Lab Day, Resources

Dichotomous Key Worksheets and Activities

Teaching dichotomous keys to students can be a dry topic but it doesn’t have to be! You may not have noticed this about me…but I love science AND art. I try to find cross curricular opportunities when possible with ALL other subjects. But by far, my favorite combination is Science + Art as I find it to be a refreshing fusion. Anyone can pull off Science + Math, but building content rich dichotomous key activities fused with trees, fish and art? That takes real finesse. Not to toot my own horn or anything (toot, toot).

What IS a dichotomous key?

A dichotomous key is a system used by scientists to identify different parts of the natural world. They can be used to identify rocks, plants, trees, birds, reptiles and mammals.

Dichotomous keys are set up in a two question format, leading users through a set of choices designed to help them correctly identify the object of their inquisition. It sounds confusing, but it really isn’t once you get the hang of it.

Start with something familiar.

Depending on the skill level of your students, you may need to practice working through keys using a small sample of familiar objects with easily identifiable differences. I recommend using something like pasta, buttons or feathers as a starting point, but honestly, just about anything will do.

Sample Lab: Gather up 4-6 different types of uncooked pasta. Assign each pasta sample a letter (i.e. Sample A, B, C, D, E). Create a dichotomous key based on the pasta you have and let students identify the pasta types using the key.

Example key using macaroni, penne, farfalle, spaghetti and fettuccini.

1a: Pasta is hollow………………………………….Go to #2

1b: Pasta is solid……………………………………..Go to #3

2a: Pasta is smooth and curved……………..Macaroni

2b: Pasta is long and straight………………….Penne

3a: Pasta is shaped like a bow-tie…………..Farfalle

3b: Pasta is long and straight………………….Go to #4

4a: Pasta is round and thin……………………..Spaghetti

4b: Pasta is flat………………………………………..Fettuccini

Bookish Ways has an EXCELLENT starter pack of free, simple dichotomous key activity worksheets to help guide students if you don’t have the time to come up with your own.

Bookish Ways Free Dichotomous Key Worksheets

Go slow.

If this is your student’s first exposure to a dichotomous key, ease them into it with a review of animal adaptations. This will familiarize them with the attention to detail required to work through and identify organisms, and eventually create a successful dichotomous key on their own.

dichotomous key example
Biology Resources for Teachers provides a great example and explanation of a simple dichotomous key.

Most dichotomous keys focus on one specific trait to lead the user to an answer, like leaf patterns on stems or fin shape of fish species. The example above chooses beak shape to help identify the mystery bird samples.

Make it interesting.

Exquisite corpse art activities are a great opportunity to closely examine animal adaptations!

Once you feel your students have mastered the concept of the dichotomous key, the real fun can begin. Adding a narrative like a fishing trip to their identification and key creation process can make a world of difference in their enthusiasm (and retention). Capping off the unit with a fun art activity will make it even more memorable.

I built four unique sets of dichotomous key activities for my students based on evergreen trees and freshwater fish, and I must admit the students were much more enthusiastic about the “Fish Frenzy” set with the exquisite corpse art activity.

NEXT: Teaching taxonomy? Make sure you read this!

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