5090_s10_06_qp_61_qn(1)(reducing sugars)

8/7/2019 5090_s10_06_qp_61_qn(1)(Reducing Sugars)

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Email: [email protected] PREPARED BY: AHMED KALEEM KHAN NIAZI | BIOLOGY CONCEPTS 1

Contact #: 0322-6666767

Biology ConceptsPrepared by: AHMED KALEEM KHAN NIAZIPaper 6: Marks Alternative to Practical

Question no 1Fruits of banana, Musa spp, change as they ripen.

(a) Describe the differences that you can see between the unripe banana fruit A, and the ripe fruitB, shown in Fig. 1.1.

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Name: _____________________ Date: _________________

17GRADE: Percentage:

Fig 1.1


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Table 1.1 shows the mass of a banana fruit measured over a period of three weeks.

(b) (i) Construct a graph of these results on the grid provided.

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(ii) Calculate the loss in mass of the banana fruit during the three weeks.

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(iii) Suggest an explanation for the loss in mass during the ripening of the fruit.

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Table 1.1


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One of the changes that takes place as a banana fruit ripens is the breakdown of starch tosugar.

(c) (i) Describe how you could carry out a test for reducing sugar on a piece of banana fruit.

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(ii) Explain how would you use this test to show that the reducing sugar content increasesduring ripening.

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EXAMINER REPORTQuestion no 1:

(a) This tested observation skills by asking for differences between the two specimens that couldbe seen, e.g. in colour and size. Some candidates wrongly recorded differences that they haddeduced from what they saw, e.g. in mass and texture.

(b) (i) The ability to read the results of an experiment and to present them in a different way wastested by the construction of a graph from data provided in a table. The majority of candidateschose correct axes, good scales and plotted points accurately but actual lines drawn were notalways ruled between points or good smooth curves.

(ii) The use of data was tested by a simple calculation that required the appropriate units ofmeasurement to be recorded as well as the numerical result, i.e. 54 g.

(iii) Explaining the result that had been calculated proved more difficult. Not many candidatesrealized that water would have been lost and even fewer that respiration would have resultedin a loss of mass through breakdown of substrate although some hinted at enzyme activitywithout stating how that would have caused the loss in mass.

(c) (i) Candidates are expected to be familiar with food tests either through carrying them outthemselves or by observing someone demonstrating how to do them. While there were manycandidates who knew that Benedicts solution is the reagent used to test food for the presenceof reducing sugars, some did not state that the food with Benedicts solution added needs tobe heated, preferably in a water bath, in order to obtain a result. The colour change showing a

positive result was often well described. A negative result after carrying out the starch test withiodine solution shows only the absence of starch and not the presence of reducing sugar assome candidates, incorrectly, stated. Other candidates confused biuret and Benedicts.

(ii) Explaining how the test described might be used to demonstrate that the level of reducingsugar ina banana increases as it ripens tested the ability to plan a practical investigation. Somecandidates correctly described carrying out the Benedicts test on banana at given stages ofripening and that the colour change or intensity of colour of any precipitate formed would givean indication of the amount of reducing sugar present. A few candidates suggested thatmeasuring the mass of any precipitate formed would give an indication of the amount ofreducing sugar that had reacted with the Benedicts solution. However some candidatesrepeated only what had been given that during ripening starch is broken down to sugar. Thisdoes not answer the question which tests the practical application of a known technique to a

new situation.


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MARK SCHEMEQuestion no 1:

(a) A is paler/yellow (green), B brown/dark/black/blotchy/speckled ;A is bigger/thicker/fatter/smaller or B converse ;A has thicker stalk or B converse ;A has smoother surface or B converse ; [2 max]

(b) (i) Graph marks: [4]

1 x-axis labelled day (R irregular numbering) ;

2 y-axis mass/g (n.b. origin label) ;3 clear, accurate plotting ;4 line ruled connections/rules line of best fit/good smooth curve ;

(ii) 54g ; [1]

(iii) drying/dehydration/loss of water/moisture ; respiration ; [2]

(c) (i) mix/crush/grind (with water) ;

add Benedicts solution and heat ;in water-bath ;colour change to yellow/orange red ; [4]

(ii) sample one banana as ripens/sample bananas of different stages of ripening ;time period of 228 days mentioned ;equal masses of banana sampled ;equal volumes of Benedicts used ;ref. more intense colour change AW ; [4 max]

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5090_s10_06_qp_61_qn(1)(reducing sugars)

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