Chapter 20 Fungi Mushrooms: ©Frans Lemmens/Corbis Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior

Chapter 20 Fungi

Mushrooms: ©Frans Lemmens/CorbisCopyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Section 20.1

Fungi Are Essential Decomposers

Fungi are the closest relatives of the animals.

Mushroom: © Corbis RF

Section 20.1


Fungi come in all shapes and sizes.

Figure 20.1Yeast cells: ©Scimat/Science Source; mildew on leaf: ©Nigel Cattlin/Visuals Unlimited; mildew inset: ©Biodisc/Visuals Unlimited; cordyceps on insect: ©Emanuele Biggi/Getty Images; Armillaria ostoyae: ©WSL Handout/Reuters/Corbis

Section 20.1


All fungi are heterotrophic eukaryotes that feed by external digestion. They excrete digestive enzymes and absorb minerals and nutrients.


Section 20.1


Fungi have unique reproductive cycles. Unlike plants and animals, the diploid stage may be brief.


Section 20.1


Some fungi have a dikaryotic stage, in which cells have two genetically unique nuclei.

Figure 20.2

Section 20.1


Figure 20.3

A fungus is more than meets the eye. A mushroom is only the fruiting body of a fungus.

Section 20.1


Figure 20.3

Underground are extensive networks of threadlike filaments, called hyphae.

Section 20.1


Figure 20.3

Underground hyphae aggregate into a mycelium.

Section 20.1


Figure 20.3

Hyphae also aggregate into a fruiting body, such as this mushroom.

Section 20.1


Figure 20.3

As the mycelium absorbs nutrients, the fruiting body produces spores, which are microscopic reproductive cells.

Section 20.1


Figure 20.3

Spores germinate into hyphae.

Section 20.1


Figure 20.23

This figure summarizes the typical fungal life cycle.

Section 20.1


Figure 20.23

Note that spores are produced either sexually or asexually.

Section 20.1


Figure 20.4

Asexual spores are called conidia. Hyphae can produce conidia by mitosis.

Mold spore: ©Dr. Dennis Kunkel/Visuals Unlimited

Section 20.1


Figure 20.5

Fungal classification is based on spore type.

Clicker Question #1

What is a dikaryotic cell?

A. A cell with two sets of chromosomes.B. A cell with two nuclei.C. A cell without any nucleic acids.D. A cell that is dividing its cytoplasm. E. Both A and B

Flower: © Doug Sherman/Geofile/RF

Clicker Question #1




20.1 Mastering Concepts

What characteristics define the fungi?

Mushrooms: ©Frans Lemmens/Corbis

Section 20.2

Chytrids Produce Swimming Spores

Figure 20.5

Chytridomycetes (chytrids) produce motile spores called zoospores.

Section 20.2


Figure 20.6

Some chytrids are single cells. Others have slender hyphae. The structures at the ends of these hyphae produce gametes.

Hyphae

Gamete-producing structures

Allomyces: ©J. Robert Waaland/Biological Photo Service

Section 20.2


Figure 20.6

Chytrids also produce flagellated zoospores.

Zoospores: R. E. Reichle, M. S. Fuller, "From The Fine Structure of Blastocladiella emersonii Zoospores," American Journal of Botany, Vol. 54, no. 1, January 1967, pp. 81-92. © 1967 Botanical Society of America All rights reserved. Used with permission.

Section 20.2


Figure 20.7

Chytrids are common in many environments, such as a cow’s digestive tract and on frog skin.

Chytrid infection: ©Lee Berger, James Cook University; frog: ©Dr. Janalee Caldwell

Section 20.2


Figure 20.7

Chytrids feed on frog skin. When it is coated with chytrids, the frog loses its ability to breath through its skin.


Section 20.2


Figure 20.7

Chytrids are therefore contributing to the decline in amphibian populations.


Clicker Question #1




Clicker Question #1





How do flagellated cells adapt chytrids to moist environments?


Section 20.3

Zygomycetes Produce Zygospores

Figure 20.8

Zygomycetes fungi are fast-growing and prolific.

