Name: _________________________________________________ Date: ______________ Period: ____ Score: _______
PART 2: Using and Constructing a Dichotomous Key – BACKGROUND
Knowing the similarities and differences in organisms
can help not only to figure out their phylogeny (evolutionary history),
but also to help sort and identify them.
Suppose you find a large colorful wildflower while walking
through the woods. Chances are the flower has already been
named and classified, but how can you learn its identity?
As an aid to help others identify unknown organisms, biologists
have developed classification keys.
Many classification keys have been developed to help
identify wildflowers and many other kinds of plants and animals.
Although these keys may vary in purpose and complexity,
they have certain features in common. These classification keys
are often called dichotomous keys. The word dichotomous
comes from the word dichotomy, meaning “two opposite parts
or categories.” A dichotomous classification key presents the
user with two opposite statements about some trait or
characteristic of an organism. By choosing the statement that best
describes the unknown organism, the user is led to further pairs of
statements. By going from one set of statements to another, the
name of the organism or its classification group is finally determined.
Do not confuse a dichotomous key with a phylogenetic tree.
A phylogenetic tree represents evolutional relationships, whereas a dichotomous key does not. However, both analyze
the similarities and differences and therefore help in the classification of organisms. `
In this investigation, you will use a classification key to identify several salamanders (Part A). You will then write
a classification key (Part B) for the Beasties you analyzed in Part 1.
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Name: _________________________________________________ Date: ______________ Period: ____ Score: _______
PART 2: Using and Constructing a Dichotomous Key – DATA SHEET
Part A: Using a Dichotomous Key
Use the dichotomous key for salamanders to identify each of the 11 salamanders, writing both their scientific name and
their common name. Remember to write the scientific name in the correct format!
Scientific Name
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Common Name
Part B: Constructing a Dichotomous Key
1. Use your data regarding the characteristics present/absent in Beasties to construct your own dichotomous key.
2. Remember that a dichotomous key includes pairs of opposing descriptions. At the end of the descriptions, the
key should either identify the organism for you or lead you to another pair of opposing descriptions.
3. HINT: Use Table 3 from the Beasties Part 1 that you used to construct your phylogenetic tree!
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Conclusion Questions
1. As you used the classification key to identify the salamanders, did you go from general to specific characteristics
or from specific to general characteristics? ________________________________________________________
___________________________________________________________________________________________
2. What two groupings (levels of classification) do the scientific names of the salamanders represent?
___________________________________________________________________________________________
___________________________________________________________________________________________
3. Was the classification key you constructed exactly like those of other students? Explain why or why not.
___________________________________________________________________________________________
___________________________________________________________________________________________
4. If you were using actual living organisms, what other characteristics could you use to identify them?
___________________________________________________________________________________________
___________________________________________________________________________________________
Critical Thinking and Application Questions
1. Do you think that there may be some closely related species of organisms that cannot be identified with a
classification key? Explain your answer. __________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
2. Why do you think biological classification keys always present two, rather than some other number, of choices
at each step? ________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
3. What types of problems would scientists have today if Carolus Linnaeus had not developed his classification and
naming system of organisms? __________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
4. Explain what is meant by the statement “Classification systems are the inventions of humans; diversity is the
product of evolution.” ________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
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