medium · Enhanced 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.
- Bubble counting is a fairly imprecise method compared with using a calibrated dissolved oxygen probe to measure the exact concentration present in mg/L.
- Green light largely reflects off the chlorophyll rather than being absorbed, so that trial actually served as a built-in control, not a true variable.
- The study really should have tested three separate species of plants to ensure results were not specific to just one type of vegetation.
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