Zygomycetes growing on a bagel.

Section 20.3


Figure 20.8

Zygomycetes reproduce both sexually and asexually. Both life cycles are dominated by haploid cells.

Micrograph of zygomycete: ©Ed Reschke

Section 20.3


Figure 20.8

During sexual reproduction, cells from two hyphae fuse, producing a diploid zygospore surrounded by a spiny coat.


Section 20.3


Figure 20.8

The zygospore undergoes meiosis, producing a haploid hypha.


Section 20.3


Figure 20.8

The hypha produces genetically unique haploid spores, each of which germinates into a hypha.


Section 20.3


Figure 20.8

Each hypha may undergo sexual reproduction, by fusing with another hypha, or asexual reproduction.


Section 20.3


Figure 20.8

During asexual reproduction, the hypha produces spore sacs by mitosis. All spores are genetically identical.


Section 20.3


Figure 20.9

Zygomycetes grow in flies, cow dung, and many other places.

Insect: ©Dwight Kuhn; pilobolus: ©Carolina Biological Supply Company/Phototake


How does the zygospore fit into the zygomycete life cycle?


Section 20.4

Glomeromycetes Colonize Plant Roots

Figure 20.10

Glomeromycetes only live in association with plant roots. A fungus-plant root combination is called a mycorrhiza.

Glomus diaphanum and inset: ©Joseph B. Morton

Section 20.4


Figure 20.10

The fungus exchanges minerals and nutrients with the plant root at structures called arbuscules.


Section 20.4


Figure 20.10

The partnership benefits both the fungus and the plant.


Section 20.4


Figure 20.10

The fungal hyphae absorb water and nutrients from the soil and share them with the plant, while the plant produces sugars

that the fungus uses for energy.



Describe a mycorrhiza?


Section 20.5

Ascomycetes Are Sac Fungi

Figure 20.13

Ascomycetes is a large group containing fungi with various lifestyles.

Truffle: ©DEA/G. Cozzi/Getty Images; morel: ©Robert Marien/Corbis RF

Section 20.5


Figure 20.13

Some decompose organic matter. Others live in symbiosis with other organisms, either as parasites or mutualists.

Truffle: ©DEA/G. Cozzi/Getty Images; morel: ©Robert Marien/Corbis RF

Section 20.5


Figure 20.11

Still others are carnivores. The fungus in the image below is wrapped around a roundworm. The fungal hyphae extend into

the worm, digesting it from the inside.

Fungus: Courtesy of George Barron and Nancy Allin, University of Guelph, Canada

Section 20.5


Figure 20.14

The ascomycete life cycle explains why they’re called sac fungi.

Section 20.5


Figure 20.14

Genetically unique haploid hyphae fuse, forming a dikaryotic cell.

Section 20.5


Figure 20.14

The nuclei eventually fuse, forming a diploid zygote.

Section 20.5


Figure 20.14

The zygote undergoes meiosis and then mitosis, forming eight ascospores contained within a sac called an ascus.

Section 20.5


Figure 20.14

Ascospores are released, and each germinates into a haploid hypha.

Section 20.5


Figure 20.14

During asexual reproduction, a hypha produces identical haploid spores, each of which germinates into a haploid hypha.


Describe asexual and sexual reproduction in an ascomycete.


Section 20.6

Basidiomycetes Are Club Fungi

Figure 20.15

Basidiomycetes contains familiar fungi, such as puffballs and mushrooms.

Puffballs: ©Bill Keogh/Visuals Unlimited; stinkhorn: ©George McCarthy/Corbis; Turkey Tail and Bird’s Nest fungus: Courtesy of George Barron, University of Guelph, Canada

Section 20.6


Figure 20.15

Wind carries the spores of puffballs and mushrooms.The putrid odor of the stinkhorn’s slimy spore mass attracts flies,which carry the spores on their feet.Raindrops splash the sporeladen “eggs” out of a bird’s nest fungus.


Section 20.6


Figure 20.15

Mushrooms are sometimes edible, although they can also be poisonous or can induce hallucinations.


