USA Biology Olympiad (USABO) Practice Exam

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Prepare for the USA Biology Olympiad with engaging flashcards and multiple choice questions. Each question is accompanied by hints and detailed explanations. Ace your exam with confidence!

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What condition is necessary for a short-day plant to flower?

A night that is longer than a certain critical length.
Exposure to continuous light for at least 12 hours.
A temperature above 20 degrees Celsius.
Presence of pollinators during the day.

The correct answer is: A night that is longer than a certain critical length.

A short-day plant requires a night that is longer than a specific critical length to initiate flowering. These plants are sensitive to the duration of darkness, and the critical length varies among species. When the nocturnal period exceeds this critical threshold, it triggers the flowering process by increasing the production of flowering hormones, like florigen. In contrast, exposure to continuous light for at least 12 hours would not benefit short-day plants; they typically require longer nights to flower. Similarly, while temperature can influence growth and development, it is not a determining factor for the flowering of short-day plants. Finally, the presence of pollinators, although important for fertilization, does not directly affect the ability of short-day plants to flower; they still rely fundamentally on the light cycle to trigger their blooming.