Protists

1
Protists

• Chapter 28

2
Classifying Protists

• Protists are the most diverse of the four
  kingdoms in the domain Eukarya.
• artificial group of convenience
• single-celled organisms
• little consensus about classification

3
Protist Classification
4
Endosymbiosis

• Theory of endosymbiosis proposes that
  mitochondria originated as symbiotic, aerobic
  bacteria.
• Each mitochondrion has its own genome in a
  circular, closed molecule of DNA.
• divide by simple fission
• directed by nuclear genes

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Theory of Endosymbiosis
6
General Biology of the Protists

• Cell surface
• possess varied array of cell surfaces
• Locomotor organelles
• chiefly flagellar rotation or pseudopodial
  movement
• Cyst formation
• dormant form of a cell with resistant outer
  covering in which metabolism is essentially shut
  down

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General Biology of the Protists

• Nutrition
• employ all forms but chemoautotrophic
• phototrophs
• heterotrophs
• phagotrophs - visible food particles
• osmotrophs - food in soluble form

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General Biology of the Protists

• Reproduction
• typically reproduce asexually
• binary fission - equal halves
• budding - progeny cell smaller
• sexual reproduction in times of stress

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Euglenoids
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Euglenozoa

• Kinetoplastids
• Trypanosomes are kinetoplastids that cause many
  serious human diseases.
• African sleeping sickness
• Chagas

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Alveolata

• Dinoflagellates
• distinctive flagella, protective coats, and
  biochemistry
• reproduce primarily by asexual cell division
• responsible for red tides

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Alveolata

• Apicomplexes
• spore-forming animal parasites
• malarial parasite - Plasmodium

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Alveolata

• Ciliates
• most feature large numbers of cilia form vacuoles
  to ingest food and regulate water balance
• Paramecium

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Stramenopila and Rhodophyta

• Stramenopila
• includes brown algae, diatoms, and oomycetes
• brown algae - conspicuous seaweeds
• alternation of generations
• diatoms (phylum Chrysophyta) - photosynthetic,
  unicellular organisms with double shells of
  opaline silica

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Stramenopila and Rhodophyta

• Rhodophyta
• Red algae range in size from microscopic to very
  large.
• origin a source of controversy
• tentatively treated as a sister clade of green
  algae (Chlorophyta)

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Chlorophyta

• Green algae are the ancestors of the plant
  kingdom.
• extensive fossil record dating back 900 million
  years
• mostly aquatic
• Chlamydomonas well-known genus
• probably represents primitive state
• Chlorophyta did not give rise to land plants.

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Chlamydomonas Life Cycle
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Choanoflagellida

• Choanoflagellates are most like the common
  ancestor of the sponges.
• contain a single emergent flagellum surrounded by
  a funnel-shaped, contractile collar

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Amoebas

• contain pseudopods that can form at any point on
  the cell body and can move in any direction
• Phylum Actinopoda (radiolarians) secrete glassy
  exoskeletons of silica.

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Foraminifera

• heterotrophic marine protists with pore-studded
  shells
• complex life cycle with alternation between
  haploid and diploid generations

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Slime Molds