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The Kingdom Fungi These morels are a type of fungus prized by many people for their distinctive flavor Unlike the violets, fungi are not plants and do.

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Presentation on theme: "The Kingdom Fungi These morels are a type of fungus prized by many people for their distinctive flavor Unlike the violets, fungi are not plants and do."— Presentation transcript:

1 The Kingdom Fungi These morels are a type of fungus prized by many people for their distinctive flavor Unlike the violets, fungi are not plants and do not produce their own food

2 The Kingdom Fungi

3 In spring, if you know where to look, you can find one of the most prized of all foods—the common morel— growing wild in woodlands throughout the United States Its ridged cap is often camouflaged by dead leaves that collect in abandoned orchards or underneath old oaks or tulip poplars Some morels grow alone, but others grow in groups They appear suddenly, often overnight, and live for only a few days What are these mysterious organisms? How do they grow so quickly?

4 KINGDOM FUNGI Diverse group of over 65,000 species Most fungi are saprophytic or parasitic, and a few are predatory –Saprophyte: Is an organism that feeds on dead organic matter –Recycling the nutrients –Referred to as decomposers »Without decomposers, nutrients would not be reused and life could not continue on earth –Parasite: Derives its nutrients from a living host organism at the host’s expense Cause many plant and animal diseases –Predatory: Captures prey for food Example: Pleurotus ostreatus capture roundworms

5 What Are Fungi? Like mushrooms and molds, morels are fungi The way in which many fungi grow from the ground once led scientists to classify them as nonphotosynthetic plants But they aren't plants at allBut they aren't plants at all fungi are very different from plantsIn fact, fungi are very different from plants

6 What Are Fungi? Fungi are eukaryotic heterotrophs that have cell walls –The cell walls of fungi are made up of chitin, a complex carbohydrate that is also found in the external skeletons of insects Recall that heterotrophs depend on other organisms for food –Unlike animals, fungi do not ingest their food Instead, they digest food outside of their bodies and then absorb it Many fungi feed by absorbing nutrients from decaying matter in the soilMany fungi feed by absorbing nutrients from decaying matter in the soil Others live as parasites, absorbing nutrients from the bodies of their hosts

7 FUNGAL EVOLUTION Precambrian fossils about 900 million years old Late Carboniferous period, fossils indicate that all modern divisions of fungi had evolved Most are terrestrial –Indicates adaptive radiation shortly after plants and animals colonized the land Like all eukaryotes, arose from prokaryotes –Arose from other heterotrophs –Present theory is that they evolved from red algae

8 Structure and Function of Fungi Except for yeasts, all fungi are multicellular hyphaeMulticellular fungi are composed of thin filaments called hyphae (singular: hypha) Each hypha is only one cell thick In some fungi, cross walls divide the hyphae into cells containing one or two nuclei –In the cross walls, there are tiny openings through which the cytoplasm and nuclei can move Other hyphae lack cross walls and contain many nuclei

9 CHARACTERISTICS Hypha: vegetative filament of the fungus –Types: Septate: –Filaments with internal cross walls (septum) –Individual cells have nuclei Coenocytic: –Filaments without internal cross walls (septum) –Filament contains many nuclei that move through the cytoplasm –Grows at the tip where new membrane material is added by the action of Golgi bodies –A mat of interwoven hyphae is called mycelium –Cell wall composed of chitin (not cellulose) Complex polysaccharide also found in the exoskeleton of insects and other invertebrates Store food as glycogen (like animals) Reproduce asexually (spores)(fragmentation) and sexually (gametes) –Heterokaryotic hypha: genetically different nuclei coexist within a hypha –Homokaryotic hypha: genetically similar nuclei coexist within a hypha

10 STRUCTURE OF FUNGI

11 Structure of Two Types of Hyphae Fungi are eukaryotes that have cell walls made of chitin Most fungi are made up of filaments called hyphae In some fungi, the hyphae are divided by cross walls These cells may contain one or two nuclei In other fungi, the hyphae lack cross walls and contain many nuclei

12 Structure of Two Types of Hyphae

13 HYPHAE TYPES

14 STRUCTURE OF FUNGI

15 Fungus Structure The bodies of multicellular fungi are composed of many hyphae tangled together into a thick mass called a mycelium The mycelium (plural: mycelia) is well suited to absorb food because it permits a large surface area to come in contact with the food source through which it grows

