Temperature Regimes and Flowering Time
| Regime | Day temperature (°C) | Night temperature (°C) | 24-hour mean (°C) | Mean days to first flower |
|---|---|---|---|---|
| Control | 24 | 14 | 19 | 44 |
| Day-warmed | 28 | 14 | 21 | 43 |
| Night-warmed | 24 | 18 | 21 | 35 |
| Both-warmed | 28 | 18 | 23 | 34 |
To investigate how temperature influences flowering in an alpine annual plant, botanist Elena Marín and colleagues randomly assigned seedlings from the same seed lot to four greenhouse regimes. Each regime had a 12-hour day and a 12-hour night. One model proposed that flowering responds chiefly to the 24-hour mean temperature, regardless of when warming occurs. An alternative model proposed that nighttime temperature has a disproportionately large influence. The researchers concluded that the results more strongly support the alternative model because ______
Which choice most effectively uses data from the table to complete the statement?
For data-based command-of-evidence questions, identify the competing claims and find the comparison that best separates them. Prioritize rows that hold a key variable constant while changing the factor under investigation, then use other rows to confirm that the resulting pattern is consistent rather than relying only on the largest or smallest value.
Hints
Find a controlled comparison
Look for two treatments that have the same 24-hour mean but differ in when the additional warmth occurs.
Use the combined treatment
After comparing those two treatments, examine whether adding daytime warmth to a night-warmed regime substantially changes the flowering time.
Step-by-step Explanation
Identify the key comparison
The two models differ over whether the timing of warming matters. Therefore, the strongest evidence comes from treatments with the same 24-hour mean but different warming schedules.
Compare the equal-mean regimes
Both the day-warmed and night-warmed regimes had a 24-hour mean of 21°C. However, plants flowered after 43 days with day warming and after 35 days with night warming, an eight-day difference.
Check the combined treatment
Warming both periods led to flowering after 34 days, only one day sooner than night warming alone. Thus, adding daytime warming after nights were already warm had relatively little additional effect.