Extension Questions 12. Scientists may design an experiment with a control group, which is a set of organisms or sam-

ples that do not receive the treatment (the independent variable) that is being tested. Scientists

can then compare normal changes in organisms or samples with those that may have occurred

because of the treatment. The idea of a control group is not the same as a controlled variable.

Suppose a scientist is doing an experiment to determine the effect of an all-organic diet on the

occurrence of cancer in rats.

a. What variables should the scientist control in the experiment?

b. Describe the control group for this experiment.

a) same species of rats

b) Some rats will not be given the all-organic diet

Explanation:

In an experiment, a control group is the group that do not receive the treatment (the independent variable) that is being tested while the control variables or constants are the variables that must be kept constant throughout the course of the experiment in order not to alter the experiment's outcome.

In this experiment where a scientist is trying to determine the effect of an all-organic diet on the occurrence of cancer in rats, the control group would be the GROUP OF RAT THAT DO NOT RECEIVE THE ORGANIC DIET. Also, a control variable would be the SAME SPECIES OF RAT USED throughout the experiment.