Ch. 24.3 Ecology of Fungi

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Where do fungi live?

Fungi colonize most habitats on Earth, including soil, sweater, plants, animals, human skin, and mucous membranes.

What enviornments do most fungi prefer?

Dark, moist, cool environments rich in organic matter.

Where are chytrids primarily found?

Aquatic environments.

Can fungi survive in extreme environments?

Yes. Some fungi live in tundra, desert, seawater, and there harsh environments.

What is an example of a fungus that lives in dry, sandy soil?

Coccidioides immitis, which can cause pneumonia when its spores are inhaled.

Why are fungi important in forest ecosystems?

They act as major decomposers and nutrient recyclers, breaking down dead plant and animal material.

Why are fungi important to food webs?

They decompose organic matter and return nutrients to the environment.

What important elements do fungi release from decaying matter?

Nitrogen, phosphorus, and trace elements.

What would happen if fungi and bacteria did not decompose organic matter?

Nutrients would remain locked inside dead organisms, making them unavailable to other organisims.

How do fungi digest food?

Digestion occurs before ingestion. Fungi release enzymes outside their cells and then absorb the smaller molecules.

What are exoenzymes?

Enzymes released by fungi that break down large organic molecules outside the fungal cell.

What happens after exoenzymes break down large molecules?

The resulting small molecules are transported into fungal cells by protein carriers in the cell membrane.

Why is moisture important for fungal growth?

Water is needed for the movement of enzymes and small molecules, making active fungal growth dependent on moisture.

What is a saprobe?

An organism that obtains nutrients from dead or decomposing organic matter.

What is the ecological importance of saprobic fungi?

They recycle nutrients, making them available to plants and other organisims.

What is a symbiosis?

An ecological interaction in which two organisms live together.

What is mutualism?

A symbiotic relationship in which both organisms benefit.

What types of organisms form mutualistic relationships with fungi?

Plants, algae, cyanobacteria, and animals.

What are mycorrhizae?

Mutualistic associations between fungi and plant roots.

What does “tyco” mean?

Fungus.

What does “rhino” mean?

Root.

How common are mycorrhizal relationships?

Nearly 90% of vascular plant species have mycorrhizal partners.

What does the fungus provide to the plant in a mycorrhizal relationship?

Water and minerals from the soil.

What does the plant provide to the fungus?

Products of photosynthesis, mainly carbohydrates.

Why are fungal hyphae useful to plants?

Their extensive network gives the fungus a large surface area for abosrbing water and minerals from soil.

What does “echo” mean in ectomycorrhizae?

Outside.

What happens in ectomycorrhizae?

Fungal hyphae form a mantle around the plant root and grow between the outer root cells.

What is a fungal mantle?

A sheath of fungal tissue surrounding the root.

What is a Hartig net?

A network of fungal hyphae that grows between the outer root cells in ectomycorrhizae.

Which fungal groups can form ectomycorrhizae?

Ascomycota, Basidiomycota, and zygomycota.

What does "endo" mean?

Inside

Where do fungi grow in endomycorrhizae?

Inside the plant root.

What is an arbuscule?

A branched, tree-like fungal structure inside plant root cells where nutrient exchange occurs.

Which fungal group forms arbuscular mycorrhizae?

Glomeromycota

What is the major difference between ectomycorrhizae and endomycorrhizae?

Ectomycorrhizae: fungus forms a mantle around the root and Hartig net between cells.

Why do orchids depend on mycorrhizal fungi?

Their tiny seeds have very little stored nutrition and often cannot germinate without fungal assistance.

Endomycorrhizae

Fungus forms arbuscules inside root cells.

What does the fungus provide to orchid seedlings?

Carbohydrates and minerals needed for growth.

Do some orchids remain mycorrhizal throughout their entire life?

Yes.

What are endophytes?

Fungi that live inside plant tissues without harming the plant.

How can endophytes benefit plants?

They can produce toxins that repel herbivores and increase resistance to microorganisms, drought, and heavy metals.

What is a lichen?

A mutualistic association between a fungus and a photosynthetic organism, such as an alga or cyanobacterium.

Is a lichen a single organism?

No. It is a symbiotic association between different organisms.

What organisms can serve as the photosynthetic partner in a lichen?

Eukaryotic algae or prokaryotic cyanobacteria.

What does the photosynthetic partner provide to the fungus?

Carbohydrates/carbon and energy produced through photosynthesis.

What does the fungus provide to the photosynthetic partner?

Minerals, protection, water retention, and attachment to the substrate.

What additional benefit can cyanobacteria provide in lichens?

Some cyanobacteria can fix atmospheric nitrogen.

What is the body of a lichen called?

A thallus.

What makes up the lichen thallus?

Fungal hyphae wrapped around the photosynthetic partner.

Where can lichens grow?

On rocks, gravestones, tree bark, and tundra, including harsh environments where plants struggle to grow.

How do lichens survive drought?

They can become completely desiccated and then rapidly become active when water becomes available.

How quickly do lichens generally grow?

Very slowly—only a few millimeters per year.

What are soredia?

Clusters of algal cells surrounded by fungal mycelium that can disperse and form new lichens.

How are soredia dispersed?

By wind and water.

Why are lichens useful as indicators of air quality?

They are highly sensitive to air pollution, especially abnormal nitrogen and sulfur compounds.

How can scientists monitor air pollution using lichens?

By measuring the abundance and health of lichen populations in an area.

What are some ecological roles of lichens?

They provide food for caribou/reindeer and shelter for small invertebrates.

What are some human uses of lichens?

They have been used to dye wool and provide pigments for litmus paper.

What do fungi gain from mutualistic relationships with animals?

Nutrients and opportunities to disperse their spores.

What can animals gain from fungi?

Protection from predators/pathogens and food.

What do leaf-cutter ants do with fungi?

They farm fungi in underground gardens.

How do leaf-cutter ants help their fungal crops?

They cut leaves and bring them to underground gardens, providing the fungi with a constant food supply.

Why can't leaf-cutter ants directly use the leaves efficiently?

They cannot efficiently digest the cellulose in the leaves.

How does the fungus help the ants?

The fungus digests cellulose into smaller sugars and becomes a food source for the ants.

How do the ants help the fungus?

They provide leaves, protection from competing fungi, and a suitable growing environment.

Why is the leaf-cutter ant/fungus relationship mutualistic?

Both benefit: ants receive food, while fungi receive leaves and protection from competition.

Mycorrhizae vs. lichens?

Mycorrhizae: fungus + plant roots.
Lichens: fungus + alga/cyanobacterium.

Ectomycorrhizae vs. endomycorrhizae?

Ecto: mantle + Hartig net, fungus primarily outside root cells.
Endo: arbuscules inside root cells.

What does the fungus provide in most fungal mutualisms?

Minerals, nutrients, protection, or water access.

What does the partner usually provide the fungus?

Carbon/organic nutrients, often from photosynthesis.