Ch. 28- Fungi
Upon first observation of a mushroom or toadstool that may appear in your yard, you might think that you are looking at a plant. Indeed, these and most fungi are multicellular organisms made up of cells have cell walls, a typical plant characteristic.
However, on closer inspection, you would notice that the fungi are lacking chlorophyll, leaving them unable to produce their own food (although many plants lack chlorophyll as well). Fungi are either decomposers or parasites, and they have extracellular digestion and absorption of organic nutrients. Another unique characteristic of the fungi is that the body of a fungus, or mycelium, is made up of many branching and unbranching filaments, called hyphae. Also, most fungi produce both sexual and asexual spores, depending on the environmental conditions. Other methods of asexual reproduction are fragmentation or budding.
The following is an outline of the phyla of fungi:
1. Characteristics: zygomycetes; lack cross walls; produce non-motile asexual spores that develop inside a sporangium (pl. sporangia) found on hyphae called sporangiophores; form sexual spores (zygospores) from the conjugation of two special hyphae.
2. Examples: bread molds and related forms, Rhizopus, Phycomyces
1. Characteristics: ascomycetes ("sac fungi"); usually reproduce asexually by forming spores (conidia) at the tip or sides of special hyphae (conidiophores); reproduce sexually by forming ascospores (usually eight, sometimes four) within an ascus (pl. asci); asci may be formed into a fruiting structure called an ascocarp), form mutulalistic associations with the roots of most trees (mycorrhizae), fungal components of most lichens.
2. Examples: most yeasts (Saccharomyces) and molds, morels, truffles, powdery mildew, Dutch elm disease, ringworm (humans).
1. Characteristics: basidiomycetes ("club fungi"); reproduce asexually by budding, fragmentation of mycelium, or forming conidia; reproduce sexually by forming a club-like basidium (pl. basidia) which bears haploid spores (usually four) on its surface; have dikaryotic stage.
2. Examples: mushrooms, plant rusts and smuts, puffballs, toadstools, shelf and bracket fungi.
1. Characteristics: deuteromycetes ("imperfect fungi"); asexual reproduction by formation of conidia; do not have sexual reproduction (at least none that we know of).
2. Examples: Aspergillus, Penicillium (some produce the antibiotic penicillin, others give Camembert and blue cheeses their flavor), athlete’s foot fungus, Candida albicans (causes thrush in the mouths of infants);Microsporum.
Most zygomycetes, including the common bread mold, are saprophytic and their vegetative hyphae do not possess septa. They produce sporangia, which are capsules where haploid spores develop from the process of mitosis. A spore is usually haploid (has half the number of chromosomes) and divides mitotically to produce a multicellular organism.
Below is the life cycle of a zygomycete.
diagram of Rhizopus here
Part 1. Zygomycetes
Obtain a Petri dish containing Rhizopus. The plates were inoculated with two different mating types (a "+" type and a "-" type). View the organisms with your dissecting scope and draw their appearance in the space below. Along the center of the plate you should see zygosporangia, formed by the fusion of the two types of hyphae. The small black, spherical structures are sporangia and form asexual spores.
Now, observe prepared slides of Rhizopus sporangia and zygosporangia and make a sketch below.
In what structure does meiosis occur?
Considering all of the fungus that you observed on the petri dish, is most of it haploid or diploid?
Part 2. Ascomycetes
Diagram of life cycle of ascomycetes here
Obtain a yeast suspension from your instructor. Prepare a wet mount of the yeast. View under the microscope. Yeast divide by budding.
Describe in your own word the process of budding. Is it sexual or asexual?
Are many of the cells that you see in your preparation undergoing budding?ALMOST ALL OF THEM ARE UNDERGOING BUDDING
Draw a cell that is budding and compare it to one that is not. Describe what you see.
Ascomycetes can form asexual spores (conidia) as well as sexual spores (ascospores).
Sexual reproduction in Sordaria:
Obtain a Petri dish containing a culture of Sordaria.
