Chapter 31 fungi by johnny elvir

1. Chapter 31 fungibyjohnnyelvir

2. Overview mighty mushrooms • Fungi are a huge and important component of the biosphere. • Their diversity alone is staggering:although 100,000 species have been described, it is estimated that there are actually as many as 1.5 million species of fungi • Fungi breakdown and recycle nutrients. • Almost all plants depend on a symbiotic relationship with fungi that helps their roots absorb minerals from the soil.

3. Two species of fungi decomposing a log

4. Concept 31.1 nutrition and fungal life style • Like animals,fungi are heterotrophs they cannot make their own food as plants and algae can. • But unlike anials,fungi do not ingest their food the digest their food while it is still in the environment by secreting powerful hydrolytic enzymes,calledexoenzymes,into their surrounding. • Exoenzymes breakdown complex molecules to smaller organic compounds that the fungi can absorb into their bodies and use.

5. Concept 31.1 nutrition and fungal life style cont. • Among the fungi are species that live as decomposers (saprobes),parasites,andmutualsticsymbionts. • Saprobic fungi break down and absorb nutrients from nonliving organic material,such as fallen logs,animalcorpses,and the wastes of living organisms. • Parasites fungi are pathogenic,including species that infect human lungs and other species that are responsible for about 80% of plant diseases.

6. Concept 31.1 nutrition and fungal life style cont. • Mutualistic fungi also absorb nutrients from a host organism,but the mutualistic fungi reciprocate with functions beneficial to the host organism,but the mutualistic fungi reciprocate with functions beneficial to the host in some way,such as aiding a plant in the uptake of minerals from the soil.

7. Concept 31.1 body structure • The bodies of these fungi typically form a network of tiny filaments called hyphea. • Hyphea are composed of tubular cell walls surrounding the plasma membrane and cytoplasm of the cells. • Unlike the cellulose walls of plants,fungal cell walls contain chitin a strong but flexible nitrogencontaining polysaccharide that is also found in the external skeletons of insects and other arthropods.

8. Concept 31.1 body structure cont. • Fungal hyphae form an interwoven mass called a mycelium that surrounds and infiltrates the material on which the fungus feeds.

9. Concept 31.1 body structure cont. • In most fungi,thehyphea are divided into cells by crosswalls,orsepta. • Coenocyticfungi,these organisms consist of a continuous cytoplasmic mass contining hundreds or thousands of nuclei. • Some species have specialized hyphea called haustoriathat enable them to penetrate the tissue of their hosts.

10. Concept 31.1 body structure cont. • Mutually beneficial relationships between such fungi and plant roots are called mycrrhizae. • Ectomycorrhizal fungi form sheaths of hyphae over the surface of a root and also grow into the extracellular spaces of the root cortex. • Endomycorrhizal fungi extends their hyphae through the root cell wall and into tubes formed by invagination of the root cell memebrane .

12. Concept 31.2 fungi produce spores through sexual or asexual life cycle • fungi propagate themselves by producing vast numbers of spores,ethier sexually or asexually. • Spores can be carried long distances by wind or water,and if they land in a moist place where there is food, they germinate,producing new mycelia. • Generalizes the many different life cycles that can produce fungal spores.

13. Generalized life cycle of fungi.

14. Concept 31.2 sexual reproduction • The nuclei of fungal hyphae and spores of most species are haploid,except for transient diploid stages that form during sexual life cycle. • Generally,the sexual reproduction in fungi begins when hyphae from two distinct mycelia release sexual signaling molecule called pheromones. • If the mycelia are of different mating types the pheromones from each partner bind to receptor on the surface of the other and the hyphea extends toward the source of the pheromones.

15. Concept 31.2 sexual reproduction cont. • When the hyphea meet they fuse,this “compatibiltytest”contributes to genetic variation by preventing hyphea from fusing with other hyphea from the same mycelium or another genetically identical mycelium. • The union of the cytoplasm of the two parent mycelia is known as plasmogamy. • In many fungi,the haploids nuclei contributed by each parent do not fuse right away. • Instead parts of the mycelia contain coexisting,genetically different nuclei.

16. Concept 31.2 sexual reproduction cont. • Such a mycelium is said to be a hetrokaryon(meaning different nuclei) • In some species,heterokaryotic mycelia become mosaics,with different nuclei restricted to different parts of the network. • In other species,the different nuclei mingle and may even exchange chromosomes and genes in a process similar to crossing over. • In some fungi ,the haploid nuclei pair off two to a cell,one from each parent.

