OVERVIEW OF FUNGI

In the Six-Kingdom classification of organisms, fungi are in their own Kingdom.  They differ from other organisms in several ways, including in Structure, in Method of Reproduction, and in Method of Obtaining Nutrients.

OBJECTIVES: Describe the origin and evolution of fungi.  Compare fungi with other Eukaryotic organisms.  Describe how fungi obtain nutrients.  Distinguish between a hypha and mycelium.

1. Fungi are Eukaryotic, Nonphotosynthetic Organisms, and Most are Multicellular Heterotrophs.

2. Most fungi are Microscopic MOLDS or YEAST.

3. MOLDS, such as the Fungus that grows on bread and oranges are tangled masses of Filaments of Cells.

4. YEAST are Unicellular Organisms whose colonies resemble bacteria.  Yeast are best known as the Microorganism that makes bread rise.

5. Fungi contribute to the food people eat, to medicine, and to the recycling process that releases nutrients from dead organisms back into the environment.

6. Fungi resemble Plants in some ways, and were once classified as Plants.  Fungi cannot move and some are edible.

7. Fungi differ from Plants in important ways:

    A.  Fungi lack Chlorophyll and are not Photosynthetic.

    B.  Fungi NEVER Reproduce by Seeds.

    C.  The Cell Walls of Fungi are made of CHITIN (KIE-tin), NOT Cellulose.

5.  Because of these differences Fungi are classified in their own Kingdom.

6. Taxonomists have classified over 100,000 Species of Fungi, and think there are more yet to be discovered.  Taxonomists have classified many Fungi by the Structures use for Sexual Reproduction.

7.  SOME COMMON CHARACTERISTICS OF ALL FUNGI:

    A.  Fungi are Eukaryotic Organisms with nuclei and mitochondria.

    B.  Fungi depend on other Organisms for their nutrition.  THEY ARE HETEROTROPHS.

    C.  Most Fungi are Multicellular Organisms, but they are not made of typical cells.

    D.  Most Fungi Cannot Move by themselves.

THE NUTRITION OF FUNGI

1. ALL FUNGI ARE HETEROTROPHS, obtaining their nutrition from other organisms.

2. MOST FUNGI ARE SAPROPHYTES, THEY OBTAIN THEIR NUTRIENTS BY DIGESTING AND ABSORBING NUTRIENTS FROM DEAD ORGANISMS.  Fungi are DECOMPOSERS or RECYCLERS.

3. Some Fungi are Parasites and obtain their nutrients from living host. A few are Predators, able to trap and kill their prey.

4. Fungi Digest Their Food OUTSIDE OF THEIR BODIES by Secreting Enzymes that break down organic material.  The Fungi then absorbs food through their Cell Walls.  Like Animals, Fungi store Energy in the form of Glycogen.

THE STRUCTURES OF FUNGI

1. The study of Fungi is called Mycology.

2. Fungi include Unicellular and Multicellular Organisms.

3. YEAST are typical Unicellular Fungi.  Yeast Cells have a Cell Wall containing Chitin, a Cell Membrane, a Nucleus, a Large Vacuole, and membrane-bound organelles.  Yeast are Eukaryotic organisms that undergo Cell Division.

4. Most Fungi are Multicellular Organisms.  Fungi have bodies composed of Unusual Cells.

5. The Body of a Fungus consists of Tiny Filaments called HYPHAE.

6. HYPHAE ARE TINY TUBES FILLED WITH CYTOPLASM AND NUCLIE, THE CELL WALLS OF HYPHAE CONTAIN CHITIN.

7.  Chitin is a complex Polysaccharide NOT Found in Bacteria, Protists, or other microorganisms but found in insects, the presence of Chitin Distinguishes Cell Walls of Fungi from those of Plants.
  

8. HYPHAE ARE THE LIVING, GROWING PART OF MULTICELLULAR FUNGI. A Mat of Hyphae visible to the unaided eye is a MYCELIUM.

9. Some Hyphae are divided by Cross Section Segments (Walls) called SEPTA.  The Septa have holes through which Cytoplasm and Organelles can move from segment to segment.

