Objectives
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To understand format of dichotomous keys. To be able to make (& later use) dichotomous key for identification.
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Standards Addressed
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Unifying concepts & processes, systems, order & organization. |
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Drawing of grasshoppers, dogs.
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Time Requirement
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30 min |
Procedure/outline
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Engage: tell Alien story (see Other Comments section below) & have class make a key emphasizing - contrasts in a & b statements (opposites). Explain: include all critters listed, be specific in descriptions, decriptions are selective (don't describe every characteristic of each animal, just contrasting ones). Explore: give groups pictures of grasshoppers with varying characteristics - spots, stripes, speckles, & have groups make keys. Evaluate: groups share keys with class. Elaborate: groups make keys for dogs (vary by size, ears, noses, hair, tails, etc). |
Modifications/Adaptions/ Extensions
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Evaluate: groups share with class. Elaborate: use a dichotomous key related to your unit of study - (Macro Invertabrates) |
Assessment
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When groups share keys note understanding of paired statements & format of dichotomous keys. |
Other Comments
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First written by Dr. Allison Wallace of MSUM Moorhead. When using dichotomous keys-start with simple ones that ocntain familiar organisms & include photos or diagrams. Advance to more detailes. ALIEN Story: An alien is visiting my farm (can be from anywhere). He has limited English ability & doesn't know the names of my animals. I don't have time to introduce him before I go to work so I'll/we'll make a key to help him out. I have a cow, sheep, pig, chicken, and a dog. Which of these animals is most different from others & how? Class will probably agee on chicken (2 legs, feathers, etc). Write key on board as discussion continues on differences & similarities. Make paired statements: 1a has _____ 1b does not have ______ Working as a class, write the key, deciding on which charactaristics to focus. Possible result: 1a has 2 legs...chicken, 1b has more than 2 legs...got to 2. 2a has short tail...go to 3. 2b has long tail...go to 4. 3a has curly, hairless tail...pig. 3b has straight fur covered tail...sheep. 4a large (taller then 3')...cow. 4b shorter then 3'...dog. Discuss what is large & maybe quantify. |
