how about a log for lunch?
by Susan Brooks and Sheveeta C. Bonner
I
t went by so fast, I didn’t get to see it!” This is a
common complaint middle school science students
make about their first experience looking at certain fast-moving protists with a compound light
microscope. Many students do not have the manual
dexterity to keep up with a fast-moving paramecium on
a microscope slide. The lowly termite, however, provides an easily observable microscopic endo-ecosystem
in an environment not usually considered by middle
school teachers. In the activity described here, students
examine the gut fauna of a termite in what is almost
guaranteed to be a successful experience viewing protists for the first time.
The termite-gut protists, which are all flagellates,
are large, slow, numerous, have many unusual features, and represent many different species that are
not difficult to distinguish. The organisms in the
termite gut are commonly so numerous that the entire field of view in the microscope will be filled with
protists. And the activity appeals to middle school students’ love of blood and guts.
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SCIENCE SCOPE
how about a log for lunch?
Student worksheet
Background information
Although termites are famous for their ability to eat wood, they
would starve if they did not have the organisms that you are
about to observe! In this activity, you will be observing symbiosis
in termites. Symbiosis means that two organisms are dependent
on each other. After you observe the organisms that live in the
termite digestive tract, you should decide what kind of symbiotic
relationship the termite and these microscopic organisms have.
Problem
How are termites able to digest the cellulose fiber found
in wood?
Safety equipment
Chemical splash goggles
Apron
Non-latex gloves
Materials
Please note: Teachers should review MSDS related to the
handling of Vaseline, saline, and bleach before preparation of
materials and before student use. Also, make sure students
do not have allergies to termites.
• termites
• slides
• probes (safety alert: sharp objects)
• forceps
• watch glass, Petri dish, or other similar container
• Vaseline
• plastic cover slips
• compound light microscope
• pipettes (Caution: No direct mouth suction!)
• insect saline (0.75% NaCl; equals 0.75 g NaCl in 100 mL
distilled water)
• diluted bleach solution (Bleach should be diluted by teacher.) Procedure
Before beginning the activity, all students in the lab must be
wearing chemical splash goggles and gloves.
1. Prepare the cover slip by dipping your little finger in the jar of
Vaseline to obtain a small amount. Scrape a small amount of
Vaseline from your little finger onto all edges of a cover slip
by holding the cover slip in one hand while gently scraping
downward with your little finger. Be careful to get only a small
strip of Vaseline (approximately 1 mm wide) around the edges
of the cover slip. Set aside the cover slip (Vaseline side up)
for later use. Caution: Glass cover slips have sharp edges
and crack easily—handle carefully to avoid cutting yourself!
[Alternatively, use plastic cover slips.]
2. Place a small drop of insect saline onto the microscope slide.
[Please note: Teachers may perform steps 3 and 4 if some
students and parents have concerns that students are
killing live animals.]
3. Using forceps (not your hands), place a termite into the watch
glass or Petri dish. Grasp the front end of the termite with the
forceps and press down on the end of the abdomen with the
probe. When the forceps and probe are pulled in opposite
directions, the termite’s thorax and abdomen will separate
and the contents of the digestive tract will spill out.
4. Drop several milliliters of insect saline quickly onto the termite
gut and mix the saline into the gut contents with the probe.
5. Transfer a few small drops of the saline mixture onto a
microscope slide and quickly cover with the previously
prepared cover slip. Termite-gut protozoa are anaerobic
(oxygen is poisonous to them); they will die upon prolonged
exposure to air. The Vaseline on the cover slip will prevent
exposure to air and will prolong the activity of the organisms
that you will observe.
6.Remove goggles and observe organisms on the slide with
the microscope. Record observations by counting the
number and kind of organisms present. Sketch at least
three different protists.
7. After you have completed your observations, put your
chemical splash goggles back on and carefully remove
the cover slips from the slides. Put the cover slips and the
slides into the labeled containers of bleach solution.
8.When you are finished, carefully wash your hands with
soap and water.
Answer the following questions
1. What do you think is the relationship between the termite and
the organisms that live in its gut (mutualism, commensalism,
or parasitism)? What is your evidence for this conclusion?
