Dichotomous Key
Description: In this lesson students will have fun learning about Dichotomous Keys.
"Dichotomous" means "divided into two parts." Therefore, dichotomous keys always give two
choices in each step that lead the user to the correct name of a given item. A “key” is a tool that
allows a user to determine the identity of items in the natural world, such as trees, wildflowers,
mammals, reptiles, rocks, and fish.
Science: Grades 5-8
Note: There can be many correct versions of a Dichotomous Key for the same
population/items. A sample Dichotomous Key for potato chips is attached.
Materials:
 4-8 brands of Potato chips (visibly different in color, shape and packaging)
- Ruffles classic and BBQ
- Pringles original, BBQ or other flavor
- Lays original and BBQ
- Baked, thick cut or other types
 4-8 zip lock bags per group
 1 permanent marker
 Paper, pencils, rulers or other measuring devices as desired
 White board or chalk board at front of room
Directions:
1) Place a sample of each kind of chip into its’ own zip-lock bag and label them. Make one set of all
the chips for each student group.
2) Place all the chips’ original packages where the students can see them. Ask the class how they
could divide the brands of potato chips into two distinct groups. (by color, tubes or bags, ridges or
plain, etc.)
3) Write the distinction on the board. For example: tubes/bags. Each dividing distinction should
have only two options like the example above.
4) Keep dividing and recording on the board until you are down to one identifiable brand each
under its own classification.
5) Now divide the students into groups. Give each group a set of the chips in the bags. Ask each
group to make their own dichotomous key. Encourage diversity.
6) Have the groups share and test their keys. Eat and enjoy your “classified” chips!
Check out this free AITC Online Resources: Tomatoes, Potatoes, Corn, and Beans, How the
Foods of the Americas Changed the World. (book) – the fascinating story of the awesome
potato and other native plants of the Americas.
Potato Facts: Oregon Potatoes were worth $151 million and ranked 7th in the top
agricultural products of Oregon in 2009! Most potatoes are grown in Morrow, Umatilla, Klamath,
Baker and Malheur counties. 2008 was the United Nations International Year of the Potato!
Provided by Oregon Agriculture in the Classroom, http://AITC.oregonstate.edu or call 541-737-1318.
Sample Dichotomous Key
Name that Potato Chip
Note: There can be many correct versions of a dichotomous key for the same population of
items. Discuss this and let the students explore real dichotomous keys used for plants or
animals, as well as other forms of keys used in science.
Remember:
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There are many layout styles for a dichotomous key.
This is just one example of many possibilities!
The population of potato chips used:
-Lays Classic
-Pringles Original
-Lays BBQ
-Lays Stax Sour Cream and Onion
-Ruffles BBQ
-Pringles Cheddar Cheese
-Ruffles Original
A Simple Dichotomous Key: Example
1a. Plastic bag packaging
1b. Hard tube packaging
2a. Chips have ridged surface - go to 3
2b. Chips have non-ridged surface- go to 4
2a. Chips orange color
= Pringles Cheddar Cheese
2b. Chips have other color-go to 3
3a. Chips orange color = Ruffles BBQ
3b. Chips tan color = Ruffles Original
4a. Orange color = Lays BBQ
4b. Tan color = Lays Classic
3a. Chips solid tan
with no speckles = Pringles Original
3b. Chips tan w/ greenish speckles = Lays
Stax Sour Cream and Onion
Options:
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Add more subtle distinctions, such as thick cut chips or baked chips which would
require some kind of measurement to distinguish between types.
Challenge your students to make a dichotomous key that does not use packaging as
a distinguishing characteristic. This will make the key much more challenging.
Change the population to include all “chips” such as, corn chips, vegetable chips, etc.
Provided by Oregon Agriculture in the Classroom, http://AITC.oregonstate.edu or call 541-737-1318