Answer: Ethylene.
- A Gibberellin
- B Ethylene
- C Auxin
- D Cytokinin
Correct answer: B. Ethylene
Explanation: The triple response (inhibition of elongation, radial swelling, and horizontal growth of seedlings) is a well-known bioassay used to detect ethylene activity.
Geometric growth (where both daughter cells keep dividing) produces this classic S-shaped curve: a slow lag phase, a rapid exponential phase, and a levelling-off stationary phase as nutrients or space become limiting - the same fundamental pattern seen in population growth.
Concept context
Phases of plant growth, the five classical plant hormones plus newer ones, photoperiodism, vernalization, and seed dormancy.