The Seedling Light Experiment
A group of students wants to know whether colored light affects how tall bean seedlings grow. They plant 30 bean seeds in identical pots filled with the same soil. They place 10 pots under a red lamp, 10 under a green lamp, and 10 under a white lamp. All lamps are the same distance from the pots and stay on for 12 hours each day. The students water every pot with 50 mL of water each morning. After three weeks, they measure each plant with a ruler. The average heights are 14 cm under red light, 9 cm under green light, and 15 cm under white light. One student says, "Red light makes plants grow tallest."
1. Identify the variables in this experiment and evaluate whether the student's conclusion is supported by the data.
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The independent variable is the color of light. The dependent variable is plant height. Controlled variables include the pot, soil, amount of water, lamp distance, and daily light time. The data show white light produced the tallest average (15 cm), red was close (14 cm), and green was lowest (9 cm). Since white gave the greatest height, the statement "red light makes plants grow tallest" is not supported. A fair conclusion is that light color is linked to growth, and green light produced the least growth here, but one trial cannot prove a general rule.
2. The students want to make their conclusion stronger. Describe two changes they could make and explain why each would help.
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First, they could repeat the whole experiment several times and compare results. Repeating helps show whether the pattern is consistent rather than a one-time result. Second, they could increase the number of plants per color from 10 to a larger number and report the spread of heights, not just averages. More plants reduce the effect of one unusually tall or short seedling. They could also measure height at several time points to see when differences appear. Any of these makes the evidence more reliable and supports a stronger claim.