Academy Curricular Exchange
Columbia Education Center
Science

Jan Devore, Westside School, Payette, ID

                         DICHOTOMOUS KEY

Appropriate for grades K-8.

OVERVIEW:  Di-chot-o-my (di kat'e me) n., pl. -mies [ < Gr. dicha,
in two + temnein,to cut] division into two parts.

PURPOSE:  To develop understanding of how a dichotomous key is
organized.

OBJECTIVES:  At the end of this activity, students will be able to
catagorize and differentiate between random items according to
like characteristics.

ACTIVITIES:  Students should be divided into small groups for this
activity.  (2-4 students)

 1.  Students identify their group of objects - record title on
     top of paper.

     figure 1.  ____________________
               |                    |
               |    Paper Clips     |
               |                    |
               |                    |
               |                    |
               |                    |
               |                    |
               |____________________|

 2.  Divide objects into two groups (large - small, square -
     round, etc.).  Groups do not have to be equal.  Name new
     groups, record information.

     figure 2.  _____________________
               |                     | 
               |     Paper Clips     |
               |   _______|_______   | 
               |   |             |   |
               | Smooth        Rough |
               |                     |
               |                     |
               |_____________________|

 3.  Choose one pile - set the other aside - divide that group.
     Record information.

     figure 3.
                     Paper Clips
                   _______|_______
                   |             |
                 Smooth        Rough
                ___|___ 
                |     |
              Large  Small


 4.  Continue dividing groups, recording information until all
     items have been differentiated.  Go back to top of paper and
      repeat this process for other side.

     figure 4.
                     Paper Clips
                   _______|_______
                   |             |
                 Smooth        Rough
                ___|___       ___|___
                |     |       |     |
              Large  Small  Large  Small
            ____|____
            |       |
          Shiny    Dull

 5.  Groups may display their keys along with their group of
     objects.  Groups might compare and try using one another's
     keys.

RESOURCES/MATERIALS NEEDED:  Materials for each group:

  *  6-10 similar objects (buttons, shells, paper clips, screws,
     keys, etc.)
  *  Large sheet of paper
  *  pencil or marker

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