Chapter 28 Protista The Origins of Eukaryotic Diversity

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Chapter 28 Protista
The Origins of Eukaryotic Diversity

• Overview
• Protista In the past, a single kingdom
• Note some closely related
• to Plants
• to Fungi
• or to Animals
• (So kingdom Protista has been abandoned !!!
  and
• various lineages are recognized as kingdoms in
  their own right)
• But protist , eukaryotes that are not plants,
• animals, or fungi

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• Protists Are Extremely Diverse
• With high structural and functional diversity
• Most, unicellular, but colonial and multicellular
  
• Complex cellular a single cell carry out all
  basic functions of specialized cells in a
  multicellular organism

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• Nutrition most diverse of all eukaryotes
• Some are Photoautotrophs, containing
  chloroplasts.
• or Heterotrophs, absorbing
  organic molecules
• or Ingesting food particles
• or Mixotrophs, combining
  photosynthesis
• and heterotrophic nutrition
• Based on their roles in biological communities
  three groups
• a- Photosynthetic algal protists
• b- Ingestive protozoans
• c- absorptive protists
• Very diverse habitats
• Life cycles vary greatly
• a- exclusively asexual
• b- sexual life cycles, meiosis and syngamy
  (The fusion of two gametes in fertilization)

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• Protistan Diversity
• 1. modified mitochondria
• In Diplomonads and parabasalids (found in
  anaerobic environments)
• a- No plastids
• b- No DNA in their mitochondria
• c- electron transport chain (ETC), and the
  enzymes needed
• for the citric acid cycle
• d- Diplomonads have two equal-sized nuclei
  and multiple flagella
• example Giardia intestinalis parasite
  that lives in the intestines
• of mammals and causes
  diarrhea
• dormant stage Giardia
  contaminated drinking water
• from feces containing the
  parasite

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• Parabasalids include trichomonads
• Example Trichomonas vaginalis, inhabits the
  vagina of human females
• T. vaginalis outcompete beneficial bacteria and
  infect the vaginal lining when the normal acidity
  of the vagina is disturbed
• The male urethra may also be infected but without
  symptoms
• The infection is sexually transmitted.
• Genetic studies of T. vaginalis suggest that non
  pathogenic species transformed by horizontal gene
  transfer from other vaginal bacteria, the gene
  allows T. vaginalis to feed on epithelial cells

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• 2. Internal structure
• Euglenozoans have flagella with a unique
  internal structure
• Euglenozoa (a clade) that includes
• a- predatory heterotrophs
• b- photosynthetic autotrophs
• c- pathogenic parasites
• Distinguished by
• a- Presence of a spiral or crystalline rod
  inside their flagella
• b- disc-shaped mitochondrial cristae
  (infoldings)
• The best-studied groups of euglenozoans are the
  kinetoplastids and euglenids

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• The kinetoplastids
• single large mitochondrion associated with a
  unique organelle, the kinetoplast, carrying
  extranuclear DNA
• symbiotic and include pathogenic parasites
• example,Trypanosoma causes
• African sleeping sickness, a disease
  spread by
• the African tsetse fly
• Chagas disease (leads to congestive
  heart failure)
• transmitted by bloodsucking bugs
• Trypanosomes evade immune detection by switching
  surface proteins from generation to generation,
  preventing the host from developing immunity
• One-third of Trypanosomas genome codes for these
  surface proteins

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• Euglenids
• Characterized by
• a- an anterior pocket from which one or two
  flagella emerge
• b- unique glucose polymer, paramylon (storage
  molecule)
• c- Euglena are autotrophic but can become
  heterotrophic in the dark
• d- Light detector swelling near the base of
  the long flagellum detects light that is not
  blocked by the eyespot as a result, Euglena
  moves toward light of appropriate intensity, an
  important adaptation that enhances photosynthesis
  
• e- Long flagellum
• f- Short flagellum
• g- Nucleus
• h- Plasma membrane
• i- Paramylon granule
• j- Chloroplast
• k- Contractile vacuole
• l- Eyespot pigmented organelle that
  functions as a light shield, allowing light
  from only a certain direction to strike the light
  detector
• m- Pellicle protein bands beneath the plasma
  membrane that provide strength and flexibility (
• Note Euglena, no cell wall
• Other euglenids can phagocytose prey

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Light detector swelling near the base of the
long flagellum detects light that is not blocked
by the eyespot as a result, Euglena moves toward
light of appropriate intensity, an important
adaptation that enhances photosynthesis
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• 3. Sacs beneath the plasma membrane
• Alveolates
• Alveolata (a clade) have alveoli, small
  membrane-bound cavities, under the plasma
  membrane
• Alveoli function is not known, but they may help
  stabilize the cell surface or regulate water and
  ion content
• Alveolata includes
• flagellated protists (dinoflagellates)
• 2) parasites (apicomplexans)
• 3) ciliates.

