Bacteria may be cultivated on agar jelly inside a Petri dish. As they grow and multiply, the transparent agar jelly turns cloudy.
Antibiotics can stop bacteria from growing. Circles of filter paper soaked in an antibiotic solution can be placed on the agar surface. If the region around a disc stays clear, the antibiotic has stopped the bacteria from growing. The larger the clear region, the more effective the antibiotic is.
A student investigated the effect of distilled water (E) and four different antibiotics (F, G, H and J) on some bacteria using the method described.
They prepared three identical Petri dishes and measured the diameter of the clear regions around the filter paper discs after a few days.
No clear region was seen around disc E in any of the Petri dishes.
Fig. 2.1 shows the results for Petri dish 3.
(a(i))[1]
Measure the diameter of the clear region around the disc with antibiotic H in Fig. 2.1 and enter the result in the table.
(a(ii))[2]
Calculate the mean diameter of the clear areas around the discs with antibiotic H. Record the result in the table to one decimal place.
(b(i))[4]
Construct a bar chart of the four mean diameters in Table 2.1 on the grid.
(b(ii))[1]
State which antibiotic was the most effective at preventing bacterial growth.
(c)[2]
The student noticed that one result was anomalous. State which measurement was anomalous and suggest what the student could have done about it.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “21 entered in the correct table cell” …