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Difficulty: MediumDetermining Control Groups and Baseline Conditions

A team of plant physiologists investigated the effect of a chemical surfactant (Surfactant X) on the water retention capacity of corn seedlings (*Zea mays*) during a simulated drought.

Four experimental groups of 20 corn seedlings each were grown in identical pots containing 500 g of soil:
- Group 1 was watered with 100 mL of pure distilled water.
- Group 2 was watered with 100 mL of a 0.1% Surfactant X aqueous solution.
- Group 3 was watered with 100 mL of a 0.5% Surfactant X aqueous solution.
- Group 4 was watered with 100 mL of a 1.0% Surfactant X aqueous solution.

All groups were maintained in the same environmental chamber at 25∘C25^\circ\text{C} with 14 hours of light daily. After 14 days, the average change in seedling biomass was recorded.

Which group served as the control group in this experiment, and what baseline condition did it establish?

  1. Group 1, because it measured seedling growth in the absence of Surfactant X to serve as a comparison baseline.Answer
  2. B
    Group 4, because it contained the highest concentration of Surfactant X to establish the maximum baseline effect.
  3. C
    Group 2, because it used the lowest concentration of Surfactant X to represent typical soil moisture conditions.
  4. D
    Groups 2, 3, and 4, because they established the range of variable conditions tested across the trial.

Answer

Group 1 served as the control group because it measured seedling growth under conditions where the independent variable (Surfactant X) was omitted, providing a baseline comparison.
In experimental design, a control group establishes a baseline by maintaining all constant parameters while omitting the independent variable being tested. Here, the independent variable is the addition of Surfactant X. Group 1 receives pure distilled water without any Surfactant X, allowing researchers to measure normal plant growth and evaluate whether adding Surfactant X produces a significant effect.

Step-by-Step Solution

1
Identify the independent variable tested in the experiment.
The independent variable is the concentration of Surfactant X added to the watering solution.
Determining what variable is intentionally manipulated helps isolate which group lacks this treatment.
2
Identify which experimental group excludes the independent variable.
Group 1 received 100 mL of pure distilled water with 0% Surfactant X.
A control group provides baseline conditions by withholding the treatment being evaluated.
3
Determine the purpose of including Group 1.
Group 1 establishes a baseline for normal seedling growth under drought conditions without any chemical additive.
Comparing the experimental groups (Groups 2–4) against Group 1 allows researchers to isolate the specific impact of Surfactant X.

Key Concept

Control Group and Baseline Identification
Estimated Time:1m 15s
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Topics

Determining Control Groups and Baseline Conditions

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