Final answer:
The control group is a part of an experiment that does not change, serving as the baseline for comparison with the experimental group.
Step-by-step explanation:
The part of an experiment that does not change and serves as a basis for comparison is known as the control group. This group is crucial in experimental design, as it helps to isolate the effect of the independent variable by providing a status quo against which changes in the dependent variable can be measured. For instance, in an experiment where fertilizer is being tested on the growth of corn, one row of corn may be treated with fertilizer (the experimental group) and the other row may not (the control group). Both rows should be treated the same way in terms of water and sunlight to ensure that any differences in growth can be attributed to the presence or absence of fertilizer. The control group in this context is row 2, the one without the fertilizer, and it allows the scientist to compare the effects of the fertilizer on corn growth.