Standards  - Question #3 (1996)#3.   

       Numerous environmental variables influence plant growth.  Three students each planted a 
    seedling of the same genetic variety in the same type of container with equal amounts 
    of soil from the same source. Their goal was to maximize their seedling's growth by 
    manipulating environmental conditions.  Their data are shown below.
					      			               
                       Plant Seedling Mass (grams)
				
 	Day 1                    Day 30
	Student A	      	   4                            24		
	Student B	       	   5                            35
	Student C	      	   4                            64

a)  Identify three different environmental variables that could account for differences in the 
    mass of the seedlings at day 30.  Then choose one of these variables and design an experiment 
    to test the hypothesis that your variable affects growth of these seedlings.
b)  Discuss the results you would expect if your hypothesis is correct.  Then provide a 
    physiological explanation for the effect of your variable on plant growth.

  
  Question Overview.
  Question #3 is composed of two discrete parts in which Part A has two components.  It was the
  decision of the readers that a perfect score of ten could not be obtained unless at least one 
  point was earned for each part or component (i.e., one point for naming three variables, plus at 
  least one point for developing an experiment linked to some variable mentioned, plus at least one
  point for results expected, and at least one point for a discussion of physiology linked with 
  the same variable.) 
  
  (A).  Environmental Variables and Experiment                                                                     
  (B).  Results and Physiological explanation 
  (A score of ten can not be earned without the point for Variables)
  
   (Variables ......need.three for 1 pt)                 (Experiment................6 Max)                               
   (Physiology ..............4 Max)                        .   
                 
  Light  (Intensity-duration-wavelength)       (1)   Control - Constants                                                     

                                               (1)   Results - linked to experiment
  Water                                   
  Temperature                                  (1)   Manipulation of variable                                                          
                                               (1)   Physiological function affected
  CO2                                                (how manipulated)                                                                       
                                                     (linked to variable)
  Humidity                           
  Wind                                         (1)  Measurement of growth                                               
                                               (1)  Concept of physiology
  Soil Type (Adj) - (Sand- vermiculite)                       (measured as [mass-length-dry-wet]                          
  (Carbon of CO2 incorp in carbon chains)
  Soil Chemistry (Adj) - (pH-fertilizers)         initial vs final - % change - duration)
                                                 Elevation                                                             
                                               (1)  Elaboration (of Results or Physiology)
  Competition                                  (1)  Verification (sample size - repetition)                        
  Hormones  (added)                                                                                                     
  Predation                                    (1)  Elaboration (of any one of above)                                                                              
                                                                                                                         
  (not an exhaustive list)                     (1)  Overall exceptional experimental
  design
   
                                               (1)  Hypothesis   (includes measurable predictions
                                                    and clearly states experimental conditions)