SUBJECT: Plants and animals for cell labs, esp. osmosis
DATE: 4/96
Does anybody know of a good substitute for Elodea in cell labs? Washington
state has banned the import of Elodea so our supply is running out. They
are
afraid of it becoming an invasive exotic in WA lakes and streams.
Thanks.
Carol T. Burton
Science Division
Bellevue Community College
Bellevue, WA 98007
cburton@bcc.ctc.edu
If you are using the elodea to demonstrate osmosis or cell structure - red
onion cells are a good substitute.
Ruth E. Beattie
Biological Sciences
University of Kentucky
Hi:
Although I've only used them for examination purposes (vs. various
experiments), I've found that common aquarium plants work fine. I've always
just purchased them from pet stores, where they're usually both cheap and
abundant.
Good luck!
Kerry Kilburn
ODU Biological Sciences
Depending on your prior use of Elodea, Mnium might be a good substitute.
This moss has large cells and was once used more commonly for
demonstrating cellular things. One can see cytoplasmic streaming, and
there is no problem with obtaining an epidermal peel since it is already
one cell thick. I have not tried an osmosis demo with it - mosses can
sometimes stubbornly refuse to plasmolyse, but as I recall, Mnium is not
one of the recalcitrant ones. Mnium seems also to repel
water and is difficult to rewet quickly, perhaps because it is "vascular"
and transports much of its water. It has a habit of trapping air bubbles
that keep the water from contacting much of the leaf, and I suspect it may
have a thin cuticle.
We have had good luck in demonstrating osmosis with earth worms, a
suggestion I got from this net last fall. By using a series of salt
concentrations, we could determine the % salt in the worm - the
concentration at which it neither gained nor lost weight.
You might also want to consider something like Spirogyra. Some of the
desmids (Closterium) are great for demonstrating brownian movement.
Janice
***********************************
Janice M. Glime, Professor
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime@mtu.edu
906-487-2546
FAX 906-487-3167
We use a method to demonstrate osmosis with deshelled chicken eggs,
immersed in various concentrations of sucrose. Eggs are deshelled with an
acetic acid solution then rinsed and equilibrated in 20% sucrose (isotonic)
for 24 hours. Students then immerse the eggs (gently!) in various
concentrations of sucrose (10%, 20%, 30% and 40% - often I include an
unknown and have them figure out the %) and weigh them at 15 minute
intervals for 1.5 hours (can be less). They can then determine which
solutions were hypo, hyper and isotonic to the cell (egg). Works really
well, very reliable as long as they handle the eggs gently! Also involves
some graphing skills and math skills by determining % change in weight.
I'd
be glad to send copies to anyone who is interested.
Robin Patterson
Butler County Community College
Butler, PA 16003
4gmen@nauticom.net
Another possibility with eggs is the removal of part of the
eggshell at one end and the insertion of a glass tube at the
other. (Shades of the osmotic carrot that never worked for
me.)
Two kinds of glue are needed: superglue and silicone
caulking.
A drop of superglue will fix one end of the egg to one end
of a short piece of dowel (best if slightly concave). Once
set and firmly grasped, the dowel will pull of a patch of
shell (whose calcite crystals, I'm told, are wedge-shaped
like the stones in a Roman arch: difficult to collapse from
above, but easy to disrupt from within, or with a good pull
once you have a good grip). The amount of exposed embryonic
membrane can be increase by careful work with a pair of dull
forceps.
Once the hole is made in the other end of the egg--and
through the membrane beneath--a glass rod can be inserted
and sealed with aquarium sealant (silicone calking). If the
end of the glass tube is fortunately placed, when osmosis
begins in earnest it will be the bright yellow of the yolk
that makes it dramatically evident.
I usually support the egg from below on the rim of a small
beaker set inside a larger beaker, both of which are filled
with distilled water. A standard pipette holder supports
the glass rod.
Michael Bucher
College of San Mateo
bucher@smcccd.cc.ca.us
Hi Biolabbers,
Osmosis using decalcified eggs is a marvellous model for helping students
learn the value of properly controlled experiments. I use the article by
Barbara Cocanour and Alease Bruce in the Journal of College Science
Teaching, vol 15, pp127-130, 1985 as reference for my students.
Interestingly enough, we can never exactly replicate their experiments,
which leads us into a secondary round of experiments to determine what the
source of the discrepancy might be.
Bill Mullin
Director of Undergraduate Studies
Department of Biology, University of New Brunswick,
FREDERICTON, N.B., CANADA, E3B 6E1
tel:506-453-4594 fax:506-453-3583 e-mail: bmullin@unb.ca
Hi Biolabbers,
I've also used the egg to demonstrate osmosis, only I used vinegar
to decalcify the egg and corn syrup as the sugar solution. (I used this
experiment in a junior high where materials were not readily available)
I
found that the experiment works best if you use large eggs that are not
fresh! The fresh eggs would burst before we could get them into the corn
syrup. ( The older the egg, the looser the egg membrane.) This experiment
used to take several days. I had to leave the egg in the vinegar overnight.
