Using and Creating a Dichotomous Key

Mary Jo Tichich, Westwood Middle School, Blaine, MN
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Summary

Students will investigate classification through a sorting activity and discussion of real-life evidence of sorting or classifying objects. Students will classify 8-10 items using student determined characteristics and methods. Students will compare and contrast methods used in classifying through group discussion. Scientific method of classification will be directly taught. Field guides and dichotomous keys will be introduced. Student groups will then develop a method (using pictures or words) of classifying the 5 kingdoms to be studied. Knowledge of domains and kingdom characteristics must taught or reviewed. Students will record their method and exchange them with another group for peer review. Students will then edit or modify their method as necessary. The various methods will be discussed as a class.

Learning Goals

Students will learn about taxonomy and scientific classification. Students will learn to identify characteristics of objects in order to classify them by making observations, comparing, and contrasting these characteristics with the end result of sorting or classifying them. Students will be introduced to field guides, dichotomous keys, and their use. Students will learn to write a dichotomous key.

Vocabulary words: classification, dichotomous key, field guide

Context for Use

grade 7, 25-35 students, in class activity, knowledge of the characteristics of the 5 major kingdoms taught in 7th grade is needed to be successful.

Materials needed: bag with 8-10 items (1 bag per group, students in groups of 3-4), paper, pencils, and colored pencils or markers (optional).

Description and Teaching Materials

Students will be grouped, 3 students per group. Each group gets a bag with 8-10 items in it. Each group is asked to sort or group the items in any manner they choose. Each group gives a brief summary of how they grouped their items. Class discussion of sorting and where we see it- library, grocery store, bookstore, department store, addresses, phone books, etc. Students are then asked to make, using pictures or words a device to help someone unfamiliar with their objects be able to identify them. Students are introduced to dichotomous keys and field guides, their use, and features are discussed. Students are then directed to make a dichotomous key using pictures or words to identify the 5 kingdoms to be studied (prior knowledge of kingdoms is needed). Student groups will exchange dichotomous keys with another group and each group will identify the items keyed out. If needed, dichotomous keys will be revised or edited for accuracy and clarity.

Teaching Notes and Tips

Students may need clarification of what makes a good characteristic to use in identifying something (what is "big or small?"). Some students may not recognize classification that they already encounter in their lives. Prior activity for dichotomous keys was directly taught.

Assessment

The assignment will be formatively assessed throughout the activity by teacher observation and self-reporting (rate yourself 1-5 fingers). The work to be handed in will be the dichotomous key written by the group and peer reviewed.

Standards

7.IV.B.4—The student will use and create dichotomous keys.

References and Resources