Answer: Polar (from shoot apex downward, basipetal).
- A Acropetal, moving upward from the root tip toward the shoot apex
- B Polar (from shoot apex downward, basipetal)
- C Non-directional, diffusing randomly through ground tissue without polarity
- D Confined entirely to root tissue, absent from the shoot system
Correct answer: B. Polar (from shoot apex downward, basipetal)
Explanation: Auxin has polar (unidirectional) transport: basipetal (away from apex, downward in shoots) via PIN efflux carrier proteins.
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.