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. Hypothesis

An appropriate hypothesis for this experiment could be: "The new antibiotic will inhibit the growth of Streptococcus pyrogenes, resulting in a zone of inhibition around the antibiotic disk in dish 2 compared to dishes 1 and 3."

Diagram for Dish 2

To represent the results that would support your hypothesis, you would illustrate dish 2 showing a clear zone of inhibition around the antibiotic disk. The area surrounding the disk should be free of bacterial growth, indicating that the antibiotic is effective against Streptococcus pyrogenes. You could use a simple circle or shaded area to represent this.

Explanation of the Diagram

The diagram supports the hypothesis because the presence of a clear zone of inhibition around the antibiotic disk in dish 2 indicates that the new antibiotic is effective in preventing the growth of Streptococcus pyrogenes. This contrasts with the growth observed in dish 1 (where no antibiotic was applied) and provides evidence that the antibiotic actively inhibits bacterial growth.

61. Preparation of Control Disk in Dish 3

To prepare the disk in dish 3 so it can serve as the control for this experiment, it should be done as follows: "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 solvent used for dissolving antibiotics. This will help to ensure that any observed differences in bacterial growth between dish 2 and dish 3 can be attributed solely to the effects of the new antibiotic."