BIO 120
Field Natural History
Spring
LECTURE 12
Fungi
Classified with plants at one time, but fungi are not plants.
I. Cell type, nutrition, habitats growth and reproduction.
A. Fungi are eukaryotes, and nearly all are multicellular.
B. Nutritional mode.
1. All fungi are heterotrophs- acquiring their nutrition from other organisms.
a. They are not green and do not photosynthesize.
2. Most are saprobes, absorbing their nutrients from dead organisms - saprophytic.
3. Many are parasitic - invading the tissue of living organisms.(Histoplasmosis, Valley fever)
4. Some fungi are mutualistic, absorbing nutrients from their hosts, but reciprocate to benefit
the host.
C. Structure – Fungi have filamentous bodies.
1. Basic unit of a fungus is the hypha (plural – hyphae). A filamentous thread.
2. A mass of hyphae are called mycelium.
3. Most hyphae divided into cells by septa (septum – singl.), which do not form a complete
barrier.
4. Fungal cell walls are made from a compound call chitin.
a. Very similar to the chitin that forms the hard external exoskeleton of insects.
5. The part of the mushroom that we are so familiar with is the fruiting body, which makes up
a small part of the fungus in time and space.
6. Largest organism? Armillaria, fungus on tree roots, spread up to 1,500 acres in Washington.
D. Growth and Reproduction
1. Fungi, like plants, are nonmotile organisms.
2. Fungi reproduce by spores that are produced either sexually or asexually.
3. Asexual repro. Occur by fragments of hyphae breaking away.
II. The diversity of fungi – 4 phyla + 1 symbiotic relationship (phylum Mycophycophyta)
A. Phylum Zygomycota (zygomycetes). Nonseptate – no cell walls except in reproductive
structures. (bread molds).
1. Live in soil on decaying plant and animal matter.
2. Most are saprobes, but some are parasites of plants, , insects or small soil animals.
B. Phylum Ascomycota (ascomycetes). Morels, truffles yeast.
1. Range in size from unicellular yeasts to elaborate multicellular fruiting bodies.
2. These are the fungi associated with algae the form the symbiotic relationship called lichen.
3. Also includes yeasts - for brewing beer, wine, sake and baking bread. Human pathogens, too.
C. Phylum Basidiomycota (basidiomycetes). Club fungi. Mushrooms. Puffalls, shelf fungi,
toadstools, Agaricus brunnescens (grocery store 'shrooms), poisonus Amanita muscaria, smut.
1. Important decomposers of wood. They can breakdown the complex polymer lignin.
2. Also includes mycorrhiza-forming mutualists and plant parasites.
D. Phylum Chytridiomycota (chytridiomycetes). Oldest group of fungi.
1. Predominately aquatic, though some live in soil.
2. Gametes still retain flagella
3. Best known as a pathogen of amphibians, but some are also plant pathogens.
E. Phylum Deuteromycota.(imperfect fungi) Fungi in which sexual reproduction does not occur.
1. Referred to as the imperfect fungi, because they lack a perfect stage, as the sexual cycle is
often called. (Penicillium – penicillin; Aspergillus – soy sauce)
2. The phylum designation has been retracted, since these fungi may not be phylogenetically
related. I’ll keep the name for the purposes of this class.
III. Important and well know fungal relationships.
A. Lichen - a symbiotic association of million of algae entangled in a mesh of fungal hyphae.
B. Mycorrhizae - are specific, mutualistic associations of plant roots and fungi.
C. Role of fungi as decomposers.
D. Pathogenic plant fungi - e.g Dutch elm disease.
E. Parasitic fungi – oyster mushroom anesthetizes nematodes; Arthrobotrys forms a noose to trap
nematodes; some fungi direct the behavior of insects (flies) so that spores will disperse well.
IV. Evolution of fungi
A. The origin of fungi is unknown.
1. The closest phylogenetic relationship is with a group of organisms called chytrids.
a. Same absorptive mode of nutrition, chitin in cell walls, hyphae.
2. Surprisingly, there is compelling evidence that animals are more closely related to fungi than
are the plants.
a. Fungi were not the ancestors of plants.
b. Believed that fungi and animals evolved from a common protist.
c. Based on comparisons of proteins and RNA (molecular systematics).
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