Fungi Flashcards

Question

How do mucoromycetes reproduce?

Answer 1

Mucoromycetes **reproduce sexually** through the formation of **zygosporangia**, which form after the fusion of specialized hyphae - Zygosporangia are resistant to harsh conditions such as freezing and drying, enabling them to survive unfavourable environments. - Karyogamy (the fusion of nuclei) and meiosis occur within zygosporangia.

Answer 2

Mucoromycota includes glomeromycetes, a clade of fungi that form mycorrhizae, mutually beneficial symbiotic relationships between fungi and plant roots. - Glomeromycetes play a **significant ecological role** by establishing **arbuscular mycorrhizae** (endomycorrhizae) with ~70–80% of plant species. - Mycorrhizae facilitate the **exchange of minerals and nutrients**, enhancing the overall health and growth of plants. - Specialized hyphae that push into plant root cells branch into tiny treelike **arbuscules**. - Glomeromycetes reproduce via asexual soil spores; no evidence of sexual reproduction.

Answer 3

Most fungi are these (~98% of fungal diversity) - Includes: edible mushrooms, yeast strains utilized in bread, beer, and cheese production, significant wooddecaying fungi, as well as various pathogens affecting both crops and humans. Characterized by: - formation of **septate hyphae** - the development of **dikaryotic hyphae** after plasmogamy Two Clades: - Ascomycetes and Basidiomycetes

Answer 4

**Ascomycetes** typically exhibit a brief dikaryotic stage, with plasmogamy and karyogamy occurring in relatively rapid succession. **Basidiomycetes** often maintain a prolonged dikaryotic phase, where dikaryotic hyphae frequently dominate the mycelium structure.

Answer 5

During the heterokaryotic stage, these fungi produce dikaryotic cells (n + n) containing two haploid nuclei, each contributed by a different parental strain.

Answer 6

Ascomycetes (phylum Ascomycota, “sac-fungi”) are the **most diverse fungi** (~90k species) and are found in a **variety of marine, freshwater, and terrestrial habitats**] - Can be very small (yeast) to very large (sup fungi, truffles) - Includes wood-decyaing fungi, symbitic organsms, pathogens, fungal lichens, yeasts **Produce sexual spores** within sac-like structures called **asci**, which are contained in specialized fruiting bodies known as **ascocarps** (carp = fruit). Ascomycetes **reproduce asexually** via the production of vast quantities of **asexual spores** termed **conidia**. - Conidia are not formed within sporangia; instead, conidia are produced at the tips of specialized hyphae called **conidiophores**.

Answer 7

Include: a range of familiar fungi, including toadstools, puffballs, shelf fungi, ectomycorrhizae, and the plant pathogens smuts and rusts. - They play crucial roles as decomposers, particularly in breaking down lignin-rich wood. Typically, the life cycle of basidiomycetes involves a **prolonged phase of dikaryotic mycelium**, where two different nuclei coexist within the same hyphal compartment. A defining feature of Basidiomycetes is their **club-shaped structures called basidia**, transient diploid stages in their life cycle (“club fungi”). In response to environmental cues, Basidiomycete mycelia undergo **sexual reproduction** by generating elaborate, multicellular fruiting bodies known as **basidiocarps**. - Basidiocarps include classic mushrooms and toadstools.

Answer 8

In response to environmental cues, Basidiomycete mycelia undergo **sexual reproduction** by generating elaborate, multicellular fruiting bodies known as **basidiocarps**. - Basidiocarps include classic mushrooms and toadstools. Within a short-lived **basidiocarp** (cap), thin vertical sheets of mycelia called gills are lined with millions of **basidia**. - Young basidia start as dikaryotic cells (n+n), which undergo karyogamy to become diploid (2n) nuclei. - At maturity, diploid basidia undergo meiosis to produce four basidiospores, each containing a single haploid nucleus. - A single mushroom cap can release up to a billion basidiospores.

Answer 9

− Decomposers − Mutualists − Pathogens

Answer 10

Most dead organic matter in soils is from plant tissues: cellulose and lignin. - While some saprotrophic bacteria and protists can decompose these materials, **fungi are the primary decomposers of most plant matter**.

