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Chapter 31 Fungi.

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Presentation on theme: "Chapter 31 Fungi."— Presentation transcript:

1 Chapter 31 Fungi

2 Overview: Mighty Mushrooms Fungi Are diverse and widespread
Are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients Figure 31.1

3 Concept 31.1: Fungi are heterotrophs that feed by absorption
Despite their diversity Fungi share some key traits

4 Nutrition and Fungal Lifestyles
Fungi are heterotrophs But do not ingest their food Fungi secrete into their surroundings exoenzymes that break down complex molecules And then absorb the remaining smaller compounds

5 Fungi exhibit diverse lifestyles
Decomposers Parasites Mutualistic symbionts

6 The morphology of multicellular fungi
Body Structure The morphology of multicellular fungi Enhances their ability to absorb nutrients from their surroundings Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae. Reproductive structure. The mushroom produces tiny cells called spores. Spore-producing structures 20 m Mycelium Figure 31.2

7 Fungi consist of Most fungi
Mycelia, networks of branched hyphae adapted for absorption Most fungi Have cell walls made of chitin

8 Some fungi Coenocytic fungi
Have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of materials Coenocytic fungi Lack septa Cell wall Cell wall Nuclei Pore Septum Nuclei Figure 31.3a, b (a) Septate hypha (b) Coenocytic hypha

9 (a) Hyphae adapted for trapping and killing prey
Some unique fungi Have specialized hyphae that allow them to penetrate the tissues of their host Nematode Hyphae 25 m (a) Hyphae adapted for trapping and killing prey Fungal hypha Plant cell wall Plant cell Plant cell plasma membrane (b) Haustoria Haustorium Figure 31.4a, b

10 Mycorrhizae Are mutually beneficial relationships between fungi and plant roots

11 Fungi propagate themselves
Concept 31.2: Fungi produce spores through sexual or asexual life cycles Fungi propagate themselves By producing vast numbers of spores, either sexually or asexually

12 The generalized life cycle of fungi
Key Haploid (n) Heterokaryotic (unfused nuclei from different parents) Diploid (2n) PLASMOGAMY (fusion of cytoplasm) stage KARYOGAMY (fusion of nuclei) SEXUAL REPRODUCTION Spore-producing structures Spores ASEXUAL Zygote Mycelium GERMINATION MEIOSIS Figure 31.5

13 The sexual life cycle involves
Sexual Reproduction The sexual life cycle involves Cell fusion, plasmogamy Nuclear fusion, karyogamy An intervening heterokaryotic stage Occurs between plasmogamy and karyogamy in which cells have haploid nuclei from two parents

14 The diploid phase following karyogamy
Is short-lived and undergoes meiosis, producing haploid spores

15 Asexual Reproduction Many fungi can reproduce asexually

16 Many fungi that can reproduce asexually
Grow as mold, sometimes on fruit, bread, and other foods 2.5 m Figure 31.6

17 Other asexual fungi are yeasts
That inhabit moist environments Which produce by simple cell division 10 m Parent cell Bud Figure 31.7

18 Many molds and yeasts have no known sexual stage
Mycologists have traditionally called these deuteromycetes, or imperfect fungi

19 Systematists now recognize Fungi and Animalia as sister kingdoms
Concept 31.3: Fungi descended from an aquatic, single-celled, flagellated protist Systematists now recognize Fungi and Animalia as sister kingdoms Because fungi and animals are more closely related to each other than they are to plants or other eukaryotes

20 Fungi probably evolved
The Origin of Fungi Molecular evidence Supports the hypothesis that fungi and animals diverged from a common ancestor that was unicellular and bore flagella Fungi probably evolved Before the colonization of land by multicellular organisms

21 The oldest undisputed fossils of fungi
Are only about 460 million years old 50 m Figure 31.8 

22 Fungi were among the earliest colonizers of land
The Move to Land Fungi were among the earliest colonizers of land Probably as symbionts with early land plants

23 Concept 31.4: Fungi have radiated into a diverse set of lineages
The phylogeny of fungi Is currently the subject of much research Molecular analysis Has helped clarify the evolutionary relationships between fungal groups, although there are still areas of uncertainty

24 Arbuscular mycorrhizal fungi
The phylogeny of fungi Chytrids Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota Figure 31.9

