Ch. 28 Fungi
I. Characteristics of Fungi
Structure of Fungi
**Fungi contribute to food, medicine, and recycling of nature
**Come in many forms (from mushrooms to yeast)
**Most fungi cell walls contain chitin (tough, flexible carbohydrate)
-Unicellular, such as yeast, are eukaryotic and undergo cell division
-Multicellular, such as mushrooms, display above-ground reproductive
structures (a stipe, an annulus, and a cap)
**Multicellular also contain individual filaments called hyphae
**Hyphae are tubules filled with cytoplasm and nuclei and may be
divided into walls called septa
**Mass of tangles, interwoven hyphae form a body of fungus called
a mycelium
There are specialized Hyphae for...
-reproduction: "sporangia" "gametangia" "conidia" etc.
-feeding/anchoring: "rhizoids"
-connection: "stolons"
...which make up each mycelium
Nutrition and Growth of Fungi
**All fungi are heterotrophs
Nutrition
-fungi obtain food through absorption
-produce enzymes in hyphae to help dissolve complex organics
-most a saprophytes or organisms that live off of dead organisms
-others depend on various symbiotic relationships
Growth
-fungi use absorbed nutrients for growth (usually rapid)
-growth in hyphae occurs at the tips, causing lengthwise growth
-underground growth of mushrooms can cover 1000 acres!
II. Origin and Diversity of Fungi
Origin of Fungi
**Mycologist: a biologist who studies mushrooms
**Fungi differ from plants!
-Plant cell walls are cellulose, fungi are chitin
-Plants are autotrophs, fungi are heterotrophs
**Due to these differences, fungi have their own kingdom!
I. Fungi grouped in four divisions based on their reproduction mode:
1. Common molds
2. Sac fungi
3. Club fungi
Note: each based on structures used in sexual reproduction
-fungi have 2 types of mating hyphae (+ and -) (plus and minus)
-sexual reproduction occurs by fusion of 2 different hyphae
-the result of such a fusion are spore production
4. Imperfect fungi (only produce asexually)
Note: fungi in all four divisions are known to reproduce asexually
II. Asexual reproduction can occur in three ways:
1. Budding (parent produces offspring in form of a small bud)
2. Regeneration (piece of mycelium breaks and forms on its own)
3. Spore production (most fungi produce spores in a fruiting body)
-spores are reproductive cells that can remain dormant or grow
into a new organism
-many produced, a typical mushroom produces 16 billion!
Common Molds
**Bread mold or shower mildew are examples (called Zygomycetes)
**This division of fungi called Zygomycota
**Found in soil or on dead animals or plants
Unique structure
-Lack septa (walls that divide hyphae into segments)
-Three types of specialized hyphae:
1. Rhizoids absorb nutrients & hold the mold to the food source
2. Stolons connect groups of rhizoids to one another
-transport cytoplasm through body of the fungus
3. Sporangia produce spores during reproduction (haploid cells)
-during other stages of the life cycle, (+) mating types (n)
merge with (-) mating types (n) to form diploid (2n)
structures called zygospores
-a zygospore undergoes meiosis and forms a sporangium
which releases spores (n) that can form new mycelium
-During asexual reproduction, upright hyphae develop sporangia that
disperses many spores
Sporangium
Sporangiophore
Rhizoid
Sac Fungi (Ascomycota)
**Diverse group includes yeasts, powder mildews, lichens, and morels
**More than 60,000 species!
**All linked due to formation of asci (a sac-like structure formed during
sexual reproduction)
**Unicellular sac fungi usually reproduce through cell division & budding
**Multicellular sexual reproduction rare! Usually asexual in involves
haploid spore production
Sexual Reproduction (of sac fungi):
1. Hyphae (n) of 2 mating types fuse to form an ascogonium
2. Ascogonium produces hyphae that become fruiting body
-end of each hyphae forms an ascus
-each ascus has two nuclei (n + n)
3. The 2 nuclei in each ascus fuse, forming diploid (2n) nuclei
-meiosis in each ascus produces haploid nuclei
4. The haploid nuclei undergo mitosis to produce 8 ascospores (n)
5. Ascospores develop into new hyphae (n)
Club Fungi (Basidiomycota)
**The common perception of a mushroom is a club fungi
**Tend to reproduce sexually:
1. Hyphae of different mating types (n) fuse, produce hyphae that
contain 2 nuclei (n + n)
2. Environmental changes cause mycelium to form visible
mushroom (basidiocarp)
3. Basidia (singular: basidium) (located on the gills under the cap)
containing 2 haploid nuclei, form in the tips of cell that line the gills
4. Nuclei in basidium fuse, forming a diploid nuclei (2n) (zygote)
-meiosis occurs, producing haploid nuclei (n)
5. Haploid nuclei mature into basidiospores (n) which are dispersed
Imperfect Fungi (Deuteromycota)
**Reproduce through asexual means only!
**Reproduction asexually by producing Conidia
**Examples: athletes foot or ringworm
**Not all are harmful, for example Penicillium produces penicillin
**They produce spores called conidia in specialized hyphae called
conidiophores
III. Fungi in the Biosphere
Ecological Roles
**Help maintain ecosystems due to their decomposing abilities
**Involved in many symbiotic relationships
Lichen: When a fungus and a photosynthetic organism work together
-example: sac fungus and green algae (algae provides food while
fungus provides home)
Mycorrhizae: Mutually beneficial relationships between plants and fungus
-example: fungus on the roots of plants
Diseases Caused by Fungi
**Some fungi act as parasites and cause disease
-example: Smuts and rust (destroy grain crops; example is great
potato famine), Dutch elm disease (trees), blight
-examples in humans: athletes foot, ringworm, UTI’s, allergies, nail
fungus and thrush
Human Uses
**Mushrooms for cooking!
-Not all are safe, some mushrooms produce toxins that can harm
**Flavor in cheeses
**Aspergillus used in making citric acid and soy sauce
**Yeasts used in baking and fermentation of beverages
Frontiers in Biology
**Alexander Fleming’s discovery of penicillin while studying
staphylococcus
**Yeasts important in genetic engineering
**Yeasts are highly studied organisms
**Although most current antibiotics are produced synthetically, many are still
based on a natural chemical made by fungi
**Because yeasts are eukaryotic, proteins made in yeasts may be more
beneficial to humans