A group of environmental scientists conducted a study to evaluate how varying concentratio… — ACT

A group of environmental scientists conducted a study to evaluate how varying concentrations of dissolved oxygen ( $2\text{ mg/L}$ , $4\text{ mg/L}$ , $6\text{ mg/L}$ , and $8\text{ mg/L}$ ) in aquatic tanks affect the average swimming speed of juvenile rainbow trout (*Oncorhynchus mykiss*). In each trial, the water temperature was maintained at $15^\circ\text{C}$ , the tank volume was held at $100\text{ L}$ , and the photoperiod was fixed at 12 hours of light per day. Which of the following best identifies the independent variable in this experiment?

The concentration of dissolved oxygen in the tanksAnswer
B
The average swimming speed of the juvenile rainbow trout
C
The water temperature in the tanks
D
The total volume of water in each tank

Answer

The concentration of dissolved oxygen in the tanks is the independent variable.

The independent variable is the specific factor that researchers intentionally change across trials to test its impact. In this study, the researchers established controlled treatments varying the dissolved oxygen concentration (

2\text{ mg/L}

4\text{ mg/L}

6\text{ mg/L}

, and

8\text{ mg/L}

), making the dissolved oxygen concentration the independent variable.

Step-by-Step Solution

Identify what the researchers systematically manipulated across experimental conditions.

The researchers established four distinct treatment groups with different dissolved oxygen levels (

2\text{ mg/L}

4\text{ mg/L}

6\text{ mg/L}

, and

8\text{ mg/L}

The independent variable is the factor that is intentionally varied by the experimenter to test its potential effects.

Distinguish the independent variable from the dependent variable and controlled conditions.

The average swimming speed is the measured output (dependent variable), while water temperature, tank volume, and photoperiod are held constant (controlled variables).

Correct identification of experimental components requires categorizing what is manipulated, what is measured, and what is kept constant.

Key Concept

Independent vs. Dependent and Controlled Variables

Estimated Time:1m 0s

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