' ' Study Notes on Protists

Chapter 28: Protists

Overview of Eukaryotic Domains

  • Eubacteria: Commonly referred to as "True bacteria"; includes entities such as mitochondria and chloroplasts.
  • Eukaryotes: Encompasses protists, plants, fungi, animals, and other complex organisms.
  • Archaea: Includes extremophiles such as methanogens, halophiles, and Sulfolobus.
  • Viruses: Often considered as a form of life that falls outside the traditional classification of living organisms.

Major Lineages of Eukaryotes

  1. Archaeplastida (Plantae)

    • Includes green plants, such as green algae (both prasinophytes and land plants), Rhodophyta (red algae), and glaucophytes (microalgae that possess cyanobacteria-like chloroplasts such as Cyanophora).

  2. Unikonts

    • Comprises organisms like animals (Metazoa), choanoflagellates, filasterea, ichthyosporea, fungi (including mushrooms, yeast, molds, etc.), and nucleariidae (a type of filose amoebae such as Nuclearia).

  3. Chromalveolates

    • A diverse group that includes alveolates (dinoflagellates, ciliates, apicomplexans), stramenopiles (water molds, diatoms, brown algae, chrysophytes), and has connections with groups such as rhizarians and excavates.

  4. Excavates

    • Exhibits features such as an excavated feeding groove and often has reduced or absent mitochondria. Notable subgroups include diplomonads, parabasalids, and euglenozoans.

  5. Rhizaria

    • A clade characterized by amoebas with threadlike pseudopodia, comprising groups like cercozoans and foraminifera.

  6. Amoebozoa

    • Includes various amoebae, slime molds, and parasitic protists.

Protist Phylogeny

  • Diagrams and figures illustrate the relationships between various protist groups:
    • Figure 28.5: Protist phylogeny indicates the evolutionary links between diplomonads, parabasalids, euglenozoans, excavates, diatoms, golden algae, brown algae, dinoflagellates, apicomplexans, ciliates, forams, cercozoans, radiolarians, the "SAR" clade, stramenopiles, alveolates, rhizarians, green algae, red algae, chlorophytes, charophytes, land plants, slime molds, tubulinids, entamoebas, nucleariids, fungi, unikonta, choanoflagellates, animals, and amoebozoans.

Endosymbiotic Theory

  • Primary and Secondary Endosymbiosis:
    • The process through which eukaryotic cells evolved from prokaryotic cells.
    • In primary endosymbiosis, a heterotrophic eukaryote engulfed a cyanobacterium, leading to the formation of plastids.
    • Red and green algae are derived from this event, whereas secondary endosymbiosis occurred in groups like dinoflagellates and euglenids, where eukaryotic cells consumed other eukaryotes containing plastids.

Protist Examples and Specific Characteristics

  • Diplomonads:
    • Unicellular organisms with two nuclei and multiple flagella. Notable example includes Giardia intestinalis, a parasite found in the gastrointestinal tract.
  • Parabasalids:
    • E.g., Trichomonas vaginalis, known for its undulating membrane and association with genital infections.
  • Euglenozoans:
    • Characterized by a unique flagellum structure; includes euglenids like Euglena and kinetoplastids such as Trypanosoma, which causes diseases like sleeping sickness and Chagas disease (transmitted via the tsetse fly).

Stramenopiles and Alveolates

  • Stramenopiles:
    • Include organisms like diatoms, brown algae, and golden algae. Diatoms known for their silica shells and diatomaceous earth.
  • Alveolates:
    • Distinguished by membrane-bound sacs (alveoli). Includes dinoflagellates (can cause red tides), ciliates (like Paramecium), and apicomplexans (like Plasmodium, the cause of malaria).

Reproduction in Protists

  • Brown Algae Reproduction:
    • Involves both haploid (n) and diploid (2n) stages spanning from sporangia to gametophytes. An example includes kelp, illustrating a complex life cycle.

Human Health and Protist Pathogens

  • Entamoeba histolytica: Responsible for amoebic dysentery, causing significant morbidity in developing nations.
  • Naegleria fowleri: Known as the brain-eating amoeba, which can cause severe neurological disease.
  • Leishmaniasis: Disease spread by sandflies causing significant tissue damage.
    • One of the leading causes of death in low-income countries—highlighted by statistics on mortality rates.

Summary of Major Groups of Protists

  • Excavata: Giardia and Trichomonas.
  • “SAR” Clade: Diatoms, golden algae, brown algae, dinoflagellates, apicomplexans, ciliates, forams, cercozoans.
  • Archaeplastida: Red algae, green algae, and land plants.
  • Unikonta: Amoeba species and fungi.

Morphological Characteristics of Major Groups

  • Excavata: Has unique flagellar arrangements, some with modified mitochondria.
  • Stramenopiles: Exhibit hair-like structures on flagella.
  • Alveolata: Contain alveoli underneath the plasma membrane for structural support.
  • Rhizarians: Possess filamentous pseudopodia for feeding and locomotion.
  • Amoebozoa: Includes organisms with irregular shaped pseudopodia for locomotion and feeding.

Summary of Key Definitions and Concepts

  • Endosymbiosis: The theory explaining the origin of mitochondria and plastids from engulfed prokaryotes within a host cell.
  • Plasmodium: A genus of parasitic protists responsible for malaria, transmitted by mosquitoes.
  • Phycoerythrin: A pigment found in red algae that masks green chlorophyll, allowing for adaptation to deeper water.
  • Zygote (2n): The diploid cell formed when two gametes fuse during fertilization; important in sexual reproduction among protists.