A student performed an experiment to measure the rate of photosynthesis in *Elodea* (an aquatic plant) by counting oxygen bubbles produced per minute under various light conditions. Four identical glass beakers were prepared with equal volumes of water and equal masses of *Elodea*:
- Setup 1: Exposed to a white light lamp at a distance of .
- Setup 2: Exposed to a blue light lamp at a distance of .
- Setup 3: Exposed to a red light lamp at a distance of .
- Setup 4: Placed inside a light-tight dark chamber with no light source.
Which setup served as the control group to establish a baseline rate of oxygen production in the absence of the test variable?
- ASetup 1, because white light contains all wavelengths of visible light.
- BSetup 2, because blue light is absorbed efficiently by chlorophyll.
- CSetup 3, because red light stimulates photosynthetic activity.
- Setup 4, because it measures background oxygen production without the presence of light.Answer
Answer
Setup 4 served as the control group because it measured oxygen output without light exposure.
Setup 4 completely removes the independent variable (light) by placing the plant in a light-tight chamber. This establishes a baseline level of oxygen production (or lack thereof) to ensure that any oxygen produced in Setups 1, 2, and 3 is directly attributable to light exposure.
Step-by-Step Solution
Key Concept
Control groups isolate the independent variable to determine baseline measurements and confirm that observed results are due to the experimental manipulation.
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