Question

germinating plants in a potting tray
alvin wanted to grow cucumbers from seeds. he read that using a heating pad to heat up potting soil could help make seeds germinate, or sprout, faster. alvin wondered whether the temperature of the heating pad would affect how quickly the seeds germinated.
alvin prepared two potting trays, each made up of ten small pots of soil. he planted one cucumber seed in each small pot and arranged the potting trays near a sunny window. he set an electric heating pad to 75°f and placed it under one potting tray. he set a second heating pad to 85°f and placed it under the other potting tray. alvin observed the pots daily, and he counted the number of days it took until a seed germinated in each pot.
which of the following was an independent variable in this experiment?
the temperature of the heating pad
the number of days until a seed germinated

Explanation:

In an experiment, the independent variable is the factor that the experimenter changes or manipulates. Here, Alvin sets the heating - pads to different temperatures (75°F and 85°F). The number of days until a seed germinates is the dependent variable, which is affected by the independent variable.

Answer:

the temperature of the heating pad