[Campbell Biology P.910] If an enzyme in field-grown soybean leaves is most active at noon a... | Practice Question

If an enzyme in field-grown soybean leaves is most active at noon and least active at midnight, is its activity under circadian regulation?

  • A: Yes, because its activity fluctuates predictably over a 24-hour cycle, indicating an internal clock.
  • B: No, because circadian rhythms are only observed in response to light, not in naturally grown plants.
  • C: It's impossible to tell without knowing the exact light/dark cycle duration.
  • D: No, because enzyme activity is usually constant throughout the day in healthy plants.

Explanation

Circadian rhythms are biological processes that oscillate with an approximately 24-hour period. If an enzyme's activity consistently peaks at noon and is lowest at midnight, it demonstrates a predictable, cyclical pattern characteristic of circadian regulation, even in a field setting where light/dark cycles are natural.