Answer: shoot tip.
- A shoot tip
- B only the root cap
- C old leaves
- D outer bark
Correct answer: A. shoot tip
Explanation: Auxin is synthesised chiefly at the growing shoot tip.
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.