Living Systems
Chapter Three:
Classifying Living Things
• 3.1 Types of Living Things
• 3.2 Dichotomous Keys
3.2 Dichotomous Keys
• A dichotomous key is a tool that helps its
user identify natural objects like birds,
trees, rocks, fungi, and insects.
• Dichotomous means "divided into two
parts.”
3.2 What is it?
• The ghost plant
(Monotropa
uniflora) lacks the
green pigment
chlorophyll, which
gives most plants
their color.
How should we
classify this species?
3.2 Dichotomous Keys
It is difficult to create a key for the kingdoms because
there are so many organisms to consider.
3.2 Dichotomous Keys
• A dichotomous key turns questions into paired
statements.
3.2 Dichotomous Keys
• Most dichotomous keys are designed to identify
small groups like trees, butterflies, and song
birds.
Can you
suggest a way
to tell these
arthropod
classes apart?
3.2 Dichotomous Keys
• Here is one solution…
Ecology Connection
Discovering a New Species
• There are still
remote regions on
Earth, even though
it may seem like
humans have been
everywhere.
Activity
Making a Dichotomous Key
• Scientists who study
the characteristics of
organisms and their
relationships to other
organisms are called
taxonomists.
• Make a dichotomous
key to identify your
classmates’ shoes.