Biology 2014-2015

Funguslike Protists

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Section 20-5 

slimemold.jpg

Slime Mold

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Slime Mold 

Funguslike Protists

§    heterotrophs that absorb nutrients from dead or decaying organic matter

§    lack chitin in their cell walls

§    Three types:

       cellular slime molds

       acellular slime molds

       water molds

 

Slime Molds

§    funguslike protists that recycle organic material

§    found on forest floors or a backyard compost pile

§    at one stage in their life cycle, they resemble amoebas

§    in the other stage, they form moldlike clumps that produce spores

 

Cellular Slime Molds

§    phylum Acrasiomycota

§    Spend most of their lives as free-living cells resembling soil amoebas

§    When food supply is gone, produce spores that can survive harsh conditions

§    Reproductive steps:

1.      send out chemical signals to attract other cells of the same species

2.      thousands of cells aggregate into a large sluglike colony that functions as a single organism

3.      produces a fruiting body, slender reproductive structure that produces spores

4.      spores are scattered

5.      each spore gives rise to a single amoeba-like cell starting the cycle all over again

 

Acellular Slime Molds

§    phylum Myxomycota

§    Begin their life cycle as an amoeba-like cell

§    When they aggregate, cells fuse to produce structures with many nuclei or plasmodia.

§    Can grow as large as several meters in diameter

§    Sporangia (small-fruiting bodies) spring up from the plasmodium

§    Haploid spores scatter and germinate forming amoeba-like cells

§    Cells fuse into a sexual union to produce a diploid zygote and the cycle is repeated

 

Water Molds

§    Resembles white fuzz growing on the surface of dead fish in the water

§    phylum Oomycota

§    thrive on dead and decaying organic matter in the water

§    some are plant parasites on land

§    NOT true fungi

       Cell walls made of cellulose and produce motile spores

§    Reproduce both sexually and asexually

       Asexual reproduction involves hyphae (thin filaments) which develop into zoosporangia (spore cases).  Flagellated spores swim away in search of food.  Spores develop into hyphae when they find food and grow into a new organism

       Sexual reproduction takes place in specialized structures that are formed by hyphae.  Antheridium produces male nuclei and oogonium produces female nuclei.  Fertilization takes place and spores form a new organism.

 

Ecology of Funguslike Protists

§    Important recycles of organic material

§    Help things rot

§    dark, rich topsoil results from their decomposition

 

 

 

 

 

 

 

§    land-dwelling molds cause mildews and blights of grapes, tomatoes and potatoes

§    protist Phytophthora infestans, an oomycete produces airborne spores that destroy all parts of the potato

§    In 1846, nearly the entire potato crop was lost in Ireland, leading to mass starvation.

§    At least 1 million people died between 1845 and 1851 causing more than 1 million people to emigrate from Ireland.