Why are sterile Petri dishes used to begin a culture of bacteria?

[HYMAN]

please help asap, quite detailed answer would be really appreciated. thank you in advance to all that take the time to help me!

 

[tigrillen]

if they are not sterile they probably would already contain various bacteria. So you would end up culturing the bacteria you intend to culture and a whole bunch of other bacteria as well.

 

[j823]

If the petri dish is, in fact, sterile, then it is to prevent other bacteria and external factors from interfering with the growth of the bacteria. It allows for an optimum speed of growth and amount of growth without other factors impeding on their growth.