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Page 1

Teaching AS Biology

Practical Skills

University of Cambridge International Examinations

1 Hills Road, Cambridge, CB1 2EU, United Kingdom
Tel: +44 1223 553554 Fax: +44 1223 553558 E-mail: [email protected] Website: www.cie.org.uk

© University of Cambridge International Examinations 2005
PSAS9700 0501

Page 47

Appendix 2

44

Practical 3 - Technical information
The identification of biological chemicals present in solutions
The apparatus and materials required for this practical are listed below.

The amount of apparatus listed is for one student or one group of students if they are
to work in groups.

1 5 small beakers or other containers as follows

label on
beaker

20 cm3 of solution in beaker

A 1 mol dm-3 glucose solution made by dissolving 18 g of glucose in 80
cm3 of distilled water and making up to 100 cm3

B 10% egg white and 1% amylase solution made up by dissolving 10 cm3
of fresh egg white (or 1 g of dried egg white) and 1 g of amylase in 80
cm3 of cold distilled water, mixing until dissolved and making up to 100
cm3

C 0.5 mol dm-3 sucrose solution made by dissolving 17 g of sucrose in 80
cm3 of distilled water and making up to 100 cm3

D no dissolved material

E polysaccharide that can be hydrolysed by amylase

2 5 test tubes in a rack and a means of washing the tubes such as a sink and
running water

3 a glass marker, such as a wax pencil or a permanent OHP pen or small
labels and pencil

4 the usual materials that the students are used to using for biuret test,
labelled appropriately

5 the usual materials and heating arrangements that the students are used to
using for Benedict’s text, labelled appropriately

6 1 mol dm-3 hydrochloric acid in a small dropper bottle, labelled hydrochloric
acid

7 Sodium hydrogen carbonate powder in a small specimen tube with a
stopper and a spatula that fits in the tube to dispense it

8 A thermostatic waterbath or plastic trough containing water at about 35°C for
use as a waterbath

Safety Precautions/Risks

Amylase = H

Benedicts solution = H, N

Hydrochloric acid (1 mol dm–3) = H

A risk assessment should be carried out as a matter of course.

Page 48

Appendix 2

45

Practical 4 - Investigation of the carbohydrates metabolised by yeast

This practical focuses on making measurements and observations, recording and
presenting data, analysis, drawing conclusions and evaluating methods. You will also
develop other assessed skills throughout the practical.

Intended learning outcomes

By the end of this practical you should be able to:

• Experience relevant methods, analysis and conclusion.

• Describe and explain the relationship between temperature and membrane
permeability.

• Evaluate procedures

Safety Information


You should wear eye protection throughout this practical.


Methylene Blue is harmful. Avoid contact with eyes and skin. It will stain
skin or clothes.



Background information

• Yeast can metabolise carbohydrates under two different conditions. When
oxygen is present aerobic respiration occurs yielding a large amount of
energy for the organism and producing carbon dioxide & water as waste
products.

• However when oxygen is in short supply (anaerobic conditions) the yeast
will break down the carbohydrate into ethanol & carbon dioxide with a
much reduced energy output (alcoholic fermentation).

• Both of these forms of respiration in addition to most metabolic processes
are catalysed by specific enzymes.

• The process of how efficient the yeast is in metabolising different
carbohydrates can be monitored by observing the time taken for Methylene
Blue to be discoloured

In this experiment you will investigate the relative efficiency with which different
carbohydrates can be metabolised by yeast.

• Read the information above

• Identify and write down the dependent and independent variables

• Consider which type of carbohydrate (monosaccharide, disaccharide,
polysaccharide) will be metabolised by the yeast and why. Explain your
reasoning.

• Write down what you expect to happen as a hypothesis in which you make
specific predictions about which carbohydrates you might expect yeast to
metabolise.

Page 94

Appendix 2

91

Practical 11 - Technical information

Investigating the role of carbon dioxide in living organisms.

The apparatus and materials required for this practical are listed below.

The amount of apparatus listed is for one student or one group of students if they are
to work in groups.

1. 3 large test-tubes each fitted with a rubber bung or cork

2. gauze or similar to support the specimens in the test-tubes whilst at the
same time allowing the transfer of gases

3. supply of distilled water to rinse each test-tube.

4. 40 cm3 of bicarbonate indicator solution, sufficient to rinse each test-tube
and have sufficient remaining to place 5cm3 into each test-tube.

The stock solution of indicator can be prepared by dissolving 0.2g of thymol
blue and 0.1g of cresol red in 20cm3 of ethanol. Also prepare a solution by
adding 0.84g of pure sodium bicarbonate to 900 cm3 of distilled water. Add
the dyes to this solution and make up to 1 dm3. To prepare the indicator for
use, pipette 25cm3 of stock solution into a graduated flask and make up to
250 cm3 with distilled water.

The solution should be equilibriated with air by aspirating atmospheric air
through the solution until it is orange/red in colour.

5. 3 germinated seeds such that they have developed green leaves and are
photosynthesising. Cress seeds that have been placed on moist cotton wool
in a Petri dish will germinate and develop leaves in only a few days. Times
will vary depending upon local conditions.

6. 3 large fly larvae that are active and not approaching pupation

7. 10cm3 graduated pipette or measuring cylinder or syringe

Additionally each student will require access to a sink and running water.

Commercial bicarbonate indicator solution is available from most chemical
wholesalers, however it is possible to make up the solution in the laboratory as
described above.

Safety Precautions/Risks.

Ethanol = F

Bicarbonate indicator solution = F

A risk assessment should be carried out as a matter of course.

Page 95

Teaching AS Biology

Practical Skills

University of Cambridge International Examinations

1 Hills Road, Cambridge, CB1 2EU, United Kingdom
Tel: +44 1223 553554 Fax: +44 1223 553558 E-mail: [email protected] Website: www.cie.org.uk

© University of Cambridge International Examinations 2005
PSAS9700 0501

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