In an experiment testing whether light color affects plant growth, identify the independent variable, dependent variable, and a proper control.

• A. Independent variable: light color; Dependent variable: plant growth; Control: identical plants, soil, water, temperature, and white light.
• B. Independent variable: plant height; Dependent variable: light color; Control: same plant type and soil.
• C. Independent variable: soil type; Dependent variable: water amount; Control: identical light.
• D. Independent variable: water amount; Dependent variable: temperature; Control: varied light.

Answer: (A)

This question tests how to identify the parts of a controlled experiment: what you change (independent variable), what you measure (dependent variable), and what you keep the same (control). For this setup, the factor being changed is the color of the light, so it is the independent variable. Plant growth is what you measure to see the effect, making it the dependent variable. To compare fairly, you keep everything else identical—same type of plant, same soil, same amount of water, and the same temperature—and use white light as a baseline reference. By keeping those factors constant, any differences in growth can be attributed to the color of the light. The other options mix up which variable is changed or omit important constants, so they don’t isolate the effect of light color as cleanly.