Protista

• The oldest widely accepted fossils of eukaryotes are of

  single-celled organisms that lived 1.8 billion years ago.
• eukaryotic cells have more

  complex organization than prokaryotic cells:
• endosymbiosis

  when a prokaryotic cell engulfed a small cell

  that would evolve into an organelle found in all

  eukaryotes, the mitochondrion.
• The small,

  engulfed cell is an example of an

  endosymbiont,
• a cell that lives within another

  cell, called the host cell.
• Serial endosymbiosis – a

  hypothesis for the origin of

  mitochondria and plastids.
• The proposed host cell was an

  archaean.
• The proposed ancestors of

  mitochondria were aerobic,

  heterotrophic bacteria,
• the

  proposed ancestors of plastids were

  photosynthetic bacteria.
• Protists

  ▫ a diverse collection of mostly unicellular

  eukaryotes.
• eukaryotes that are not plants, animals, or fungi.

  Protists
• autotrophs, producing their food by

  photosynthesis (e.g. algae)
• mixotrophs (capable of both photosynthesis

  and heterotrophy, depending on availability of light and

  nutrients, e.g. Euglena)
• Heterotrophs are organisms that cannot produce their own food and rely on consuming other organisms for energy. (e.g. protozoans, parasites)
• Free-living protists

  ▫ Mostly aquatic.

  Terrestrial habitat such as damp soil and leaf litter
• zooplankton, a population of organisms that constitutes

  one of the primary sources of energy in aquatic

  ecosystems
• Parasitic protists

  ▫ Several species cause a variety of serious human diseases

  including malaria, dysentery, and giardiasis
• SAR Stands for Stramenopila, Alveolata, and Rhizaria,
• SAR: Stramenopiles

  Unifying feature:

  presence of a textured,

  or “hairy,” flagellum
• SAR: Stramenopiles

  DIATOMS

  ▫ Unicellular algae; one of the most important

  photosynthetic organisms on Earth

  ▫ the organic molecules these microscopic algae

  produce are a key source of food in all aquatic

  environments.

  ▫ Some diatoms store food reserves in the form of lipid

  droplets as well as carbohydrates.
• SAR: Stramenopiles

  BROWN ALGAE

  ▫ include many of the species commonly called

  seaweeds.

  ▫ We use the word seaweeds here to refer to marine

  algae that have large multicellular bodies but lack the

  roots, stems, and leaves found in most plants

  ▫ Fish, sea lions, sea otters, and gray whales regularly

  use these kelp “forests” as their feeding grounds.
• Brown algae called Kelp

  Anchored to the seafloor by rootlike

  structures, kelp may grow to heights

  of 60 m, taller than a 15-story

  building
• SAR: Stramenopiles

  WATER MOLDS

  ▫ Heterotrophic, unicellular stramenopiles that typically

  decompose dead plants and animals in freshwater

  habitats.

  ▫ also include plant parasites such as the notorious

  genus Phytophthora, whose name comes from Greek

  roots meaning plant destroyer

  ▫ causes late blight of potato, the disease responsible for

  a devastating famine in Ireland in the mid-1800s
• Alveolates

  • Dinoflagellates

  • Ciliates
• DINOFLAGELLATES

  ▫ A diverse group that includes unicellular autotrophs,

  heterotrophs, and mixotrophs, are also very common

  components of marine and freshwater
• plankton

  (communities of organisms that drift in aquatic

  environments).
• Blooms - population explosions—of autotrophic

  dinoflagellates
• warm coastal waters

  to turn pinkish orange, a phenomenon known as red

  tide
• CILIATES

  ▫ named for their use of cilia to move and to sweep

  food into their oral groove, or cell mouth
• 
  

  ▫ Paramecium, a common freshwater protist
• Plasmodium, causes malaria, kills half a million

  people a year.
• SAR: Rhizaria

  Unifying feature:

  threadlike or needle-like

  pseudopodia
• The two largest groups in Rhizaria, foraminiferans and

  radiolarians,
• Amoebas move and feed by means of thread-like
• (rather than tube or lobe-shaped) pseudopodia

  , which are temporary

  extensions of the cell.
• Which groups of Stramenopila, Alveolata,

  and Rhizaria include autotrophs?

  Stramenopila: diatoms, brown algae

  Alveolata: dinoflagellates

  Rhizaria: none
• Supergroup Excavata

  Include protists with

  excavated feeding

  groove
• Many excavates have modified mitochondria that lack

  functional electron transport chains and use anaerobic

  pathways, such as glycolysis, to extract energy
• Trichomonas vaginalis is a common sexually

  transmitted parasite that causes an estimated 4

  million new infections each year. The parasite travels

  through the reproductive tract by moving its flagella

  and undulating part of its membrane.
• Trypanosoma are parasites that can be transmitted to

  humans by insects.