Final answer:
Including a control in experimental manipulations is crucial to establish a baseline for comparison, ensuring that observed effects can be attributed to the independent variable and not other factors.
Step-by-step explanation:
Purpose of Including a Control in Experimental Manipulations
When conducting experimental manipulations to test a hypothesis, the purpose of including a control is to provide a baseline for comparison. This allows researchers to observe what happens when the active treatment or experimental manipulation is not applied. The control group receives a placebo or no treatment, which helps to ensure that any differences observed in the experimental group can be attributed to the experimental manipulation and not to other variables. By using a control group, researchers can eliminate alternative explanations for the outcomes, thereby strengthening the validity of the experimental results. The control is critical in an experiment as it helps to single out the effect of the independent variable on the dependent variable, which is the focus of the hypothesis. For example, in an experiment testing the effect of a nutrient on algal growth, ponds without the nutrient serve as control groups, ensuring that any observed algal growth difference is indeed due to the presence of the nutrient.
Experimental designs that do not include a proper control group can lead to confounding variables affecting the results, thus making it difficult to establish a cause-and-effect relationship.