Question

what is the element of the experiment that tells you whether it is a controlled or comparative experiment? they compare plants exposed to bpa and those that had bpa removed. they manipulate a variable for some plants. they dont use a control. they compare the activity of many different enzymes. they compare two different treatments.

Explanation:

In a controlled experiment, there is a control group and an experimental group where a variable is manipulated. In a comparative experiment, two or more different treatments are compared. The key - difference is the use of a control in a controlled experiment. If there is no control and just comparison of treatments, it's a comparative experiment. So, the lack of a control is what differentiates a comparative experiment from a controlled one.

Answer:

They don't use a control.