17. Concept 31.2 sexual reproduction cont. • Such a mycelium is said to be dikaroyotic(meaning two nuclei). • As a dikaryotic mycelium grows,the two nuclei in each divide in tandem without fusing. • Hours,days,or even centuries may pass between plasmogamy and the next stage in the sexual cycle,karyogamy. • During karyogamy,the haploid nuclei contribute by the two parent fuse,producing diploid cells.

18. Concept 31.2 sexual reproduction cont. • Zygotes and other transient structure form during karyogamy the only stage in which diploidy exists in most fungi. • The heterokaryotic condition also offer some of the advantages of diploidy in that one haploid genome may be able to compensate for harmful mutation in the other.

19. Chapter 31.2 asexual reproduction • In addition to sexual reproduction ,many fungi can reproduce asexually. • Clones are produced by mitotic production of spores which can be spread by air or water. • Some species only reproduce asexually. • Some fungi that can reproduce asexually grow as mold. • Mold grow rapidly as mycelia and produce spores.

20. Chapter 31.2 asexual reproduction cont. • Many species that can grow as mold can also reproduce sexually if they come in contact with other mating types. • Another asexual fungi is yeast. • Yeast inhabit liquid or moist habitats,including plant sap and animal tissue. • Instead of producing spores,yeast species can also grow as filamentous mycelia,depending on the availabilty of nutrients. • Sometimes yeast can produce sexually.

21. Penicillium a mold commonly encountered as a saprobe on food.

22. Yeatsaccharomycescerevisiae in various stages of budding(SEM).

23. Chapter 31.2 asexual reproduction cont. • Many molds and yeasts have no known sexual stage. • Mycologists,have traditionally called such fungi deuteromycetes(traditional classification for a fungus with no known sexual stage)or imperfect fungi. • Whenever a sexual stage of a so-called deuteromycete is discovered,the species is classified in a particular phylum,depending on the type of sexual structure is formed.

24. Concept 31.3fungi desending from an aquatic single-celled,flagellatedprotist • Fungi and animalia are sister kingdom. • While the majority of fungi lack flagella,thelinages of fungi thought to be the earliest to diverge do have flagella. • Most of the protist that share a close common ancestor with animals and fungi also have flagella. • These three groups of eukaryotes-the fungi,animals,and their protistan relatives-are called opishokonts,members of the cladeopisthokonta.

25. Concept 31.3fungi desending from an aquatic single-celled,flagellatedprotist cont. • Phylogenetic evidence also suggests that the ancestor of fungi was uncellular. • Based on molecular clock analysis,scientists have estimated that the ancestors of animals and fungi diverged into separate linages l.5 billion years ago. • However the oldest undisputed fossils of fungi are only about 460 million years old. • One possible explanation for this discrepancy is that the microscopic ancestors of terrestrial fungi fossilized poorly.

26. Fossil fungal hyphae and spores from the ordovician period (about 460 million years ago;LM).

27. Concept 31.3 the move to land • Much of the fungal diversity we observe today may have had its phylogenetic origin in adaptive radiation when life began to colonize land. • Fossils of the earliest known vascular plants from the late silurian period contain evidence of mycorrhizae,the symbiotic relationship between plants probably existed in this symbiotic relationship from the earliest periods of colonization of land.

28. Concept 31.4 chytride • Fungi classified in the phylum chytridiomycota,calledchytrids,are ubiquitous in lake and soil. • Some are saprobes;other parasitize protists,plants,or animals. • Like other fungi,chytrides have cell walls made of chitin,and they also share certain key enzymes and metabolic pathways with other fungal group.

29. Phylogency of fungi

30. Concept 31.4 chytride cont. • Chytrides are unique among fungi in having flagellated spores,calledzoospores. • Until recently,systematists thought that fungi lost flagella only once in their history,afterchytrids had divergance from other linage. • Molecular data indicate that somechytrides are actually more closly related to another fungal group the zygomycetes,if this is true then flagella were loston more than one occasion during the evolution of fungi.

31. Concept 31.4 zygomycetes • The approximatly 1,000 known species of zygomycetes(fungi in the phylum zygomycota)exhibit a considerable diversity of life histories. • This phylum includes fast growing molds responsible for rotting produce such as peaches,strawberries,and sweet potatos during storage. • Horizontal hyphae spread out over the food,penetrate it and absorb nutrients.

32. Concept 31.4 zygomycetescont. • The hyphae are coenocytic,with septa found only where reproductive cells form. • The parents in a sexual union are mycelia of different mating types that possess different chemical markers,although they may appear identical. • Plasmogamy produces a sturdy structure called a zygosporangium,in which karyogamy and the meiosis occur.

33. Concept 31.4 zygomycetescont. • Zygosporangosporangia are resistant to freezing and dying and are metabolically inactive. • When condition improve,azygosporangium undergoes meiosis,germinates into a sporangium,and releases genetically diverse haploid spores that may colonize a new substrate.

