Campbell Biology Chapter 31 -- Fungi

How do fungi obtain energy?

Fungi are heterotrophs who use hydrolytic exoenzymes to digest their food before ingesting it.

What key characteristics define fungi? (5)

Nutrition and energy: heterotrophs who digest food before ingesting it; made up of saprobes, parasites, and mutualists.

Body structure: Multicellular filaments and single cells together; form a network of tiny filaments called hyphae; have a cell wall made of chitin

Non-vascular

Reproduce using sexual or asexual spores

Typically non-motile

Hyphae

Tiny filaments that make up the multicellular mycelia, consisting of a tubular cell wall surrounded by the plasma membrane and cytoplasm of the cells.

Chitin

A strong but flexible polysaccharide that makes up the fungal cell wall.

How does the chitin-rich cell wall enhance fungal feeding?

As fungi absorb nutrients from the environment, the concentrations of those nutrients in its cells increase, causing water to move into cells by osmosis. The movement of water would cause fungal cells to burst if not for the rigid cell wall of chitin.

Septa

Cross-walled divisions in hyphae that have pores large enough to allow ribosomes, mitochondria, and even nuceli to flow from cell to cell.

Coenocytic fungi

Fungi that lack septa. These organisms consist of a continuous cytoplasmic mass having hundreds or thousands of nuclei.

Yeasts

Single-celled fungi that often inhabit moist environments such as animal tissues where there is a ready supply of soluble nutrients like sugars and amino acids.

What are the general characteristics of phylum Chytridiomycota? (3 important; 3 less important)

Have a flagellated stage called a zoospore (unique to this phylum).

Mostly aquatic saprobes and parasites.

Once thought to be protists, but modes of absorptive nutrition, chitinous cell walls, and hyphae link them to fungi.

Molecular evidence indicates that some chytrid lineages diverged early in fungal evolution. Zoospores support this hypothesis.

Share cell wall and enzyme pathways with other fungal groups.

1000 species classified

What are the general characteristics of phylum Ascomycota? (3)

Called the sac fungi due to their saclike asci, which produce spores.

Inhabit marine, freshwater, and terrestrial habitats.

Pathogenic and 25% are mutualistic with green algae, forming lichens or mycorrhizae with plants.

Reproduce sexually by enormous numbers of asexual spores called conidia.

65,000 species

How are conidia formed?

Conidia are not formed inside sporangia; they are produced asexually at the tips of specialized hyphae called conidiophores.

How are conidia dispersed?

Wind

Give the hierarchy of the ascomycetes reproductive structures.

Spores are called ascospores.

Ascopores are contained within the saclike asci.

Asci are contained within fruiting bodies called ascocarps.

What are the general characteristics of the phylum Zygomycota? (2)

Mainly terrestrial saprobes

Use sexually reproductive mode as a strategy to survive harsh environmental conditions by forming a zygosporangium by plasmogamy.

1000 species

What are the general characteristics of the phylum Glomeromycetes? (2)

Were once considered zygomycetes but are reclassified into this clade.

Typically plant symbionts, which form a distinct type of endomycorrhizae called arbruscular mycorrhizae that extend into plant cells and expand into a brushlike structure

160 species

What are the general characteristics of the phylum Basidiomycota? (5)

Club-shaped bastidium, a cell in which karyogamy and meiosis occur ("club fungus").

Mostly saprobes but also some plant parasites and plant mutualists. Good at breaking down wood.

Life cycle usually includes long-lived dikaryotic medium.

In response to environmental stimuli, the mycelium reproduces sexually by producing elaborate fruiting bodies called basidiocarps.

The numerous basidia in a basidiocarp are sources of sexual spores called basidiospores.

30,000 species

What are mycelia?

Fungal hyphae form an interwoven mass called a mycelium.

What do mycelia do?

They infiltrate the material on which a fungus feeds.

How do mycelia help fungi grow so quickly?

Not only is the structure of the mycelium well-suited for growth, the fungus will concentrate on adding hyphal length and thus overall absorptive surface area by streaming proteins and other synthesized materials into the tips of extending hyphae.

How does the structure of the mycelium aid in growth?

The structure of mycelium maximizes its surface-to-volume ratio, making feeding very efficient. Just 1 cm3 of rich soil my contain as much as 1 km of hyphae with a total surface area of 300 cm2 in contact with the soil.

Though fungi are not motile in the typically sense, how are they able to move?

Fungi can grow into new territory by extending the tips of their hyphae. Essentially, fungi will grow into new territory.

General: What are the steps of fungal sexual reproduction? (6)

Pheremones signal the presence of a nearby mating fungus.

