Fungi-like Protists & Fungi

Question 1

Oomycetes

Answer 1

Water molds, white rusts and downy mildews
- Once considered fungi based on morphological studies
- Use filaments (hyphae) that facilitate nutrient uptake
- Unlike fungi, the cell wall of water molds is made of cellulose, not chitin
- Most are decomposers or parasites

Question 2

Unikonts

Answer 2

A supergroup that includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)

Question 3

Amoebozoans

Answer 3

Amoeba that have lobe or lube-shaped pseudopodia
Includes: Slime molds, Gymnamoebas, Entamoebas

Question 4

Slime molds

Answer 4

Once thought to be fungi
- Have similar morphology and produce fruiting bodies to distribute their spores
- Example of convergent evolution
Two main branches
- Plasmodial slime molds
- Cellular slime molds

Question 5

Why are slime molds in the Amoebozoa clade?

Answer 5

Their molecular systematics

Question 6

Plasmodial slime molds

Answer 6

• The plasmodium is undivided by membranes and contains many diploid nuclei
• It extends pseudopodia trough decomposing material, engulfing food by phagocytosis

Question 7

Cellular slime molds

Answer 7

The feeding stage of the life cycle consists of solitary cells that function individually, but when food is depleted the cells form a multicellular aggregate that functions as a unit and aids in spore dispersal
(20% of cells form the stalk)

Question 8

What are obligated cheaters?

Answer 8

Cells that never form the stalk, linked to a single gene mutation in cell surface protein
- may gain a reproductive advantage
- rare/absent in the wild
Non-cheaters preferentially aggregate with other non-cheaters
Primitive form of cooperative behavior and model for evolution of multicellularity

Question 9

Gymnamoebas

Answer 9

Unicellular amoebozoans in soil and aquatic habitats. Most are heterotrophic and actively seek and consume bacteria and other protists

Question 10

Entamoebas

Answer 10

Unicellular parasites eg. Entamoeba histolytica causes amebic dysentery

Question 11

What are fungi essential for?

Answer 11

The well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

Question 12

How do fungi feed?

Answer 12

They’re heterotrophs so they feed by absorption
- do not ingest their food
- secrete exoenzymes that break down complex molecules, absorb the smaller compounds
- versatility of these enzymes contributes to fungi’s ecological success

Question 13

What are the two most common body structures of fungi?

Answer 13

Multicellular filaments and single cells (aka yeasts)
- the morphology of multicellular fungi enhance their ability to absorb nutrients
- some species grow as either filaments or yeast; others grow as both
- most fungi have cell walls made of chitin

Question 14

Hyphae

Answer 14

Tiny filaments used for absorption

Question 14

What do filamentous fungi consist of?

Answer 14

Mycelia, networks of branched hyphae adapted for absorption

Question 15

What are the two main structures of hyphae

Answer 15

Septate hyphae - divided into cells by septa, with pores allowing cell-to-cell movement
Coenocytic fungi - lack septa (nuclear division without cytokinesis)

Question 16

Haustoria

Answer 16

Specialized hyphae that can extract nutrients from plant cells
- Only some mutualistic and parasitic fungi have them
- Increase surface area contact with plasma membrane
- Remains separated from the plant cell’s cytoplasm by the plant plasma membrane

Question 17

Mycorrhizae

Answer 17

Mutually beneficial relationships between fungi and plant roots
- fungi are more efficient at absorbing minerals than roots
- fungus increases water uptake and rates of mineral absorption
- plants provide fungi with supply of sugar

Question 18

Ectomycorrhizae

Answer 18

From the Greek ektos - out
- form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex
- results in plant roots that are thicker, more branched, and lack root hairs
- 10% of plant species have ectomycorrhizae, mainly woody species

Question 19

Endomycorrhizae

Answer 19

From the Greek endos - in
- extend hyphae through the cell walls of root cells and into tubes formed by invaginatoin of the root cell membrane
- also called arbuscular mycorrhizae
- found in 85% of plant species, including many crops

Question 20

Endophytic fungi

Answer 20

Harbored by plants, live inside leaves or other plant parts
- May make toxins that deter herbivores and defend against pathogens
- increase plant tolerance to heat, drought, or pollutants
- Increase plant productivity (the rate of production of new biomass by an individual, population or community)

Question 21

Plasomogamy

Answer 21

The union of two parent mycelia
- attracted together by the release of signaling molecules called pheremones
- fuse when they meet
- in many fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon (different nuclei)
- In others, the haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic (two nuclei)

Question 22

Karyogamy

Answer 22

When the haploid nuclei fuse, producing diploid cells
- may take hours, days, or even centuries before it occurs
- the diploid phase is short-lived and undergoes meiosis, producing haploid spores

Question 23

How does mold reproduce?

