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Difficulty: MediumIdentifying Independent, Dependent, and Controlled Variables

An environmental science team investigated the effects of soil moisture on soil microbial respiration rates. In five experimental plots, they adjusted the soil volumetric water content to values ranging from 10%10\% to 50%50\%. Throughout all trials, they kept the soil temperature constant at 22∘C22^\circ\text{C} and maintained a uniform soil bulk density. At the end of 48 hours, they measured the total carbon dioxide (CO2CO_2) efflux from each plot.

Match each experimental component listed on the left with its correct variable classification on the right.

  • Soil volumetric water contentIndependent variable
  • Soil carbon dioxide (CO2CO_2) effluxDependent variable
  • Soil temperatureControlled variable

Answer

Soil volumetric water content corresponds to the independent variable, Soil carbon dioxide efflux corresponds to the dependent variable, and Soil temperature corresponds to the controlled variable.
Soil volumetric water content is manipulated by the researchers across plots, so it is the independent variable. Soil CO2CO_2 efflux is measured as the experimental response, making it the dependent variable. Soil temperature is maintained at a constant 22∘C22^\circ\text{C}, making it a controlled variable.

Step-by-Step Solution

1
Identify the factor intentionally manipulated across experimental trials.
The soil volumetric water content was deliberately set to different values (10%10\% to 50%50\%).
The variable systematically changed by the researchers is the independent variable.
2
Identify the outcome or metric measured to evaluate the effect of the manipulation.
The soil CO2CO_2 efflux was recorded at the end of 48 hours for each plot.
The response variable that changes as a result of the independent variable is the dependent variable.
3
Identify parameters kept uniform or unchanged throughout the experiment.
Soil temperature was held constant at 22∘C22^\circ\text{C} in all plots.
Conditions intentionally kept identical to isolate the effect of the independent variable are controlled variables.

Key Concept

Identifying Independent, Dependent, and Controlled Variables
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Topics

Identifying Independent, Dependent, and Controlled Variables

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