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