[Students may see small particles of wood in the cytoplasm of
certain of the larger protists in the termite gut.This might suggest
mutualism or parasitism.Accept whatever answer students give
that they can support with observational evidence.]
2. What type(s) of organisms did you observe? [Students may
see organisms that they may identify as ciliates, flagellates,
and amoeboid-type organisms. Depending on the microscopes
that you have available, they may be able to see bacteria.]
3.Devise a way that, if you had any kind of laboratory
equipment you needed, you could test whether the protozoa
are benefiting the termite. Imagine that you are a professor
at a university and you wanted to assign this project to your
students. How would you tell them to proceed?
F e b r u a r y 2 0 08
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how about a log for lunch?
But that’s not all! The termite itself provides an example of an organism from one of the major kingdoms,
and the organisms that populate the termite’s gut reveal
another kingdom of organisms, as well as another layer
of complexity. Termites and their gut fauna exhibit symbiosis, specifically mutualism. This mutualistic relationship can be used as an investigative inquiry tool.
Background information
and preparation
Before introducing this activity, the teacher should
familiarize students
with the operation and correct use of the
compound light
microscope.
(Safety note: If
microscopes have
electric light illumination for field of view, use only
cir cuits pr otected by ground fault circuit interrupters [GFCIs].)
Although most middle school science classrooms are
not equipped with fancy extras, if you should be lucky
enough to have mechanical stages on your microscopes, it will be easier to track the termite protozoa
or any other protists that students observe. (See
NSTA’s position statement, “Responsible Use of Live
Animals and Dissection in the Science Classroom” at
www.nsta.org/about/positions/animals.aspx and “Debugging Safely” at www.nsta.org/middleschool.)
Before beginning this activity, students should
be familiar with the definition of symbiosis and
the different types of symbiotic relationships. To
learn this vocabular y, Frayer models work well. A
Frayer model is a graphic organizer that includes
the vocabular y word, a definition of the word, a
description of the word, examples of the vocabular y word, and nonexamples of the vocabular y
word (Marzano, Pickering, and Pollock 2004).
Symbiosis describes the relationship between
two or more organisms. When both partners in
the relationship depend upon each other and
benefit from one another, the relationship is
termed mutualism. Should one par tner gain
an advantage, and the other partner is neither
harmed nor does it benefit from the presence of
the other, commensalism is used to describe the
relationship. In parasitism, only one of the symbiotic partners benefits, while the other partner
suffers. If one of the partners in symbiosis lives
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SCIENCE SCOPE
inside of the other partner’s body, the relationship is
called endosymbiosis. In ectosymbiosis, both partners
exist outside one another.
The termite and its gut fauna, which include bacteria
as well as protozoa, have a mutualistic relationship. Although termites are famous for their ability to eat wood,
causing damage to
wooden structures
and recycling cellulose in the soil,
they are unable to
digest the wood
that they eat. The
termite’s gut fauna
ar e r esponsible
for breaking down
wood cellulose for
the ter mite. The
protists and bacteria are, in turn,
provided a food source and place to live.
The protists in the termite gut are classified
as flagellates. Flagella are long, whip-like structures that extend out from the cell and move in an
undulating fashion. In some species, the flagellum
may be attached for part of its length along the cell
boundary forming a structure called an undulating
membrane. The flagella vary in number from one
to so many that the termite-gut protozoa actually more closely resemble ciliates than flagellates.
They may have one or two nuclei. In some species,
the posterior portion of the cell has an amorphous
shape reminiscent of an amoeba. There are other unusual cellular structures such as axostyles (stiffened
rod-like structures) and parabasal bodies (oval structures next to the bases of the flagella).
The scientific names of these organisms are
tongue twisters: Trichonympha campanula, Holomastigotes elongatum, Trichonympha agilis, and
Streblomastix strix. These names present a good
opportunity to discuss binomial nomenclature
and the derivation of some scientific names from
ancient languages such as Latin and Greek. My
own favorite is Saccinobaculus ambloaxostylus. The
genus name, Saccinobaculus, means, “stick in a
sack,” which is a wonderfully descriptive name for
the wild gyrations that this organism makes. For
examples of line drawings, see Jahn, Bovee, and
Jahn 1949; Kudo 1966; and Sleigh 1973. For photomicrographs, see Resources.
