Symbiotic
Relationships
8th Grade Science
Objectives of the Symbiotic
Relationships Lesson
 Students will investigate how organisms or populations
interact with one another through symbiotic
relationships and how some species have become so
adapted to each other that neither could survive
without the other. (Ohio Academic Standards LS 7.1)
 Students will be able to define and identify the following
relationships:
 Parasitism
 Mutualistism
 Commensalism
 Neutralism
 Competition
Symbiotic Relationships:
An Introduction
 Click on the picture
of the leaf cutter at
the left or on this link
to view a video about
symbiosis.
Leaf cutter video
 You must be
connected to the
Internet to view this
video.
Symbiotic Relationships
 Definition: A relationship between two
kinds of organisms that lasts over a
period of time is called symbiosis.
 The word symbiosis can be broken down
into two parts to determine its meaning.
 sym means together (like in the words
sympathy and symphony)
 bio means life (like in the words biology and
biome)
Types of Symbiosis
 There are five types
of symbiotic
relationships.





Parasitism
Mutualism
Commensalism
Neutralism
Competition
 Each relationship
can be shown using
+ - or 0.
 The chart below
shows these
relationships.
Parasitism
 Parasitism is the
situation where one
organism benefits
while the other is
harmed.
 A + / - relationship.
Parasitic Isopod on fish
Commensalism
 Commensalism is
where one species
benefits while the
second species
remains unaffected.
 A + / 0 relationship
Barnacles adhering to the skin of a
whale
Mutualism
 Mutualism is where
both organisms
benefit from the
relationship.
 A + / + relationship.
The clownfish and sea anemone are an example of
mutualism. Although these anemones stun and devour
other species of fish, clownfish are not harmed.
Clownfishes were thought to be commensal on the
giant sea anemones, but there now is evidence that
the aggressively territorial clownfishes chase away
butterfly fishes, who eat anemone tentacles.
Neutralism and Competition
 Neutralism is the
situation where both
species remain
unaffected.
 A 0 / 0 relationship.
 Competition is where
neither species
benefits.
 A - / - relationship.
Now Try this
A lion stalks a herd of antelope wading in a
pond. A flock of water birds on the shore
become startled by the sound of the lion’s
approach and fly away with a great deal of
noise. The bird’s sudden departure gives
warning to the antelope, and they are also
able to escape safely. What type of
relationship exists between the birds and the
antelope?
a) Competition
b) Mutualism
c) Commensalism
d) Parasitism
Try again
 For a relationship to be competition, the
end result on both sides of the
relationship is a negative. This isn’t the
case in this relationship.
 Return to the question.
Not quite
 If the relationship was mutualistic, then
both sides of the relationship would have
a positive result from the relationship.
While the antelope did have a positive
from the birds (the warning) the birds
didn’t get a positive from the antelope.
 Return to the question.
You are CORRECT!
 In the antelope and water bird
relationship, the antelope gets a warning
of the coming danger (+) the water birds
don’t get anything from the antelope
though.
 Next example
Think about this again
 For a relationship to be parasitic, one
organism benefits from the relationship
while the other has negative effects from
the relationship. In this example the only
negative is for the lion, but we are looking
at the antelope and water birds.
 Return to the question.
For Practice
A lichen is a combination of two organisms, an
alga and a fungus. The fungus gets its food
from the alga while the alga gets water from
the fungus. This is an example of which
relationship?
a) Competition
b) Mutualism
c) Parasitism
d) Commensalism
Let’s look at this again
 If this were an example of competition,
both of the organisms would be effected
negatively. However, in this example
neither organism is effected negatively.
 Return to the question.
Good Job!
 You’re right! This is an example of a
mutualistic relationship. The alga gains
water from the fungus and the fungus
gains food from the alga. Both need each
other to live and gain something from the
other organism.
 Go to the assignment
It’s interesting that you
think this
 In a parasitic relationship, one organism
gains a positive while the other organism
receives a negative. In this example,
neither organism receives a negative.
 Return to the question.
Can we talk about the
example
 In a commensalistic relationship, one
organism gains something positive. The
other organism remains unaffected by the
relationship. In this example, both
organisms are effected by the
relationship.
 Return to the question.
References
 Abbott, D. (2000, May). Retrieved September 22, 2006, from
Sybiosis Web site: http://www.msstarship.com/sciencenew/symbiosis.htm
 Examples of Commensalism. Retrieved September 22, 2006,
Web site:
http://www.cbu.edu/~seisen/ExamplesOfCommensalism.ht
m
 Meyer, J. R. (1998, January 3). Symbiotic Relationships.
Retrieved September 22, 2006, Web site:
http://www.cals.ncsu.edu/course/ent591k/symbiosis.html
 Mutualism. Retrieved September 22, 2006, Web site:
http://userwww.sfsu.edu/~biol240/labs/lab_03symbiosis/pa
ges/mutualism.html
 Symbiotic Relationships. Retrieved September 22, 2006, Web
site: http://necsi.org/projects/evolution/coevolution/symbiosis/co-evolution_symbiosis.html