Exam 3 - Cont. Flashcards
are fungi heterotrophs? what makes them different
`yes but they are unique
they do not eat their food the same they acquire food through absorption
secrete enzymes that digest food extracellular and then absorb the resulting nutrients
is fungi more closely related to animals or plants
animals
where are fungi found
in soil and water
can fungi be parasitic
yes
they are essential decomposers in most ecosystems but some are also parasitic
parasitic fungi obtains their nutrients at the expense of plants or animals
what are typically fungi composed of
hyphae
cell wall
what is a fungi hyphae
threadlike filaments which branch repeatedly forming a feeding network known as mycelium
what is the hyphae surrounded by and what is it usually made of
surrounded by the cell wall
the cell wall is usually made of chitin
chitin is strong and flexible made of a nitrogen containing polysaccharide
what are cross walls
the hyphae of the fungi consists of chains of cells separated by cross walls
the cross walls contain pores large enough to permit the exchange of large organelles such as ribosomes mitochondria and nuclei to pass from cell to cell
do all fungi have cross walls
some fungi lack cross walls entirely
so they contain many nuclei within a single mass of cytoplasm
explain fungal mycelium growth
grows at a 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 kilometer of new hyphae each day
does fungi reproduce asexually or sexually
they c an reproduce in both ways
how are the fungal spores transported
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 a food supply it will germinate producing new fungus
when does sexual reproduction of fungi result
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 heterokaryotic stage
explain the heterokaryotic stage
when 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
what are some examples of fungi that can only reproduce asexually
molds and yeasts
called imperfect fungi
describe molds
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
describe yeasts
refers to any single celled fungus reproduce asexually via budding these inhibit moist habitats and liquids animal tissues plant sap
how many fungal species have been described
more then 100 000
maybe even 1.5 million
where did fungi diverge from and when
unikont ancestor more then 1 billion years ago
fossilized evidence exists from 460 million years
how are the fungal species typically classified by
sexual reproductive structures
all but one of the five groups of fungal lack flagellated spores
what are the 5 groups of fungi
chytrids zygomycetes glomeromycetes ascomycetes basidiomycetes
describe chytrids
the only group of fungi with flagellated spores
thought to represent the earliest lineage of fungi
found in lakes ponds and soil
some are decomposers others are parasitic to plants animals or protists
decline in some frog populations attributed to chytrid infection
describe zygomycetes
characterized by their resistant zygosporangium
diverse group that includes fast growing molds like black bread mold
molds that rot produce like strawberries
some are animals parasites
what is the zygosporangium
within this structure haploid spores form by meiosis
describe glomeromycetes
form distinct mycorrhizae
80% of plants have a symbiotic partnership with Add to dictionary
the glomeromycetes deliver phosphate and other minerals to plants while receiving organic nutrients in exchange
what are mycorrhizae
hyphae that invade roots branch into tiny treelike structures called arbuscules
describe ascomycetes
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 such as lichens
describe basidiomycetes
also called club fungi
most well know group of fungi and includes mushrooms
named for club shaped spore producing structure called basidium
many of these species are excellent at breaking down the lignin found in wood
therefore they play key roles as decomposers
include two groups of destructive plant parasites
1) rusts
2) smuts
how do zygomycetes reproduce
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 explain this
this young zygosporgangium develops into a thick walled structure able to tolerate dry or harsh environments
when conditions become favourable the two parent nuclei fuse and the diploid nucleus undergo meiosis
haploid spores are produced
how do ascomytes reproduce when conditions are favourable
asexually
when does sexual reproduction occur for many fungal species
the fall
the haploid spores mature in the spring
the genetic diversity of these new spores increases the likelihood that at least one genotype will survive and successfully establish itself in the new environment encountered in the new season
surviving individuals will reproduce asexually for many generations before once again reproducing sexually
explain the life cycle of a basidiomycete
a 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 (the gills) haploid nuclei fuse forming diploid nuclei
each 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 a food source they will germinate and become haploid mycelia
how many fungi are parasitic
30% are parasites or pathogens
mainly plants
explain Dutch elm disease
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 trees across the eastern US
what plant was completely wiped out by dutch elm disease
English elms
DNA analysis revealed that all of these trees were genetically identical
they were derived by asexual reproduction and therefore all equally susceptible
crops are usually genetically identical and thus highly susceptible to fungal disease
what causes 80% of plant disease what does this affect
caused by fungi
leads to huge economic losses
explain animal and fungal infections
animals are much less susceptible
range from minor like athletes foot to very serious like coccidiomycosis a fungal infection of the lung
yeast infections
define mycosis
a fungal infection
what is smut
a club fungus that infects corn
describe corn infected smut
grayish growth are called galls
galls are made of herterokaryotc hyphae which invade a developing corn kernel and eventually displace it
the mature gall will open releasing thousands of grayish black spores
define 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 hyphae
such a close interaction that lichens are named as a single species
the fungus obtain food from the photosynthetic partner and the fungal mycelium provides a suitable habitat for the algae which helps the algae to absorb and retain water minerals
describe lichens
able to live in areas with little or no soil
important pioneers on new land
some tolerate severe cold and severe draught and can live in the arctic tundra
opportunists growing in spurts while conditions are favorable
describe lichens and climate
when it rains the lichens absorb water and photosynthesizes
in dry air the lichens dehydrates and photosynthesis stops indefinitely while the fungus remains alive
what does the death of lichens signify
lichens are very sensitive to air borne pollutants such as sulfer dioxide
the death of lichens is a sign of poor air quality
fungi receives most of its nutrients and minerals from the air
explain fungi and ants
have a mutually beneficial relationship
fungi are decomposers which produce enzymes that digest plant material such as cellulose
ants and termites take advantage of this and take the leaves to the host
the fungi feed on leaves using their enzymes
the ants eat the swollen fungal tips
queen ant takes fungal hyphae
some of these fungi are so dependent that they may no longer survive without ants
