Chapter 24

Chytridiomycetes

(also, chytrids) primitive phylum of fungi that live in water and produce gametes with flagella

Basidiomycota

(also, club fungi) phylum of fungi that produce club-shaped structures (basidia) that contain spores

Zygomycota

(also, conjugated fungi) phylum of fungi that form a zygote contained in a zygospore

Ascomycota

(also, sac fungi) phylum of fungi that store spores in a sac called ascus

Ectomycorrhizae

A type of mycorrhizae in which the mycelium forms a dense sheath, or mantle, over the surface of the root. Hyphae extend from the mantle into the soil, greatly increasing the surface area for water and mineral absorption.

Compare plants, animals, and fungi, considering these components: cell wall, chloroplasts, plasma membrane, food source, and polysaccharide storage. Be sure to indicate fungi's similarities and differences to plants and animals.

Animals have no cell walls; fungi have cell walls containing chitin; plants have cell walls containing cellulose. Chloroplasts are absent in both animals and fungi but are present in plants. Animal plasma membranes are stabilized with cholesterol, while fungi plasma membranes are stabilized with ergosterol, and plant plasma membranes are stabilized with phytosterols. Animals obtain N and C from food sources via internal digestion. Fungi obtain N and C from food sources via external digestion. Plants obtain organic N from the environment or through symbiotic N-fixing bacteria; they obtain C from photosynthesis. Animals and fungi store polysaccharides as glycogen, while plants store them as starch.

What are the evolutionary advantages for an organism to reproduce both asexually and sexually?

Asexual reproduction is fast and best under favorable conditions. Sexual reproduction allows the recombination of genetic traits and increases the odds of developing new adaptations better suited to a changed environment.

Septa

Cell wall division between hyphae. Tiny holes in the septa allow for the rapid flow of nutrients and small molecules from cell to cell along the hypha (perforated septa).

Vegetative stage

Consists of a tangle of slender thread-like structures called hyphae

Why can superficial mycoses in humans lead to bacterial infections?

Dermatophytes that colonize skin break down the keratinized layer of dead cells that protects tissues from bacterial invasion. Once the integrity of the skin is breached, bacteria can enter the deeper layers of tissues and cause infections.

Fungi

Fungi are eukaryotes, and as such, have a complex cellular organization. Fungal cells contain a membrane-bound nucleus. The DNA in the nucleus is wrapped around histone proteins, as is observed in other eukaryotic cells. A few types of fungi have structures comparable to bacterial plasmids (loops of DNA); however, the horizontal transfer of genetic information from one mature bacterium to another rarely occurs in fungi. Fungal cells also contain mitochondria and a complex system of internal membranes, including the endoplasmic reticulum and Golgi apparatus. The rigid layers of fungal cell walls contain complex polysaccharides called chitin and glucans

Nutrition of Fungi

Fungi are heterotrophs; they use complex organic compounds as a source of carbon. Fungi do not fix carbon dioxide (conversion of atmospheric C to carbon compounds, eg, sugars, as do some bacteria and most plants). Fungi do not fix nitrogen (conversion of atmospheric N to ammonia, nitrites, and nitrates). Like animals, they must obtain it from their diet. Fungi do transport exoenzymes out of the hyphae to process breakdown and obtain environmental that are absorbed through the large surface area of the mycelium. As with animal cells, the polysaccharide of storage is glycogen, rather than starch, as found in plants.

asexual reproduction in fungi

Fungi reproduce asexually by fragmentation, budding, or producing spores

Reproductive stage

Fungi reproduce sexually and/or asexually. Perfect fungi reproduce both sexually and asexually, while the so-called imperfect fungi reproduce only asexually (by mitosis). fungi produce spores that disperse from the parent organism by either floating on the wind or hitching a ride on an animal.

Mycetismus

Ingestion of toxins in poisonous mushrooms

Lichens again

Lichens are not a single organism, but rather an example of a mutualism, in which a fungus lives in close contact with a photosynthetic alga or a cyanobacterium. Lichens fulfill many ecological roles: Food, protection for small invertebrates that hide in the mycelium and textile dyes.