10. Hyphae whose Cells Are divided by Septa are called SEPTATE HYPHAE.

11. The Hyphae of species that do not have Septa are called COENOCYTIC. (SEE-noh-SIT-ik)

12. Multicellular Fungi consist of a mass of Hyphae.  The Mass of tangled, interwoven Hyphae that form the Body of a Fungus is called a MYCELIUM.  The Stalk of a Mushroom is Mycelium made of tightly packed Hyphae.  

THE GROWTH OF FUNGI

1. Fungi can grow rapidly because of the structure of their Mycelium.  All the Hyphae in a Mycelium share the same cytoplasm.

2. Hyphae increase Length by Cellular Growth and Division at the TIP.  As the Hyphae grow, the size of the Mycelium increase.

3. Materials can move quickly through the whole Mycelium.

4. Because materials from the whole Mycelium are available to the growing Hyphae, Fungi can grow rapidly.

5.  Several species of Fungi are able to change their form in response to change in their environment.

6. For example, Histoplasma capsulatum, which causes a severe disease in humans that can resemble tuberculosis, Normally Grows as Mycelium on the Ground, but when it invades a human, the increased temperature and available nutrients causes the Fungus to grow Unicellular like a Yeast. 

7.  This ability to change is called DIMORPHISM (die-MOR-FIZ-uhm).

REPRODUCTION IN FUNGI

1. Many Fungi Can Reproduce BOTH Asexually and Sexually.

2. Asexual Reproduction which produces offspring that are Genetically Identical to the Parent, is Most Common when Nutrients and Water are Abundant.

3. Sexual Reproduction occurs in Fungi mostly when Nutrients or Water become Scarce.

ASEXUAL REPRODUCTION

1.  Asexual Reproduction in Fungi can occur in several ways: 

    A.  Some unicellular fungi can reproduce by Mitosis.

    B.  Yeast Cells reproduce by a process called BUDDING. An Asexual Process in which part of the cell pinches itself off to produce small offspring.

    C.  Most fungi can grow from a small piece of Mycelium called FRAGMENTATION. The Fungus that causes Athlete's Foot grows this way.

D.  Most fungi can reproduce Asexually by SPORES.

2.  Spores are the means by which Fungi are Dispersed.  Each Spore contains a Nucleus and Dehydrated Cytoplasm surrounded by a Protected Coat.

3.  A SPORE IS A HAPLOID REPRODUCTIVE CELL, USUALLY ONE-CELLED, THAT IS CAPABLE OF DEVELOPING INTO A NEW INDIVIDUAL.

4.  Asexually, Fungi produce thousands of Genetically Identical Haploid Spores, usually on Modified Cells of Hyphae.

5.  When a Spore lands on a moist surface (favorable environmental conditions) where nutrients are available, the Cytoplasm absorbs water and forms Hyphae.  The Hyphae will then form new Mycelium.

6.  THE REPRODUCTIVE STRUCTURES OF FUNGI THAT PRODUCE SPORES ARE CALLED FRUITING BODIES.

7.  A FRUITING BODY CONSISTS TYPICALLY OF A STALK AND A SAC IN WHICH SPORES ARE PRODUCED.  IN A MUSHROOM, THE CAP CONTAINS THOUSANDS OF FRUITING BODIES.

8. A variety of Asexual Spores are formed by different Fungi.

9. SPORANGIOPHORES are specialized Hyphae that look like upright Stalks.  On top of the Sporangiophore is an enclosed Sac called a SPORANGIUM. Inside each sporangium, Spores called SPORANGIOSPORES are made.  Rizopus, bread mold, is an example of Sporangiospore forming Fungus.

10. Other Fungi form Spores called CONIDIA, which are formed Without the Protection of an Enclosed Sac.  Conidia are formed on top of a stalk-like structure called a CONIDIOPHORE. Penicillium, which produces Penicillin and Cheese, is a Fungus that Reproduces Asexually by means of Conidia.  

11. When Fungi are ready to reproduce, Fruiting Bodies form.  Fruiting Bodies may form as a result of Either an Asexual or Sexual process.

12. All the Spores released by Fungi are Haploid.

13. Fungal Spores cannot move themselves, but spores are small and light and can be dispersed by wind, animals, insects, or water.  Fungal spores can be found most everywhere.
 
SEXUAL REPRODUCTION

1. There are no male or female fungi.  The Two mating types are called PLUS (+) Mating Type and the Minus (-) Mating Type.

