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DRAFT

DRY UP BABY ! ANHYDROBIOSIS (freeze drying)

Overview
In this lab activity, students will explore how organisms are able to survive the extreme environmental conditions found in the Polar regions. Students will draw a rotifer and/or Tardigrade from microscopic observations. Students will design experiments using Tardigrades and rotifers to expand their knowledge and understanding of normal behavior followed by experiments to explore anhydrobiosis.


Rationale
How are organisms able to live through the long frozen Antarctic winters where temperatures often fall below -80 Celsius? How do they stay alive? Why don't the cell membranes rupture from freezing? What sort of mechanism has given these organisms a survival advantage? Anhydrobiosis is a process where by microscopic organisms slowly lose body water by evaporation in response to dry and cold temperatures. By using this process, organisms can survive the most extreme cold environments found on the planet earth. When their environment warms up and liquid water is made available, they "spring back to life". Many of the Antarctic Dry Valley organisms exposed to extreme temperatures use anhydrobiosis to survive the severe winters. Students will have the opportunity to investigate the parameters of an organism's survival strategies under Polar desert conditions.


Grade Level/Discipline
Grades 6 - 12


Objectives
Students will

  • observe and draw active living rotifers and Tardigrades.
  • document some behaviors shown by living rotifers and Tardigrades.
  • understand that cells can survive extreme environmental conditions by a process called anhydrobiosis.
  • discuss the design of possible experiments to collect evidence about anhydrobiosis in lab groups
  • share experimental ideas and agree on several experiments to do in lab groups
  • design and perform experiments to collect data on anhydrobiosis
  • explain their results and evaluate each others data


National Standards

  1. Inquiry Teaching Standard A
  2. Content Standard- structure and functions in living systems


Teacher Preparation for Activity

Materials

  • Organism ordered* or collected locally.
  • Two types of freezers, if possible---frost free or not frost free
  • School cafeteria freezer, if you have access to it.
  • Slides
  • Microscope
  • Containers - Petri dish size or smaller.
  • Droppers
  • Have organisms and freezers available.

Time Frame
Three consecutive class periods to begin the experiment plus additional periods for data collection and analysis.


Teaching Sequence

Engagement and Exploration (Student Inquiry Activity)
Have several poster-sized pieces of paper ready to write the student hypotheses about how they think the organisms survive. Perhaps one or two students can assume the role of class recorders. Subsequent results will be compared to these predictions. Students can also document the discussion in their lab notebooks.

Ask the students to share their thoughts on how they think the animals they observed and drew manage to survive the Antarctic winters.
In the Polar regions there are organisms that survive temperatures less than minus 80 degrees below zero Celsius! How do they do it? What happens to the microscopic animals that live in the lakes in your own area during the winter? How do they survive the winter?

Ask students to think about any cells that might be able to survive freezing.
Students may think about how artificial insemination in agriculture makes use of frozen sperm cells. Are there other types of cells that we know survive freezing? Is this the same as an independent animal surviving using anhydrobiosis?

Explanation (Discussing)
What kinds of experiments can you do to learn more about how these organisms survive the severe winters? What types of questions can you ask?
Decide on a controlled experiment that will investigate the survival of tartigrades and rotifers in temperature below which most organism freeze at . (Students may suggest various methods such as rate of freezing, freezing in water, freezing out of water, freezing with dry dry ice, varying length of time frozen, etc..)

How many variables should we explore?
Let the class decide on how many questions can be explored. Decide on what variables you need to control.
Each lab group of 2 - 4 students could work with a specific variable.
List the possible variables with which your class decides to experiment. Each group may want a separate variable.

Discuss the controlled variables.
These are all of the things that you want to keep the same for each of the lab groups' experiments. You all need to agree on what they should be during a class discussion time. By doing this, you will be able to compare the results from all of the lab groups in the class.

How will you recognize results? What do you expect to have happen in each experiment?
Decide on what changes to look for during the experiment. What kinds of things will you keep track of during the experiment. How often will you check the experiment.

Make predictions about what you might see happening. List all of the possibilities your class suggests. Decide on how and when to record any data for the experiment.

Make a chart or table of your data.

Document all of the things you do with the experiment. Write the date and time when all observations and measurements are made.

List potential problems that could impact your experiment. Some things you can not control or measure, such as mass loss in an individual organism. You should list those things too.

