Examples or Definitions of a negative control?

Hey Guys! I'm doing an assignment and they are asking me about negative controls. I don't understand what a negative control is and after looking a various sites including Wikipedia I still don't understand. Could you guys explain it to me or give me some examples to try and help me out?





Thanks :)Examples or Definitions of a negative control?
When you run an experiment you usually run a negative control to check for contamination.


A negative control is exactly what it sounds like, a controlled part of the experiment in which negative results are expected.





For example, if we are interested in answering the question ';In what temperature does yeast grow the best in?'; We would go about making petri dishes of the yeast and putting them in various temperature conditions, such as 15C, 20C and 25C incubators. The negative control would simply be a blank petri dish that we would put in the incubator. After looking at the plates days later, we would expect growth on some of the yeast, and no growth on the negative control.





The reason we include the negative control is to show that there is no contamination in the yeast plates. If something were to grow in the negative control, we would have reason to believe that all the other yeast plates were contaminated as well which would give us skewed or bad data.





Hope that makes sense.