The purpose of a control group in an experiment is to establish a baseline for comparison, isolating the effect of the independent variable. By keeping all conditions the same except for the variable being tested, researchers can determine if any observed effects are genuinely due to the experimental treatment. Control groups enhance the reliability of an experiment by minimizing potential confounding factors that could bias the results. This practice is essential for validating findings and ensuring that conclusions drawn from the experiment are scientifically sound and credible.