Presentation on theme: "Biology: Life on Earth Eighth Edition Biology: Life on Earth Eighth Edition Lecture for Chapter 22 The Diversity of Fungi Lecture for Chapter 22 The Diversity."— Presentation transcript:
These honey mushrooms are part of the visible portion of the largest organism on Earth. A single honey mushroom colony in Oregon covers and area of 8.9 sq. km (2200 acres).
Chapter 22 Outline 22.1 What Are the Key Features of Fungi? p What Are the Major Groups of Fungi? p How Do Fungi Interact with Other Species? p How Do Fungi Affect Humans? p. 433
Section 22.1 Outline 22.1 What Are the Key Features of Fungi? –Fungal Bodies Consist of Slender Threads –Fungi Obtain Their Nutrients from Other Organisms –Fungi Propagate by Spores –Most Fungi Can Reproduce Both Sexually and Asexually
Fungal Body Structure Most fungi are multicellular Cells are surrounded by cell walls composed of chitin, a nitrogen-containing polysaccharide Body of almost all fungi is a mycelium, an interwoven mass of threadlike filaments called hyphae (singular, hypha)
FIGURE 22-1 (part 1) The filamentous body of a fungus (a) A fungal mycelium spreads over decaying vegetation. The mycelium is composed of (b) a tangle of microscopic hyphae, only one cell thick, portrayed in cross section (c) to show their internal organization.
Fungal Body Structure Hyphae of most species are divided into many cells by partitions called septa (singular, septum); each cell possesses one or more nuclei –Pores in the septa allow cytoplasm to stream from one cell to the next Hyphae of some fungi lack septa, consisting of single elongated cells with hundreds or thousands of nuclei The nuclei of most species are haploid
FIGURE 22-1 (part 2) The filamentous body of a fungus The mycelium is composed of (b) a tangle of microscopic hyphae, only one cell thick, portrayed in cross section (c) to show their internal organization.
Nutrition and Fungal Lifestyles All are heterotrophic Secrete enzymes outside their bodies and absorb the digested nutrients Have diverse lifestyles –Fungal decomposers (saprobes) feed on dead organic material and wastes –Fungal parasites absorb nutrients from cells of living hosts and may cause disease –Some symbiotic fungi live in mutually beneficial relationships with other organisms –Fungal predators consume living organisms
Propagate by Spores Spores are haploid reproductive cells capable of developing into an adult fungus –Usually produced in large numbers –Dispersed by animals or air currents Both asexual and sexual reproduction involve the production of spores within fruiting bodies
FIGURE 22-2 Some fungi can eject spores A ripe earthstar mushroom, struck by a drop of water, releases a cloud of spores from the fruiting body that will be dispersed by air currents.
Asexual Reproduction Typically occurs under stable conditions Can occur either by: –Fragmentation of the mycelium –Asexual spore formation Haploid mycelium produces haploid asexual spores by mitosis Spores germinate and develop into a new mycelium by mitosis Results in the rapid production of genetically identical clones
Sexual Reproduction Typically occurs under conditions of environmental change or stress –Neighboring haploid mycelia of different, but compatible mating types come into contact with each other –The two different hyphae fuse so that the nuclei share a common cell –The different haploid nuclei fuse to form a diploid zygote –Zygote undergoes meiosis to form haploid sexual spores
Sexual Reproduction Spores germinate and develop into a new mycelium by mitosis Results in the production of genetically diverse fungal bodies
Section 22.2 Outline 22.2 What Are the Major Groups of Fungi? –Chytrids Produce Swimming Spores –Zygomycetes Can Reproduce by Forming Diploid Spores –Ascomycetes Form Spores in a Saclike Case –Basidiomycetes Produce Club-Shaped Reproductive Structures –Some Fungi Form Symbiotic Relationships
Classification of Fungi Fungi have been assigned to four phyla based upon the way they produce sexual spores –Chytridiomycota (chytrids) –Zygomycota (zygote fungi) –Ascomycota (sac fungi) –Basidiomycota (club fungi)
FIGURE 22-3 Evolutionary tree of the major groups of fungi
Table 22-1 The Phyla of Fungi
The Chytrids –Most are aquatic –Reproduce both asexually and sexually –Form flagellated spores that require water for dispersal –Figure 22-4, p. 426, illustrates the chytrid fungus Allomyces in the midst of sexual reproduction
FIGURE 22-4 Chytrid filaments These filaments of the chytrid fungus Allomyces are in the midst of sexual reproduction. The orange structures visible on many of the filaments will release male gametes; the clear structures will release female gametes. Chytrid gametes are flagellated, and these swimming reproductive structures aid dispersal of members of this mostly aquatic phylum
The Chytrids Most feed on dead aquatic material Some species are parasites of plants and animals –One chytrid species is a frog pathogen believed to be a major cause of the current worldwide die-off of frogs According to evolutionists, primitive chytrids are believed to have given rise to the other groups of modern fungi
Zygomycetes Most live in soil or on decaying plant or animal material Reproduce both asexually and sexually –Sexual spores are thick-walled zygospores During asexual reproduction: –Haploid spores are produced via mitosis in black spore cases called sporangia –Spores disperse and germinate to form new haploid hyphae Figure 20-5, p. 427, depicts the asexual reproduction in Rhizopus, black bread mold
FIGURE 22-5 The life cycle of a zygomycete
Ascomycetes Live in a variety of marine, freshwater, and terrestrial habitats Each fruiting body contains numerous saclike cases called asci (singular, ascus) Reproduce both asexually and sexually –Sexual spores form in saclike asci
FIGURE 22-7a Diverse ascomycetes The cup-shaped fruiting body of the scarlet cup fungus (top) The morel (bottom), an edible delicacy. (Consult an expert before sampling any wild fungus – some are deadly!)
