Methods Read these instructions carefully before you start work. Activity 1 – Preparation of sample 1.
Wash your hands or wear gloves.
2.
On the underside of the agar plate, use a marker pen to divide the plate into five equal sections.
3.
Using sterile forceps, dip one paper disc into each of the antiseptic solutions and allow excess antiseptic to drain off. (Use a separate pair of forceps for each paper disc.) Place the disc carefully onto the respective section on the unsealed agar plate containing the bacteria, as shown in Figure 1.
4.
Place the used forceps into the beaker of disinfectant.
5.
Seal the plate with tape, ensuring there is a gap so that oxygen can enter and condensation can escape.
6.
Place the plate upside down and incubate for three or four days below 25 °C.
7.
Place any used equipment in the beaker of disinfectant.
Figure 1
Activity 2 – Analysis of sample 1.
Remove your agar plate from where it has been incubating and seal around the edge with extra adhesive tape.
2.
Measure the diameter of the clear zone around each disc by placing the ruler across the centre of the disc. Record the measurement in the Measurement 1 column of Table 1.
3.
Measure again at 90° to the first measurement and record the measurement in the Measurement 2 column of Table 1.
4.
Calculate the mean diameter. Record this in the final column of Table 1.
Record your results Table 1 – Diameter of clear zones Diameter of clear zone (mm)
Type of antiseptic Measurement 1
AQA GCSE (9–1) Biology Required Practicals Lab Book
Measurement 2
6
Mean
© HarperCollinsPublishers Limited 2018