Ch 29 Fungi

How do fungi meet nutritional needs?

Fungi are absorptive heterotrophs that use extracellular digestion, secreting digestive enzymes outside their hyphae to break down complex organic compounds which are then absorbed.

What are the three primary ecological roles of fungi?

1. Saprophytes (Decomposers): Digest dead matter and recycle nutrients.

2. Mutualists: Partner with living organisms, exchanging soil minerals for sugars.

3. Parasites: Absorb nutrients from living hosts, potentially causing disease.

What are hyphae?

Narrow, thread-like cellular filaments forming the basic units of multicellular fungi, with a high surface-area-to-volume ratio for efficient nutrient absorption; typically haploid with chitin cell walls.

What is a mycelium?

An interwoven network of thousands of interconnected hyphae that absorbs nutrients and can condense into reproductive structures like mushroom caps.

What are septa?

Internal cross-walls that divide hyphae into cell-like compartments, containing pores that allow movement of cytoplasm, nutrients, and organelles.

What are coenocytic hyphae?

Hyphae without septa, forming one large multinucleate cell with thousands of haploid nuclei sharing the same cytoplasm for rapid internal transport.

What is plasmogamy?

The first stage of sexual reproduction in fungi where the cytoplasm of two compatible haploid mycelia fuses while their nuclei remain separate.

What is a heterokaryon?

A cell or hypha that contains two or more genetically distinct haploid nuclei within a shared cytoplasm, formed after plasmogamy.

What does the term dikaryotic (n + n) mean?

A specialized heterokaryotic state in which each compartment has exactly two haploid nuclei, one from each parent, persisting for months or years.

What is karyogamy?

The final stage of fertilization in fungi where two haploid nuclei fuse to form a diploid zygote nucleus, which is short-lived and quickly undergoes meiosis.

Phylum Chytridiomycota

Fungal phylum found in aquatic environments; possesses flagellated gametes and spores; exhibits alternation of generations. Example: Allomyces macrogynus.

Phylum Zygomycota

Terrestrial molds with coenocytic hyphae; forms zygosporangium for zygote protection; reproduces asexually via wind-dispersed spores. Example: Rhizopus stolonifer.

Phylum Glomeromycota

Closely related to zygomycetes; forms arbuscular mycorrhizae with plants; obligate mutualists with no commonly observed sexual cycle.

Phylum Ascomycota

Known as 'sac fungi'; sexual reproduction in cup-shaped ascocarps; produces eight haploid ascospores per ascus. Example: Cookeina speciosa.

Phylum Basidiomycota

Known as 'club fungi'; includes mushrooms and rusts; dominated by dikaryotic mycelia; produces basidiocarps and spores. Example: Amanita muscaria.

What is the morphological difference between yeasts and molds?

Yeasts are single-celled fungi reproducing by budding; molds are multicellular fungi with filamentous mycelia.

Contrast Ectomycorrhizal Fungi (EMF) and Arbuscular Mycorrhizal Fungi (AMF).

EMF forms sheaths around roots, does not penetrate cell walls, and provides nitrogen; AMF penetrates root tissues and forms arbuscules, primarily providing phosphorus.

What is a lichen and its unique relationship?

A mutualistic partnership between a fungus (usually ascomycete) and a photosynthetic partner; the fungus provides structure and protection, while the partner produces sugars.

How do lichens reproduce as a single unit?

Through soredia, tiny packets of algal cells wrapped in fungal hyphae that can disperse and form new lichens.

What are the negative impacts of fungi?

Fungi can cause major plant diseases and human infections such as athlete's foot, ringworm, and systemic infections.

What are the positive impacts of fungi?

Fungi serve as food sources, are used in fermentation processes, and produce medically important compounds like antibiotics.