Lab 4







            In communities (coherent assemblages of organisms, e.g., the organisms that live in a pond), organisms interact in interesting ways.  Competition and predation are examples of types of interactions.  For example, aquatic plants may compete for sunlight by spreading their leaves over other plants.  Various species of fish in the pond prey on insect larvae of different types, and on other aquatic life.  Some of the most amazing interactions among organisms are called symbioses, situations in which two species form close or tight relationships.  Symbioses are of the following types:  parasitism, commensalism, and mutualism.



Competition — interactions among organisms striving for the same resource (food, living space, mates, and so on).  Interactions can occur between individuals within a species (intraspecific competition), or between organisms in different species (interspecific competition).  Competition affects populations negatively because resources that could have been used to reproduce are used instead to compete.

Predation — the consumption of one living organism, in whole or in part, by another organism.


Symbiosis — a relationship in which two or more species live together in a close association; a symbiont is one member of such a relationship.

Parasitism — a symbiotic relationship in which two organisms, of different species, live together in an intimate association in which the parasite is benefitted, while the host is harmed.

Mutualism — a symbiotic relationship in which both organisms benefit from the association.

Commensalism — a type of symbiosis in which one organism benefits and the other is neither harmed nor benefited.


            During this activity you will observe organisms living together in different types of associations.  You should develop an understanding of the characteristics of different types of associations, determine the role each organism plays in the relationship, and evaluate the effects on each.

            Interactions among organisms can occur among closely related organisms, among very distantly related organisms or anywhere in between. 

            Organisms that are very distantly related to one another may belong to different kingdoms.  Biologists find it useful to group organisms into five kingdoms on the basis of cell qualities and nutritional modes.  The following chart describes the five kingdoms by major characteristics. 








Prokaryotic; no membrane-bound intracellular structures

Eukaryotic; nucleus, mitochondria, some have chloroplasts

Eukaryotic; nucleus, mitochondria, but no chloroplasts; cell wall of chitin

Eukaryotic; nucleus, mitochondria, chloroplasts; cell wall of cellulose

Eukaryotic; nucleus, mitochondria, but no chloroplasts; no cell wall

Solitary, filamentous, or colonial

Mostly solitary, some colonial or multicellular

Some unicellular, most grow in thread-like branches

Multicellular, most sedentary on land

Multicellular, most motile

Aerobic or anaerobic

Mostly aerobic

Mostly aerobic

Strictly aerobic

Strictly aerobic

Autotrophic or heterotrophic

Autotrophic or heterotrophic

Mostly saprophytic

Mostly photosynthetic autotrophs


Bacteria of diverse types, including cyanobacteria, formerly called "blue-green algae"

Amoeba, paramecia, algae and seaweeds

Yeasts, molds, mushrooms

Mosses, ferns, flowering plants

Sponges, worms, snails, insects, mammals



            The diagram on page 4.4 shows the hypothetical evolutionary relationships among the organisms of the five kingdoms.  When you are studying interactions today, use the chart above and the diagram to place the organisms in their proper kingdom.



• To develop an understanding of different types of interactions among organisms.

• To define terms that describe various interactions.

• To analyze several interactions using the microscope.

• To learn the major characteristics of the five kingdoms of life.

• To recognize characteristics that are used to group organisms into five kingdoms.

• To review skill of estimating measurements of microscopic objects.


A.  Theory

            Before you begin the lab work today, summarize the effects on organisms in different interactions, using the following symbols:  (+) = beneficial; (-) = harmful; 0 = neutral.  Using your text and your own experience and understanding, give an example of each interaction.


Interaction type

Organism 1

Organism 2
































Kingdoms of Life

The five kingdoms are arranged in a manner that suggests their phylogenetic relationship to each other.  The underlying kingdom, known as Monera, is now being reorganized into two kingdoms, Archaebacteria and Eubacteria, containing two quite diverse groups of prokaryotes.  Above this is the large assemblage provisionally called Protista.  Some of its members are descended from the same lines that gave rise to plants, fungi, and animals.

B.  Interactions

            We’ll begin the lab by viewing a film, Within the Coral Wall, which depicts the ecology of Australia’s Great Barrier Reef.  During the film, watch for examples of the various types of interactions described above.  Your instructor may ask you to list of as many of these interactions as you can on a paper to be handed in later.  For example, you’ll see Anemone Fish lurking among the stinging tentacles of a large Sea Anemone.  The fish have a special slime coating their bodies so the stings don’t hurt them.  They are protected against predators by hiding in the anemone.  The anemone is neither harmed nor helped by this interaction.  So this is clearly a case of commensalism.


            In the second part of our laboratory today, you will investigate four living interactions or symbiotic relationships.  You also will observe several interactions as demonstrations.  Using the instructions here and at the laboratory bench and pages provided at the end of the lab write-up, complete the table found on page 4-9.


            As you work, keep your eye on the screen at the front of the room.  The instructor will be preparing slides just like yours and will project them on the screen, with an explanation.


            At least one symbiotic relationship exists in each of the following:  Azolla, a pond fern; lichen, a composite organism that grows on rocks; termites; and Paramecium bursaria, a protist.  Using the microscope, you will try to identify a) the type of symbiotic relationship; b) the two organisms involved; c) the evidence that supports your conclusion. 