I assume that the acetic acid concentration that you are using is higher
than that of vinegar. Can this experiment be run in a three hour lab?
I love these experiments, which I call Mac Guyver science. The
extraction of DNA using Woolite has become one of my favorites. These
experiments allow educators to demonstrate difficult concepts to all
levels, with the added benefit that the experiments can be performed using
items from home. With budget cuts, poor school systems, etc. these
experiments are wonderful. Just felt like adding my two cents.
Kirsten Mahovlich
Lab Tech
University of Toledo
I'm kind of surprised at the lab which uses earthworms to demonstrate
osmosis. The most memorable (as in nightmare) lab I ever did as a
student involved injecting frogs with various solutions to
demonstrate osmosis. For this reason, I only use red blood cells,
Elodea, or dialysis tubing to demonstrate osmosis. I'm surprised that
students don't object to the use of earthworms in this lab.
Carol Morris <MORRISC@sunytccc.edu>
Carol Morris wrote to say that her most "....most memorable experience
(as in nightmare)..." for a lab was using frogs to demonstrate osmosis.
She went on to say that she only uses Elodea, blood cells and dialysis
tubing to demonstrate osmosis ".... for this reasons...".
She said that she is surprised that students don't object to the use of
earthworms.
We need to respect student sensitivity. However, we also need to provide
some level of teaching into the nature of whole animal models for research
and demonstration. And perhaps it's not beyond our abilities to help
students come to grips with the notion of levels of sentience, and with
what constitutes a stimulus of what type for different kinds of organisms.
I'm not advocating that we have TA's teach students to pith frogs with
such insensitive statements as a TA I once worked with who said
"....scramble his brains -- then he won't feel sh__." But I have
found
that some level of sensitivity in explaining the nature of a demonstration
and respect for the students concerns has led to greater understanding and
respect on the part of the student for the value of whole animal models.
Just my contribution for what it's worth :-).
Dave McNeely, Biology, University of Texas at Brownsville, 80 Fort Brown,
Brownsville, TX 78520; mcneely@utb.edu
Dear Biolabbers,
Carol Morris raised an important question when she suggested that using
worms to examine osmosis was cruel. I am assuming that there is a
certain range of tolerance for the worms, but I have asked my students
who are designing this lab to tell me if the worms live and how they
behave in the experiments. I agree that we should not do an experiment
that demonstrates cruelty to an animal with a nervous system if something
else that is not cruel will accomplish the objective as well. I will
report on our results.
Thank you, Carol, for reminding me of something I should have thought
about myself.
Janice
***********************************
Janice M. Glime, Professor
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime@mtu.edu
906-487-2546
FAX 906-487-3167
***********************************
I don't know if my original post on this question reached biolab or not,
since I never received it from biolab myself. Janice Glime is correct that
Carol Morris raised an important question about "cruelty," but
there are
many questions embedded in the question of "cruelty" that are
not
addressed by raising the question.
Students today often are quick to recognize "cruelty", often when
it
exists or potentially exists, and often when it is not a factor or not
potentially a factor.
Janice is right that when "cruelty" is inflicted by a procedure
or a
protocol and some "non-cruel" alternative serves the purpose (demonstration,
data collection and so on as well, then the "cruelty" should be
avoided.
But students today are often quick to reject use of whole animal models,
without a basis for such rejection. Use of an earthworm, not known to be
sentient but certainly with a nervous system (to my knowledge all animals
have some means of receiving and integrating stimuli) may serve as a basis
for discussion of levels of sentiency, complexity of organization and
integration, and the values of whole animal models in study and research.
Certainly in a freshman course, when the purpose of the osmosis demonstration
is to illustrate the mechanism and give students experience at collecting
and
interpreting data a whole animal model is unnecessary. But I resist now,
as I have in the past and will continue to in the future, the notion that
we should necessarily reject whole animal models for teaching and especially
for research. Students must learn how to properly use whole animal models.
Some "animal rights" groups advocate (and sometimes insistently
so) complete
elemination of not only whole animal models for demonstration and research,
but even elemination of dissections because animals were killed so that
students might learn. Please deliver me from such an anti-intellectual
atmosphere, and let me get on with my job, while not needlessly killing
and not needlessly inflicting suffering.
