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Content

Students will be part of an active research project to document the distribution of a new species of tardigrade, a microscopic invertebrate animal. The project is part of a nationwide online collaborative research project. Samples collected in the field will be examined for water bears, using microscope. Students will gain knowledge of scientific classification through the use of an online taxonomic key. Keeping a biological journal will also be part of the assignment.

Prerequisites

Students will need to know how to keep a biological journal. They must be familiar with the use of microscopes and must know how to practice good scientific methods. Finally they must become familiar with tardigrades, commonly called water bears, especially their physical characteristics. The a good introduction to water bears can be found at http://www.iwu.edu/~tardisdp.


Objectives

1. To instruct students in proper scientific field methods when collecting samples of mosses and lichens; to provide practice keeping a field and lab journal of activities.

2. To instruct students in methods of making slides of live animals, primarily water bears; to provide practice with using dissecting and compound microscopes and making detailed drawings of animals.

3. To provide instruction in the use and methods of classification of water bears.

4. To develop a class website describing the bear hunt and tardigrade biology. It should include 5 specific areas related to the project.

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Instructional Procedures
  • This project can be a one day lab in class or it could take up to four or five days depending on the amount of preparation that is done ahead of time by the teacher.
  • It is very important that the students are familiar with tardigrade anatomy before they begin looking at them otherwise students will have difficulty locating the animals. If possible have students look at the website for one class period. Otherwise a lesson should be prepared using the information provided on the website.
  • Water bears are not found in every sample of mosses or lichens. You may want to check some of the samples ahead of time to ensure you will have animals during class.
  • Water bears can be cultured for at least a week and possibly longer if care is taken to keep them in water that is clean and that they have plant material or rotifers or nematodes to eat, depending on the species. These can be obtained from the samples of mosses or lichens you will be examining.
  • A final note of caution, it is very easy to accidentally squish and kill a water bear while looking at it under a microscope. This may alarm some students.
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Materials
  • Samples of mosses or lichens that have been stored in paper bags
  • Culture dishes in a variety of sizes
  • Pipettes
  • Turkey baster
  • Spring water or tap water that has set out for 24 hours
  • Dissecting microscope
  • Compound microscope
  • Immersion oil for oil objective on compound scope
  • Microscope slides
  • Overspills
  • Vaseline or modeling clay
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Procedures

1. Soak half of each sample of moss or lichens in a large culture dish for at least 3 to 24 hours. (This may have been done for you by your teacher.)

2. Stir the debris in the dish to dislodge animals. Using a turkey baster, remove some of the water and a small amount of debris from the culture dish. Squirt water into a small culture dish and examine using a dissecting microscope.

3. Begin looking for water bears. As you find them, suck them up using a pipette and place them in a small clean culture dish with a small amount of water. If you are having trouble finding them you may want to try getting another sample from your original culture dish.

4. After you have collected a large number, you will want to make a slide to examine them. For the best results you will want them to be in anoxybiosis, a deathlike state. You should place a portion of your animals in a small vial, fill it with water, and seal it. It should only take a few hours for the animal to go into anoxybiosis but they can stay this way over night. They will be in "dead man's float" not moving and bloated with their legs extended.

5. To make a slide, use a pipette to suck one animal out of your vial and place it on a microscope slide with a drop of water. (You can look at moving tardigrades from the original sample as well.) Add a cover slip, placing a small amount of Vaseline or modeling clay on each corner to keep from squishing the animal.

6. You can now examine the water bear using a compound microscope. Make a careful drawing of the animal to help you in identifying what species you have found.

7. When you are done you can place the animal back in a culture dish and keep it a live for quite awhile. Just make sure it has enough food (rotifers, and nematodes) and does not dry out.

 

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Assessment

Students will create a class web page describing their experience through this project.

The site should include

  • A description of collection sites date, time, location, type of substrata
  • Explanation of scientific method and its importance, including examples from project
  • General description of tardigrades
  • Descriptions of the specific genera found
  • Brief description of taxonomy

A group of students will write each part of the website and as a class it will be combined into one big website.

Students' biological journals will also be evaluated. Criteria include neatness, accuracy, and completeness. It should include original drawings and thoughts and questions students have while performing their investigation.

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Lesson Plan
Website Authors: Karen Lindahl and Professor Susie Balser in affiliation
with Illinois Wesleyan University. Last revised 1 Oct. 1999.