16 Structure of a Multicellular Fungus The body of a mushroom is part of a mycelium formed from many tangled hyphae The major portion of the mycelium grows below ground visible portion of the mycelium is the reproductive structure, or fruiting body, of the mushroomThe visible portion of the mycelium is the reproductive structure, or fruiting body, of the mushroom

17 Structure of a Multicellular Fungus

18 Fungus Structure mushroom is actually the fruiting body of a fungusWhat you recognize as a mushroom is actually the fruiting body of a fungus A fruiting body is a reproductive structure growing from the mycelium in the soil beneath it Clusters of mushrooms are often part of the same mycelium, which means that they are part of the same organism

19 Fairy Rings Some mycelia can live for many years As time goes by, soil nutrients near the center of the mycelium become depleted As a result, new mushrooms sprout only at the edges of the mycelium, producing a ring People once thought fairies dancing in circles during warm nights produced these rings, so they were called “fairy rings” Over many years, fairy rings can become enormous—from 10 to 30 meters in diameter

20 Reproduction in Fungi Most fungi reproduce both asexually and sexually Asexual reproduction takes place when cells or hyphae break off from a fungus and begin to grow on their own Some fungi also produce spores, which can scatter and grow into new organisms –Recall that a spore is a reproductive cell that is capable of growing into a new organism by mitosis alone sporangiaIn some fungi, spores are produced in structures called sporangia (singular: sporangium) Sporangia are found at the tips of specialized hyphae called sporangiophores

21 Reproduction in Fungi Sexual reproduction in fungi usually involves two different mating types they are not called male and femaleBecause gametes of both mating types are about the same size, they are not called male and female Rather, one mating type is called “+” (plus) and the other “−” (minus)Rather, one mating type is called “+” (plus) and the other “−” (minus)

22 Reproduction in Fungi When hyphae of opposite mating types meet, they start the process of sexual reproduction by fusing, bringing plus and minus nuclei together in the same cell After a period of growth and development, these nuclei form a diploid zygote nucleus producing haploid sporesIn most fungi, the diploid zygote then enters meiosis, completing the sexual phase of its life cycle by producing haploid spores these spores are also capable of growing, by repeated rounds of mitosis, into new organismsLike the spores produced asexually, these spores are also capable of growing, by repeated rounds of mitosis, into new organisms

23 How Fungi Spread Fungal spores are found in almost every environment This is why molds seem to spring up in any location that has the right combination of moisture and food Many fungi produce dry, almost weightless spores These spores scatter easily in the wind On a clear day, a few liters of fresh air may contain hundreds of spores from many species of fungi

24 How Fungi Spread If these spores are to germinate, they must land in a favorable environment There must be the proper combination of temperature, moisture, and food so that the spores can grow Even under the best of circumstances, the probability that a spore will produce a mature organism can be less than one in a billion

25 How Fungi Spread Other fungi are specialized to lure animals, which disperse fungal spores over long distances Stinkhorns smell like rotting meat, which attracts flies When they land on the stinkhorn, the flies ingest the sticky, smelly fluid on the surface of the fungus The spore-containing fluid will pass unharmed out of the flies' digestive systems, depositing spores over many kilometers

26 FUNGI CLASSIFICATION Four Divisions: –Based primarily on the structure of hyphae or on the type of reproduction

27 Classification of Fungi The kingdom Fungi has over 100,000 species Fungi are classified according to their structure and method of reproductionFungi are classified according to their structure and method of reproduction The methods by which fungi reproduce are unlike those of any other kingdom The four main groups of fungi are: –Common molds (Zygomycota) –Sac fungi (Ascomycota) –Club fungi (Basidiomycota) –Imperfect fungi (Deuteromycota)

28 CLASSIFICATION OF FUNGI

29 The Common Molds phylum Zygomycota, also called zygomycetesThe familiar molds that grow on meat, cheese, and bread are members of the phylum Zygomycota, also called zygomycetes Zygomycetes have life cycles that include a zygospore A zygospore is a resting spore that contains zygotes formed during the sexual phase of the mold's life cycle The hyphae of zygomycetes generally lack cross walls, although the cells of their reproductive structures do have cross walls

30 DIVISION ZYGOMYCOTA Approximately 600 species Mostly terrestrial organisms Commonly found in soil and dung Coenocytic hyphae Example: Rhizopus Stolonifer –Bread mold –Three different types of hyphae: Rhizoids: –Anchoring hyphae that penetrate the bread –Produce digestive enzymes, and absorb nutrients Stolons: –Hyphae that grow across the surface of the bread Sporangiophores: –Upright hyphae that produce sporangia at their tips which produce spores

