Biology II Chapter 29

Gametangia

When hyphae of opposite mating types grow in close proximity, they signal one another with pheromones. In response to these chemical signals, the tips of the hyphae come together and form gametangia, which serve as gametes - Plasmogamy occurs as the gametangia fuse. Then karyogamy occurs as the (+) and (−) nuclei fuse to form the diploid zygote nucleus. The zygote develops into a zygospore

Yeasts

A unicellular fungus (ascomycete) that reproduces asexually by budding or fission, and sexually by ascospores

Conidia

An asexual spore

Endomycorrhizal Fungi

As each hypha pushes forward, the plasma membrane of the root cell surrounds it - Because they penetrate the cell wall, these fungi are referred to as endomycorrhizal fungi

Budding

Asexual reproduction of yeasts is mainly by budding; in this process a small protuberance (bud) grows and eventually separates from the parent cell

What evidence supports the hypothesis that chytrids were the earliest fungal group to evolve from the common ancestor of fungi?

Chytrids, like other opisthokonts but unlike all other fungi, produce flagellate cells at some stage of their life cycle.

Monokaryotic

Hyphae that contain only one nucleus per cell are described as monokaryotic

Fungi Reproduction

Most fungi (but not all) reproduce both asexually and sexually

Heterothallic

The bread mold is heterothallic, meaning that an individual fungal hypha mates only with a hypha of a different mating type (+ with -)

Zoospores

A flagellated motile spore produced asexually by chytrids - Develop into new diploid thalli

Fungi

A heterotrophic eukaryote belonging to the opisthokont clade, with chitinous cell walls and a body usually in the form of a mycelium of branched, threadlike hyphae. Most fungi are decomposers; some are parasitic

Chytridiomycetes

A member of a phylum of fungi characterized by the production of flagellate cells at some stage in their life history. - Chytrids are small, relatively simple fungi that inhabit ponds and damp soil. A few species have been found in salt water - No other fungal group has flagellate cells

Fruiting Bodies

A multicellular structure that contains the sexual spores of certain fungi; refers to the ascocarp of an ascomycete and the basidiocarp of a basidiomycete - The familiar part of a mushroom is a large fruiting body

Primary Mycelium (n)

A mycelium in which the cells are monokaryotic and haploid; a mycelium that grows from either an ascospore or a basidiospore

Fungi Form Symbiotic Relationships with Some Animals

Because animals do not have the enzymes necessary to digest cellulose and lignin, cattle and other grazing animals cannot, by themselves, obtain needed nutrients from the plant material they eat. Their survival depends on fungi that inhabit their guts

Fungi are...

Eukaryotes and Opisthokonts

Zygomycetes

Fungi characterized by the production of nonmotile asexual spores and sexual zygospores. - Most zygomycetes are decomposers that live in the soil on decaying plant or animal matter. Some zygomycetes form a type of symbiotic association (mycorrhizal relationship) with plant roots.

Dikaryotic

Hyphae that contain two genetically distinct, sexually compatible nuclei within each cell are described as dikaryotic (n+n) - The presence of a dikaryotic stage is an important defining character of the ascomycetes and basidiomycetes

Soredia

Lichens reproduce mainly by asexual means, usually by fragmentation, a process in which special dispersal units of the lichen, called soredia break off and, if they land on a suitable surface, establish themselves as new lichens

Ascomycetes

Member of a phylum of fungi characterized by the production of nonmotile asexual conidia and sexual ascospores - include yeasts - In most ascomycetes asexual reproduction involves production of spores called conidia

Ascospore

One of a set of sexual spores, usually eight, contained in a special spore case (an ascus) of an ascomycete

Hyphae

One of the threadlike filaments composing the mycelium of a water mold or fungus. - most fungi are multicellular

Mycotoxins

Poisonous chemical compounds produced by fungi, e.g., aflatoxins that harm the liver and are known carcinogens

Microsporidia

Small, unicellular, fungal parasites that infect eukaryotic cells; classified with the zygomycetes.

Homothallic

Some species of ascomycetes are heterothallic; while others are homothallic, which means that they are self-fertile and have the ability to mate with themselves

In what ways (both positive and negative) are fungi important in modern biology and medicine?

Studies of fungi such as Saccharomyces, Aspergillus, and Neurospora as model organisms have yielded important insights in biology and medicine. Some fungi produce valuable medications, while others are responsible for causing serious diseases.

Basidia

The clublike spore-producing organ of basidiomycetes that bears sexual spores called basidiospores

Basidiocarp

The fruiting body of a basidiomycete, e.g., a mushroom.

Karyogamy

The fusion of two haploid nuclei; follows fusion (plasmogamy) of cells from two sexually compatible mating types.

