A researcher wanted to test the effectiveness of a new antibiotic on Streptococcus pyrogenes, the species of bacteria that causes strep throat. Bacteria were added to dish 1, dish 2, and dish 3. A disk soaked in the new antibiotic was then placed in dish 2. Dish 3 was set up as the

Question

control. The dishes are shown in the diagram below.


59 State one appropriate hypothesis for this experiment. [1]

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60 All three dishes were placed in an incubator at 37°C for 24 hours. The results for dish 1 are shown to the right.

Complete (color in) the diagram of dish 2 below to represent an example of experimental results that would support your hypothesis. (Use the “Draw” tab in Microsoft Word)

Explain how your diagram supports your hypothesis. [1]
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61 Describe how the disk in dish 3 should be prepared so it can serve as the control for
this experiment. [1]

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Answer 1

59. One appropriate hypothesis for this experiment could be: "The new antibiotic will inhibit the growth of Streptococcus pyrogenes in dish 2, resulting in a zone of inhibition around the antibiotic disk."

60. To illustrate the experimental results in dish 2: The area around the disk soaked in the new antibiotic should show a clear zone where the bacteria have not grown, indicating that the antibiotic is effective against Streptococcus pyrogenes. The rest of the dish, away from the disk, should show bacterial growth.

Explanation: The clear zone (zone of inhibition) around the antibiotic disk in dish 2 indicates that the antibiotic is effective in killing or inhibiting the bacteria, thus supporting the hypothesis that the new antibiotic can inhibit the growth of Streptococcus pyrogenes.

61. The disk in dish 3 should be prepared by soaking it in a solution that does not contain the new antibiotic, such as sterile water or a different type of non-antibiotic substance (e.g., saline). This will allow dish 3 to serve as a control to compare the effects of the antibiotic in dish 2 with the natural growth of bacteria in the absence of the antibiotic.