Biology 2013-2014

Common Mold/Sac Fungi/Club Fungi/Fungi Imperfecti

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Section 21-2

    Fungi are classified according to their structure and method of reproduction.

    The four main groups are:

1.      common mold - Zygomycota

2.      sac fungi - Ascomycota

3.      club fungi - Basidiomycota

4.      imperfecti fungi - Deuteromycota

 

The Common Molds

    Phylum Zygomycota are the familiar molds that grow on meat, cheese and bread

    Their life cycles include a zygospore.

    A zygospore is a resting spore that contains zygotes formed during the sexual phase of the mold's life cycle.

 

Structure and Function of Bread Mold

    Rhizopus stolonifer is black bread mold.

    There are two different kinds of hyphae on bread mold.

1.      rhizoids - rootlike hyphae that penetrate the bread's surface

        anchor the fungus to the bread, release digestive enzymes, and absorb digested organic materials

2.      stolons - stemlike hyphae that run along the surface of the bread

       sporangiophores push up from the stolon and form sporangia at their tips

       a single sporangia may contain 40,000 spores

 

Life Cycle of Molds

    They have both a sexual and asexual phase.

    The sexual phase begins when hyphae from different mating types fuse and produce gametangium ( gamete­ forming structures)

    Haploid gametes fuse to produce diploid zygotes.

    The zygospore develops a thick wall and can remain dormant for a long period of time.

    The zygospore germinates and a sporangia emerges.

    The sporangia reproduces asexually by releasing haploid spores produced by meiosis.

 

The Sac Fungi

    Phylum Ascomycota is named for the ascus, a reproductive structure that contains spores.

    It is the largest phylum of the kingdom Fungi.

 

Life Cycle of Sac Fungi

    Life cycle includes both asexual and sexual reproduction.

    In asexual reproduction, tiny spores called conidia, are formed at the tips of conidiophores (specialized hyphae) which can be released under good conditions forming haploid mycelium.

    Sexual reproduction occurs when haploid hyphae of two different mating types grow close together.

    They produce a fruiting body where sexual reproduction continues.

    The ascus forms within the fruiting body that contains two nuclei of different mating types which fuse to form a diploid zygote.

    Meiosis is follows by mitosis producing ascospores which under the right conditions germinate and grow into haploid mycelium.

 

Yeasts

    Yeasts are unicelluar fungi.

    Humans use them for baking and brewing.

    The dry granules contain ascospores, which become active in a moist environment.

    They reproduce asexually by budding (cell division in rapidly growing yeast cells)

    Yeasts use the process of alcoholic fermentation to obtain energy.

    The byproducts are carbon dioxide and alcohol.

    The alcohol in bread dough evaporates during baking and the carbon dioxide make the bread dough rise.

    These yeasts are called "sugar fungi" due to the fact that they grow in a nutrient rich mixture.

 

 

 

 

 

 

 

 

 

 

 

 

 

The Club Fungi

    Phylum Basidiomycota or club fungi gets its name from a specialized reproductive structure that resembles a club.

    Basidium is the spore-bearing structure.

    Basidia are found on the gills on the underside of mushroom caps.

 

Life Cycle of Club Fungi

    It is the most elaborate life cycle of all the fungi.

    A basidiospore germinates to produce a haploid primary mycelium, which begins to grow.

    Mycelia of different mating types fuse to produce a secondary mycelium.

    Secondary mycelia might grow in the soil for years reaching an enormous size making them the largest organism in the world.

    When conditions are right, fruiting bodies (mushrooms) push above the ground.

    The fruiting bodies expand with great speed and may appear overnight.

    This is caused by cell enlargement NOT cell division.

    The hyphae enlarge rapidly by taking in water.

    The mushroom cap exposes hundreds of gills lined with basidia.

    Basidiospores form at the edge of each basidium and are ready to be scattered.

    A single mushroom can produce billions of spores, and giant puff balls can produce trillions.

 

Diversity of Club Fungi

    Basidiomycetes include:

       Mushrooms

       Shelf fungi

       Puffballs

       Earthstars

       Jelly fungi

       Rusts (plant parasites)

 

Edible and Inedible Mushrooms

    Many types of mushrooms have been considered delicacies.

    Some types are cultivated for food such as the mushrooms on your pizza, portobello mushrooms on your filet and shiitake mushrooms.

    Wild mushrooms are a different story.

    The result of eating a poisonous mushroom can be severe illness, or even death.

 

The Imperfecti Fungi

    Phylum Deuteromycota is an extremely varies phylum.

    It is composed of fungi that do not fit into any other phylum because they do not have a sexual phase in their life cycle.

    They resemble ascomycetes or basidiomycetes or even zygomycetes.

    The term imperfecti refers to fungi that DO NOT appear to have sexual reproduction.

    Penicillium is one of the best known imperfecti fungi.

    This mold grows on fruit and is the source of the antibiotic penicillin.

    Penicillium reproduces asexually by means of conidia, so it may have evolved from an ascomycete that lost the sexual phase of its life cycle.