Final answer:
A comparative investigation always includes an independent variable, which is manipulated or controlled by the researcher, and a dependent variable, which is the outcome that is measured. These are crucial to test hypotheses and understand the relationships between different variables in scientific research.
Step-by-step explanation:
A comparative investigation in scientific research includes an examination of how different variables interact with each other. Specifically, it will always include an independent variable and a dependent variable. The independent variable is the one that is being manipulated or controlled by the experimenter to observe the effects on the dependent variable, which is the outcome that is measured.
In the presented example, the experiment is designed to investigate whether the bacteria would grow faster on gel A or gel B. The gel type (A or B) is the independent variable since it's what the researcher is changing. The count of bacteria after 24 hours is the dependent variable because it is the result being observed.
Comparative investigations are a key part of the scientific method, as they enable researchers to systematically explore relationships between variables, and ultimately support or reject their hypothesis. Setting up experiments with controlled and consistent conditions is crucial for obtaining reliable and accurate data. Furthermore, a hypothesis is a tentative assumption made based on what is already known and is an integral part of the scientific inquiry process.