Protists

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Protists
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Classifying Protists

• Protists are paraphyletic (physically similar,
  but unrelated) as compared to members of other
  eukaryote kingdoms (fungi, plants, animals)
• Artificial category containing diverse members
  that are not plants, animals or fungi
• Most are single-celled organisms
• Classification is not fully resolved

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Phylogenetic relationships of Eukaryotes

• protists are everything except animals,
  plants and fungi

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General Biology of the Protists

• Size lt0.2um to 60 m

Many protists are about the size of a typical
animal cell (larger than bacteria)
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General Biology of the Protists

• Cell surface
• cell membrane only, cell wall, or silica test

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General Biology of the Protists

• Locomotion
• Use flagellum, pseudopodia

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General Biology of the Protists

• Cyst formation
• Cysts are a dormant form
• of a cell with resistant outer covering in
  which
• metabolism is essentially
• shut down

Life cycle of Entamoeba histolytica, a parasite
of humans
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General Biology of the Protists

• Nutrition
• Employ all forms except chemoautotrophic
• Many are phototrophs and heterotrophs

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General Biology of the Protists

• Reproduction
• Several different methods
• asexual reproduction
• binary fission 2 equal halves
• budding - progeny cell smaller
• multiple fission
• sexual reproduction in times of stress
• gametic meiosis - produces gametes
• alternating haploid and diploid forms
  (alternation of generations)

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For exampleComplex life cycle of Dictyostelium
This protist uses several different reproductive
methods
Some protists can assume different physical forms
during their lifecycle (Note the haploid (n) and
diploid (2n) generations this is known as
alternation of generations)
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Where did multicellular organisms come from?
Unicellular
Colonial
Multicellular
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Diversity of Protists

• Seven major named lineages
• Excavata
• Discicristata
• Alveolata
• Stramenopila
• Cercozoa
• Plantae (paraphletic if land plants excluded)
• Amoebozoa
• (there are other groups related to animals and
  fungi)

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Excavata

• Includes Giardia
• about 400 described species
• most live in guts of animals
• some parasitic
• mostly asexual reproduction

Giardia lamblia an important water-borne parasite
of humans
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Discicristata

• Euglenoids (Euglena)
• 1000 species, most are freshwater
• about one-third are photosynthetic
• no sexual reproduction

Euglena is phototrophic and heterotrophic
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Discicristata

• Includes Trypanosoma
• Trypanosomes cause many human diseases.
• African sleeping sickness
• Chagas disease

Trypanosome diseases are transmitted by insects
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Alveolata

• Dinoflagellates
• distinctive paired flagella, protective coats,
  and biochemistry
• responsible for red tides

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Alveolata

• Also includes
• spore-forming animal parasites
• malaria parasite Plasmodium
• Free-living Paramecium

Lifecycle of Plasmodium
Malaria control entails disease treatment and
mosquito control
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Stramenopila

• Includes brown algae, diatoms, and oomycetes
• Brown algae - conspicuous seaweeds
• alternation of generations

California kelp forest
Bull kelp
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Stramenopila

• Diatoms 10,000 spp.
• photosynthetic, unicellular organisms with double
  shells of opaline silica (glass like material)

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Stramenopila

• Oomycetes - parasites or saprophytes (agents of
  decay)
• water molds, white rusts, downy mildews

Saprolegnia on a fish
Phytophthora on a pumpkin
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Cercozoa - Foraminifera

• Heterotrophic marine protists with mineralized
  shells
• complex life cycle with alternation of
  generations
• May be used as environmental indicators shell
  susceptible to acids (CO2 and ocean
  acidification)

White cliffs of Dover are calcium carbonate
sediments derived from protists
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Plantae - Rhodophyta

• Red algae range in size from microscopic to
  very large
• 6000 species
• Use calcium rich minerals to build reefs
• nori

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Plantae - Chlorophyta

• Green algae are relatives of plants
• Extensive fossil record dating back 900 million
  years
• Mostly aquatic
• Ranges from very small and simple (Chlamydomonas)
  
• to larger and more complex (plant-like green
  algae)

Includes green seaweeds
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Amoebozoa - Amoebas

• Possess pseudopods that can form at any point on
  the cell body and can move in any direction

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Fungi
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Fungi are not plants

• Fungi are more closely related to animals than to
  plants

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Fungi

• One of three diverse kingdoms of (mostly)
  multicellular eukaryotes
• As many as 1.5 million spp.

Shagy parasol, Lepiota rhacodes
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Fungi

• Heterotrophic (get energy by digesting organic
  matter)

Cordyceps sp. digesting a fly these fungi alter
insect behavior to disperse
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Fungi

• Cell walls made of chitin (not cellulose, as in
  plants)

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Lifestyles of fungi

• Single-celled fungi are called yeasts

Budding is a form of asexual reproduction
Saccharomyces cerevesiae, bakers yeast cells
budding
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Mushrooms vs. Mycelia

• Many multicellular fungi spend most of their
  lives as hyphae - filamentous cells

Hyphae of Podospora anserina
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• Hyphae
• Hyphae joined end-to-end divided by cross-walls
  (septa)
• Rarely form complete barrier
• Cytoplasm freely streams in hyphae