Good day,
Dave McNeely, Associate Professor of Biology, University of Texas at
Brownsville, 80 Fort Brown, Brownsville, TX 78520; mcneely@utb.edu
I think there is a time and place for whole animal models in biology
instruction. For the last three years I've taught both 1st semester
freshmen and jr/sr level labs. I have found that many of the labs that
freshman do with animal models are illustrations of well-established
biological principles such as the compound action potential, and the
classic frog gastocnemius muscle experiment. While these experiments work
well, I have been systematically eliminating them from the freshman
curriculum. I feel that the principles illustrated may be learned just as
well in a lecture setting. The cost of removing enough frogs from the
environment to run these labs for 500 students doesn't exceed the benefit
to the students for me. We do use some animal models in behavioral
studies, but nothing is "hurt".
I think is *is* appropriate for students to gain some direct experience
with and appreciation for whole animal systems in the upper level courses.
I teach a 500 level animal physiology lab that primarily uses the rat as
the experimental animal. Most of my students are pre-professional or wish
to go to grad school. We do one entire lab on anesthesia and catheter
placemnt techniques. The students are careful to keep their animal
appropriately anesthetized. Reaction to this lab has been very positive
from the student perspective. This year one of my students applied for a
lab tech position at another university and was thrilled to be able to
check off many items on their animal related skills check-sheet. I do
spend some time talking with them the first day about animal use as a
privilege and one that entails certain responsibilities on their part. We
run enough animal labs so that each student must do duty as anesthetist,
surgeon, and assistant surgeons on given days.
Mary H. Gray D.V.M.
Department of Biological Sciences
Lilly Hall of Life Science
Purdue University
West Lafayette, IN 47907
(317)-494-8185
FAX (317)-494-0876
Dear Biolabbers,
I asked my students about the effects of the salt solution on the worms
and whether we may be killing them or traumatizing them. Since
nature is likely to provide differing salt concentrations over the
course of an earthworm's life, I felt there was room for some
degree of experimentation.
Following the greater than signs is their answer, and my conclusion is
that the experiment is non-harmful as we have designed it. We need to
caution the students to be careful with their solutions, but that problem
should be minimized by pre-mixed solutions.
I think it is important for students to see that we can experiment with
live animals in a non-harmful way to learn about those animals, and
sometimes for the very purpose of being able to protect greater numbers
of them. Does anyone see any problems with this osmosis
experiment from an ethical point of view, with freshmen biology majors?
> > > >
> Janice, > The only time the worms seemed to be traumatized by the
salt
> > solutions was when the concentrations were about 5% or above.
the
> > solutions we're using in this lab are only up to 2% at the strongest.
I
> > don't think that the worms are really affected by these concentrations
too
> > much, especially since we only plan to leave them in solution
for more
> > than a half hour to 45 minutes, max. Does this help any?
> >
> > Laura
> >
> ***********************************
> Janice M. Glime, Professor
> Department of Biological Sciences
> Michigan Technological University
> Houghton, MI 49931-1295
> jmglime@mtu.edu
> 906-487-2546
> FAX 906-487-3167
> ***********************************
There is a reference (including a diagram) in the 1958 version of "A
Sourcebook for the Biological Sciences" by Morholt, Brandwein, and
Joseph (second edition; third edition has it also; does first?) of the
osmosis with eggs demonstration. They creidt Amy Applegate of Bloom
Township High School, Chicago Heights, Ill. for the idea. Anyone want to
make a bet that even Amy got her idea from someone else? The idea has
certainly been around a long time. Like most laboratory activities, it
might be extrememly difficult to determine who actually originated the
idea. If we go back in old lab manuals and the like we find most
demonstrations are actually quite old.
***************************************************************
Louise Baxter email: baxterl@cwu.edu
Department of Biological Sciences phone: 509-963-2745
Central Washington University fax: 509-963-2730
Ellensburg, WA 98926
Sheryl Shanholtzer gave credit for this experiment to " Dr. Marsha
Fanning of Lenoir-Rhyne College in N.C. She presented it as a
mini-workshop at the 1988 meeting of ABLE. At that time abstracts of the
mini-workshops were not published so credit for them has been lost with
time. She deserves credit as well as the ABLE workshops. "
I was a public school teacher from 1982 to 1994, and I used this lab in
several forms, including the one cited. It comes from an old "magic"
trick
of deshelling the egg, placing it in Karo syrup to shrink it, putting it
in
a small--mouth jar or bottle, rehydrating it with distilled water, and
asking your friends how you got the egg in the bottle (if you do it
carefully, you cannot tell that there's no shell on the egg). I saw
several versions given as workshops at various teacher conferences during
these years, and even gave a couple myself, based on things I did with my
students in this lab.
I suspect the origins are far older than any of us.
JodyLee Estrada Duek jduek@u.arizona.edu
Faculty Development Specialist 520/626-2203
Division of Academic Resources 520/626-6707
U. of Arizona School of Medicine 520/626-4879 (fax)
1501 N. Campbell Avenue
Tucson, Arizona 85724-5120