Mutualistic, Commensal, and Parasitic Relationships

Kristen Parker

• Content Area: Science

• Grade Level: 5

• Summary: The purpose of this instructional PowerPoint is for

students to learn how to classify interspecific relationships with an

ecosystem as mutualism, commensalism, or parasitism.

• Learning Objective: Given information about the different

mutualistic, commensal, and parasitic relationships, the student will

classify the characteristics of each relationship with 100% accuracy.

• Content Standard: SPI 0507.2.2 Distinguish among symbiotic,

commensal, and parasitic relationships.

Mutualistic Relationships• A mutualistic relationship is when two organisms

of different species “work together,” each benefiting from the relationship.

• Each organism was part of the other’s environment, so as they adapted to their environment, they “made use of” each other in a way that benefited both.

Ex.) The relationship between the oxpecker (a kind of bird) and the zebra. Oxpeckers land on zebras and eat ticks and other parasites that live on their skin. The oxpeckers get food and the zebras get pest control.

Parasitic Relationships• A parasitic relationship is one in which one organism (the

parasite) lives off of another organism (the host) harming it and possibly causing death.

• The parasite lives on or in the body of the host.• Usually, although parasites harm their hosts, it is in the

parasite's best interest not to kill the host, because it relies on the host's body and body functions, such as digestion or blood circulation, to live.

Ex.) Fleas harm their hosts, such as dogs and cats, by biting their skin, sucking their blood, and causing them to itch. The fleas, in turn, get food and a warm home.

Commensal Relationships

• Commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral.

• The neutral organism isn’t rewarded but remains unharmed as well.

Ex.) The remora (aka suckerfish) has special suckers attached to its fins. It attaches itself to the bodies of sharks, and uses the shark for transportation as well as protection from its predators. It also eats up the scraps of food that are left over when the shark eats its prey. The remora does all of this and does not in any manner harm or benefit the sharks.

Tapeworms attach themselves to the insides of the intestines of animals such as cows, pigs, and humans. They get food by eating the host’s partly digested food, which deprives the host of nutrients.

a) Mutualistic relationship

b) Commensal relationship

c) Parasitic relationship

This is an example of a…

THAT’S RIGHT!That was a parasitic relationship because the tapeworm benefits from causing harm to its host.

Bees fly from flower to flower gathering nectar, which they make into food, benefiting the bees. When they land in a flower, the bees get some pollen on their hairy bodies, and when they land in the next flower, some of the pollen from the first one rubs off, pollinating the plant. This benefits the plants.

a) Mutualistic relationship

b) Commensal relationship

c) Parasitic relationship

This is an example of a…

THAT’S RIGHT!

That was a mutualistic relationship because both the bee & the flower benefit from each other.

A great number of army ants trail on the forest floor, and while moving, stir up many insects lying in their path. The birds follow these army ants and eat up the insects that try to escape from them. The birds benefit by catching their prey easily, while the army ants are totally unaffected.

a) Mutualistic relationship

b) Commensal relationship

c) Parasitic relationship

This is an example of a…

THAT’S RIGHT!

That was a commensal relationship because the bird benefits from the army ants without the ants receiving any harm or benefit.

Lets review what we’ve learned:There are 3 different relationships that

exist within an ecosystemCommensal relationships involve one

organism benefiting while the other organism is neither benefiting nor being harmed

Parasitic relationships involve one organism benefitting by harming another organism

Mutualistic relationships involve both of the organisms benefitting from each other

Now that you have learned about the commensal, parasitic, and mutualistic relationships within an ecosystem….

1)Think about the most interesting thing that you learned

2)Discuss it with a classmate3)Share it with the classroom

Try again!

WHOOPS!