Fungi& Lichen Lab
Equipment:.Compound and
dissecting microscopes, slides and coverslips, forceps, prepared slides, living
specimens.
Purpose: to illustrate the
anatomy and life cycles of various types of fungi
to show the relationships that
fungi have developed with other plants.
Background:
Commonly
known as yeasts, molds, mildews, rusts, blights, mushrooms and puffballs, the
fungi are common organisms in the ecosystem.
The typical body of a fungus is in the shape of long filaments called hyphae.
The hyphae branch to form a dendritic pattern of interconnecting
filaments collectively known as mycelium. No tissues are found in the mycelium and all
cells are generalized to preform most of the functions of the organism. The hyphae are surrounded by cell walls made
of chitin. In some fungi, the hyphae
are divided by cross walls called septae,
but these can be perforated allowing cytoplasm to flow from one compartment to
the next. Most fungi are
coenocytic...many nuclei are found in a single large cytoplasm. During the life cycle each nucleus is
usually haploid.
Fungi
are heterotrophic but because of their chitinous cell walls, they can’t engulf
food so the hyphae secrete digestive enzymes that can break down organic matter
which is then absorbed into the hyphae.
Some
parasitic fungi produce haustoria,
which penetrates the hosts cells and absorb food materials produced by the
host.
Asexual
reproduction usually occurs and hyphae can differentiate into sporangia that produce asexual spores.
Sexual
reproduction occurs in a few ways, 1.
fusion of gametes, and 2. fusion of a motile gamete with a specialized
reproductive structure called a gametangium 3. fusion of gametangia.
Lab Instructions:
In this exercise you will examine the anatomy, life cycle and biology of
several fungi.
1. Sac
Fungi(fig.16.3): Mildew
is a term used to describe discoloration and odors caused by fungi growing in
moist areas. Plant pathologists use this
term to describe diseases of plants in which fungi grows on the leaf
surfaces. Examine the life cycle of
powdery mildew (fig.16.3) and examine the mildews and discolored leaves on the
lab table with both types of microscopes.
(palm
leaves, sago leaves, rose leaves and the others that are discolored)
What stages in the life cycle can be observed?
Find
the modified hyphae, the haustoria, that projects into the cells of the leaf
and absorb nutrients in a parasitic relationship. Projecting up from the leaf are other
modified hyphae called conidiophores
that form asexual spores called conidia.
Draw and label using these terms next to the
life cycle
Examine
and draw examples of Microshaera alni and
Aspergillus. Also check out the rust
on the wheat..
2. Molds: Examine the rotting
fruits. Remove a small piece and place
it on a drop of water on a slide, tease it apart, add the coverslip and gently
press on it with a pencil eraser to spread the tissue. Examine the specimen for hyphae, conidiophores, and conidia dispersed among the fruit
cells.
Do the hyphae grow between the cells or
penetrate them?
Are the hyphae septate?
Sketch what you see in the space provided
near the life cycles.
Examine
the slide of Penicillium conida, draw
it.
3. Cup Fungi (fig. 16.4): The fruiting bodies of some ascomycete fungi grow to a
large size and are known as ascocarps. Obtain a slide of a section of Peziza
and examine its structure.
Compare it to the drawing. Can you see individual hyphae on the slide?
Are the septate or coenocytic?
4. Basidiomycota (fig. 16.6): This is a varied group of saprophytic and
parasitic fungi characterized by basidia,
club shaped structures that each produce four spores (basidiospores). Puffballs,
mushrooms, toadstools, and bracket fungi
are the familiar fruiting bodies (basidiocarps) of this group. Beneath the fruiting bodies are extensive
dispersed mycelial mats which feed on decaying vegetation. The hyphae are always septate.
Examine
the structure of the edible mushroom.
Note the cap(pileus) with the gills on its undersurface and the
supporting stalk (stipe). This fruiting
body, a basidiocarp, is an aggregate of hyphae as is the ascocaarp in the cup
fungi. These fungi are
heterothallic. Hyphae of the + or - type grow from separate spores and will
fuse to form a dikaryotic hyphae.
Vegetative growth of such hyphae results in a mushroom.
Split your mushroom longitudinally
through the cap and stalk. Look t the cut surface with the dissecting
scope.
Can you see hyphae?
Examine
the gills for basidiospores hanging from the surface of the basidium.
Examine
a prepared slide of a mushroom’s gills and use the compound
microscope to locate a basidium.
Examine
the slide of the mushroom cross-section...draw it.
Examine
the special handout that goes with the mushroom
slide.
5. Zygomycota (fig. 16.2): These fungi live in the
soil on dead plants and animals. The
zygomycetes do not produce flagellated spores nor do they produce a distinct
egg or sperm. In sexual reproduction, two
mating types of zygomycete hyphae fuse to produce a zygospore, a thick walled sexual spore that develops from the
zygote. Asexual spores are also produced
from sporangia on the ends of
modified erect hyphae. Rhizopus,
the black bread mold, illustrates the life cycle of the zygomycete group.
Examine
the slides of Rhizopus,, both the
sporangia and those conjugating , draw
and label what you see. Compare it to
the life cycle.
6. Two
others: Examine
the slide of yeasts (Saccharomycetes)
and the water mold slide, Saprolegnia.
Draw
each.
7. Lichens (fig. 16.7): Lichens are unique organisms in that they are
made up of algae and fungi in a symbiotic relationship and they can now
colonize environments that neither could inhabit alone. The fungus absorbs minerals and moisture from
the environment and the algae, nestled in the hyphae where they benefit from
the absorptive processes, in turn produce carbohydrates and other organic
molecules from photosynthesis.
Three
types of lichens occur...1. Crustose, grow as a crust on surfaces,
2. Foliose are more or less leafy in
appearance and 3. Fruiticose are shrublike with branching and intertwined fibrous
parts.
Examine
the examples of lichens in the lab...
Look
at a slide of a foliose lichen with the compound
microscope...can you see the algae concentrated around the hyphae?
Examine
the different lichens supplied...especially the red one. Draw it!
8. Mycorrhiza (fig. 16.8): Examine the slide of this important
fungi. Compare it to the picture.