Fungi Invade
the Land
17.1 Complex Multicellularity
Complex multicellular organisms
Individuals are composed of many highly
specialized cells that coordinate their activities
Three kingdoms exhibit multicellularity
Plants
Animals
Fungi
17.1 Complex Multicellularity
Two key characteristics distinguish between complex
multicellular and simple multicellular organisms
Cell specialization
Different cells use different genes
They therefore develop in different ways
Intercell coordination
Cells adjust their activity in response to what
other cells are doing
17.2 A Fungus Is Not a Plant
The study of fungi is called mycology
Fungi have traditionally been included in the plant
kingdom
However, there are significant differences
between fungi and plants
Fungi are heterotrophs
Fungi have filamentous bodies
Fungi have nonmotile sperm
Fungi have cell walls made up of chitin
Fungi have nuclear mitosis
17.3 Reproduction and Nutrition
of Fungi
Fungi have three types of reproductive structures
Fig. 17.3
Gametangia
Form haploid gametes
that fuse to form zygote
Sporangia
Produce haploid spores
that are dispersed
Puffball
spores
Conidiophores
Produce asexual spores
Spores are a common means of fungal reproduction
17.3 Reproduction and Nutrition
of Fungi
Fungi obtain nutrients by external digestion
They secrete digestive enzymes into their surroundings
and absorb the resulting organic molecules
Some fungi are active
predators
Immobilizes nematodes
then eats them!
Fig. 17.4 The oyster mushroom
17.4 Kinds of Fungi
73,000 species of fungi have been named so far
There are divided into four phyla
Zygomycota
Distinguished primarily
Ascomycota
by their mode of
Basidiomycota
sexual reproduction
Chitrydiomycota
A fifth group, the imperfect fungi, is artificial
It’s a “catch-all” grouping of fungi in which sexual
reproduction has not been observed yet!
17.5 Zygomycetes
Zygomycetes make up < 1% of
named fungi
They include
Bread molds
Some pathogens
Candida
Rhizopus
Zygomycetes typically undergo
asexual reproduction
17.6 Ascomycetes
Phylum Ascomycota, the
ascomycetes, is the largest
of the four phyla
Yeasts, morels and truffles
Many plant fungal pathogens
Dutch elm disease and chestnut
blight
Reproduction is usually
asexual
Morel
17.7 Basidiomycetes
Phylum Basidiomycota
contains the most familiar
of the fungi
Mushrooms, toadstools,
puffballs
Many plant fungal pathogens
Asexual reproduction is
rare
Amanita
17.8 Chytridiomycetes,
Imperfect Fungi, and Yeasts
Chytridiomycetes
Aquatic, flagellated
fungi
Most closely related
to ancestral fungi
Include
Plant pathogens
A frog pathogen
Fig. 17.8 The pathogenic chytrid,
Batrachochytrium dendrobatidis
17.8 Chytridiomycetes,
Imperfect Fungi, and Yeasts
Imperfect fungi
Fungi where sexual
reproduction has not
been observed
Fungi that cause
ringworm infections
Fig. 17.9 The imperfect fungus,
Verticillium alboatrum
A pathogen of alfalfa
17.8 Chytridiomycetes,
Imperfect Fungi, and Yeasts
Yeasts
Generic name given
to unicellular fungi
Baker’s yeast
~ 250 named species
Reproduction is
mostly asexual
Fig. 17.10 Budding in the yeast
Saccharomyces cerevisiae
17.9 Ecological Roles of Fungi
Fungi, together with bacteria, are the principal
decomposers in the biosphere
Fungi are virtually the only organisms that can break down
lignin
Fungi cause
animal diseases
Fungi are the most
harmful pests of
living plants
Fig. 17.11 Armillaria: World’s
largest organism?
Coniferous
forest
8 hectares
17.9 Ecological Roles of Fungi
Many commercial products are dependent on the
biochemical activities of fungi
Bread
Beer
Cheese
Soy sauce
Penicillin
Fungal Associations
Mutualism is a form of symbiosis in which each
partner benefits
Two kinds of mutualistic associations between fungi
and autotrophic organisms are ecologically important
1. Mycorrhizae
2. Lichens
Mycorrhizae
Symbiotic association between a fungus and the
roots of plants
Fungus helps plant absorb minerals and nutrients
Plant provides fungus with food (organic molecules)
No mycorrhizae
Fig. 17.12 Mycorrhizae on the
roots of pines
Fig. 17.13 How mutualism
aids plant growth
Mycorrhizae
Endomycorrhizae vs. Ectomycorrhizae
Far more
common type
Hyphae penetrate
root cells
Fig. 17.14
Hyphae do not
penetrate root
cells
Lichens
Symbiotic association between a fungus and a
green algae or cyanobacterium
Lichens are found
in the harshest of
habitats
They are often the
first colonists in
such harsh areas
Lichens are
pollution indicators
Fig. 17.15 Lichens growing on rock