18
(p. 388)
18.1 Complex Multicellularity (p. 388)
A.
In complex multicellular organisms, individuals are composed of many highly specialized cells that coordinate their activities.
B.
There are three kingdoms made up of complex multicellular organisms: plants, animals, and fungi.
C.
Cell specialization and intercell coordination separate complex multicellular organisms from multicellular marine algae.
D.
Cell specialization reflects development, during which genes are expressed in some cells while not being expressed in other cells.
18.2 A Fungus Is Not a Plant (p. 388; Figs. 18.1, 18.2, 18.3)
A.
Mycologists believe there are about 74,000 kinds of fungi.
B.
Fungi are characterized as heterotrophs with filamentous bodies, nonmotile sperm, cell walls made of chitin, and nuclear mitosis.
C.
The Body of a Fungus
1.
The main body of a fungus is composed of slender, elongated filaments called hyphae, which are long chains of cells with incomplete separations called septa between them.
2.
Cytoplasm can flow freely from one cell into the next.
3.
Fungi exist as hyphae most of the time and produce a mass called a mycelium.
18.3 Reproduction and Nutrition of Fungi (p. 390; Figs. 18.4, 18.5)
A.
How Fungi Reproduce
1.
Fungi reproduce both sexually and asexually.
2.
When two mating strains (the fungal alternative to male and female) exchange genetic material, the nuclei do not fuse immediately.
3.
Hyphae that have nuclei from two genetically distinct parents are called heterokaryonic, while those with nuclei from genetically identical parents are homokaryonic.
4.
Reproductive structures produced by fungi include gametangia, in which haploid gametes are produced, sporangia that give rise to haploid spores, and conidiophores that produce asexual, multinucleate spores called conidia.
5.
When conidia or spores land in a hospitable location, they can germinate and give rise to new fungal hyphae; spores and conidia can travel long distances.
B.
How Fungi Obtain Nutrients
1.
Fungi secrete digestive enzymes into their surroundings so the fungus can absorb nutrients into the mycelium, a mode of nutrition called external digestion.
2.
A number of fungi are active predators.
(p. 391)
18.4 Kinds of Fungi (p. 391; Figs. 18.6, 18.7, Table 18.1)
A.
The fungi are a diverse group that are at least 400 million years old.
B.
The fungal phyla are distinguished primarily by their mode of sexual reproduction.
C.
Fungi whose sexual stage has not been observed are lumped into the “imperfect fungi.”
D.
There are eight fungal phyla, distinguished by DNA differences and modes of sexual reproduction: Microsporidia, Chytridiomycota, Blastocladiomycota, Neocallimastigomycota,
Zygomycota, Glomeromycota, Basidiomycota, and Ascomycota.
18.5 Microsporidia Are Unicellular Parasites (p. 392; Fig. 18.8, Table 18.1)
A.
Microsporidia lack mitochondria; however, the presence of mitochondrial genes indicates that at one time an ancestral form possessed them.
B.
As obligate parasites, microsporidians cause human disease.

18.6 Chytrids Have Flagellated Spores (p. 393; Figs. 18.9, 18.10, 18.11)
A.
Three closely related phyla, Chytridiomycota, Blastocladiomycota, and
Neocallimastigomycota, have flagellated zoospores.
B.
Chytrid refers to the potlike shape of the structure releasing the zoospores.
C.
Blastocladiomycetes have uniflagellated zoospores.
D.
Neocallimastigomycetes aid ruminant animals in digesting cellulose.
18.7 Zygomycetes Produce Zygotes (p. 394; Fig. 18.12)
A.
Members of the phylum Zygomycota are unusual in that fusion of gametes produces a diploid zygote in this group, not a heterokaryon.
B.
Only 1,050 species are in this group, which includes the bread molds and many fungi of decay.
C.
Zygomycete reproduction is mostly asexual, and an erect stalk is formed in which haploid spores are produced.
D.
Sexual reproduction occurs only during times of stress, and results in the production of a sturdy and resistant zygosporangium.
18.8 Glomeromycetes Are Asexual Plant Symbionts (p. 395; Fig. 18.13)
A.
Glomeromycetes are a monophyletic fungal lineage.
B.
Their obligate symbiotic relationship with the roots of many plants appears to be ancient and may have made it possible for terrestrial plants to evolve.
C.
The associations of fungi with plant roots are called mycorrhizae, and there are two principal types of mycorrhizae. In arbuscular mycorrhizae, the fungal hyphae penetrate the outer cells of the plant root and extend out into the surrounding soil. In ectomycorrhizae, the hyphae surround but do not penetrate the cell walls of the roots.
