The Wonder in Spider Thread Chemistry Neil Glickstein Wrioht Center for Science Education. Tufts Universitv. Medford. MA02155 ani~hd-rhe Waring School, Beverly, ~ ~ 0 1 9 1 5 It is easy to lose sight of the wonder inherent i n the chemical phenomena of the natural world. With spider thread a s a theme, I have attempted to tap students'natural curiosities and to rekindle the fascination for nature so commonlv found i n children hut all too absent in the adolescent and adult years. This interdisciplinary unit leads students into an investigation of the complexities of silk generation through literature, visual arts, natural history, and mvtholom The result is a discussion-oriented, thematic approach to a technical topic that has appealed to students whose abilities lie in realms other than the 1 0 ~ cal-mathematical intelligence so often stressed i n t h e study of chemistry. Clearly, students learn most effectively when interested i n the tbpic and when asked to emplo; individual natural abilities and strengths ( I ) . I prepare students to consider the nature of spider silk by first completing a unit on phase change and another on the chemistry of carbon. My chemistry class is loosely based on the ChemCom text, though this unit could be equally successful within a more traditional treatment. We then read Primo Levi's "The Spider's Secret" ( 2 ) i n which he contrasts common mechanisms for liquid to solid phase changes with that of the spider's natural production of thread from a liquid precursor. This short piece is heautifully written and offers a novel avenue into a technical topic that could otherwise overwhelm the reluctant student. Initially, Levi offers three concrete examples of practical problems that were presented to him a s an industrial chemist. A s ~ e c i a l i sin t the ~roductionof varnishes. he describes his fascination with the processes that result in liquid to solid phase changes and lists several common phase change mechanisms including cooling, coagulatkn of blood, evaporation of a solvent and polymerization. With this a s a foundation, Levi considers the production of spider t h r e a d by rejecting each of t h e above-mentioned mechanisms as a n explanation for the solidification of this fine fiber so necessary to the arachnid lifestyle. Finally, he suggests that the irreversible solidification is due to "traction" hut offers neither a mechanism nor any further discussion of the problem. "No chemist has yet succeeded in reproducing so elegant, simple and clean a process," concludes Levi. "We have surpassed and violated nature in many fields, but we still have much to learn from nature" ( 2 ) .Readers are left in a state of suspense; many questions typically arise i n the ensuing class discussion. With student interest oioned. I brine a more technical e r and ~ l ' l k from " Scientific article to the group: ' ' ~ ~ i dwebs American (3).Here exists an opoortunity to help students learn to find the informationLtheyneid. ~ ~ ~ i c they a l l ~ , need midance and practice in retrieving useful informarlon from jnnrnal :irricl(*i,.;(I aret>xplort:tlic pierr together. On an;ll\.iis, thv :iurhor ihcds light or1 thr chemistry of the process i n question. He suggests that if a shearing force (traction) is of sufficient strength to break the hydrogen bonds of the alpha-helix liquid state of the silk composite, then beta-pleated sheets result. These heta-pleated sheets are solid a t environmental temperatures. Here is a n explanation a t the molecular level for the solidification of the silk material, consistent with observation yet different
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Journal of Chemical Education
from the mechanisms for phase changes in systems studied so far in the text. Once considerable &dent interest in the topic of phase change has been generated by the Levi essay, several interdisciplinary connections are possible. In addition to having a terrarium designed to be a spider habitat in the laboratory, I have explored liaisons with other classes. The consideration of the Arachne mvth in a humanities class and the discussion of the famo& Velazquez painting, "The Spinners," representing the fable of Arachne in art, have met with a favorable response. Students seem to enjoy and profit from exchanging ideas between classes when these parallel linkages are possible. Also, I have offered students a n opportunity to submit spider-inspired artwork with marvelous results. (See the figure.) For too long we. in the "hard sciences." have valued onlv a narrow ran& of abilities in our students and the n u i bers of those who continue their study may reflect, in some part, this bias. With the arachnid theme, I have been able to emphasize a chemical bridge to biology, highlight a new perspective on phase change, encourage observation of the natural world and teach how to use technical articles. The incorporation of literature, mythology and a r t has stimulated more students to participate actively during class. As a model for the development of future curricula, the thematic approach offers significant potential. Students learn better when their interest is cantured and when their oarticular talents are valued. In addition to providing a useful technique for helping students to enhance their science literacy, this approach also encourages natural links among colleames in different de~artments.serves to continue our own e&cations and helps us to see bur institutions from a broader perspective. Literature Cited 1. Gardner H. Mnllfplr Inirllismma:Thr T h m v in Prnclirr. Basic: New Yark. 1993. 2. kvi.!F "TheSpider's Semet", in The Mrrinr Moker Schocken Books: New York, 1989:
158-162.
3. Vollrrth. F Sci. Anrer 1992.26fi 131, 70-76.
