Question

One set of a plant was grown at $12$ hours day and $12$ hours night period cycles and it flowered while in the other set night phase was interrupted by flash of light and it did not produce flower. Under which one of the following categories will you place this plant?

• A. Long day
• B. Darkness neutral
• C. Day neutral
• D. Short day

Answer 1

The Correct Option is D

The given question describes an experiment with two sets of plants exposed to different light conditions. The first set is grown under a cycle of 12 hours of daylight and 12 hours of night, which results in flowering. The second set undergoes an interruption in the night period with a flash of light and does not produce flowers. To determine the category to which this plant belongs, we need to understand the plant photoperiodism and how it responds to light and darkness.

1. Understanding Photoperiodism: Photoperiodism is the physiological reaction of organisms to the length of day or night. It is commonly observed in plants with respect to their flowering time. There are three main categories:

   • Short day plants: These plants require a long period of uninterrupted darkness (greater than the critical night length) to flower. They typically bloom when nights are long, i.e., in late summer, fall, or winter.
   • Long day plants: These plants flower when they are exposed to short nights (less than the critical night length), typically during late spring or early summer.
   • Day neutral plants: These plants do not depend on the length of daylight or darkness for flowering; they flower when they reach a certain growth stage.

2. Analyzing the Situation: The plant in the problem flowers when subjected to a 12-hour dark period. This suggests it requires a certain length of darkness to initiate flowering. When the dark period is interrupted (flashed with light), it fails to flower, indicating that continuous darkness is essential for it to bloom.

3. Conclusion: The described plant behaves like a short day plant. It needs an uninterrupted long night (more than a certain critical length) to trigger the flowering process. The interruption of the night period by a flash of light disturbs this requirement, hence preventing flowering.

The correct option, therefore, is Short day.