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The Gene Hunters
 
Teaching Guide

As you saw in "Genes for Youth", Cynthia Kenyon experiments on a simple type of worm called a nematode. Because nematodes have such a short life span (about 2 weeks), she has found them ideal for her work on aging and genes. Through these experiments, Kenyon has made exciting breakthroughs in understanding the genes that control the way we age.

Nematodes comprise one of the most abundant groups of animals found in soils all over the world. Some nematode species, such as the Caenorhabditis elegans used in Kenyon's research, move actively through a watery film found within their surroundings. You can exploit this mobility to collect your own samples of active nematodes using a device called a Baermann Funnel. Here's how.

 

 

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OBJECTIVE
This activity page will offer:

  • Assemble a worm collection device called a Baermann Funnel
  • Collect Caenorhabditis elegans or other active nematodes from local soil samples
  • Observe the appearance and behaviors of these worms

MATERIALS

  • Paper toweling
  • Fine mesh screen (metal)
  • Small wire basket (or plastic food basket)
  • Funnel
  • Tubing (that fits the base at the bottom of the funnel)
  • Clamp
  • Microscope, slides, cover slips and petroleum jelly (for observing specimens)

PROCEDURE
Extracting Nematodes

  1. Obtain several samples of local soil.
  2. Separate the soil in each sample by passing it through the fine mesh screen.
  3. Once the larger chunks have been broken down, spread the sample on a paper tissue. The soil should form a layer about 1-cm thick.
  4. Wrap up the soil within this tissue and place it within the wire basket or plastic fruit basket.
  5. Slip a hose with a clamp onto the neck of a large funnel. Position the basket and soil in the funnel. SEE DIAGRAM
  6. Make sure that the clamp is set on the hose. Fill the funnel with enough water so that the bottom of the soil is positioned beneath the surface of the water.
  7. Leave undisturbed for 2-3 days. You may have to refill the funnel to replace water lost to evaporation.
  8. During this time, active nematodes will move out of the soil and into the water. They'll fall to the bottom of the funnel and collect in the tube. To retrieve these specimens, release the clamp allowing water to flow through the hose into a collection beaker.
  9. Use a microscope to examine the worms living in the water. Describe their appearance and behavior. Can you identify young and old individuals? What factors will you use to differentiate these animals? Do you think all soils will contain similar populations of nematodes? Explain.


THINK ABOUT IT
Baermann Limits
Although the Baermann Funnel can be used to collect active nematodes, it is not an effective tool for extracting inactive species.
Why? Can you design a collection tool that will extract nematodes that are immobile? Share your thoughts and design with classmates. With your instructor's approval, assemble and test this device.

EXTENSIONS
Critically Examining Human Aging
Identify ten different changes you associate with human aging. Which are the most critical changes? Which changes have the most social impact? Which changes might have the greatest impact to prehistoric human ancestors? Why? Do you think males and females "age" at the same rate? How do societal images affect our concept of aging?

The Big Picture - Future Shock
Write a futuristic science fiction story about a civilization in which the wealthy have the technology available to arrest their aging process. In contrast, the poor have accelerated aging due to the environmental toxins created by the industries of the richer and more powerful class.

Use the Web!
What is the typical life expectancy of a person in the United States? Is life expectancy the same for males and females? If not, what social and genetic factors might affect life span? How does life expectancy in the US compare with life expectancies in other nations? Research how average life span has changed over the centuries. Which advances in science and medicine had the greatest impact on life span? Were genetic factors also responsible for any observed increase?

WEB CONNECTION

Worm Links
This site provides links to the laboratory use of Caenorhabditis elegans.

Phylum Nematoda
An introduction to the phylum Nematoda

Genetics of Aging
Learn more about aging in this Science Friday piece. Listen to it in real audio!

Scientists Discover Cellular Fountain of Youth
A CNN overview of aging and genes.

For more Web links on this topic - visit our Resources Section.


Answers

The activities in this guide were contributed by Michael DiSpezio, a Massachusetts-based science writer and author of "Critical Thinking Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing Co., NY).

Academic Advisors for this Guide:

Corrine Lowen, Science Department, Wayland Public Schools, Wayland, MA
Suzanne Panico, Science Department, Fenway High School, Boston, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland, MA

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