Beacon Lesson Plan Library

Building a Dichotomous Key

Jacqueline Roberts
Bay District Schools

Description

A dichotomous key helps us understand diversity and identify unknown organisms. In a laboratory/classroom setting students design a dichotomous key.

Objectives

The student uses effective strategies for informal and formal discussions, including listening actively and reflectively, connecting to and building on the ideas of a previous speaker, and respecting the viewpoints of others.

The student knows of the great diversity and interdependence of living things.

Materials

WHOLE GROUP ACTIVITY - Make available pictures OR list on the blackboard or overhead projector the following animals: Snake, Hummingbird Bear, Elk, Manta Ray, Texas Long Horn, Frog, Sting Ray, Tortoise.
PRACTICE - Make available leaves or photocopies of leaves, per each group (Long -leaf pine, Florida Torreya, Florida Maple, Mockernut Hickory, Southern Red Oak, Black Willow, Catalpa, Box elder and Black Walnut (see additional resource material)
ACTIVITY - Make available leaves or photocopies of leaves, per each group (general assortment) OR add two or four new leaves to the previous group of leaves (PRACTICE) OR teacher may use eight to fifteen items of choice.
-Overhead projector
-Visa-Vie

RESOURCES:
Johnson, George B., Biology: [Visualizing Life]. Holt, Rhinehart and Winston, Inc., Orlando, Florida, 1994 and 1998.

Kaskel, Albert., Hummer, Paul J. and Daniel, Lucille. [Biology: An Everyday Experience]. Charles E. Merrill Publishing Co., Columbus, Ohio 1988.

ADDITIONAL RESOURCES: (optional but helpful)
-Anderson, Robert., [Guide to Florida Trees], Winner Enterprises, January 1988.

-Nelson, Gil and Cook Marvin., [Trees of Florida: A Reference and Field Guide], Pineapple Press Inc., February 1994

-Petrides, George A., [Peterson Field Guide to Eastern Trees], Houghton Mifflin Co., Houston, New York, 1998.

-[Forest Trees of Florida], Florida Department of Agriculture and Consumer
Service., 1999 ed.

Preparations

Teacher Preparation

1. Review definitions of property, trait, characteristic, organization, classification and dichotomous key.
2. Review definition of diversity.
3. Understand the following leaf terminology: simple leaf, compound leaf; leaf shapes (lance, oval, heart, circular, triangle and elliptical); leaf arrangement (alternate,
opposite); leaf margins (smooth, wavy, toothed, lobed).
4. Review leaves for accurate visual identification.
4. Keep in mind the number of students participating in this activity. Provide identical sets of 6-15 items for each lab station or group of 2-3 students. The teacher is not limited to suggested items but student groups should have identical sets.
5. Take inventory of supplies and materials necessary to complete lesson and secures items.
6. Review -Hints for Constructing a Dichotomous Key-.
7. Organize lab groups.
8. Using the attachments as transparencies, prepare Dichotomous Key materials.
9. Demonstrate what a key -looks like-. (SEE ALL ATTACHMENTS).
10. Set up WHOLE GROUP ACTIVITY: DICHOTOMOUS KEY (ATTACHMENTS 1,2 ,3)
11. Set up PRACTICE: DICHOTOMOUS KEY (student lab identifying leaves - attachment 4)
12. Set up ACTIVITY: DESIGNING A KEY. (ATTACHMENT 5 - Template)

( Once the basic concept -how to set-up- a key is understood this lesson can be adapted for use in any science course for identification of unknown animate and inanimate objects.

Procedures

PRIOR KNOWLEDGE AND/ OR CLASS DISCUSSION IS NECESSARY BEFORE BEGINNING THIS ACTIVITY.
THIS LESSON IS DESIGNED TO FOLLOW: INTRODUCTION TO CLASSIFICATION (Beacon Learning Web Site)

A. PRIOR KNOWLEDGE
1. Understands what is meant by characteristic and trait.

2. Understands definition of dichotomous key.

3. Understand what a dichotomous key -looks like-.

4. Understands that a dichotomous key is based on alternative statements describing the features of items.

5. Understands only one of the alternative statements describes the item being keyed.

6. Understands the following leaf terminology: simple leaf, compound leaf; leaf shapes (lance, oval, heart, circular, triangle and elliptical); leaf arrangement (alternate,
opposite); leaf margins (smooth, wavy, toothed, lobed).

7. Understands that assessment is based on student oral presentation of classification chart, dichotomous key and laboratory work.

