Lichens

The idea

Lichens are symbiotic associations of an autotrophic alga, which photosynthesises and provides food, and a heterotrophic fungus, which provides protection.

Patches on a wall

White-green patches grow on damp walls and tree trunks. They are lichens.

How many kinds of organisms do you think make up a lichen?

• Two, an alga and a fungus
• One, a single plant
• Two, a moss and a fern

Two partners

Open each tab.

Sharing the work

Each partner gives something to the other. The alga makes food by photosynthesis, and the fungus gives protection. Neither job is done by the other, so living together helps both.

Lichens are symbiotic associations of an autotrophic alga, which photosynthesises and provides food, and a heterotrophic fungus, which provides protection.

Notes

A lichen is a symbiotic association: an autotrophic alga that provides food and a heterotrophic fungus that provides protection.

Check yourself

What two organisms make up a lichen?

Which partner photosynthesises and provides food?

What does the fungal partner provide?

What does symbiotic mean here?

• A moss and a fern. Mosses and ferns are separate plant groups, not the partners of a lichen.
• An alga and a fungus — correct. Yes!
• A bacterium and a mushroom. The book names an alga and a fungus as the partners.
• The fungus. The fungus is heterotrophic and provides protection.
• Neither partner. The autotrophic alga photosynthesises and provides food.
• The alga — correct. Yes!
• Protection — correct. Yes!
• Food by photosynthesis. The alga photosynthesises and provides food.
• Oxygen for the soil. The book says the fungal partner provides protection.
• One organism eating the other. The book describes symbiosis as a mutual association of two organisms.
• A mutual association of two organisms — correct. Yes!
• Two organisms living far apart. In symbiosis the two organisms live together in an association.