SUBJECT: Changing verification labs, especially those on food molecules
DATE: 2/96
I just subscribed to biolab and was suprised to see a discussion about
benedicts solution since I just got done doing a lab today with it. I am
an ecologist and we have just recently changed our general biology class
such that I am now teaching the cellular molecular stuff which is new to
me. I have relied on past expeiments that other faculty members have done
and this was one. My question is, how do you make a lab interesting
testing for proteins, carbs, fats? I found the lab boring and
just veification of what we already know. Eg. "Iodine turns starch
blue.
Put some in a potato solution andrecord your result".
I have really tried to steer away from what I call verification labs and
try to test hypotheses by designing real experiments for which I truly do
not know the results. I have been quite successful at this for
ecologically oriented labs, but now I have to do this for all levels of
biological inquiry. Forgive me if I offend anyone but most of the
standard lab manuals I have looked at are not worth much. they are full
of demonstration labs.I want the students to learn to do real science and
not just look at demonstations of what we already know! Any suggestions
for good labs on the cellular molecular level would be most appreciated.
Thanks,
Mark Brenner
Warren Wilson College
PO Box 9000
Asheville, NC 28815-9000
(704) 298-3325 ext 366
brenner@warren-wilson.edu
Mark,
I do a foods lab that I used first with high school kids in Bioathlon
competition. My general botany students seem to enjoy it. First, we give
each group of four students an envelope with some brief instructions that
they must discover how to determine the starch and sugar content of the
foods we will present to them. We have reduced the number to 12 as I
recall. The foods are numbered and set out in separate weighing pans as
a
set for each group of students. The students are also provided with
labelled bottles containing Benedicts solution, I2KI, starch, and table
sugar. There is a hot plate on the table, boiling water, test tube
holders, test tubes, test tube rack, and knife or spoon. There is a
variety of foods high in starches or sugars or both or neither that we
have tested ahead of time. The students are given 30 minutes in which to
devise a test for each, carry it out on each food, clean up, list all the
contents for each on a chart, and draw a conclusion. We also ask them to
list the plant part or parts they tested. We then score these and assign
points. The group with the most points in each lab gets bonus points for
the course, and the best score in all the labs gets an additional bonus.
As I recall, each bonus is 10 points. It is fun to watch the students try
to figure out what to do, and some get most of the way through before they
realize they don't have to boil the iodine. Others never figure out they
need to heat the benedicts.
The high school students were more fun. Some put starch, iodine, sugar,
and benedicts all into one test tube with the food, then didn't know what
to do next. When we suggested that they could try again, they did the
same thing again. The college students do much better, and many of them
remember the iodine test, but few if any have ever done a benedicts test.
I first did these tests in an ecology course to determine what some
animal had eaten. You could take an ecological approach, although with
all the restrictions, that is a bit cumbersome.
Following the contest, the students test for vitamin C and protein,
using foods of their choice from an array. They compare cooked and
uncooked, canned, fresh, or frozen, or whatever they choose. We even
provide some algae just for fun, and I think we should add mushrooms,
since most don't have a clue what is in them. ( I don't know what they
have among these choices.)
Janice
***********************************
Janice M. Glime
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime@mtu.edu
906-487-2546
FAX 906-487-3167
***********************************
The students do need to know (1) how we test for the presence of certain
molecules and (2) why we would want to do such tests.
Janice Glime provided an example of putting these tests in context for the
students. I would like to add some of the labs we do to meet these two
objectives:
1. Testing for digestive enzymes in insect organs. E.g., if the crop is
isolated
and mixed with start, does it possess the enzymes to digest starch? Students
must test for the presence of starch...and they are learning about enzymes
and
digestive systems.
2. Testing for cell culture products made in a bioreactor. E.G., students
separate fractions in column chromatography and look for presence of enzymes
such as amylase.