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Fruiting bodies (mushrooms, puffballs, etc.)
are composed of masses of hyphae
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• How Fungi Reproduce
• Fungal mitosis
• Not associated with cell division (nuclear
  division)
• Nuclear envelope does not break down and re-form
• spindle apparatus formed within nucleus
• spindle plaques take place of centrioles

Each compartment of the hypha can contain one,
two or more nuclei monokaryotic - each
compartment has a single nucleus dikaryotic -
two distinct nuclei within each hyphal
compartment (or cell)
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How Fungi Reproduce

• Fungi reproduce sexually after two hyphae of
  opposite mating type fuse
• Two methods
• In some fungi two haploid cells fuse to form a
  diploid cell (2n)
• Some have dikaryotic stage (cell has two haploid
  nuclei) before parental nuclei fuse to form
  diploid nucleus (fusion of nuclei inside one cell)

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How Fungi Reproduce

• Spores are most common means of fungal
  reproduction
• may form from asexual or sexual processes
• most often dispersed by wind but some spread by
  insects or other small animals

Fungal spores on a rose leaf
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Generic fungal life cycle
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How Fungi Obtain Nutrients

• All fungi obtain food by secreting digestive
  enzymes and then absorbing the organic molecules
  produced (external digestion)
• extensive hyphae network provides enormous
  surface area for absorption
• many fungi able to break down cellulose in wood

Turkey tail, Trametes versicolor a
wood-digesting fungus
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The oyster mushroom Pleurotus ostreatus secretes
an enzyme that immobilizes nematodes, which it
then eats
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Agaricus bisporus, button and portobello
mushrooms
Uses of fungi

• Many edible species

• Naturally white, but brown strains have been
  produced
• Widely cultivated, very tasty, commonly used on
  food

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Cantharellus cibarius

• Chanterelle worlds best-tasting mushroom?
• Grows beside hardwoods and conifer treees

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Uses of fungi

• Antibiotics
• Penicillin fungus produces antibiotic chemicals

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Uses of fungi
Uses of fungi
Anaerobic fermentation provides flavor for wine
and cheese
Veins in blue cheese are pockets of sporulating
Penicillium roquefortii
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Uses of fungi
Fermented food products
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Classification of Fungi
Traditional groups now known to be paraphyletic
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Relationship of fungi to protists

• Microsporidians - single celled parasites of
  animals, taxonomy is not certain
• They are known to cause
• diseases
• Has a spore stage and a
• motile stage with a flagella
• Intermediate group between
• protists and fungi?

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Chytridiomycota

• Mostly aquatic fungi 1000 spp.
• possess flagellated zoospores
• exhibit many ancestral features
• lack septa between cells

flagellated zoospores of Blastocladiella emersonii
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Zygomycota

• Includes common bread molds 1050 species
• Sexual reproduction occurs by fusion of
  gametangia
• Asexual reproduction most common
• Hyphae produce
• sporulating stalks

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Zygomycota
Mucor sp. blooming on a peach Mucor
sporangium
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Fig. 30.10b(TE Art)
Life cycle of Rhizopus, a zygomycete mold on fruit
Sporangiophore
Sporangium
Spores
Rhizoid
Mating strain
Sporangium
Hypha
MEIOSIS (occurs during germination)
n
2n
Mating strain
FUSION OF GAMETANGIA
Germinating zygosporangium
Zygosporangium
Gametangia
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Basidiomycota

• Most familiar fungi (mushrooms, toadstools,
  puffballs, rusts, and smuts) about 22,000 species

Geastrum sp.
Coprinus comatus
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Basidiomycota

• Named for characteristic sexual reproductive
  structure, basidium
• Fusion of nuclei
• in the basidium
• creates only diploid
• stage

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Basidiomycota

• Mycelium made up of monokaryotic hyphae is called
  primary mycelium
• fusion of different mating types forms
  dikaryotic, secondary mycelium
• mushrooms (basidiocarps) are always made of
  secondary mycelium

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Fig. 30.11b(TE Art)
Life cycle of basidiomycete fungi
Gills lined with basidia
Basidiocarp
n n
Zygote

2n
n
Basidium
Secondary mycelium (dikaryotic)
Sterigma
MEIOSIS
Strain
Formation of basidio- spores
Basidiospores
Fusion of and hyphae
Strain
Primary mycelium (monokaryotic)
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Basidiomycete structure
The gills of a mushroom are lined with
spore-producing basidia These may produce
millions of spores
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Diversity of basiodiomycetes
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Ascomycota

• Very large group including yeasts, molds, cup
  fungi and morels 45,000 species

Cookeina tricholoma
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Many yeasts are ascomycetes
Saccharomyces cerevisiae Candida albicans
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Ascomycota

• Named for reproductive structure ascus
• asci form within ascocarp

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Ascomycota

• Asexual reproduction takes place via spores
  called conidia at the end of conidiophores

Conidia of Penicillium and Aspergillus
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Fig. 30.12c(TE Art)
Asexual spores (conidia)
Ascospore
Each haploid nucleus divides once by mitosis
Strain
Ascogonium
Antheridium
bridge allows strain nuclei to pass
into ascogonium
Strain
Monokaryotic
n
MEIOSIS

Dikaryotic
2n
Young ascus
hyphae form from ascogonium
Zygote
Formation of young ascus
Fully developed ascocarp composed of
dikaryotic hyphae and sterile hyphae