31 Structure and Function of Bread Mold Black bread mold, Rhizopus stolonifer, is a familiar zygomycete Expose preservative-free bread to dust, and you can grow the mold Keep the bread warm and moist in a covered jar, and in a few days dark fuzz will appear With a hand lens, you can see delicate hyphae on moldy bread There are two different kinds of hyphae: rhizoids –The rootlike hyphae that penetrate the bread's surface are rhizoids Rhizoids anchor the fungus to the bread, release digestive enzymes, and absorb digested organic material stolons –The stemlike hyphae that run along the surface of the bread are stolons The hyphae that push up into the air are the sporangiophores, which form sporangia at their tips –A single sporangium may contain up to 40,000 spores

32 Life Cycle of Molds The life cycle of black bread mold is shown in the figure gametangia (Its sexual phase begins when hyphae from different mating types fuse to produce gamete-forming structures known as gametangia ( singular: gametangium) –Haploid (N) gametes produced in the gametangia fuse with gametes of the opposite mating type to form diploid (2N) zygotes –These zygotes develop into thick-walled zygospores, which may remain dormant for months When conditions become favorable, the zygospore germinates, then undergoes meiosis, and new haploid spores are released The significance of this sexual process—zygote formation followed by meiosis—is that it produces new combinations of genetic information that may help the organism meet changing environmental conditions

33 ZYGOMYCOTA RHIZOPUS STOLONIFER

34 Life Cycle of a Black Bread Mold Zygomycetes have life cycles that include a zygospore During sexual reproduction in the bread mold Rhizopus stolonifer, hyphae from two different mating types form gametangia The gametangia fuse, and zygotes form within zygospore The zygospore develops a thick wall and can remain dormant for long periods The zygospore eventually germinates, and a sporangium emerges The sporangium reproduces asexually by releasing haploid spores produced by meiosisThe sporangium reproduces asexually by releasing haploid spores produced by meiosis

35 Life Cycle of a Black Bread Mold

36 DIVISION ZYGOMYCOTA ASEXUAL REPRODUCTION Hormonal action causes upright sporangiophores to form –Sporangia form at the tips of sporangiophores producing spores (sporangiospores) that are dispersed by the wind

37 SEXUAL AND ASEXUAL REPRODUCTION OF ZYGOMYCOTA

38 ZYGOMYCOTA LIFE CYCLE

39 DIVISION ZYGOMYCOTA SEXUAL REPRODUCTION Called Conjugation Two filaments line up next to each other Hyphae of two mating strains come close together Each hyphae encloses haploid (1N) nuclei Hormones cause short branches to form on each hypha and grow outward until they touch Septa form near the tip of each branch –Resulting cell is a gametangium (1N) that contains several nuclei –Gametangia fuse; then nuclei fuse in pairs (2N) Each pair contains one nucleus from each mating strain (2N) Zygote contains many diploid (2N) nuclei –Wall surrounding the zygote (2N) thickens forming a protective, temporary structure called a zygospore (2N) »Meiosis occurs when the zygospore germinates forming new hyphae (1N)

40 SEXUAL AND ASEXUAL REPRODUCTION OF ZYGOMYCOTA

41 ZYGOMYCOTA LIFE CYCLE

42 ZYGOMYCOTA SEXUAL REPRODUCTION CONJUGATION

43 ZYGOTE

44 DIVISION ZYGOMYCOTA ASEXUAL/SEXUAL REPRODUCTION Provide adaptive advantages Asexual Reproduction: –During periods when the environment is favorable –Rapid formation of spores ensures the quick spread of the species Sexual Reproduction: –In periods of environmental stress –Ensures genetic recombination before the hyphae die

45 The Sac Fungi Sac fungi, also known as ascomycetes, belong to the phylum Ascomycota The phylum Ascomycota is named for the ascus, a reproductive structure that contains spores There are more than 30,000 species of ascomycetes, making it the largest phylum of the kingdom Fungi Some ascomycetes, such as the cup fungi, are large enough to be visible when they grow above the ground Others, such as yeasts, are microscopic

46 DIVISION ASCOMYCOTA Sac fungi Approximately 30,000 species Largest Division of Fungi Live in a variety of habitats, including freshwater and saltwater Morels, powdery mildews, yeast, and cup fungi

47 ASCOMYCETE EDIBLE MOREL

48 Life Cycle of Sac Fungi The life cycle of an ascomycete usually includes both asexual and sexual reproduction The life cycle of a cup fungus is shown in the figure at right