3. Student's test their own saliva for amylase; they test the action of
pepsin;
they look for carbos, proteins, and fats in foods. (nonmajors lab)
4. I assume that this is an early lab in the semester so students are learning
some techniques and reference tests for future use. If this is the desired
goal
then spice up the labs with unknowns. How do we know whether a product contains
a certain amino acid....paper chromatography. And they students could have
an
unknown consisting of two amino acids they must identify. This can be done
with
carbos too. Everyone enjoys the hunt of an unknown.
Christine Case
Skyline College
case@smcccd.cc.ca.us
We also teach these methods because they are useful tools of botanical
study. But, we couple them with investigative labs where the tools can be
employed to get answers. What can possibly be more boring than learning
techniques without applying them! For example, we use the starch test as
an
indirect measure of photosynthetic activity in a standard experiment to
ascertain the action spectrum of photosynthesis. Leaves of bean plants held
for a full day in total darkness can then be masked with certain portions
exposed to light (we use fiber optics to get enough intensity) filtered
through different colored cellophanes (of known wavelength trasmittance,
or
you can measure it). Starch will be deposited at the site of
photosynthesis in varying amounts depending on the wavelength used. You
can
then develop the results by boiling the excised leaf in water, followed
by
boiling in 95% ethanol, and finally cold ethanol. You can then rehydrate
the leaf, spread it out and flood it with iodine solution. Most of the leaf
will lack starch,but those areas exposed to light will stain nicely.
We use this approach in most of labs - teach techniques and skills you want
the students to have, then have them design experiments geared to use those
techniques in meaningful way.
Good luck!
Greg Anderson
Department of Biology
44 Campus Ave.
Bates College
Lewiston, ME 04240
ganderso@bates.edu
(207)786-6110
Followinig up the starch/amylase thread, there are really neat
tests for the ability of bacteria to digest starch. Basically
you make agar media containing some starch, spread isolates of
bacteria on it and let them grow, then flood the plate with
iodine solution - Gram's iodine works fine. Bacteria that
digest starch produce a dramatic clearing of the blue stain
around their growth. If they make an extracellular enzyme,
there is a wide zone of clearing, if the enzyme is
cell-associated then only the bacterial colonies or streak are
cleared. Most microbiology lab manuals have this test, take
your pick.
You can also do enrichment cultures for bacteria that grow on
starch, by inoculating mineral media that contains starch as the
carbon source with soil or whatever. Again this is in most
manuals. An ecologist should have no difficulty making this
type of exploration interesting.
Another thought comes from my beer-making days... The reason you
have to use malt and not just grain is that the starch has to be
digested by the grain itself before the yeast can use it. You
can buy ready-made malt, and it could be a barrel of fun for
students to figure out how to do the malting themselves, testing
for starch content, sugar, amylase, and the ability to support
growth of yeast or bacteria that are known to digest starch or
not (see above). Enough for now.
----------------------------------------------------------------------
Walter Ogston ogston@hobbes.kzoo.edu
Department of Biology Phone: (616)337-7010
Kalamazoo College Fax: (616)337-7251
Kalamazoo, MI 49006-3295
I've found that the Bacillus work the best for this type of expieriment.
Especially B. cereus.
Kirsten
Lab tech
University of Toledo
kmahovl@uoft02.utoledo.edu
Along with what Walter Ogston said...
The Plant Physiology lab manual by Cleon Ross has a experiment on amylase
release in barley seeds using the same type of starch-agar assay with halved
seeds. Variables suggested in the lab manual include presence or absence
of
embryo, GA3, and cycloheximide. I have a mid-70's edition of this manual
(from
Wadsworth) but I assume it's still going if the Salisbury/Ross textbook
is.
From: "Jean Dickey" <Jean_Dickey@quickmail.clemson.edu>
On how to make the molecular tests interesting -
I had my non majors students bring in foods from home. They had to make
hypotheses and predictions about what they thought was in the food before
they did the test. It was interesting to hear what they thought was in
their foods. I was not concerned with them knowing the specifics of each
test, but with the idea that they felt some ownership of the activity,
practiced critical thinking, and learned something about a food they ate.