Paramecium bursaria

1.      Place a drop of the Paramecium bursaria culture fluid on a microscope slide along with a small drop of Protoslo, a viscous substance that slows down the rapidly swimming paramecia. Add a cover slip, and observe this organism using the various powers of the microscope.


2.      Draw the organism in some detail.  What evidence, if any, do you see of a symbiosis?


3.      Now prepare a wet mount slide, including Protoslo, of Paramecium caudatum, a    species that does not have another organism living with it in symbiosis.  Observe and draw this organism.


4.      What differences do you notice between the two species of Paramecium?




1.      Place a very small piece of the soft, bushy lichen called Reindeer Moss on a slide.  As a rule of thumb, when making slides, less is best.


2.      Add a drop of water and chop up the lichen with a razor blade.  Add a cover slip.


3.      With your finger, carefully squash the slide.  More squashing will result in a better slide.


4.   Observe the preparation and draw what you see.  What evidence, if any, do you see of a symbiosis?




1.      Make a wet mount slide of a small piece of an Azolla, a water fern.   Pop leaves by carefully squashing them, and note that chains of small, green cells emerge.


2.      Observe the preparation using your microscope; look for evidence of two species, and draw what you see.



1.      Termites are insects characterized by having three body regions.  You will make a wet mount slide of the abdomen, the bag-like posterior part of the body without any legs.


2.  Place a large drop of Ringer's solution on a slide.  Obtain a termite from the live  

     culture and place the abdomen in the drop. 


3.      Place a cover slip on the drop and crush the abdomen by gently squashing the cover slips against the glass slides. 


4.      Look for evidence of symbiosis.  Record your observations.




1.      From the tray, take a prepared microscope slide labeled “Trypanosome gambiense smear.”  You will need to use the high power objective to see the cells on this slide well.  You should be able to find two main cell types. The very round cells are mammalian red blood cells, and the other crescent-shaped cells are single-celled organisms known as trypanosomes.  These crescent-shaped cells have flagella and undulating membranes (observable if you look closely) that propel the cells through the blood.  The trypanosomes are injected into the blood of mammals including humans by bite of the tsetse fly, causing African sleeping sickness in humans.  What kind of interaction is this? __________________ How many organisms are involved?  Estimate the size of the blood cells.


2.      Oak galls form on both leaves and branches of oak trees.  Galls are swellings of plant tissue that form in response to the presence of insect larvae.  The insects feed on the gall material.  Which type of interaction is this? _______________________.


3.      Spanish moss, a relative of the pineapple, is commonly seen in low woods and maritime forests in the coastal plains of southern states.  Examine these rootless epiphytic plants in our lab, particularly noting their habit of growth.  What kind of interaction is this? __________________________.




1.          Read the next lab, The Cell Cycle and Cell Division.



Levine and Miller (1994) Biology:  Discovering Life.   Lexington, MA:  D. C. Heath.

Mix, Farber and King (1993) Activity Manual to accompany Biology:  the Network of Life.  New York, NY:  HarperCollins Publishers.

Wallace, Robert A., Gerald G. Sanders, and Robert J. Ferl (1996) Biology:  the Science of Life (4th ed.).  New York:  HarperCollins Publishers.


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Spanish Moss












Coral Reef














 Interactions among Organisms


1.  Paramecium bursaria have living algae inside. The algal cells are of the genus Zoochlorella sp. and are the producer in this symbiosis. Obviously the cells that contain the algae are protozoa, in the kingdom Protista. The protozoan symbiont provides a home for the algae, moving these algae into areas that are sunny.

2.  Lichens are a symbiosis in which the green cells, algal protists or cyanobacteria, the kingdom Monera, are the producer, supplying the energy for life for themselves and the fungal component of the lichen. The fungal hyphae are clear threads that form support for the algae, providing moisture, protection, and minerals.

Foliose Lichen

"Reindeer moss" is fruticose lichen and the other specimen available in our lab is referred to as foliose lichen, found on the bark of trees.

Fruticose Lichen   

Crustose Lichen

 LICHENS (not a division, but rather a symbiotic association of an alga and a fungus)

3.  Azolla is a tropical water fern that grows in rice paddies throughout the world. Cyanobacteria, kingdom Monera, called Anabaena grow in association with the fern, and fix nitrogen, an important nutrient for all living cells. The cyanobacteria are filaments of cells that have special cells called heterocysts that look a little different and are the sites of nitrogen-fixation. The water fern provides shade for the cyanobacteria in the harsh tropical sun.  Finally the whole water fern/cyanobacteria complex breaks down and fertilizes the rice.

water fern

Rice planted; paddies flooded


4. Termites are the hosts of several different internal symbionts--(l) several species of protozoa and (2) some cork- screw-like Monerans. The protozoa are covered with flagella that undulate and move the protozoa through the gut contents. The termite provides the meal by eating the wood (mainly cellulose) which is then digested by the symbionts, because the symbionts have an enzyme (cellulose) which the termite does not produce for itself. The termites and their symbionts can use as nutrient the sugar molecules of the digested cellulose. Actually very few organisms produce the cellulose-digesting enzyme, and that is a good thing. Civilization would not exist as we know it-wooden structures would not last long and there would be no paper. It would all be digested.