Fun with Classification
Librarians, store owners and many other professions will group objects together for convenience. Biologists are equally overwhelmed as they try to keep track of more than 2.5 million living organisms in the world. Experiment in this activity and learn the general principles of grouping objects (classification).
- Dichotomous key
We know from history that humans have always looked for logical ways to organize things into groups. The types of groups that resulted were based upon the observations and experience of the people doing the grouping.
In biology, the beginnings of grouping have been lost in ancient history. Classification may have started when early people separated items that were edible from items that were not. Perhaps people grouped what they saw in nature as either dead or alive. Now, as then, biologists attempt to sort all of nature in the logical or sensible groups based on how similar they are and the features they have in common. Grouping makes it easier to see relationships of one thing to another. It makes the study of biology more understandable and systematic.
The number of different kinds of organisms in the world is mind-boggling. Keeping track of all the various species and trying to identify relationships between them presents a great challenge. Imagine trying to identify relationships between organisms as diverse as giraffes, bacteria, fish and oak trees. Just trying to sort out one species, such as ants, is difficult enough. Biologists like to group “like things” with “like things,” that is, put them into logical categories. The question becomes—what logic, whose logic and what is logical? The field of biology that involves identifying and classing organisms into categories is called taxonomy.
Taxonomists analyze shared characteristics to determine possible relationships among different organisms. As more and more information is collected about various species, the relationships (categories) often change. The field of taxonomy is a changing one and one that often results in serious disagreements about how and why things are placed in specific groups.
In this activity, rubber fishing lures will be used to explore and set up a dichotomous key.
Classification Flow Chart
Classification Data Table
Dichotomous Key Worksheet
Rubber fishing lures, 10
Follow all normal classroom guidelines. Be sure to wash hands after performing this activity.
- Spread the rubber fishing lures on a work table.
- Observe the rubber fishing lures carefully. Discuss with your lab partner the differences and similarities of the objects. What features are important in distinguishing the objects one from the other?
- Record the features for each lure in the Classification Data Table. Assign each lure a letter, A–J.
- Based upon your observations and knowledge, separate the fishing lures into two meaningful groups. (The method used in this grouping is called dichotomous key because every feature will be used to divide the total number of samples into two new groups.) Physically separate the fishing lures into these two groups on the tabletop.
- On the Classification Flow Chart write in the letters for the fishing lures for one group in the box marked “2.” Write the letters of the second group in the box marked “3.”
- Write a brief description of the items in each group next to the appropriate box on the Classification Flow Chart. Be brief and include only the key characteristics used to place the items in the group. Try to create a description that would enable any person to create the exact same groups.
- On the Dichotomous Key Worksheet, write a key descriptor for the items in box 2 on line 1a of the worksheet. Then write the opposite of this key descriptor for the items in box 3 on line 1b. For example, purple lures versus non-purple lures.
- Set the group of objects in group 3 aside temporarily.
- Focus on the objects in group 2. How can this group be further subdivided into two meaningful groups? Divide group 2 into two more groups based on a new feature. Separate them on the tabletop.
- Write the letters of the objects in the two new groups in the appropriate boxes on the Classification Flow Chart.
- Write a key descriptor for these objects on their appropriate lines on the Dichotomous Key Worksheet.
- Create new flow chart boxes on the Classification Flow Chart as new groups are created. Place a successive number in the corner of each box created. Then write the descriptions on the next available line on the Dichotomous Key Worksheet as each group is completed. Write “go to ___” on the end of lines as appropriate and label the lines on the flow chart for each dichotomous choice point in the flow chart.
- Eventually a group will contain only one fishing lure. When this happens the object has been identified and there is no need to “go to” any further. At the end of the choices, where there is only one object left, write the letter (name) of the fishing lure at the end of the line on the Dichotomous Key Worksheet. For example, an ending line for object A might look like the following:
7a If lure is orange with claws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lure A
- When all the fishing lures from group 2 have been classified, return to group 3 and classify all these lures as done above. Continue this dichotomous classification key creation process until all the fishing lures A–J have been identified as single object groups on the dichotomous classification key. Be sure to label all lines on the Classification Flow Chart and to include all of the objects in the key.
- When the classification key is complete, put it to the test. Give the lures and the created dichotomous classification key to a person who has not worked in your group. Can the person use the key and identify the name (letter) of each lure? Observe the person using the key and ask that person to explain each of their dichotomous choices.
- Answer the questions on the Classification Data Table sheet.
- All objects in this laboratory can be reused. Consult with your instructor for appropriate disposal procedures when required.