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Areas of Interest:
 

 
 
 
 

The Fungi Test

 
 
 
 

 


 

Objectives:
 

  • You Will Be Able To List the Basic Characteristics and Structure of Fungi
  • You Will Be Able To Discuss Fungi's Economic Importance
  • You Will Be Able To Describe the Ways In Which Fungi Reproduces

 
 
Physical Characteristics

Most fungi are unicellular (comprised of one cell), but some fungi are composed of masses of coenocytic (multicellular filaments). 
Hypha - (as seen in the picture at the left) is a fungal filament - all of the hyphae of a single organism are called - mycelium

The walls of hyphae are composed of chitin. Chitin is a polysaccharide (multiple sugar) that is never found in plants.  It is found in the exoskeleton (hard outer covering) of insects.  Mushrooms are mostly comprised of tightly packed hyphae specialized for the production of spores. 
Mycelium usually arise from the germination and outgrowth of a single spore.  The growth only takes place at the tips of the hyphae.  All fungi are unable to move but often time their spores are carried by the wind.  The growth of the mycelium usually substitutes for mobility (movement) by introducing the organism with new food sources and different mating strains.  The hyphae can grow in a new group of hyphae very rapidly sometimes even in 24 hours.
All fungi are heterotrophs therefore they always live closely to their environment (soil, water).  The fungi's walls are very rigid, restricting them from engulfing small microorganisms or other particles.  They obtain their food by absorbing dissolved inorganic or organic materials.  Parasitic fungi have specialized hyphae, called haustoria, that absorb nourishment directly from the host cells. 

 
Fungi's Economic Importance

Although most people view fungi as very poisonous, most fungi are very important to the environment.  The fungi, together with the bacteria, are principle decomposers of organic matter. It is estimated that the top 20 centimeters of fertile soil is fungi. 
Fungi is mostly viewed by humans as destructive.  It is the green mold that destroys our bread and cheese and it is the source behind what is killing the tree outside of your house.  But fungi really is essential for every person.  Fungi is used in the production of all the following products:

 

Fungi is used in the use of yeast to raise the bread.

Fungi is used in the production of cheese.  Blue cheese is made of mold.

Fungi is used in the fermentation of wine.
Fungi is the main source
in many antibiotics.  Penicillin is primarily 
made up of mold.

 
 
Fungi Reproduction:

The diagram above represents the life cycle of fungi.  The mushroom starts out and the spores are fertilized.  Meiosis occurs and the spores are released.  Next, the germination of the spores occurs and the mycelia grows.  Then, is the fusion of the hyphae and finally the growth of the two nuclei mycelium occurs.
Fungi reproduce both asexually and sexually. 

Asexual reproduction  happens with fragmentation of the hyphae (which is when each fragment becomes a new one) or by the production of spores.  The spores are produced in the Sporangia.  The colors and textures of many molds are due to their spores.  The spores can go a long time without food or water and often spread themselves out among large distances due to the wind. 

Sexual Reproduction involves specifying portions of the hyphae to form a gametangia - a place where gametes (sex cells) are produced.  The contents of the gametangia are separated by a cell wall known as the septum. This can occur in a variety of ways. 

  • By the fusion (to come together) of the gametes that are released by the gametangia
  • By the fusion (to come together) of the gametangia
  • By the fusion (to come together) of the unspecified hyphae

 
  
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Objectives:
 
 
  • You Will Be Able To Identify the Criteria Used In Classifying Fungi
  • You Will Be Able To Explain the Differences In the Divisions of Fungi

 
 
The members of the Kingdom Fungi are generally classified into three principal divisions: Zygomycota, the zygomycotes; Ascomycota, the ascomycetes; and Basidiomycota, the basidiomycetes.  The criteria used in distinguishing these three divisions involve both features of basic structure and reproduction patterns, particularly sexual reproduction.  An additional taxon, Deuteromycota, or the Fungi Imperfecti, which includes all fungi in which sexual reproduction is unknown.  The chart below describes the different characteristics of each division in which they were classified into.

