Why is it necessary to sterilize the petri dishes before investigation?

Question

Why is it necessary to sterilize the petri dishes before investigation?

Answer 1

Most of the time the conditions under which you are growing your subject are also ideal conditions for mold or bacterial growth. If you don't sterilize all of your equipment you risk growing populations of unwanted bacteria or mold that could potentially harm your organism or compete for resources with it and thus alter your results.

Answer 2

to eliminate unwanted contamination.

Answer 3

If unsterilized, the dishes would have contaminants which could (and probably would) effect the outcome of what you are trying to examine or grow.