Name:
Date:
The Dichotomous Key: Leaf Analysis and Key Construction
Learning Objective:
-Be familiar with and able to explain how dichotomous keys are created and used to organize the diversity
of life found on Earth.
Introduction:
How can you identify an organism that you find in your back yard or the park? One method used by
amateur and professional biologists is the dichotomous key. In the lab Using and Constructing a
Classification Key you used an existing dichotomous key to classify salamanders. In this lab you will
construct your own key to classify leaf samples.
Procedure:
1. Divide your leaves into two groups according to easily seen contrasting characteristics. You may use
leaf shape, edge, length of leaf stalk, divisions into leaflets, vein pattern, etc. Place the criteria used into
the first two boxes of the dichotomous key diagram. If you don’t have physical leaves, use the image
bank provided at the end of the lab.
2. Repeat this process with each of your two groups. You may not use all of the blank spaces in the far
right-hand column of the dichotomous key diagram. If one of the leaves is separated from the rest by box
3 or box 4, box 5 remains blank. Include the plant name in the last space that you use.
3. Go through your chart with each of your leaves. If there is an error, correct it.
4. Exchange your chart with another team. Check their chart as you checked your own in step 3. Discuss
any problems you find.
5. You may be asked to translate your chart into a key (see page 205 of Using and Constructing a
Classification Key for an example).
6. Answer the Critical Thinking and Application Questions. You should use information from both this
lab and Using and Constructing a Classification Key to answer these questions.
Analysis and Conclusion:
1. Was the classification key you constructed exactly like those of other students? Explain why or why
not. _________________________________________________________________________________
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Biology 11: Dichotomous Key, Leaves
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Critical Thinking and Application:
*Note: Information from Using and Constructing a Classification Key and this lab should be used to
answer these 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. __________________________________________________
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2. Why do you think biological classification keys always present two, rather than some other number, of
choices at each step? _________________________________________________________________
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3. What types of problems would scientists have today if Carolus Linnaeus had not developed his
classification and naming system for organisms? _____________________________________________
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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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Biology 11: Dichotomous Key, Leaves
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Leaves Dichotomous Key
Biology 11: Dichotomous Key, Leaves
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Leaves Image Bank
Biology 11: Dichotomous Key, Leaves
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