Stacey
******************************************************************
@ Stacey Kiser
@ Research Assistant
@ Workshop Biology
@ Department of Biology
@ 1210 University of Oregon
@ Eugene, OR 97403-1210
@ phone (503) 346-5092
@ fax (503) 346-6056 from
There's nothing wrong with having students verify a few
known facts- after all, they need to see that what they learn
in class is based on data and not authority. Let them see
things with their own eyes even if you've already seen it 100
times.
The bacterial starch hydrolysis and examination of insect
digestion are great ideas for letting students take a basic
skill and then use it to go further. Another experiment we
do is to have them make a dialysis bag full of starch/
glucose solution- with the basic tests students can track what diffuses
out and what is trapped inside and learn something about size exclusion.
We need to keep basic concepts in mind when we plan
these activities. I generally have students use the Benedict's
and IKI tests on a set of mono- and disaccharides and then
starch. Nothing unusual here. But have them examine the
results in the light of the concepts of polymers and
monomers- note how the properties change as you increase
in size. Then spit in some starch and see it act like a sugar-
the polymer can be chopped up into monomers.
We follow that up in later weeks with labs on
macromolecules, including "weighing" proteins with SDS
gels and building wire models of proteins. They don't
discover anything "new", but hopefully by the time we work
with enzymes they have a picture in their heads of big
polymeric proteins that really can grab substrate molecules
and can relate that picture and the abstract concepts to
some lab work they did with their own hands.
John Dickerman
Northern Illinois University
DeKalb, IL 60115
T80JWD1@WPO.CSO.NIU.EDU
Mark.
You should check out "Laboratory Investigations for Biology" by
Jean Dickey published by Benjamin/Cummings. It isn't your standard
label-and-learn variety manual. It certainly opened my eyes to new
possibilities.
Sometimes you need to do some very fundamental exercises in order
to build towards a goal of independent investigation or to reinforce
concepts. For example, I believe that students have to look at a cell at
some point. They need to see it, observe it, and think about it as the
fundamental unit of life. It is fundamental, observational, and
predictable. (Except for the occassional pond scum I can't identify, I
know what will happen.)
I believe that if you talk to anyone who has responded on the
evaluation of laboratory exercises thread they will tell you that it is
the
presentation of the material that makes all the difference. If you tell
students to do these three steps and obtain this product and then grade
them on that product, they will be bored, you will be bored, and they will
work hard (honestly or otherwise) to obtain that product. Not much
learning will occur You can do the same experiment with the same materials
and the same protocol and still challenge the students to think and to be
active participants in their own learning. Janice's description of the
design your own test for sugar and starch is a great example. (Thanks
again Janice).
You need to decide what message you want to convey in each lab and
then focus on getting that message across to the students. Is the purpose
of the lab to support a lecture concept? Introduce a technique? Design
and implement an experiment? All of the above? We too do the "food
lab".
We focus on experimental design and nutrition. Our dual message is that
macromolecules exist in your real life and that controlled experiments are
very important. This is the first wet lab of the semester. The students
have already been exposed to scientific method and experimental design.
Students learn to use the reagents to identify macromolecules in the
context of positive and negative controls. They choose a food sample, make
a hypothesis about what macromolecules it contains (we usually include beer
and diet soda). They test the unknowns and then use that information to
try to identify the proper nutrition label for the food. Some TA's run it
as a competition to see who can identify the proper label first. From here
we also go onto the "enzyme lab" where students use the techniques
they
learned in the "food lab" to design an experiment to test factors
that
affect the activity of alpha amylase.
By the way, I've moved in the opposite direction from the
cell/molecular to the ecol/env. sci. I'd love trade ideas. --cmw
From: cwaggon@bgnet.bgsu.edu (Waggoner, Charlene)
Charlene wrote:
>...If you tell
>students to do these three steps and obtain this product and then grade
>them on that product, they will be bored, you will be bored, and they
will
>work hard (honestly or otherwise) to obtain that product. Not much
>learning will occur You can do the same experiment with the same
>materials...etc.