2. Fertilization occurs when the Hyphae from a Plus Mating Type and a Minus Mating Type Fuse.

3. These fused Hyphae give rise to a specialized structure, which produces and scatters Genetically Diverse Spores.

4. Unlike most Eukaryotes, Most Fungi are Haploid throughout most of their lives.

5. The ability to reproduce Both Sexually and Asexually provides an Adaptive Advantage:

    A. When the Environment is Favorable, Rapid Asexual Reproduction Ensures an increase spread of the species.

    B. During Environmental Stress, Sexual Reproduction Ensures Genetic Recombination, increasing the likelihood that Offspring will be better Adapted to the New Environment.

EVOLUTION

1. The First Fungi were probably Unicellular Organisms that might have clung together after mitosis to form long filament of cells.

2. Biologist think Fungi colonized land at about the same time that early plants did.

3. They reason that Fungi, like other Eukaryotes, arose from Prokaryotes, possibly by Endosymbiosis.

4. According to fossil record, all modern Phyla of fungi had evolved by 300 million years ago; ZYGOMYCOTA, BASIDIOMYCOTA, AND ASCOMYCOTA.  

THE CLASSIFICATION OF FUNGI

The approximately 100,000 species of fungi are classified in Three Phyla.  Traditionally, fungi have been classified according to their structures and form of sexual reproduction.  While these are no longer the sole basis of classification, these characteristics are still useful in identifying fungi.

OBJECTIVES:  List the characteristics that distinguish the three phyla of fungi.  Identify the common sexual reproduction traits of the three phyla of fungi.  Define mycorrhiza and lichens, and distinguish between them.  Explain the importance of micorrhizae and lichens to the environment.

PHYLUM ZYGOMYCOTA - COMMON MOLDS

1. Most species in the Phylum Zygomycota are Terrestrial Organisms found primarily in Soil that is rich in organic matter.

2. The Hyphae of Zygomycetes are Coenocytic - or they Do Not have Septa.

3. Bread Molds, Black Bread Mold, Rhizopus stolonifera, not only grow on Bread, but anywhere there are water and nutrients.

4. Common Molds HAVE NO SEPTA (Cross Walls) in their Hyphae.  Their Hyphae are therefore long, continuous tubes containing many Haploid Nuclei.

5. The Hyphae of Common Molds show some specialization of function:

    A. RHIZOIDS -  (Root-Like Structures) THE PART OF THE HYPHAE USED BY THE FUNGUS TO ANCHOR TO ITS SOURCE OF FOOD.  They penetrate the food surface.

    B. STOLONS -  HYPHAE THAT CONNECT ONE GROUP OF RHIZOIDS TO ANOTHER. They spread across the surface of the food source.

6. Common Molds life cycles includes both Asexual and Sexual Stages.

7. COMMON MOLDS REPRODUCE ASEXUALLY MORE OFTEN THAN THEY DO SEXUALLY.

8. When Hyphae of different Mating Types or Strains grow close to each other the Mold may Reproduce Sexually by Conjugation. 

9. The mold develops special extensions for mating called GAMETANGIUM (gam-eh-TAN-jee-uhm). The Gametangia from the Two Types Grow Together and FUSE.

10.  Nuclei from the two types Mix and form a THICKED WALLED STRUCTURE CALLED A ZYGOSPORANGIUM WHICH IS A RESTING STAGE (Becomes Dormant) OF A FUNGUS THAT CONTAINS MANY NUCLEI.

11.  A Zygosporangium can survive hostile environmental conditions.  When conditions improve, the Dipoild Zygosporangium cracks open and a SPORANGIOSPHORE grows and forms a  SPORANGIUM (spor-AN-jee-um).  The SPORANGIUM RELEASES THOUSANDS OF Haploid SPORES.

PHYLUM BASIDIOMYCOTA - CLUB FUNGI

1. Basidiomycetes are often called Club Fungi because they produce small Club-like Reproductive Structures called BASIDIA during Sexual Reproduction.

2. This Phyla includes MUSHROOMS, BRACKET FUNGI, SHELF FUNGI, PUFFBALLS, STINKHORNS AND SEVERAL MOLD LIKE FUNGI CALLED RUSTS AND SMUTS, THAT DAMAGE GRAINS, FOOD CROPS, AND OTHER PLANTS.

