Fungi (sing: fungus) were previously classified as part of the plant kingdom, but removed because they lack chlorophyll and are not photosynthetic. These organisms probably evolved from the fungus-like_protists. They are heterotrophs, but are not active seekers of food and do not ingest their food. Rather, they use enzymes to digest nutrients outside their bodies then absorb the nutrients. In other words, they are saprobes (saprophytes). Most species are non-motile. There are +/- 80,000 species most of which are terrestrial forms. Most are filamentous_molds. There are three fungal nutritional modes:
(1) Saprobes (saprophytes or saprotrophs), or nutrient absorbers. Some are decomposers, a special class of saprobes.
(2) Mutualistic_symbionts, which associate with, assist and benefit from other organisms (the lichens are an example).
(3) Parasitic_symbionts, which absorb nutrients from a living host and may harm the host. The parasitic forms are pathogenic and produce special intrusive hyphae called haustoria. The haustoria can penetrate the host’s body. EX: Trichophyton_mentagrophytes the causative agent of athlete’s foot as well as ringworm.
Fungi may be beneficial or harmful. Some may change their capacity as their environment changes (like the vaginal yeasts). Examples of beneficial interactions include:
(1) They can be used as a food or in the production of food, such as the production of bread and beer (from yeasts), mushrooms, truffles, various cheese molds (including those that create Camembert, Blue, Brie, Roquefort, and Stilton cheeses) and soy_sauce production from Aspergillus_oryzae.
(2) They produce medicines, such as penicillin from the Penicillium mold and LSD (for psychotherapy) from Claviceps_purpura. C. purpura is the infective agent of rye (ergot_poisoning) and the basis for the witchcraft legends.
The general body structure of a fungus includes:
(1) Hyphus (Hyphae): Thread-like (filamentous) basic unit of body structure.
(2) Septum (Septae): Cross-walls that separate one hyphus from another.
(3) Mycelium (Mycelia): Tangles mass of hyphae. The body of the fungus.
(4) Chitin: Carbohydrate component of fungus cell walls.
Reproductive processes of fungi occur after the rapid growth of hyphae leads to the formation of the twisted body mass called the mycelium. The mycelium is located within a food source. Where hyphae touch the surface of the substrate, small projections called rhizoids are extended into the substrate. The rhizoids act as anchors, and also increase surface area to enhance the absorption of nutrients. Hyphae that create a horizontal path across the surface of the substrate are called stolons. When the mycelium matures, reproductive hyphae grow and produce spore chambers that produce spores.
When the spore chambers mature, spores are released. A positive growth environment provides for the production of asexual_clones. When environmental conditions become unfavorable, sexual_gametes will be produced.
Asexual reproduction is accomplished by either vegetative_propagation or the production of asexual_spores. Asexual spores develop in a structure called a sporangium (pl: sporangia).
Sexual reproduction involves production of haploid spores that develop in a structure called a fruiting_body. Sexual reproduction is called syngamy and is the sexual union of two individuals.
The Ascomycota (Ascomycetes) includes the yeasts, many molds, mildews and the truffles. Ascomycota specializations include a septate body structure with perforations in the cell walls to accommodate cytoplasmic movement among cells. Their asexual stage is the conidiophore, which produces conidia spores rapidly when environmental conditions are favorable. Their sexual phase is via the production of the ascocarp, which is created by the asexual phase. The ascocarp produces asci and the asci contain ascospores, which are haploid. Approximately 30,000 species exist, 300 of which are unicellular yeasts.
This slide shows asci (sing: ascus) with ascospores in the hymenial layer. The central layer of tissue is asexual supporting tissue, and is referred to as the peridium.