Wild Dichotomous Keys

Lesson Title: Wild Dichotomous Keys

Intro text: A look at how dichotomous keys are constructed with a nifty assessment of learning at the end!

LESSON INFO

Author: Eric Bingham, Logan High School

Grade Level: High School Biology

Subject Area: Observation of Organisms

Curriculum Standard: Utah State Core, Standard 5, Objective 3.a: Classify organisms using a classification tool such as a key or a field guide.

Materials Needed:

3 brown paper bags
30 toothpicks
30 candy kisses
30 pennies
A deck of cards
Worksheet found at http://pelotes.jea.com/preactivities/UseADichotomousKey.pdf
Bird field guide
Pictures of birds from the field guide
Copy of "Where the Wild Things Are" by Maurice Sendak
Wild Things pictures

Time Needed: 1 class period

Best season for this lesson: All-season

Background information: Nice introduction to use of dichotomous keys. The students don't need any other exposure to the topic prior to this series of activities.

Engage:

Bring three brown paper bags labeled bag 1, bag 2, and bag 3. Each of the bags will have something small in it with enough for each person in the class to have one. Example: Bag 1 has 30 toothpicks, Bag 2 has 30 candy kisses, and bag 3 has 30 pennies.
Tell the students that each person in the class may ask one question about the bags, but you can only answer yes or no. When everyone has had a chance to ask a question, the class must choose a bag, and everyone in the class will share the contents of the bag.
After the students have picked a bag, briefly discuss what type of questions were the most helpful and why.

Explore:

Organize the class into partners and give each student in the class a card from a deck of playing cards. Tell the students that they may only ask yes and no questions, and they are trying to guess which card their partner has with as few questions as possible.
After the class is finished, see who needed to ask the fewest number of questions.
Discuss which questions were most helpful and why.

Explain:

Explain to the students that, by asking yes or no questions to narrow down their choices, they have been making their own mental dichotomous key.
“Di” means two, and “tomous” means to divide.
Explain that a Dichotomous key is a way of classifying organisms based on a series of choices between two characteristics. Example: If we were to make a dichotomous key to identify a student named Jose, what type of questions might be good to ask first?
Explain how a dichotomous key is usually organized, not as a flow chart with arrows, but as a series of numbered questions which take you to other questions (like a choose your own adventure book). Give them the worksheet on bird dichotomous keys that can be found at this site: http://pelotes.jea.com/preactivities/UseADichotomousKey.pdf
- Students should only need 5-7 minutes to complete the worksheet and name all of the birds shown.

Elaborate:

Explain that dichotomous keys can be very helpful in identifying and classifying organisms, but most field guides are organized more like “polychotomous key” (have the students try to guess what a polychotomous key is, and how it might be different from a dichotomous key.)
Show a bird field guide and explain that birds are classified into several broad categories. (Ducks, shorebirds, hawks, eagles, woodpeckers, warblers, sparrows, etc...)
Have the students come up with ideas about the type of things that make these categories unique (webbed feet, hooked beak, body shape, habitat etc...)
Show the students a picture of a bird, (example: a Northern Flicker), and have them decide what things might be unique about that bird (bill size, posture, etc...)
Help guide the students through a field guide until they find the Northern Flicker.
Ask what characteristics were most helpful in identifying this bird?
Divide the class into small groups and give each group a bird field guide and several pictures of a raptor (the same picture for everyone).
Have the class use the field guides to try to identify their group’s raptor.

Evaluate:

Read the story “Where the Wild things Are” by Maurice Sendak.
Provide each group with two copies of the “Wild Thing” pictures below. Each group needs to name the wild things and write their names on the first copy. This will be their key. They then create a dichotomous key for other groups to use to find out what names go with what wild things.
Each group exchanges dichotomous key with another group, and the group must use that key to find out what each of the monsters is named. They write the names in below the monsters, and then compare their names with the answer key from the group that made the dichotomous key.
Ask how many groups got 100% right. For those groups that didn’t get them all right, was it a problem with the dichotomous key, or with using the dichotomous key?
What questions were most helpful?