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Fungi
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Video: Fungi
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Discovery Channel video 2 mins
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Fungi
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Fungi can be found anywhere from athlete’s foot to
spoiled food, and even on our dinner plate.
There are more than one million species of fungi,
many of which are just mushrooms.
Fungi are more closely related to animals than to
plants.
The few fungi that are single celled are called yeasts;
most fungi are multicellular and are called molds.
They have cell walls made of chitin.
Their threadlike fungal filaments are called
hyphae.
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A fungus usually consists of a mass of threadlike
hyphae
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Called a mycelium
Hypha
Mycelium
Figure 17.15B, C
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Fungi
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Although a few species of fungi can cause
disease, most fungi are essential to our
ecosystem.
They break down organic material and recycle
nutrients, allowing other organisms to obtain
nutrients that they need.
Humans also benefit from fungi in various
industries such as agriculture, forestry, and
products ranging from bread to antibiotics.
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Fungi
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Plants are autotrophs (they make their own
food out of sunlight), but fungi are
heterotrophs like animals because they
cannot make their own food.
They cannot run or fly in search of food as
most animals can.
But unlike animals, fungi do not ingest (eat)
their food.
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Fungi
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Instead, fungi are similar to bacteria because
fungi use extracellular digestion to obtain
their nutrients.
They digest their food while it is still in the
environment by secreting powerful enzymes
into their surroundings.
These enzymes break down large molecules
into smaller ones that the fungi can absorb and
use.
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Fungi absorb food after digesting it outside their
bodies
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Fungi are heterotrophic organisms that digest their
food externally and absorb the nutrients
Figure 17.15A
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Videos
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Fungi are heterotrophic 2 mins
Fungi Reproductive Structures 2 mins
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Fungi
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Some fungi are decomposers which live off of
dead animals, feces, and vegetation (saprobes),
some are parasites (live on a host, causing
damage to the host; about 80% of plant
diseases are caused by fungi), and some are
symbiotic (live with a host in a relationship
that is beneficial to the fungi as well as the
host).
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DECOMPOSERS
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They are important decomposers in most
ecosystems; they help to recycle organic matter.
They decompose organic material, including the
tough cellulose of plant cell walls.
Some Fungi can even consume jet fuel and wall paint.
Fungi and bacteria are primarily responsible for
keeping ecosystems stocked with the inorganic
nutrients essential for plant growth.
Without fungi, carbon, nitrogen, and other elements
would become bound up in the soil and unavailable
for use.
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SYMBIOTIC RELATIONSHIPS
WITH PLANTS AND ANIMALS
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Most known species of fungi are not
parasitic.
Fungi have symbiotic relationships with plants,
algae, bacteria, and animals.
All of these relationships have profound
ecological effects.
Almost all vascular plants rely on fungi for
essential nutrients.
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Fungi Help Animals
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Some fungi share their
digestive abilities with
animals, helping to
break down plant
material in the intestines
of cattle and other
grazing mammals.
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Fungi Help Animals
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Many species of ants and termites take advantage of
the digestive power of fungi by raising them in on
“fungi farms”.
These insects even scour tropical forests in search of
leaves, which they carry back to their nests and feed
to the fungi.
The fungi break down the leaves into a substance that
the insects can digest.
The fungi from these ant farms have become so
dependent on their caretakers that in many cases they
no longer can survive without the insects.
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Fungi also form mutualistic relationships with
animals
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Some animals benefit from the digestive abilities of
lichens
Figure 17.21
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Video: Leaf-Cutting Ants
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Discovery Channel video
2 mins
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Fungi Help Plants
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Fungi are found associated with the earliest
plant fossils.
They helped plants become terrestrial by
forming mycorrhizal (fungi roots)
associations with plants and helping early
plants to extract mineral nutrients from
hostile soils.
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LICHENS
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A lichen is an association between a fungus and
cyanobacteria or green algae.
Lichens are a mass of photosynthetic microorganisms
(algae and bacteria) that are held in place by fungi
filaments.
They form a green carpet that hugs the surface of
rocks, logs, trees, etc.
The merger of fungus, algae, and bacteria is so
complete that lichens are actually given scientific
names as though they were single organisms.
There are more than 13,000 species of lichens,
making up 1/5 of all known fungi.
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Lichens consist of fungi living mutualistically
with photosynthetic organisms
Lichens consist of algae or cyanobacteria
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Within a fungal network
Fungal
hyphae
Algal
cell
Figure 17.20A, B
Colorized SEM 1,000 
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Lichens
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Each partner organism within lichens provides
something that the others could not obtain on their
own.
The algae provide carbon compounds, the bacteria
provide nitrogen, and the fungi provide a suitable
environment for growth.
The physical arrangement of the fungi filaments
allow for gas exchange, protects the other partners,
and retains water and minerals.
Some fungi produce a toxin that prevents the lichens
from being eaten by animals.
The free-living fungus called Penicillium (provides
the antibiotic penicillin) is believed to be a
descendent of a lichen fungus.
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Lichens
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Lichens are important pioneers on new
land, rocks, and logs from burned forests.
