lecture 17 Flashcards
1
Q
fungi
A
- 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
Q
a typical fungus is composed of
A
- 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
Q
fungi and spore production
A
- 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
Q
two types of fungi and spore production
A
- 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
Q
five groups of fungi
A
- 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
Q
five fungi
A
- chytrids
- zygomycetes
- glomeromycetes
- ascomycetes
- basidiomycetes
7
Q
chytrids
A
- 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
Q
zygomycetes
A
- 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
Q
glomeromycetes
A
- 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
Q
asomycetes
A
- 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
Q
basidiomycetes
A
- 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
Q
reproductive differences among the five fungal groups : zygomycetes
A
- 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
Q
reproductive differences among the five fungal groups: ascomycetes
A
- 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
Q
reproductive differences among the five fungal groups: basidomycete
A
- 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
Q
parasitic fungi
A
- 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
