Dichotomous Keys

Using Dichotomous Keys

What is a dichotomous key?

In order to classify organisms, scientists use physical or behavioural features that distinguish them. One way to help classify organisms is to present features in a dichotomous key. A dichotomous key is a set of steps that helps us identify objects by giving two choices at each step.

An easy way to remember this is that "di-" means two, so "dichotomous" means branching into two.

Multiple Choice

How many choices are given at each step in a dichotomous key?

• 1

• 2

• 3

• 4

Multiple Choice

To understand a dichotomous key you should start from?

• The bottom

• Any step

• Step 1

• From the name

Features of dichotomous keys

A dichotomous key is a tool used to identify organisms.

A dichotomous key asks a series of questions that can be answered by

yes or no.

Dichotomous keys work like a funnel. It narrows down the characteristics to a specific organism/item.

Two common formats

There are two common formats for dichotomous keys, branching and tabular.

Tabular format asks a question in each section with each answer giving a direction as to where to move next. Sometimes you will go from section to section in order when other times you might move from section 1 to section 5 in one answer.

Tabular Format

Branching flows down like roots of a tree. Each conjunction asks a questions and the answers dictates which way you move down the branch.

Branching Format

Two common formats

Multiple Choice

True or False, A Branching dichotomous key allows you to skip sections depending on the answer to the question?

• True

• False

What makes a strong key?

Strong key characteristics need to be constant and specific for each item/species number of legs, body shape.

Characteristics aren’t going to change with the perception of each person doing the key.

Characteristics aren’t going to change with the age of the organism.

What makes a weak key?

Weak key characteristics can change for each item/species colour, size

Different people perceive colour and size differently. For example; What is big? What is blue?

The colour and size of an organism may be different when it is young compared to old. For example; Eastern Brown Snake

Try to fill in the blanks of your Tabular dichotomous key with the following.

​

Having a go

Answers:

Try creating your own

Now choose your own.

1. Select 8 animals
2. Create both a Branching and Tabular key.
3. Try challenging yourself and use their scientific names