B. HINTS ON CONSTRUCTING A DICHOTOMOUS KEY

1. Use only observable traits.

2. Use traits that are clear and unambiguous - the organism either has the trait or it does not have the trait.

3. Use traits that are not seasonal.

4. Descriptions are based on alternative statements describing the organism's features.

5. Only one of the alternative statements describes the organism being keyed.

6. Whenever possible make alternative choices positive - organism -is- instead of organism -is not-.

7. Each organism is placed in its own unique category (no overlap).

8. Use measurement (standard or metric) rather than terms like -big- and -small-.

WHOLE GROUP PRACTICE: DICHOTOMOUS KEY

1. Preparation
a. Prepare students to work in both large group and smaller -break-out- groups. (Teacher may select small group partners or allow students to chose their own partners.)
b. Pass out pictures OR places list on the blackboard or overhead projector of the following animals: Snake, Hummingbird Bear, Elk, Manta Ray, Texas Long Horn, Frog, Sting Ray, Tortoise.
c. Teacher and students prepare a short introductory list of animal traits and characteristics on blackboard or overhead projector.

2. Breakout Groups
a. Students working in small groups (2-3 per group) generate a list of at least three observable characteristics per organism (SEE ATTACHMENT 1.)
b. Students discus and come to a consensus regarding similar and dissimilar traits (compare and contrast) of the organisms. EXAMPLE: lives on land; lives in the water; breathes with lungs; breathes with gills etc.
c. Students use similar and dissimilar traits to sort organisms. (SEE ATTACHMENT 2)
d. Allow approximately 20 minutes to accomplish these tasks. Add or subtract time according to your needs.
e. Monitor and assist where necessary.

3. Whole Group
a. Student groups present their sorting models to class.
b. Students form a consensus for criteria used to organize Dichotomy Model.
c. OPTIONS FOR DESIGNING A KEY: (Dependant upon student knowledge and ability.)
1) Demonstrate what a dichotomous key -looks like-. (SEE ATTACHMENT 3)
2) Students and teacher work together to build a key. (SEE ATTACHMENT 3, 5).
3) Students in small groups design a dichotomous key. (SEE ATTACHMENT 5).



STUDENT PRACTICE: BUILDING A DICHOTOMOUS KEY (Cooperative Learning Model )
1. Students work in groups of 2 to 3 students per group.

2. Students record on data sheet name of the leaf and 2 to 3 observable characteristics (SIMILAR TO ATTACHMENT 3).

3. Students compare/discuss leaf characteristics.

4. Students chose one characteristic and its alternative to record on data sheet. This is usually the most obvious characteristic. (example: leaves are broad and flat, leaves are needle -like).

5. Students separate leaves into two groups.

6. Students make sure that each group has distinct characteristics but does not overlap characteristics of the other group.

7. Students place the two most obvious characteristics on the data sheet labeling these groups 1a and 1b.

8. Students begin separation by answering questions -IF YES GO TO- or IF No GO TO-.

9. Students assign a number to the -IF YES GO TO- or -IF NO GO TO- box. This tells students where they go to either identify leaf or get additional information.

10. Keeping in mind that at each further division, students record a choice between two descriptions of characteristics (example: does have the characteristic; does not have the characteristic), students continue to divide each group until they can divide the groups no further.

11. Students demonstrate their knowledge by paring and sharing with another group. Each group, using the dichotomous key developed by the other group, sorts leaves that have been completely disorganized.


STUDENT ACTIVITY: DESIGNING A DICHOTOMOUS KEY

1. Students work in groups of 2 to 3 students per group.

2. Students record on data sheet name of the item and 2 to 3 observable characteristics
(SIMILAR TO ATTACHMENT 3).

3. Students compare/discuss characteristics.

4. Students chose one characteristic and its alternative record on data sheet. This is usually the most obvious characteristic. (example: leaves are broad and flat, leaves are needle -like).

5. Students separate items into two groups.

6. Students make sure that each group has distinct characteristics but does not overlap characteristics of the other group.

7. Students place the two most obvious characteristics on the data sheet labeling these groups 1a and 1b.

8. Students begin separation by answering questions -IF YES GO TO- or IF No GO TO-.

9. Students assign a number to the -IF YES GO TO- or -IF NO GO TO- box. This tells students where they go to either identify leaf or get additional information.

10. Keeping in mind that at each further division, students record a choice between two descriptions of characteristics (example: does have the characteristic; does not have the characteristic), students continue to divide each group until they can divide the groups no further.

11. Students demonstrate their knowledge by paring and sharing with another group. Each group, using the dichotomous key developed by the other group, sorts leaves that have been completely disorganized.

12. Students explain their dichotomous key, its development, and rationale to the teacher.

Assessments

1. Whole group activity and practice activity are formative assessments.
2. Summative assessment - Small group
a. In a small group setting students present orally their dichotomous key model. This is assessed by the ORAL RUBRIC
b. Laboratory worksheets to be turned into teacher and assessed by rubric .

Extensions

This lesson is designed to be used immediately following the Beacon lesson, Introduction to Classification.

Attached Files

The Dichotomous Key Worksheets, Template, Oral and Lab Rubrics.     File Extension: pdf

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