A student wishes to study the effect of potassium on root growth.  They select 40 identical plants and split them into 2 groups of 20 which they call group A and group B. Both groups are planted in the same type of soil and get the same amount of water and light.  However, group A plants get 20 mg of potassium while group B plants get not potassium.  After 10 weeks the student measures the root length of all of the plants.  The student finds that the average root length of group A (the group that got potassium) was 10 inches while the average root length of group B was 8 inches.  She concludes that potassium might help the root development of plants. 

Identify the:

1.) Independent variable:

2.) Dependent variable:

3.) 2 constants:

4.) The control

5.) The data that was collected

6.) Was this a good setup?  why or why not.