A scientist conducted two experiments to study soil respiration (measured as the rate of c… — ACT

A scientist conducted two experiments to study soil respiration (measured as the rate of carbon dioxide release, $R_s$ , in $\text{g CO}_2/\text{m}^2/\text{day}$ ) from a forest soil sample under different conditions.

Experiment	Soil Temperature ( $^\circ\text{C}$ )	Soil Moisture Content (SMC)	Observed Trend in $R_s$
1	$20^\circ\text{C}$ (constant)	Varied ( $10\%$ , $20\%$ , $30\%$ )	$R_s$ increases as SMC increases
2	Varied ( $15^\circ\text{C}$ , $25^\circ\text{C}$ , $35^\circ\text{C}$ )	$20\%$ (constant)	$R_s$ increases as temperature increases

Suppose a scientist wants to determine if the positive relationship between SMC and $R_s$ observed at $20^\circ\text{C}$ remains positive at a near-freezing temperature of $2^\circ\text{C}$ . Which of the following modifications to the experimental design would best allow the scientist to test this hypothesis?

Measure $R_s$ of soil samples at a constant temperature of $2^\circ\text{C}$ while varying the SMC at $10\%$ , $20\%$ , and $30\%$ .Answer
B
Measure $R_s$ of soil samples as the temperature is decreased from $20^\circ\text{C}$ to $2^\circ\text{C}$ while keeping the SMC constant at $20\%$ .
C
Measure $R_s$ of soil samples at temperatures of $2^\circ\text{C}$ , $10^\circ\text{C}$ , and $20^\circ\text{C}$ while allowing the SMC to vary freely for each sample.
D
Measure the rate of water evaporation from the soil samples at $2^\circ\text{C}$ as the SMC is varied at $10\%$ , $20\%$ , and $30\%$ .

Answer

Measure

R_s

of soil samples at a constant temperature of

2^\circ\text{C}

while varying the SMC at

10\%

20\%

, and

30\%

To determine if the positive relationship between soil moisture content (SMC) and soil respiration rate (

R_s

) is preserved at a new constant temperature (

2^\circ\text{C}

), the scientist must isolate SMC as the independent variable. This is accomplished by holding the temperature constant at

2^\circ\text{C}

and measuring

R_s

across the same range of SMC values (

10\%

20\%

, and

30\%

) used in the original experiment.

Step-by-Step Solution

Identify the goal of the proposed follow-up experiment.

The goal is to determine if the positive relationship between SMC and

R_s

holds at

2^\circ\text{C}

Understanding the hypothesis is necessary to determine which variables must be manipulated and measured.

Identify the independent and dependent variables required to test the hypothesis.

The independent variable must be SMC (varied at

10\%

20\%

, and

30\%

) and the dependent variable must be

R_s

(soil respiration rate).

To see if the relationship between moisture and respiration is altered, moisture must be varied while measuring respiration.

Identify the necessary control variables.

The temperature must be held constant at the new temperature of interest (

2^\circ\text{C}

If temperature is not held constant at

2^\circ\text{C}

, the effect of temperature will confound the results.

Select the option that matches these design criteria.

Varying SMC while maintaining a constant temperature of

2^\circ\text{C}

and measuring

R_s

is the correct experimental design.

This setup isolates the effect of SMC at the specific temperature of

2^\circ\text{C}

without introducing confounding variables.

Key Concept

To test the relationship between an independent variable and a dependent variable under a new constant condition, the independent variable must be varied while keeping all other conditions constant.

Estimated Time:2m 0s

Question

Answer

Step-by-Step Solution

Key Concept

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