protists

• Bio 152: Introductory Biology II
• Dr. Huynh
• Most eukaryotes are single-celled organisms
• Eukaryotic cells

  • More complex than prokaryotic cells
  • Membrane bound organelles
  • DNA contained in a nucleus
• Protists

  • Outside of fungi, plants, and animals, other eukaryotes are collectively referred to as protists
  • Most species are single-celled
  • Some colonial and multicellular species
  • Protists are an informal group (i.e. paraphyletic); not a 'good' phylogenetic grouping or clade

  
• Characteristics of protists

  • Movement (cilia, flagella, pseudopodia)
  • Metabolism (autotrophs, heterotrophs, mixotrophs)
  • Life cycle and reproduction (asexual, sexual, both)
• Four 'Supergroups' of eukaryotes

  • Excavata
  • 'SAR' clade
  • Archaeplastida
  • Unikonta
• Protists are not a "good" clade
• Excavata supergroup includes the diplomonads, parabasalids, and euglenozoans

  
• Excavata supergroup

  • Characterized by reduced mitochondria (diplomonads and parabasalids)
  • Unique crystalline rod in flagella (euglenozoans)
  • 'Excavated' feeding tube

  
• Excavata: Euglenozoans

  • Trypanosoma spp. (sleeping sickness, Chagas' disease)

  
• SAR supergroup has 3 subgroups: Stramenopiles, Alveolates, Rhizarians
• SAR: Stramenopiles

  • Most have 2 flagella (a "hairy" and a "smooth" one)
  • Includes diatoms, golden algae, brown algae, oomycetes

  
• SAR: Alveolates

  • Have membrane-bounded sacs called alveoli under the plasma membrane
  • Includes dinoflagellates, apicomplexans, ciliates

  
• SAR: Alveolates: Dinoflagellates

  • Photosynthetic coral symbionts
  • Cause of harmful "red tides"
• SAR: Alveolates: Apicomplexans

  • Almost all are parasitic
  • Have complex organelles at their apical end for entering cells
  • e.g. Plasmodium malariae
• SAR: Alveolates: Ciliates

  • Have cilia on their surface that help them move and feed
  • Many are predators
  • Have a large "macronuclei" and smaller "micronuclei"

  
• SAR: Rhizarians

  • Mainly amoeboid
  • Move and feed by thread-like pseudopodia
  • Includes radiolarians, foraminiferans, cercozoans
• SAR: Rhizarians: Radiolarians

  • Internal skeletons of silica
  • Radiating pseudopodia capture small microorganisms and cytoplasmically stream them to the center of the cell

  
• SAR: Rhizarians: Forams

  • Porous multichambered calcium carbonate shells called tests
  • Pseudopodia extend through the pores of the test
• Archaeplastida supergroup

  • Defining characteristic - photosynthetic due to a cyanobacterial endosymbiont (i.e. chloroplasts)
  • Includes red algae, green algae, land plants (not protists)

  
• Green algae


  Photosynthetic lichen symbionts
• Unikonta supergroup

  • Defining characteristic - DNA evidence
  • Includes amoebozoans and opisthokonts

  
• Amoebozoans


  • Lobed-shaped pseudopodia
  • Amoeba proteus
  • Slime molds
• Opisthokonts


  • (highly diverse)

  
• Protists play key roles in ecological communities