Centre Number Candidate Number Candidate Name

NAMIBIA SENIOR SECONDARY CERTIFICATE

BIOLOGY HIGHER LEVEL 8321/3PAPER 3 Practical Test 1 hour 30 minutes

Marks 40 2013

Additional Materials: As listed in Instructions to subject teachers.

INSTRUCTIONS AND INFORMATION TO CANDIDATES

Candidates answer on the Question Paper in the spaces provided.•Write your Centre Number, Candidate Number and Name in the spaces at the top of this page.•Write in dark blue or black pen.•You may use a soft pencil for any rough work, diagrams or graphs.•Donotusecorrectionfluid.•You may use a non-programmable calculator.•Do not write in the margin • For Examiner’s Use.

Answer • all questions.

The number of marks is given in brackets [ ] at the end of each question or • part question.

This document consists of 9 printed pages and 3 blank pages.

Republic of NamibiaMINISTRY OF EDUCATION

[Turn over© MoE/DNEA

For Examiner’s Use

1 2 Total

8321/3/13

Marker

Checker

HIGHER LEVEL

11

02

16

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You are provided with 20% glucose solution in a test-tube marked 1 X and dried yeast powder.

Proceed as follows.

Set up a retort stand, clamp and boss head as shown in Fig. 1.1.1

Label test-tube 2 Y.

retort stand

boss headand clamp

Fig. 1.1

Pour 25 cm3 3 of distilled water into test-tube Y and place it back in the test-tube rack.

Prepare a yeast suspension in the beaker, labelled yeast suspension, 4 by adding the 2 g of dried yeast to the 5 cm3 of water in the beaker. Stir.

Using a clean syringe or pipette, add 2.5 cm5 3 of yeast suspension to test-tube X. Care must be taken not to spill any suspension against the test-tube wall. Ensure that the content of the test-tube is mixed well.

Using a clean syringe or pipette, add 5 cm6 3 of cooking oil to the surface of the mixture in test-tube X. Make sure that the cooking oil runs down against the side of the test-tube.

Prepareawaterbathbyhalffillinga400cm7 3 beaker with warm water to 40oC. Place the water bath on the retort stand. Make sure throughout the experiment that the water temperature remains constant. Call for assistance if more hot water is needed. Use the syringe to remove water from the water bath when neccessary to prevent the water bath fromoverflowing.

Use the rubber bungs on the delivery tubing to close test-tubes 8 X and Y. The delivery tube in Y must be below the surface of the water. See Fig. 1.2.

NB: Handle the glass delivery tubing with care as it can break easily.

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Make sure that the test-tubes are more or less at the same level.9

Place test-tube 10 X in the water bath as shown in Fig. 1.2.

delivery tube

water bathat 40oC

yeast in glucose solution

(test-tube X)

thermometertest-tube Y

water

layer of oil

test-tube rack

Fig. 1.2

Start the stopwatch and count the number of bubbles in test-tube11 Y foroneminuteatfiveminuteintervalsforamaximumof30minutes.Remember to check and regulate the temperature of the water bath.

(a) (i) Complete Table 1.1 to record your results.

Table 1.1

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Describe your results.(ii)

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Explain why the oil was used to cover the yeast glucose mixture.(iii)

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The glucose solution was made with boiled distilled water. (iv) Suggest a reason for this.

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Suggest what has happened to the number of yeast cells in test-tube (v) X during the experiment.

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(b) (i) Name the chemical process occuring in the test-tube X.

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(ii) Write down the chemical equation in symbols of the chemical process taking place in test-tube X.

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(c) Describe one way in which you could ensure that the experiment is carried out safely.

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(d) Using the same apparatus, describe how you would identify the gas that forms the bubbles in test-tube X.

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You are provided with 0.1% ascorbic acid, two different fruit juices and a blue 2 dye, solution D, in four different 50 cm3 glass/plastic beakers.

Proceed as follows.

Use a marker pen and label the test-tubes 1 U, V and Z in a test-tube rack.

Use a 2 cm2 3 syringe to place 1 cm3 solution D into each test-tube.

ascorbicacid solution

U Vfruitjuice

Zfruitjuice

1

21.5

0.5

1 cm3solution D

Use a fresh syringe to draw up 2 cm3 3 of 0.1% ascorbic acid solution.

Draw the solution into the syringe until the bottom of the plunger is 4 against the 2 cm3 mark on the barrel of the syringe.

Squeeze the plunger of the syringe carefully so that you add one drop 5 at a time of ascorbic acid solution to the solution D in test-tube U.

Shake the tube and go on adding the ascorbic acid from the syringe 6 until solution D just changes to a colourless liquid.

Stop adding the ascorbic acid solution as soon as solution 7 D turns colourless.

If you empty the syringe before solution 8 Dgoescolourless,refillitandadd 2 cm3toyourfinalvolume.

Note the position of the plunger in the syringe and subtract the reading 9 from 2.0 to give you the volume of ascorbic acid solution you have added.

Write this volume into the appropriate space at10 (a) and remember to add 2 cm3foreachtimeyourefilledthesyringe.

Wash the syringe.11

Repeat the steps 3 to 11 with the two fruit juices.12

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(a) Complete the following.

Volume of ascorbic acid (U) needed to decolourise solution D.

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Volume of juice (V) needed to decolourise solution D.

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Volume of juice (Z) needed to decolourise solution D.

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(b) Identify solution D.

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(c) Suggest another name for ascorbic acid solution.

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(d) (i) State which fruit juice contained the highest concentration of ascorbic acid.

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Explain your reasons for (ii) (i).

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Explain (iii) one way in which your experiment was not very accurate.

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(e) Table 2.1 shows the results of a similar experiment which was carried out to test the concentration of ascorbic acid in a plant root over 12 weeks.

Table 2.1

week ascorbic acid content/mg0 452 405 287 14

10 12

(i) Plot the data from Table 2.1 on the grid below.

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(ii) Use your graph to estimate the concentration of ascorbic acid after 4 weeks. You must show on your graph how you obtained this result.

Concentration of ascorbic acid............................................................ [2]

(iii) Suggest how much ascorbic acid would be present after 13 weeks.

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(f) Boiled vegetables contain less ascorbic acid than raw vegetables. Suggest two reasons for the loss of ascorbic acid during boiling in water.

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(g) Ascorbic acid is added to food during manufacturing as a preservative.

(i) State twodifferenttypesoffoodadditivesanddescribetheirbenefits.

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(ii) Name one type of food additive and explain why it causes health problems.

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