Protista

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Protista

• A World in a Drop of Water

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A World in a Drop of Water

• Even a low-power microscope
• Can reveal an astonishing menagerie of organisms
  in a drop of pond water

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The Diversity of Protists

• Morphological Diversity
• Organelles
• Divide a Large Cell into Compartments
• Structures for Support and Protection
• Nutrition
• Photoautotrophs
• Heterotrophs
• Mixotrophs
• Habitat
• Fresh water
• Marine
• Reprodution
• Sexual and Asexual
• Variation in Life Cycles

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Endosymbiosis in Eukaryotic Evolution

• considerable evidence
• protist diversity has its origins in
  endosymbiosis
• plastid-bearing protists
• Evolved into red algae and green algae
• Red algae and green algae
• underwent secondary endosymbiosis
• they were ingested
• Diversity of plastids produced by secondary
  endosymbiosis

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The Endosymbiosis Theory

• Symbiosis occurs when individuals of two
  different species live in physical contact
• Endosymbiosis occurs when an organism of one
  species lives inside an organism of another
  species.

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Supporting Data

• Mitochondria and chloroplasts are about the size
  of an average bacterium.
• Both organelles replicate by fission, as do
  bacteria, and have their own ribosomes to
  manufacture their own proteins.
• Mitochondria and chloroplasts have genes that
  code for the enzymes needed to replicate and
  transcribe their own genomes.
• Both organelles have double membranes, consistent
  with the engulfing mechanism.

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Impacts on Human Healthand Welfare

• The most spectacular crop failure in history,
  the Irish potato famine, was caused by a protist
  Phytophthora infestans.

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Malaria

• Malaria, the world's most chronic public health
  problem, is caused by Plasmodium

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Other Human Health Problems Caused by Protists
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Ecological Importance of Protists

• Protists represent just 10 of the total number
  of named eukaryotic species and have relatively
  low diversity but are extraordinarily abundant.

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Primary Producers.

• Species that produce chemical energy by
  photosynthesis
• Diatoms
• rank among the leading primary producers in the
  oceans
• abundant
• Production of organic molecules in the worlds
  oceans
• responsible for almost half of the total carbon
  that is fixed on Earth.

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Protists Play a Key Role in Aquatic Food Chains

• Bacteria and photosynthetic protists are primary
  producers in the aquatic food chain
• A food chain describes nutritional relationships
  among organisms.

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Plankton and Phytoplankton

• Plankton
• Small organisms that live near the surface of
  oceans or lakes
• drift along or swim only short distances
• Phytoplankton
• photosynthetic species of plankton
• organic compounds producedare the basis of food
  chains in freshwater and marine environments

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Protists Act as Carbon Sinks

• Play key role in the global carbon cycle
• Could help reduce global warming
• Carbon sink
• a long-lived carbon reservoir.

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Themes in the Diversification of Protists

• Several general evolutionary themes tie together
  the diversity of eukaryotes.
• The key to understanding the protists is to
  recognize that a series of important innovations
  occurred, often repeatedly, as eukaryotes
  diversified.

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Morphological Diversity

• Metabolism inside the eukaryotic cell can
  outstrip the cell's transport and exchange
  capabilities because as cells get larger, the
  surface area/volume ratio decreases.

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Organelles Divide a Large Cell into Compartments

• Eukaryotes solve the problem of size by dividing
  their cell volume into compartments

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The Evolution of Multicellularity

• Eukaryotic cells have many internal compartments
  with distinct, specialized functions.
• After ingesting a bacterium, for example, a
  Paramecium surrounds it with an internal
  membrane, forming a compartment called a food
  vacuole.
• When the food has been digested and nutrients
  have diffused out of the food vacuole, the
  vacuole merges with the plasma membrane at the
  anal pore and expels waste molecules
• The cytoskeleton supports and organizes the
  interior of the cell, including the organelles

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The Evolution of Multicellularity

• Differentiation of cell types is a crucial
  criterion for defining multicellularity.
• In contrast, colonial growth defines groups of
  cells that all perform the same function

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Structures for Supportand Protection

• Protists have a complex intracellular structure
• many have a rigid internal skeleton or a hard
  external structure that provides support or
  protection, or both
• shell
• test

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Ingestive Feeding

• Some protists are large enough to surround and
  ingest other protists through engulfment by long,
  fingerlike projections called pseudopodia

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• Species that feed by beating their cilia to
  create water currents often attach themselves to
  a substrate and collect food by sweeping
  particles into their mouths Organisms that filter
  food out of water in this way are called filter
  feeders, or suspension feeders.

