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Flashcards in lecture 17 Deck (22):
1

fungi

-one of four kingdoms in the domain eukarya
-heterotrophs
-do not eat their food like most hetertrophs
-acquire food via absorption
-secrete enzymes that digest food extracellularly and then absorb the resulting nutrients
-more closely related to animals than to plants
-found in soil and in water
-essential decomposers in most ecosystems
-although many fungi are beneficial some are parasitic
-parasitic fungi obtain their nutrients at the expense of plants or animals

2

a typical fungus is composed of

-hypae: threadlike filaments which branch repeatedly forming a feeding network known as mycelium
-hyphae are surrounded by a cell wall which is usually made of chitin
-chitin is strong and flexible: made of a nitrogen-containing polysaccharide
-usually hyphae consist of chains of cells seperated by cross-walls
-the cross-walls contain pores large enough to permit the exchange of large organelles such as ribosomes, mitocondria, and nuclei to pass from cell to cell
-some fungi lack cross- walls entirely and contain many nuclei within a single mass of cytoplasm
-fungal mycelium grow at very rapid pace
-branches through food sources and explores new territories
-grow longer without corresponding increase in thickness
-acts to increase the surface area for secretion of digestive enzymes and absorption
-a mycelium can add as much as 1 km of new hyphae each day

3

fungi and spore production

-fungi can usually reproduce sexually or asexually
-a large number of haploid spores are released and are transported over large distances by either wind or water
-if the spore lands in a moist environment with food supply it will germinate producing new fungus
-sexual reproduction of fungi results when:
-two haploid mycelia of different mating types release sexual signals, growing toward one another and fusing
-the cytoplasmic fusion is not immediately followed by fusion of the nuclei
-this stage is called a heterkaryotic stage in which cells contain two genetically distinct haploid nuclei
-hours, days, or even centuries may pass before the nuclei fuse, giving rise to the generally short lived diploid phase
-zygotes undergo meiosis within special reproductive structures, producing haploid spores

4

two types of fungi and spore production

-molds and yeasts only reproduce asexually
-called imperfect fungi
1. mold- refers to any rapidly growing fungus that reproduces asexually via spore production
-spores are usually at the tips of specialized hyphae
-found on rotting fruits and bread
2.- refers to any single-celled fungus
-reproduce asexually via budding
-these inhabit moist habitats and liquids:
-animal tissues
-plant sap

5

five groups of fungi

-more than 100,000 fungal species have been described
-may be more than 1.5 million
-diverged from a uniknot ancestor more than 1 billion years ago
-fossilized evidence exists from 460 million years ago
-sexual reproductive structures are often used to classify species
-all but one of the five groups of fungi lack flagellated spores

6

five fungi

1. chytrids
2. zygomycetes
3. glomeromycetes
4. ascomycetes
5. basidiomycetes

7

chytrids

-the only group of fungi with flagellated spores
-thought to represent the earliest linage of fungi
-found in lakes, ponds, and soil
-some are decomposers other are parasitic to plants, animals or protists
-decline in some frog populations attributed to chytrid infection

8

zygomycetes

-characterized by their resistant zygosporagium
-within the zygosporangium haploid spores form by meiosis
-diverse group
-includes fast growing molds ex) black bread mold
-molds that rot produce ex) strawberries
-some are animals parasites

9

glomeromycetes

-form distinct mycorrhizae
-hyphae that invade plant roots branch into tiny tree like structures called arbuscules
-80% of plants have a symbiotic partnership with glomeromycetes
-the glomeromycetes deliver phosphate and other minerals to plants while receiving organic nutrients in exchange

10

asomycetes

-also called sac fungi
-contain sac-like structures called asci that produces spores via sexual reproduction
-live in marine, freshwater and terrestrial habitats
-wide range in size
-unicellular to large multicellular structures
-some of the most devastating plant pathogens
-other live in symbiosis with green algae and bacteria ex) lichens

11

basidiomycetes

-also called club fungi
-most well known group of fungi and includes mushrooms
-named for club shaped spore producing structure called a basidium
-many of these species are excellent at breaking down the lignin found in wood
-therefore play key roles are decomposers
-include two groups of destructive plant parasites
1. rusts
2. smuts

