Dichotomous Key

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Objective

SWBAT: identify local, native trees buy using a dichotomous key.

Big Idea

In this Cross-Curricular Science/Language Arts lesson, students use descriptive language to observe and identify tree species.

Lesson

55 minutes

The amazing science teachers on my team really helped in the creation of this lesson. Because I'm working on my Claims and Evidence Unit, we found a natural connection.

So, if you are a Language Arts teacher (and I assume you are, because you're here), you might need a little refresher on what a dichotomous key actually is...It's a way of identifying objects using observations and descriptions--by using a series of choices. Think Choose Your Own Adventure, Science Version.

The first thing the students do it collect samples. We told them to get at least 15 samples, knowing that they might choose some weeds, vines, or bushes. The samples had to be leaves from actual, regional trees. You might also want to encourage them to choose conifer samples, as well. It's nice to mix it up.

When they get back to class, they should fill up the observation guide. Here's a student sample of what that might look like. As a Language Arts teacher, this part is really important. I am circulating to ensure they are using very descriptive words, like "smooth," "glossy," and "jagged." These adjectives can really be the difference between being able to correctly identify the species, and not being able to.

Next, the students use the Dichotomous key to identify their species. Using the descriptive words, they answer a series of questions to find possible species. Once they think they've found a match, they use the Identified species chart to check their answers. Oftentimes, this is difficult, because they are so sure from using the key that their sample matches the guide, but they have to retrace their steps and see where they went wrong. Did they describe their leaf as "jagged," when it was really "toothed?" There is a fine line here, so those with an extensive vocabulary tend to do well on this activity.

Lastly, they fill out the Dichotomous Key Reflection. This reflection anticipates some of the problems I thought they might have, and has them work through those problems. What could they have done differently? What went wrong and why?