Symbiosis-Honors
Mutualism describes a type of symbiotic relationship between two organisms where both are
dependant upon one another to survive. The relationship allows each access to resources which would be
otherwise limited or unavailable.
A. Fruticose Lichen
Lichens are a successful alliance between a fungus and an algae. As a decomposer, the fungus has access
to nitrogen, needed to build molecules. Algae are photosynthetic, therefore providing the means to
convert energy to a usable organic form. Together they inhabit niches unavailable to either on their own.
1. Using a stereoscope (dissecting) microscope, focus on a section of lichen. This type of lichen has a
central core of fungus, around which the alga is wrapped.
2. Diagram (draw and label) the green algal cells and the grey hair-like hyphae cells of the fungi.
3. Tear off a small piece of lichen and place it on a microscope slide. Using dissecting needles pull it
apart until you have pieces too small to continue to break down. Add a drop of water and a cover slip.
4. Using a compound microscope again diagram the algae and fungi cells.
Questions for discussion: What type of symbiotic relationship is this? How is each species affected?
What are the typical habitats of lichen? Why are lichen called pioneer species? What are the normal
habitats of alga and fungi? How does the relationship free each from their normal habitat?
B. Subterranean Termites Reticulitermes spp.
Subterranean termites are scavengers, feeding on wood cellulose. Like you and I, termites are unable to
digest cellulose, and so receive no energy or nutrients from this complex carbohydrate. However,
termites have microscopic protozoa in their intestines that provide enzymes to digest cellulose.
1. Place the termite on the dissecting scope. Focus and diagram one termite.
2. Move your termite onto a microscope slide. With a pin or dissecting needle in each end of the termite,
pull in opposite directions. This should open the alimentary canal (gut).
3. Add a drop of water (either distilled or weakly saline) to the slide to flush the protist Tricohonympha
from the canal. Place the cover slip on top, squash, and place on the compound microscope stage.
4. Under low power, focus on the area immediately surrounding the opened gut.
5 . Diagram the oval shaped Tricohonympha microoganisms, with multiple hair-like flagella. Progress to
higher power, using only the fine focus knob as needed.
Questions for discussion: What type of symbiosis is this? How is each organism affected bby the other?
How does this endosymbiotic relationship differ from the relationship between intestinal worms and
some mammals? (endo=inside; exo=outside). Complex carbohydrates are long chains of sugars, how did
the plant create these?
C. Analysis-What IS symbiosis? How are both of these an example of symbiosis (and of what type,
why)? Why do organisms engage in symbiotic relationships? What are the other kinds?