STPM Biology - chapter 11: Revision essay question 1

1. a.The control of flowering in some plants involved phytochrome. Describe the role of phytochrome                                  
       in the flowering of short day plant.                                                                                              [6]

Answer: 





- two forms or PFR / P730, and, PR/ P660
- red light / 660nm / daylight changes PR to PFR
- far red light / 730nm / dark changes PFR to PR, slowly in dark or at night
- PFR is the biologically active form
- SDP's flower, if day length below / dark above, a critical night length
- SDP's really long night plants
- PFR inhibits flowering in SDP's
- therefore SDP flower when PFR converted to PR, a high concentration of PR promote flowering in
  SDP's
- a decrease in the level of PFR and increase level of PR stimulated conversion of inactive precursor to
  florigen. This induced flowering in SDP's

* for animation: http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591896__