 

The Kingdom Fungi

 
 
Division
Number of Species
Examples
Distinctive Characteristics
Diseases
Economic Uses
Zygomycota
About 600
Black bread mold
Formation of zygospores
Few
None
Ascomycota
30,000
Neurospora, yeasts, morels, truffles
Formation of fine asexual spores; sexual spores in asci; hyphae divided by perforated septa; dikaryons
Powdery mildews of fruits, chestnut blight, Dutch elm disease, ergot
Food (morels, truffles); wine-, beer-, and bread-making (yeasts)
Basidiomycota
25,000
Toadstools, mushrooms, rusts, smuts
Sexual spores in basidia; hyphae divided by perforated septa; dikaryons
Rusts, smuts
Food (mushrooms)

 
Deuteromycota
(Fungi Imperfecti)
25,000
Penicillin
Fungi with no known sexual cycles
Ringworm, thrush
Cheeses, antibiotics

 
 
  
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Objectives:
 
  • You Will Be Able To Identify the Main Divisions of Fungi
  • You Will Be Able To Explain the Characteristics of Each Division of Fungi

The  main divisions of Fungi:
 
 
 

Division Zygomycota
 

Division Ascomycota
 

Division Basidiomycota
 

Division Deuteromycota























 
The zygomycetes are fungi that primarily feed on dead plant or animal matter. The sexual reproduction is characterized by the formation of zygospores - thick-walled, resistant spores. 


 
The drawing above represents a typical zygomycete.  One of the most common members of this division is Rhizopus stolonifer which is black bread mold  (as seen to the right). 

 
  
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The ascomycetes are the largest division of fungi, with 30,000 species and an additional 25,000 species that are found only in lichens.  Examples of ascomycetes are:

 

Yeast

Truffles

Blue-green mold

 
 
Members of this division also are the cause of many plant diseases and are the source of many antibiotics.  The bread mold Neurospora, which played a major role in the history of modern genetics, is an ascomycete. 

 
  
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The most familiar basidiomycetes are mushrooms and toadstools.  There are some 25,000 species.  The mushroom is composed of masses of tightly packed hyphae (as seen below in the diagram). 

 
The basidiomycetes, like the ascomycetes, have the hyphae subdivided by perforated septa.  Sexual reproduction is initiated by the fusion of haploid hyphae to form a dikaryotic mycelium.  Eventually, some of the nuclei fuse (to come together) to form diploid nuclei that immediately undergo meiosis.  Fusion and meiosis always take place in specialized hypha called a basidium (the greek word for "club").  The spores are produced externally on the basidium.

 
  
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The deuteromycetes, or Fungi Imperfecti, are generally fungi in which sexual reproduction is unknown.  Among the 25,000 species that have been described, some are causes of diseases such as ringworm and athletes foot, and in the production of penicillin, cheeses, and cyclosporin (used in organ transplants). 

 
  
Return to List of Divisions

 


 

Objectives:
 
  • You Will Be Able To Define the Terms Lichen and Mycorrhizae
  • You Will Be Able To Explain How the Terms Above are Involved in a Symbiotic Relationship

  

Lichen - an organism composed of a fungus and a green algae or a cyanobacterium that are symbiotically associated.


In other words - A lichen is what forms when a specific fungus and a cyanobacterium or green algae come together.

Lichens are important for telling whether the air is clean, making antibiotics, making nitrogen in the air usable for plants, homes for spiders and insects, as dye for wool, and for people to eat (but don't try that one at home).

 
Lichens can be found in a variety of places.  They occur most commonly in the arid desert regions to the Arctic and grow on bare soil, tree trunks, sun baked rocks, fence posts, and windswept Alpine peaks all over the world.

 
 
 
Mycorrhizae - are symbiotic associations       between a particular species of fungi and the roots of vascular plants.

In other words - A mycorrhizae is when a certain species of fungi and roots of a plant come together.

Mycorrhizae offers several benefits to the host plant, including faster growth, improved nutrition, and greater drought resistance. 

 
 
The Symbiotic Relationships - Lichens and Mycorrhizae

When the phrase "symbiotic relationships" is used it refers to the association between two or more organisms of different species. 
This includes three types of relationships: 

  • a relationship in which the association is beneficial to both organisms (mutualism)
  • a relationship in which one of the organisms benefits and the other is neither harmed nor benefited (commensalism)
  • a relationship in which one organism benefits and the other organism is harmed (parasitism)
Lichen are able to survive under adverse environmental conditions where neither partner could exist independently.  The lichen represents a symbiotic relationship in which a fungus encloses photosynthetic cells and is dependent upon them for nourishment.  This is a form of commensalism.

Mycorrhizal associations facilitate the uptake of minerals by the roots of the plant and provide organic molecules for the fungus.  They are thought to have played a key role in enabling plants to make transition to land.  This is a form of mutualism.

 
 Characteristics of Fungi
Classification of Fungi
Divisions of Fungi
Symbiotic Relationships of Fungi
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