Make a fair plant comparison
Identify a changed variable, measured outcome and limit of a small study.
Supplied materials
- Supplied fictional results; do not grow or handle anything for this activity.
- Six same-species seedlings started at 4 cm tall. Three received 6 hours of light daily and grew 2, 3 and 4 cm in a week. Three received 3 hours and grew 1, 2 and 3 cm. Pots, water and room temperature were kept alike.
Learn the idea
A fair comparison changes the factor being studied while keeping other relevant conditions similar. The changed factor here is daily light time; the measured outcome is growth in centimetres.
Repeated plants help reveal variation: plants in the same group did not grow identically. A difference between these small groups suggests a result worth testing again, not a rule for every species or setting.
- List the changed condition and two conditions held alike.
- Add growth within each group and divide by three.
- Compare the two group means.
- Write a conclusion limited to these six seedlings.
See the method in action
The 6-hour mean is (2 + 3 + 4) ÷ 3 = 3 cm. The 3-hour mean is (1 + 2 + 3) ÷ 3 = 2 cm. The observed mean difference is 1 cm in this supplied week.
Check your reasoning
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See the answer and explanation
These seedlings averaged 1 cm more growth in the 6-hour group; repeat the comparison before generalizing.
The supplied group means differ by 1 cm, but only six seedlings and one week were observed. The results do not show every plant doubling its growth, and water was held alike.
Take it further
Replace the 6-hour growth values with 2, 2 and 2 cm. Check that both means are now 2 cm and revise the conclusion.
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Longer courses for learners ages 14+
These related courses have their own preparation and projects. They are not early-grade assignments.
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