hello and welcome to the wonderful world
of fungi or fungi both are acceptable
pronunciations but i say fungi because
it's fungus not fungious though fungus
is also fun to say fungi are a little
bit like plants and more like animals
than you might think they diverged from
protists about a billion years ago and
today scientists estimate that there are
about 1.5 million species of fungi on
the earth though in a formal taxonomic
way we only know about a hundred
thousand or so of them those that we
have met are wonderful weird and in some
cases deadly the fact is death is pretty
much what fungi are all about sure there
are the fun fungi like the single-celled
saccharomyces also known as yeast
without them we wouldn't have beer or
wine or bread it's also true that fungi
are responsible for all kinds of
diseases from athlete's foot to
potentially deadly histoplasmosis aka
spelunker's lung caused by fungus found
in bird and bad droppings fungi can even
make people crazy when the fungus
claviceps properia grows on grains used
to make bread or beer it causes gangrene
nervous spasms burning sensations
hallucinations and temporary insanity
one compound in this fungus lysergic
acid is the raw material used to make
lsd and finally there's the destruction
that some fungi bring onto other animals
more than 6 million bats in north
america have died since just 2007 due to
a fungal disease called white nose
syndrome and a fungus has been
implicated in several extinctions of
amphibians and threatens many more
perhaps as many as a third of all
amphibians on earth but none of this is
what i mean when i talk about fungi and
death while some members of the fungus
family are total bummers all of them
together perform perhaps the most vital
function in the global food web they
feast on the deceased remains of almost
all organisms on the planet and by doing
that they convert the organic matter
that we're all made of back into soil
from which new life will spring so fungi
they thrive on death and in the process
make all life possible
ah you didn't expect to see me in the
chair so soon but before we go any
deeper into the kingdom of fungi i
wanted to make a toast to louis pasteur
in the form of a biology
by pastor's time beer had been brewed
for thousands of years in cultures all
over the world some experts think it may
have been the very reason that our
hunter-gatherer ancestors started
farming and cobbled together
civilization in the first place but for
all those millennia no one understood
how its most important ingredient worked
until brewers could actually see what
yeast were doing the magic of
fermentation was essentially magic
pasteur himself was never a big beer
drinker but part of his academic duties
in france required him to help find
solutions to problems for the local
alcohol industry and as part of this
work in 1857 he began studying yeast
under a microscope and discovered that
they were in fact living organisms in a
series of experiments on the new found
creatures he found that in the absence
of free oxygen yeast were able to obtain
energy by decomposing substances that
contained oxygen we now know that
pasteur was observing yeast undergoing
the process of anaerobic respiration aka
fermentation breaking down the sugars in
grains like malted barley and converting
them into alcohol carbon dioxide and the
range of flavors that we associate with
beer along the way pasteur also
discovered that beer was often
contaminated by other bacteria and fungi
the growth of these beer-spoiling
microbes he found could be thwarted for
up to 90 days by keeping the beer
between 55 and 60 degrees celsius for a
short period of time
today we call that heating process
pasteurization and it's used in
everything from milk to canned foods to
syrups to wines for our purposes the
thing to hold onto here is pasteur
discovered that yeasts decompose sugars
to get energy and it turns out most
fungi spend most of their time
decomposing all kinds of organic matter
often the matter is dead when fungi get
to it but not always when a tree or a
person or a deer keels over fungi move
in and start the work of decomposition
same goes for that orange you forgot at
the bottom of the fruit bowl if it
weren't for this fungal function plants
and the animals that eat them couldn't
exist because the elements that they
take from the soil would never return
thankfully the decomposition performed
by fungi recycles the nutrients for the
enjoyment of plants and animals as well
as for other fungi all of this points to
one of the main traits that all fungi
have in common from single-celled yeast
to giant multicellular mushrooms fungi
like us are heterotrophs but instead of
eating they absorb nutrition from their
surroundings they do this mostly by
secreting powerful enzymes that break
down complex molecules into smaller
organic compounds which they use to feed
grow and reproduce multicellular fungi
contain networks of tiny tubular
filaments called hyphae that grow
through and within whatever they're
feasting on unlike plant cell walls
which are made of cellulose the cell
walls of fungi are strengthened by the
nitrogenous carbohydrate chitin the same
material found in the exoskeletons of
insects spiders and other arthropods the
interwoven mass of hyphae that grows
into the food source is called the
mycelium and it's structured to maximize
its surface area which as we've learned
in both plants and animals is the name
of the game when it comes to absorbing
stuff mycelia are so densely packed that
one cubic centimeter of rich soil can
contain enough hyphae to stretch out one
kilometer if you laid them end to end so
as high fees secrete the digestive
enzymes fungi used the food to
synthesize more proteins and the hyphae
continued to grow allowing the fungi to
conquer new territory and grow even more
as a result fungi can get crazy big
record holding big a single honey
mushroom in the blue mountains of oregon
is thought to occupy some 2
386 acres by area the largest organism
on the planet now there are all kinds of
crazy ways that fungi are classified but
probably the easiest and most useful is
organizing them by how they interact
with other organisms the straight-up
decomposers that break down dead stuff
the mutualists which form beneficial
relationships with other organisms