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• Apicomplexans
• parasites of animals
• some cause serious human diseases
• Sporozoites (tiny infectious cells)
• The parasites spread through their host as
  sporozoites
• The sporozoites have at their apex a complex
  of
• organelles specialized for penetrating
  host cells and
• tissues of the host
• Nonphotosynthetic plastid (apicoplast vital
  functions including the synthesis of fatty acids)
• Intricate life cycles
• (sexual and asexual stages and often require
  two or more different host species for
  completion. Example Plasmodium, the parasite
  that causes malaria, spends part of its life in
  mosquitoes and part in humans)

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The two-host life cycle of Plasmodium, the
apicomplexan that causes malaria
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• The Malaria, a human disease
• Caused by Plasmodium, (spends part of its life in
  mosquitoes (Anopheles) and part in humans)
• Managed In the 1960s through
• a- insecticides against the Anopheles
  mosquitoes
• b- drugs that killed the parasites in humans
• But
• Resistant varieties of Anopheles, to
  insecticides made
• Plasmodium come back ( 300 million people
  are infected in the tropics, and up to 2 million
  die each year)

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• Plasmodium can escape from the immunity system
  (is evasive)
• It can change its surface protein
• No successful vaccine developed
• thereby changing its face to the human
  immune system
• It spends most of its time inside human
  liver and blood cells
• The expression of most of the Plasmodiums
  genes at specific points in its life cycle
  identified (2003)? potential new targets for
  vaccines
• Chloroquine (an antimalarial drug)
• but malaria Plasmodium developed
  resistance
• Identification of the resistance gene
• block drug resistance in Plasmodium

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• Ciliates
• a- diverse group of protists
• b- use of cilia to move and feed
• c- cilia
• cover the cell surface
• clustered into rows or tufts
• leg-like structures constructed from many
  cilia
• cilia are associated with a submembrane
• ciliary movements coordinated by
• submembrane system of microtubules

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• Ciliates Nuclei
• Two types of nuclei
• 1- Macronuclei, large macronucleus (general
  cell regulation)
• 2- Micronuclei, tiny micronucleus
  (reproduction)
• Macronucleus has dozens of copies of the
  ciliates genome.
• The genes are not organized into chromosomes
  but are
• packaged into small units with
  duplicates of a few genes
• Genes control the everyday
  functions of the cell such as
• feeding, waste removal, and
  water balance
• Ciliate reproduction
• generally, asexually by binary fission of the
  macronucleus (no mitotic division)
• ExampleParamecium caudatum

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Paramecium conjugation

• Genetic variation results from the sexual
  shuffling of genes which occurs through
  conjugation, during which two individuals
  exchange haploid micronuclei.
• In ciliates, reproduction and conjugation are
  separate processes.
• In a real sense, ciliates have sex without
  reproduction.

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• 4. Stramenopiles have hairy and smooth flagella.
• The clade Stramenopila includes both
  heterotrophic and photosynthetic protists (some
  group of algae).
• The name of this group is derived from the
  presence of numerous fine, hairlike projections
  on the flagella.
• The heterotrophic stramenopiles, the oomycetes,
  include water molds, white rusts, and downy
  mildews.
• Stramenopile flagella
• Many oomycetes have multinucleate filaments that
  resemble fungal hyphae.

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• Diatoms
• unicellular algae
• highly diverse group of protists, with an
  estimated 100,000 species
• They are abundant members of both freshwater
  and marine plankton
• store food reserves as the glucose polymer
  laminarin or, in a few diatoms, as oil
• glasslike walls composed of hydrated silica
  embedded in an organic matrix
• Wall divided into two parts that overlap
  (like a shoebox and lid)
• walls allow live diatoms to withstand immense
  pressure
• defense for them from the crushing jaws of
  predators
• Massive accumulations of fossilized diatoms
  are major constituents of diatomaceous earth
• Reproduction
• diatoms reproduce asexually by mitosis
• each daughter cell receiving half of the cell
  wall and regenerating a new second half
• Some species form cysts as resistant stages
• Sexual stages are not common
• Sexual, involves the formation of eggs and
  amoeboid or flagellated sperm

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• Brown algae, or phaeophytes, (Seaweeds)
• The largest and most complex protists known
• Multicellular
• most species are marine
• Common along temperate coasts in areas of cool
  water and adequate nutrients
• Their brown or olive color presence of
  carotenoids in their plastids
• Seaweeds (largest marine algae),
• Brown, Red, green
• Habitat
• the intertidal and subtidal zones of
  coastal waters
• (This environment is characterized by extreme
  physical conditions, including wave forces and
  exposure to sun and drying conditions at low
  tide)
• Anatomy
• complex multicellular anatomy
• some differentiated tissues and organs that
  resemble those in plants
• thallus, or body, of the seaweed.
• a root-like holdfast
• a stem-like stipe,
• Leaf-like photosynthetic blades

