Academic journal article The Science Teacher

A Glue from Slug Slime? Student-Made Sticky-O-Meters and Measuring the Effectiveness of Glue

Academic journal article The Science Teacher

A Glue from Slug Slime? Student-Made Sticky-O-Meters and Measuring the Effectiveness of Glue

Article excerpt

[ILLUSTRATION OMITTED]

Yuuuck!" "Gross!" "Cool!" The response to slugs is never indifference. These slimy creatures are perfect for captivating students' imagination and curiosity, and they are ideal subjects to introduce investigative science. This article describes a classroom activity in which students design a research investigation to answer the question: "Is slug slime a good glue?" Through a series of guided steps, students work in small groups to decide how to measure the success of an adhesive. Each research team invents a unique tool, the "Sticky-O-Meter," to quantify glue stickiness. Students compare results for slug slime with those from a commercial adhesive.

This lab was originally developed as a Howard Hughes Medical Institute-funded workshop for teachers on experimental design and has been used successfully with middle and high school students in life science and biology classes. While the lab emphasizes the importance of quantifying the responding or dependent variable in an experiment, it is also just plain fun!

Slugs, slime, and bioadhesives

My own fascination with slugs began many years ago when I was looking for a research system for studying cervical mucus. My graduate adviser, Ingrith Deyrup-Olsen, an animal physiologist at the University of Washington, was then a leading slug expert. Affectionately called "the slug lady," she brought banana slugs national attention by appearing (with her slugs) on such popular television shows as Bill Nye the Science Guy and The David Letterman Show. Deyrup-Olsen's own research used banana slugs as a model for studying the biological properties of mucus (Deyrup-Olsen, Luchtel, and Martin 1983). The basic biochemistry she described provided insights into many other areas, including the chemistry behind mucus buildup in the lungs of people with cystic fibrosis (Marmor 2004).

Mucus, an enormously interesting material, is the general term for specialized secretions of epithelial cells of multi-cellular animals (except arthropods). It is composed mostly of water, salts, and small amounts of mucin--a carbohydrate-protein (glycoprotein) molecule. Wherever living cells are in contact with elements of the environment, mucus can be found: in the lungs, stomach, eyes, ears, nasal passages, cervix, and on the living skin of slugs. Delicate living cells are protected by a coating of mucus from potential insults such as particles of dust, harmful chemicals, and bacteria.

Mucus, like glue, is also a kind of adhesive. People have made glues from diverse sources, such as egg whites, milk, horses' teeth, and spruce gum. The natural world is filled with examples of highly effective adhesives, from the slime a limpet uses to stick to rocks, to the hardened foam egg-cases the female praying mantis wraps around a plant stem, to the silk rope the spider uses as glue. For an adhesive to work, it must stick well to both of the materials it is joining together. Most adhesives stick to some materials better than others. Starch-based glues work well with materials such as paper, wood, or cotton but not with plastics. What kind of glue could effectively glue skin? The answer may be bioadhesives! Research scientists are working hard to develop this new generation of nontoxic adhesives made from natural materials for use in the building industry and for medical applications such as setting bones, surgery, and drug delivery.

A slug's slime acts as both a glue and a lubricant, allowing the slug to crawl up walls and across ceilings without falling off. The slug pushes until the structure of the glue gives way and the slug slides forward. When the slug stops, the glue structure reforms and the slug sticks securely to the surface.

Can we make a glue from slug slime? The remarkable physical properties of mucus make it a good candidate for research, especially in the K-12 science classroom.

Classroom guidelines

Students need time handling and familiarizing themselves with slugs before they are ready to apply themselves to the research activity (see "Collection and care of slugs," p. …

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