CELL QUESTION 1992:				L. PETERSON/AP BIOLOGY

  A laboratory assistant prepared solutions of 0.8 M, 0.6 M, 0.4 M, and 0.2 M sucrose,   
  but forgot to label them. After realizing the error, the assistant randomly labeled the   
  flasks containing these four unknown solutions as flask A, flask B, flask C, and flask D.

  Design an experiment, based on the principles of diffusion and osmosis, that the 
  assistant could use to determine which of the flasks contains each of the four unknown 
  solutions. 
  Include in your answer 

	(a) a description of how you would set up and perform the experiment;
	(b) the results you would expect from your experiment; 
  and 		
	(c) an explanation of those results based on the principles involved. 

   	(Be sure to clearly state the principles addressed in your discussion.)
 
  STANDARDS:
  
  A.  EXPERIMENTAL SET-UP (1 point each)
  
  ___   1.  Experiment based on concentration gradient
  
  ___   2.  Experiment based on semipermeable membrane 
               (dialysis tubing, thistle tubes, plant or animal cells)
  ___ *3.  Experimental set-up (design) adequate to produce measurable results
  
  ___ *4.  (2 max) Experimental variables are eliminated 
               (mass, volume, time, temperature, tissue type, etc.)
  ___ *5.  Experimental set-up is exemplary 
               (must include semipermeable membrane)
  
  B.  RESULTS ( 1 point each)
  
  ___ *1.  Describes a measurable change
  
  ___ *2.  Correctly correlates the observed changes with molarities of unknowns
  
  C.  APPLICATION OF PRINCIPLES TO RESULTS (1 point each)
  
  ___ *1.  Correctly applies principles of diffusion and osmosis in the interpretation of 
     results
     (a correct analysis)
  ___   2.  Demonstrates an understanding of the concept of water potential 
     (hydrostatic/turgor pressure) in analysis of results
  
  D.  PRINCIPLES (1 point each)
  
  ___   1.  Demonstrates an understanding, or gives a correct definition of diffusion
  
  ___   2.  Demonstrates an understanding, or gives a correct definition of osmosis
                    ** (must include both water and semipermeable membrane)
  ___   3.  Demonstrates an understanding, or gives a correct definition of selective 
     permeability
  
  ___   4.  Describes how solute size and/or molar concentration (hypertonic/hypotonic)      
     affects the process of diffusion through a membrane
  _______________________
      Max possible = 14
  
  *  No points if the lab will not work.
  
  **Osmosis: the diffusion of water through a selectively (semi)permeable membrane in 
      the following directions:
       -from higher water potential toward lower water potential
       -from hypotonic (hypoosmotic) solution toward hypertonic (hyperosmotic) solution   
       -from higher water concentration toward lower water concentration
       -from lower solute concentration toward higher solute concentration
       -from region of lower osmotic pressure toward regions of higher osmotic pressure
       -from region of higher osmotic potential toward region of lower osmotic potential