Name: ___________________________________________
Classifying Organisms Using Dichotomous I(eys
One of the biologist's essential skills is the ability to place an organism in its
correct classification group and to identify it by name. One such way organisms can be
identified is by a detailed comparison of their physical features ( what they look like ) or
other defining characteristics (where they live, what they eat, their niche, etc.). By using
a system of contrasting traits, whereby the biologist can only answer "true" to one, a
series of choices are made that eventually leads to the name of the organism. Such a
classification tool is called a dichotomous key. The word dichotomy means to "split into
two" and a key is a source of "answers".
For example, when trying to identify an organism, a simple set of contrasting
choices might be whether the organism is a plant or an animal. Simply by choosing one
of these, vastly decreases the possible identity of the organism in question.
Classification Key
1. Can move about ... Go to 2
Can't move about ...Go to 9
2. Has one leg ...Go to 3
Has one or more 'propellers ... Go to 6
3. Has one or more antennae ...Go to 4
Has no antennae .. ,. Go to 5
4. Has one antenna ... Podus monoantenna
Has two antennae ...Podus biantennae
Has three antennae ... Podus triantennae
S. Has one large eye ... Podus cyclops
Has no eyes ... Podus anoculus
6. Has wings ...Go to 7
Has no wings ... Go to 8
7. Has one large eye ... Dipteron cyclops
Has many eyes ... Dipteron polyoculus
8. Circular shape ...Helikopteron coccus
Rod shape ...Helikopteron bacillus
9. Lives on land ...Sessilis terrestris
Lives in water ... Sessilis aquatilis
Write the creatures' scientific names in the spaces below.
A. ___________________________
B. __________________________
c. __________________________
D. ___________________________
E. _______________________________________________
G. _____________________________________
H.
I.
J.
K. _______________________
F.
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Creature Feature: Making A Dichotomous Key
Directions:
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From the half sheet of paper I gave you, cut out each of the 10 creatures.
Observe each creature carefully making note of its characteristics (those you can see and those
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you may not see but can infer)
Group the creatures into two large categories using a very broad, general characteristic.
Subdivide each group using more specific features, always using TWO opposing characteristics.
Using the key on the reverse side of this sheet as an example, construct a dichotomous key for
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these 10 organisms.
Identify each organism with a common name (required) and a scientific name (optional)
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Paste each picture next to its appropriate description on a sheet of paper with the names.
Note: This may seem hard to get started. To see other examples that are similar to the front
page of this assignment, do a Google search of “Dichotomous Keys” and then click images.