poster paper or transparency and vis-a-vis pens
Pre - activity set up
Order rotifers from a biological supply such as Carolina Biological Supply or Wards. Ask
for Bdeltoid rotifers. Make sure to order lots of rotifers. Students will use rotifers, one at
a time, however, they may unintentionally kill some rotifers and need to get more. Start
with ~100 rotifers.Your students may want to repeat their experiments several times. If
you worked with the anhydrobiosis experiments, this one follows nicely and can use the
same supply of rotifers. Order them once and get lots! If you find a ready local supply,
have students collect and bring them in. Expect variable results when rotifers come from a
wide variety of locations.
*Ordered cultures can be separated into petri dishes for each class doing the experiments.
Look at the rotifers and become familiar with the anatomy. The movement of the teeth
found within the visibly movable part called the mastex is an indication of feeding.
Tools and techniques (from the web site)
For serious work a stereo microscope and a good compound microscope are necessary.
Besides the usual slides, cover glasses, petri dishes, etc., one also needs at least a couple
of very fine wires or very fine insect pins attached to handles (I tape mine to the ends of
pencils or old pens). To form a scoop-like structure, flatten the free tip of the wire or the
pin by pounding on it with a hammer. This tool is used under a stereo microscope to pick
up and transfer a bdelloid rotifer from one culture to another or to a drop of water on a
slide. The use of a pipette to transfer an active bdelloid rotifer should be avoided, because,
usually the rotifer remains attached inside the pipette regardless of how many times and
how forcefully the pipette is filled and emptied. On the other hand, with some practice, one
can learn how to scoop up and transfer a bdelloid rotifer with a fine wire. Keep another
wire ready to dislodge a bdelloid rotifer should it attach itself to the first wire.
I have also had success using thin plastic tubing with a capillary tube or small pipette
inserted into one end. The capillary tubes or small pipette is heated until the glass is soft
followed by a qquick pull to form a tiny opening. It is then separated at the thinest point
and briefly fire polished to form a fine tiny opening. I then put one end of the fine plastic
tube in my mouth and ³hunt² the single rotifers under the stereo scope, suck them into the
pipette and blow them gently out onto a slide. this is not for students to do, but works well
if you are picking up lots of simgle rotifers during many weeks of research. The tiny
pipettes work fine if you are quick. :)
Prepare the rotifer food.
- Use regular yeast that is available in any grocery store. (I have used both cake yeast
and powder yeast.)
- Follow the directions on the package to get a good culture of yeast cells growing. I
usually start with 150 ml of water.
- Take a small amount of the yeast culture and heat to boiling in the microwave or on a
hot plate. The heating will break down the glyco-protein covering on the cells and allow
the dye to penetrate the cells.
- The add aceto-oricen stain. The yeast will become bright red and are easy to see.
- Make a slide and check for concentration of cells.
- You will probable have to dilute the cells for student use.
- Use care so as to not have so many cells that students can not possibly keep track of
feeding rates. Check the dillution before setting it out for your students.
When students actually begin their experimenting, encourage them to observe and count
feeding rates of only one organism at a time. Each student should have their own
microscope, however, they can work in pairs having one student observe and call out
information while the partner records the data. Encourage students to document everything
that happens and stress that PATIENCE is ESSENTIAL!
Log on to the web and read through the web site for Bdeltoid rotifers. The site has good
information and pictures of rotifer anatomy. If facilities permit, you may want students to
look at the site as well. The Bdeltoid rotifers are the ones with which I worked in Lake
Hoare. Also check out my journal pages for January 20 - 24, 1997 to see the kinds of
experiments that I did while in the dry valleys.
http://member.aol.com/bdelloid1/deloid.htm
Time Frame
- Engagement, Exploration, and Explanation; 2 class periods
- Exploration 2 class periods
- Sharing results 1-2 class periods
- Extensions can be at the discretion of the teacher. Some students may want more
individual time to explore other ideas.
Teaching Sequence
Engagement and Exploration ( teaching sequence)
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.
Ask students to share their ideas about food webs and food chains in their
local area. Then ask students to discuss in small groups what they think
might be part of the food web in the perennially ice covered Lake Hoare in
the Taylor Valley in the trans-antarctic mountains.
Ask students to consider the kinds and numbers of things living in a local lake. Then
compare the list to what they think might be in the Antarctic lake. Why might the
populations and bio-diversity be different? What are some possible causes for the
differences/ How big to you think the top organisms in the for chain are? How numerous
relative to the organisms supporting them?
Ask students whether eating rates make a difference? If so, how? Why?
How could you measure feeding rates?
Have students think about food availability. Does food availability influence population
sizes? Where does food come from in Lake Hoare? How could we find some answers to
these kinds of questions?
Have students read the Journal entries of Barb Schulz on January 20, 21,
22, 24, 1997.
These pages describe experiments done on feeding rates of Bdeltoid rotifers found along
the wet shores of lake Hoare where a small moat of melt water exists for a short time
during the austral (southern hemisphere) summer.. You might see some of the experiments
and experiences as well as some of the problems encountered by this researcher!
Let students see rotifers.
Students should make slides and observe rotifers for both anatomy, movement patterns and
possible feeding. Students should make accurate drawings of their rotifers. This
frequently takes an entire class period depending on students skill level with microscopes.
many students really like the rotifers and some even want to give their rotifers pet names!
Explanation (discussing)
Ask students to share observations of the rotifers.
