1. Fungi are osmiotrophs, which absorb nutrients through their cell membranes.

2. They grow as saprobes or saprophytes on decaying, dead organisms or as parasites on living organisms.

3. All fungi have cell walls made largely of chitin.

4. Fungi demonstrate no trace of flagella at any stage in their life cycle.

5. Fungi make use of the a-aminoadipic acid (AAA) pathway for lysine synthesis.

1. Basidiomycota

2. Ascomycota

3. Zygomycota

1. The hyphae of some fungi are coenocytic, having many nuclei with little or no division of the cytoplasm into individual cells.

2. In other fungi, the hyphae are divided by crosswalls and are actually multicellular.

3. Hyphae have walls of chitin, a tough polysaccharide that also forms the arthropod exoskeleton.

4. Hyphae make intimate contact with their sources of nourishment in soil, water, or the bodies of other organisms where they insinuate themselves.

5. Fungi grow aerobically by respiration, although many yeasts are facultative anaerobes.

1. At some time in their life cycle, all fungi form spores.

2. Spores are single-celled reproductive structures, usually one that can grow (asexually) into the next stage in the life cycle.

3. Mitospores (always haploid) are vehicles for spreading and proliferating.

4. Meispores are haploid cells produced when a zygote nucleus undergoes meiosis.

1. Mushrooms are really fruiting bodies, which are spore-producing reproductive structures that arise from a fine mycelium buried in the substratum.

2. A mycelium begins with a single basidiospore, which is the fungal spore characteristic of the basidiomycetes.

1. Little club-shaped structures called basidia develop on the surfaces of these gills or pores.

2. In each basidium, two haploid nuclei fuse, and the resulting diploid nucleus immediately undergoes meiosis to make four haploid cells that develop into basidiospores.

3. Of the four haploid basidiospores, two are of the plus type (+) and two are of the minus type (-).

4. Basidiospores are external and drop off as they mature (Figure 31.5).

1. Some basidiomycetes have complex genetic systems that determine mating type and prevent inbreeding; only certain types are able to mate with each other.

2. When mycelia of opposite types (plus or minus) meet, one cell from each mycelium unites and they grow into a dicaryotic mycelium containing both types of haploid nuclei within each cell.

3. This dicaryotic secondary mycelium eventually produces mushrooms.

1. In dicaryotic mycelia, the formation of a clamp connection at each division ensures that each cell will contain one nucleus of each type (Figure 31.6).

2. These connections are made with nuclear movements like those of secondary pit formation in the red algae and like another kind of nuclear movement in ascomycetes.

1. Fungus called rusts and smuts are among the worst enemies of domestic crops.

2. Smuts get their name from the black, smutty patches of spores they form on infected plants.

3. A careful comparison of the rust life cycle with a red algal life cycle shows the close similarity between them.

1. The simplest ascomycetes are the yeasts, which reproduce asexually by either transverse fission or by budding.

2. Yeasts also can reproduce sexually by means of spores.

3. The spores, once mature, break out of the ascus and grow vegetatively.

4. Yeasts are very simple fungi that have evolved into a simple form from a more complex ancestor.

1. Neurospora has hyphae that grow into visible fluffy, red mycelia.

2. In Neurospora, sexual reproduction only occurs between hyphae of opposite mating types, but each hypha generally produces both male and female gametangia, the structures that bear gametes or nuclei that function as gametes.

3. The female gametangium, or ascogonium, is larger and often bears a narrow trichogyne (like red algal cells).

4. The male gametangium, or antheridium, is smaller than the ascogonium.

5. Fusion of male and female gametangia creates a dicaryotic cell that grows into an ascogenous hypha, from which fruiting bodies grow.

1. Morels, which are generally counted among the most delicious mushrooms available, bear their asci in the recesses of their spongy heads.

2. Truffles, which grow underground, are also famous delicacies.

1. A victim of ergotism suffers fever, convulsions, and psychotic delusions like those experienced by LSD users.

2. Since the drug causes muscle contraction and constricts blood vessels, the extremities may lose their circulation, become blackened with gangrene, and drop off.

1. Deuteromycetes include some notorious pathogens that cause infections of the skin, scalp, nails, and mucous membranes.

2. Candida albicans, a common pathogen of the mouth, vagina, and uterine cervix, is a typical opportunistic fungus that can cause illness if given the opportunity to overpopulate a region.

3. Certain strains of Penicillium are used to make the antibiotic penicillin while other types are used to produce cheeses such as Roquefort and Camembert.

4. Aspergillus is grown industrially to produce citric acid and gluconic acid, which are used in many foods.

1. Aspergillus fumigatus is an imperfect fungi that causes respiratory infections in humans.

2. Ceratocystis ulmi is a plant parasite that is the cause of Dutch elm disease that killed millions of trees earlier in the century.

1. Some of these organisms can grow at or just below freezing and can therefore appear on stored frozen foods.

2. The life cycle of Rhizopus is typical of zygomycetes (Figure 31.10).

3. Rhizopus grows asexually through aerial hyphae that spread over a surface.

4. When a Rhizopus hypha touches the substratum, it sends out a cluster of rootlike rhizoids and another cluster of hyphae that grow into sporangiophores, reproductive structures that bear haploid mitospores at their tips. When the spores fall to the surface, they germinate into new hyphae.

1. Hyphae of opposite types mutually induce each other to form gametangia, which grow together.

2. The gametangia form a zygosporangium in which many + and - nuclei fuse by pairs to form zygotes which go through meiosis.

3. The zygote develops a heavy, thorny wall and eventually breaks open as haploid hyphae grow out of it (Figure 31.11).

1. Normal soybean protein contains an inhibitor of trypsin, one of the principal proteases of the intestine, so it is largely indigestible to humans.

2. If soybean protein is mixed with Rhizopus oligosporus, the fungus destroys the inhibitor and makes the protein more digestible and nutritious.

1. The best-known mutualism is lichen symbiosis, in which a fungus and an alga associate so intimately that they create a distinctive structure that neither partner shows by itself (Figure 31.12).

2. The minority algae can grow amid the moist fungus body and photosynthesize, providing organic nutrients for both partners, while the fungus provides minerals and protection from drying and harsh light.

1. Trees living in a forest have roots that are intertwined with roots of other plants, causing competition for water and nutrients.

2. Tree roots are commonly entwined with a rich mycelium that grows deep into the root tissue (Figure 31.13); the mycelium, being much finer than the roots, creates an enormous surface that absorbs nutrients from the soil and carries them into the plant.

1. Orchid seeds are unable to contain food stores, as most seeds do.

2. In 1904, Nöel Bernard found that orchid seeds will germinate in the presence of certain fungi, and this method has been used ever since.

3. The fungus provides an environment rich in carbohydrates and vitamins to nurture the young plant until it can grow its own root system and maintain itself; the fungus then forms a mycorrhizal association with the orchid and promotes its growth.

4. Some species of orchids have become so dependent on a fungal association that they do not grow their own roots at all.