Good Science Victorian Curriculum Year 7

BIOLOGICAL SCIENCES
2.2
CLASSIFICATION
KEYS
LEARNING INTENTION
At the end of this lesson I will be
able to describe some different
types of simple keys and apply
this knowledge to design and
construct my own.
KEY TERMS
dichotomous
divided into two parts
1
Classification systems are based on keys. A key is a system for
identifying important characteristics.
Keys for identifying living things may use pictures, words,
numbers and instructions. They are used mainly to find the
names of organisms.
Some keys divide groups using branches
A common type of key is a branching key, which has two or more
branches at each level to separate groups. As you move down the
branches, you identify characteristics until you determine the right
organism.
Consider a small group of animals: a bird, an earthworm, a lizard and
a cat. You can use this branching key to identify each organism:
bird, earthworm, lizard, cat
key
a system for identifying
characteristics
bones
bird, lizard, cat
no bones
earthworm
LITERACY LINK
feathers
no feathers
SPEAKING
In your own words, explain
to another student what
dichotomous keys are and
how they are used.
bird
fur
cat
lizard, cat
no fur
lizard
NUMERACY LINK
GRAPHING
Joachim found the following
creatures in his backyard:
7 worms, 3 birds, 5 snails,
9 woodlice and 4 spiders.
Draw a bar chart to show this
information.
2
How does a branching key work?
Dichotomous keys use questions
Another type of key is a dichotomous key. Dichotomous means ‘divided
into two parts’, so this key uses statements or questions with only two
choices at each step. When a statement is correct, you follow directions
to reach the next question, until you determine the organism.
Let’s look back to the earlier group of animals – bird, earthworm, lizard
and cat. A dichotomous key for identifying this group may look like this:
1
2
3
a Skeleton of bone .................................................. go to statement 2
b Does not contain bones ...................................... earthworm
a Covered in feathers ............................................. bird
b Not covered in feathers ....................................... go to statement 3
a Covered with dry scales ..................................... lizard
b Covered with fur .................................................. cat
What are two types of classification keys?
20 GOOD SCIENCE VICTORIAN CURRICULUM 7