DICHOTOMOUS KEYS

CLASSIFICATION DIAGRAM

  

Suppose you come upon an unknown organism.  Before you can classify that organism you will need to identify it. The most widely used type of key is the dichotomous key that is based on a set of paired choices.

For example, 

• does the individual fly or not fly? 
• Does it make its own food or feed on others? 

Eventually you move through the key or series of statements until you arrive at an answer. It would be very difficult to do this for all organisms living on this planet. Generally, keys are limited to identifying a collection or range of organisms such as the dragonflies in Missouri, or the organisms found in ponds. 

Using dichotomous keys

Scientists use taxonomic keys to determine the identity of an unknown organism. You will next view a dichotomous key used to indentify common beans. This is a very simple key, but to assure that you understand how it works, identify at least two of the beans shown in the pictures.

DICHOTOMOUS KEY HANDOUT