Biochemists investigated the catalytic activity of the enzyme carbonic anhydrase under var… — ACT

Biochemists investigated the catalytic activity of the enzyme carbonic anhydrase under various environmental conditions across three distinct experimental setups, as summarized in the table below.

Setup	Temperature ( $^\circ\text{C}$ )	Hydrostatic Pressure ( $\text{atm}$ )	Solution $\text{pH}$	Initial Velocity, $v_0$ ( $\mu\text{mol/L}\cdot\text{s}$ )
Trial 1	$20, 25, 30, 35$	$1.0$	$7.4$	Measured
Trial 2	$25$	$1.0, 50, 100, 150$	$7.4$	Measured
Trial 3	$25$	$1.0$	$6.0, 6.5, 7.0, 7.5, 8.0$	Measured

Based on the experimental design shown for Trial 3, which of the following correctly identifies the independent variable, the dependent variable, and a key controlled variable, respectively?

Independent variable: Solution $\text{pH}$ ; Dependent variable: Initial velocity ( $v_0$ ); Controlled variable: Temperature ( $25^\circ\text{C}$ )Answer
B
Independent variable: Initial velocity ( $v_0$ ); Dependent variable: Solution $\text{pH}$ ; Controlled variable: Hydrostatic Pressure ( $1.0\text{ atm}$ )
C
Independent variable: Hydrostatic Pressure; Dependent variable: Initial velocity ( $v_0$ ); Controlled variable: Solution $\text{pH}$
D
Independent variable: Solution $\text{pH}$ ; Dependent variable: Hydrostatic Pressure; Controlled variable: Initial velocity ( $v_0$ )

Answer

The correct response identifies the Solution

\text{pH}

as the independent variable, Initial velocity (

v_0

) as the dependent variable, and Temperature (

25^\circ\text{C}

) as a controlled variable for Trial 3.

In Trial 3, the experimenter systematically varies the solution pH from 6.0 to 8.0 to test its impact on carbonic anhydrase activity. The initial velocity (

v_0

) is the output measured as a function of pH, establishing it as the dependent variable. Temperature (

25^\circ\text{C}

) and hydrostatic pressure (

1.0\text{ atm}

) are deliberately kept constant during Trial 3 to eliminate potential confounding influences, qualifying them as controlled variables.

Step-by-Step Solution

Examine the data for Trial 3 in the table to find the variable intentionally changed by the experimenter.

Solution

\text{pH}

is listed with multiple values (

6.0, 6.5, 7.0, 7.5, 8.0

), making it the independent variable.

The independent variable is the condition purposefully altered to observe its effects.

Determine the factor that is being measured or observed in response to changing the independent variable.

Initial velocity (

v_0

) is designated as 'Measured', making it the dependent variable.

The dependent variable represents the experimental outcome or response measured by the researcher.

Identify the conditions that are held constant across all conditions within Trial 3.

Temperature (

25^\circ\text{C}

) and Hydrostatic Pressure (

1.0\text{ atm}

) remain fixed throughout Trial 3, making them controlled variables.

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

Key Concept

Identifying Independent, Dependent, and Controlled Variables in Multi-Trial Experimental Designs

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