FIGURE 22-6 The life cycle of a typical ascomycete
Ascomycetes Better known examples include –Most of the food-spoiling molds –Morels and truffles (edible delicacies) –Penicillium, the mold that produces penicillin (the first antibiotic) –Yeasts (single-celled fungi)
Basidiomycetes Live in a variety of marine, freshwater, and terrestrial habitats Each fruiting body contains numerous club-shaped structures called basidia (singular, basidium) Usually reproduce sexually –Sexual spores form in club-shaped basidia –Figure 22-9, p. 429, depicts an overview of sexual reproduction in a basidiomycetes
FIGURE 22-9a Diverse basidiomycetes (a) The giant puffball Lycopedon giganteum may produce up to 5 trillion spores. FIGURE 22-9b Diverse basidiomycetes (b) Shelf fungi, some the size of dessert plates, are conspicuous on trees.
FIGURE 22-9c Diverse basidiomycetes (c) The spores of stinkhorns are carried on the outside of a slimy cap that smells terrible to humans, but appeals to flies. The flies lay their eggs on the stinkhorn, and inadvertently disperse the spores that stick to their bodies.
Basidiomycetes Better known examples include –Mushrooms (some are edible, others are poisonous) –Puffballs –Shelf fungi (decomposers of wood) –Stinkhorns –Rusts and smuts (plant parasites) –Yeasts
Fairy Rings A fairy ring is a circular pattern of mushroom growth Fairy rings form at the leading edge of an expanding underground fungal mycelium –The wider the diameter of the ring, the older the mycelium –Some fairy rings are estimated to be 700 years old
FIGURE A mushroom fairy ring Mushrooms emerge in a fairy ring from an underground fungal mycelium, growing outward from a central point where a single spore germinated, perhaps centuries ago.
Section 22.3 Outline 22.3 How Do Fungi Interact with Other Species? –Lichens Are Formed by Fungi That Live with Photosynthetic Algae or Bacteria –Mycorrhizae Are Fungi Associated with Plant Roots –Endophytes Are Fungi That Live Inside Plant Stems and Leaves –Some Fungi Are Important Recyclers
Symbiotic Relationships A symbiosis is a close interaction between organisms of different species over an extended period of time The fungal member of a symbiotic relationship may be harmful (a parasite of plants or animals) or beneficial (lichens and mycorrhizae)
Lichens Lichens are symbiotic associations between fungi (usually an ascomycete) and algae or cyanobacteria –Fungus provides photosynthetic partner with shelter and protection –Photosynthetic partner provides fungus with food (sugar)
FIG The lichen: A symbiotic partnership Most lichens have a layered structure bounded on the top and bottom by an outer layer formed from fungal hyphae. The fungal hyphae emerge from the lower layer, forming attachments that anchor the lichen to a surface, such as a rock or a tree. An algal layer in which the alga and fungus grow in close association lies beneath the upper layer of hyphae.
Lichens Grow on a wide variety of materials (soils, tree trunks and branches, rocks, fences, roofs, and walls) Are able to survive environmental extremes (newly formed volcanic islands, deserts) Are very diverse in form
FIG 22-12a Diverse lichens (a) A colorful encrusting lichen, growing on dry rock, illustrates the tough independence of this symbiotic combination of fungus and algae. (b) A leafy lichen grows from a dead tree branch.
Mycorrhizae Mycorrhizae (singular, mycorrhiza) are symbiotic associations between fungi and plant roots –Fungus provides plant with water, minerals, and organic nutrients it absorbs from the soil –Plant provides fungus with food (sugar) 80% of plants with roots have mycorrhizae Relationship may have helped plants colonize land
FIGURE Mycorrhizae enhance plant growth Hyphae of mycorrhizae entwining about the root of an aspen tree. Plants grow significantly better in a symbiotic association with these fungi, which help make nutrients and water available to the roots.
