IF

Microbial Life: Protists Notes

  • Protists: Overview

    • Extremely diverse group of mostly unicellular eukaryotes found in aquatic or moist habitats.
    • Categorized into three nutritional modes:
    • Autotrophic: Known as algae.
    • Heterotrophic: Often referred to as protozoans.
    • Mixotrophic: Capable of both photosynthesis and heterotrophy (e.g., Euglena).

  • Cellular Structure and Movement

    • Various organelles specific to protists, e.g., dinoflagellates possess ocelloids (eye-like organelles).
    • Movement mechanisms include:
    • Flagella
    • Cilia
    • Amoeboid motion
    • Nonmotile forms

  • Reproduction in Protists

    • Some reproduce asexually; others exhibit both asexual and sexual phases.
    • All basic types of sexual life cycles (plant, animal, fungal) are represented.

  • Endosymbiosis in Eukaryotic Evolution

    • Much of protistan diversity arises from endosymbiotic relationships wherein one organism lives within the cells of another.
    • Mitochondria and plastids descend from engulfed bacteria in early eukaryotic ancestors.
    • Evidence suggests:
    • Mitochondria evolved before plastids, from an alpha proteobacterium.
    • Molecular data indicate that both mitochondria and plastids evolved once in the history of life.
    • The ancestral host was a complex cell with eukaryotic features; suggested lineages include lokiarchaeotes.

  • Protist Diversity

    • Four major supergroups of protists:
    1. SAR (Stramenopiles, Alveolates, Rhizaria)
      • Stramenopiles: Diatoms, brown algae, water molds
      • Alveolates: Dinoflagellates, ciliates, some parasites
      • Rhizarians: Foraminiferans, radiolarians
    2. Excavata
      • Modified mitochondria, includes Giardia, Trichomonas, Euglena
    3. Archaeplastida
      • Includes red and green algae, land plants
    4. Unikonta
      • Includes amoebozoans, fungi, and animals

  • Details on SAR supergroup

    • Stramenopiles:
    • Diatoms:
      • Unicellular, silica-based walls (frustules), significant CO2 sinks, contribute to diatomaceous earth.
    • Brown Algae:
      • Kelp, multicellular, common in temperate coasts.
    • Alveolates:
    • Possess alveoli (membrane-bound sacs) beneath the plasma membrane.
    • Dinoflagellates: Contribute to red tides, possess two flagella.
    • Apicomplexans: Parasitic (e.g., Plasmodium causing malaria) with complex life cycles.
    • Ciliates: Use cilia for feeding/movement, e.g., Paramecium.
    • Rhizaria:
    • Foraminifera: External shells (tests) made of calcium carbonate.
    • Radiolarians: Utilize silica for symmetrical skeletons.

  • Excavata

    • Include anaerobic protists with modified mitochondria.
    • Examples: Giardia, Trichomonas, Euglena.

  • Unikonts

    • Includes amoebozoans that are closely related to fungi and animals.
    • Amoebozoans: Lobe-shaped pseudopodia for movement and feeding.
    • Slime Molds: Include both cellular and plasmodial types.
    • Entamoebas: Parasitic forms, e.g., Entamoeba histolytica, causes dysentery.

  • Archaeplastida

    • Red and green algae contribute to coral reef structures.
    • Include land plants, closely related to charophytes (green algae).

  • Life Cycle of Algae

    • Involves alternation of generations: haploid gametophyte and diploid sporophyte stages.

  • Key Differences in Chromosome Number:

    • Test your understanding of gametophyte (haploid) vs sporophyte (diploid) phases during this cycle.