Slide 1 This lecture introduces the Kingdom
Fungi � there will not be time to cover
this in lecture so this short presentation
plus the laboratory demonstrations provide
the material you need to know about this important
Kingdom of life.
Slide 2 When you see mushrooms growing you
may not realize that most of the body of the
fungus is not visible � it is hidden in
the substrate (the ground, a rotting log,
a piece of fruit) that the the fungus is growing
on. This underground organism can be huge
- the biggest living organism on earth is
a honey mushroom growing underground in the
Blue Mountains in Oregon.
Slide 3 This hidden fungal body is made up
of threadlike filaments called hyphae � each
with a diameter of only 2 � 10 micrometers
in diameter. These filaments are made up of
cells with haploid nuclei and the cell walls
are made of chitin � these chitinous cell
walls are one piece of evidence that fungi
are more closely related to animals than to
plants. These threadlike hyphae are able to
lengthen at a very fast rate to enable the
fungus to spread rapidly within its substrate.
There are also some fungi which have a different
growth form � these are single celled forms
usually referred to as yeasts.
Slide 4 The many many threadlike hyphae form
a network called a mycelium � when you poke
through a rotting log in the woods and see
the white �fuzzy� material, this is the
fungal mycelium.
Slide 5 Here�s another view of a fungal
mycelium � in this case the substrate that
this particular fungus is growing on is strawberries,
and the mycelium undoubtedly permeates into
the fruit. What we often refer to as mold
is usually a fungal mycelium.
Slide 6 The structure of the mycelium is very
important to the way fungi ingest nutrients.
Fungi are heterotrophs, like animals, but
fungi digest their food outside of their bodies
and then absorb the organic products. They
accomplish this by excreting enzymes, which
break down the organic material around the
mycelium into organic molecules that can be
directly absorbed into the body of the fungus.
Slide 7 Fungi are critical in many ecological
processes, one of the most important is decomposition.
By infiltrating and breaking down the dead
bodies of plants and animals, fungi are critical
in recycling nutrients. The sprouting mushrooms
on this fallen tree are evidence that the
trunk is riddled with decomposing fungi that
will eventually return all the organic molecules
back into the nutrient cycle. The tomato will
also decompose at a much faster rate than
it would without the fungus.
Slide 8 Another critical ecological impact
of fungi is the formation of mycorrhizae.
The mycelium literally wraps itself around
the roots of the plant � and, with it�s
huge surface area, is able to provide much
more water and minerals to the plant than
the roots alone could. Corn, carrots, tomatoes,
apples, onions coffee�.. And most of our
other fruits and vegetables depend on this
relationship between the plant roots and the
fungal mycelium for successful growth. The
fungus benefits also (mutualism!) through
access to sugars produced by the plant.
Slide 9 Fungi also provide food for many animals,
including humans. Mushrooms are the fruiting
bodies of fungi many play an important role
in the diet of both humans and other animals.
Of course you should never eat a mushroom
you find � many are deadly. The blue/green
veins in some cheeses are actually the mycelium
of special fungi that are placed very deliberately
into the cheese as it is being made � to
add flavor. And remember mycorrhizae � without
this relationship many of our food plants
would be grow well at all.
Slide 10 Some fungi are parasitic and have
had some profound impacts. A fungus that infects
rye grass, if eaten (ground up into flour
for example) can cause hallucinations and
death. There is speculation that some people
accused of being witches during the Salem
witch trials in Massachusetts in the 17th
century, was actually caused by ingestion
of this fungus.
Slide 11 There are also some fungi which have
had a devastating impact on 3 notable N. American
trees. The American Chestnut used to be the
dominant tree of the eastern forests of the
U.S. but the huge trees of many years ago
are all but gone. The fungus destroys all
the above ground parts of the tree � roots
survive and can resprout � so we do see
this tree growing as a shrub. And Penn State
and the State University of New York have
developed a strain of this tree that appears
to be resistant to the fungus. Elm trees and
butternuts have also been devastated by fungal
infestations.
Slide 12 Fungal spores are everywhere and
mainly do not cause harm to animals. There
are some fungi that live on skin and mucous
membranes and normally do not cause harm,
but some species under certain circumstances
can become a health issue.
Slide 13 Returning to the beneficial impacts
of fungi. Our modern antibiotics began with
the discovery of a substance produced by a
genus of fungus called Penicillium. Species
in this genus grow on a variety of foods � and
not one of us has not benefitted from their
powerful healing properties. And the action
of a species of yeast (remember � that�s
a form of fungi that grows as single cells
rather than threadlike hyphae) cause the reactions
that makes bread rise and beer brew.
Slide 14
Slide 15 Many fungi can reproduce asexually
� a single individual can give rise to new
individuals without the fusion of sperm and
egg. In this generalized diagram, specialized
hyphae will produce special cells � called
spores � which are released to the air.
If they land on a suitable substrate, they
can grow into a new individual fungus, which
will be genetically identical to the parent.
Remember, the nuclei in all the cells in this
asexual life cycle are haploid and only mitosis
is needed to produce the spores and the new
organism.
Slide 16 This figure shows the different types
of sexual life cycles found in animals, plants
and fungi. Notice that in all three types,
there is an alternation of a diploid (2n)
and a haploid (1n) form. The process of meiosis
(which reduces the chromosome number from
diploid to haploid) alternates with the process
of fertilization (where two haploid cells
join to form a single diploid cell � the
zygote). In lab, we will examine the sexual
life cycles of three Phyla of fungi. Understanding
these general life cycles will be important
and helpful as we add specific details.
Slide 17 The sexual life cycles of fungi are
complicated and contain lots of terminology
that you have not heard before. Expect to
spend some time with this general diagram
� the processes and structures here are
critical to your understanding of fungal life
cycles. Beginning in the top left, note that
two hypha from genetically different individuals
(indicated by the plus and minus) come together.
Then a process called plasmogamy (literally
the �marriage of cytoplasm�) occurs � joining
the cytoplasm but NOT the nuclei of the different
individual cells. Note that in the resulting
hyphae, you see two distinct and genetically
different nuclei (the plus and minus) coexisting
inside the same cellular space. This cell
is described as �dikaryotic� or �heterokaryotic�
because it contains two different nuclei.
Think about how this is different than a diploid
cell � which has two sets of chromosomes
within the same nucleus. These dikaryotic
hyphae can grow and divide to form a �fruiting
body� � the most familiar are mushrooms.
Eventually, the dikaryotic cells will undergo
the process of karyogamy (�marriage of nuclei�),
resulting in a diploid nucleus. This diploid
nucleus immediately undergoes meiosis to form
haploid nuclei, which will be enclosed by
cell walls and released as spores. Two very
important points to note here are that these
spores, unlike the ones formed in the asexual
life cycle, are genetically different than
either parent, and typically there is a huge
surface area over which these processes happen
� resulting in the production of huge numbers
of spores.
Slide 18 The fruiting bodies of fungi take
on many forms � but each is designed to
maximize spore production and dispersal. We�ll
look at fruiting bodies more closely 
in lab.
Slide 19