49 Life Cycle of an Ascomycete The life cycle of ascomycetes includes both asexual and sexual reproduction During asexual reproduction, spores called conidia are formed at the tips of specialized hyphae called conidiophores During sexual reproduction, hyphae of two mating types fuse to form hyphae with two haploid (monoploid) nuclei (N + N) The N + N hyphae then form a fruiting body, which eventually releases ascospores Ascomycetes are named for the ascus, the reproductive structure that contains ascosporesAscomycetes are named for the ascus, the reproductive structure that contains ascospores

50 Life Cycle of an Ascomycete

51 Life Cycle of Sac Fungi In asexual reproduction, tiny spores called conidia (singular: conidium) are formed at the tips of specialized hyphae called conidiophores These spores get their name from the Greek word konis, which means “dust” If a conidium lands in a suitable environment, it grows into a haploid mycelium

52 Life Cycle of Sac Fungi Sexual reproduction occurs when the haploid hyphae of two different mating types (+ and −) grow close together The N + N hyphae then produce a fruiting body in which sexual reproduction continues but the haploid (N) nuclei do not fuseGametangia from the two mating types fuse, but the haploid (N) nuclei do not fuse Instead, this fusion produces hyphae that contain haploid nuclei from each of the mating types (N + N)Instead, this fusion produces hyphae that contain haploid nuclei from each of the mating types (N + N)

53 Life Cycle of Sac Fungi The ascus (plural: asci) forms within the fruiting body Within the ascus, two nuclei of different mating types fuse to form a diploid zygote (2N)Within the ascus, two nuclei of different mating types fuse to form a diploid zygote (2N) –The zygote soon divides by meiosis, producing four haploid cells In most ascomycetes, meiosis is followed by a cycle of mitosis, so that eight cells known as ascospores are produced In a favorable environment, an ascospore can germinate and grow into a haploid mycelium

54 DIVISION ASCOMYCOTA Sexual Reproduction: –Hyphae of the Ascogonium (female gametangium) fuses with the Antheridium (male gametangium) Gametangia fuse, and male nuclei move into the ascogonium Male and female nuclei pair but do not fuse Cell divide forming heterokaryotic hyphae that intertwine forming an ascocarp –Reproductive body of an ascomycete –Sacs called asci form on the surface »Each ascus encloses two nuclei »Nuclei fuse »Diploid nucleus undergoes meiosis producing four haploid nuclei followed by a mitotic division resulting in 8 haploid ascospores »Ascus ruptures releasing ascospores into the air »Ascospores germinate into new hyphae on the ground

55 ASCOMYCOTA Asexual Reproduction: –Produces spores called conidium Conidia form on the ends of specialized branches called conidiophores

56 ASCOMYCETE REPRODUCTION

57 ASCOMYCOTA LIFE CYCLE

58 Yeasts Yeasts are unicellular fungiYeasts are unicellular fungi The yeasts used by humans for baking and brewing are classified as ascomycetes because they form asci with ascospores during the sexual phase of their life cycle

59 Yeasts You might think of yeast as a lifeless, dry powder that is used to make bread Actually, the dry granules contain ascospores, which become active in a moist environment To see this for yourself, add a spoonful of dry yeast to half a cup of warm water that contains some sugar In about 20 minutes, when you examine a drop of this mixture under a microscope, you will be able to see cell division in the rapidly growing yeast cells buddingThe process of asexual reproduction you are observing is called budding

60 Yeasts The common yeasts used for baking and brewing are members of the genus Saccharomyces, which means “sugar fungi” These yeasts are grown in a rich nutrient mixture containing very little oxygen Prior to baking, the nutrient mixture is a mound of thick dough Lacking oxygen, the yeasts within the mixture use the process of alcoholic fermentation to obtain energy –The byproducts of alcoholic fermentation are carbon dioxide and alcohol The carbon dioxide gas makes beverages bubble and bread rise (by producing bubbles within the dough) The alcohol in bread dough evaporates during baking In brewing, alcohol remains in the resulting alcoholic beveragesIn brewing, alcohol remains in the resulting alcoholic beverages

61 DIVISION ASCOMYCOTA –Yeast: unicellular Asexual Reproduction: budding Sexual Reproduction: formation of a zygote by the fusion of two ascospores 600 species –Saccharomyces cerevisiae used in brewing processes Ability to breakdown carbohydrates forming ethyl alcohol and carbon dioxide gas makes yeast useful in industry –Baking and brewing

