Passage
A group of students studied how the amount of daily light affects the growth of bean seedlings. All plants were the same variety, grown in identical pots and soil, watered equally, and kept at the same temperature. Only the daily light exposure was varied.
Study 1: Seedlings were divided into groups, each given a different number of hours of light per day. After 3 weeks, the mean height of the plants in each group was measured (Table 1).
| Light exposure (hours/day) | Mean plant height after 3 weeks (cm) |
|---|
| 2 | 6 |
| 4 | 11 |
| 6 | 17 |
| 8 | 22 |
| 10 | 25 |
| 12 | 26 |
Study 2: A separate group of the same seedlings was given 8 hours of light per day. The mean height of this group was measured at the end of each week for 4 weeks (Table 2).
| Week | Mean plant height (cm) |
|---|
| 1 | 5 |
| 2 | 12 |
| 3 | 22 |
| 4 | 30 |
In both studies, all conditions other than the one being tested were held constant.