34. Concept 31.4 microsporida • Microsporidia are unicellular parasites of animals and protists. • They are often used in the bilogical control of insect pests. • While microsporidia do not normally infect humans,they do pose a risk to people with AIDS and other immune-compromised conditions.

35. a eukarayotic cell infected by microsporidia. Host cellnucleus Developingmicrosporidian Spore

36. Concept 31.4 glomeromycetes • The glomeromycetes,fungi assigned to the phylum glomeromycota,were formally thought to be zygomycetes. • In spite of their small numbers-only 160 species have been identified to date-the glomeromycets are an ecoligically significant group. • All glomeromycetes form a distinct type of endomycorrhizae called arbuscularmycorrhizae. • The tips of the hyphae that puch into plant root cells branch into tiny treelike structure known as arbusculares.

37. Abusculare mycorrhizae

38. Concept 31.4 ascomycetes • Mycologists have described more than 32,000 of ascomycetes(fungi in the phylum ascomycota)from a variety of marine,freashwater,and terrestrial habitats. • The defining feature of ascomycetes is the production of sexual spores in saclike asci(singular,ascus);thus they are commonly called sac fungi. • Unlike zygomycetes,mostascomycetes bear their sexual stages in fruiting bodies,orascocarps,which rang in size from microscopic to macroscopic.

39. Concept 31.4 ascomycetes cont. • Unlike zygomycetes,mostascomycetes bear their sexual stages in fruiting bodies,orascocarps,which range in size from microscopic to macroscopic. • Ascomycetes vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels. • They include some of the most devastating plant pathogens.

40. Figure 31.16 Morchellaesculenta,etasty morel Tuber melanosporum, a truffle

41. Concept 31.4 ascomycetes cont. • Altough the life cycle of various ascomycete group differ in details of their reproductive structure and processes,there are some common element. • Ascomycetes reproduce asexually by producing enormous number of asexual spores called condia. • Condia are formed inside sporangia,as are the asexual spores of most zygomycetes.

42. Concept 31.4 ascomycetes cont. • Incontrast to the life cycle of zygomycetes,extendeddikaryotic stage of ascomycetes(and also basidiomycetes) provides increased opportunity for genetic recombination.

43. Concept 31.4 basidiomycetes • Approximtely 30,000 fungi,including mushrooms and shelf fungi,are called basidiomycetes and are classified in the phylum basidiomycota. • The name of the phylum derives from the basidium(latin for “little pedestal”),a cell in which a transient diploid stages occurs during the fungal life cycle. • The club-like shape of the basidium also gives rise to the common name club fungus.

44. Puffballs emittingspores (Dic)

45. Concept 31.4 basidiomycetes cont. • The life cycle of a basidiomyete usually include a long-lived dikaryotic mycelium . • Periodically,in response to enviormental stimuli the mycelium reproduces sexually by producing elaborate fruiting bodies called basidiocarps(a mushroom is a fimulare example). • The numerous basidia in a basidiocarp are the sources of sexual spores called basidiospores. • The mushroom’s cap supports and protects a large surface area of basidiaon gills.

46. Concept 31.5 decomposer • Fungi are well adapted as decomposers of organic material, including the cellulose and lignin of plant cell walls. • Fungi and bacteria are primarily responsible for keeping ecosystems stocked with the inorganic nutrients essential for plant growth. • Without these decomposers,carbon,nitrogen,and other elements would become tied up in organic matter.

47. Concept 31.5 mycorrhizae • Mycorrhizae are enormously important in natural ecosystem and agriculture. • It is relatively easy to demonstrate the significance of mycorrhzae by comparing the growth of plants with and without mycorrhizae. • Foresters commonly inoculate pine seedlings with ectomycorrhizal fungi to promote vigorous growth in the tree.

48. Concept 31.5 fungus-animal symbiosis • Some fungi share their digestive service with animals,helping breakdown plant material in the guts of cattle and other grazing mammals. • Many species of ants and termites take advantage of the digestive power of fungi by raising them in farms. • The insect scour tropical forests in search of leaves,which they carry back to their nest and feed it to the fungi. • The fungi have been so dependent on their caretakers that in many cases they can no longer survive without the insect.

49. Ant taking a stem of a plant to take it to the fungus.

50. Concept 31.5 lichens • Lichens are a symbiotic association of millios of photosynthetic microorganisms held in a mass of fungal hyphae. • They form a surface-hugging carpet that can be found growing on rocks,rottinglogs,trees,and roofs in various shrub-like,leaf-like,or encrusting forms. • The merger of fungus and alga or cyanobacterium is so comeplete that lichens are actually given scientific names as though they were single organism.