School Improvement in Maryland
Physics-Instructional Strategies
Example for Analyzing Responses
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  Student Response
Analysis: Student ResponseA
  CORRECT ANSWER   Size of cell would decrease because ... water moves outside cell 
  ANALYSIS OF SITUATION    Compare concentration of water in and outside cell
  SYNTHESIS OF IDEAS   Saltwater is hypertonic 
Saltwater has lower concentration of water than cell's environment 
Diffusion of water inside cell across cell membrane by osmosis/diffusion 
Movement to establish equilibrium 
Movement of water causes decrease in cell size 
 Cell Membrane
The size of the cell would decrease because of diffusion across the cell membrane. The saltwater environment is hypertonic because it has a lower concentration of water than the environment inside the cell. This causes the water inside the cell to diffuse by osmosis to the outside in order to reach equilibrium. The water moving out of the cell would decrease the cell's size.
Physics-Instructional Strategies