18.9 Basidiomycetes Are the Mushroom Fungi (p. 396; Fig. 18.14)
A.
Phylum Basidiomycota includes the familiar mushrooms, toadstools, and shelf-shaped fungi among its 22,000 species.
B.
Basidiomycetes typically reproduce sexually.
C.
When two hyphae fuse, the result is a dikaryotic hypha that includes only two nuclei within each cell, rather than several nuclei per cell as is seen in the ascomycetes.
D.
The dikaryotic hyphae go on to form a dikaryotic mycelium, and eventually a complex structure made of dikaryotic hyphae called a basidiocarp, or mushroom.
E.
Sexual reproduction occurs in a basidium, a club-shaped structure, when the two nuclei of dikaryotic cells fuse to form a zygote.
F.
Meiosis occurs in each basidium, forming haploid spores, which can then germinate to form monokaryotic hyphae.
18.10 Ascomycetes Are the Most Diverse Fungi (p. 397; Fig.18.15)
A.
The phylum Ascomycota contains about 32,000 species, including the yeasts, pathogens such as Dutch elm disease and chestnut blight, and edible morels and truffles.
B.
Reproduction is mostly asexual among this group, and hyphae have incomplete septa.
C.
Sometimes a complete septum walls off a cell at the end of a hypha, and the cell develops into a structure producing multinucleate, haploid asexual spores, called conidia.
D.
Sexual reproduction occurs rarely, with the production of an ascus in which two different strains of hyphae fuse to form a zygote.
(p. 398)
18.11 Ecological Roles of Fungi (p. 398; Figs. 18.16, 18.17, 18.18, 18.19)
A. Decomposers and Disease Agents
1.
Fungi, together with bacteria, are the principal decomposers in the biosphere.
2.
Fungi also sometimes attack plant and animal cells and cause diseases in both plants and animals.
3.
Fungi are the most harmful pests of living plants as well as food products.
B. Commercial Uses
1.
Many fungi are used commercially, such as in the production of bread, beer, wine, and cheese, in the manufacture of organic chemicals, and in the production of antibiotics, such as penicillin.

2.
At least 3 species of fungi are capable of removing toxic substances in the environment.
C. Edible and Poisonous Fungi
1.
Many types of fungi are edible, including portobello, chanterelle, and shiitake mushrooms.
2.
Many mushrooms contain toxins and are poisonous when eaten.
D. Mycorrhizae
1.
The roots of about 80% of plants are involved in symbiotic associations with fungi called mycorrhizae.
2.
The fungus increases the plant’s ability to absorb nutrients, and the plant, through photosynthetic activity, makes organic material available to the fungus.
3.
Two types of mycorrhizae exist, endomycorrhizae and ectomycorrhizae. a.
In endomycorrhizae, fungal hyphae penetrate the root cells. b.
In ectomycorrhizae, fungal hyphae grown between the cells of roots.
4.
Ectomycorrhizae are especially important in commercially important forest trees, while endomycorrhizae are typical of more primitive plants.
E. Lichens
1.
Lichens are a type of association in which a fungus and a photosynthetic organism
(cyanobacterium or green alga) are in intimate contact and derive benefit from each other.
2.
The photosynthesizers contribute organic compounds that are the products of photosynthesis, while the fungus transmits biochemical signals that direct the cyanobacteria or green algae.
3.
Lichens can inhabit some of the harshest habitats because of their unique relationship, but they are not at all tolerant of air pollutants and have been driven out of many major cities and recreational areas.
 complex multicellular organisms (p. 388) These organisms show coordination between cells, unlike the aggregate or colonial forms seen in the algae.
 mycologist (p. 388)
 cell specialization (p. 388) This is the result of the turning on or off of specific genes within different cells.
 intercellular coordination (p. 388) Cells adjust their activities in response to the activities of other cells.
 development (p. 388)
 hyphae (p. 389) Hyphae are slender fungal filaments with incomplete septa between cells.
 mycelium (p. 389) A mycelium is a mass of fungal hyphae.
 heterokaryon (p. 390) This is an unusual concept, based on comparisons to animals and plants, but fungi can have hyphae with nuclei derived from two genetically distinct individuals.
 dikaryotic (p.390)
 spores (p. 390)
 external digestion (p.390)
 chytridiomycetes (p. 393)
 zygomycetes (p. 394)
 mycorrhizae (p. 395) About 80% of all plants have these associations between fungi and the plant roots.
 basidiomycetes (p. 396)
 ascomycetes (p. 397)
 ascus (p. 397)
 lichen (p. 399) Lichens are symbiotic relationships between fungi and either green algae or cyanobacteria.

