Dichotomous Keys

Learning Objective: I will understand dichotomous keys.

Have you ever heard of a dichotomous key?  Do you know what one is?  Well, just in case you have never heard of one, here is a GREAT definition:

Dichotomous Key: is constructed using contrasting characteristics to divide the organisms in the key into smaller and smaller groups; each time a choice is made, a number of organisms are eliminated. If sufficient characteristics are contrasted, the number of possibilities for the identity of the unknown organism is eventually reduced to one. Keys that are based on successive choices between only two statements are known as dichotomous keys and are the type of key preferred by most biologists.

"Dichotomous" comes from a Greek word that means cut into two parts. Therefore, dichotomous keys always give two choices in each step.

An example of a dichotomous key

Aristotle was one of the great thinkers of his time. One of his achievements was to outline a scientific classification of animals.   He observed many animals to find features by which to classify them.  

This figure is a dichotomous key which shows animals classified by the characteristics determined by Aristotle.

Watch the videos below so you can learn how to make your own dichotomous keys. They can be used to classify pretty much anything! A bonus to watching the video. . .the narrator has an accent! Gotta love that!!!

 


IF YOU WERE ABSENT ON FRIDAY!!! Below is the SAFETY VIDEO to watch so that you can finish the worksheet :)

 Good luck!!!