Agar/Bacteria?

I'm stumped on the first question of my bacteria lab...It says:





What was the purpose of this control? Did bacteria develop on it? Can you propose a hypothesis to explain this?





What we did was put 3 samples of bacteria into 3 quadrants of a petri dish. We left one quadrant clean (only the agar in it) for our control. We observed it every 2 days. The 3 samples became foggy and visible bacteria could be seen. The third didn't develop any bacteria, but became foggy. Would that be considered bacteria on the control? Because of the agar? Would the purpose of the control be to show what type of bacteria forms on the agar? How would I form a hypothesis?

Agar/Bacteria?
The control show's no growth, so long as your technique was aseptic, (that you didn't contaminate it). If they became foggy, that would most likely be condensation. your supposed to put the plates lid side down to prevent that.
Reply:Bacteria did not develop on your control plate. When you say became foggy I think you are referring to the condensation that formed on the lid of the petri dish. This is because of the water content of the agar, not because of bacteria.





The control shows that your aseptic technique was good. I suspect you plated a blank sample (no bacteria) on your control plate. Had it developed bacteria, it would indicate that either your equipment or your media was contaminated.
Reply:Do you understand what a control is, what it's for?





What did you expect when you plated the bacteria onto the first three quadrants?





What did you expect when you did NOT plate bacteria onto the last quadrant?