Fungi

C 31.1: Heterotrophs by absorption

Hydrolytic enzymes break down complex organic molecules into smaller compounds that can be absorbed by fungal hyphae.
Parasitic fungi absorb nutrients from cells of livings hosts. Some are pathogenic.
Mutualistic fungi absorb nutrients from a host, but they reciporcate with actions that benefit the host.

Consist of multicellular filaments and single cells (yeasts).
Yeast will occupy often moist environments, such as plant sap and animal tissues.
Hyphae are bodies of fungi which form a network of tiny filaments.
- Tubular cell walls surrounding plasma membrane and inner cytoplasm.
Chitin is an strong flexible polysaccharide which give strength, flexibility and absorption.
Septa are cross-walls/septas that have pores large enough to allow smaller organelles and cytoplasm to pass between adjacent cells.
- Coenocytic fungi lack Sepa, instead containing continuous cytoplasm with multiple nuclei, which allows for rapid growth and efficient nutrient transport within the mycelium.
Fungal Hyphae form an interwoven mass called Mycelium, that infiltrates material on which fungus feeds. Grows rapidly, focuses on surface area than girth.

Haustoria is an modified hyphae which allows them to extract nutrients from plants.
Arbuscules are specialized hyphae that exchange nutrients with their plant hosts.
- Mycorrhizae → mutualistic relationships between fungi and plant roots that enhance nutrient uptake for the plant while providing the fungus with carbohydrates.
Mycorrhizal fungi (fungi that form mycorrhizae) can improve delivery of phosphate ions and other essential nutrients, thereby bolstering plant health and increasing crop yields.
Ectomycorrhizal fungi form sheaths of hyphae over the surface of a root and typically grow into extracellular spaces of the root cortex.
Arbuscular mycorrhizal fungi extend arbuscules through invagination of the root cell plasma membrane.
Spores of mycorrhizal fungi spread the fungi in absence of humans.

Puffballs are the reproductive structures of certain fungal species.
- Spores can be carried long distances by wind or water.
If an spore lands in a favorable environment, it germinates and develops into a new fungal mycelium, which can then grow and produce additional spores.

Nuclei of fungal hyphae and spores of most fungi are haploid, although some can have diploid stages.
Sexual reproduction occurs when hyphae from two mycelia release pheromones.
- Pheromones will do a compatibility test, this process contributes to genetic variation.
Plasmogamy is the union of the cytoplasms of two compatible fungal cells, leading to the formation of a dikaryotic mycelium where two nuclei coexist in the same cell.
Heterokaryon (“different nuclei”) → parts of fused mycelium contain coexisting, genetically different nuclei.
Dikaryotic (“two nuclei”) → Haploid nuclei pair off two to a cell, one from each parent.
Karyogamy → haploid nuclei then fuse and produce diploid cells.
- Zygotes and other transient structures form during karyogamy, only diploid stage in most fungi.
Meiosis then restores haploid condition, leading to formation of genetically diverse spores.

Molds are a informal definition when asexually reproducing filamentous fungi produce haploid spores by mitosis, producing visible mycelia.
Spread incredibly quickly by massive dumps of spores while some do budding cells.
- “Bud cells” → asexual yeast growth where an ordinary cell division acts as a process that leads to the formation of new, genetically identical yeast cells, allowing for rapid population expansion.
- Many yeasts and filamentous fungi have no known sexual stage in their life cycle.
Deuteromycetes (second fungus) → fungi lacking any known sexual stage.

Opisthokonts →
Nucleariids → a group of amoeboid protists thought to be closely related to fungi, characterized by their ability to feed on bacteria and their similar DNA sequences.
Multicellularity evolved in animals and fungi independent, form different single-celled ancestors.
Despite knowledge us claiming fungi are from an aquatic nature, we have terrestrial “fossils” proving otherwise.