62 The Club Fungi The phylum Basidiomycota, or club fungi, gets its name from a specialized reproductive structure that resembles a club The spore-bearing structure is called the basidium (plural: basidia) Basidia are found on the gills that grow on the underside of mushroom caps

63 DIVISION BASIDIOMYCOTA Approximately 25,000 species Called club fungi Examples: mushrooms, toadstools, puffballs, rusts, and smuts

64 DIVISION BASIDIOMYCOTA Basidiocarp: mushroom –Reproductive body of a basidiomycete –Formed when underground hyphae grow upward and intertwine –Cap (fruiting body) is attached to a stalk (stem) Underside are radiating rows of gills which contain specialized club-shaped reproductive cells called basidia –In each basidium two nuclei become isolated by a complete septum –Nuclei fuse and form a diploid zygote –Meiosis then results in four nuclei that are pushed into cytoplasmic extensions to form basidiospores –At maturity, the basidiospores are released and germinate into new homokaryotic hyphae –As the homokaryotic hyphae grow, septa form so that each cell contains one nucleus »These homokaryotic, septate hyphae are called the primary mycelium –Primary hyphae grow and fuse with hyphae from another mating strain resulting in the formation of secondary hyphae »Hyphae of these mycelium are heterokaryotic, containing one nucleus from each mating strain in each cell –Secondary mycelium intertwines and forms a basiocarp

65 Life Cycle of Club Fungi Basidiomycetes undergo what is probably the most elaborate life cycle of all the fungi As shown in the figure at right, a basidiospore germinates to produce a haploid primary mycelium, which begins to grow Before long, the mycelia of different mating types fuse to produce a secondary mycelium The cells of the secondary mycelium contain haploid nuclei of each mating type Secondary mycelia may grow in the soil for years, reaching an enormous size A few mycelia have been found to be hundreds of meters across, making them perhaps the largest organisms in the worldA few mycelia have been found to be hundreds of meters across, making them perhaps the largest organisms in the world

66 Life Cycle of a Basidiomycete The club fungi are named after the club shape of their reproductive structure, the basidium The cap of a basidiomycete such as a mushroom is composed of tightly packed hyphae The lower side of the cap is composed of gills—thin blades of tissue lined with basidia that produces basidiospores

67 Life Cycle of a Basidiomycete

68 BASIDIOMYCETE REPRODUCTION

69

70 BASIDIOMYCOTA LIFE CYCLE

71 FRUITING BODY BASIDIOCARP

72

73

74

75

76 PUFFBALL OF BASIDIOMYCETES

77 Life Cycle of Club Fungi When the right combination of moisture and nutrients occurs, spore-producing fruiting bodies push above the ground mushroomsYou would recognize these fruiting bodies as mushrooms Each mushroom begins as a mass of growing hyphae that forms a button, or thick bulge, at the soil's surface

78 Life Cycle of Club Fungi Fruiting bodies expand with astonishing speed, sometimes producing fully developed mushrooms overnight This remarkable growth rate is caused by cell enlargement, not cell divisionThis remarkable growth rate is caused by cell enlargement, not cell division The cells of the hyphae enlarge by rapidly taking in waterThe cells of the hyphae enlarge by rapidly taking in water

79 Life Cycle of Club Fungi When the mushroom cap opens, it exposes hundreds of tiny gills on its underside Each gill is lined with basidia forming clusters of haploid basidiosporesThe two nuclei in each basidium fuse to form a diploid (2N) zygote cell, which then undergoes meiosis, forming clusters of haploid basidiospores –The basidiospores form at the edge of each basidium and, within a few hours, are ready to be scattered Mushrooms are truly amazing reproductive structures—a single mushroom can produce billions of spores, and giant puffballs can produce trillionsMushrooms are truly amazing reproductive structures—a single mushroom can produce billions of spores, and giant puffballs can produce trillions

80 Diversity of Club Fungi In addition to mushrooms, basidiomycetes include shelf fungi, which grow near the surfaces of dead or decaying trees The visible bracketlike structure that forms is a reproductive structure, and it, too, is a prolific producer of spores Puffballs, earthstars, jelly fungi, and plant parasites known as rusts are other examples of basidiomycetes

81 Edible and Inedible Mushrooms Many types of fungi have long been considered delicacies, and several different species of mushrooms are cultivated for food You may have already tasted sliced mushrooms on pizza, feasted on delicious sautéed portobello mushrooms, or eaten shiitake mushrooms When properly cooked and prepared, domestic mushrooms are tasty and nutritious

