Fungi-like Protists & Fungi Flashcards
Oomycetes
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
Unikonts
A supergroup that includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)
Amoebozoans
Amoeba that have lobe or lube-shaped pseudopodia
Includes: Slime molds, Gymnamoebas, Entamoebas
Slime molds
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
Why are slime molds in the Amoebozoa clade?
Their molecular systematics
Plasmodial slime molds
- The plasmodium is undivided by membranes and contains many diploid nuclei
- It extends pseudopodia trough decomposing material, engulfing food by phagocytosis
Cellular slime molds
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)
What are obligated cheaters?
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
Gymnamoebas
Unicellular amoebozoans in soil and aquatic habitats. Most are heterotrophic and actively seek and consume bacteria and other protists
Entamoebas
Unicellular parasites eg. Entamoeba histolytica causes amebic dysentery
What are fungi essential for?
The well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients
How do fungi feed?
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
What are the two most common body structures of fungi?
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
Hyphae
Tiny filaments used for absorption
What do filamentous fungi consist of?
Mycelia, networks of branched hyphae adapted for absorption
What are the two main structures of hyphae
Septate hyphae - divided into cells by septa, with pores allowing cell-to-cell movement
Coenocytic fungi - lack septa (nuclear division without cytokinesis)
Haustoria
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
Mycorrhizae
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
Ectomycorrhizae
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
Endomycorrhizae
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
Endophytic fungi
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)
Plasomogamy
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)
Karyogamy
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
How does mold reproduce?
Asexually
- many of these species grow as mold on fruit, bread, and other foods
