Answer: Auxin activity.
- A Cytokinin activity
- B Gibberellin level
- C Ethylene amount
- D Auxin activity
Correct answer: D. Auxin activity
Explanation: The degree of curvature of an oat (Avena) coleoptile is proportional to the amount of auxin applied, so it is used to assay auxin.
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.