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Anatomy of Fungi

Most fungi are made up in a large part of their mycelia, the underground net of threads called hyphae. Each hypha is surrounded by a rigid wall made of chitin (the same material that makes up the exoskeleton of insects). As a group in the mycelium, the hyphae merge together and their cytoplasms (and the nutrients contained within them) flow freely among them. Their organelles (and nuclei), however, stay in one place.
In some species of fungi, namely those in the Basidiomycota Phylum, as the mycelium develops it produces a structure that grows above ground and contains spores (the reproductive element of fungi). This structure usually grows above ground in order to disperse the spores more effectively. This above-ground portion of the fungi is what is commonly referred to as the mushroom, the fruiting body that is often eaten (such as crimini mushrooms, oyster mushrooms, shitake mushrooms, etc). As with agaricus fungi, this portion is made up of a stalk and a cap. With most polypores, the fungi will appear like shelves coming off of trees.

Above: an anatomy diagram of a common capped club fungi


In all cases, though, this above-ground structure contains spores. This way, the spores, which are the reproductive system of fungi (much like seeds in plants), can be carried and spread. Spores are generally released from the gills of a mushroom. Other fungi, such as polypores, have things other than gills.


Below: Stringy, white mycelium growing at the surface of the soil next to a rock
Below that: Mycelium observed under a microscope; note that the cell's cytoplasms are adjoined

Mycelium: Underneath the molds and mushrooms you see growing beneath trees or on your bread is an interlaced mesh of stringy white mycelium. Mycelium, or intricate underground weavings of hyphal cell, makes up a sort of ‘root’ system for fungi. Mycelium is made up of special diploid or haploid cells, hyphae, which are arranged in a line. The hyphae’s cytoplasms are all joined so that materials can be transported from hypha to hypha quickly but the nucleus of each hyphal cell remains separate. The Mycelium draws up minerals which are essential to both the fungi and fungi’s symbiotic partners. All fungi sprout from their Mycelium; if you dig near a mushroom you are sure to find the small white filaments growing in the soil. These filaments can survive without a mushroom/mold/sac fungi above and are therefore commonly in soil when no mushroom (etc.) is present. Some primitive fungi are nearly 100% composed of mycelium.



 

 

 

 





 

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Fungal Reproduction:

Alternation of Generation
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Each generation of Fungi Kingdom is opposite of its parents generation. A generation of fungal cells can either diploid, with two copies of each chromosome, or haploid, with only one copy of each chromosome. Most fungi that you would recognize as fungi, for example mushrooms (club fungi), the fruiting bodies of sac fungi and molds that appear above ground, are diploid. On the other hand, haploid fungi make up the hyphae cells and underground mycelium before the mycelium undergoes sexual reproduction. For the most part, the underground hyphae-roots which often sustain fungi that grow above the ground are of a haploid generation while fungi that grow above the soil or on the sides of trees are of a diploid generation.

Each of the two generations of fungi undergoes a different type of reproduction. Haploids sexually reproduce, joining the two nuclei of two different strands of hyphae cells to produce a new strand of diploid hyphae cells which will the sprout into an above-earth mushroom (etc.) Diploids, on the other hand, produce special haploid cells using Mitosis to be released as spores into the ground. The children of diploids become haploid mycelium that will produce more diploids.


Three Types of Fungi Reproduction

There are five, debatably six, phylums of fungi (see evolution section): Conjunction, Club, Sac, Imperfect, primitive and, perhaps, lichen. Each phylum has its respective method of reproduction. In this section, we will cover the three most important types of Fungi Reproductions: that of Molds/Conjunction Fungi (Zygomycota), Club Fungi (Basidiomycota) and Sac Fungi (Ascomycota). Enjoy fungi sex!

Phylum Zygomycota: Molds (Conjunction Fungi)

Sexual Reproduction: (1) When two haploid strands of hyphae, one (+) and one (-), meet, they fuse at the edges and begin to form a multi-celled, thick-walled zygosporangium. (2) The nuclei from the opposite hyphal cells fuse together inside the zygosporangium, forming a diploid-celled zygospore. (3) The diploid zygospore grows upwards into the air by undergoing meiosis. This mold protrusion is called sporangium (haploid). (4) The sporangium releases haploid spores into the air. (5) A spore lands into its final destination (e.g. in the earth, in bread, etc.) and begins to undergo mitosis forming new mycelium.

Asexual Reproduction: (1) Haploid mycelium sprouts into haploid sporangium without ever creating a diploid zygospore. (2) Spores are released into the air; the spores begin to sprout mycelium when they land.


Phylum Basidiomycota: Club Fungi (Mushrooms)

Sexual Reproduction: (1) Two strands of haploid mycelium, one (+) and one (-), fuse to create a diploid mycelium strand that contains two nuclei in each of its adjoined hyphal cells. (2) When above earth environmental changes become favorable, a visible mushroom forms above the diploid hyphae. (3) On the gills of the mushroom, diploid basidia (which will form into spores) begin to form; each basidia cell contains two nuclei. (4) The two nuclei in the basidia cells fuse creating a – still diploid – basidium. (5) Each basidia cell then undergoes meiosis producing haploid nuclei that matures into basidiospores. (6) The basidiospores are dispersed; when they land in their final destination points, they germinate, forming haphae

Asexual Reproduction: Basidiomycota only EXTREMELY rarely ever asexually reproduces, so don’t sweat it!



Phylum Ascomycota: Sac Fungi

Sexual Reproduction:
Sac Fungi seldom reproduce sexually. (1) Two strands of haploid hyphae, one (+) and one (-), come in close contact: both form a haploid Ascogonium out of hyphae. The Ascogonium is a sac with many fungi cell nuclei compacted close. (2) Out of the Ascogonium, many strands of hyphae grow above earth. These filaments synthesize to form the structure of the “fruiting” body of the fungi. At the tip of the fruiting body, each hyphae strand forms into an ascus. Each ascus contains two nuclei. (3) The nuclei in the ascus fuse to create a diploid ascus. Then, each ascus undergoes meiosis, producing haploid nuclei. (4) The haploid nuclei undergo meiosis again, resulting in eight ascospores in each ascus. Each ascus bursts, releasing the ascospores into the air. (5) When an ascospore reaches its destination, hyphae develop and a new generation of fungi is propogated.

Asexual Reproduction:
Sac Fungi USUALLY reproduce asexually. (1) Haploid hyphae grow above earth, producing some haploid spores. (2) The spores are dispersed. (3) When a spore reaches its destination, hyphae develop and a new generation, identical to its parent, is propogated.



Sources:

All photographs acquired using google image search
All diagrams and illustrations are hand drawn by Jon, Chuck and Jesslyn
Reproduction diagrams adapted from:
http://www.sirinet.net/~jgjohnso/fungireproduction.html
Info adapted from:
Biology; Concepts and Applications: Fifth Edition
http://www.sirinet.net/~jgjohnso/fungireproduction.html
All text written / website design done by Chuck Goldhaber, Jonathan Wachter and Jesslyn Jamison


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