How to Use a Dichotomous Key: Lesson Plan for Biology Class
Objective
This dichotomous key lesson plan will help students understand why scientists use a dichotomous key, as well as giving them practice in creating and using one.
Preparation
Before class, copy over the dichotomous key listed in the Resources section at the bottom of this article. Leave out the common name of the organism, however, so that only the scientific name of the organism remains. (This will ensure that groups actually use the key correctly, rather than simply choosing the organism that sounds right.) In addition, print out online pictures of the organisms listed on the key (e.g., blue-ringed octopus, tiger snake).
Group Activity
Start the class by dividing students into small groups, and handing each of them a copy of the key. Then distribute the pictures of the organisms to the groups so that each group receives one picture. Challenge students to figure out how to use the dichotomous key to identify the scientific name of the organism they have received.
Class Discussion
As a class, discuss how using the dichotomous key helped them figure out the classification of the organism they were given. Explain how scientists use the same technique to categorize all sorts of organisms, and to share their knowledge about these organisms with other scientists. Discuss various practical applications of the dichotomous key, such as to identify fossils, to find a specific endangered species, or to locate plants to treat a certain illness. Mention that online dichotomous keys have become more common, and are much more efficient, than their written predecessors.
Review Activity
To review the concept of a dichotomous key, divide the class into two. Have each half of the class work together to create a dichotomous key to identify students in the class. They can use objective physical traits, such as eye color, hair color, and height to create their key, but they can also use more “fun” criteria, such as “color of shirt” or “hairstyle.” Students should write their completed key on a long piece of butcher paper in large enough letters that it can be seen from several feet away. When both halves of the class have completed their keys, they should swap with each other and take turns identifying classmates based on the keys they are using.
Assessment
To determine whether students have completely understood the material, let each student orally describe how they would use the key created in the review activity to identify a classmate. They should also be able to explain why a scientist would use a dichotomous key. For a more formal assessment, ask students to write out their thought processes when using a dichotomous key, as well as why dichotomous keys are important.
This dichotomous key lesson plan will keep students actively engaged in learning about this important scientific tool. Students will enjoy the lesson - and they may not even realize how much they have learned!
Resources
Center for Biology Education. “Dichotomous Key Examples.” https://cbe.wisc.edu/assets/docs/pdf/biolearn/Classification/WhatIsLife/dichotomous_key.pdf
