Variables and Constants

Independent Variable: Amount of light earthworms are exposed to (manipulated variable)

Dependent Variable: Distance crawled towards opposite end of apparatus (responding variable)

Control: earthworm in pan without differing amounts of light (no shady side all neutral light)  (The control is the trial that is run with the independent variable removed in order to insure that the change in data is indeed a product of manipulating that variable.)

Constants: Same testing pan, same time (therefore amount of sunlight), same soil, same worm throughout a trial (the constants are the variable that were the same for each trial, they are necessary in order to be sure that the experiment tests just what is meant to be tested)