Endophytes Endophytes are fungi that live inside the above-ground tissues of plants Some are parasites that cause plant diseases Some are beneficial to host plants –Some ascomycete species live inside grasses and produce substances that are distasteful or toxic to insects and grazing mammals, protecting the grasses from predation
Recyclers Fungi are Earth’s undertakers, feeding on the dead of all kingdoms Fungal saprophytes (feeding on dead organisms) release extracellular substances that digest the tissues of the dead and liberate carbon, nitrogen, phosphorus compounds, and minerals that can be reused by plants
Section 22.4 Outline 22.4 How Do Fungi Affect Humans? –Fungi Attack Plants That Are Important to People –Fungi Cause Human Diseases –Fungi Can Produce Toxins –Many Antibiotics Are Derived from Fungi –Fungi Make Important Contributions to Gastronomy –Fungal Ingenuity
Fungi Attack Plants Fungal parasites cause the majority of plant diseases –Ascomycete parasites cause Dutch elm disease and Chestnut blight –Rusts and smuts are basidiomycete parasites that cause considerable damage to grain crops
FIGURE Corn smut This basidiomycete pathogen destroys millions of dollars' worth of corn each year. Even a pest like corn smut has its admirers, though. In Mexico this fungus is known as huitlacoche and is considered to be a great delicacy.
Fungi Attack Plants Fungi can destroy plant material that has been harvested for human use –Cause wooden structures to rot –Damage cotton and wool fabrics
Fungi Attack Plants Some fungi benefit agriculture –Used to control insect pests such as rice weevils, tent caterpillars, aphids, citrus mites, and grasshoppers Fungi identified that attack mosquitoes that transmit malaria
FIGURE 22-15a Helpful fungal parasites Fungal pathogens can be helpful to humans. For example, fungi such as (a) the Cordyceps species that has killed this grasshopper are used by farmers to control insect pests.
FIGURE 22-15b Helpful fungal parasites (b) Some fungi might one day be used to help protect humans from disease. A malaria-carrying mosquito infected by Beauveria species is transformed from a healthy animal (top) to a fungus-encrusted corpse in less than two weeks.
Fungi Cause Human Diseases Athlete’s foot, jock itch, and ringworm are caused by fungi that attack the skin Valley fever and histoplasmosis are caused by fungi that attack the lungs –Infection occurs when victim inhales spores
Fungi Cause Human Diseases Most vaginal infections are caused by the yeast Candida albicans
FIGURE The unusual yeast Yeasts are unusual, normally non-filamentous ascomycetes that reproduce most commonly by budding. The yeast shown here is Candida, a common cause of vaginal infections.
Fungi Produce Toxins Molds of the genus Aspergillus produce aflatoxins, highly toxic, carcinogenic compounds –Infect foods such as peanuts
Fungi Produce Toxins Claviceps purpurea (an ascomycete) produces several toxins –Infects rye plants and causes ergot disease –Symptoms of ergot poisoning include vasoconstriction of blood vessels, vomiting, convulsive twitching, hallucinations, and death
Fungi Produce Antibiotics Penicillin –First antibiotic to be discovered –Used to combat bacterial diseases
FIGURE Penicillium Penicillium growing on an orange. Reproductive structures, which coat the fruit's surface, are visible, while hyphae beneath draw nourishment from inside. The antibiotic penicillin was first isolated from this fungus.
Fungi Produce Other Drugs Cyclosporin –Used to suppress the immune response during organ transplants
Fungi Contribute to Gastronomy Certain ascomycete molds impart flavor to some of the world’s most famous cheeses –Roquefort –Camembert –Stilton –Gorgonzola
Fungi Contribute to Gastronomy Yeasts are used in the production of wine, beer, and bread Wine is produced when yeasts ferment fruit sugars; ethyl alcohol is retained, while CO 2 is released
Fungi Contribute to Gastronomy Beer is derived when yeasts ferment sugars in germinating grains (usually barley); ethyl alcohol and CO 2 are retained Bread rises when yeasts ferment sugar that has been added to bread dough; both ethyl alcohol and CO 2 escape during baking
Fungi Contribute to Gastronomy Some fungi are consumed directly –Mushrooms (a basidiomycete) –Morels (an ascomycete) –Truffles (an ascomycete)
FIGURE The truffle Truffles, rare ascomycetes (each about the size of a small apple), are a gastronomic delicacy.
Fungal Ingenuity The truffle has evolved an effective adaptation for dispersal of its spores –Releases an odor which causes pigs and other animals to dig it up, scattering spores to the winds The zygomycete Pilobolus has evolved bulb tops that blast off, spreading spores
FIGURE An explosive zygomycete The delicate, translucent reproductive structures of the zygomycete Pilobolus literally blow their tops when ripe, dispersing the black caps with their payload of spores.
Fungal Ingenuity Arthrobotrys cleverly traps and “strangles” microscopic roundworms called nematodes to obtain nutrients
FIGURE Nemesis of nematodes Arthrobotrys, the nematode (roundworm) strangler, traps its prey in a noose-like modified hypha that swells when the inside of the loop is contacted.