But aren't we getting back to evaluating the learning experience? Isn't
looking into a lab book to see if the student has the "product"
(the right
answer in the right blank) easier to evaluate than trying to measure how
broad their smile becomes when the "ah-ha!" of true discovery
takes place?
Of course, Charlene is right. The lab experience is more important than
the
answers; the problem solving process is more important than the problem.
But how do you measure it accurately, fairly, and consistantly? Aren't we
as science teachers, trying to quantify (by giving a grade) the creative
experience of scientific investivation?
For those of us with one quarter (or semester) introductory courses-courses
I would call "Biology Appreciation"-is there really time to culture
the art
of investigation? If we are educating majors and maybe another Jonas Salk,
we need to cultivate research techniques. What is our obligation to the
rest?
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
ED BURLING
DeAnza College
E-mail: eb04124@tiptoe.fhda.edu
Tel: (408) 864-8625
Cupertino, CA 94014
John Dickerman (T80JWD1@WPO.CSO.NIU.EDU) says
>
> There's nothing wrong with having students verify a few
> known facts- after all, they need to see that what they learn
> in class is based on data and not authority. Let them see
> things with their own eyes even if you've already seen it 100
> times.
>
Indeed I agree. I find in microbiology the students get very
interested in confirming known results when they have tested an
unknown and are not sure how to interpret the results. For
instance after they have tried to Gram stain some unknown (to me
too) they eagerly get to work on "genuine" E coli and Bacillus
so they know what it "ought" to look like. The same approach
can be used to introduce known sources of amylase, and so on.
>From here the idea of experimental controls flows naturally.
----------------------------------------------------------------------
Walter Ogston ogston@hobbes.kzoo.edu
Department of Biology Phone: (616)337-7010
Kalamazoo College Fax: (616)337-7251
Kalamazoo, MI 49006-3295
John,
Thanks for the suggestions on starch/sugar labs. I agree that some
verifications of known facts are ok. My problem is that most lab manuals
have nothing but this type. I find students are always exposed to labs
where we know what the answer is and they come away with the impression
that scientists always know the answers before doing experiments. I
think they need to learn that the reason we do experiments is to answer
questions to which we do not know the answer. This leads to behavior like
I saw in this lab we just finished in which students kept asking me What
are we supposed to see? It also leads to the problem that if a hypothesis
is not suppported they think it is a failed experiment, even when it
conclusively answers a question. I find students recording data of what
they are supposed to see (because that's what it says in the book) rather
than what they actually see.
Mark Brenner
Warren Wilson College
PO Box 9000
Asheville, NC 28815-9000
(704) 298-3325 ext 366
e-mail: brenner@warren-wilson.edu
Mark Brenner wrote:
<< I find students are always exposed to labs where we know what the
answer is and they come away with the impression that scientists always
know the answers before doing experiments. I think they need to learn that
the reason we do experiments is to answer questions to which we do not know
the answer. This leads to behavior like I saw in this lab we just finished
in which students kept asking me What are we supposed to see? >>
Of course that's the big problem- students are so
conditioned by tests and quizzes to look for the "right"
answer that they are very timid in the lab. A related
phenomenon is the classic lab report where the conclusion
consists of a list of reasons/excuses for why the experiment
didn't work the way they expected. I'm not sure how
we can teach them to do reliable lab work without a little
of that. I recall a stint with a company doing enzyme R&D
where I had to first show I could accurately perform assays
on old products before they'd let me do any "real" research.
You can't look for answers until you have some techniques
down. I think Walter Ogston's comment about using this
situation to show the importance of controls is a pretty good
way to balance verification with using unknowns.
John Dickerman
Northern Illinois University
DeKalb, IL 60115
T80JWD1@WPO.CSO.NIU.EDU
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