Answer: Is a calcium sensor that, when Ca 2+ bound, activates multiple target enzymes (kinases, phosphatases, NOSs).
- A Functions as a receptor tyrosine kinase embedded directly in the plasma membrane structure under most conditions encountered
- B Is a calcium sensor that, when Ca<sup>2+</sup> bound, activates multiple target enzymes (kinases, phosphatases, NOSs)
- C Operates mainly within guard cells, largely absent from other plant tissues studied as frequently observed in practice
- D Is itself a diffusible plant hormone synthesized within the shoot apex region in many documented cases
Correct answer: B. Is a calcium sensor that, when Ca<sup>2+</sup> bound, activates multiple target enzymes (kinases, phosphatases, NOSs)
Explanation: Calmodulin: ubiquitous Ca<sup>2+</sup>-binding protein. Ca<sup>2+</sup> binding changes its conformation, enabling it to activate/inhibit target proteins, transducing Ca<sup>2+</sup> signals to diverse cellular responses.
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.