3. THE MOST FAMILIAR CLUB FUNGI ARE MUSHROOMS.  BEWARE NOT ALL MUSHROOM ARE EDIBLE.

4. MUSHROOMS ARE ACTUALLY REPRODUCTIVE STRUCTURES.

5. CLUB FUNGI SELDOM REPRODUCE ASEXUALLY.

6. CLUB FUNGI REPRODUCE SEXUALLY BY FORMING SPORES IN A STRUCTURE CALLED A BASIDIUM (BASIDIA) WHICH CAN BE FOUND LINING GILLS INSIDE THE BASIDIOCARP (THE MUSHROOM CAP).

7. The Basidiocarp consists of a Stem called a STALK and a Flattened structure known as a CAP.

8. On the underside of the Cap are rows of GILLS that radiate out from the center.

9. Each Gill is lined with Thousands of DIKARYOTIC BASIDIA.  Cells containing Two Nuclei are called Dikaryotic. Cells that contain One Nucleus are called MONOKARYOTIC.

10. In each Basidium, Two nuclei fuse to form a Zygote.  The Zygote undergoes meiosis to form Four Haploid Nuclei, that develop into four BASIDIOSPORES which are released into the air.

11. Under favorable conditions the Basidiospores Germinate and grow New Hyphae and Mycelia.

PHYLUM ASCOMYCOTA - SAC FUNGI
 

1. Ascomycetes are distinguished by the presence of Saclike Compartments where Sexual Production of Spores Form.

2. This Phyla includes the UNICELLULAR YEAST, CUP FUNGI, TRUFFLES, MORRELS AND MILDEWS THAT ARE DESTRUCTIVE PARASITES OF FOOD CROPS.

3. Sac Fungi can reproduce both Sexually and Asexually.

4.  SAC FUNGI REPRODUCE ASEXUALLY BY FORMING SPORES AT THE TIPS OF THEIR HYPHAE.

5. SAC FUNGI REPRODUCE SEXUALLY BY FORMING AN ASCUS (ASCI) - A SAC STRUCTURE IN WHICH SPORES ARE FORMED.

6. Sexual Reproduction takes place when the Hyphae of Two Compatible mating types form Male and female Haploid Gametangia.

7. The Female gametangia is called an ASCOGONUIM (as-koh-GOH-nee-um). The Male Gametangia is called an ANTHERIDIUM.

8.   As the Ascogonium and Antheridium approach one another, a tube forms between them and the nuclei from the Antheridium cross and enters the Ascogonium.

9. The Parent Fungi form a visible Cup-like Sexual Reproductive structure called the ASCOCARP.

10. Within the Ascocarp, the Sacs called ASCI develop at the tips of the Hyphae and Form ASCOSPORES, which are released.

11. Brewer's and Baker's YEAST are Unicellular are Unicellular Sac Fungi that can Reproduce Sexually by forming Asci.

DEUTEROMYCOTA - FUNGI IMPERFECTI  (OTHER FUNGI)

1. The one characteristic shared by all Fungi Imperfecti is an apparent ABSENCE of Sexual Reproduction.

2. Most species of Fungi that were formerly classified as Fungi Imperfecti can now be classified in the Phylum Ascomycota.

MYCORRHIZAE AND LICHENS

1. A MYCORRHIZA (MIE-koh-RIE-zah) is a Symbiotic Association between a Fungus and Plant Roots.

2. Fungi are vital for the growth of many plants.  MYCORRHIZAE are mutualistic associations between a Fungus and the Roots of a Plant. Over 90 percent of Plants contain Fungi on their Roots.

3. The Fungus benefits because it can absorb nutrients (Sugars) made by the Plant during Photosynthesis, the Fungus provides the plant with Two Important Advantages:

    A.  The Hyphae of the Fungus acts as Root Extensions.  This increases the Plants Roots ability to absorb water from the soil.

    B.  The digestive enzymes secreted by the Fungus help breakdown organic matter in the soil, which the plant can then absorb as nutrients and minerals.

4. LICHEN is a symbiotic (Mutualistic) association between a Fungus and a Photosynthetic Organism.

5. The Fungus in Lichen is usually an Ascomycetes (Sac Fungus), and the Photosynthetic Organism is either a Green Alga or a Cyanobacterium.

