A team of environmental microbiologists investigated the enzymatic biodegradation of polye… — ACT

A team of environmental microbiologists investigated the enzymatic biodegradation of polyethylene terephthalate (PET) microplastics. In five separate bioreactors, identical $1.0\text{ g}$ PET film samples of uniform thickness ( $0.05\text{ mm}$ ) were incubated in $250\text{ mL}$ of synthetic seawater solution. Each bioreactor was inoculated with a different bacterial strain ( $S_1$ through $S_5$ ) of *Ideonella sakaiensis*. All five bioreactors were kept at a constant temperature of $30^\circ\text{C}$ and continuously stirred at $150\text{ rpm}$ . After 14 days, the scientists measured the total mass loss (in $\text{mg}$ ) of the PET film in each bioreactor to evaluate degradation efficiency.

Based on the described experimental design, which of the following correctly pairs the independent variable with a controlled variable?

Independent variable: The bacterial strain ( $S_1$ through $S_5$ ); Controlled variable: The incubation temperature ( $30^\circ\text{C}$ )Answer
B
Independent variable: The total mass loss of PET film (in $\text{mg}$ ); Controlled variable: The incubation temperature ( $30^\circ\text{C}$ )
C
Independent variable: The bacterial strain ( $S_1$ through $S_5$ ); Controlled variable: The total mass loss of PET film (in $\text{mg}$ )
D
Independent variable: The volume of synthetic seawater solution ( $250\text{ mL}$ ); Controlled variable: The total mass loss of PET film (in $\text{mg}$ )

Answer

The independent variable is the bacterial strain (

S_1

through

S_5

) and a controlled variable is the incubation temperature (

30^\circ\text{C}

The correct response accurately pairs the independent variable with a controlled variable. The researchers deliberately varied the bacterial strain (

S_1

through

S_5

) to observe its effect, making bacterial strain the independent variable. Meanwhile, temperature (

30^\circ\text{C}

) was intentionally held constant across all bioreactors to ensure a fair test, making it a controlled variable.

Step-by-Step Solution

Identify the variable intentionally changed or manipulated by the experimenters across trial groups.

The researchers changed the specific bacterial strain (

S_1

through

S_5

) inoculated into each bioreactor. Therefore, bacterial strain is the independent variable.

The independent variable is the condition or factor altered systematically to test its effect.

Identify the variable being measured as an outcome of the experiment.

The researchers measured the total mass loss of the PET film after 14 days. This is the dependent variable.

The dependent variable represents the response or outcome measured to assess the effect of the independent variable.

Identify variables kept strictly uniform across all experimental setups.

Factors kept identical across all five bioreactors include incubation temperature (

30^\circ\text{C}

), agitation speed (

150\text{ rpm}

), initial PET mass (

1.0\text{ g}

), film thickness (

0.05\text{ mm}

), and solution volume (

250\text{ mL}

). These are controlled variables.

Controlled variables must be held constant so that any observed changes in the dependent variable can be attributed solely to the independent variable.

Key Concept

Experimental Variable Classification

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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