Name: __________________________________________Class: _________________Date: __________
Understanding A Dichotomous Key
What is a dichotomous key?
Dichotomous means “divided into two parts.” A ‘key’ is an answer page.
Dichotomous keys can be used to identify living organisms based on their
characteristics. You are always given two statements that describe the organism.
Decide which statement best describes the organism and follow the direction to
the next set of choices until you arrive at the name of the organism.
Before we create a dichotomous key, we need to understand how items are
sorted. Look at the example below for sorting a bag of candy.
Now we can make a dichotomous key from the diagram of candy.
Our bag of candy can be sorted into chocolates and non-chocolates. If we look at
the group of chocolates, we can divide them into round chocolates, and
non-round chocolates. You can see that each group is sorted based on a
characteristic until there is only one type of candy in that group.
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Name: __________________________________________Class: _________________Date: __________
Now we can use the diagram to create a dichotomous key for the candies. For
the purpose of this activity, let’s make up some names for the candies.
The first division was based on chocolate/not-chocolate. Let that characteristic
be your first set of two statements. The next divisions were round/not round,
and peppermint/not peppermint – see below.
Once the dichotomous key is finished, it can be used to identify unknown items or
organisms. For instance, if you give your friend a piece of candy from the bag,
he/she can use the dichotomous key to identify the name of the candy!
1 a. The candy is chocolate………………………………………….………………….…….Go to 2
b. The candy is not chocolate……………………………………….……………….……Go to 5
2 a. The candy is round………………………………………………….………………….….Go to 3
b. The candy is not round………………………………………….………………….……Go to 4
3 a. The candy is candy-coated…………………………………….…….…Sally’s Chocolates
b. The candy is covered with foil……………………………….………Devonshire Treats
4 a. The candy is square-shaped……………………..……………….….…… Choco-Chunky
b. The candy is oval-shaped………………………………………………..……..Luna Lindies
5 a. The candy is peppermint……………………………………………….………………Go to 6
b. The candy is not peppermint…………………………………………….…………..Go to 7
6 a. The candy is a pink peppermint……………………….…………..……Cosmic Candies
b. The candy is a white peppermint…………………..…………..……Celestial Delights
7 a. The candy is gooey/gummy………………………………………..….………Sky Rangers
b. The candy is hard candy………………………………………………………………..Go to 8
8 a. The candy is raspberry flavored…………………………….……..…….Raspberry Bits
b. The candy is lime flavored……………………………………….…………Lime Smashers
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Name: __________________________________________Class: _________________Date: __________
Making a Dichotomous Key
Purpose: To create a dichotomous key for the purpose of identification.
Materials: a group of assorted items
Instructions:
1. Your teacher will give you a bag or cup of items. Sort the items into two
groups based on an observable trait – one group has the trait, the other
does not.
2. Now you have two groups. Divide each group by another observable trait.
3. Continue sorting and grouping your items based on characteristics until
there is only one item in each group.
4. Record the characteristic of each group on the diagram below. Add
another group out to the side if needed. Give the item a unique name.
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Name: __________________________________________Class: _________________Date: __________
Make a dichotomous key based on the items and characteristics you chose. Let
the first sorted group be reflected in the first pair of statements.
1 a. ________________________________________________Go to ____
b. _________________________________________________Go to ____
2 a. __________________________________________________________
b. __________________________________________________________
3 a. __________________________________________________________
b. __________________________________________________________
4 a. __________________________________________________________
b. __________________________________________________________
5 a. __________________________________________________________
b. __________________________________________________________
6 a. __________________________________________________________
b. __________________________________________________________
7 a. __________________________________________________________
b. __________________________________________________________
8 a. __________________________________________________________
b. __________________________________________________________
9 a. __________________________________________________________
b. __________________________________________________________
On a separate sheet of paper, record the item and the name you have chosen for it.
Exchange items and keys with another group. Let them use your key and see if they can correctly
identify the items you have named!
Clean-up: Follow your teacher’s instructions.
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Name: __________________________________________Class: _________________Date: __________
Teacher Notes
Preparation and suggestions for items: place about 9-12 items in a baggie or plastic cup for
each student, or pair of students. Items can be anything you have available such as beads,
candies, paper clips, checkers, bingo chips, balls/marbles, etc. The accompanying handout,
“Understanding A Dichotomous Key” may give them some ideas about grouping. If the
students are familiar with dichotomous keys, you may not need to make copies of the candy
handout for them.
Give each student or pair of students a copy of the “Making A Dichotomous Key” handout.
During the activity, try to have them stay away from vague descriptive characteristics such as
large/small, but encourage them to look at shapes, colors, extensions, clear/opaque, bounce,
sticky, breakable, stretchy, etc.
After they make their dichotomous key, let them exchange keys with another group. That group
would need to identify the items based on the key the first group created. Make sure they have
recorded their answers on a separate sheet of paper so that they can remember the names they
created for the items. That way there will be no dispute when the second group uses the first
group’s key to name the items.
Science Standard: Student will examine organisms or their structures and use dichotomous
keys for identification.
You might want them to tackle the “Dichotomous Key to Snowmen” and then create their own
dichotomous key, “Create a Dichotomous Key to Snowmen”.
Once students understand how to create and use a dichotomous key, any dichotomous key can
be used by students to identify insects, trees, birds, or leaves.
An example of using a dichotomous key to leaves can be found at the following website:
http://www.shelterwoodbooks-teacherresources.com/dichotomouskey.html
Many sites are available with ready-made keys to use which you can download and let the
students practice.
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