Interrupting the night with a flash of light can trigger flowering in a long-day plant. Why doesn't introducing a short period of darkness during the day cause a short-day plant to flower?

Question

A.  Sunlight contains enough far-red light to inhibit phytochrome induction of flowering.
B.  A brief dark period is not sufficient to trigger flowering.
C.  Phytochrome is only active in the dark.
D.  The circadian clock is less responsive during the day than at night.
E.  The phytochrome response also requires cool nighttime temperatures.

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

Gather Content
What do you already know about long-day and short-day plants? What other information is related to the question?

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

B.  A brief dark period is not sufficient to trigger flowering.

Clarify Question
What is the key concept addressed by the question?
        · This question is asking you to analyze the mechanics of flowering within a short-day plant.
What type of thinking is required?
        · Analyze level:
            o This is an analyze question because you have to break the flowering mechanisms of long-day and short-day plants into their component pieces to understand how they function.

Gather Content
What do you already know about long-day and short-day plants? What other information is related to the question?
        · Long-day plants can be induced to flower by an extra burst of light.
        · Short-day plants and long-day plants are stimulated to flower by the length of uninterrupted periods of darkness.

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
        · Circadian clock responsiveness is not affected by the time of day, so this answer can be discarded. Phytochrome can be active during periods of light, so references to inactivation during daytime hours are not accurate. The correct answer lies in the idea that plants are affected by the length of uninterrupted darkness, therefore a brief exposure to the dark should not be expected to have an impact on the timing of flowering.

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
· Analyze level:
        o Answering this question correctly depended not only on distinguishing between the action of phytochrome and photoperiod in stimulating flower production, but on your ability to break down, or analyze, the mechanism of flowering regulation. If you got an incorrect answer, did you remember that flowering regulation includes the action of phytochrome, or that the period of uninterrupted darkness regulates flower production? Did you have trouble breaking down flowering regulation to determine the correct answer?