What term is used for substances that exist independently of the experiment?

The correct term for substances that exist independently of the experiment is independent variables. Independent variables are the factors that are manipulated or changed by the researcher to observe how they affect other variables. They are not influenced by other variables in the experiment, allowing the researcher to establish a cause-and-effect relationship.

In the context of an experiment, independent variables are crucial because they determine the conditions and outcomes of the study. When these substances are altered, the impact on the dependent variables can be measured.

Other terms like extraneous factors refer to variables that could potentially influence the outcome but are not the main focus of the study. Controlled variables are those that are kept constant to ensure a fair test. Dependent variables, on the other hand, are what the researcher measures in response to changes in the independent variables. Each of these terms relates to the structure of an experiment but does not describe substances existing independently in the way that independent variables do.