Ch 19 Fungi

19.1 Fungi are essential decomposers Fungi live nearly everywhere on earth. There are more than 80,000 species. Some fungi can cause disease or spoil food, but many are used for food and drink production. Fungi are vitally important ecologically.

A. Fungi are eukaryotic heterotrophs that have external digestion Fungi are more closely related to animals than plants. Characteristics of fungi- Eukaryotic Heterotrophs that release digestive enzymes then absorb the nutrients Cell walls are made of chitin similar to exoskeletons of some animals Energy storage form is glycogen like animals Most are multicellular, but yeasts are unicellular

Unique reproductive cycles- in most species the only diploid cell is the zygote- the zygote undergoes meiosis, yielding haploid nuclei, then they divide mitotically as the organism grows Some have a dikaryotic stage which is unique to fungi Most of a fungus is the underground feeding structure consisting of threadlike hyphae- hyphae can aggregate as a mass to form visible strands called mycelium- hyphae cannot be seen in food until the reproductive structure emerges at the surface. Spores are the reproductive cells. They land on food source and produce feeding hyphae

Spores can be produced by sexual or asexual reproduction Spores produced asexually are called conidia Sexually produced spores are more complex- hyphae aggregate to form a fruiting body which is the above ground mushroom, puffball or truffle that is visible.

B. Classification of fungi Five major groups- chytridiomycetes, glomeromycetes, zygomycetes(not sure of evolutionary relationships) Ascomycetes and basidiomycetes are sister groups that are the most complex

19.2 Chytridiomycetes Phylum Chytridiomycota- 1,000 species- main feature is production of zoospores- which are motile spores with a flagella. They are powerful decomposers. They live in the digestive tract of ruminant animals, helping to break down cellulose. They also contribute to the decline of amphibian populations- Batrachochytrium dendrobatadis infects the skin of frogs and feeds on keratin- it interferes with the frogs ability to absorb oxygen through the skin.

19.3 Zygomycetes 1000 species, includes black mold that grows on foods Fast growing- reproductive structures fuse to form a zygospore The zygospore undergoes meiosis to form haploid hyphae which produces a spore sac that releases many spores.

19.4 glomeromycetes Phylum Glomeromycota- smallest group only 200 known species Unusual feature- live only in association with plants- called mycorrhiza Mycorrhiza- colonize plant roots where they absorb water and nutrients which is shared with the plant They produce large asexual spores- no sexual spores are produced.

19.5 Ascomycetes- sac fungi Phylum Ascomycota- Largest group- 50,000 species. Examples- Pests that cause Dutch Elm disease, athletes foot, molds that ruin flooded homes. Some benefit humans, such as- food like morels and truffles, Penicillin, yeast(Saccharomyces), cyclosporine used as an immunosuppressant

Still 19.5 Ascomycetes reproduces sexually and a sexually by producing spores. In Sexual reproduction, hyphae fuse, but the individual nuclei do not fuse. This produces dikaryotic spores. The fruiting body is made of tightly woven hyphae that are dikaryotic. Eventually, the nuclei fuse to form a diploid zygote. The zygote immediately undergoes meiosis to form haploid ascospores. The ascospores develop in the ascus which is sac-like. The ascospores are dispersed producing new haploid individuals.

19.6 Basidiomycetes Phylum Basidiomycota- 30,000 species- club fungi Includes- mushrooms, puffballs, stinkhorns, shelf fungi, and birds nest fungi Some are edible, some are deadly, others are hallucinogenic. Smuts and rusts are plant pathogens. Vital to the carbon cycle. Cause wood to dry rot.

Still 19.6 Reproduction in basidiomycetes- can reproduce asexually, but sexual reproduction cycle is the most prominent. Fused haploid hyphae form a dikaryotic myclelium. The mycelium usually stays imbedded in the food source, but once conditions are right, the mushrooms with emerge. The gills of the mushroom are lined with club shaped basidia. The basidia house a diploid zygote that undergoes meiosis to form four haploid cells. These cells migrate to the basidiospore and are dispersed.

19.7 Fungi interact with other organisms A. endophytes live in aerial plant parts Some fungi live between the cells of plant leaves and stems without causing disease. Some actually help the plant defend against herbivores.

B. Mycorrhizal fungi live on or in roots 80% of all land plants form mycorrhizae. Some cannot live without them. Glomeromycetes form the most common type of mycorrhizae which pierces the plant roots so that the plant and fungi exchange materials. Ascomycetes and basidiomycetes form a different type called ectomycorrhizae which to not penetrate the roots of the plant. Many edible fungi depend on trees and cannot be commercially cultivated.

C. Some ants cultivate fungi Leaf cutter ants use leaves to grow a basidiomycete called Lepiota. They eat the hyphae before the mushroom can form. It is a mutualistic relationship. D. Lichen are distinctive dual organisms- lichens form when an ascomycete or basiodiomycete harbor algae between their hyphae. They appear to be one organism and can have a variety of shapes. Lichens are very ecologically important because they break down rock to form soil. They can grow everywhere and survive drought and harsh conditions. They are particularly sensitive to pollution so they are used as ecological indicators.