They break down the surface by physically
penetrating with their roots and chemically
breaking down the rock, and binding together
particles of soil that blow in.
In this way, solid rocks and dead vegetation
gradually break down into fertile soil.
This makes it possible for new plants to grow.
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Lichens
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Some lichens are thousands of years old.
Lichens can withstand severe drought and
can tolerate severe cold but as lichens are
they are sensitive to air pollution.
They are particularly sensitive to sulfur
dioxide and other poisons that can accumulate
in the air.
The death of sensitive lichens is an early
warning sign that air quality is deteriorating.
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Fungi can be good or bad
Toadstools
Spores
Lichen
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Parasitic fungi harm plants and animals
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Parasitic fungi cause 80% of plant diseases
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And some serious human mycoses
Dutch Elm
Disease
Corn smut
Ergots on rye
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PATHOGENS
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About 30% of fungi make their living as
parasites, mostly on plants.
For example, Dutch Elm disease has
drastically changed the landscape in the
northeastern United States when it was
accidentally introduced to the US on the logs
that were sent from Europe to help pay World
War I debts.
It was carried from tree to tree by bark beetles.
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PATHOGENS
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Fungi are also serious
agricultural pests.
Between 10% and 50%
of the world's fruit
harvest is lost each year
fungal attacks, such as
black stem rust on
wheat.
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PATHOGENS
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Some of the fungi that
attack food crops are also
toxic to humans. For
example, a certain species of
mold called Aspergillus may
contaminate improperly
stored bread, peanuts, and
jelly, where it secretes a
carcinogenic (cancercausing) liver toxin called
an aflatoxin.
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PATHOGENS
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Therefore, a peanut butter
and jelly sandwich is a triple
whammy for aflatoxin. It
dissolves in the jelly, so
scooping it off the top
surface of the jar will not do
any good.
To prevent aflatoxin, only
buy peanut butter and jelly
in the size jars you use up
quickly, keep them
refrigerated (the bread, too),
and use a clean knife each
time. Don’t leave the lid off
for long, because that’s
when it gets in.
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PATHOGENS
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Another example of a toxic
fungus is one that forms purple
structures called ergots on rye
grains.
If diseased rye is accidentally
mixed into flour and eaten,
poisons from the ergots can cause
ergotism, a condition
characterized by gangrene,
nervous spasms, burning
sensations, hallucinations, and
temporary insanity.
An epidemic of ergot poisoning in
944 AD killed more than 40,000
people in France.
One of the compounds from
ergots is a hallucinogen found in
LSD.
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PATHOGENS
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Animals are much less susceptible to
parasitic fungi than plants.
Only about 50 species of fungi are known to
parasitize humans and other animals, but these
relatively few species do considerable damage.
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Mycosis: Ringworm
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The general term for a fungal
infection is mycosis.
Mycosis of the skin includes the
disease called ringworm, named
because it appears as circular red
areas on the skin.
Ringworm (not a worm, but a
fungus) can appear on almost
any skin surface, including the
hair of the head, beard, pubic hair,
and bare skin.
It forms tiny watery blisters which
are extremely itchy; when the
blisters are scratched open, the
fungus is released and spreads to a
new area.
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Mycosis: Athlete’s Foot
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Fungal infections of the
feet are called athlete’s
foot.
You get it by just
walking barefoot,
exposing the skin to the
air where spores are.
Although healthy skin is
resistant to these spores,
if there is a slight
scratch in the skin, the
fungi can get in.
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Mycosis: Nails
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Fungus can also infect
the nails, causing them
to become thick,
crumbly, and yellow.
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Mycosis: Treatment
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Fungal infections of the
skin are relatively easy
to treat with anti-fungal
creams, but nail fungus
is extremely difficult to
cure, and may require
harsh oral medicines
that can be toxic to the
liver.
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Systemic Mycosis
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Mycosis within the body (systemic mycosis) spreads
throughout the body and is extremely serious. They
are typically caused by fungal spores that are inhaled.
Histoplasmosis is a disease from a fungus that is
found in soil that is rich in nitrogen, especially caves
with bat droppings (guano). Such caves are moist,
rich in nitrogen, and have dead organic material there,
which are ideal conditions for molds.
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Histoplasmosis
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Spelunkers are
people who explore
caves, usually on
their hands and
knees.
Their nose is close to
the floor, so they
inhale the spores.
Hunting dogs get it
the same way.
When you hear the
word “cave”, think
of Histoplasmosis.
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San Joaquin Valley Fever
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A respiratory disease with symptoms similar to
tuberculosis.
This organism differs from histoplasmosis in that it
requires long periods of dry (arid) weather, and then a
heavy rain.
That makes it endemic to west Texas, Mexico, Baha,
South America, southern California, Arizona, and
New Mexico.
The blood of everyone who lives in the San Joaquin
Valley tests positive for the organism, but they don’t
usually get the disease.
That’s because you need to be exposed to a large
amount to get sick; therefore farmers are at risk.
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San Joaquin Valley Fever
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Caesar Chavez fought for
the rights of immigrant farm
workers, who were given
short tools to weed the
farms, so their noses were
close to the ground to inhale
the spores.
