In-Depth Notes on Protists Classification and Characteristics

Classification of Protists

• Definition: Protists are diverse eukaryotic organisms not classified as plants, animals, or fungi.
• Domain: They belong to the Eukaryote domain.
• Monophyly: Unlike animals, plants, and fungi, protists do not form a true monophyletic group but consist of various lineages.

Categorization of Protists

• Protists are categorized based on traits and characteristics:
  • Animal-Like Protists (Protozoans):
  • Heterotrophic: They ingest their food.
  • Unicellular: Most are single-celled.
  • Habitats: Mostly found in freshwater; some in marine and damp terrestrial environments.
  • Types: Classified based on locomotion mode:
    • Ciliated Protozoans:
    • Use cilia for movement and feeding.
    • Example: Paramecium
      • Function: Moves by beating cilia in unison; uses contractile vacuole to manage water in various salinities.
    • Flagellated Protozoans:
    • Move using flagella.
    • Example: Trichonympha
      • Mutualism with termites; helps them digest cellulose in exchange for protection.
    • Amoeboid Protozoans:
    • Flexible, with no cell walls.
    • Move using pseudopodia (extensions of cytoplasm).
    • Example: Amoeba
      • Naegleria fowleri: A brain-eating amoeba with a 97% fatality rate, causes a rare disease (PAM).
    • Spore-Forming Protozoans:
    • Parasitic; transmitted via vectors.
    • Example: Plasmodium
      • Infects red blood cells, causes malaria; transmitted by mosquitos.

Fungus-Like Protists

• Plasmodial Slime Molds:
  • Heterotrophs that decompose organic matter in terrestrial, shady, moist environments.
  • Types include cellular slime molds and plasmodial slime molds.
  • Example: Physarum
  • Note: Avoid the reproductive stage when studying.

Plant-Like Protists

• Euglenids:

  • Unicellular freshwater algae, capable of both autotrophy (photosynthesis) and heterotrophy.
  • Characteristic: Possess one flagellum and an eyespot for detecting light.
  • Example: Euglena

• Diatoms:

  • Unicellular algae found in marine and freshwater; have silica cell walls, impermeable yet with pores.
  • Unique feature: Cell walls made of glass; they can form chains or colonies.

• Dinoflagellates:

  • Unicellular marine algae with two flagella.
  • Characteristics:
  • Cellulose protective layer resembling armor.
  • Can cause harmful algal blooms and red tides.
  • Bioluminescence and symbiotic relationships (e.g., with corals).

• Green Algae (Chlorophyta):

  • Uni- and multicellular forms:
  • Chlamydomonas (unicellular), Ulva (multicellular marine), Codium (multinucleate), Spirogyra and Cladophora (filamentous morphology).
  • Volvox: A colonial green alga with identical cells in each colony.

• Brown Algae (Phaeophyta):

  • Multicellular, dominant in marine environments.
  • Types:
  • Kelps: Largest protists; grow in underwater forests.
  • Rockweeds: Form mats visible during low tide.

• Red Algae (Rhodophyta):

  • Multicellular marine algae found deeper in the ocean, occasionally shallow.