A good introduction to the scientific naming
of organisms in general, and microorganisms
in particular, is to provide students with some
how about a log for lunch?
simple Latin and Greek prefixes, suffixes, and root
words such as pod for foot, bi for two, stoma for
mouth, cyclo for circle, and plast for body, and ask
students to provide names for “stick” figures using
combinations of these words. For example, an organism consisting of a circular body with a mouth and
two feet could be named Cycloplast bipod.
This exercise will require 30 minutes of preparation
to set up the stations. Though it increases preparation
time, collecting your own termite samples makes this
a low-cost activity; termites may be captured in the
wild during warmer months. Try peeling bark from
rotting logs and look for termites crawling into tunnels
that have been made in the wood. Termites can also be
ordered from scientific supply houses. The other materials are commonly available in most middle school
science classrooms. See the student worksheet, which
outlines the activity procedure.
Safety precautions and extensions
Students should follow usual safety precautions when
working with glass (the microscope slides and cover
slips, if glass ones are used). Students should wear
disposable, nonlatex gloves and aprons when “dissecting” the termites, and chemical splash goggles
when preparing and cleaning the slides. Students
must wash their hands with soap and water after finishing the activity.
A possible extension that might answer the question
of the essential nature of the termite symbiotes to the
termite’s survival is to deprive the termite of its gut
organisms. The protozoa, but not the termite, can be
killed by (a) devising a chamber in which the termites
are exposed to 100% oxygen for 24 hours or more, or
(b) incubating termites at 36ºC, or (c) starving termites
for 6 to 10 days. Termites treated by any of the above
methods will starve to death, even if they eat large
quantities of wood; the food simply passes through
their bodies undigested. However, if they are fed the
feces or intestinal contents of untreated termites, they
become reinfected with flagellates and are able to regain their ability to digest wood.
Conclusion
Middle school students love this activity. They are very
excited to see under the microscope organisms that
they never suspected were there. Their speculations
on what the termite fauna are doing in the termite’s
gut provide a touchstone for discussion of symbiosis.
Students may be able to see small particles of wood
enclosed in the cytoplasm of the protists. However, this
is not conclusive evidence that the relationship is mu-
tualistic because, by seeming to compete for the same
food source, the protists may be thought to be parasitic.
These observations are not sufficient to lead to the
conclusion that, indeed, the relationship between the
termite and its gut fauna is mutualistic. Students may
also be asked to investigate similar relationships in the
human digestive tract.
The National Science Education Standards addressed in this activity include the abilities necessary
to do scientific inquiry and understandings about scientific inquiry, structure and function in living systems,
regulation and behavior, populations and ecosystems,
and diversity and adaptations of organisms. Through
this activity students have the opportunity to use tools
and instruments to observe, measure, and manipulate
materials in scientific activities. They are expected to
communicate scientific ideas and activities clearly, and
they examine the dependence of organisms on one another and on their environments. n
Acknowledgments
The authors wish to thank the late Dr. Jerome J. Paulin
of the University of Georgia, Dr. Steve Baker of the
Oxford Institute for Environmental Education at Emory
University at Oxford, and Dr. Nancy Devino of Agnes
Scott College.
References
Jahn, T.L., E.C. Bovee, and F.F. Jahn. 1949. How to know
the protozoa. Boston: WCB/McGraw-Hill.
Kudo, R.R. 1966. Protozoology. Springfield, IL: Charles
C. Thomas.
Marzano, R.J., D.J. Pickering, and J.E. Pollock. 2004.
Classroom instruction that works. Alexandria, VA:
ASCD.
Sleigh, M. 1973. The biology of protozoa. New York:
American Elsevier.
Resources
Termite gut symbionts—www.microscopy-uk.org.uk/mag/
wimsmall/termite.html
Glorious Guts—http://ebiomedia.com/gall/guts/guts1.
html
Susan Brooks ([email protected]) is a teacher
at Renfroe Middle School in Decatur, Georgia, and
Sheveeta C. Bonner ([email protected].
k12.ga.us) is a teacher at Shamrock Middle School
in Decatur, Georgia.
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