Mutualistic Relationships

Lichens

One of the best known mutualistic relationships is found in lichens. Lichens are found almost everywhere; from the arctic tundra, where they provide food for the reindeer in the winter, to the equatorial forests. They are often the first plants to grow on bare rock and they are able to survive the hot sun in exposed areas.

The lichen is made up of two organisms; a fungus and an alga. The algal cells live inside the hyphae of the fungus. The algal cells photosynthesize and give sugars and oxygen to the fungus. In return the fungus provides protection, water and salts for the small algal cells. Also, the fungus is able to grow on bare rock and other areas where other plants cannot. This is because the fungus is able to take a firm hold where most plant roots are unable to penetrate.

Neither the fungus nor the alga would be able to survive in these hostile areas on its own. Together, however, they can compete successfully with other plants for light and space.

Johnny's Fact File No.63 In the human gut there are millions of microorganisms - bacteria, fungi and protozoa which live by feeding on the non-digested food which reaches the colon and the rectum. Also, human skin is covered with microorganisms which feed on dead skin cells and sweat. Many of these micro-organisms can be classed as being mutualistic since some produce chemicals, such as vitamins, which we absorb.

Ruminants and Micro-organisms

In the animal world a good example of mutualism is that between a ruminant and the many millions of micro-organisms which live in its rumen. You will remember that a ruminant, such as a giraffe, has a sac called a rumen situated just before the stomach in its gut.

When a ruminant swallows its food, which is vegetation, the food goes into the rumen. Here the plant material is digested by the microorganisms. The micro-organisms make a special chemical which can break down the plant cells but the ruminant is not able to make this chemical.

The micro-organisms digest the plant material for both themselves and the ruminant. In return the ruminant provides them with a constant supply of vegetation as well as a safe and a warm place in which to live.

More Examples of Mutualistic Relationships

• Introduction
• Parasitic Relationships
• Chapter Summary (useful for revison)
• Questions relating to this chapter
• Top of Page

© Paul Billiet and Shirley Burchill 2009