Answer: Cell elongation and phototropism.
- A Cell elongation and phototropism
- B Cell division at root tip
- C Leaf senescence
- D Stomatal closure
Correct answer: A. Cell elongation and phototropism
Explanation: Auxin (IAA) promotes cell elongation in stems and is responsible for phototropism (bending toward light).
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.