The Simplest Eukaryotes Protists and Fungi

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The Simplest Eukaryotes Protists and Fungi

• Biology 1030
• Principles of Biology

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Protists Differ from Prokaryotes

• Have a nucleus and organelles
• Have proteins associated with DNA
• Use microtubules in a cytoskeleton, spindle
  apparatus, and cilia and flagella
• May contain chloroplasts
• May divide by mitosis and meiosis

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Major Lineages

• Heterotrophs
• Chytrids
• Water molds
• Slime molds
• Protozoans
• Sporozoans

• Autotrophs
• Red algae
• Brown algae
• Green algae
• Golden algae
• Diatoms

• Mix or Both
• Euglenoids
• Dinoflagellates

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The Most Ancient Groups

• Flagellated protozoans
• Euglenoids
• Amoeboid protozoans

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Animal-Like Flagellates

• Move by means of flagella
• All are heterotrophs
• Free-living species in freshwater and marine
  habitats
• Many are internal parasites

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Body Plan of a Trypanosome
Undulating membrane
mitochondrion
basal body of flagellum
free flagellum
nucleus
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Euglenoids

• Free-living flagellated cells that live in
  freshwater
• Majority are photoautotrophs
• Some are heterotrophs that feed on dissolved
  organic compounds

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Euglenoid Body Plan
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Amoeboid Protozoans

• Have false feet (pseudopods) means of motility
• Include
• Naked amoebas
• Radiolarians
• Foraminiferans

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Naked Amoebas

• Change shape constantly
• Move by means of pseudopods
• Most are free-living cells that engulf their
  prey
• Some are symbionts in animal guts
• A few are opportunistic pathogens

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Ciliated Protozoans

• Also called ciliates
• All heterotrophs
• Arrays of cilia allow movement and direct food
  into oral cavity

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Body Plan of Paramecium
food residues being ejected
gullet
cilia
trichocysts (harpoons)
food vacuole
contractile vacuole emptied
contractile vacuole full
macronucleus
micronucleus
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Ciliate Conjugation

• Most ciliates have two different nuclei
• Large macronucleus
• Smaller micronucleus
• Micronucleus participates in sexual reproduction
  (conjugation)
• Partners exchange micronuclei

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Apicomplexans

• Parasitic alveolates equipped with a microtubular
  device that can attach to and penetrate a host
  cell
• More than 4,000 apicomplexan species are known to
  parasitize animals ranging from insects to humans
• Include four species of Plasmodium that cause
  malaria

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Malaria

• Symptoms have been known for more than 2,000
  years
• Most prevalent in tropical and subtropical parts
  of Africa
• Kills a million Africans each year
• Transmitted by Anopheles mosquitoes

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Plasmodium Life Cycle
sporozoites
sporozoites
Gametes form in mosquito gut, combine to form
zygotes
merozoite
Offspring enter blood, cause malarial symptoms
Male and female gametocytes in blood
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Dinoflagellates

• Single-celled alveolates that most often have
  cellulose plates just beneath the plasma
  membrane, a flagellum at the posterior end, and
  another one in a groove that runs around the cell
  body
• Include key producers in freshwater and marine
  habitats

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Algal Blooms

• Huge increases in populations of aquatic
  protists, most often dinoflagellates
• Example is a red tide

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The Stramenopiles

• Flagellated stramenopiles are among the most
  ancient eukaryotic lineages
• Include oomycotes, chrysophytes, and brown algae

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Oomycotes

• Heterotrophs
• Include water molds, downy mildews, and white
  rusts
• Phytophthora ramorum is responsible for sudden
  oak death

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Chrysophytes

• Mainly free-living photosynthetic cells
• Four groups
• - Golden algae - Diatoms
• - Yellow-green algae - Coccolithophores

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Brown Algae

• Most live in temperate or cool seas
• Range from microscopic filaments to plantlike
  forms 30 meters tall
• Include the kelps, the largest of the protists

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Red Algae

• 6,000 species
• Most abundant in tropical seas
• Can grow at great depths
• Complex life cycles may include very different
  forms

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Green Algae

• Resemble plants
• Chlorophylls a and b
• Starch grains in chloroplasts
• Cell walls of cellulose, pectins

Ulva
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Plasmodial Slime Molds

• Cell walls break down during aggregation
• Plasmodium migrates, then differentiates to form
  spore-bearing structures

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Cellular Slime Mold
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Fungal Classification

• Fungi known from 900 mya
• 56,000 known species
• Three major lineages
• Zygomycota
• Ascomycota (sac fungi)
• Basidiomycota (club fungi)
• Imperfect fungi are those not yet classified

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Fungi Are Heterotrophs

• Cannot carry out photosynthesis
• Must acquire organic molecules from the
  environment
• Most are saprobes
• Get nutrients from nonliving organic matter
• Some are parasites
• Extract nutrients from a living host