Nutrition

Like animals, fungi are heterotrophs; they use complex organic compounds as a source of carbon, rather than fix carbon dioxide from the atmosphere as do some bacteria and most plants. In addition, fungi do not fix nitrogen from the atmosphere. Like animals, they must obtain it from their diet. digestion precedes ingestion

Fungus/Plant Mutualism

One of the most remarkable associations between fungi and plants is the establishment of mycorrhizae. The fungal mycelia use their extensive network of hyphae and large surface area in contact with the soil to channel water and minerals from the soil into the plant. In exchange, the plant supplies the products of photosynthesis to fuel the metabolism of the fungus.

Epiphytes

Photosynthetic plants that grow on other trees rather than supporting themselves. They form small seeds without much storage to sustain germination and growth. Their seeds will not germinate without a mycorrhizal partner. After nutrients in the seed are depleted, fungal symbionts provide carbohydrates and minerals, sometimes throughout the life of the orchid.

Why does protection from light actually benefit the photosynthetic partner in lichens?

Protection from excess light that may bleach photosynthetic pigments allows the photosynthetic partner to survive in environments unfavorable to plants.

Basidiomycete life cycle

SEXUAL: meiosis-->basidiospore (mushroom develops) ASEXUAL: fragment of mycelium -Important decomposer of wood & other plants. Also contains destructive plant parasites: rusts and smuts

sexual reproduction in fungi

Sexual reproduction introduces genetic variation into a population of fungi. In fungi, sexual reproduction often occurs in response to adverse environmental conditions. During sexual reproduction, two mating types are produced, homothallic and heterothallic mycelia. Stage 1: two haploid cells fuse, leading to a dikaryotic stage where two haploid nuclei coexist in a single cell (Plasmogamy). Stage 2: the haploid nuclei fuse to form a diploid zygote nucleus (Karyogamy.) Stage 3: Finally, meiosis takes place in the gametangia (singular, gametangium) organs, in which gametes of different mating types are generated. At this stage, spores are disseminated into the environment.

Historically, artisanal breads were produced by capturing wild yeasts from the air. Prior to the development of modern yeast strains, the production of artisanal breads was long and laborious because many batches of dough ended up being discarded. Can you explain this fact?

The dough is often contaminated by toxic spores that float in the air. It was one of Louis Pasteur's achievements to purify reliable strains of baker's yeast to produce bread consistently.

Plasmogamy

The fusion of the cytoplasm of cells from two individuals

Eucomycota (true fungi)

The true fungi are a polyphyletic group of organisms that share characteristics rather than sharing a single common ancestor. True fungi have a true nucleus and membrane-bound organelles

Growth

The vegetative body of a fungus is a unicellular or multicellular thallus. Dimorphic fungi can change from the unicellular to multicellular state depending on environmental conditions.

Why are fungi important decomposers? They produce many spores. They can grow in many different environments. They produce mycelia. They recycle carbon and inorganic minerals by the process of decomposition.

They recycle carbon and inorganic minerals by the process of decomposition.

two morphological stages of fungi

Vegetative and reproductive

What term describes the close association of a fungus with the root of a tree? a rhizoid a lichen a mycorrhiza an endophyte

a mycorrhiza

ascus

a sac-like structure that contains haploid ascospores

Positive effects of arbuscular (endotrophic) mycorrhizal or (AM) colonization

arbuscular mycorrhizal fungi (AMF) extends beyond the depletion zone (grey), accessing a greater area of soil for phosphate uptake. Benefits from colonization include tolerances to many abiotic and biotic stresses through induction of systemic acquired resistance (SAR).

Sporangium (sporangia)

asexual spore-producing bodies

During sexual reproduction, a homothallic mycelium contains all septated hyphae all haploid nuclei both mating types none of the above

both mating types

Which polysaccharide is usually found in the cell wall of fungi? starch glycogen chitin cellulose

chitin

Which of these organelles is not found in a fungal cell? chloroplast nucleus mitochondrion Golgi apparatus

chloroplast

Lichens

close association of a fungus with a photosynthetic alga or bacterium that benefits both partners

basidia

club-shaped fruiting body of basidiomycete

soredia

clusters of algal cells and mycelia that allow lichens to propagate

A fungus that climbs up a tree reaching higher elevation to release its spores in the wind and does not receive any nutrients from the tree or contribute to the tree's welfare is described as a ________. commensal mutualist parasite pathogen

commensal

homothallic

describes when both mating types are present in mycelium

Heterothallic

describes when only one mating type is present in an individual mycelium

Types of mycorrhizal fungi

ectomycorrhizal fungi, endotrophic mycorrhizal fungi, and epiphytes

Digestion

exoenzymes are transported out of the hyphae, where they process nutrients in the environment. Then, the smaller molecules produced by this external digestion are absorbed through the large surface area of the mycelium. As with animal cells, the polysaccharide of storage is glycogen, rather than starch, as found in plants.

