Dichotomous Keys

Lesson Goal: Students will be able to…• Recall the definition of a dichotomous key and identify one• Describe characteristics common to dichotomous keys• Use dichotomous keys to identify objects and organisms

Identifying Dichotomous Keys

• Animals with backbones can be divided into different groups, including mammals, reptiles, birds, amphibians and fish. List some characteristics that define each of the groups.

Animal group Characteristics MammalsReptilesBirdsAmphibiansFish

Classifying Living Things

Classification Systems

Features used for classifying animals

Animal Classification Game

Quick Quiz

• How are living organisms classified in the modern classification system?• How have microscopes dramatically changed our understanding and

classification of microbes?• Consider the case where 1 000 organisms have been divided into

dozens of groups. How could someone identify which group a particular organism belongs to?

Keys• Have you ever used a book called a field guide to identify an

animal or plant in your local area or while on holidays? These books usually focus on a group of animals and an area or type of environment, such as ‘Birds of Southern Australia’ or ‘Desert Reptiles’.

• You usually search through the book to find a picture or description of characteristics that match the organism you have observed. The risk in using this method is that an incorrect match may be made. It can also take a long time if you have to browse through a lot pages.

Many scientists who focus on a particular group often use a key to identify the organisms. A key can be presented as a branching diagram, where the user makes a series of choices.

Dichotomous Keys

Definition of dichotomous keys

• As a class, individually or in groups, use the Frayer Diagram on the next slide to explore the concept of dichotomous keys.

• Click the diagram on the next slide to open a printable Frayer Diagram

A dichotomous key is a hierarchical branching identification key that uses physical characteristic couplets to group objects or organisms.

Homework:Use the key to identify each of the animals shown at the top of the page.