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Fungi as Decomposers

• Break down organic compounds in their
  surroundings
• Fungi carry out extracellular digestion and
  absorption
• They secrete enzymes that digest organic matter
  into bits cells can absorb
• Plants benefit because some carbon and nutrients
  are released

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A Variety of Roles

• In addition to their roles in lichens,
  mycorrhizae, and as decomposers, fungi are also
• Pathogens of plants, animals, humans
• Spoilers of food supplies
• Used to manufacture substances
• Antibiotics
• Cheeses

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Fungal Life Cycle

• No motile stage
• Asexual and sexual spores produced
• Spores germinate after dispersal
• In multicelled species, spores give rise to a new
  mycelium

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The Mycelium

• Most fungi produce a multicellular feeding
  structure called a mycelium
• It consists of branching tubular cells called
  hyphae
• Cell walls contain chitin

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Extracellular Digestion

• Mycelium grows into food source
• Tips of hyphae secrete digestive enzymes
• Enzymes break down organic material into simple
  forms that can be absorbed by hyphae

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Diversity of Club Fungi

• 25,000 species
• Mushrooms
• Shelf fungi
• Coral fungi
• Stinkhorns
• Puffballs

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Some Club Fungi

• Agaricus brunnescens
• commonly sold edible mushroom
• Armillaria bulbosa
• one of the largest known organisms
• Amanita phalloides
• death cap mushroom

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Club Fungus Life Cycle
Diploid Stage
nuclear fusion
meiosis
Haploid Stage
spore (n)
Cells with two nuclei (n n) form on gills
Spores are released
gills
Spores germinate, mycelium forms
cap
stalk
cytoplasmic fusion
dikaryotic (n n) mycelium
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Fungal Spores

• Made up of one or a few cells
• Can resist dehydration
• Remain dormant until environmental conditions
  favor germination
• May be produced asexually or sexually
• Fungal classification is based on type of sexual
  spores

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A Zygomycete Life Cycle - 1

• Rhizopus stolinifer can reproduce sexually or
  asexually
• Sexual reproduction occurs, then hyphae of mating
  strains meet
• At the point of contact, the hyphae form
  gametangia

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A Zygomycete Life Cycle - 2

• Tips of gametangia fuse to form a zygosporangium
• Nuclei inside the zygosporangium fuse to produce
  a diploid zygospore
• Zygospore may remain dormant
• Eventually zygote nuclei undergo meiosis to
  produce haploid spores

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Life Cycle of Rhizopus
zygospore (2n)
Diploid Stage
nuclear fusion
meiosis
Haploid Stage
spores (n)
germinating zygospore
young zygospore
mycelium develops from germinated spore
spores (n)
gametangia fusing
stolon
stolon
ASEXUAL REPRODUCTION
contact between hyphae of two mating strains
rhizoids
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Sac Fungi

• Produce sexual spores in sac-shaped cells call
  asci
• Multicelled species form reproductive structures
  made of tightly woven hyphae that enclose the
  asci
• Include
• Edible morels and truffles
• Saccharomyces cerevisiae yeast for bread making

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Fungal Foes

• Most fungi are vital decomposers and plant
  symbionts
• A small proportion are plant pathogens
• A tiny minority adversely affect human health

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Human Pathogens Toxins

• Fungi cause
• Histoplasmosis
• Valley fever
• Candida (yeast) infections
• Ringworm
• Athlete's foot
• Ergotism
• Eating some basidiomycetes can be fatal

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Histoplasmosis

• Respiratory disease
• Caused by inhalation of spores of Ajellomyces
  capsulatus
• Spores are found in soil, especially where there
  are bird or bat droppings
• Can be fatal in people with weakened immune
  systems

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Claviceps purpurea

• Fungus that parasitizes cereal grains
• Produces alkaloids
• Some have been used medically
• Ingestion causes ergotism
• Hallucinations, vomiting, diarrhea

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Fungi as Mutualists

• Endophytic fungi
• Lichens
• Mycorrhizae

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Endophytic Fungi

• Symbionts that live inside leaves and stems of
  most plants, with helpful or neutral effects

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Lichens

• Fungal mycobiont plus a photosynthetic photobiont
  
• Fungal component usually is ascomycete
• Photobiont is cyanobacteria or green algae
• Fungus composes bulk of the structure

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Lichen Cross Section
dispersal fragment
photosynthetic species
outer fungal cells
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Ecological Roles of Lichens

• Survive in hostile habitats and colonize new
  habitats
• Absorb mineral ions from substrates
• Cyanobacteria-containing lichens can fix nitrogen
• Convert atmospheric nitrogen to a form plants can
  use

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Mycorrhiza

• Fungus-root
• Mutualism between a fungus and a tree root
• Fungus gets sugars from plant
• Plant gets minerals from fungus
• Many plants do not grow well without mycorrhizae

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Fungi in Decline?

• Numbers and kinds of mushrooms are declining
• Decline correlates with rising air pollution
• If the fungal symbionts of trees and other plants
  are killed, ecosystems will be disrupted