[Campbell Biology P.909] According to Figure 39.20, which of the following light/dark cycles... | Practice Question

According to Figure 39.20, which of the following light/dark cycles would prevent a short-day plant from flowering?

  • A: Long dark period without any light interruption.
  • B: Dark period interrupted by a flash of red (r) light.
  • C: Dark period interrupted by a flash of red (r) followed immediately by far-red (fr) light.
  • D: Dark period interrupted by a flash of far-red (fr) light only.

Explanation

Figure 39.20 shows that a flash of red light r during the dark period shortens the effective dark period, which prevents flowering in short-day plants that require a long, uninterrupted night.