- 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.
Concept context
Phases of plant growth, the five classical plant hormones plus newer ones, photoperiodism, vernalization, and seed dormancy.