Transcript Investigating how we can kill microbes

Investigating how we can kill
microbes
Lesson Aims:
To study how we can kill microbes
and to safely set up an experiment
to compare different disinfectants.
Lesson outcomes
By the end of the lesson you should be able
to:
• use key scientific vocabulary
• appreciate how to use agar plates to
compare disinfectants and achieve reliable
results
• recognise that scientists worked
collaboratively to develop the antibiotic
penicillin
Use the resources available in the
room to find the meaning of the
following key vocabulary
• a substance made by one living thing
• Antibiotic –.
that kills another living thing.
• Disinfectant –
• Antiseptic –
•a substance that kills
micro-organisms.
•a substance that kills
micro-organisms and is safe to
use on skin.
Comparing disinfectants
The purpose of the next 2 lessons is to present evidence in
the form of a written report and write a formal letter back
to the hospital domestic supervisor (completed in next
lesson) summarising your overall findings.
SAFETY : You must wear goggles
DO NOT open the lid after you have added the filter paper
(Dangerous bacteria may grow)
Secure the lid with 3 pieces of sticky tape
Cover any open skin and wash hands with soapy water
before and after the practical
Clean your work area
Comparing Disinfectants
• There has been an outbreak of an infectious
bacterial disease at Lincoln Hospital.
• The domestic supervisor is responsible for
ensuring that the correct cleaning methods and
procedures are complied with to reduce the
spread of the disease.
• You are a microbiologist who works at the
hospital and the domestic supervisor has
requested that you test 4 disinfectants to assess
which one is the more effective in killing the
bacteria causing the disease.
• The agar jelly in the plates already contains the
micro-organism. If left unaffected these can grow
• Instructions
• 1. Using the OHT pen write your initials and date at the outer edge on
the bottom dish of the agar plate. Using the china clay pencil divide your
agar plate into fifths and label the five areas A, B, C,D and E. Write on
the base, not the lid.
•
BA
•
C E
D
• 2. Areas A, B, C,and D will be treated with the three disinfectant
solutions you are testing.
• 3. To apply the disinfectants to areas A, B, C,D and to apply distilled
water to E as a control
• b) using clean forceps aseptically remove one filter paper disc, saturate
it in the solution of disinfectant.
• c) Remove excess liquid by blotting the wet disc briefly on a paper towel.
• d) Gently lay the wet disc (in the appropriate position) on the surface of
the seeded agar. Take care not to drip chemical on other parts of the
plate.
• Repeat for the different disinfectants and the distilled water .
• Make sure you record which disinfectant solution was used in each area.
• 4. Close the agar plate and secure with sticky tape, go over the top and
bottom of the plate. Do not go round the edge as air must be able to
get in.
• 6. The plates will be placed in a warm oven, base up, until next lesson.
In your exercise book draw a diagram
of your agar plate , label each area
(A,B,C,D,E) and record which solution
you added to each section
Make a prediction which disinfectant
will be the best and explain why.
Read pages 87-88 Spectrum Biology
• Answer questions 10-15
• Extension questions 7-10
Lesson outcomes
Can you?
• use key scientific vocabulary
• appreciate how to use agar plates to
compare disinfectants and achieve reliable
results
• recognise that scientists worked
collaboratively to develop the antibiotic
penicillin