Deuteromycota

former form phylum of fungi that do not have a known sexual reproductive cycle (presently members of two phyla: Ascomycota and Basidiomycota.) Most members live on land, with a few aquatic exceptions. Form mold.

ascocarp

fruiting body of ascomycetes

basidiocarp

fruiting body that protrudes from the ground and bears the basidia

Hyphae

fungal filament composed of one or more cells.

mycosis

fungal infection

endophytes

fungi that live inside tissue without damaging the host plant. Endophytes release toxins that repel herbivores, or confer resistance to environmental stress factors, such as infection by microorganisms, drought, or heavy metals in soil.

Karyogamy

fusion of nuclei

Yeasts

general term used to describe unicellular fungi

Fungal cells also contain:

internal membrane-enclssed organelles: mitochondria, endoplasmic reticulum, and Golgi apparatus. Some have structures similar to bacterial plasmids. No chloroplasts.

Fungal DNA

is in a membrane-bound nucleus.

Mycelium

mass of fungal hyphae

haustoria

modified hyphae on many parasitic fungi that penetrate the tissues of their hosts, release digestive enzymes, and/or absorb nutrients from the host

Mycorrhiza

mutualistic association between fungi and vascular plant roots

arbuscular mycorrhizae

mycorrhizae commonly involving Glomeromycetes in which the fungal hyphae penetrate the cell walls of the plant root cells (but not the cell membranes)

arbuscular mycorrhiza

mycorrhizal association in which the fungal hyphae enter the root cells and form extensive networks

Ectomycorrhizae

mycorrhizal fungi that surround the roots with a mantle and have a Hartig net that extends into the roots between cells

saprobes

organism that derives nutrients from decaying organic matter; also saprophyte

Faculative anaerobes

organisms that can perform both aerobic and anaerobic respiration and can survive in oxygen-rich and oxygen-poor environment

Obligate anaerobes

organisms that only perform anaerobic respiration and often cannot survive in the presence of oxygen

Obligate aerobes

organisms, such as humans, that must perform aerobic respiration to survive

Endotrophic or arbuscular mycorrhizae

penetrate into root cells and are characteristic of the Glomeromycetes

Glomeromycota

phylum of fungi that form symbiotic relationships with the roots of trees

Mycotoxicosis

poisoning by a fungal toxin released in food

Oomycota

produce oospores, have diploid nuclei in their hyphae, and do not have chitin in their cell walls

Mycology

scientific study of fungi

The wall dividing individual cells in a fungal filament is called a thallus hypha mycelium septum

septum

Coenocytic hyphae

single hypha that lacks septa and contains many nuclei

zygospores

structure with thick cell wall that contains the zygote in zygomycetes

A fungal infection that affects nails and skin is classified as ________. systemic mycosis mycetismus superficial mycosis mycotoxicosis

superficial mycosis

Commensalism

symbiotic relationship in which one member benefits while the other member is not affected

Parasitism

symbiotic relationship in which one member of the association benefits at the expense of the other

mold

tangle of visible mycelia with a fuzzy appearance

*Yeast is a facultative anaerobe. This means that alcohol fermentation takes place only if: the temperature is close to 37°C the atmosphere does not contain oxygen sugar is provided to the cells light is provided to the cells

the atmosphere does not contain oxygen But can't facultative anaerobes live in oxygen rich and oxygen depleted?

heterotrophic

using complex organic compounds as sources of energy and carbon

Thallus

vegetative body of a fungus

The advantage of yeast cells over bacterial cells to express human proteins is that: yeast cells grow faster yeast cells are easier to manipulate genetically yeast cells are eukaryotic and modify proteins similarly to human cells yeast cells are easily lysed to purify the proteins

yeast cells are eukaryotic and modify proteins similarly to human cells