medium · Act science
A biologist studying the effect of light color on photosynthesis placed an aquatic plant in red light for 10 minutes and measured the oxygen bubbles produced. Then, they used the same plant in blue light for 10 minutes, and finally in green light.
What is the primary design flaw?
- Using the same plant sequentially causes the later trials to be affected by the physiological 'fatigue' or carry-over effects from the earlier trials.
- Oxygen bubble counting is an imprecise method compared to using a dissolved oxygen probe to measure the exact concentration in mg/L.
- Green light is known to be reflected by chlorophyll, so the green trial acted as a negative control rather than an experimental variable.
- The experiment should have used three different species of plants to ensure that the results were not specific to just one type of vegetation.
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