Examkin

Question

Difficulty: MediumDetermining Control Groups and Baseline Conditions

To study the effectiveness of a new liquid antimicrobial agent, Agent Y, researchers performed an experiment using agar plates inoculated with *Escherichia coli*. Four plates were prepared under identical conditions:

* Plate 1: Treated with 5 mL5\text{ mL} of a 20%20\% Agent Y solution dissolved in distilled water.
* Plate 2: Treated with 5 mL5\text{ mL} of a 10%10\% Agent Y solution dissolved in distilled water.
* Plate 3: Treated with 5 mL5\text{ mL} of a 5%5\% Agent Y solution dissolved in distilled water.
* Plate 4: Treated with 5 mL5\text{ mL} of pure distilled water.

All plates were incubated at 37∘C37^\circ\text{C} for 24 hours24\text{ hours}. Afterward, the diameter of the zone of inhibition (the clear area where bacterial growth was prevented) was measured in millimeters (mm\text{mm}).

Which of the plates serves as the control group to determine the baseline bacterial growth in the absence of the antimicrobial Agent Y?

  1. Plate 4, because it contains only distilled water without Agent Y.Answer
  2. B
    Plate 3, because it has the lowest concentration of Agent Y.
  3. C
    Plate 1, because it has the highest concentration of Agent Y and is expected to produce the largest zone of inhibition.
  4. D
    All four plates serve as control groups because they were incubated at the same temperature and for the same duration.

Answer

Plate 4, because it contains only distilled water without Agent Y.
The correct answer is the option stating that Plate 4 serves as the control group because it contains only distilled water without Agent Y. In an experiment testing the effectiveness of a chemical agent, a control group is required to show what happens in the complete absence of that agent. This establishes a baseline level of bacterial growth under the experimental conditions, proving that any zone of inhibition observed in the other plates is due specifically to the presence of Agent Y and not to other factors like the solvent (water) or incubation conditions.

Step-by-Step Solution

1
Identify the independent variable being tested in the experiment.
The independent variable is the concentration of Agent Y.
Understanding the variable being manipulated helps determine which groups represent active experimental treatments.
2
Determine the baseline condition that lacks the active treatment.
Plate 4 contains 0%0\% Agent Y (only distilled water).
A control group must represent the baseline condition where the independent variable is absent or kept at a natural/untreated state.
3
Differentiate between the control group and controlled experimental variables.
Plate 4 is the control group, whereas incubation temperature and duration are controlled variables held constant across all plates.
This ensures the baseline group is correctly identified separate from the shared experimental conditions.

Key Concept

Determining Control Groups and Baseline Conditions
Rate this question

Topics

Determining Control Groups and Baseline Conditions

More questions from this topic