82 FUNGI IN INDUSTRY

83 Edible and Inedible Mushrooms Wild mushrooms are a different story: Although some are edible, many are poisonous Because many species of poisonous mushrooms look almost identical to edible mushrooms, you should never pick or eat any mushrooms found in the wildBecause many species of poisonous mushrooms look almost identical to edible mushrooms, you should never pick or eat any mushrooms found in the wild mushroom gathering should be left to experts who can positively identify each mushroom they collectInstead, mushroom gathering should be left to experts who can positively identify each mushroom they collect The result of eating a poisonous mushroom can be severe illness, or even death

84 The Imperfect Fungi Fungi are usually classified by the sexual phase of their life cycleFungi are usually classified by the sexual phase of their life cycle –So, what do biologists do when they discover a fungus that does not seem to have a sexual phase? –Until a sexual phase is discovered, scientists place it in the phylum called Deuteromycota, or the imperfect fungi imperfect,The term imperfect, by the way, doesn’t mean that there’s anything wrong with these organisms –It simply means that our understanding of their life cycles may not be perfect The Deuteromycota are fungi that cannot be placed in other phyla because researchers have never been able to observe a sexual phase in their life cycles A majority of the imperfect fungi closely resemble ascomycetes Others are similar to basidiomycetes, and a few resemble the zygomycetes

85 The Imperfect Fungi PenicilliumOne of the best-known genera of the imperfect fungi is Penicillium The species Penicillium notatum is a mold that frequently grows on fruit and is the source of the antibiotic penicillin Like the ascomycetes, Penicillium reproduces asexually by means of conidia, leading many biologists to conclude that Penicillium evolved from an ascomycete that lost the sexual phase of its life cycle

86 DIVISION DEUTEROMYCOTA Sometimes called the imperfect fungi or, Fungi Imperfecti 10,000 species Classification based on type of asexual reproduction No sexual reproductive phase discovered –Placed in this Division until a sexual phase, if it exist, is identified Some forms cause ringworm and athlete’s foot Aspergillus used to ferment soy beans in the production of soy sauce

87 Ecology of Fungi Fungi have been around since life first moved onto land In fact, the oldest known fossils of fungi were formed about 460 million years ago At that time, the largest land plants were small organisms similar to mosses Paleontologists think that fungi helped early plants to obtain nutrients from the ground Their early appearance suggests that fungi may have been essential to plants' successful colonization of the land, one of the key events in the history of life

88 Ecology of Fungi Over time, fungi have become an important part of virtually all ecosystems, adapting to conditions in every corner of Earth Because most fungi live their lives out of our sight, people often overlook them But without fungi, the world would be a very different place

89 All Fungi Are Heterotrophs As heterotrophs, fungi cannot manufacture their own food Instead, they must rely on other organisms for their energy Unlike animals, fungi cannot move to capture food, but their mycelia can grow very rapidly into the tissues and cells of plants and other organisms Many fungi are saprobes, organisms that obtain food from decaying organic matter Others are parasites, which harm other organisms while living directly on or within them Still other fungi are symbionts that live in close and mutually beneficial association with other species

90 All Fungi Are Heterotrophs Although most fungi feed on decaying matter, a few feed by capturing live animals Pleurotus ostreatus is a carnivorous fungus that lives on the sides of trees As roundworms crawl into the fungus to feed, they are exposed to a fungal chemical that makes them become sluggish fungal hyphae penetrate their bodies, trapping them in place and then digesting themAs the worms slow to a stop, fungal hyphae penetrate their bodies, trapping them in place and then digesting them

91 Fungi as Decomposers Fungi play an essential role in maintaining equilibrium in nearly every ecosystem, where they recycle nutrients by breaking down the bodies and wastes of other organisms Many fungi feed by releasing digestive enzymes that break down leaves, fruit, and other organic material into simple molecules These molecules then diffuse into the fungusThese molecules then diffuse into the fungus The mycelia of fungi produce digestive enzymes that speed the breakdown of wastes and dead organisms In so doing, they promote the recycling of nutrients and essential chemicals, helping to maintain ecosystem equilibriumIn so doing, they promote the recycling of nutrients and essential chemicals, helping to maintain ecosystem equilibrium

