Ogden Nature Center

Pre-Visit Activity, Grades 4-6

Adapted from Instructor, S. Markle, 1989 

Objective

Students will learn to use a dichotomous key. 

Materials

• Pencil and paper for each student
• Copy of the "Martian Road Signs-A Dichotomous Key" for each student

Background

A dichotomous key is an arrangement of items, in this case pretend road signs, into groups having similar characteristics.  An unknown specimen may be identified by starting at the beginning of the key and determining which of the two choices are the most appropriate.  An individual then works through the successive choices until the item is identified.  Naturalists use keys to help them identify plants and animals they are unfamiliar with. 

Procedure

1.  Copy each Martian Road Signs onto the blackboard or make copies for the students. Write the letters underneath the signs if you choose to copy them onto the board.

2.  Have the students list the letters A-Q down the side of their paper.

3.  Explain to the class that they have been chosen as an advance party to take a trip to Mars and they must translate the traffic signs for all those who will follow. 

Show that you have drawn these signs on the board or give them a copy at this time.  To determine what the signs are telling the students, they are going to use a "puzzle" called a dichotomous key.  This type of puzzle will always give them two choices. 

4.  Pass out copies of the dichotomous key.  Explain to students that once they have deciphered the meaning of one road sign they should write it next to the corresponding letter on their paper and move on to the next one.  You may need to go over some vocabulary words used in the key.  For example make sure your students understand the terms:  diagonal, horizontal, and vertical.