Kayla had two Petri dishes full of Euglena. Euglena are unicellular protists that are able to move via a flagellum and can sense light with an eye spot. She exposed one dish to a light source. Then she measured the number of Euglena that moved in the direction of the light. She kept the other dish in the dark. Finally, she measured the direction of movement of the Euglena in the dark.
What is the dependent variable in this experiment?