Protists

1
Protists

• Chapter 28

2
YOU MUST KNOW

• Protista are no longer considered a kingdom.
• How chloroplasts and mitochondria evolved through
  endosymbiosis.
• The major clades of protists text page 598.

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The Classification of Protists

• Most eukaryotes are single-celled organisms!
• The term protist is now used to refer to any
  eukaryote that is neither a plant, animal, or
  fungi.
• Biologists no longer consider Protista a kingdom
  because it is paraphyletic.
• Protists vary in structure and function more so
  than any other group of eukaryotes.
• Most are unicellular
• Most use aerobic metabolism and have mitochondria.

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Endosymbiosis

• Mitochondria and chloroplasts evolved through
  endosymbiosis. They were originally unicellular
  organisms engulfed by other cells that ultimately
  became organelles in the host cell.

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Groups of Protists

• There are three major categories of protist
• Plant-Like (photosynthetic algae)
• Animal-Like (heterotrophic protozoans)
• Fungus-Like (absorptive)
• Most protists are aquatic and are important
  constituents of plankton.
• All protists are capable of asexual reproduction,
  but some may reproduce sexually as well.
• Many other protists live as symbionts in other
  organisms.
• Because they are such a diverse group, the
  classification of protists continues to undergo
  revision.

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Protozoa Animal-Like Protists

• Includes all protists that ingest food.
• Rhizopoda the amoebas that travel from place to
  place using pseudopods (false feet) that are
  extensions of their cells. As they eat, they
  undergo phagocytosis.
• Foraminifera Marine protists whose name is
  derived from the word foramen because of the
  presence of calcium carbonate shells full of
  holes.
• Actinopoda Major constituent of plankton.
• Apicomplexa Parasitic protists (formerly known
  as sporozoans). An example is plasmodium, the
  causative agent of malaria.
• Zooflagellates known for their flagella and can
  be parasitic. Tryanosoma causes African sleeping
  sickness.
• Ciliophora use cilia to travel. Live in water
  and have two types of nuclei a macronucleus
  (controls daily activities) and a micronuclei
  (functions in conjugation. Paramecium is an
  example.

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• Exploring structure and function in a ciliate

Contractile Vacuole
Figure 28.12
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Life Cycle of Plasmodium
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Ecology of Animal Like Protists

• Not so Good Can be parasitic/cause disease
• Malaria, African Sleeping Sickness,
  Cryptosporidium
• Good Symbiosis
• Termites have beneficial animal like protists
  called Trichonympha in their stomachs
• Break down cellulose in wood so termites can use
  it as food

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Molds Fungus-Like Protists

• Fungus-like protists include slime molds and
  water molds.
• Myxomycota heterotrophic includes plasmodial
  slime molds they do not eat alone, but instead
  they eat and grow as a single, clumped
  unicellular mass known as a plasmodium.
• Acrasiomycota the cellular slime molds, when
  food is plentiful, they eat alone as solitary
  beingsbut when food becomes scarce, they clump
  together in a manner similar to slime molds and
  work together as a unit.
• Oomycota the water molds can be parasitc or
  saprobes. Use filaments known as hyphae to
  release digestive enzymes on food. Often found
  to be multicellular, or coenocytic.

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Life Cycle of a Plasmodial Slime Mold
12
The life cycle of a cellular slime mold
(Dictyostelium)
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Ecology of Fungus-Like Protists

• The ecological impact of oomycetes can be
  significant
• Phytophthora infestans causes late blight of
  potatoes Irish Potato Famine
• Overgrowth of water mold caused by wet and cool
  conditions
• Slime molds and water molds are the MOST
  important recyclers of organic material
• Why is the earth not littered with dead
  organisms?
• Tissues broken down by Fungi Like Protists and
  other decomposers

14
Algae Plant-Like Protists

• Dinoflagellates have 2 flagella, important
  producers in aquatic food chains.
• Golden Algae chrysophyta, constituent of
  plankton.
• Diatoms bacillariophyta, major constituent of
  phytoplankton most abundant organisms on Earth
  - have cell walls made of silica to protect them
  (diatomaceous Earth/fossilized diatom walls).
  Major primary producers in freshwater ecosystems!
• Green Algae chlorophyta have chlorophyll a and
  b.
• Brown Algae phaeophyta multicellular and live
  in marine environments (kelp and seaweed),
  contain fucoxanthin pigments.
• Red Algae rhodophyta contain phycobilin
  pigments, mostly multicellular, live in ocean.
  Many live in deep water and absorb nonvisible
  light via accessory pigments.

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Euglenophytes
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Algal Blooms
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Red Tides

• Great blooms of the dinoflagellates have occurred
  in recent years on the east coast.
• These blooms are known as red tides.
• These species release a potentially harmful toxin
  that infect certain shellfish.
• Eating these infected shellfish can be harmful or
  fatal.

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Ecology of Plant-Like Protists

• Most unicellular species beneficial
• Act as producers in the marine food chain
• Form Phytoplankton for consumer organisms to eat
• Approx. ½ of the photosynthesis on earth!!!
• Produce large amount of oxygen
• Symbiosis Coral Reefs, Clams
• Provide food via photosynthesis, receive a home

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Beneficial Aspects of Algae

• Food for humans
• Food for invertebrates and fishes in mariculture
• Animal feed
• Soil fertilizers and conditioners in agriculture
• Treatment of waste water
• Diatomaceous earth ( diatoms)
• Chalk deposits
• Phycocolloids (agar, carrageenan from red algae
  alginates from brown algae)
• Drugs
• Model system for research
• Phycobiliproteins for fluorescence microscopy

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Detrimental Aspects of Algae

• Blooms of freshwater algae
• Red tides and marine blooms
• Toxins accumulated in food chains
• Damage to cave paintings, frescoes, and other
  works of art
• Fouling of ships and other submerged surfaces
• Fouling of the shells of commercially important
  bivalves