Answer 11

Saprotrophs (sapro = detritus) are organisms that obtain their nutrition by decomposing organic matter from dead organisms or waste material. - Saprotrophic fungi play a crucial role in ecosystems by breaking down complex organic molecules into simpler, inorganic forms, which are then recycled back into the environment

Answer 12

1. Endophytes (fungus-plant mutualisms) 2. Mycorrhizae (The roots one) 3. Lichens 4. Animal-fungus mutualisms

Answer 13

Plants host many harmless symbiotic **fungal endophytes**, which reside in the intercellular spaces of leaves or other plant tissues. - This relationship is often mutualistic, as endophytes enhance the health and survival of host plants by producing toxins that deter herbivores and pathogens. - Most fungal endophytes are Ascomycetes

Answer 14

Mycorrhizae (fungus-plant mutualisms) are mutually beneficial symbiotic relationships between fungi and the roots of many plant species Mycorrhizal fungi **supply plant roots with water and essential nutrients**, such as phosphorus and nitrogen, extracted from the soil. - In return, the fungi receive carbohydrates from their plant hosts. - Mycorrhizae play a crucial role in natural ecosystems and agriculture. - Plants grown with mycorrhizae typically exhibit better growth compared to those without, especially in nutrient-poor soils. **Around 80–90% of plant species form some type of mycorrhizal associations**, primarily of two types: - **Ectomycorrhiza** (limited to ~6,000 mostly woody species, e.g. conifers). - **Endomycorrhiza** (all other mycorrhizal associations). Evidence from the fossil record indicates that mycorrhizal associations likely existed with the earliest vascular plants, suggesting a co-evolutionary history between plants and fungi on land.

Answer 15

Ectomycorrhizal fungi **envelop the roots of plants without penetrating the root cells**. - The mycelium forms a dense sheath of hyphae (mantle) over the root, while hyphae extend into the surrounding soil. - Hyphae also penetrate the spaces between the cell walls of the root. - Ectomycorrhizae are found across multiple fungal groups (mucoro-, asco- and basidiomycetes) and are believed to have evolved independently on multiple occasions. - Ectomycorrhizal associations are **limited to about 5–10% of plant species**, primarily in certain tree families, including pines, oaks, and birches. - Play a crucial role in nutrient cycling in temperate and boreal forest ecosystems

Answer 16

The most common endomycorrhizae are **arbuscular mycorrhiza**. - Hyphae of arbuscular mycorrhizae penetrate the cell walls of root cells, forming intricate invaginations of the root cell membrane. - Highly branched hyphal structures (arbuscules) greatly expand the surface area available for nutrient exchange. Arbuscular mycorrhizae are a low diversity (~300 species) monophyletic group (clade Glomeromycetes) within Mucoromycota. - Arbuscular mycorrhizal associations are found in ~70–80% of plant species and are most common among herbaceous plants, grasses, and crop species.

Answer 17

Lichens are mutually beneficial (symbiotic) associations between photosynthetic microorganisms and fungi. - A lichen appears, functions, and **reproduces as a single organism**. - The photosynthetic component can come from ~100 species of green algae (Chlorophyta) or cyanobacteria (prokaryote). - ~20,000 lichen species of lichen that are named for the fungal partner. - **Most (>90%) of lichen fungi are Ascomycetes**. **Fungi provide an environment for photosymbiont growth and reproduction** (protection, free from competition, fungal mycelia retains water and minerals). The algae or cyanobacteria provide organic carbon compounds and, in the case of nitrogen-fixing cyanobacteria, organic nitrogen. **Lichens are pioneers of mineral surfaces**. - Some lichens grow on rocks without soil, breaking down the rocks into soil for plants. - Lichen secretes weak acids that dissolve rock. - The swelling of hyphae in cracks promotes the fracturing of rock. - Lichens trap windblown particles. Lichens may have helped colonization of land by plants 550–600 mya by promoting soil formation.

Answer 18

The fungi of lichens can reproduce **sexually or asexually**. - Asexual reproduction is through fragmentation or the formation of soredia, small clusters of hyphae containing embedded algae

Answer 19

Some fungi share their digestive services with animals, such as cellulose-digesting chytrid mutualists inhabiting the guts of sheep and cattle. Ex. Many species of leafcutter ants utilize the digestive power of fungi by cultivating them in “farms” to feed their larvae, while adult ants feed on leaf sap

