NAMIBIA SENIOR SECONDARY CERTIFICATE

BIOLOGY HIGHER LEVEL 8321/3PAPER 3 Practical Test

2013

INSTRUCTIONS TO SUBJECT TEACHERS

(For preparation of laboratories)

This document consists of 3 printed pages and 1 blank page.

Republic of NamibiaMINISTRY OF EDUCATION

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Instructions to teachers

Question 1

In cases where learners do not have access to taps and basins please provide beakers (500 cm3) labelled clearly "for washing" and "for waste".

One day before the practical, enough quantity of water should be boiled to prepare a 20% glucose solution with boiled water while still warm and without shaking. Store the solution in stoppered containers. Provide each learner with 15 cm3 of the prepared solution in one boiling tube which is part of the glass delivering tubing set, and label it as X-20% glucose solution.

Instructions for glucose solution:

20% glucose solution should be made by dissolving 20 g of glucose in 50 cm3

boiling water and then adding 50 cm3 of boiled cold distilled water. Each learner will require 15 cm3. Pour correct amount (15 cm3) in one boiling tube which is part of the delivery tubing set. Label it as X - 20% glucose solution. Place it in the test-tube rack. Close the test-tube with the additional solid bung provided as part of the delivery tubing set.

Set up the glass delivery tubing 50 cm long, fitting it with the two rubber bungs and outlet tube.

NB: Handle delivery tubing with care as it will break easily. Instructions on how to set up the glass delivery tube set is given after question one.

Weigh out 2 g dried bakers yeast, per learner in a petri dish.

Access to hot and cold water in beakers (250 cm3) to regulate water bath temperature. Take note: access to hot water should be available throughout the practical examination duration and should be provided to any learner that may need more to regulate the water bath temperature.

Prepare 3 x 50 cm3 beakers per candidate as follows:

30 cm(i) 3 distilled water - label beaker as distilled water

6 cm(ii) 3 cooking oil - label beaker as cooking oil

5 cm(iii) 3 boiled, cooled distilled water - label beaker as yeast suspension.

Each learner/work station should be provided/equipped with:1 x retort stand

1 x boss head

1 x clamp

1 x 400 cm3 glass beaker - to be used for water bath

2 x 250 cm3 glass beakers - filled with hot and cold water respectively - to be used for regulating water temperature.

3 x 50 cm3 beakers - filled with 30 cm3 distilled water, 6 cm3 cooking oil and 5 cm3 boiled, cooled distilled water.

2 x boiling tubes (145 mm long, 20 mm diameter) - one tube must have the prepared 20% glucose solution in it. The second tube candidates have to

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label themselves as test-tube Y.1 x glass delivery tubing 50 cm long + 2 fitted bungs (a 1 and 2 hole bung and an outlet tube, fitted to the two hole bung).

1 x marker pen

1 x stop watch

1 x 10 cm3 graduated pipette or 1x 10 cm3 syringe (NB learners may find it easier to work with the syringe)1 x pipette filler (only neccessary when graduated pipette is used)

1 x 2 cm3 syringe

1 x thermometer (- 10 - 110°C)

1 x test-tube rack

1 x petri dish - filled with 2 g dried bakers yeast

How to set up the glass delivery tube set1 Take the light blue rubber stopper (l hole) into the LEFT hand

2 Take the glass delivery tube set into the RIGHT hand - short end

3 Turn the rubber stopper with the left hand over the glass tube

4 Take the dark blue rubber stopper (2 holes) into the LEFT hand

5 Insert the "Chimney"/outlet tube a little bit into the SMALL hole

6 Take the glass delivery tube set into the RIGHT hand - long end

7 Turn the rubber stopper with the left hand over the glass tube

Question 2:

6 cm3 of 0.1% of dichlorophenol-indophenol (DCPIP) in one 50 cm3 (glass) beaker labelled solution D.

10 cm3 of 0.1% ascorbic acid in one 50 cm3 (glass) beaker labelled solution U.

1 x test-tube rack (the same one used in question 1)

3 x test-tubes

2 x 50 cm3 glass beakers - for solutions D and U - mentioned in the first two sentences

2 x 50 cm3 glass beakers - for juices V and Z

2 x 2 cm3 disposal syringes (one is just for solution D)

3 x labels/1 x marker pen

10 cm3 of different fresh/tinned/bottled fruit juices

lemon juice - for example tru - lem in one 50 cm• 3 beaker labelled solution Vorange juice - for example the Rietfontein brand is suggested as it is available in most • shops - in one 50 cm3 beaker labelled solution Z

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