Answer 23

Asexually
- many of these species grow as mold on fruit, bread, and other foods

Question 24

Conidia

Answer 24

Clusters of bead-like structures (in the SEM - conidiospores at the end of aerial hyphae - image on the slide)

Question 25

Who won the Nobel prize in physiology in 1945? Why?

Answer 25

Sir Alexander Fleming, Ernst Boris Chain and Sir Howard Walter Florey for the discovery of penicillin and its curative effect in various infectious diseases

Question 26

How does yeast reproduce?

Answer 26

Asexualy
- Inhabits moist environmnets
- uses cell divisision rather than spore production

Question 27

Who won the Nobel prize in physiology in 2001? Why?

Answer 27

Leland H. Hartwell, Tim Hunt and Sir Paul M. Nurse for their discoveries of key regulators of the cell cycle

Question 28

How are most fungi classified?

Answer 28

Based on appearance of fruiting bodies or spores
- Mycologists have traditionally called these deuteromycetes or imperfect fungi

Question 29

What did fungi descend from?

Answer 29

An aquatic single-celled, flagellated protist
- Systematists now recognize that fungi and animals are more closely related to each other than they are to plants or other eukaryotes

Question 30

What is the origin of fungi?

Answer 30

Molecular evidence supports the hypothesis that fungi and animals diverged from a common unicellular, flagellated ancestor
- probably diverged about a billion years ago, oldest undisputed fossils of fungi only about 460 million years old

Question 31

Chytrids

Answer 31

Found in freshwater and terrestrial habitats
- decomposers, mutualists, or parasites
- molecular evidence supports that chytrids diverged early in the fungal evolution
- have flagellated spores, called zoospores

Question 32

Zygomycetes

Answer 32

Includes fast-growing molds, parasites, and commensal symbionts
- named for their sexually produced zygosporangia
- exhibit great diversity of life histories
- zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions

Question 33

How do fungi interact with other organisms?

Answer 33

Decomposers
- are everywhere, common on the forest floor
Mutualists
- mycorrhizae (with plants)
- fungus-animal
- lichens
Pathogens (~30% of fungi are parasitic)
- absorb nutrients from a living host
- responsible for ~80% of plant diseases

Question 34

What do fungi perform as decomposers?

Answer 34

Essential recycling of chemical elements between the living and nonliving world
- fungi and bacteria are primarily responsible for keeping ecosystems stocked with the inorganic nutrients essential for plant growth
- without decomposers, carbon, nitrogen, and other elements would become tied up in organic matter. Plants and animals that eat them could not exist because elements taken from the soil would not be returned

Question 35

Fungus-Animal Symbiosis

Answer 35

Some fungi share their digestive services with animals
- help break down plant material in the guts of cows and other grazing mammals
- many species of ants and termites use the digestive power of fungi by raising them in “farms”

Question 36

Can fungi be used for biofuel production?

Answer 36

Cellulosic ethanol
- US Department of Energy is investing in efforts to convert waste agricultural products
- Identifying enzymes from fungi such as
cellulases - that breakdown plant cell walls
- Developing heat-tolerant industrial-strength
host cell systems to drive these reactions

Question 37

Lichen

Answer 37

A symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae
- crustose lichens important as pioneer species of new rock:
- Physically and chemically attack rock, trap soil
- Lichens predate land plants
- fungus gives a lichen its overall shape and structure
- algae/cyanobacteria occupy an inner layer below the lichen surface
- soredia, small clusters of hyphae with embedded algae
- Algae provides sugar
- Cyanobacteria can fix nitrogen

Question 37

Pathogens

Answer 37

About 30% of known fungal species are parasites, mostly on or in plants
- some fungi that attack food crops are toxic to humans
- animals are much less susceptible to parasitic fungi than are plants
- general term for a fungal infection in animals in mycosis

Question 38

What are “zombie ants”?

Answer 38

Ants with fungus infecting their brain
- suffer convulsions unable to climb high and stay in cool, damp leaf understory
- fungus synchronizes ant behavior, forcing infected ants to bite the stem on the underside of the leaf at solar noon, when sun is strongest