№ 003 · Scientific literacy · Design and evaluate scientific enquiry
Plants and light: is the experiment fair?
Students analyse two classmates' experiment, explain why no conclusion can be drawn from it and propose a fair test.
Material for students
Dana and Arman tested how light affects a plant
They took two identical bean seedlings.
- Plant A stood on the windowsill and was watered every day.
- Plant B stood in a dark cupboard and was watered once a week.
After two weeks plant A was 14 cm tall and plant B was 6 cm. They concluded: “Light makes plants grow faster.”
Illustrative data.
Questions
Teacher's guide
Skill: evaluating and designing scientific enquiry: controlling variables, fair comparison, reliability.
Full answer: 1) Two things changed at once: light and watering, so we cannot tell what caused the difference. 2) Only light changes; watering, soil, pot, temperature and seed type stay the same. 3) One plant's result may be due to chance; the average of several is more reliable.
Typical mistake: saying “too few plants” and missing the main flaw — different watering.
In your subject
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