They also were not paid
well and had poor nutrition,
so they would get the
disease.
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San Joaquin Valley Fever
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Once the spores get into the lungs, the person
has flu-like symptoms, and then it can
disseminate into the bones, skin, and brain.
It is a recurring disease with treatment but no
cure.
In large amounts, it is so deadly that it is now
considered a potential biological weapon.
Video: Fungus in the Lungs 2 mins
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Opportunistic Mycosis
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Only causes disease in
people with a weakened
immune system.
An example is a type of
fungus that can cause
pneumonia; it lives in soil
rich in nitrogen, especially
bird droppings.
It is common in urban areas
(cities) because of the
pigeons. Not as common in
rural (country) areas.
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Candida
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Another opportunistic mycosis is a species of
yeast called Candida.
It is a type of fungus that is normally found in
the moist areas of the skin such as the mouth
and vagina.
It does not cause disease unless it invades
through a break in the skin or excess nutrients
become available, allowing it to grow in
greater numbers than normal.
This is called a yeast infection.
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Opportunistic Mycosis
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Antibacterial and antibiotic medicines do not kill
fungi; an antifungal agent is needed.
If a female takes oral antibiotics for a bacterial
infection elsewhere in the body, the normal bacteria
in the vagina can be killed off as well, although
antibiotics usually do not kill yeasts or other fungi.
With the elimination of bacteria that compete for
nutrients, the yeasts to have extra food and grow to
excess, causing itchiness and a vaginal discharge.
Vaginal yeast infections are the result of an
overgrowth of a fungus.
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Opportunistic Mycosis
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Newborn infants do not
have a strong immune
system; as they pass
through the vaginal
canal during birth, their
mouth can pick up an
excess number of
Candida organisms
which causes an
overgrowth in the
mouth, a disease called
candidiasis or “thrush”.
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Opportunistic Mycosis
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AIDS patients also have a
weakened immune system,
and are susceptible to
candidiasis; so are the
elderly and people with
diabetes.
Candidiasis can also occur
in wet areas of the skin and
is common among
dishwashers.
Candidiasis can be mistaken
for “jock itch” or diaper
rash, which is a bacterial
infection and requires a
different type of medicine.
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Black Mold
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One particular species
of fungus called “black
mold” has been the
subject of many news
reports.
Black mold thrives in
damp buildings and has
been implicated as the
cause of a wide variety
of human diseases.
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PRACTICAL USES OF FUNGI
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The dangers posed by fungi should not
overshadow the immense benefits we derive
from this remarkable species.
We depend on their ecological services as
decomposers and recyclers of organic matter.
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Fungi have enormous ecological benefits and
practical uses
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Fungi are essential decomposers
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And provide antibiotics and food
Staphylococcus
aureus
Figure 17.22A, B
Penicillium
Zone of
inhibited
growth
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PRACTICAL USES OF FUNGI
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Mushrooms are a
popular food, but they
are not the only fungi
we eat.
The distinctive flavors
of certain kinds of
cheeses, including
Roquefort and blue
cheese come from the
fungi used to ripen
them.
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PRACTICAL USES OF FUNGI
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The soft drink industry
uses a species of fungus
to produce citric acid for
colas and soy sauce.
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PRACTICAL USES OF FUNGI
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Morels and truffles are
expensive mushrooms
which are highly prized for
their complex flavors.
They can cost several
hundred dollars per pound.
Truffles are rare and
delicious and sell for up to
$100 each!
In the past, hunting dogs
and pigs were used to sniff
out where truffles were
growing in the woods.
Truffles
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PRACTICAL USES OF FUNGI
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Humans have used yeast to
produce alcoholic beverages
and raise bread for
thousands of years.
The yeasts ferment sugars to
alcohol and carbon dioxide,
and so can be used to make
alcohol from grapes or used
in bread to make it rise.
It is also used to make beer.
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PRACTICAL USES OF FUNGI
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Many fungi have great medical value as well.
For example, a compound extracted from ergots is
used to reduce high blood pressure and to stop excess
bleeding after childbirth.
Some fungi produce antibiotics that are essential in
treating bacterial infections.
In fact, the first antibiotic discovered was from a
fungus that made penicillin, when a mold was found
growing on a Petri dish as an accidental contaminant.
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SEM 6,500
Bread Mold
Figure 17.17B, C
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PRACTICAL USES OF FUNGI
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The same yeast used to make beer is also a
studied in biotechnology.
Scientists are gaining insight into the genes
involved in human diseases such as
Parkinson's disease and Huntington's disease
by examining the genes in this yeast because
its cells are easy to culture and its genes are
easy to manipulate.
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PRACTICAL USES OF FUNGI
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Genetically modified
fungi are being used in
medicine and in
industry.
One of the medical
benefits of GM fungi is
that they are used to
produce certain
medicines such as
insulin.
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PRACTICAL USES OF FUNGI
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One of the benefits in
industry is to harness
fungal metabolism to
produce paper pulp
from rotted wood.
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