PLANT REPRODUCTION QUESTION 1984:			L. PETERSON/AP BIOLOGY

	Define the following plant responses and explain the mechanism of 
	control for each. Cite experimental evidence as part of your discussion.
	a)  Phototropism
	b)  Photoperiodism 

  
  
  STANDARDS:
  PHOTOTROPISM:     
     Max. = 9 points if experimental evidence is given
     Max. = 7 points if experimental evidence is lacking
  
  __  Definition - movement in response to light (involving growth) - 2 points
  __  Possibility of negative response
  
  Mechanism
  __  Auxins
  __  Distribution (apex -> stem or lateral)
  __  elongation of cells
  __  stem tip or coleoptile
  
  Evidence (2 points for any of the following)
  __  Darwin - covered coleoptiles
  __  Paal - cut coleoptiles - agar, uneven placement
  __  Boysen-Jensen - mica
  __  Went - bioassay
  
  PHOTOPERIODISM:
     Max. = 9 points if experimental evidence is given
     Max. = 7 points if experimental evidence is lacking
  __  Definition - response to light/dark periods
  __  flowering (or other response)
  
  Mechanism
  __  Categories of plants (LDP, SDP)
  __  Receptor in leaf
  __  LDP (if night shorter than minimum)
  __  SDP (if night longer than minimum)
  __  night not day
  __  existence of phytochrome in two forms
  __  PFR/PR  interconvertible
  __  PFR active form
  __  ratio (PR/PFR) important
  __  possible hormonal involvement
  
  Evidence
  __  light flash in dark
  __  grafting
  __  ratio of PR/PFR