The student added 100 mm3 of each bacterial culture from its glass bottle onto a separate agar plate. She spread each bacterial culture evenly over the agar using a spreader.

Describe the aseptic techniques she should use.

On each agar plate, the student cut a well (a hole) in the agar.

The well had a diameter of 6 mm. The student added 50 mm3 of cinnamon oil into the well.

Calculate the minimum depth of the well to allow the addition of 50 mm3 of cinnamon oil. Use the following equation in your calculation:

Volume of a cylinder = πr2 × l

Use 3.14 as the value for π.

Show your working.

Answer ______________ mm

The student kept the plates at 25 °C for 24 hours.

Figure 5 shows what one of her plates looked like after 24 hours.

The student measured the diameter of the clear zone with no bacterial growth around each well. She made these measurements to the nearest whole mm

Table 1 shows her results.

Suggest exactly what the student added to the wells to get the positive control and negative control results.

Complete Table 1 to show the median and mean diameters.

The mean ± 2 standard deviations includes over 95% of the data.

Use this information to consider whether the standard deviations suggest the differences in means are likely to be due to chance.

Explain your answer, including at least one calculation.