25 A review of fungal phyla
Table 31.1

26 Fungi classified in the phylum Chytridiomycota, or chytrids
Are found in freshwater and terrestrial habitats Can be saprobic or parasitic

27 Chytrids are unique among fungi
In having flagellated spores, called zoospores 25 m 4 m Hyphae Flagellum Figure 31.10

28 Zygomycetes and other chytrids
Until recently, systematists thought that Fungi lost flagella only once in their history Molecular data Indicate that some “chytrids” are actually more closely related to another fungal group, the zygomycetes Glomeromycetes, ascomycetes, and basidiomycetes Some chytrids Zygomycetes and other chytrids Key Figure 31.11 Common ancestor Loss of flagella

29 Fungi in the phylum Zygomycota, the zygomycetes
Exhibit a considerable diversity of life histories Include fast-growing molds, parasites, and commensal symbionts Are named for their sexually produced zygosporangia

30 The life cycle of Rhizopus stolonifer Is fairly typical of zygomycetes
Mycelia have various mating types (here designated +, with red nuclei, and , with blue nuclei). 1 Neighboring mycelia of different mating types form hyphal extensions called gametangia, each walled off around several haploid nuclei by a septum. 2 Rhizopus growing on bread ASEXUAL REPRODUCTION Mycelium Dispersal and germination MEIOSIS KARYOGAMY PLASMOGAMY Key Haploid (n) Heterokaryotic (n + n) Diploid Sporangium Diploid nuclei Zygosporangium (heterokaryotic) 100 m Young zygosporangium (heterokaryotic) SEXUAL REPRODUCTION Mating type (+) Mating type () Gametangia with haploid nuclei 50 m Sporangia A heterokaryotic zygosporangium forms, containing multiple haploid nuclei from the two parents. 3 The spores germinate and grow into new mycelia. 8 9 Mycelia can also reproduce asexually by forming sporangia that produce genetically identical haploid spores. The sporangium disperses genetically diverse, haploid spores. 7 4 This cell develops a rough, thick-walled coating that can resist dry environments and other harsh conditions for months. 5 When conditions are favourable, karyogamy occurs, followed by meiosis. 6 The zygosporangium then breaks dormancy, germinating into a short sporangium. Figure 31.12

31 Some zygomycetes, such as Pilobolus
Can actually “aim” their sporangia toward conditions associated with good food sources 0.5 mm Figure 31.13

32 Zygosporangia, which are resistant to freezing and drying
Are capable of persisting through unfavorable conditions Can undergo meiosis when conditions improve

33 Microsporidia Microsporidia
Are unicellular parasites of animals and protists Are now classified as zygomycetes 10 m Host cell nucleus Developing microsporidian Spore Figure 31.14

34 Fungi assigned to the phylum Glomeromycota
Glomeromycetes Fungi assigned to the phylum Glomeromycota Were once considered zygomycetes Are now classified in a separate clade

35 All glomeromycetes Form a distinct type of endomycorrhizae called arbuscular mycorrhizae 2.5 m Figure 31.15

36 Fungi in the phylum Ascomycota
Ascomycetes Fungi in the phylum Ascomycota Are found in a variety of marine, freshwater, and terrestrial habitats Are defined by the production of sexual spores in saclike asci, which are usually contained in fruiting bodies called ascocarps

37 Ascomycetes Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels (a) The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus. (b) The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards. (c) Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open. (d) Neurospora crassa feeds as a mold on bread and other food (SEM). 10 m Figure 31.16a–d

38 Ascomycetes reproduce
Asexually by producing enormous numbers of asexual spores called conidia

39 A dikaryotic ascus develops.
The life cycle of Neurospora crassa, an ascomycete Ascomycete mycelia can also reproduce asexually by producing haploid conidia. 7 Dispersal ASEXUAL REPRODUCTION Germination Mycelium Conidiophore Mycelia Asci Eight ascospores Ascocarp Four haploid nuclei MEIOSIS KARYOGAMY PLASMOGAMY SEXUAL REPRODUCTION Diploid nucleus (zygote) Ascogonium Ascus (dikaryotic) Dikaryotic hyphae Mating type () Conidia; mating type () Key Haploid (n) Dikaryotic (n  n) Diploid (2n) Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae. 1 A dikaryotic ascus develops. 2 Karyogamy occurs within the ascus, producing a diploid nucleus. 3 The developing asci are contained in an ascocarp. The ascospores are discharged forcibly from the asci through an opening in the ascocarp. Germinating ascospores give rise to new mycelia. 6 5 Each haploid nucleus divides once by mitosis, yielding eight nuclei. Cell walls develop around the nuclei, forming ascospores (LM). The diploid nucleus divides by meiosis, yielding four haploid nuclei. 4 Figure 31.17

