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Difficulty: MediumDetermining Control Groups and Baseline Conditions

A plant physiologist conducted an experiment to investigate stomatal conductance in *Phaseolus vulgaris* (bean plant) leaves under various treatments of a synthetic phytohormone analog, Compound Y. Match each experimental group to its specific baseline or functional role within the experimental design.

  • Group 1: Intact leaves sprayed with a 0.1%0.1\% ethanol vehicle solution without Compound YNegative control establishing baseline stomatal conductance under vehicle solvent exposure without active Compound Y
  • Group 2: Intact leaves sprayed with 10 μM10\text{ }\mu\text{M} Compound Y dissolved in a 0.1%0.1\% ethanol vehicle solutionPrimary experimental group testing the baseline response to a moderate dosage of Compound Y
  • Group 3: Leaves on root-excised stems sprayed with 10 μM10\text{ }\mu\text{M} Compound Y dissolved in a 0.1%0.1\% ethanol vehicle solutionExperimental control testing whether intact root signaling is required for the stomatal response to Compound Y
  • Group 4: Intact leaves sprayed with 50 μM50\text{ }\mu\text{M} Compound Y dissolved in a 0.1%0.1\% ethanol vehicle solutionExperimental group evaluating dose-dependent changes in stomatal closure at an elevated treatment concentration

Answer

Group 1 matches the negative control for vehicle solvent baseline without Compound Y; Group 2 matches the primary experimental group for moderate chemical concentration; Group 3 matches the control testing the necessity of intact root signaling; Group 4 matches the experimental group assessing high-concentration dose dependency.
Each experimental setup plays a distinct role: Group 1 provides the negative control for solvent effects; Group 2 and Group 4 assess moderate and high active chemical doses; Group 3 controls for systemic root-tissue participation.

Step-by-Step Solution

1
Identify the group where the independent variable (Compound Y) is completely absent.
Group 1 receives only the vehicle solution (0.1%0.1\% ethanol).
Negative controls isolate background effects of the delivery vehicle/solvent to set a true baseline.
2
Analyze the purpose of modifying plant anatomy in Group 3 while keeping chemical concentration identical to Group 2.
Excising roots isolates leaf-tissue responses from systemic root signaling.
This serves as a targeted control to verify whether systemic root-derived factors mediate stomatal closure.
3
Distinguish between the two intact treatment groups (Group 2 and Group 4).
Group 2 uses a moderate concentration (10 μM10\text{ }\mu\text{M}) whereas Group 4 uses a higher concentration (50 μM50\text{ }\mu\text{M}).
Varying concentration allows researchers to determine dose-dependent physiological relationships.

Key Concept

Distinguishing between negative baseline controls, structural variable controls, and active treatment groups in multi-variable experimental setups.
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Topics

Determining Control Groups and Baseline Conditions

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