You have some old plastic Petri dishes that you would like t…
You have some old plastic Petri dishes that you would like to use for pouring bacteriological agar plates. These plates are old enough that you are unsure if sterility has been maintained in the plates. The only method of physical sterilization available is ultraviolet radiation with your germicidal UV light. (You cannot use the autoclave because it will melt the plastic). After sterilizing the plates, pouring sterilized agar medium, and then leaving the plates out at room temperature for a couple days to check for contamination, you find bacterial colonies growing on the agar surface of several plates. Choose the most likely reason for this result from the answers below.
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