40 Fungi in the phylum Basidiomycota
Basidiomycetes Fungi in the phylum Basidiomycota Include mushrooms and shelf fungi Are defined by a clublike structure called a basidium, a transient diploid stage in the life cycle

41 Basidiomycetes Figure 31.18a–d
(a) Fly agaric (Amanita muscaria), a common species in conifer forests in the northern hemisphere (b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat (c) Shelf fungi, important decomposers of wood (d) Puffballs emitting spores Figure 31.18a–d

42 The life cycle of a basidiomycete
Usually includes a long-lived dikaryotic mycelium, which can erect its fruiting structure, a mushroom, in just a few hours Figure 31.19

43 The life cycle of a mushroom-forming basidiomycete
A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia. 2 Two haploid mycelia of different mating types undergo plasmogamy. 1 PLASMOGAMY Dikaryotic mycelium Basidiocarp (dikaryotic) KARYOGAMY Key MEIOSIS Gills lined with basidia SEXUAL REPRODUCTION Mating type () Mating type () Haploid mycelia Dispersal and germination Basidiospores Basidium with four appendages Basidium containing four haploid nuclei Basidia (dikaryotic) Diploid nuclei Basidiospore 1 m Basidium Haploid (n) Dikaryotic (n  n) Diploid (2n) 3 Environmental cues such as rain or temperature changes induce the dikaryotic mycelium to form compact masses that develop into basidiocarps (mushrooms, in this case). In a suitable environment, the basidiospores germinate and grow into short-lived haploid mycelia. 8 When mature, the basidiospores are ejected, fall from the cap, and are dispersed by the wind. 7 The basidiocarp gills are lined with terminal dikaryotic cells called basidia. 4 Each diploid nucleus yields four haploid nuclei. Each basidium grows four appendages, and one haploid nucleus enters each appendage and develops into a basidiospore (SEM). 6 Karyogamy in the basidia produces diploid nuclei, which then undergo meiosis. 5 Figure 31.20

44 Concept 31.5: Fungi have a powerful impact on ecosystems and human welfare

45 Fungi are well adapted as decomposers of organic material
Performing essential recycling of chemical elements between the living and nonliving world

46 Fungi form symbiotic relationships with
Symbionts Fungi form symbiotic relationships with Plants, algae, and animals

47 Mycorrhizae Mycorrhizae
Are enormously important in natural ecosystems and agriculture Increase plant productivity Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants’ roots. EXPERIMENT The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae. CONCLUSION These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant’s ability to take up phosphate and other needed minerals. Figure 31.21 RESULTS RESULTS

48 Fungus-Animal Symbiosis
Some fungi share their digestive services with animals Helping break down plant material in the guts of cows and other grazing mammals

49 Many species of ants and termites
Take advantage of the digestive power of fungi by raising them in “farms” Figure 31.22

50 Lichens Lichens Are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae (a) A fruticose (shrub-like) lichen (b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichens Figure 31.23a–c

51 The fungal component of a lichen Is most often an ascomycete
Algae or cyanobacteria Occupy an inner layer below the lichen surface Ascocarp of fungus Fungal hyphae Algal layer Soredia Algal cell Fungal hyphae 10 m Figure 31.24

52 (b) Tar spot fungus on maple leaves
Pathogens About 30% of known fungal species Are parasites, mostly on or in plants (a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on rye Figure 31.25a–c

53 Some of the fungi that attack food crops
Are toxic to humans

54 Practical Uses of Fungi
Humans eat many fungi And use others to make cheeses, alcoholic beverages, and bread

55 Antibiotics produced by fungi
Treat bacterial infections Staphylococcus Penicillium Zone of inhibited growth Figure 31.26

56 Genetic research on fungi
Is leading to applications in biotechnology

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