CONSTRUCTING A DICHOTOMOUS KEY
MARGARET BANKHEAD ROBERT A. BLACK MAGNET SCHOOL
9101 SOUTH EUCLID AVE.
CHICAGO, IL 60649
To construct and use dichotomous keys.
Shoes (Use one shoe from each of 10 students).
Worksheets: "Using A Dichotomous Key"
1.Arrange chairs in a circle.
2.Instructor takes off one shoe and place it on the floor in the middle of
3."There's one of my shoes, so let's have a shoe from about ten of you".
4.Tell the students that they are to divide the shoes into two piles. Tell
them the piles don't have to have equal numbers of shoes but, that they all
have to agree on some obvious characteristic that will distinguish the shoes
in one pile from the shoes in the other pile.After agreement is reached,tell
the students a record of the agreement will be kept on the board.
5.Draw two horizontal lines some distance apart on the chalkboard. Label the
lines with the agreed upon characteristics. (Fig.1).
6.Return to the pile of shoes. Tell the students one pile will be pushed
aside for the moment but, now they must again divide the pile of shoes into
two distinct piles. After agreement is reached add this information to the
chalkboard sketch. (Fig.2).
7. Continue the procedure of dividing the shoes into two distinct piles and
adding the information to the sketch until there is only one shoe with the
identifying characteristic, at which point the shoe is identified and the
owners name is added to the sketch (Fig.3). ______________
8. Divide the second pile of shoes in the same manner as the first pile
until all the shoes have been identified.
9. Push all the shoes back together in one pile[Adding perhaps a shoe from
the distance past or one with characteristics unlike those used in the
Discuss the meaning of the term dichotomous explaining that the word
means "two forks".
10. Tell the students that dichotomous keys usually appear in a more
compact form and that the diagram can be easily converted by adding numbers
to each characteristic used. Label the diagram in numerical sequence
following the same order the characteristics were agreed upon.
11. Have the students redeem their shoe by taking it from the pile and
placing it on the correct branches of the key which will lead to its'
correct identification. After all the shoes have been redeemed the shoe
added earlier should remain. Ask a student to follow the key until the shoe
is identified. Students should discover that a key works only for
identification of those items used in its' original construction.
12. Pass out the two worksheets. Complete the " Using A Dichotomous Key"
sheet in class. Assign the " Imaginary Animals" sheet for homework.
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