Lecture Notes on Protists

Ciliates

• Supergroup: "SAR" – alveolate clade
• Movement and Feeding: Use cilia
• Diversity: Very diverse group
• Lifestyle: Mostly free-living (e.g., Paramecium sp.)
• Nuclei: Multinucleate with macronucleus and micronucleus
• Cilia Function: Operate synchronously
• Osmoregulation: Contractile vacuole
• Reproduction:
  • Asexual: Binary fission
  • Sexual: Conjugation
    • Micronuclei undergo meiosis
    • Exchange of nuclei with other paramecium
    • Fusion leads to new individuals

Fungi-like Protists

• Characteristics: Fungi-like due to some shared traits
  • Spread by spores
  • Heterotrophic, many saprobic (decomposers)
• Water Molds, White Rusts, and Downy Mildews:
  • Part of "SAR" Stramenopile clade (resemble fungi due to convergent evolution)
  • Habitat: Aquatic or on moist substrates
  • Ecology: Decomposers and some are parasitic
    • Example: Cottony growth on aquarium fish
  • Pathogens: Some attack plants (e.g., mildew on grapes)
  • Historical Impact: Irish potato famine (1845-1860) due to Phytophthora infestans
    • Economic and sociological significance
    • Led to mass emigration from Ireland
• Slime Molds:
  • Fungi-like due to fruiting bodies producing spores
  • Types:
    • Cellular Slime Molds:
      • Supergroup Unikonta - Amoebozoa clade
      • Amoeboid single cells
      • Prey on bacteria and yeast
      • Aggregate into "slug" stage under nutrient scarcity
      • Form fruiting bodies and disperse spores
    • Plasmodial Slime Molds:
      • Bright yellow or orange, large multinucleated cell
      • Grow and use pseudopodia for feeding

Plant-like Protists = Algae

• Classification:
  • Formerly part of Kingdom Protista
  • Includes single-celled (phytoplankton) and simple multicellular (seaweeds) photosynthetic organisms
• Lineages:
  • Diatoms, brown algae (Stramenopile clade), dinoflagellates (Alveolate clade) in "SAR" supergroup
  • Green algae share common ancestry with land plants (Kingdom Plantae) in Supergroup Archaeplastida
• Evolutionary Note:
  • Major algal lineages result from secondary symbiotic events
  • Originated through endosymbiosis, first producing mitochondria, then plastids
  • Secondary endosymbiotic events led to different algal plastids