Creating a Dichotomous Key

In this activity, you will prepare a dichotomous key for four organisms and then analyze the use of such keys.

A dichotomous key is a tool used to determine an organism's identity. Dichotomous keys consist of a series of choices that lead the user to the correct name of a given item. "Dichotomous" means "divided into two parts." Therefore, dichotomous keys always give two choices in each step.

Estimated time to complete: 30 minutes

**Part A**

A dichotomous key works on the principle of asking yes-or-no questions about the organism. To identify it, the answers for that organism are then compared to existing organisms to identify it. Prepare a list of four to five questions about each of the organisms listed below to help you create your own key. For each question, make sure the answer isn't the same for all four organisms. For example, "Does the organism have cells?" would be an inappropriate question because all the organisms have cells.

- Brewer's yeast (Saccharomyces cerevisiae)
- E. coli bacteria (Escherichia coli)
- Green hydra (Hydra viridissima)
- House cat (Felis catus)