Chapter 4, Problem 41A

Summary Introduction

To describe:

The three different types of symbiosis.

Introduction:

Organisms living in an ecosystem thrives by interacting with the abiotic as well as biotic components. The physical or abiotic factors help the organism to better suit to its environment.

Explanation of Solution

As living organisms live together in abiotic and biotic community, they interact with each other. Organisms compete with other organisms for food, shelter or other basic needs while other organisms depend upon one another for successful survival.

When in an interaction between two organisms, they depend on each other. Organisms may benefit or harm from the association. When survival of the organisms depend on the relationship developed with other organisms, it is known as symbiotic relationship. In the process of symbiosis, the organisms exist in close association with one another.

On the basis of benefit obtained from the association, symbiosis can be of three types:

A. Mutualism.

B. Commensalism.

C. Parasitism.

When two organisms live together in a close association and both of them benefit from the association and neither of them are harmed, such a type of symbiotic relationship is known as mutualism. Lichens are an association between algae and fungi. In lichens, the fungi provides habitat for the algae while algae provides food for the fungi. Thus, the two basic needs, food and shelter, is mutually gained by both algae and fungi.

When in a relationship between two organisms, one of them derives benefit from the other but the other member is neither harmed nor benefitted from the association. This is known as commensalism. In the relation between the tree and lichens growing on the tree trunk, the lichen benefits by getting more exposure and sunlight which is helpful for its growth. However, the tree does not get any benefit but it is not harmed either.

In an association between two organisms, one of the member derives benefits at the cost of wellbeing of the other member or organism, is known as parasitism or parasitic relationship. The organisms which derives benefit in the form of nourishment and shelter is known as parasite, while the other organism which is harmed is known as the host. Many disease causing organisms get nourishment at the expense of their host.

Conclusion

Organisms are always in an association with other components of the ecosystem which helps the ecosystem to thrive and grow. Often the association may be harmful or beneficial to the organism which in turn brings about diversity in an ecosystem and thus organisms evolve for better survival.