12

reproductive differences among the five fungal groups : zygomycetes

-hyphae expand through food and the fungus reproduces asexually
-produces spores in sporangia at the tips of hyphae
-when food is depleted the fungus reproduces sexually
-mycelia of different mating types join and produce a cell containing nuclei from both parents
-this young zygosporangium develops into thick walled structure able to tolerate dry or harsh environments
-when conditions become favourable the two parent nuclei fuse and the diploid nucleus undergoes meiosis
-haploid spores are produced

13

reproductive differences among the five fungal groups: ascomycetes

-also reproduce asexually when conditions are favourable
-the haploid spores than mature in the spring
-the genetic diversity of these new spores increases the likeihood that at least one geneotype will survive and successfully establish itself in the new environment encountered in the new season
-surviving individals will reproduce asexually for many generations before once again reproducing sexually

14

reproductive differences among the five fungal groups: basidomycete

-life cycle: mushroom
-heterokaryotic stage begins when two hyphae from two different mating types fuse
-heterokaryotic mycelium is formed and grows producing the mushroom
-in club shaped cells called basidia (line the gills of the mushroom) haploid nuceli fuse forming diploid nuclei
-eech diploid nucleus undergoes meiosis producing haploid spores
-mushrooms may release up to a billion spores
-should the spores land on moist matter that may serve as food source they will germinate and become hapoid mycelia

15

parasitic fungi

-approx 30% of all known fungi are parasites or pathorgens: mainly of plants
-dutch elm diease:
-accidentally introduced into the US from europe on logs which were destined to become furniture
-over a number of decades the fungus destroyed 70% of elm tress across the eastern US
-english elms were completely wiped out
-DNA analysis revealed that all of these trees were genetically identically
-they were derived by asexual reproduction and therefore all equally susceptible to dutch elm diease
-crops are usually genetically indentical and thus highly susceptible to fungal diease
-approx 80% of plant dieases are caused by fungi
-leads to huge economic losses

16

corn infected with smut (club fungus)

-grayish growth called galls
-galls are made of heterokaryotic hypae which invade a developing corn kernal and eventually displace it
-the mature gall will open releasing thousands of grayish black spores

17

mycosis

a fungal infection

18

animals are much less susceptible to fungal infections

-animal fungal infections range from minor infections which are predominately irritating such as athletes foot to very serious infections such as coccidiomycosis, a fungal infection of the lung which can become sytemic
-yeasts are also what cause vaginal infections and many of the opportunities infections in AIDS patients and other immunocompromised patients

19

lichens

-lichens are fungi living in close association with photosynthetic organisms
-the association of millions of green algae or cyanobacteria wrapped tightly around a mass of fungal hypae
-such a close interaction that lichens are named as a single species
-the fungus obtians food from the photosynetheic partner and the fungal mycelium provides a suitable habitat fro the algae
-helps the algae to absorb and retain water and minerals

20

lichens are able to live in areas with little or no soil

-important pioneers on new land
-some tolerate severe cold
-carpets of them cover the arctic tundra
-they can also withstand severe drought
-opportunists growing in spurts while conditions are favorable
-when it rains the lichen absorbs water and photosynthesizes
-in dry air the lichen dehydrates and photosynthesis stops indefinitely while the fungus remains alive
-lichens are very sensitive to air borne pollutants such as sulfur dioxide
-death of lichens is a sign of poor air quality
-fungi receives most of its nutrients and minerals from the air

21

fungi and ants

-some fungi have mutually benefical relationships with ants
-fungi are decomposers which produce enzymes that digest plant material such as cellulose
-ants and termites take advantage of this
-the cellulose digesting enzymes are important to the ants which raise the fungus in farms
-they cultivate fungal gardens bringing leaves to the host
-the fungi feed on leaves using their enzymes to break down cellulose which ants cannot digest on their own
-the ants harvest the swollen fungal tips as food
-when a queen ant establishes a new colony she takes the fungal hyphae along with her in pouch in her mouth
-some of these fungi are so dependant that they may no longer survive without their ants

22

importance of fungi

-mushrooms are fungi
-some cheeses such as blue cheese come from fungi
-yeast are also used by humans to produce alcoholic beverages
-some fungi are also important for antibiotic production
-penicillium mold is responsible for producing penicillin