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Unformatted text preview: Exam 3wed. Oct. 14- Tuesday Oct.20 Kingdom Fungi History Appear in the fossil record about 46 MYA Very diverse group- over 100,000 known species, but may be >1.5 million species (fig. 31.9) Structure They are eukaryotes Some are unicellular (the yeast but most are composed of filaments called hyphae) They hyphae possess typical eukaryotic cellular structures- nuclei, mitochondria Cell walls are composed principally of chitin (some animals eg. Insects, produce chitin as well) Most hyphae are divided into individual cells by cross-walls called septa The septa have pores Some fungi lack septa and have coenocytic hyphae Mass of hyphae is called a mycelium (fig. 31.2) Mycelia can be huge- one individual of the species Armillaria ostoyae was reported to have a mycelium spread through 2,400 acres of soil (estimated to weigh hundreds of tons) Specialized hyphae Arthrobotrys-a nematode trapping fungus/ Haustoria- allow penetration of host cells Fungal Nutriton All fungi are chemoheterotrophs Aquire nutrients by absorption: o Fungus secretes enzymes outside its body o Food is digested o Smaller molecules absorbed (distinct from ingestion) Ecological significance extremely important as decomposers of dead organisms, waste products, ect. Also important as both mutualists and pathogens DNA sequence comparisons indicate that fungi and animals are more closely related to each other than either are to plants Five Phyla: (fig. 31.11) Chytridiomycota Zygomycota Sexual reproduction is known to occur in most fungi In most fungi the zygote is the only 2N cell of the life cycle. 5 phyla in kingdom fungi based on sexual reproductive structures Deuteromycetes have no known sexual stages and cant be assigned to a phylum Phylum Chytridomycota Mainly aquatic, single-celled or filamentous (mostly coencytic hyphae) with cell walls made of chitin About 1,000 known species Only group of extant fungi in which flagella are produced (allomyces and chytridium) Amphibian chytridiomycosis Some species of chytrids are parasites of amphibians May be involved in the world-wide decline in amphibian populations Phylum Zygomycota 1,000 known species Have doenocytic hyphae Mostly terrestrial Produce resistant zygosporangia (fig.31.5) Zygosporangium Resistant to harsh conditions Contains many 2N zygotes, each of which will undergo meiosis to produce 1N spores Sporangium Produces haploid spores by mitosis for asexual reproduction Phylum Glomeromycota Only 160 known species Important in forming arbuscular mycrrhizae (endomycorrhizae) with various plant species 90% of all plants have mycorrhizal relationships with members of this phylum Mycorrhizae Mostly members of glomeromycota- some basidiomycota and ascomycota Roots of almost all vascular plant species form mycorrhizal relationships Very important inn allowing plants to accumulate mineral nutrients...
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