You may use either rotifers or Tardigrades to study anhydrobiosis. Both of these organisms are microscopic and found world wide in watersheds. Rotifers are typically found filter feeding on smaller organisms living in ponds, lakes and shallow waters. Tardigrades are found living in moss growing on the bark of trees (except those in the dry valleys of Antarctica). They can also be found in alga mats in shallow ponds in the dry valleys of Antarctica. You may wish to find your own organisms or your teacher can supply them for you.

Elaboration (Polar Applications)
Discuss with students the evidence we have that organisms survive the Antarctic winters.

Have students read journal entries of Barb Schulz (http:// and read information on her rotifer research.
Rotifers were plentiful along the shores of Lake Hoare. We know that they survived the winter and reproduce in great numbers.

Exchange (Students Draw Conclusions)
Ask each lab group to:
List all of the things you know for sure about anhydrobiosis based on the results of your experimentation.
What additional questions do you have about anhydrobiosis?
What opinions do you have about the survival advantage of an organism with anhydrobiosos abilities?

Ask lab groups to share with the class:
Have several poster-sized pieces of paper ready to record results of the experimentation. Perhaps one or two students can assume the role of class recorders. Students can also document the discussion in their lab notebooks. What do you know for sure about anhydrobiosis?
What further experiments could you do to get more information?
Will your results help explain how the Antarctic organisms survive? Convince me!
Ask your own question about anhydrobiosis. Design an experiment to help answer your question. If you have time, set up your own experiment. Make sure you identify the variables and decide on what data to look for. Good Luck!

Evaluation (Assessing Student Performance)
Assessment: embedded in the procedure.


Authors
Barb Schulz
Lakeside School
Seattle, Washington


Background


Resources


Student Reproducible Masters

Student Procedure sheet #1 Day 1

Observation and drawing of Rotifers and Tardigrades.
Materials

  • microscope
  • slides
  • medicine dropper
  • drawing paper
  • lots of patience
  • colored pencils
  • supply of organisms in labeled containers
  • your own collection from which you will look for rotifers and Tardigrades.

Procedure

  1. Make a slide with either a rotifer or Tardigrade without a coverslip. Use one or two drops of water containing a rotifer. You will have to be quick with the dropper to catch it in the dropper.
  2. Observe the organism under 10x . Focus carefully remembering that your critter is alive and swimming around. Follow it ! : )
  3. Document an estimate of size, color and unique features that stand out to you.
  4. You may wish to look at the organism under high power. If so, you will need to use a coverslip and use care so as to not kill the critter with the pressure of the cover slip.
  5. Make a drawing of your organism. Use the diagrams to label only those parts that are clearly visible to you. Compare your organism with the examples provided. How similar are they?
  6. Observe some of the behavior and become familiar with what you consider normal. Use care so as to not kill the organism with too much heat from the microscope light.


Student Procedure Sheet #2 Day 2

Experimental design

Materials
Student recorder for each lab group
Student reporter for each lab group
Poster size paper to record ideas and a marker

Procedure

After class introduction, students meet in lab groups to discuss the kind of experiment they wish to do.

Students record experimental ideas.

Decide how long you wish to leave the organisms in the freezer.

How fast or slow should you cool the organisms?

How many organisms should you use?

Decide how much water to use when you expose the animal to the cold.

Record temperature at which experiments are conducted as well as conditions and locations.

Decide if you can use the winter outdoor environment where you live as a source of cold

Decide what variables may influence the results of the experiment if you don't control them.

Decide on what kind of data you want to record. What is important to keep track of?

Decide how much time you might need - day,or weeks, or months.

Decide on how to document your results. Decide on how you will recognize when an organism has used anhydrobiosis.

Share your ideas with the class and come to some agreement as to how the group will proceed.

Student Procedure Sheet #3 Day 3

Materials
Materials as needed and requested by students depending on their own experimental design.
Many of the same materials from day I plus containers , freezer capability and thermometers.

Procedure

  1. At this point you may want to do a web search on the internet to find a reasonable length of time to leave the organism in the freezer. Remember, you are now the scientist and need to make some decisions about your experiment. Use a search engine and search for either Rotifer or Tardigrade.
  2. Decide on how many organisms are needed for each experiment and how many times each experiment should be repeated. How many trials are necessary to know for sure that you have good evidence?
  3. Meet in lab groups and set up experiments. Be sure to document time, date, conditions of experiment and anything else that happens. Remember that many times, discoveries are made from informed mistakes. You are now the scientist and need to make some decisions about your experiment.
  4. Determine the time when the class will share data.

Analysis

Please review this activity.



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