Gills

The spore-bearing, platelike structures under the caps of mushrooms

Mycology

The study of fungi

Rhizoids

The thallus may have slender extensions, called rhizoids, that anchor it to a food source and absorb food

Mycelium

The vegetative body of most fungi and certain protists (water molds); consists of a branched network of hyphae. - fungi that form mycelia are often called molds

Zygosporangia

The zygospores are typically produced in spore sacs called zygosporangia

Which statement is not true of the chytrids?

Their cells are dikaryotic

Arbuscules

Tree-like branched structures inside root cells produced by hyphae of endomycorrhizal fungi known as glomeromycetes

Opisthokonts

Within the Unikonts supergroup, the clade opisthokonts includes the choanoflagellates, the animals, and the fungi.

Which of the following does not have a mycelium?

Yeast

Ectomycorrhizal Fungi

basidiomycetes also form mycorrhizal connections, but their hyphae coat the plant root rather than penetrate its cells. These species are referred to as ectomycorrhizal fungi.

When a fungus infects a plant, it

enters leaves or stems through stomata

Glomeromycetes...

form arbuscular endomycorrhizae with tree roots

Glomeromycetes

have coenocytic (no septa) hyphae. They reproduce asexually with large, multinucleate spores called blastospores - form Mycorrhizae associations

The ascomycete life cycle typically includes

the production of eight haploid ascospores within an ascus

Which statement is not true of the basidiomycetes?

they have a diploid thallus that produces zoospores

Fungi Digestion

they infiltrate a food source and secrete digestive enzymes onto it. Digestion takes place outside the body

Lichen

A compound organism consisting of a symbiotic fungus and an alga or cyanobacterium - combo of a fungus and a photoautotroph

Secondary Mycelium (n+n)

A dikaryotic mycelium formed by the fusion of two primary hyphae - the two haploid nuclei remain separate within each cell

Chitin

A nitrogen-containing structural polysaccharide that forms the cell walls of many fungi

Spores

A reproductive cell that gives rise to individual offspring in plants, fungi, and certain algae and protozoa.

Asci

A saclike spore case in ascomycetes that contains sexual spores called ascospores

Zygospores

A sexual spore produced by a zygomycete

Sporangia

A spore case, found in plants, certain protists, and fungi

Alternation of Generations

A type of life cycle characteristic of plants and a few algae and fungi in which they spend part of their life in a multicellular n gametophyte stage and part in a multicellular 2n sporophyte stage. - Allomyces, a large, common chytrid, undergoes this

Distinguish among 1. ascocarp, ascus, and ascospore and among 2. basidiocarp, basidium, and basidiospore.

An ascocarp is a fruiting body that produces ascospores (sexual spores) in asci. A basidiocarp is a fruiting body that produces basidiospores (sexual spores) on basidia.

Coenocytes

An organism consisting of a multinucleate cell - the nuclei are not separated from one another by septa

n + n cell means:

Dikaryotic

Basidiospores

Each basidium is an enlarged hyphal cell that undergoes meiosis to form four basidiospores - Note that basidiospores develop on the outside of a basidium, whereas ascospores develop within an ascus.

Rhizopus stolonifer

Familiar zygomycete. Black bread mold

Pheromones

Fungi communicate chemically by secreting signaling molecules called pheromones

Septa

In fungi, the walls that divide a hypha into cells

Haustoria

In parasitic fungi, a specialized hypha that penetrates a host cell and obtains nourishment from the cytoplasm

Plasmogamy

In sexual reproduction the hyphae of two genetically compatible mating types come together, and their cytoplasm fuses

Lichens and Air Quality

Lichens absorb minerals from the air, rainwater, and the surface on which they grow. They cannot excrete the elements they absorb - this is why they are a good indicator of air purity, if the air is too polluted they would die off

Basidiomycetes

Member of a phylum of fungi characterized by the production of sexual basidiospores - include the largest and most familiar of the fungi: the mushrooms, bracket fungi, and puffballs

Thallus

Most chytrids are unicellular or composed of a few cells that form a simple body, called a thallus

Mycorrhizae

Mutualistic associations of fungi and plant roots that aid in the plant's absorption of essential minerals from the soil - improve the soil by decreasing water loss and erosion - occur in about 80% of plants

What are the distinguishing characteristics of each of the following fungal groups: zygomycetes, glomeromycetes, ascomycetes, and basidiomycetes?

Zygomycetes: produce sexual zygospores. Glomeromycetes: sexual spores are large, multinucleate blastospores. Ascomycetes: asci produce sexual ascospores. Basidiomycetes: basidia produce sexual basidiospores.

With the exception of chytridiomycetes, fungi are generally disseminated by

airborne spores

Conidiophores

are specialized hyphae that produce asexual spores called conidia

Which statement is not true of the zygomycetes?

many members of this group form endomycorrhizae with tree roots