Dichotomous Key
Dichotomous Key: A tool for categorizing objects
Purpose: Learn to construct and use a dichotomous key.
A dichotomous key identifies an object by eliminating groups to which it does not belong and narrowing
down the group to which it does belong. It is a tool that scientists can use to help identify a particular
specimen. The specimen could be a chemical that is identified by its physical properties, an insect or
animal or plant identified by its markings and traits, or even a rock sample based on its different
properties. The term dichotomous begins with the prefix of "di" which means two. The dichotomous key
allows for the scientist to ask a series of questions.
Example:
Each branch on the key is a question. The answer to this question divides everything in the group into
two distinct categories. The questions must be phrased appropriately for the objects to be divided into
one of two categories. Learners may need some practice creating appropriate questions for their
objects.
Dichotomous Key
Dichotomous Key
Activity 1: Learners make and use a dichotomous key to categorize shoes
Making a key:
1. Form groups of four learners. Each learner will put their right shoe on the table.
2. List all the shoes by 3 characteristics (color, material, design) and create a question that can separate
them into distinct categories.
3. Create a chart of shoe groups and the questions that separate them into subgroups.
4. Continue until you have only one shoe per sub group. You have made a dichotomous key!
Using the key:
5. When you finish categorizing these 4 shoes, swap shoes with another group.
6. Classify these 4 new shoes. Place them into the top of your chart and continue through the chart. If
these new shoes don’t fit in the chart, modify it to accommodate
7. Switch again and categorize 4 new shoes, modifying the chart if necessary.
Questions to discuss with the whole class:
1. What were some of the common characteristics that you used to classify your shoes?
2. Did you have any trouble classifying them? Explain.
3. Was it difficult to use your chart for the 4 new shoes? What were problems you ran into?
4. Is there more than one way you could have classified the shoes?
5. What else could be categorized in this manner? How could this tool be useful to scientists?
Activity 2: Learners make and use a dichotomous key to categorize letters
Making a key:
Write the capital letters A through J on the board. Ask learners to create a key to categorize these
letters. Learners must create groups for the letters such as vowels vs. consonants or curvy vs. loopy
shapes.
Using the key:
After the learners have the first 10 letters classified, give them 3 to 4 additional letters. The learners
must use the key they created to classify the new letters. If the letter doesn't match one of the original
groups, learners can modify their keys to accommodate the new letters.
Further activities:
Have learners observe and classify animals/insects/plants in their local environment. Guide them to
use the techniques listed above to develop questions to organize these organisms into a dichotomous key.
Then, challenge learners by giving them new organisms and asking them to use their key to categorize
these organisms.
Dichotomous Key