Answer: High auxin levels produced by the apical bud itself.
- A Ethylene released from leaves undergoing senescence
- B Gibberellin transported upward from the root system
- C High auxin levels produced by the apical bud itself
- D Cytokinin moving downward from the shoot tip
Correct answer: C. High auxin levels produced by the apical bud itself
Explanation: Auxin produced by the actively growing apical bud moves downward and suppresses the growth of lateral (axillary) buds, a phenomenon called apical dominance.
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.