LAB 5
THE FUNGI
Fungi are ubiquitous and important parts of every ecosystem. Many fungi function as decomposers with
their exoenzymes breaking down nutrients that are released into the environment to be utilized by other
organisms like plants. Fungi may also act as pathogens and mutualists, which we will see in later labs.
Fungi are also important to humans as edible mushrooms and industrially useful products. We will explore
the kingdom fungi today.
Learning objectives

Learn the characteristics that distinguish between the five phyla of fungi and the deuteromycetes.

Be able to place the specimens you observe in the life cycle of its phylum.

Determine the relative importance of sexual and asexual reproduction for each phyla.

Describe the two vegetative growth forms of fungi, including the general features of hyphae and
yeasts.

Observe the prevalence of fungi in the environment through specimens collected by previous
classes.

Learn about poisonous and edible mushrooms.
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VEGETATIVE GROWTH FORMS
Since the fungi as a group represent a heterogeneous array of microorganisms, you might expect a certain
amount of variation in their vegetative growth and modes of reproduction. In this exercise you will
examine some of the variation to be found among those forms. The vegetative growth form in a great
majority of the fungi consists of a system of thread-like, walled, more or less cylindrical, hyphae (singular
--hypha) making up what is called a mycelium (plural--mycelia). However, hyphae are not found in many
of the simplest forms such as the single-celled yeasts.
NON-FILAMENTOUS FORMS — SINGLE-CELLED YEASTS
Mount a small drop of a suspension of activated baker’s yeast, Saccharomyces cerevisiae (Ascomycota),
place a clean cover slip over it, and examine the cells microscopically. Do the yeast cells have a definite
shape or is there considerable variation? Can you detect any subcellular structure? Are any of the cells
dividing? Draw some yeast cells.
FILAMENTOUS FORMS – WITH HYPHAE
Examine the young hyphae of Morchella (Ascomycota) or some other filamentous fungus growing on agar
by removing the petri plate cover and placing a clean cover slip over the margin (edge) of the colony. Place
the open culture on the microscope stage and observe at all magnifications. Does the hypha have a regular
geometric form or is it irregular? How would you describe the general hyphal structure? What is the
general form of a hyphal tip (i.e. tapered, hemispherical, flat, etc.) Does the hypha appear to be segmented
into cells; i.e. are septa (cross walls; singular--septum) present? Draw some hyphae.
Yeast
Hyphae
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GLOMEROMYCOTA
Members of the recently-recognized phylum Glomeromycota form endomycorrhizae with many types of
plants. What does “endomycorrhizae” mean?
Endo =
myco =
rhizae =
What do these fungi do to benefit the plant they associate with?
What do the plants do to benefit the fungi?
What do we call a mutually beneficial symbiosis like this?
Examine several prepared slides of grass roots colonized by mycorrhizal fungi. Diagram what you see
below, noting the direction of the flow of fixed C and nutrients between the plant and fungus.
We will be examining mycorrhizae in greater detail in a later lab.
CHYTRIDIOMYCOTA
Observe the displays of Chytridiomycota available in the lab. What characterizes this phylum? What
are some interesting ecological niches occupied by members of this group?
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ZYGOMYCOTA
The Zygomycota are commonly known as the “black bread molds.” Most of their reproduction is
accomplished by means of spores produced asexually in sporangia (see figure below). View slides of
sporangia and draw them in the appropriate area on the next page.
Under certain conditions and when the right mating types are present, Zygomycota reproduce sexually by
means of thick walled resting structures called zygospores (see below). Observe the prepared slide of
Rhizopus hyphae and zygospores (aka “zygotes”). The zygospores are held up by inflated cells called
suspensors, the remnants of the gametangia. You should be able to observe zygospores in several stages
of development, from thin-walled to those with thick ornamented walls. Draw a zygospore with
suspensors on the following page.
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Sporangia
Zygospore with suspensors
Why do you suppose you rarely see sexual reproduction of the Zygomycota on bread? (hint: think about
the way the bread is infected by a single spore).
ASCOMYCOTA
BLUE CHEESE
Blue cheeses such as Roquefort are made from milk solids that have been “ripened” by Penicillium
roquefortii. With the forceps provided, mount a very small piece (less than 0.25 mm on each side) of the
blue part of the cheese in water, add a coverslip and observe. Do you see any fungal structures? Draw
them below.
Do you think this is asexual or sexual reproduction? Why?
