Identifying organisms

Biologists often want to identify an organism that they have found. A good way to start is to look at pictures in a reference book, or on the internet. The biologist may be able to find a picture of the organism, with its name. But this does not always work.

Biologists also use keys to help them to identify organisms. A key is a set of questions about the organism you want to identify. The answer to each question takes you to another question. You work through all of the questions until you arrive at the name of the organism.

Here is a simple key to help someone to identify an organism. It is a dichotomous key. Dichotomous means ‘branching into two’.

You will have to imagine that you have the whole animal to look at, not just these pictures.

• Choose one organism you want to identify.
• Starting at the top of the key, answer the first question – yes or no?
• Follow the line to the next question. Keep going until you arrive at the name of the organism.

Another way to show the same key

Keys are sometimes arranged differently. Here is the same key set out in a different way.

Instead of a question, the key starts with a pair of statements to choose from. Instead of arrows pointing to where you go next, there is a number telling you which pair of statements to go to next.

Try it: Work through the key to identify the dragonfly. You will follow steps 1a, 2a, 4a.