6. Many Lichens absorb chemical nutrients, such as nitrogen and sulfur from the air. Becuase Lichens absorb nutrients from the air they can grow on almost any surface: rocks, tree trunks, buildings, and monuments.  When lichen grow on bare rock, they help breakdown rock to SOIL.

7. The photosynthesizer synthesizes sugars for the Fungus, while the Fungus provides moisture, shelter, and anchorage for the photosynthesizer.

8. Lichens are identified according to their distribution and structure. CRUSTOSE Lichens grow as a layer on the surfaces of rocks and trees.  FRUTICOSE Lichens are shrub-like, and grow up to 1.5 m in length.  FOLIOSE Lichens live on soil surfaces, where they form mat-like growths with tangled bodies.
 
FUNGI AND HUMANS

Fungi are important to humans. Some fungi cause devastating human and plant diseases, while others serve as important food sources for humans.  Fungi are also used to produce chemicals, fuels, and pharmaceutical compounds.

OBJECTIVE:  Describe three ways that fungi cause disease in humans.  Describe the types of food that fungi provide.  Provide examples of fungi's industrial importance.

FUNGI AND HUMAN DISEASE

1. Fungi can sometimes attack the tissues of Living Plants and animals and cause disease.

2. Fungal disease is a major concern for humans because fungi attack not only us, but, our Food source.

3. Mold Spores can cause mild to serious Allergies in some people, sniffling, sneezing, and respiratory distress.

4. Fungi can also infect and poison humans - lists some infectious human Fungal diseases.

5. Fungi may infect the skin, hair, nails, and tissues of the Body.

6. Fungi on the Skin can cause Athlete's foot or Ringworm. 

7. Fungi can cause Yeast Infections.  Yeast is commonly found in the mouth, intestines, and, in women, in the vaginal tract.

8. Serious fungal diseases that involve the Internal Organs are often caused by Dimorphic Fungi.  If their Spores are Inhaled, they can cause severe respiratory illness and spread to many organs.

9. Some Mushrooms are Poisonous to Humans,  Amanita mushroom "death angel" or "destroying angle". They contain Extremely Dangerous Toxins.  When in Doubt, Don't Eat a Mushroom! 

10.  Other fungal poisons include the AFLATOXINS, poisons produced by some species of Aspergillus.  Aflatoxins cause liver cancer.  Fungi that make aflatoxin may be found as contaminants in peanuts and in grains such as corn and grain sorghum.
 
FUNGI IN INDUSTRY

1. Many Fungi are Valuable Food sources for humans.  Yeast, such as Saccharomyces, is an important nutritional supplement because it contains vitamins, minerals, and other nutrients.

2. Mushrooms are an important Food. Agaricus (White Button), shiitake, and portabella mushrooms are often found in grocery stores.

3. In other places in the world, people prize the taste of Truffles and Morels, which are Ascocarps found near the Roots of Trees. 

4. Many Fungi are Plant Pathogens that attack grain and fruit.  Wheat Rust is a Basidiomycete that attacks wheat grains.  Other Fungi can attack food crops such as corn, beans, onions, squashes, and tomatoes.

5. Fungi are used to produce Chemical Compounds that are important to the food-processing industry such as Citric and Gluconic Acid. Citric Acid is used in soft drinks and candies.  Gluconic Acid is fed to chickens to enhance the hardness of eggshells.

6. Ashbya gossypii is a producer of Vitamin B2, an important nutritional supplement.

FUNGI AND THE ENVIRONMENT

1. Most Fungi are either SAPROPHYTES OR DECOMPOSERS THAT BREAK DOWN AND FEED ON DECAYING ORGANIC MATERIAL OR DEAD ORGANISMS.

2. Fungi obtain nutrients to absorb by secreting digestive enzymes onto the food source.  The enzymes break down, or digest, the food.

3. The breakdown, or digestion, of organic material can also be called DECOMPOSITION.  Any organism that causes decomposition can be called a DECOMPOSER.

4. Fungi work along with the Monerans and Protists to decompose the waste and remains of plants and animals.

5. When fungi secretes digestive enzymes into a food source, the Nutrients are released to be used by the fungus and other organisms.

6. The Nutrients are RECYCLED and Returned to the Environment.

7. Without decomposers, ecosystems would collapse, because many organisms would not obtain enough nutrients to stay alive.