1.
Different Forms of Fungi.
Bring into the classroom a variety of specimens of fungi. You will find that most students are aware of certain kinds of fungi, such as the mushrooms sold in the grocery store, but are unfamiliar with the wide variety of shapes and forms found in this interesting and diverse group.
Include such specimens as: Rhizopus stolonifer, the common black bread mold that is also a zygomycete; Saccharomyces cerevisiae, baker's yeast, an ascomycete; and Coprinus lagopus, the inkycap mushroom that is a basidiomycete. If you do not have access to a collection of fungi, many biological supply houses (i.e., Carolina Biological Supply or Ward's Biology, as listed in the appendix) have specimens for sale at a reasonable cost. Many students have never seen, or perhaps have never noticed, lichens, especially if they are from cities where air pollution has stopped lichen growth. Be sure to include the three growth forms of lichens in your demonstration.
2.
Commercial Uses of Fungi. Conduct a student taste test using a test panel and several different types of cheese. Cheese may have been developed as long ago as 8,000 years. Although the enzyme rennin or a
''starter culture'' is used to produce curds in cheese, for some cheeses, fungal spores are added during processing to impart a particular flavor and aroma. Penicillium roqueforti spores are added to curds to make blue cheese and Roquefort. Have students try samples of these two types of cheese, perhaps comparing major brands for taste. Another type of cheese, Camembert, is produced by adding spores of Penicillium camemberti.
Limburger cheese, known for its unusual aroma, is soaked in brine that helps specific fungi and bacteria develop to add flavor to the cheese. Add fresh bread, with the aroma of yeast, to the taste test. To make bread rise, yeast ( Saccharomyces cerevisiae ), is added to the batter.
Yeast produces carbon dioxide during its fermentation, and bubbles are added to the bread batter, increasing the volume of the batter. Yeasts are also used to make wines, beers, and ales, and a number of different mushrooms are eaten directly.
3.
Human Diseases Caused by Fungi. Many of us have experienced diseases caused by fungi, but may not be aware that a member of this diverse group was the culprit. Share information with your students such as the following about a number of diseases caused by fungi. Since fungi are primarily terrestrial, many have become pathogenic and infect animals and plants. Many of the major plant diseases are caused by fungi. In humans, one of the most common diseases caused by fungi is ringworm, which may be caused by one of several types of fungi. A person can have ringworm of the beard (tinea barbae), ringworm of the body (tinea corporis), ringworm of the scalp (tinea capitis), ringworm of the feet (tinea pedis), ringworm of the groin (tinea cruris), ringworm of the hands (tinea manuum), or ringworm of the nails (tinea unguium). Some fungal diseases are opportunistic—that is, they occur more frequently in an immune-compromised host. Often these diseases occur during or after a prolonged course of antibiotic treatment that has killed off the body's natural microflora. There are several opportunistic fungal diseases, but the one with which we are most familiar is candidiasis. This fungus, Candida albicans, is present on our bodies or within our respiratory tracts all the time, but is kept in check by the presence of bacteria. When skin or mucous membranes are overly moist and air does not circulate around them adequately, candidiasis can result. Examples include vaginitis, diaper rash, or oral candidiasis, known as thrush. Thrush occurs in newborns whose mothers had high numbers of vaginal fungal hyphae during the birth process. Candida albicans can also be transmitted from the female to the male during intercourse, which can trigger the development of balanitis, or inflammation of the folds of the penis.
4.
Aflatoxins . A number of fungal-produced toxins are highly poisonous to any consuming organism, and the aflatoxins are among the most deadly. The fungus Aspergillus flavus produces these compounds when growing on peanuts, grains, or nut products. These toxins act at the level of DNA, producing mutations, and are highly carcinogenic. Many animals have become ill or died from eating “moldy” grains. Indeed, people in underdeveloped countries have greater incidences of cancer because the standards for aflatoxin-tainted grains and nuts are not as stringent as they are in the United States.

1.
Discuss whether external digestion as seen in the fungi is a primitive or an advanced trait.
2.
Of what advantage would it be to fungi to have cell walls made up of chitin rather than cellulose?
3.
Explain how lichens can be used as indicators of the presence of air pollution.