When growing bacteria, does the petri-dish needs to be open or close?

every petri dish is supposed to come with a loosely fitting lid.

this will allow air to reach the plate (you're usually incubating under aerobic conditions) - but it will prevent (or largely prevent) airborne particles such as fungal spores to reach the agar and contaminate your experiment.

It all depends on your hypothesis.

For you to be certain that the bacteria only came from the source you're choosing, you usually should have two petri dishes and both must be prepared identically.

Then, if you are hypothesizing that bacteria are in the air and fall into the petri dish, you'll leave one petri dish uncovered and the second dish covered.

If you are hypothesizing that the bacteria are already in the chicken bouillon, then you must first sterilize some bouillon and put it in one dish. In a second dish, you must put some unsterilized bouillon. You'll cover both petri dishes.

You should use a loosely fitting petri dish lid. If you are using an incubator, it should be inverted (after it solidifies completely) so that the condensation accumulates on the lid instead of on the surface

Loosely cover each Petri dish with plastic wrap and allow the solution to cool and harden for at least an hour.

and here is the link for all the instructions:

http://www.stevespanglerscience.com/experiment/000...

u will need a mosquito n an experimental thing like a sparrow..

closed.. i would think.