DISEASE TRANSMISSION PRACTICAL
Disease transmission practical
This practical work illustrates for learners the importance of taking careful
notes in scientific investigation. Each learner must take individual notes at
the time to be able to successfully complete the exercise.
Several versions of this experiment are provided for use as appropriate with
your learners.
Introduction
Some people are carriers of disease. These carriers show either no symptoms
associated with that disease or only mild symptoms. At some point they may
eventually become ill. The danger to others is that a carrier may not be
recognised as having the disease. Carriers have the pathogen inside them,
however, and may spread it to people they come into contact with. In this way
carriers may spread HIV hepatitis, and a number of other diseases. It is one of
the reasons HIV spreads so quickly.
For some diseases, public health officials must identify the original carrier.
This person is sometimes referred to as the ‘Typhoid Mary’. By identifying
such a person and finding out who he/she came in contact with, officials learn
how the disease is being passed from person to person.
In this activity, one of you will be the original carrier of a ‘disease’. (This
disease is perfectly harmless, if handled properly. You will carry it in a testtube, rather than in your body.) The original carrier will make contact with
several learners in the class who will then make contact with others. Then all
learners will be tested to see who has become infected.
In this activity you will trace the path by which a disease spreads, using a
pipette to transfer solutions from one test -tube to another, and testing a
solution for the presence of an acid or a base.
Materials and equipment needed
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Pasteur or disposable pipette with bulb, 3 ml
Test-tubes with stoppers/corks, 14–18 ml
Phenol red
0.001 mol/l hydrochloric acid (HCl, stock solution of non-carriers)
0.1 mol/l sodium hydroxide (NaOH, stock solution of the carrier)
Safety goggles
Lab coat
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DISEASE TRANSMISSION PRACTICAL
 Gloves
 Marker pen/pencil
Pre-activity discussion
Acids and bases are very often colourless solutions. Concentrated acids and
bases can result in serious burns, especially to exposed membranes such as
those of the eyes. They can damage clothing and furniture. Acids and bases
must, therefore, be properly labelled. The acids and bases you use in this
activity are relatively dilute and pose little harm unless they get in your eyes
or mouth.
The concentration of an acid or base is indicated by a number called the
molarity (mol/l). Look at the materials and equipment list. Which is greater in
molarity, the acid (HCl) or the base (NaOH)?
Phenol red is a pH indicator. It changes colour depending upon whether the
solution it is added to is an acid or a base. If phenol red is added to an acid,
the solution will be yellow. If it is added to a base, the solution will be red.
Safety precautions
 Do not allow acids and bases to come into contact with your skin or
clothing.
 Wear gloves, goggles and a lab coat through the entire procedure.
 Ensure that you do not transfer spills or drips from gloves to other
surfaces such as pens where you may transfer contamination to your
hands and mouth.
Method
1.
2.
3.
4.
5.
6.
2
Collect your sample of unknown solution and , using a Pasteur or
disposable pipette, transfer three pipettes of your unknown solution to a
clean sample tube. Make sure you label your tube so it doesn’t get
mixed up with another sample and keep your original sample secure.
You may need to use it for checking later on.
Choose someone at random from the group to be your cont act in the
first round.
Remove one pipette of solution from your sample tube.
Empty your pipette into your contact’s sample tube at the same time as
he/she does the same to you.
Replace the lid on your sample tube and shake your tube gently to mix
the solutions.
Record the name of the person with whom you exchanged solutions in
the Round 1 contacts column.
ADVICE AND GUIDANCE FOR PRACTITIONERS (NATIONAL 5, BIOLOGY)
© Crown copyright 2012
DISEASE TRANSMISSION PRACTICAL
7.
When everyone has completed Round 1, repeat steps 2 –5, recording the
name of the contact in the Round 2 column.
Make sure you meet a new contact each time by choosing someone from a
different table or group.
8.
Once everyone has completed Round 2, repeat steps 2 –5 for Round 3.
9.
When you have exchanged solutions with three different contacts, it is
time to think about the test.
(a)
(b)
(c)
Is the disease curable? Some diseases may have no cure as yet,
e.g. HIV.
What are the consequences of being found positive?
Do you feel you need more information or sup port in the form of
counselling?
When ready proceed to step 10.
10.
Add one drop of phenol red to your test -tube to see if you are infected
with the disease. Two test results are possible:
Solution turns red – you have the disease. What are the implications?
Solution turns yellow – you are not infected.
11.
Record your result in the table. Indicate a red with a positive (+), and
yellow with a negative (–).
Learner name
Test
result
Round 1
Contacts
Round 2
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Round 3
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DISEASE TRANSMISSION PRACTICAL
Collate data
You should now collate the class data (names, contacts and test results) into
the data table provided.
Trace the transmission of the disease to each learner who tested positive. Can
you determine who the original carrier was?
Carrier: …………………………………………………………………………..
Result of confirmation test: ………………………………………… ……….…
(Adapted from Applied Biology/Chemistry, Unit 7 ‘Disease and Wellness’
(1990), The Centre for Occupational Research and Development, Waco,
Texas.)
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ADVICE AND GUIDANCE FOR PRACTITIONERS (NATIONAL 5, BIOLOGY)
© Crown copyright 2012
DISEASE TRANSMISSION PRACTICAL
Data table
Learner name
Test
result
Round 1
Contacts
Round 2
Round 3
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2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
ADVICE AND GUIDANCE FOR PRACTITIONERS (NATIONAL 5, BIOLOGY)
© Crown copyright 2012
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