Materials Included In Kit

Additional Materials Required

Prelab Preparation

Make enough copies of the Classification Flow Chart and the Classification Key Worksheet for student use.

Safety Precautions

Some of the objects in the kit have sharp edges; encourage students to handle these objects carefully. This lab is considered nonhazardous. Follow all standard laboratory safety practices.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All objects in this laboratory can be reused. There is no disposal required.

Teacher Tips

• Enough object collections are provided for 30 students working in pairs. This activity can be completed in one 50-minute class period. All materials are reusable.

• The key to the success of this activity is that students can physically manipulate the objects as they develop their key. Seeing the dichotomous grouping of the real objects makes the process more concrete than just reading or using a key.
• There are no right or wrong student keys. As long as they are dichotomous and follow the logical format, consider it a job well done. Students’ ability to formulate key descriptors of groups will vary considerably. Knowing about bolts and screws is not the key idea of the activity. The exchange of keys and objects is a very revealing step in the activity. The logic of the criteria used for grouping is not always obvious to individuals reading the criteria for the first time. This part of the activity really points out the difficulty in writing and using keys.
• Have some biological keys available for student inspection after completing this activity. You might have students make a dichotomous key with biological items (e.g., leaves, insects), following the procedures outlined in this activity.
• After creating a dichotomous key, it is a perfect time to make a field trip and use dichotomous keys in the field.
• Be sure to discuss some of the problems in making keys. Is there a right or wrong key? Are some keys better than others? What happens when a new object is discovered? How is it incorporated into a key? How do biologists come to agree on key subdivisions? Or do they?

Introduction

Ever go into a large hardware store and feel like you will never find what you want? Imagine if all the items in the store were not categorized! Biologists are equally overwhelmed as they try to keep track of all the living organisms in the world. Experiment to learn the general principles of grouping objects (classification).

Concepts

• Classification

• Dichotomous key

Background

Historically, humans have continually looked for logical ways to organize objects and organisms into groups. These groups have been based upon the observations and experience of the person doing the grouping.

In biology, the beginnings of grouping are lost in ancient history. It may have started when early people separated things that were edible from things that were not. Perhaps they grouped things as either dead or alive. Groups are developed according to their important likenesses. Grouping makes it easier to understand relationships between one organism and another. It makes the study of organisms more understandable and systematic.

The number and 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, microbes, fish and oak trees. Trying to sort out one species, such as ants, is a real challenge. 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 identifies and classifies organisms into categories is called taxonomy.

Taxonomists analyze shared characteristics to determine possible relationships between 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 organisms are placed in specific groups.

Materials

Safety Precautions

Some of the objects to be classified have sharp edges; be careful when handling these objects.

Procedure

1. Spread the object collection on your work table.
2. Use string tags to label each object in the collection. Label them A, B, C, D, E, etc.
3. Study the set of objects 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?
4. Based on your observations and knowledge, separate the objects into two meaningful groups. (The method used in this grouping is called dichotomous because every feature will divide each group into two groups.) Physically separate the objects into these two groups on your table top.
5. On the Classification Flow Chart write in the letters for one of your groups in the box marked “2.” Write the letters of the second group in the box marked “3.”
6. Compose a concise written description of the items in each group. 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.
7. On the Classification Key Worksheet, write key descriptors for the items in box 2 on line 1A of the worksheet. Then write the key descriptors for the items in box 3 on line 1B.
8. Set the group of objects in group 3 aside temporarily.
9. Focus on the objects in group 2. How can this group be divided into two meaningful groups? Divide this group into two groups. Separate them on your table top.
10. Write the letters of the objects in the two new groups on the Classification Flow Chart in box 4 and box 5.
11. Now write the key descriptors for the objects in box 4 and 5 on their appropriate lines on the Classification Key Worksheet. Write the descriptors for box 4 on line 2A and those for box 5 on line 2B. Write “go to 4” on the end of line 2A and “go to 5” on the end of line 2B.
12. Now set group 5 aside temporarily.
13. Continue your dichotomous grouping on the objects in group 4. Divide group 4 into two clearly described groups.
14. 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 your descriptors on the next available line on the Classification 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.
15. Eventually a group will contain only one object. 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 object at the end of the line on the Classification Key Worksheet. For example, an ending line for object A might look like the following: 

7A If object is silver metal, long screw, Phillips head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Object A

16. When all items in group 4 have been classified, return to group 5 and classify all the objects in group 5. When group 5 is complete return to group 3 and classify all the items in group 3. Continue this dichotomous key creation process until all objects A–N are identified as single object groups on your dichotomous key. Be sure to label all lines on your flow chart and have all the objects included in your key.
17. When your key is complete, put it to the test. Remove a label from one of the objects and give the object and your dichotomous key to a person who has not worked in your group. Can the person use your key and identify the name (letter) of the object? Observe the person using your key and ask that person to explain each of their dichotomous choices. Repeat this procedure with other objects and other people.
18. Answer the following questions on the back of the Classification Key Worksheet:

1. How could your key be improved based on actual use? Which descriptor in your key worked the best? Which descriptor didn’t work or was confusing?
2. Would your key work with a bolt or screw not in your original group? Explain.

19. All objects in this laboratory can be reused. Consult with your instructor for appropriate disposal procedures when required.

Student Worksheet PDF

10257_Student1.pdf