Section 20.6


Figure 20.15

Basidiomycetes can reproduce asexually by producing haploid spores (conidia). They can also reproduce sexually.


Section 20.6


Figure 20.16

Sexual reproduction begins when haploid hyphae fuse, forming a dikaryotic cell.

Section 20.6


Figure 20.16

Mitosis of the dikaryotic cell produces a dikaryotic mycellium.

Section 20.6


Figure 20.16

Dikaryotic hyphae aggregate into a mushroom.

Section 20.6


Figure 20.16

The mushroom cap contains gills on which club-shaped cells called basidia form.

Section 20.6


Figure 20.16

Within each basidium, the two haploid nuclei fuse into a diploid zygote. The zygote then divides by meiosis, forming four haploid, genetically unique spores.

Section 20.6


Figure 20.16

Each spore germinates into a haploid hypha and the cycle begins anew.

Clicker Question #2

Spores germinate into a mushroom, which produces feeding hyphae from its base.

A. TrueB. False


Clicker Question #2

Spores germinate into a mushroom, which produces feeding hyphae from its base.

A. TrueB. False



Describe the sexual life cycle of basidiomycetes.


Section 20.7

Fungi Interact with Other Organisms

Figure 20.1

Fungi decompose dead plants and animals, and are food and medicine sources.

Man: ©Ed Young/Corbis

Section 20.7


Figure 20.17

Endophytes are fungi that live in plants but do not trigger disease symptoms. All plants harbor endophytes.

Endophyte: ©Dr. Elizabeth Arnold

Section 20.7 Figure 20.10, 20.18

As described on a previous slide, mycorrhizal fungi colonize plant roots, benefiting both the fungus and the plant.


Glomus: ©Joseph B. Morton; ectomycorrhizal roots: ©Dr. John D. Cunningham/Visuals Unlimited; root tip: ©R.L. Peterson/Biological Photo Service

Section 20.7 Figure 20.10, 20.18

Glomeromycetes form the most common types of mycorrhizae. Basidiomycetes and ascomycetes form ectomycorrhizae, in which the fungal hyphae wrap around the root but do not penetrate root cells.


Glomus: ©Joseph B. Morton; ectomycorrhizal roots: ©Dr. John D. Cunningham/Visuals Unlimited; root tip: ©R.L. Peterson/Biological Photo Service

Section 20.7 Figure 20.19

Leaf-cutter ants cultivate fungi. The leaves are deposited underground, where fungi use them as a food source. Ants eat the growing hyphae.


Ant: ©Martin Harvey/Corbis


Lichens are fungi with green algae or cyanobacteria living among their hyphae. The fungi absorb minerals and water while the autotrophic algal cells produce sugars.


Fungal hyphae: ©V. Ahmadijian/Visuals Unlimited; lichen: ©William H. Mullins/Science Source

Clicker Question #3

Which of the following is physically the largest?

A. sugar moleculeB. hyphaC. fungal sporeD. lichen


Clicker Question #3

Which of the following is physically the largest?

A. sugar moleculeB. hyphaC. fungal sporeD. lichen


Clicker Question #4

What kind of fungus produces zoospores with flagella?

A.Basidiomycetes B.AscomycetesC.ZygomycetesD.ChytridsE.Glomeromycetes


Clicker Question #4

What kind of fungus produces zoospores with flagella?

A.Basidiomycetes B.AscomycetesC.ZygomycetesD.ChytridsE.Glomeromycetes


LeConte


How are lichens similar to mycorrhizae?



Investigating Life: The Battle for Position in Cacao Tree Leaves

Cacao trees harbor many endophytes.

What does the tree gain from allowing the fungi to thrive in its tissues?

Cacao tree: ©Robert van der Hilst/Corbis



When cacao trees were inoculated with a pathogenic water mold, trees with endophytes were damaged less than those without.



What does the tree gain from allowing the fungi to thrive in its tissues?

Endophytes help defend the plant against parasites.

Cacao tree: ©Robert van der Hilst/Corbis

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Chapter 20 Fungi Mushrooms: ©Frans Lemmens/Corbis Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior