CHAPTER 31 – FUNGI
31.1 FUNGI ARE HETEROTROPHS THAT FEED BY ABSORPTION
N UT RI T I O N
AN D F UN G AL L I F E ST Y L E S
One important trait shared by all fungi is the way they derive nutrition
 Fungi are all heterotrophs
 Absorb all nutrients from outside the body
 Secrete powerful hydrolytic enzymes (exoenzymes) into their surroundings
 Break down complex molecules to smaller organic compounds that fungi can use
 Some enzymes used to penetrate walls of plant cells; enables absorption of nutrients
out of plant cells
B O D Y S T R U CT U R E
The morphology of multicellular fungi enhances their ability to absorb nutrients from their surroundings
Hyphae – Network of tiny filaments
 Tubular cell walls surrounding the plasma membrane and cytoplasm
Chitin – Strong but flexible nitrogen-containing polysaccharide that is also found in the external skeletons of
insects and other arthropods
Mycelium – the densely branched network of hyphae in a fungus
 Infiltrates the material on which the fungus feeds
 Mycelium’s structure maximizes the ratio of its surface area to its volume, making feeding more
effective
Septa – One of the cross walls that divides a fungal hypha into cells
 Generally have pores large enough to allow ribosomes, mitochondria, and even nuclei to flow
from cell to cell
Coenocytic Fungi – A fungus that lacks septa and whose body is made up of a continuous cytoplasmic mass that
may contain hundreds or thousands of nuclei
 Condition results from repeated divison without cytokinesis
Haustoria – Certain symbiotic fungi use a specialized hypha to penetrate the tissues of host organisms
Mycorrhizae – Mutually beneficial relationships between fungi and plant roots
 Vast networks of mycorrhizal fungi are more efficient than plant roots at acquiring phosphate
ions and other minerals from the soil
31.2 FUNGI PRODUCE SPORES THROUGH SEXUAL OR ASEXUAL LIFE CYCLES
S EX U A L R EP R O D U CT I O N
Pheromones – In animals and fungi, a small molecule released into the environment that functions in
communication between members of the same species
Plasmogamy – The union of the cytoplasm of the two parent mycelia. Occurs at one stage in fertilization
Heterokaryon – A fungal mycelium that contains two or more haploid nuclei per cell
Dikaryotic – A fungal mycelium with two haploid nuclei per cells, one from each parent
A S E XU A L R EP R O D U CT I O N
Molds – Fungus that grows as a filamentous fungus, producing haploid spores by mitosis and forming a visible
mycelium
Yeasts – Reproduce asexually by simple cell division or by the pinching of small “bud cells” off a parent cell
Deuteromycetes – Classification for a fungus with no known sexual stage
31.3 FUNGI DESCENDED FROM AN AQUATIC, SINGLE -CELLED, FLAGELLATED
PROTIST
T H E O RI GI N O F F UN GI
Opisthokonts – Member of the diverse clade Opisthokonta, organisms that descended from an ancestor with a
posterior flagellum, including fungi, animals, and certain protists
Ancestors of animals and fungi may have diverged into separate lineages 1.5 billion years ago, but on fossils from
460 million years ago have been discovered
Moved to land accompanying plants
31.4 FUNGI HAVE RADIATED INTO A DIVERSE SET OF LINEAGES
C H YT RI D S
Fungi classified in the phylum Chytridiomycota
 Some are saprobes, and other are parasites
 Diverged earliest in fungal evolution as they have flagellated spores called zoospores
Z YGO M Y CE T ES
Phylum Zygomycota includes fast growing molds responsible for rotting produce, as well as parasites and neutral
symbionts
 Life cycle varies among zygomycetes, but many share common traits
 Hyphae spread out over food, penetrate it, and absorb nutrients. These hyphae are coenocytic,
with septa found only where reproductive cells are formed
 In the asexual phase, bulbous black sporangia develop at the tips of upright hyphae. Hundreds of
haploid spores develop and disperse in the bulbs
 If environmental conditions deteriorate, zygomycetes may reproduce sexually
G LO M E RO MY C ET E S
Fungi in the phylum Glomeromycota are ecologically significant
 Form a distinct type of endomycorrhizae called arbuscular mycorrhizae
 Tips of hyphae push into plant root cells and branch into tiny treelike structures
 About 90% of all plants have such symbiotic partnerships
A S CO M YC E T E S
Defining feature is the production of saclike asci
 Bear their sexual stage in fruiting bodies called ascocarps
 Life cycles share some common elements
 Reproduce asexually by forming spores called conidia
 Conidia are produced externally at the tips of conidiophores
 Conidia may also be involved in sexual reproduction, which fuses with hyphae, and is followed by
plasmogamy, resulting in an ascogonium. This ascogonium extends hyphae forming dikaryotic
cells, each with two haploid nuclei. The cells at the tips of these hyphae develop into asci, where
meiosis divides the cells and allows them to develop and discharge.
B A SI DI O M Y C ET ES
The name of the phylum derives from basidium, a cell in which a transient diploid stage occurs during the fungal
life cycle. These fungi are often club shaped, and thus are called club fungus.
 They are important decomposers of wood and other plant material
 Life cycle of basidiomycete includes a long-lived dikaryotic mycelium, where, in response to
environmental stimuli, the mycelium produces fruiting bodies called basidiocarps
 Concentrated growth in the hyphae quickly erects these fruiting bodies in little time
 Asexual reproduction is not common in basidiomycetes
31.5 FUNGI HAVE A POWERFUL IMPACT ON ECOSYSTEMS AND HUMAN
WELFARE
F UN GI A S D E CO MP O SE R S
 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.
 Carbon, nitrogen, and other elements would remain tied up in organic matter without these
decomposers.
F UN GI
A S M UT UA LI ST S
Fungi may form mutualistic relationships with plants, algae, cyanobacteria, and animals
Lichen - symbiotic association between a photosynthetic microorganism and a fungus in which millions of
photosynthetic cells are held in a mass of fungal hyphae (grow on rocks, rotting logs, trees, and roofs, etc)
 provide their photosynthetic partners with a suitable environment for growth
 important pioneers on newly cleared rock and soil surfaces
 breakdown the surface by physically penetrating and chemically attacking it
Soredia - in lichens, a small cluster of fungal hyphae with embedded algae
F UN GI
A S P AT HO G EN S
30% are parasites, mainly of plants
Mycosis - general term for fungal infection that are known to parasitize animals
P RA CT I C A L U S E S
O F F U N GI
 Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread.
 Antibiotics produced by fungi treat bacterial infections
 Genetic research on fungi is leading to applications in biotechnology