Ch. 1Lesson 3

How do we classify invertebrates?

invertebrates

mollusks worms arthropods

no backbone

cnidarians

mollusks

• soft body w/o bones• eg. snails, clams

Biologists classify worms into three major phyla—flatworms,

roundworms, and segmented worms.

worms

flatworms roundwormssegmented

worms

• live in wet places

• live in water or land

• eg. earthworms

arthropods

• bodies divided into parts• eg. insects, lobsters

complete metamorphosis

Millipedes in the Great

Smoky Mountains

National Park in Tennessee

cnidarianscnidarians

• eg. jellyfish & coral• eg. jellyfish & coral

jellyfish & coral

dichotomous key• Used to identify unknown organisms

• Compares characteristics of unknown organism with characteristics of known organisms

• Uses a series of yes or no questions

Dichotomous Key pg. 21

Candy Dichotomous

Key

• Figure out your partner’s candy by following the steps of this dichotomous key:

1. Is the candy hard? (If the answer is YES, go to question #2. If the answer is NO, go to question #3)

2. Is the candy round? (YES: go to #4. NO: go to #5)

3. Does the candy come in different colors? (YES: go to #6. NO: go to #7)

4. Does the candy have a stick? (YES: go to #11. NO: go to #1)

5. Is the candy three different colors? (YES: go to #8. NO: go to #9)

6. Is the candy in the shape of a bear? (YES: go to #12. NO: go to #10)

7. Is the candy long and thin? (YES: go to #13. NO: go to #9)

8. Is the candy shaped like a triangle? (YES: go to #14. NO: go to #2)

9. Is the candy chocolate? (YES: go to #16. NO: go to #1)

10. Is the candy in the shape of a worm? (YES: go to #15. NO: go to #7)

11. Your candy is a lollipop!

12. Your candy is a gummy bear!

13. Your candy is a Twizzler!

14. Your candy is candy corn!

15. Your candy is a gummy worm!

16. Your candy is a Snickers!

Activity - Designing a Dichotomous Key • 1. Distribute to each group of 3-4 students: Thumbtacks, paper clips, wooden ruler, pencil, and plastic pen  • 2. Ask students to look at the objects and, as a group, have them brainstorm how the objects are similar to and different from each other.

Then, bring the class together to list on the board the different ways the objects are alike and different. Give the students about 2-3 minutes to do this. 

• 3. Grouping possibilities could be: metal, plastic, and wood  • 4. Once this is done tell the students that science uses these similarities and differences to classify the natural world around them. The tool

that they use for this is the dichotomous key. From a dichotomous key, one can learn the name of any object/plant/animal, which has been included in the key. In using a key, the student is led through a series of alternatives until the name of the object/plant/animal is reached. A dichotomous key, in its simplest form, has a few             basic rules that make writing one easy.                

• · Rule #1: Each step involves making choices between two characteristics. These characteristics are grouped 1a and 1b, 2a and 2b, and so forth. 

• · Rule #2: Each step in a group distinguishes one or more objects (plants, animals, etc.) into two smaller units.  • · Rule #3: Each unit either identifies and names an object (plant, animal, etc.) or gives directions as to where to go next in the key. 

· Rule #4: At each step, students must choose one of the groups, steps, and units at a time and not more than one of each.                                5. Next you will want to illustrate the process by making a basic key to illustrate the rules. It will not be necessary to have real objects in front of the students because the objects will be well known

• .  Write on the board the following four objects:  · tennis shoes · belt · celery · french fries

• Ask the students to list the characteristics of these items and place them into two groups.  • Group one should include: “sneaker" and "belt" as "Clothing Items"  • Group two should include: "celery" and "french fries" as "Food" 

               •             Example Key: 

            Objects: sneaker, belt, celery, french fries  •             1a. Clothing: Go to 2 

            1b. Not clothing: Go to 3  •             2a. Fits on your feet: Sneaker 

            2b. Fits around your waist: Belt  •             3a. Crunchy green vegetable: Celery 

            3b. Crunchy fried snack: French fries                               

Activity - Designing a Dichotomous Key page 2 •

                             

• 6. Now go back to the original objects laid out for the students (Thumbtacks, paper clips, wooden ruler, pencil, and plastic pen) and create a dichotomous key for them as well. Make sure that students understand this format before moving on. 

•             1a. Objects made of metal: go to step 2              1b. Objects not made of metal: go step 3 

•             2a. Flat, without pointed ends, curved on two sides: Paper clip              2b. Round base, pointed, sharp end: Thumbtack 

•             3a. Objects made of wood: Go to step 4              3b. Objects not made of wood: Objects is made of plastic, round,  writing utensil: Pen 

•             4a. Flat measuring device: Ruler              4b. Round, writing utensil: Pencil 

•                Wrap-up                

• Tell students that scientists use dichotomous keys to help them identify a variety of species.  Scientists who design dichotomous keys are called Taxonomists.  When a taxonomist designs a dichotomous key it will only identify objects that have been previously included in the key. 

• Ask students: How might this be a problem?Maybe there is a new species that is not in the key. Ask students: Can a dichotomous key be too large? Why? If the key is too big it may take a long time to find what you need.