The fungus changes the flavor and texture of the cheese. How does the texture of this cheese differ from
that of “regular” cheese such as cheddar or Swiss? How do you suppose the fungus does this to the
cheese?
Penicillium roquefortii
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MORELS
Morels are delicious edible mushrooms that form in the spring. These “sponge mushrooms” are much
sought after by mycophagists (people who eat mushrooms). They can usually be found around dead elm
trees or in old apple orchards when “the oak leaves are the size of a squirrel’s ear.”
You have already observed the vegetative hyphae of the morel. After observing preserved specimens of
Morchella and drawing some of the fruiting bodies (= ascocarps), examine prepared slides of an ascocarp
cross-section. You should be able to see the asci and cells of the ascocarp. How many spores are there in
each ascus? Draw a complete ascus below. Notice that the ascocarp is hollow! Looking at the slide,
figure out where the outside of the ascocarp is with respect to the asci. What conclusion can you make
about the orientation of the ascus tips with respect to the outside opening?
Morchella fruiting body
Morchella ascus
Now that you have had a chance to look at some of the structures of the Ascomycota, see where those
structures fit into the morel life cycle below. Remember to identify the parts of the life cycle that are
haploid (n), diploid (2n) and dikaryotic (n + n)!
Life cycle of Morchella. Volk, Thomas J. and TJ Leonard.
1990. Cytology of the life cycle of Morchella. MYCOLOGICAL RESEARCH 94: 399-406.
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“DEUTEROMYCETES”
The deuteromycetes are commonly known as the ‘molds’. These organisms are often considered ‘second-class
fungi’ as they have no known sexual state during their life cycles. Therefore, reproduction in this group is by
asexual means alone which results in the production of spores via mitosis. Although these organisms are
clumped into this broad, diffuse group, they tend to show a close relationship to members of the Ascomycota in
about 90% of the cases. These members are also known as the ‘fungi imperfecti’ due to their imperfect life
cycles (lacking sexual reproduction). If the sexual state of one of these organisms is discovered, it is re-classified
under one of the major taxonomic phyla that we will be investigating today. Remember that this cluster of fungi
is just a ‘dumping ground’ for fungi that have no known sexual state – deuteromycetes is not a true phylogenetic
designation! Observe the Petri dishes that you and your classmates inoculated this past week. What conclusion
can you draw from looking at these plates?
BASIDIOMYCOTA
COPRINUS AND AGARICUS BASIDIA
Basidiomycota bear their sexual spores externally on club-shaped structures called basidia. Look at the prepared
slide of Coprinus to see basidia. With the forceps remove a small piece of a gill of one of the Agaricus button
mushrooms on display. Can you observe basidia? Draw a basidium with attached spores below. In addition, we
have the mycelium of a member of the Basidiomycota growing in an artificial log – make a wet mount from the
sample (using a drop of water and a coverslip) and look at it under the microscope. Draw what you see in the space
below.
Coprinus
Agaricus
Basidium with attached spores
Mycelium from artificial log
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Now that you have seen some of the life-cycle structures that occur in the Basidiomycota, see where they fit
into the generalized life cycle for this phylum below. Be sure to take note of what stages are haploid,
diploid and DIKARYOTIC! Also be sure to note where plasmogamy and karyogamy occur!
SURFACE AREA
Since most fungi have a very specialized habitat, they can very often run out of nutrients in a particular
area. In order to “move” to a new substrate these fungi produce enormous numbers of spores on or in
their fruiting bodies. Observe the fruiting bodies on display and make note of the various methods by
which fungi increase the surface area for bearing their spores. Draw some representatives below. You
should be able to recognize where the spores are being borne on each specimen
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MUSHROOM POISONINGS
Many kinds of mushrooms are poisonous, but the deadly poisonous mushrooms account for less than 1%
of the total number of species. About 5% will make you sick in one way or another, usually
gastrointestinal upset. About 5% are good edible mushrooms. Most of the rest are either too tough or
too bitter or too boring to bother eating.
Some specimens or models of poisonous mushrooms are on display. Note that there is no foolproof way
of knowing whether a mushroom is poisonous or not EXCEPT by learning how to identify them!! So to
be on the safe side you should be sure and take Mycology the next time it is offered!
Terms and Concepts for Lab 5
Ascocarp
Ascospore
Ascus
Basidia
Basidiocarp
Basidiospores
Hyphae
Mycelium
Septa
Zygosporangia
Zygospore
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