What would be a good negative control for this experiment? Hint: a negative control should have NONE of the dependent variable - if it does, that tells you your experiment may have been contaminated.

  • A different type of agar plate
  • A TSA agar plate with no bacteria streaked on it
  • A TSA agar plate with no antibiotic discs placed on it
  • A TSA plate that was not placed in the incubator

Expert Answers

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Since you have not mentioned an experiment, I am assuming your experiment is based on finding out which antibiotic is resistant to bacteria and which antibiotic is most effective against bacteria.

First, think why the control group is used in any experiment. What is the main difference between experimental group and control group? You have to think do we use any independent variable in control group?

In most of the experiment we use one control group.

Since you ask “What would be good negative control for your experiment?”

this means you will have to use a positive control group as well as a negative control group.

In the positive control group, you will be using an independent variable just to check if you get the expected result. But for the negative control group, don't give it any treatment.

You have provided four choices and have to select which we can use as a negative control group. If we go through the first choice, A different type of a agar plate,then think if can we use as this negative control group. Adifferent agar plate is just used for bacterial growth.

For the next choice, A TSA agar plate with no bacteria streaked on it,think if TSA is selective or non selective, if it is differential or non-differential growth media.

If you are trying to find out if specific bacteria is used against specific antibiotics, then we will need to streak bacteria on TSA agar plate.

For the next choice, A TSA plate that was not placed in the incubator, you should think about what the expected result would be if we don't keep any nutrient plate in incubator.

For the final choice, A TSA agar plate with no antibiotic discs placed on it: If you are trying to find out which is best antibiotic against specific bacteria, then just think can we use above solution as negative control group. If we use TSA agar plate without any antibiotic and if still shows bacterial growth, what will be the result indicate?

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