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Absorptive Feeding

• Absorptive feeding occurs when nutrients are
  taken up directly from the environment.
  Decomposers feed on dead organic matter, or
  detritus. Parasites live inside other organisms
  and absorb their nutrition directly from the
  environment inside their host, causing damage to
  the host (Figure 28.16).

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Photosynthesis

• A wide variety of protists are photosynthetic.
  The major photosynthetic groups of protists are
  distinguished by the pigments they contain and
  many live symbiotically with animals or other
  protists.

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Key Lineages of Protists

• Excavata
• Excavata - Diplomonadida
• Excavata - Parabasalida
• Discicristata
• Discicristata - Euglenida
• Alveolata
• Alveolata - Ciliata
• Alveolata - Dinoflagellata
• Alveolata - Apicomplexa

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Key Lineages of Protists

• Stramenopila (Heterokonta)
• Stramenopila - Oomycota
• Stramenopila - Diatoms
• Stramenopila - Phaeophyta (Brown Algae)
• Cercozoa
• Cercozoa - Foraminifera
• Plantae
• Rhodophyta (Red Algae)
• Amoebozoa
• Myxogastrida (Plasmodial Slime Molds)

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Evaluating Molecular Phylogenies

• Current phylogenetic tree based on sequence data
  
• Eight major lineages of eukaryotes
• Paraphyletic
• they do not constitute all the descendants of a
  single common ancestor

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Excavata

• Are adapted to anaerobic environments
• Lack plastids
• Mitochondria that lack
• DNA
• an electron transport chain
• citric-acid cycle enzymes
• Diplomonads (e.g., Giardia)
• two nuclei
• lack a cell wall
• reproduce asexually
• Parabasalids (e.g., Trichomonas)
• lack a cell wall
• reproduce asexually (some also reproduce
  sexually)
• feed by engulfing

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Diplomonads

• Diplomonads
• Have two nuclei and multiple flagella

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Parabasalids

• Parabasalids include trichomonads
• Which move by means of flagella and an undulating
  part of the plasma membrane

Flagella
Undulating membrane
5 µm
(b) Trichomonas vaginalis, a parabasalid
(colorized SEM)
Figure 28.5b
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Discicristata

• Euglenids
• lack an external wall
• reproduce asexually
• most ingest bacteria or other small cells
• have flagella with a unique internal structure
• Clade includes
• predatory heterotrophs
• photosynthetic autotrophs
• pathogenic parasites

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Kinetoplastids

• Kinetoplastids
• Have a single, large mitochondrion that contains
  an organized mass of DNA called a kinetoplast
• Include free-living consumers of bacteria in
  freshwater, marine, and moist terrestrial
  ecosystems

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Kinetoplastid

• The parasitic kinetoplastid Trypanosoma
• Causes sleeping sickness in humans

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Alveolata

• Ciliates
• micronucleus and macronucleus
• reproduce asexually or by conjugation
• use cilia for locomotion
• spiral or crystalline rod of unknown function
  inside their flagella
• Dinoflagellates
• About half are photosynthetic
• asexual and sexual reproduction occur.
• Cells from sexual reproduction may form tough
  cysts that allow them to remain dormant

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Alveolata

• Apicomplexans
• Are parasites of animals and some cause serious
  human diseases
• apex, contains a complex of organelles
  specialized for penetrating host cells and
  tissues
• Have apicoplast
• a nonphotosynthetic plastid, the

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Alveolates

• Members of the clade Alveolata
• Have membrane-bounded sacs (alveoli) just under
  the plasma membrane

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Dinoflagellates

• Each has a characteristic shape
• That in many species is reinforced by internal
  plates of cellulose
• Two flagella
• Make them spin as they move through the water

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Red Tides

• Rapid growth of some dinoflagellates
• Is responsible for causing red tides, which can
  be toxic to humans

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Apicomplexa

• Parasitic
• Apical complex at one end
• specialized for penetrating cells
• Membrane-bounded sacs (alveoli) just under the
  plasma membrane
• Reproduce
• sexually
• asexually

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