Answer: Transcription factors that interact with Pfr form of phytochrome and are degraded upon light activation, derepressing light-responsive genes.
- A Red light receptors themselves, which absorb photons directly through a bound chromophore group structure according to conventional understanding
- B Transcription factors that interact with Pfr form of phytochrome and are degraded upon light activation, derepressing light-responsive genes
- C Plastid-localized enzymes responsible for synthesizing the phytochrome chromophore precursor molecule in routine practice overall in most cases
- D DNA repair proteins that are activated specifically in response to ultraviolet light exposure events under typical conditions according to standard textbooks
Correct answer: B. Transcription factors that interact with Pfr form of phytochrome and are degraded upon light activation, derepressing light-responsive genes
Explanation: PIFs: bHLH transcription factors. In dark, PIFs accumulate and repress light responses. Light converts phytochrome to Pfr; Pfr binds PIFs and promotes their phosphorylation and proteasomal degradation.
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.