A biochemist conducted an experiment to investigate how substrate availability influences … — ACT

A biochemist conducted an experiment to investigate how substrate availability influences cellular respiration rates in yeast. Five identical incubation flasks were prepared, each containing $50\text{ mL}$ of yeast suspension in a buffer solution maintained at a constant temperature of $30^\circ\text{C}$ and a $\text{pH}$ of $6.5$ . Different masses of glucose— $0.5\text{ g}$ , $1.0\text{ g}$ , $1.5\text{ g}$ , $2.0\text{ g}$ , and $2.5\text{ g}$ —were added to Flasks 1 through 5, respectively. The volume of carbon dioxide ( $\text{CO}_2$ ) gas generated by each flask was measured after $10\text{ minutes}$ .

Which of the following operational parameters represents the independent variable in this experiment?

The mass of glucose added to each incubation flaskAnswer
B
The volume of carbon dioxide gas generated after 10 minutes
C
The constant incubation temperature of 30°C
D
The total duration of 10 minutes for gas collection

Answer

The independent variable in this experiment is the mass of glucose added to each incubation flask.

The mass of glucose added to each flask is the independent variable because it is the specific factor intentionally changed by the experimenter across the experimental treatments to assess its effect.

Step-by-Step Solution

Identify the experimental factor being intentionally manipulated by the researcher across trial groups.

The researcher varied the mass of glucose (

0.5\text{ g}

2.5\text{ g}

) across Flasks 1 through 5.

The factor directly changed by the experimenter to observe an outcome is the independent variable.

Distinguish the independent variable from dependent and controlled variables.

Glucose mass is the independent variable;

\text{CO}_2

gas volume produced is the dependent variable; temperature,

\text{pH}

, suspension volume, and reaction time are controlled variables.

Clear differentiation ensures proper identification of cause and effect in experimental design.

Key Concept

Identifying Independent, Dependent, and Controlled Variables

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