NAEP Science Grade 12

Category - Biology

Bean leaves growing under constant environmental conditions in a laboratory raise and lower their leaves on a 26-hour cycle. This is an example of a:
  1. Phototropism.
  2. Circadian rhythm.
  3. Day-neutral behavior.
  4. Photoperiodic response.
Explanation
Correct Response: B. Circadian rhythms are periodic biological responses that occur on an approximately 24-hour cycle. Circadian rhythms are independent of external stimuli and would thus continue to occur under constant environmental conditions. Phototropism (A) is a directional response in which plants grow toward a light source. A day-neutral behavior (C) is independent of the relative amount of light and dark hours received by a plant. However, day-neutral behaviors do not occur on a 24-hour cycle. A photoperiodic response (D) depends on the ratio of light-to-dark hours a plant receives and would not occur under constant environmental conditions.
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