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• The term seaweed refers to brown algae as well
  as some species of green and red algae.
• The giant seaweeds known as kelps live in deep
  water beyond the intertidal zone (Kelp forest)
• The stipes of these algae may be as long as 60 m
• Intertidal zone Seaweeds
• cope with rough water
• twice-daily low tides (expose the algae to hot
  sun and risk of desiccation)
• Seaweeds as sources of food and commodities
• Many seaweeds are eaten by coastal people,
• Laminaria (kombu in Japan) in soup
• Porphyra (Japanese nori)
• sushi wraps
• Gel-forming substances, extracted in commercial
  operations
• Algin from brown algae
• Agar and carrageen from red algae are used
  as thickeners in
• food, lubricants in oil drilling, or
  culture media in microbiology

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• 5. Cercozoans have threadlike pseudopodia
• Cercozoa a newly recognized clade
• Contains the amoebas (amoeba protists that
  move and feed by means of pseudopodia)
• Pseudopodia, cellular extensions that bulge from
  the cell surface
• Amoeba movement,
• It extends a pseudopodium and anchors
  the tip
• Cytoplasm then streams into the
  pseudopodium
• Cercozoa amoeba threadlike pseudopodia
• Cercozoans include
• Foraminiferans and are closely related to
  Radiolarians,
• which also have
  threadlike pseudopodia

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• Foraminiferans, or forams
• Named for their porous shells, or tests.
• Forams have
• multi-chambered, porous shells,
  consisting of
• organic materials hardened with
  calcium carbonate
• Pseudopodia extend through the pores
  for swimming,
• shell formation, and feeding
• symbioses with algae
• live in marine and fresh water
• Most live in sand or attach to rocks
  or algae
• abundant in the plankton
• forams fossils (90 of the described
  forams)
• calcareous skeletons of forams are
  important components
• of marine sediments
• Note Fossil forams are often used as
  chronological markers
• to correlate the ages of sedimentary
  rocks from different
• parts of the world.

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• 6. Amoebozoans have lobe-shaped pseudopodia
• Many species of amoebas that have lobe-shaped
  pseudopodia belong to the clade Amoebozoans, a-
  gymnamoebas
• 
  b- entamoebas
• 
  c- slime molds

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• 7. Red algae and green algae
• closest relatives of land plants
• Red algae have no flagellated stages in their
  life cycle (other eukaryotic algae do)
• More than 6,000 known species of red algae,
• Reddish due to the accessory pigment
  phycoerythrin
• Coloration varies among species
• Coloration depends on the depth that they
  inhabit
• Some species lack pigmentation
• Not pigmented, parasites on other red algae.

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• Red algae are the most common seaweeds in the
  warm coastal waters of tropical oceans
• Inhabit deeper waters than other photosynthetic
  eukaryotes
• Phycobilins (photosynthetic pigment) allows
  them to absorb blue and green wavelengths that
  penetrate down to deep water, more than 260 m
  (Bahamas cost)
• Some red algae live in fresh water or on land.
• Most red algae are multicellular, with some
  reaching a size large enough to be called
  seaweeds.

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• The thalli of many red algal species are
  filamentous
• The base of the thallus is usually differentiated
  into a simple holdfast
• The life cycles of red algae are especially
  diverse
• In the absence of flagella, fertilization depends
  entirely on water currents to bring gametes
  together

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• Green algae
• grass-green chloroplasts
• Similar in ultrastructure and pigment
  composition
• to chloroplasts of plants
• Green algae and land plants are closely related
  evidence from
• Molecular systematics
• Cellular morphology provide considerable
  
• Divided into two main groups,
• a- Chlorophytes 7,000 species, most are
  identified
• b- Charophyceans.
• Most live in fresh water, but many are marine
  inhabitants.
• Some chlorophytes inhabit damp soil, while others
  are specialized to live on glaciers and
  snowfields

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• Snow-dwelling chlorophytes carry out
  photosynthesis despite
• subfreezing temperatures
• intense visible and ultraviolet radiation
• protected by radiation-blocking compounds
  in
• their cytoplasm and by the snow itself
  (shield)
• Some chlorophytes live symbiotically with fungi
  to form lichens, a mutualistic collective.
• Large size and complexity in chlorophytes has
  evolved by three different mechanisms
• Formation of colonies of individual cells (e.g.,
  Volvox).
• The repeated division of nuclei without
  cytoplasmic division to form multinucleate
  filaments (e.g., Caulerpa).
• The formation of true multicellular forms by cell
  division and cell differentiation (e.g., Ulva).

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• Some multicellular marine chlorophytes are
  seaweeds, large and complex
• Complex life cycles, with both sexual and asexual
  reproductive stages
• Most sexual species have biflagellated gametes
  with cup-shaped chloroplasts
• Alternation of generations evolved in the life
  cycles of some green algae
• The other main group of green algae are most
  closely related to land plants

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