Dichotomous Key Lab

Dichotomous Key Lab

Introduction:

Biologists organize and store information about organisms in a dichotomous key. A dichotomous key is a diagram that groups organisms by their characteristics. This activity will show you how a dichotomous key works.

Shoes come in various sizes, styles, and shapes. The shoes in your closet can be classified according to their characteristics. Construct a dichotomous key using the shoes found in your house.

In constructing dichotomous keys, keep the following in mind:

· Use constant characteristics rather than variable ones.

· Use measurements rather than terms like "large" and "small."

· Use characteristics that are generally available to the user of the key rather than seasonal characteristics or those seen only in the field.

· Make the choice a positive one—something "is" instead of "is not."

· If possible, start both choices of a pair with the same word.

· If possible, start different pairs of choices with different words.

· Precede the descriptive terms with the name of the part to which they apply.

Materials:

10 different shoes, ruler

Procedure:

1. Collect one shoe from 10 different pairs of shoes in your home.

2. Make a list of all the shoes you have collected using at least three characteristics (e.g., Black Wingtip Dress shoe).

3. Divide the shoes into two groups. Every shoe in one group must have a feature that no shoe in the other group has. Write this distinguishing feature down as 1A on your dichotomous key. Its opposite will be 1B.

4. Record these statements, and if there is more than one shoe sharing the distinguishing feature in each group, add GO TO another statement at the end. (E.g., if your first pair of statements is “Has a heel that is flat” and “Has a heel that is raised,” and you have more than one kind of flat-heeled shoe, you would write the first statement as “1A. Has a heel that is flat—GO TO 2.”)

5. Select only one pile of shoes. Pick another feature that allows you to divide the remaining pile of shoes into two smaller groups. Write this feature and its opposite after 1A, as 2A and 2B. Continue numbering each feature in numerical order—3, 4, 5, etc. Continue to divide the subgroup of shoes into two groups by characteristics or measurements and record how you have divided each group, until there is only one shoe in a group.

6. At the point that a group has reached one shoe, identify the shoe on the key using the label description you gave the shoe in step 2.

7. Go back to the pile that was left behind in step 3 and repeat the steps to complete the rest of the groupings for these shoes. Write each feature as a new division, continuing to number in numerical order.

8. Put all the shoes back into a pile and randomly pick out one shoe. Work through your key and make sure that you reach the proper description of the shoe at the end.

Analysis:

1. What are some of the common characteristics that you used to identify your shoes?

2. Did you have any problems creating your dichotomous key? Explain.

3. Is there more than one way that you could have classified the shoes? Justify your answer.