the activity of the enzyme .

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(b) (i) Suggest reasons for the difference in the results for the two students.

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(ii) If you were to carry out this investigation, describe what steps you would take toensure that your results were as reliable and valid as possible .

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[Total:18]

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62 Fig.2.1 shows the lower surface of a dicotyledonous leaf.

Magnification x 1Fig. 2.1

(a) Make a labelled drawing of the leaf in Fig. 2.1. Your drawing should be the same sizeas that shown in Fig. 2.1.

[4]

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