The Moldy Bread Investigation
A student investigates what makes bread mold grow faster. She places four slices of the same bread in four bags. Bag 1 is kept in a warm, dark cabinet. Bag 2 is kept in a warm, sunny window. Bag 3 is kept in a cold refrigerator. Bag 4 is kept in a warm, dark cabinet but the bread is sprayed with water first. After 5 days she records mold coverage: Bag 1 shows a little mold, Bag 2 shows a little mold, Bag 3 shows no mold, and Bag 4 shows a lot of mold. She concludes, "Moisture is the only thing that matters for mold growth."
1. Is the student's conclusion supported by her data? Explain which bags you compare.
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The conclusion is not fully supported. Comparing Bag 1 (warm, dark, dry) with Bag 4 (warm, dark, wet) shows that added moisture increased mold, so moisture does matter. But comparing Bag 1 with Bag 3 shows that temperature also matters: the cold refrigerator slice had no mold while the warm slice did. So temperature is another factor. The data do not support the word "only." A better conclusion is that both moisture and temperature affect mold growth.
2. What does the comparison between Bag 1 and Bag 2 tell you, and what does it not tell you?
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Bag 1 (dark) and Bag 2 (sunny) both showed only a little mold, so light versus dark did not make a large difference in this experiment. However, this comparison does not prove light has no effect, because only one trial was done and the amount of mold was described vaguely ("a little"). To be confident, the student would need repeated trials and a way to measure mold coverage more precisely. The comparison suggests light is less important than moisture or temperature here, but it is not strong evidence that light has no effect.