Astudent conducts an experiment to determine how the amount of water given to a plant affects its growth.
which of the following is not a control for this experiment?
a. the type of plant
b. the amount of soil
c. the amount of water
d. the amount of time in the sun

The answer is c. the amount of water.

A control of the experiment is an element that is not changed during the experiment. Not changing it allows comparison with the variables that are being tested.
So a student will use several plants of the same type, put it in the same amount of soil and leave it in the sun for the same amount of time. These are control elements. He will change only the amount of water to determine how different amounts of water will affect a plant growth. All these suggest that in this experiment, the amount of water is not a control.

The answer is C. the amount of water.

In every experiment, you must determine a set of controls to maximize its accuracy and reliability. Controls are the ones that are kept constant in a series of trials during an experiment. So if you want to determine the how the amount of water (independent variable) given to a plant affects its growth (dependent variable), you must not make the amount of water a control in the experiment.