1. Is the pasta a hollow tube? If so, go to #2. If not, go to #4. 2. Is the pasta straight? If so, it’s penne rigate. If not, go to #3.
Those are the first two of a total of five questions comprising the dichotomous key which Katie L. is wielding in the photo above and, yes, the piece of uncooked pasta in her hand is indeed penne rigate, penne sporting ridges. Dichotomous keys are incredibly useful tools for classifying, well, just about anything. Best of all, they’re quite straightforward to use. One moves down through the dichotomous key, at each step choosing between two different, readily discernible physical characteristics of the specimen to be IDed. The first step in our pasta classification key asked students whether a given piece of pasta was tubular or non-tubular. Since penne are tubular, the next dichotomy was straight versus curved. Penne are straight.
We’ve been reading Sy Montgomery‘s The Octopus Scientists (a recent addition to the excellent Scientists in the Field series) with some of our students. The scientists featured in Montgomery’s book spend weeks on the Polynesian isle of Mo’orea, searching for octopus dens, collecting the remnants of the creatures’ meals (empty crab carapaces, scallop shells, and the like), and administering personality tests designed to characterize the octopuses’ psyches. A passage in Chapter 5 explains how a member of the team tasked with identifying the octopuses’ prey species goes about his work.
The actual words
dichotomous key don’t appear in the text, perhaps edited out due to concerns that loading the book down with terminology might blunt its appeal to some younger readers. Nevertheless, dichotomous keys are what Montgomery is describing on pages 36-37. Many of our students are aspiring scientists and engineers, so we wanted to ensure they’d be acquainted with the concept. First, we drew their attention to that portion of the book and introduced the term during our in-class read-and-discuss periods. That week’s reading comprehension homework assignment included a question intended to hone their understanding of this method of classifying things. Half of the reading comprehension section of last week’s quiz challenged them to actually use a dichotomous key — to classify pieces of pasta.
We drew inspiration from a similar exercise included by the Cornell Institute for Biology Teachers in their dichotomous key lab, but we wrote our keys from scratch, used a different mix of pasta types, and worked to make the activity fit the constraints of a quiz-taking situation. It turned out to be a heck of a lot of fun!
We have something even more special planned for the coming week’s quiz, which will cover the material in the final three chapters of The Octopus Scientists. As the saying goes, watch this space!