Examine the Petri dish with a dissecting microscope. Note the small, dark, pear-shaped structures. These are called perithecia and contain the asci and ascospores. Gently remove one of the perithecia and place it on a microscope slide in a drop of water. Examine it under low power of a compound microscope. Then, add a coverslip. Tap on the coverslip with a dissecting needle or the eraser of your pencil to gently crush the perithecium and release its contents. Examine the results. Draw what you see in the space below.
What color are the ascospores? BLACK/BROWN
How many spores are in each ascus? 8
If meiosis typically yields 4 products, how do you explain the number of spores observed within each ascus?
AFTER MEIOSIS, THE 4 HAPLOID NUCLEI UNDERGO MITOSIS TO FORM 8 ASCOSPORES
Is this sexual or asexual reproduction? SEXUAL
Considering the 8 spores found in each ascus, how many different genotypes are present?
4- THE 4 GENETICALLY DIFFERENT OFFSPRING OF MEIOSIS DUPLICATE THEMSELVES BY MITOSIS AND STILL YIELD ONLY 4 GENOTYPES
Obtain a prepared slide of Peziza, a cup fungus. Make a sketch below and label the asci and ascospores.
Part 3. Basidiomycetes
Diagram of life cycle of Basidiomycota here.
Obtain one of the mushrooms provided in lab. This is the basidiocarp, or fruiting body of the fungus. Mushrooms also have an extensive underground mycelium similar to that of bread molds or Sordaria. Sketch the appearance of the basidiocarp, noting the cap, gills, stalk, and annulus (if present).
Carefully remove one of the gills and place it on a microscope slide. You should be able to see tiny basidiospores attached to sexual cells called basidia.
Now obtain a prepared stained slide of a gill. Draw and label what you see.
Part 4. Fungi Imperfecti.
In this group you would find examples such as Penicillium and Aspergillus both of which reproduce asexually by conidia.
Obtain a prepared slide of Penicillium and Aspergillus. Make a sketch below and label the conidia.
Part 5. Lichens
Lichens are symbiotic relationships between fungi and algae.
Observe three growth forms of lichens. Sketch the different structures of the lichen and add descriptions of the structures you see.
Obtain prepared slides of a lichen and sketch what you see.
In your opinion, are both the algae and fungi benefiting from this relationship? Explain.
BOTH ALGAE AND FUNGI BENEFIT FROM THE SYMBIOTIC RELATIONSHIP IN WHICH ALGAE PROVIDES THE FUNGI WITH FOOD AND THE FUNGI PROVIDES THE ALGAE WITH A SUITABLE PLATFORM FOR GROWTH.
Do NOT put headphones on until the CD has started. Volume can be controlled by the two small buttons on the right of the computer.
Double click the "Five Kingdoms" icon.
Double click the "Power CD" icon.
The program will begin to run by itself. Once started, click and hold down on "Contents", choose "Feature Presentations", then double click #15(The Fungi).
This Fungi part of the CD should lasts approximately 15 minutes. It is normal for it to pause for a few seconds every now and then. When it does pause, be patient, it will start back up.
Answer the questions provided as the program progresses and turn in to your TA as part of your assignment this week.
NOTE: If the program goes a little too fast, you can click on the middle button on the lower left of the screen (the one with two vertical lines). This will stop the program until you click the button again.
FUNGI CD-ROM ASSIGNMENT
1. What mode of nutrition is characteristic of all fungi?
2. What type of fungi feed on decaying materials?
3. Is it possible for cytoplasm to pass between cells of certain fungi?
4. How many major groups (phyla) of fungi exist? 4
5. How does Pilobolus disperse its spores?
IT SHOOTS ITS SPORES
6. What tasty fungus is prized by many mushroom hunters?
7. How many spores can a puffball produce?
8. What type of fungus produces dark, lumpy growth on corn plants (its actually edible!)?
9. What organisms use soredia as a method of dispersal?
10. What are ectomycorrhizae?
SPECIALIZED HYPHAE OF SOIL FUNGI- TERMED "EXTERNAL FUNGAL ROOTS"