Answer: Red and far-red light (Pr and Pfr forms).
- A Blue light exclusively, detected through a flavin chromophore
- B Red and far-red light (Pr and Pfr forms)
- C Ultraviolet light absorbed by UVR8 photoreceptor proteins
- D Green light wavelengths absorbed by chlorophyll-associated pigments
Correct answer: B. Red and far-red light (Pr and Pfr forms)
Explanation: Phytochrome exists as Pr (absorbs red 660 nm, inactive) and Pfr (absorbs far-red 730 nm, active). Controls germination, flowering, shade avoidance.
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.