92 Fungi as Decomposers Imagine a world without decomposers Without decay, the energy-rich compounds that organisms accumulate during their lifetimes would be lost forever Many organisms, especially plants, remove important trace elements and nutrients from the soil If these materials were not returned, the soil would quickly be depleted, and Earth would become lifeless and barrenIf these materials were not returned, the soil would quickly be depleted, and Earth would become lifeless and barren

93 Fungi as Parasites As useful as many fungi are, others can infect both animals and plants, disrupting their internal equilibrium and causing disease Parasitic fungi cause serious plant and animal diseases A few cause diseases in humans

94 Plant Diseases Fungi cause diseases such as corn smut, which destroys corn kernels Mildews, which infect a wide variety of fruits, are also fungi Fungal diseases are responsible for the loss of approximately 15 percent of the crops grown in temperate regions of the world In tropical areas, where high humidity favors fungal growth, the loss of crops is sometimes as high as 50 percentIn tropical areas, where high humidity favors fungal growth, the loss of crops is sometimes as high as 50 percent Fungi are in direct competition with humans for food Unfortunately for us, sometimes fungi win that competition

95 Plant Diseases One fungal disease—wheat rust—affects one of the most important crops grown in North America Rusts are caused by a type of basidiomycete that needs two different plants to complete its life cycle Spores produced by rust in barberry plants are carried by the wind into wheat fields There, the spores germinate and infect wheat plants The patches of rust produce a second type of spore that infects other wheat plants, allowing the disease to spread through the field like wildfire

96 Plant Diseases Later in the growing season, a new variety of spore is produced by the rust These tough black spores easily survive through the winter In spring, they go through a sexual phase and produce spores that infect barberry plants Once on the barberry leaves, the rust produces the spores that infect wheat plants, and the cycle continues Fortunately, once agricultural scientists understood the life cycle of the rust, they were able to slow its spread by destroying barberry plantsFortunately, once agricultural scientists understood the life cycle of the rust, they were able to slow its spread by destroying barberry plants

97 Human Diseases Fungal parasites can also infect humans deuteromyceteOne deuteromycete can infect the areas between the toes, causing the infection known as athlete's foot The fungus forms a mycelium directly within the outer layers of the skinThe fungus forms a mycelium directly within the outer layers of the skin –This produces a red, inflamed sore from which the spores can easily spread from person to person it produces a red scaling sore known as ringworm, which is not a worm at allWhen the same fungus infects other areas, such as the skin of the scalp, it produces a red scaling sore known as ringworm, which is not a worm at all

98 FUNGAL DISEASES

99 Human Diseases The microorganism Candida albicans, a yeast, can disrupt the equilibrium within the human body, causing fungal disease Candida, which grows in moist regions of the body, is usually kept in check by competition from bacteria that grow in the body and by the body's immune system This normal balance can be upset by many factors, including the use of antibiotics, which kill bacteria, or by damage to the immune system When this happens, Candida may produce thrush, a painful mouth infection Yeast infections of the female reproductive tract usually are due to overgrowth of CandidaYeast infections of the female reproductive tract usually are due to overgrowth of Candida

100 FUNGAL DISEASES

101 Other Animal Diseases As problematic as human fungal diseases can be, few fungal diseases are as deadly as the infection by one fungus from the genus Cordyceps This fungus infects grasshoppers in rain forests in Costa Rica Microscopic spores become lodged in the grasshopper, where they germinate and produce enzymes that slowly penetrate the insect's tough external skeleton The spores multiply in the insect's body, digesting all its cells and tissues until the insect dies To complete the process of digestion, hyphae develop, cloaking the decaying exoskeleton in a web of fungal material Reproductive structures, which will produce more spores that will spread the infection, then emerge from the grasshopper's remains, as shown in the photograph

102 Grasshopper Infected by a Fungus This grasshopper is the victim of Cordyceps, a fungus Once the fungus's tiny spore enters the insect's body, it multiplies rapidly and digests body tissues The structures growing out of the grasshopper's body are the fungus's fruiting bodies

103 Grasshopper Infected by a Fungus

104 Symbiotic Relationships Fungi often grow in close association with members of other species in symbiotic relationships Although fungi are parasites in many of these relationships, that is not always the case Some fungi form symbiotic relationships in which both partners benefit Two such mutualistic associations, lichens and mycorrhizae, are essential to many ecosystems

105 Lichens Lichens are not single organisms they are symbiotic associations between a fungus and a photosynthetic organismRather, they are symbiotic associations between a fungus and a photosynthetic organism The fungi in lichens are usually ascomycetes, although a few are basidiomycetes The photosynthetic organism is either a green alga or a cyanobacterium, or both The figure below shows the structure of a lichen

