A team of environmental engineers conducted an experiment to evaluate how varying concentr… — ACT

A team of environmental engineers conducted an experiment to evaluate how varying concentrations of copper sulfate ( $\text{CuSO}_4$ ) in water affect the photosynthetic rate of *Chlorella vulgaris* algae. Four identical $500\text{ mL}$ glass bioreactors were prepared with equal initial algal cell densities. Each bioreactor received a different concentration of $\text{CuSO}_4$ ( $0.0\text{ mg/L}$ , $0.5\text{ mg/L}$ , $1.0\text{ mg/L}$ , and $1.5\text{ mg/L}$ ). All bioreactors were maintained at a constant temperature of $22^\circ\text{C}$ and exposed to continuous artificial light of $150\text{ }\mu\text{mol}\cdot\text{m}^{-2}\cdot\text{s}^{-1}$ for 72 hours. At the end of the trial, the total dissolved oxygen produced ( $\text{mg/L}$ ) was measured to quantify the photosynthetic rate of the algae.

Which of the following identifies the dependent variable in this experiment?

The total dissolved oxygen produced by the algaeAnswer
B
The concentration of $\text{CuSO}_4$ added to the bioreactors
C
The temperature of the bioreactors
D
The initial cell density of *Chlorella vulgaris*

Answer

The total dissolved oxygen produced by the algae is the dependent variable.

The dependent variable in a scientific experiment is the variable observed and measured to assess the effect of the treatment. In this investigation, the researchers measured total dissolved oxygen production to quantify photosynthetic rate in response to varying copper sulfate concentrations.

Step-by-Step Solution

Identify the factor intentionally altered or varied by the researcher.

The concentration of

\text{CuSO}_4

(

0.0\text{ mg/L}

1.5\text{ mg/L}

) is systematically changed, identifying it as the independent variable.

The independent variable is the cause or manipulated input.

Identify the factors intentionally kept identical across all experimental setups.

Temperature (

22^\circ\text{C}

), light intensity (

150\text{ }\mu\text{mol}\cdot\text{m}^{-2}\cdot\text{s}^{-1}

), bioreactor volume (

500\text{ mL}

), trial duration (

72\text{ hours}

), and initial cell density are all controlled variables.

Controlled variables ensure a fair test by keeping confounding factors constant.

Identify the response parameter measured to assess the effect of the independent variable.

The total dissolved oxygen produced (

\text{mg/L}

) is measured to determine the rate of photosynthesis, making it the dependent variable.

The dependent variable represents the effect or measured output of the experiment.

Key Concept

In an experiment, the independent variable is manipulated by the researcher, the dependent variable is the measured outcome, and controlled variables are kept constant to ensure valid results.

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Key Concept

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