A short-day plant and a long-day plant each have a critical dark period of 10 h…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A short-day plant and a long-day plant each have a critical dark period of h. Both are kept in four different days. No flash falls in any night.
| Day | Hours of light | Hours of dark |
|---|---|---|
| P | 8 | 16 |
| Q | 14 | 10 |
| R | 16 | 8 |
| S | 12 | 12 |
- In which days does the short-day plant flower?
- In which days does the long-day plant flower?
Need a reminder? The key ideaShow
Photoperiodism is the response to the relative lengths of day and night. A short-day plant flowers when the unbroken dark period is longer than its critical dark period. A long-day plant flowers when it is shorter. A flash in the night breaks the dark period. The leaf perceives it, and florigen moves to the shoot tip.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Compare the dark periods. The critical dark period is h. In P it is h, in Q it is h, in R it is h and in S it is h.
Step 2. (a) The short-day plant needs a dark period of h or more: P, Q and S.
Step 3. (b) The long-day plant needs a dark period shorter than h: R only. In Q the dark period is exactly h, which is not shorter, so it does not flower.
Answer: (a) P, Q and S; (b) R.
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