ACT Science Question of the Day
Test your knowledge with a hand-picked multiple-choice question.
Background
Plants take in nutrients through extensive root systems, as well as from the air through leaves or needles. Many coniferous evergreens are able to survive for a few weeks after being cut down due to their water-saving needles.
A group of students investigated the properties of several types of coniferous evergreens once they had been extracted from their environments. The students compared the length of time before needles (modified leaves) began to fall from the trees. They placed recently severed, seven-foot trees in spaces with controlled temperature and environmental conditions, and then monitored them closely over several days.
Experiment 1
The students placed representative samples of several varieties of coniferous evergreen in a controlled environment: 20°C, 1 atm, and 35% humidity. They recorded the number of days before needles began to fall for each species.
Results: Experiment 1
| Species Name | Days Before Needle Drop |
|---|---|
| Grand Fir | 28 |
| Virginia Pine | 29 |
| Douglas Fir | 35 |
| Pinyon Pine | 32 |
Experiment 2
The students used the Douglas Fir to conduct a second experiment. They placed new trees in enclosed spaces, varied the temperature and humidity of the trees' environments, and recorded the number of days before needles began to fall.
Results: Experiment 2
| Temperature | Humidity | Days Before Needle Drop |
|---|---|---|
| 20°C | 55% | 37 |
| 30°C | 55% | 33 |
| 20°C | 45% | 36 |
| 30°C | 45% | 32 |
| 20°C | 65% | 39 |
| 30°C | 65% | 35 |
Based on the results of Method 2, what effect does humidity have on the water retention of Douglas Firs?