A student investigated the antimicrobial effects of tea tree oil on bacterial growth.
They prepared three separate agar plates inoculated with E. coli bacteria and placed a paper disc soaked in a different concentration of tea tree oil at the center of each plate. The plates were then incubated at 25 ∘C25\space^{\circ}\text{C}25 ∘C for 48 hours.
The concentrations of tea tree oil used were 5%, 15%, and 40%.
The results are shown in the diagram below:
Explain which agar plate (X, Y, or Z) contains the paper disc with the 40% tea tree oil solution.