Hyphae meet and fuse, undergoing a compatibility test.

Plasmogamy.

Karyogamy

Meiosis

Germination

How do fungi signal mating?

They use pheremones, which are sex-signaling molecules. If the mycelia are of two different mating types, the pheremones from each partner bond to receptors on each other, and their hyphae extend toward the source of the pheremones.

How do fungi ensure genetic diversity during sexual reproduction?

Some species undergo a compatibility test, which ensures they are not meeting with hyphae from the same mycelium or genetically identical mycelia.

What occurs during plasmogamy?

Plasmogamy is the union of cytoplasms of two parent fungi. In most fungi, the haploid nuclei contributed by each parent do not fuse right away. Instead, parts of the fused mycelium contain coexisting, genetically diffeerent nuclei.

What is a heterokaryon?

A mycelium containing coexisting, genetically different, haploid nuclei.

What occurs during karyogamy?

Karyogamy is the fusion of the two parent nuclei, which were brought together during plasmogamy. This forms a diploid cell, as well as zygotes and other transient structures

What happens after karyogamy?

Meiosis restores the haploid condition, ultimately leading to the formation of genetically diverse spores. Spores produced in this way are called sexual spores.

How do fungi typically asexually reproduce?

By growing as filamentous fungi that produce haploid spores by mitosis. These are generally called molds.

By growing as single-celled yeasts. Instead of producing spores, reproduction occurs by ordinary cell division or the pinching of small bud cells off a parent cell.

Why are deuteromycetes a problem?

This group contains all fungi with no known sexual stage. Once a sexual stage is discovered, the fungus is then reclassified into its appropriate group.

What are mycorrhizae?

Mutually beneficial relationships between fungi and plant roots.

What do mycorrhizae do?

They improve delivery of nutrients because the vast mycelial networks of the fungi are more efficient than the plants' roots at acquiring minerals from the soil. In exchange, the plants supply the fungi with organic nutrients such as carbohydrates.

Ectomycorrhizal

Form sheaths of hyphae over the surface of a root and typically grow into the extracellular spaces of the root cortex.

Arbruscular Mycorrhizal

Extend branching hyphae through the root cell wall and into tubes formed by invagination of the root cell plasma membrane.

Why are mycorrhizae important?

Almost all vascular plants have them and rely on them for essential nutrients.

Know the haploid and diploid stages of each reproductive step and the relative order.

1) Plasmogamy: The fusion of cytoplasm -- heterokaryotic

2) Karyogamy: The fusion of nuclei -- diploid

3) Meiosis: Produces spores -- haploid

OR

Asexual reproduction producing haploid spores.

What was the common ancestor of fungi like?

Phylogenetic analyses suggest that fungi evolved from a flagellated protist.

What evidence supports the proposed ancestor of the fungi? (4)

DNA sequence data indicate that these three groups of eukaryotes--fungi, animals, and protists--form a clade. Members of this clade are called opisthokonts, which refers to the location of the flagellum.

DNA sequence data indicate fungi are more closely related to several groups of single-celled protists than to animals, suggesting their ancestor was unicellular (for example, the nucleariids)

DNA evidence indicates animals are more closely related to another group of protists than to fungi or nucleariids.

Using molecular clock analyses, scientists have estimated that the ancestors of animals and fungi diverged into seprate lineages 1-1.5 billion years ago. Fossils of certain unicellular, marine eukaryotes that lived as early as 1.5 billion years ago have been interpreted as fungi, but those claims remain controversial.

What are lichens?

Lichens are mutualistic relationships between green algae and fungi in which millions of photosynthetic cells are held in a mass of fungal hyphae.

What are some of the benefits humans derive from fungi? (3)

Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread.

Some fungi are used to produced antibiotics -- penicillium

Genetic research on fungi is leading to applications in biotechnology; for instance, insulin-like growth factor can be produced by a certain type of fungus.

What are some of the dangers fungi present to humans?

About 30% of known fungal species are parasites or pathogens, mostly on or in plants. Some fungi that attack food crops are toxic to humans.

Essentially, fungal infections can be dangerous. For instance, fungal respiratory infections like aspergillis or pneumonia are very unpleasant but are more common in the immunocompromised.

How do Chytridiomycota interact with the environment?

Mostly aquatic saprobes and parasites

How do Zygomycota interact with the environment?

Mainly terrestrial saprobes

How do Glomeromycetes interact with the environment?

Mainly plant symbionts

How do Ascomycetes interact with the environment?

Many are pathogenic; others form mutualistic relationships with algae called lichens; others are decomposers