Protists and Plant Evolution Notes

Plant-Like Protists - Algae

  • Contain pigments (mostly chlorophyll) in chloroplasts for photosynthesis.
  • Phylum Chrysophyte (Diatoms):
    • Single-celled, autotrophic, free-floating aquatic organisms (phytoplankton).
    • Important food source.
    • Rigid cell walls with silica.
  • Phylum Pyrrophyta (Dinoflagellates):
    • Marine phytoplankton with 2 flagella for twirling motion.
    • Reproduce quickly, causing algal blooms.
    • Some have red pigments, causing red tides.
  • Euglenoids (Phylum Euglenophyta):
    • In shallow fresh water.
    • Have chloroplasts and flagella; autotrophic in light, heterotrophic in dark.
  • Large Multicellular Algae - Seaweeds:
    • Red algae (Phylum Rhodophyta): Appear red, common in food (carrageenan).
    • Brown algae (Phylum Phaeophyta): Largest protists, form underwater forests.
    • Green algae (Phylum Chlorophyta): Most plant-like, cellulose cell walls, store starch.

Protist Characteristics

  • Eukaryotic and mostly unicellular.
  • Simple organization.
  • Autotrophic or heterotrophic.
  • Diverse mechanisms of reproduction (sexual/asexual).
  • Classified into animal-like (protozoa), fungi-like (slime molds & water molds), and plant-like (algae) based on nutrition.

Animal-Like Protists (Protozoa)

  • Heterotrophic protists that ingest or absorb food.
  • Phylum Cercozoa:
    • Amoeba: Change shape using pseudopods for movement and feeding.
  • Phylum Ciliophora:
    • Paramecium: Cilia for locomotion and feeding.
  • Phylum Zoomastigina:
    • Flagellates: Flagella for propulsion.
  • Phylum Sporozoa:
    • Parasitic, nonmotile; Example: Malaria-causing protist.

Fungi-Like Protists

  • Heterotrophs that absorb nutrients.
  • Phylum Myxomycota:
    • Plasmodial Slime molds: Creep over decaying matter, engulfing food.
  • Phylum Acrasiomycota:
    • Cellular Slime molds: Aggregate into pseudoplasmodium when food is scarce.
  • Phylum Oomycota:
    • Water molds: Live on dead organic matter, resemble fungi.

Shift to Land - Plant Evolution

  • First land plants lacked vascular tissue (xylem and phloem).
  • Vascular tissue evolved later for water and molecule transport, enabling root evolution.
  • Roots provide anchoring and water absorption.
  • Leaves evolved after vascular tissue to increase surface area for gas exchange and photosynthesis.

Plant Diversity & Classification

  • Plants classified based on presence/absence of vascular tissue and seeds.
  • Four main divisions:
    • Seedless non-vascular plants.
    • Seedless vascular plants.
    • Gymnosperms: Vascular plants with exposed seeds.
    • Angiosperms: Vascular plants with seeds enclosed in a fruit.

Non-Vascular & Seedless Plants (Bryophytes)

  • Require moist environments for reproduction and dissolving substances.
  • Lack vascular tissue; rely on diffusion and osmosis.

Gymnosperms: Seeded Vascular Plants

  • Seeds exposed on cone scales.
  • Include conifers (pines, firs, etc.).

Angiosperms: Flowering Plants

  • Produce flowers which house seeds.
  • Further classified by cotyledons (embryonic seed leaves):
    • Monocots: One cotyledon.
    • Dicots: Two cotyledons.