Answer 20

1. Plant-parasitic fungi 2. Invertebate-parasitic fungi 3. Vertebrate-parasitic fungi

Answer 21

Fungi are the **2nd most important pest of plants** after insects Some fungal pathogens targeting food crops **can produce toxins hazardous to human health**. - Ex. ergot - Causes ergotism in mammals The globalization of trade has facilitated the spread of plant-parasitic fungi - Ex. Dutch elm disease, Mountian pine beetle (blue-stain fungus)

Answer 22

A plant parasitc fungi that can lead to **ergotism** in humans and other mammals when contaminated grains are consumed - Ergot replaces seed with its mycelium mass, which produces alkaloid toxins, including lysergic acid derivatives, which are similar to psychedelic drugs (LSD), that affect circulation and neurotransmission. - Ergotism is characterized by gangrene, nervous spasms, burning sensations, hallucinations, and temporary insanity. - More than 40,000 people died from ergotism during the Middle Ages (“St. Anthony’s Fire”).

Answer 23

Caused by plant parasitic fungi - Dutch elm disease was accidentally introduced into North America in the 1930s in imported elm wood. - Ascomycete fungi (two Ophiostoma species) are spread by elm bark beetles. - The tree blocks its xylem to prevent fungal infection, causing the tree to wilt, eventually leading to death.

Answer 24

Fungi can parasitize arthropods, such as insects and arachnids. - Arthropods have **chitin-reinforced exoskeletons**. - Fungi have **chitin cell** walls and can digest chitin to reabsorb old mycelia. Invertebrate-parasitic fungi often act as parasitoids that slowly kill their hosts. - Examples: Entomophthora (Zoopagomycota), which produces spores inside hosts; Ophiocordyceps unilateralis (Ascomycota), known as the zombie-ant fungus, which produces fruiting structures that burst through the host’s body

Answer 25

Fungi can infect vertebrates causing **mycosis**, fungal infections of animals or humans. - A **cutaneous mycosis** occurs on the outer layers of the skin, e.g. fungi digest keratin (structural proteins of the skin). - e.g. human skin disease called ringworm (ring-shaped growth of hyphae). - e.g. the global decline of amphibians has been linked to chytrid infections. - **Systemic mycosis** occurs when a fungal pathogen spreads widely inside the host’s body to many organs. - Immuno-compromised people are susceptible to systemic fungal infections.

Answer 26

Candida albicans is commonly found in the gut microbiome and on moist surfaces where it is usually harmless. Candida albicans infections are **opportunistic**: - Cause oral or genital infections under humid conditions, e.g. diaper rash. - Colonizes mucous membranes if the normal microbiota is absent, or if chemical conditions change, e.g. following antibiotic treatment.

Answer 27

Histoplasmosis is a **systemic mycosis** commonly found in North America. - Histoplasma capsulatum (ascomycete) fungus **grows in soil contaminated with bird or bat droppings**. - Disturbing the substrate leads to the inhalation of asexual spores. - Histoplasmosis **primarily affects the lungs** where the fungus morphs into yeast at body temperature. - Can spread from the lungs to other organs, becoming systemic and fatal if left untreated. - This disease poses a **significant risk to immunocompromised individuals**.

Answer 28

Humans consume a variety of fungi: - The common cultivated mushroom (Agaricus bisporus), a basidiomycete. - Originally domesticated in France during the 17th century, its annual worldwide production is ~1 million tons. - Varieties such as white, crimini, and portobello mushrooms are widely cultivated and consumed. - Other mass-produced mushrooms species, include oyster and shiitake. - Certain high-value wild fungi, such as truffles and morels, are prized for their unique flavours and are often used in gourmet dishes. - Some fungi possess psychoactive properties, as seen in “magic” mushrooms, which have been used for ceremonial and recreational purposes in various cultures. Fungi in food production: - Penicillium camemberti, an ascomycete, is utilized in cheese-making processes, contributing to the distinctive flavours and textures of cheeses like Camembert. - In fermentation processes, Saccharomyces cerevisiae (ascomycete), commonly known as brewer’s or baker’s yeast, is integral to the production of alcoholic beverages and leavened bread.

Answer 29

A **cutaneous mycosis** occurs on the outer layers of the skin, e.g. fungi digest keratin (structural proteins of the skin). - e.g. human skin disease called ringworm (ring-shaped growth of hyphae). - e.g. the global decline of amphibians has been linked to chytrid infections. **Systemic mycosis** occurs when a fungal pathogen spreads widely inside the host’s body to many organs. * Immuno-compromised people are susceptible to systemic fungal infections

Fungi Flashcards

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