Question

Long day plants require-

• A. 10 hours day length
• B. 12 hours day length
• C. 14 hours day length
• D. More than 14 hours day length

Hint:

Photoperiod rule: Short-day<12 hrs, Long-day>14 hrs, Day-neutral = unaffected by day length.

Answer 1

The Correct Option is D

Step 1: Define photoperiodism.
Photoperiodism is the response of plants to the relative lengths of day and night. It affects flowering and other physiological processes.
Step 2: Long day plants.
Long day plants flower when the day length exceeds a certain critical value, typically more than 14 hours of light per day.
Examples include spinach, wheat, barley, lettuce, and radish.
Step 3: Checking options.
- 10 hours: Too short, this is suitable for short-day plants.
- 12 hours: Borderline neutral day length, not for long-day species.
- 14 hours: Minimum requirement, but most need slightly longer.
- More than 14 hours: Correct, fits the definition of long-day plants.
Step 4: Conclusion.
Thus, long-day plants require more than 14 hours of day length.