An experiment is conducted to find out if plants grow towards light. A potted plant is lit from one side, and you see if it grows towards the lamp. However, there's something more that has to be done; we must obtain a second plant and light it from above. We need this second plant to provide a standard with which to compare the first plant. The second plant in the experiment is called the control. It is essential that the two plants are kept in exactly the same conditions, except for the light they receive. That is, you must keep all the variables constant except for the one whose effect we are investigating.

• What are the dependent and independent variables for the plant experiment?