Final answer:
An independent variable is manipulated by the experimenter, while the dependent variable is measured or observed to determine its response to the independent variable. In the given experiment, the independent variable was the type of gel (gel A and gel B), and the dependent variable was the number of bacteria after 24 hours on each gel.
Step-by-step explanation:
An independent variable is a variable that is manipulated or controlled by the experimenter. In the context of an experiment, it is the variable that is intentionally changed in order to observe its effect on the dependent variable. The dependent variable, on the other hand, is the variable that is measured or observed to determine how it is influenced by the independent variable.
In the given experiment, the independent variable is the type of gel (gel A and gel B) on which the bacteria were grown. The dependent variable is the number of bacteria present after 24 hours on each type of gel. The scientist wanted to find out if the bacteria would grow faster on gel A or gel B.