A student conducted an experiment to measure the rate of water loss from a certain plant species under different relative humidity levels. The experimental design is summarized in the table below:
| Trial | Relative Humidity (%) | Temperature () | Plant Species | Exposure Time (hours) |
|---|---|---|---|---|
| 1 | 20 | 25 | Fern | 2 |
| 2 | 40 | 25 | Fern | 2 |
| 3 | 60 | 25 | Fern | 2 |
| 4 | 80 | 25 | Fern | 2 |
Suppose the student wants to perform a follow-up experiment to determine how temperature affects the water loss of this same plant species. Which of the following modifications to the experimental design would best allow the student to isolate the effect of temperature?
- Vary the temperature across trials while keeping the relative humidity, plant species, and exposure time constant.Answer
- BVary both the temperature and the relative humidity across trials while keeping the plant species and exposure time constant.
- CVary the temperature and use a different plant species for each trial while keeping the relative humidity constant.
- DVary the temperature across trials while increasing the exposure time for each increase in temperature.
Answer
Vary the temperature across trials while keeping the relative humidity, plant species, and exposure time constant.
To investigate the effect of a new independent variable (temperature), that variable must be varied while holding all other variables constant. The correct option describes changing the temperature across trials while maintaining constant relative humidity, plant species, and exposure time, which successfully isolates the effect of temperature.
Step-by-Step Solution
Key Concept
Scientific Control of Variables in Follow-Up Experiments