Biochemical engineers investigated the enzymatic degradation of polyethylene terephthalate… — ACT

Biochemical engineers investigated the enzymatic degradation of polyethylene terephthalate (PET) microplastics using a newly isolated bacterial hydrolase.

Study 1
Four identical $250\text{ mL}$ reaction flasks were prepared, each containing $100\text{ mL}$ of a $50\text{ mg/L}$ PET microplastic suspension buffered at $\text{pH } 7.5$ . To each flask, $0.10\text{ mg/mL}$ of hydrolase was added. The flasks were incubated for 24 hours at constant temperatures of $25^\circ\text{C}$ , $35^\circ\text{C}$ , $45^\circ\text{C}$ , and $55^\circ\text{C}$ , respectively, while continuously stirred at $200\text{ rpm}$ . At the end of the 24-hour period, the mass loss of PET (in $\text{mg}$ ) in each flask was recorded.

Study 2
The procedure of Study 1 was repeated at a constant temperature of $45^\circ\text{C}$ , but the enzyme concentration was varied across the four flasks ( $0.05\text{ mg/mL}$ , $0.10\text{ mg/mL}$ , $0.15\text{ mg/mL}$ , and $0.20\text{ mg/mL}$ ). PET mass loss was again measured after 24 hours.

In Study 1, which of the following correctly identifies the independent variable and the dependent variable?

Independent variable: Incubation temperature; Dependent variable: PET mass lossAnswer
B
Independent variable: PET mass loss; Dependent variable: Incubation temperature
C
Independent variable: Enzyme concentration; Dependent variable: PET mass loss
D
Independent variable: Incubation temperature; Dependent variable: Stirring speed

Answer

In Study 1, the independent variable is the incubation temperature (

25^\circ\text{C}

35^\circ\text{C}

45^\circ\text{C}

55^\circ\text{C}

), and the dependent variable is the PET mass loss.

In Study 1, the researchers systematically altered the incubation temperature (

25^\circ\text{C}

35^\circ\text{C}

45^\circ\text{C}

, and

55^\circ\text{C}

) across identical setups to evaluate its impact on enzymatic activity. Thus, incubation temperature is the independent variable. The resulting mass loss of PET was the quantity measured at the end of the 24-hour reaction period, making PET mass loss the dependent variable.

Step-by-Step Solution

Identify the factor directly manipulated by the experimenters in Study 1

Incubation temperature was set to four distinct values (

25^\circ\text{C}

35^\circ\text{C}

45^\circ\text{C}

55^\circ\text{C}

) across the flasks.

The variable intentionally changed by the experimenter to test its effect is the independent variable.

Identify the factor measured at the conclusion of Study 1

PET mass loss (in

\text{mg}

) was recorded after 24 hours.

The variable measured to observe the effect of the independent variable is the dependent variable.

Distinguish independent and dependent variables from controlled factors

Enzyme concentration (

0.10\text{ mg/mL}

), reaction volume (

100\text{ mL}

\text{pH}

(

7.5

), and stirring speed (

200\text{ rpm}

) were kept constant in Study 1.

Controlled variables are kept fixed to ensure that changes in the dependent variable are solely attributable to the independent variable.

Key Concept

Identifying Independent, Dependent, and Controlled Variables in Experimental Designs

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic