Plants which form flowers only when day length exceeds 12 hours

Plants which form flowers only when day length exceeds 12 hours

• A. Short-day
• B. Day-neutral
• C. Long-day
• D. Long-night

Answer: (C)

The key idea is photoperiodism—the way flowering is driven by the length of day and night. Some plants need long days to bloom, while others flower as days shorten, and some flower regardless of day length. Here, flowering occurs only when daylight is longer than 12 hours, which fits the pattern of a long-day plant. In practical terms, as spring days lengthen past about 12 hours, these plants switch into bloom; when days are shorter, they stay vegetative. Short-day plants would bloom with shorter days, day-neutral plants don’t care about day length, and long-night refers to a group that requires long nights to flower—not the case described here.

The key idea is photoperiodism—the way flowering is driven by the length of day and night. Some plants need long days to bloom, while others flower as days shorten, and some flower regardless of day length. Here, flowering occurs only when daylight is longer than 12 hours, which fits the pattern of a long-day plant. In practical terms, as spring days lengthen past about 12 hours, these plants switch into bloom; when days are shorter, they stay vegetative. Short-day plants would bloom with shorter days, day-neutral plants don’t care about day length, and long-night refers to a group that requires long nights to flower—not the case described here.