A soil scientist investigated the effect of varying soil copper (\text{Cu}^{2+}) concentra… — ACT

A soil scientist investigated the effect of varying soil copper ( $\text{Cu}^{2+}$ ) concentrations on the rate of nitrate uptake in spinach roots. Five groups of ten plants each were grown in identical hydroponic solutions containing $\text{Cu}^{2+}$ concentrations of $0\text{ }\mu\text{M}$ , $5\text{ }\mu\text{M}$ , $10\text{ }\mu\text{M}$ , $25\text{ }\mu\text{M}$ , and $50\text{ }\mu\text{M}$ , respectively. Throughout the 14-day experiment, all plant groups were maintained at $22^\circ\text{C}$ under a constant 16-hour light / 8-hour dark cycle. At the conclusion of the experiment, the researcher recorded the total nitrate concentration ( $\mu\text{mol/g}$ ) remaining in the nutrient solutions.

In this investigation, which factor serves as the independent variable?

The copper ( $\text{Cu}^{2+}$ ) concentration in the hydroponic solutionAnswer
B
The total nitrate concentration remaining in the nutrient solutions
C
The ambient temperature ( $22^\circ\text{C}$ ) maintained during the trial
D
The duration of the photoperiod (16-hour light / 8-hour dark cycle)

Answer

The copper (

\text{Cu}^{2+}

) concentration in the hydroponic solution

The independent variable is the specific factor that the experimenter purposely alters or varies between groups to observe its effect. In this study, the scientist systematically changed the copper concentration across five experimental groups (

0\text{ }\mu\text{M}

50\text{ }\mu\text{M}

), making copper concentration the independent variable.

Step-by-Step Solution

Identify the factor being systematically changed or manipulated by the researcher.

The researcher intentionally established five different hydroponic solution treatments with distinct copper (

\text{Cu}^{2+}

) concentrations (

0

5

10

25

, and

50\text{ }\mu\text{M}

The manipulated condition across experimental setups defines the independent variable.

Distinguish the independent variable from dependent and controlled variables.

The nitrate remaining in solution is the measured outcome (dependent variable), while temperature and light cycle are kept constant across groups (controlled variables).

Ensures that the variable directly tested is isolated from confounding factors and measured outputs.

Key Concept

Identifying Independent, Dependent, and Controlled Variables

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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