Suzie Q wants to know the effect of different colors of light on the growth of plants. She believes that plants can survive best in white light. She buys 5 ferns of the same species, which are all approximately the same age and height. She places one in white light, one in blue light, one in green light, one in red light and one in the closet. All of the ferns are planted in Miracle-Grow and given 20 mL of water once a day for 2 weeks. After the two weeks, Suzie observes the plants and makes measurements. What is the independent variable in this experiment? The plant species The amount of water that each plant gets The amount of time The different types of light the plants were put under.

In general, in experiments there are independent variables, dependent variables, and controlled variables. Since the question is about the independent variable, I will focus the analysis on independent and dependent variables.

The goal of an experiment is to determine the effect of a variable that is changed as the scientist/observer chooses, which is named independent variable, on other variable that can be measured, which is named the dependent variable.

The dependent variable responds to the changes on the independent variable, i.e. by changing the independent variable, different outcomes for the dependent variable are expected.

In the proposed experiment the goal is to know the effect of different colors of light, so this is by definition the independent variable. That is revealed when Suzie Q changes the different type of lights (white, blue, green, red, and none light). Thus, she wiill observe and measure the growth of the plants, which will be the dependent variable.