PLANT REPRODUCTION QUESTION 1992:		 	L. PETERSON/AP BIOLOGY

	Survival depends on the ability of an organism to respond to changes in its 
	environment. Some plants flower in response to changes in day length. Some 
	mammals may run or fight when frightened. For both of these examples, 
	describe the physiological mechanism involved in the response.  
  
  
  STANDARDS:
      FLOWERING RESPONSE 
  ADAPTIVE  (1 point MAX)
  __ Value to plant - in balance with pollinators - greater reproductive efficiency
     - controls distribution - or Day/night length less variable than temperature 
     - to set photoperiod response, etc.
  MECHANISM
  __ Minimum size to flower (ripeness to flower)
  __ Photoperiodism - basic explanation = relative lengths of day/night
  __ Importance of dark period over light period (controversy of what is measured)
  __ Statement of short day, long, day, day-neutral plants
  __ Plants vary as to response to light/dark intervals - contrasting categories
        a.  short-day    b.  long-day   c.  day-neutral
  __ Detailed information, such as:
        Short day - (explanation) Flower in late summer, fall or winter or example
        Chrysanthemums, poinsettias, soybean, strawberry, primrose, cocklebur,
        goldenrod, ragweed
  __    Long day - (explanation) Flower in late spring or early summer or example
        Petunias, iris, lettuce spinach, henbane, wheat, potatoes, clover, tobacco
  __    Day neutral - (explanation) Unaffected by photoperiods or example
        Tomatoes, dandelions, garden peas, rice, gorse, rose, snapdragons
  __ Phytochrome - Pr and Pfr
  __ Phytochrome = Blue-green pigment
  __ Absorption at 660 nm converts Pr to Pfr. Absorption at 730 nm converts 
        Pfr to Pr
  __ Slowly decays back to Pr in darkness
  __ Phytochrome located in plasma membrane
  __ Pfr - biologically active form - or the ratios of Pr and Pfr
  __ Description of phytochrome
  __ Internal (biological) clock - circadian rhythm interaction with phytochrome to
     trigger physiological change
  
  EFFECT
  __ Evidence that effect is transported throughout plant - grafts - etc.
  __ "Florigen" - (hormones) much debate and remains in doubt
  __ Other possibilities than "florigen" - balance between gibberellins/cytokinins 
     or gibberellins/auxins or giberellins alone
  
  MAXIMUM OF 7 points - one point must be about phytochrome