especially plants and then there are the
predators and the parasites the composer
fungi secrete enzymes that break down
and absorb nutrients from non-living
organic materials such as that tree that
nobody heard fall in the forest in fact
the ability of fungi to break down
lignin which is like what makes wood
woody and break it into glucose and
other simple sugars is crucial for the
cycle of life they're pretty much the
only organism that can do that they can
even decompose proteins into component
amino acids basically all the black bits
in the soil in your backyard are tiny
fragments of former plants digested by
fungi mutualist fungi are a smaller
group many have specialized hyphae
called hostoria that tangle themselves
with plant roots for the benefit of both
organisms these guys help plants absorb
nutrients especially phosphates by
breaking them down more efficiently than
the roots can themselves in turn the
fungi send out their hyphae into the
plant's root tissue and withdraws like a
finder's fee basically in the form of
energy-rich sugars these mutualistic
relationships are known as mycorrhizae
from the greek words mics or fungus and
rhizon or root mycorrhizae are
enormously important in natural
ecosystems as well as in agriculture
almost all vascular plants in fact have
fungi attached to their roots and rely
on them for essential nutrients growers
of barley the main ingredient in beer
will even inoculate barley seed beds
with specific mycorrhizal fungi to help
promote growth other fungi aren't nearly
so kind to their hosts predatory fungi
actively capture prey with their hyphy
the soil fungus arthrobatrus uses
modified hoops on its filaments to snare
nematodes and absorb their inner tissue
then there are the parasites those fungi
that feed on living organisms without
killing them at least for a while i
think one of my personal favorites the
zombie ant fungus or ophic cordyceps it
shoots spores into an ant where their
hyphae grow into its body and absorb
nutrients from non-essential ant organs
when the fungus is ready to reproduce it
invades the ant's brain and directs it
to march to a cool moist location in the
forest where its so-called fruiting
spores erupt through the ant's head to
spread even more spores
and just to prove that even fungi have
superheroes in 2012 scientists
discovered that these zombie spores have
themselves been targeted by another
parasitic fungus not a lot is known
about this ant saving fungus other than
it sterilizes many of the zombie spores
through a process like into chemical
castration that is so messed up
weird right now since i brought that up
we should talk briefly about fungus sex
fungi reproduce any way they can either
sexually or asexually some species even
do it both ways but whichever way they
choose most propagate themselves by
producing enormous numbers of spores
much like we saw in non-vascular plants
and the simplest vascular plants the
ferns but and this is a big but sexual
reproduction in fungi isn't like sex in
any other organism we've studied so far
the concepts of male and female don't
apply here at all some fungi reproduce
on their own others can reproduce with
any other individual that happens to be
around and still others can only mate
with a member of a different so-called
mating type they're not different sexes
they just have different molecular
mechanisms that either make them
compatible or not sometimes these types
are called plus and minus and other
times one and two in any case it's still
considered sexual reproduction because
each parent contributes genetic
information when they make with the
spore making it all starts with this
beautiful chemical mating dances the
mycelium from one fungus sends out
pheromones that are picked up and bound
to receptors by another willing and able
partner this binding compels each
mycelium to send its hyphy toward the
other when they meet they fuse the
cytoplasm of their cells a stage of
reproduction called plasmogony sometime
between hours and centuries later yes it
can literally take hundreds of years for
fungi to have sex this union leads to
the production of spores that each
fungus is then able to disperse certain
types of fungi including the tasty morel
produce spores in a sack like acai
contained in fruiting bodies known as
ascocharps that is the part that you
pick when you're wandering through the
forest some fungi shoot their spores off
into the breeze others spores float away
on the water more enterprising spores
will hitch a ride on passing critters
hopefully to be dropped off somewhere
where there's plenty of nutrients to
absorb so they too can grow send out
sexual pheromones when their time comes
and let their hyphy do the tango finally
for some fungi sexual reproduction just
isn't all it's cracked up to be they'd
rather just get on with it themselves
some of these grow filamentous
structures that produce spores by
mitosis these structures are visible and
they're called molds the stuff on the
orange in the bottom of the fruit bowl
or on the heel with a piece of bread
that you left for a roommate who decided
to leave it for the other roommate who
thought that you'd rather have it in the
unicellular yeast the asexual
reproduction occurs by old-fashioned
cell division or the formation of buds
that get pinched off into separate
organisms since some species of yeast
like our beer making friends
saccharomyces cerevisiae convert sugars
into alcohol brewers create conditions
that encourage high rates of yeast
production like giving them lots of
sugar and oxygen since more yeast means
more alcohol so yeah fungi they feast on
death and they can make us go insane and
turn ants into unholy zombies of the
night but because of their hard work in
strange ways they make possible stuff
like agriculture and beer and everything
else worth living for so thanks to the
fungus and also thanks to you for
watching this episode of crash course
biology and of course thanks to the
people who helped me put it together
they're awesome thank you guys there's a
table of contents over there if you want
to click on it and go review any of the
stuff that you want to reinforce in your
brain and if you have questions or
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down in the comments below we'll see you
next time
you