106 Structure of a Lichen Lichens are a mutualistic relationship between a fungus and an alga or a cyanobacterium, or both The protective upper surface of a lichen is composed of fungal hyphae cyanobacteria or algaeBelow this is the layer of cyanobacteria or algae with loosely woven hyphae The third layer consists of loosely packed hyphae bottom layer is a protective surface covered by small projections that attach the lichen to a rock or treeThe bottom layer is a protective surface covered by small projections that attach the lichen to a rock or tree

107 Structure of a Lichen

108 Lichens Lichens are extremely resistant to drought and cold Therefore, they can grow in places where few other organisms can survive—on dry, bare rock in deserts and on the tops of mountains Lichens are able to survive in these harsh environments because of the relationship between the two partner organisms The algae or cyanobacteria carry out photosynthesis, providing the fungus with a source of energy The fungus, in turn, provides the algae or bacteria with water and minerals that it collects and protects the delicate green cells from intense sunlight

109 Lichens Lichens are often the first organisms to enter barren environments, gradually breaking down the rocks on which they grow In this way, lichens help in the early stages of soil formation Lichens are also remarkably sensitive to air pollution, and they are among the first organisms to be affected when air quality deteriorates

110 SYMBIOTIC RELATIONSHIP TOP: MYCORRHIZAE BOTTOM: FOLIOSE LICHEN

111 MUTUALISM Type of symbiosis in which both organisms benefit

112 MYCORRHIZAE Symbiotic association between fungi and plant roots Occurs in about 80% of plants Helps plants absorb water and nutrients, such as phosphorus and potassium, by forming extensive networks of fungal hyphae in the soil increasing the surface area in the soil for absorption Digestive action of the fungal enzymes provides nutrients that can be readily absorbed by the plant Fungi absorbs some of the sugars created by the plant during photosynthesis

113 Mycorrhizae Fungi also form mutualistic relationships with plants Almost half of the tissues of trees are hidden beneath the ground in masses of tangled roots These roots are woven into a partnership with an even larger web of fungal mycelia These associations of plant roots and fungi are mycorrhizae (singular: mycorrhiza)

114 Mycorrhizae Scientists have known about this partnership for years, but recent research shows that it is more common and more important than was previously thought Researchers now estimate that 80 percent of all plant species form mycorrhizae with fungi

115 Mycorrhizae How do plants and fungi benefit from each other? The tiny hyphae of the fungi aid plants in absorbing water and minerals They do this by producing a network that covers the roots of the plants and increases the effective surface area of the root system This allows the roots to absorb more water and minerals from the soil In addition, the fungi release enzymes that free nutrients in the soil The plants, in turn, provide the fungi with the products of photosynthesisThe plants, in turn, provide the fungi with the products of photosynthesis

116 Mycorrhizae The presence of mycorrhizae is essential for the growth of many plants The seeds of some plants, such as orchids, cannot germinate in the absence of mycorrhizal fungi Many trees are unable to survive without fungal symbionts Mycorrhizal associations have even been cited as an adaptation that was critical in the evolution of land plants from more-aquatic ancestors

117 Mycorrhizae Mycorrhizal relationships are often very specialized For example, the Douglas fir forests of the Pacific Northwest are dependent on the presence of a particular species of white truffle In Europe, black truffles are found growing with oak and beech trees The fly agaric grows mostly with birch and pine trees

118 Mycorrhizae Why is this networking relationship so important? The partnership between plant and fungus does not end with a single plant The roots of each plant are plugged into mycorrhizal networks that connect many plants What's more astounding is that these networks appear to connect plants of different species

119 Mycorrhizae A recent experiment showed that carbon atoms from one tree often end up in another nearby tree In an experiment using carbon isotopes to track the movement of carbon, ecologist Suzanne Simard found that mycorrhizal fungi transferred carbon from paper birch trees growing in the sun to Douglas fir trees growing in the shade sun-starved fir trees thrived, basically by being “fed” carbon from the birchesAs a result, the sun-starved fir trees thrived, basically by being “fed” carbon from the birches

120 Mycorrhizae Simard's findings suggest that plants are far from being isolated individuals, as was previously thought Instead, plants—and their associated fungi—may be evolving as part of an ecological partnershipInstead, plants—and their associated fungi—may be evolving as part of an ecological partnership


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