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Difficulty: EasyComparing and Contrasting Multiple Experimental Designs

Students conducted two experiments to study the growth of *Arabidopsis thaliana* plants over a 30-day period.

Experiment 1
Five groups of 10 plants were grown in identical pots containing the same soil type. Each group received a different concentration of Fertilizer X (0%, 1%, 2%, 3%, or 4% by volume) dissolved in water. All plants were kept under continuous white light at a constant temperature of 22°C and watered daily with 50 mL of their respective solution. The average height of the plants in each group was measured at the end of 30 days.

Experiment 2
Five groups of 10 plants were grown under the same conditions as in Experiment 1, except that all plants received a 2% solution of Fertilizer X, and each group was exposed to a different color of light (blue, green, red, yellow, or white).

Based on the descriptions of the two experiments, which of the following variables was kept constant in Experiment 1 but was varied in Experiment 2?

  1. A
    The concentration of Fertilizer X
  2. The color of light the plants receivedAnswer
  3. C
    The type of soil used to grow the plants
  4. D
    The duration of the growth period

Answer

The color of light the plants received
The correct answer is the color of light the plants received. In Experiment 1, all plants were kept under continuous white light (a constant condition). In Experiment 2, the light color was the independent variable, meaning it was varied (blue, green, red, yellow, or white) across the different groups of plants.

Step-by-Step Solution

1
Identify the independent variable (what is varied) and the constants (what is kept the same) in Experiment 1.
In Experiment 1, the fertilizer concentration is varied (0% to 4%), while the light color (white light), soil type, temperature (22°C), watering volume (50 mL), and duration (30 days) are kept constant.
This establishes the control parameters and experimental variable for the first study.
2
Identify the independent variable and the constants in Experiment 2.
In Experiment 2, the light color is varied (blue, green, red, yellow, white), while the fertilizer concentration (2%), soil type, temperature, watering volume, and duration are kept constant.
This establishes the control parameters and experimental variable for the second study.
3
Compare the two sets of variables to find which condition is constant in Experiment 1 but varied in Experiment 2.
Light color is constant in Experiment 1 (white light) but varied in Experiment 2 (different colors).
This directly answers the comparative question asked in the stem.

Key Concept

Comparing and Contrasting Multiple Experimental Designs
Estimated Time:45s
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Topics

Comparing and Contrasting Multiple Experimental Designs

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