Lab activity – Building an Animal
Dichotomous Key
Background: The Greek origin of the word dichotomous mean
“divided into two parts.” A dichotomous key is a method for
determining the identity of an unknown object or organism. The
identity is determined by going through a series of choices; each
alternative leads to another question until eventually the user is able
to identify the specimen.
For example, let’s say you found a leaf on the ground and
would like to determine from which tree it came. A choice in the dichotomous key might be something like, “The
leaves are flat or the leaves are needle like.” If the answer was “needle-like,” then the next choice might be
something like, “The needles are in a bunch or the needles are spread along the branch.” Eventually, when enough
choices have been made, the identity of the tree is revealed!
Objective: The purpose of this lab activity is to construct your own dichotomous key eight common animals. Ultimately,
someone should be able to use your dichotomous key to easily and correctly identify each animal!
Things to consider when constructing a dichotomous key…

Use constant characteristics rather than variable ones.
Use measurements rather than terms like "large" and "small".
 Make the choice a positive one - something "is" instead of "is not".
 If possible, start both choices of a pair with the same word.
 If possible, start different pairs of choices with different words.
 Be as specific as possible!

Directions:
1. When constructing a dichotomous key, you must be aware of the characteristics of the objects you are
classifying. You will be given a bag containing various species of a single animal group (ex: you might have eight
species of FISH).
2. Discuss some of the distinguishing characteristics that are easily visible on each of your animals.
3. Determine a characteristic which will allow you to clearly classify your animals into two categories.
 This is the first choice in your dichotomous key!
 Write this down on your dichotomous key chart. See example below.
Dog is this color
All dogs
Dog is that color
4. Place the second pile of animal cards off to the side for later use. Continue to classify one group of animals into
separate subgroups, using couplets of characteristics, filling in your dichotomous key chart as you go along.
5. Once you have classified and separated your first major groups of animals, do the same with the second major
group of animals, working until you have identified every single animal.
6. Use the choices you created on your classification chart to create a dichotomous key with paired statements.
Each choice should result in either the next step or the identification of the animal! See examples below.
Remember, to identify eight animals, you should have SEVEN steps!
Step 1. The dog has a smooth coat (short fur)…..Go to step 2
The dog has a fluffy coat (long fur)…..Go to step 6
Step 7. The dog is black and white…..Border Collie
The dog is tan and white…..Collie
7. Place all your animal cards back in the bag. Give the bag and your completed dichotomous key to your teacher.
You must finish writing your dichotomous key by the end of class today!
8. Tomorrow, two other groups will receive a bag of your pictures (without names). They will then attempt to
identify your animals using your dichotomous key. After checking the answer key, they will evaluate and rate the
quality of your paired statements dichotomous key.
Keep in mind – this assignment is worth ten points. You points will come from the average of the two evaluations
by other groups. As you evaluate other groups, please be sure to evaluate only the quality of their work. The
writer of the dichotomous key should not be penalized for user error.
Dichotomous Key Rubric
Who created the dichotomous key? ____________________________________________________________________
Group #1 Evaluation
1. Where you able to correctly identify ALL EIGHT animals? Circle: Yes / No
a. If not, how many animals did you incorrectly identify? _________
2. How would you describe the quality of this group’s paired statements? Were the statements easily
understood, specific, written in the correct format, etc?
3. Provide at least one way this dichotomous key could have been improved.
4. From one to ten, how would you rate the overall quality of this group’s dichotomous key?
1
2
3
4
Incomplete or impossible
to identify animals
5
7
6
Difficult to identify animals
8
9
10
Statements clear. Animals
a breeze to identify!
Group #2 Evaluation
5. Where you able to correctly identify ALL EIGHT animals? Circle: Yes / No
a. If not, how many animals did you incorrectly identify? _________
6. How would you describe the quality of this group’s paired statements? Were the statements easily
understood, specific, written in the correct format, etc?
7. Provide at least one way this dichotomous key could have been improved.
8. From one to ten, how would you rate the overall quality of this group’s dichotomous key?
1
2
3
Incomplete or impossible
to identify animals
4
5
7
6
Difficult to identify animals
8
9
10
Statements clear. Animals
a breeze to identify!