Answer: Asymmetric distribution of auxin efflux carriers (PIN proteins) on the cell membrane.
- A Auxin's inability to cross the plasma membrane in either direction
- B Auxin being synthesized only at the base of the stem
- C Asymmetric distribution of auxin efflux carriers (PIN proteins) on the cell membrane
- D Passive diffusion alone, without involvement of any membrane transport proteins
Correct answer: C. Asymmetric distribution of auxin efflux carriers (PIN proteins) on the cell membrane
Explanation: Polar auxin transport depends on the asymmetric, unequal localization of PIN efflux carrier proteins on the plasma membrane, directing the movement of auxin predominantly toward the base of the shoot.
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.