A marine biologist set up four tanks to investigate how varying concentrations of dissolve… — ACT

A marine biologist set up four tanks to investigate how varying concentrations of dissolved sodium chloride ( $\text{NaCl}$ ) affect the cellular respiration rate of a microalgae species. Each tank contained $500\text{ mL}$ of purified water and $10^6$ algal cells maintained at a constant temperature of $20^\circ\text{C}$ .

Tank	Added $\text{NaCl}$ Concentration (g/L)	Temperature ( $^\circ\text{C}$ )
Tank 1	$0$	$20$
Tank 2	$15$	$20$
Tank 3	$30$	$20$
Tank 4	$45$	$20$

After 4 hours, the biologist measured oxygen consumption in each tank. Which tank served as the control group in this experiment?

Tank 1Answer
B
Tank 2
C
Tank 3
D
Tank 4

Answer

Tank 1 served as the control group because it maintained a baseline condition with zero added sodium chloride.

The control group provides a baseline measurement by withholding the independent variable being tested. Because the experiment measures the effect of added sodium chloride, the setup containing

0\text{ g/L}

of added sodium chloride (Tank 1) is the control group.

Step-by-Step Solution

Identify the independent variable tested in the experiment.

The independent variable being manipulated across the tanks is the concentration of added sodium chloride (

\text{NaCl}

Understanding what variable is being changed helps isolate which group lacks that treatment.

Define the requirement for a control group.

A control group must serve as a baseline where the independent variable is set to zero or standard conditions.

Comparing experimental results against a zero-treatment baseline isolates the specific effect of the independent variable.

Examine the table to find the setup with no added

\text{NaCl}

Tank 1 has

0\text{ g/L}

of added

\text{NaCl}

, while all other tanks contain active non-zero concentrations.

Tank 1 allows researchers to observe baseline microalgae respiration without salt stress.

Key Concept

Determining Control Groups and Baseline Conditions

Estimated Time:45s

Question

Answer

Step-by-Step Solution

Key Concept

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