Question

A student placed a disk of filter paper in each of the following solutions: disinfectant 1, disinfectant 2, disinfectant 3, and distilled water. While the four disks were soaking in their respective solutions, she streaked a sterile nutrient agar dish with a culture of E. coli bacteria. Then, she placed each disk carefully onto the nutrient agar dish, placed the lid on the dish, taped it shut, and incubated the dish at 37°C for several days. The diagram shows how the nutrient agar dish looked on Day 1 and Day 4. The shaded portion of the plate on day 4 indicates the bacterial growth. Look at the dishes in the diagram. Which disinfectant was the most effective at controlling the growth of E. coli? A. Disinfectant 2 B. Disinfectant 1 C. Distilled water D. Disinfectant 3

Answer 1

I found the exercise on the internet. Attached is the diagram of the observed results.
Correct answer: "B. Disinfectant 1"
As shown in the diagram, the whole dish was plenty of E. coli. The only areas that did not have bacterial growth were those around the disks soaked in disinfectant 1 and disinfectant 3. However, the diameter of the area around the disk soaked in disinfectant 1 was the largest, meaning that this disinfectant had the most effective power at controlling the growth of E. coli.