School Improvement in Maryland
Physics-Instructional Strategies
Example for Analyzing Responses
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  Student Response
Analysis: Student Response.
  CORRECT ANSWER   Cell shrivels because of osmosis 
  ANALYSIS OF SITUATION    Salt content of water is greater than freshwater 
  SYNTHESIS OF IDEAS    Osmosis occurs because equilibrium altered 
Equilibrium altered because salt content of saltwater is greater than freshwater 
Salt water is hypertonic 
Water diffuses out through differentially permeable membrane 
To create equilibrium 
Cell dehydrated itself 
 Differentially Permeable Membrane 
The cell shrivells and collapses in on itself. This is true because of osmosis. Osmosis occurs when the body of this water dwelling organism is taken out of equilibrium. The equilibrium is lost because the salt content of the salt water is much greater than that of the freshwater. The salt water is a hypertonic solution. Therefore water diffuses out of the cell through the differentially permeable membrane and into the salt water in order to create equilibrium. Ultimately, there isn't enough water inside the cell to create equilibrium and it dehydrates itself.
Physics-Instructional Strategies