"Finding Your Sweet Tooth"- An Introduction to the Dichotomous Key
Intermediate, 6th Grade
Various candies listed on key (enough for each student to have five different pieces)
related worksheets and rubrics
LCD projector and computer
SMART Board, networked computer, LCD projector
The following web site was used:
Candy Key-(page 2 of worksheet only): created by Susan Frack
Raymond Central H.S. Raymond, NE
Holt, Reinhart and Winston. (1999) Holt Science and Technology
Related worksheets and rubrics.doc
- Upon entering the room, students will complete the following Do-Now Activity in their science journals:
Our common name is "humans." What is our scientific name-genus and species? Explain the importance of having scientific names for species.
- Class discussion of Do-Now will ensue with teacher posing the problem to students that there are insurmountable specimens in our world to be identified and classified.
- Students will then be shown a large jar of mixed candy. Students will be asked to identify these "specimens" as a whole or in "general". Students will then be asked to give characteristics of some of these candies that help to specifically identify certain samples.
- Students will be reminded that to classify objects, you must notice details of size, shape, position, and structure to name a few. Differences in color and texture are often necessary as well. You must learn to observe carefully to distinguish these differences in different, yet related, objects.
- Students will then be introduced to a handy device known as the dichotomous key to aid in identifying unknown specimens-in this case candy.
- Students will participate in today's lesson, which involves them using a dichotomous key to identify the "specimens" in their bag. Although they might already know the common names, they need to identify the scientific or Latin names, as well as some other data. Students will be reminded that proper lab safety never includes tasting or eating of objects to be studied unless specifically instructed to do so by their teacher.
- Students will be given the worksheet. Teacher and students will go over the activity worksheet and we will do one sample together for modeling the proper way to use this key.
- Students will then be given necessary supplies/materials for activity and will begin working independently.
- Teacher will circulate throughout the room posing inquiry-based, open-ended questions regarding students’ data collection.
- Class will come together and discuss data results and how useful this device can be. Students will be shown a bunch of tree branches and asked if they know what kinds of trees they came from. Could a dichotomous key be created to identify the types of trees they came from? What characteristics might we include? Think of something humans classify (i.e. library books, food/items in a supermarket, etc.) Begin thinking about some objects you classify because shortly, you are going to be creating your own dichotomous keys for us to identify your unknown objects.
- Students will be instructed to report to the computer lab for the next two days. Tomorrow we will be working with dichotomous keys for tree identification. The following day we will be finalizing our data from today's lab activity into a formal lab report and PowerPoint Presentation. Further instructions and rubric for presentation will follow.
Day 2-Computer Lab
Students will report directly to the computer lab.
- Students will be instructed by the teacher to go to the following URL: http://www.dnr.state.wi.us/org/caer/ce/eek/veg/treekey/index.htm
- Students and teacher will read as a whole class the directions for participating in this on-line dichotomous key activity that has the students using a dichotomous key to identify their mystery tree.
- Students will explore and experience this site and record their pathway/data along with the teacher utilizing the SMART Board for whole class viewing as well.
- Teacher and computer teaching assistant will circulate among the students and individually conference with them as they solve the identities of their mystery tree.
- Class will come together and discuss the identities of the trees and the solution to the pathways as shown on the SMART Board.
- The usefulness of this tool will once again be considered.
- Teacher will collect student work to be graded as a computer lab activity.
- Students will be instructed to bring dichotomous candy key worksheets/data to computer lab tomorrow.
Day 3-Computer Lab
Teacher will instruct students to conform to known expectations for writing up a formal lab report on the Candy Keys experienced which will be due tomorrow.
- Students will create PowerPoint presentations consisting of six to eight slides that are indicative of expectations on rubrics that we will go over in a whole class setting as viewed on the SMART Board.
- Students will be instructed to save their PowerPoint's to the network which will be viewed on the SMART Board upon completion in a whole class setting.
- Teacher will individually conference with students regarding creation of PowerPoint presentations and how they creatively express what they experienced as a result of our dichotomous key explorations.
Assessment will be on going and consist of:
analysis of Candy Key worksheet/formal lab report
student-generated dichotomous keys
web-based dichotomous key activity responses
individual and group conferencing
related rubrics and lab evaluation forms
Post Lesson Activity
Students will be required to create their own dichotomous keys based on something that they need to classify.
The students have been introduced to the basic steps involved in the scientific method and this will serve as a unifying theme throughout the year. The main premise that this lesson focuses on is that of observation.
Every living thing on Earth is classified and named by a set of rules used by all scientists across the world. We call these names scientific names and they are based on the taxonometric way of organizing organisms according to the similarities between them. In essence, scientists have created labels for all the living things on Earth. These labels describe the organism from general names to specific names.
Taxonomists have developed special guides to aid in identifying unknown organisms. One such guide is the dichotomous key ("dichotomous" means "divided into two parts."), which provides for easy and quick identification of an unknown organism. This type of key is the most widely used in biological sciences. A dichotomous key consists of several pairs of descriptive statements that have only two alternative responses. From each pair of statements, the person trying to identify the unknown organism chooses the appropriate statement. From there, the person is directed to another pair of statements. By working through the statements in the key, the person can eventually identify the organism.
Through the use of this lesson the students will be offered numerous opportunities to further enhance their observational skills as well as hands-on experiences utilizing a vital tool. It will also serve to reinforce previous knowledge of the classification system. This lesson is an introduction to a type of key that will be used extensively in the future. It should also be noted that dichotomous key usage is a new curriculum spiral requirement that is on the new eighth grade assessment. Multimedia components will consist of students interacting with an online dichotomous key web site as well as creating their own PowerPoint presentations to showcase their conclusions of this lab activity.
Dichotomous Key Online Activity
Behavioral Objectives: The students will be able to
Classify candy according to observable characteristics.
Use a dichotomous key to identify their bag of "treats."
Record facts about their candy.
Describe how dichotomous keys help in identifying organisms.
Present his or her data as a communicative tool through the use of technology (at a later date in computer lab).
Design a self-generated dichotomous key.