Homework Help

Why are petri plates inverted after they cool?

user profile pic

imie8987 | Student, Undergraduate | eNotes Newbie

Posted May 27, 2009 at 11:10 PM via web

dislike 1 like

Why are petri plates inverted after they cool?

1 Answer | Add Yours

user profile pic

marilynn07 | High School Teacher | (Level 3) Associate Educator

Posted May 27, 2009 at 11:35 PM (Answer #1)

dislike 1 like

Inverting Petri plates after they cool reduces the risk of contamination by air-borne particles. Inverting the petri dish makes it more difficult for contaminants to enter the growing medium.

When in the incubator growing cultures, Petri dishes are inverted because moisture condenses on the lid and will drop down onto the agar/growth medium causing moisture problems.  If there are separate bacteria colonies on the growth medium, dripping water droplets would cause the colonies to be able to migrate and mix with each other.

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes