1D Identifying Organisms (which have been sampled): Keys

Click the following link for the printable notes for this section.

Why do we use Keys?

(N3 + N5) When sampling ecosystems unknown organisms may be collected.

It is possible to take an organism to someone who is likely to know, but it would be ecologically damaging if everyone removed organisms from their natural habitats. Equally the scientist could try identifying the organism from a suitable book but that can take a very long time. Therefore, scientists use biological keys to identify plants and animals.

Keys allow for easy identification of unknown organisms. They are more reliable than pictures. Keys ae possible because organisms show variation (they all look different, have different features).

After identification organisms should always be returned to their natural habitats so that as little disturbance as possible is caused to the ecosystem

There are two different types of keys

  • (N3) Branching Keys
  • (N5) Paired statement Keys

Both these keys are example of Dichotomous Keys, you do not need to know this term, however sometimes you will see or hear this term on-line when you are studying.

The following video shows you how to use both types of keys.

Branching Keys

A branching key a type of flowchart used to identify organisms. The animals and plants are sorted into their correct groups by asking yes or no questions. By answering these questions about the characteristic of an organism you are led in a specific direction through the chart, that will lead you to the name of the organism you are investigating. Branching keys are most useful when there are only few living things to be sorted or identified.

The diagram below shows a branching key

By using the chart you could identify for example a butterfly

  • Alternatively if you know you have a butterfly and want to describe its characteristic you can work backwards through the key. e.g…..
  • Not Active at night
  • Has wings
  • Has legs

Paired Statement Keys

A paired statement key is a numbered list of statements. Looking at the organism and decide which of the first two statements fit it best. At the end of each statement, a number signifies which statement to use next. The numbers are followed until the name of the organism is found.


(L5) Working back – Remember at Level 5 you need to work a paired statement key backwards.

A paired statement key can be worked backwards to summarise the information concerning organisms e.g. Using the above key on soil animals. A snail has the following characteristics…

  • Shell present
  • Body not worm like
  • Body not divided into sections
  • Body has no legs

This Video explains how to use a Paired Statement Key (remember another name for these are dichotomous keys)

Making a paired statement key.

At level 5 you should be able to make a simple paired statement key on your own. It doesn’t need to be as complicated as the example above.

Remember we done this activity to differentiate the individuals in our class.

This clip shows you how to turn your branching key into a paired statement key.