medium · Enhanced ACT science
A student hypothesized that increasing the concentration of CO_2 would increase the growth of algae. They placed one tank near a window (high CO_2 via a pump) and another tank in a dark closet (low CO_2, no pump). The window tank grew more algae.
Why is this experiment flawed?
- The experiment failed to isolate CO_2 as the only variable, as the tanks also differed in their exposure to light and temperature.
- Algae growth should be measured by dry mass rather than by observing the color or thickness of the water in the two different tanks.
- The student did not specify the species of algae used, which limits the ability of other scientists to replicate the growth conditions.
- A pump was used in only one tank, which could have increased the dissolved oxygen levels, acting as a nutrient for the algae growth.
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