Make a class list of what students have seen and what they know from observations. Ask
if anyone saw the rotifers eating? How can you tell? Tell students that they will be
supplyibg the rotifers with a supply of stained yeast cells as a food source. Students
should make a slide with a few yeast cells and be able to identify the yeast. The cells will
be tiny and bright red under 40x lens. As they become digested, a change in pH levels may
cause the yeast cells to become blue. See if students can see this change. Patience is
required. Steady observation is a must.
Ask students to design an experiment that would help scientists measure the
feeding rates of rotifers.
Work in small groups. Record your ideas both in your science notebook and have a group
reporter record on a transparency to use with the overhead projector as you share ideas with
the class. How can you tell if the rotifer eats ?
Ask students to list possible ways to conduct feeding experiments.
Identify variables that will need to be controlled. Students should agree on what makes a
good experiment. Each lab group could work on a different variable if you wish. Discuss
how many trials are necessary before you have enough evidence to make a statement about
rotifer feeding rates.
Ask students to come to agreement on how the class will conduct their
experiments before you begin.
Students can all do the same thing or each lab group
can vary the procedure they develop. Be aware that the microscope light will heat up the
animals and may influence the feeding. Consider the amount of daylight exposure as well.
Elaboration
Allow students to work on their experiments. Offer suggestions and ask them questions.
Provide the stained yeast as a food source to start with.
Have students:
- think about temperature
- think about edible things that might already be in the water that that rotifers might eat
- think about when rotifers might get hungry
- think about the chlorine in tap water (make distilled water available)
- possibly provide lake water and sterilize in a pressure cooker or autoclave
- think about when the rotifers reproduce and how that might influence the feeding rates
- think about light and how that might influence feeding rates, etc
Try not to tell them how they should do the experiment. Perhaps a student lab group will
creatively design a useful technique to measure feeding rates and thereby make a
contribution to the ongoing studies of ecosystems. See student data sheets and procedure
sheets at the end of this document.
Evaluation
Students should collect and analyze their data. What to they know for sure? Finding what
does not work is as good as finding what does work. It is important to stress this aspect of
experimentation. This is not an exercise in rediscovering what we already know. This is
an activity that can help the scientific community discover a way to measure and collect
data that is significant in the energy relationships of the ecosystem being studied. Scientists
must figure out ways to solve problems. Here is the chance to do real science.
Students should present their methods and data to the class. Collectively the class should
decide what they have discovered.
Author
Barbara Schulz
Biology Teacher, Lakeside School
Seattle, WA
Background
History
Among those who have studied bdelloid rotifers, the Scottish naturalist James Murray
(1865-1914) deserves special mention. He started his professional carrier as a sculptor, but
moved to natural history in his early 30s (Greaves, 1996). Although Murray had not had
any formal training as a biologist, he quickly became an expert in the study of
microscopic organisms. In a relatively short span of 11 years, Murray described a large
number of new species of bdelloid rotifers from locations around the world he visited
during various expeditions, including Great Britain, Antarctica, New Zealand, Australia,
Hawaii, South America, Canada and Africa. He spent more than a year in Antarctica with
Ernest Shackleton's expedition. Murray apparently continued working even under the most
adverse physical conditions. For example, in his report of the rotifers of Canada (Murray,
1911), which he crossed by train on the way back from Antarctica, Murray complained that
"the train did not offer great facilities for microscoping, the Microscope having to stand on
a yielding cushioned seat." Nevertheless, he recorded 42 species of bdelloid rotifers,
including 5 new ones, from Canada. Murray also studied monogonont rotifers and
tardigrades. He knew David Bryce and the two often consulted each other on rotifer
matters. Murray and several others were tragically killed while attempting to reach the land
from their icebound ship during Vilhjalmur Stefansson's ill-fated expedition to the
Arctic.
Resources
http://member.aol.com/bdelloid1/deloid.htm
"If we use excessively elaborate apparatus to examine simple natural phenomena Nature
herself may escape us."
Karl von Frisch, preface to The Dancing Bees, 1953
"People who have never tried to fathom the mysteries of the bottom of brook or pond are to
be pitied."
Anna Botsford Comstock, Handbook of Nature Study, 1939
Student handout pages on following pages.
Bdeltoid Rotifer Observation
Materials
- microscope
- slides
- coverslips
- drawing paper and pencils
- medicine dropper
Procedure
- Get materials
- Make a slide without a coverslip first.
- Look at the slide only under 10x if there is no coverslip.
- Watch and follow the rotifer by moving the slide around
- Draw a rotifer with as much detail as you can.
- Write a brief description of the behavior you see
- Share your results with your lab group
Experimental Design
Rotifer feeding rates
Methods: record how you plan to make the slides and collect data.
Variables
List variables that you will control such as
- the kind of water used
- how many drops of water you use
- how much food you use in drops on the slide
- approximently how many yeast cells per drop
- how long you leave the slide under the microscope exposed to the light
- temperature
- time of day data is collected
Results
- Write what you see and what happened with each slide that you make!
- Documentation of what you do is very important!!
- Give numbers when ever possible
- Document any change in conditions from one slide to another
- write down any questions that come to mind while you do your experiments
- share ideas with your lab partners
- draw findings if you think it will help clarify what you see
Analysis
- Organize your information with your lab partners
- create a data table that is useful for the whole lab group
- collaborate and discuss what each of you found
Collaborate
