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preAP Biology
Symbiotic Relationships Assignment
PURPOSE: Students will analyze ecological relationships between organisms of two different species in order to
determine the type of symbiotic relationship the organisms share.
Symbiosis is a close, permanent ecological relationship between organisms of two different species. Ecologists
use a different term for each type of symbiotic relationship:
 Mutualism – both species benefit
 Commensalism – one species benefits, the other is unaffected
 Parasitism – one species benefits, the other is harmed
Part 1
Look at each relationship that is described. Determine if the relationship is one of mutualism, commensalism
or parasitism. Using complete sentences, explain your reason for each answer.
1. Paramecium bursaria is a unicellular protist that lives in fresh water. It engulfs unicellular green algae into
vacuoles within its cell. The paramecium benefits from the food synthesized by the alga. (It can be grown
without the alga, but it must be given extra food.) The algae benefits from the carbon dioxide produced by its
host as well as the host’s ability to transport it to a spot where there is ample light to perform photosynthesis.
Relationship:
Explanation:
2. The Nile crocodile opens its mouth to permit the Egyptian plover (a bird) to feed on any leeches attached to its
gums. The crocodile does not harm the plover.
Relationship:
Explanation:
3. The remora is a bony fish that has a modified dorsal fin. The fin has been modified into a sucker with which it
forms a temporary attachment to the shark. When the shark feeds, the remora picks up scraps of food. The
shark makes no attempt to prey on the remora.
Relationship:
Explanation:
4. Several species of the flower Rafflesia grow in jungles of Southeast Asia. Rafflesia arnoldii is the largest, its
blossom attains a diameter of 1 meter and can weigh up to 11 kg. It produces no leaves, stems or roots but
lives on the Tetrastigma vine. Only the flower or bud can be seen; the rest of the plant exists only as filaments
within the host vine. The Rafflesia drains nourishment and gains physical support from the host vine.
Relationship:
Explanation:
1
5. During the day the bobtailed squid, Euprymna scolopes, remains buried in the sand of shallow reef flats. As the
sun sets, the nocturnal animal emerges from its safe hiding place and searches for food. In the moonlit night,
the squid would appear as a dark silhouette when it swims through the water and would be easily detected by
predatory fish from below. The squid camouflages itself by projecting light downward from its light organ.
Inside the light organ are luminescent bacteria, Vibrio fischeri, that produce light. The squid provides an
environment for the bacteria to live that is very rich in amino acids.
Relationship:
Explanation:
6. Mycobacterium leprae is a bacterium that takes up residence in the Schwann cells (part of nerve cells in
humans). The bacterium receives nourishment. This bacterium eventually triggers the host to produce an
autoimmune attack on the cells that leads to the cell’s destruction. The resulting loss of sensation makes it
difficult to avoid injury to the extremities.
Relationship:
Explanation:
7. A fungus called Cladonia cristatella lives with a green algae called Trebouxia erici. (This particular algae may
live with other fungi as well). The algae provides food for the fungus. The algal cells eventually are killed by
the fungus, but are continuously replaced by new algal cells.
Relationship:
Explanation:
8. Legumes, a type of plant, can survive independently of a symbiotic relationship if they live in soil that is rich in
nitrates. Rhizobia, a type of bacteria, can live freely in soil. However, Rhizobia do not fix nitrogen if they live
alone. If the soil is nitrate poor, then the legume will form a relationship with Rhizobia. The bacteria live
within the tissue of the legume and receives nutrition. The bacteria will then fix nitrogen so the legumes will
receive nitrogen in order to make proteins and DNA.
Relationship:
Explanation:
9. Barnacle are sedentary, highly modified crustaceans resembling conical pyramids. Barnacles live by using long,
feathering appendages to sweep the surrounding water for small, free-floating organisms. The critical resource
for barnacles is a place to stay. Barnacles attach to rocks, ships, shells, whales, and just about anywhere else
they can gain a foothold. The barnacle gains a place to live and the organism is not harmed by the presence of
the barnacles.
Relationship:
Explanation:
2
10. Pseudoscorpions are small, predaceous arthropods, mostly less than 1 centimeter is length. These scorpionlike animals have pincers (chelicerae) like scorpions, but lack a sting. Pseudoscorpions are common, but
usually overlooked because of their small size and because they are concealed in the soil or under the bark of
trees A few species of pseudoscorpions disperse by concealing themselves under the wing covers (elytra) of
large beetles such as the cerambycid beetle. The pseudoscorpions gain the advantage of being dispersed over
wide areas while simultaneously being protected from predators. The beetle is unaffected by the presence of
the hitchhikers.
Relationship:
Explanation:
Part 2
Below are three sets of graphs used to show mutualism, commensalisms or parasitism. Identify each set of
graphs by its type of symbiotic relationship. Then explain why that set of graphs is mutualism, commensalisms
or parasitism.
Set A
Average
number of
Organism
When Living
Together
Average
number of
Organism
When Living
Separately
3
6
9
Time (months)
12
3
6
9
12
Time (months)
Relationship:
Explanation:
3
Set B
Average
Number of
Organism
When Living
Separately
Average
Number of
Organism
When Living
Together
3
6
9
12
3
6
Time (months)
9
12
Time (months)
Relationship:
Explanation:
Set C
Average
Number of
Organism
When Living
Separately
Average
Number of
Organism
When Living
Together
3
6
9
Time (months)
12
3
6
9
12
Time (months)
Relationship:
Explanation:
4