Comprehensive Study Notes on Protists Part II

PROTISTS PART II

Course Details

  • BIOL 126: Biology II

  • Spring 2026

Major Protist Groups

  • Diplomonads

  • Excavates

  • Euglenoids

  • Dinoflagellates

  • Apicomplexans

  • Ciliates

  • Chromalveolates

  • Alveolates

  • Water molds

  • Diatoms

  • Stramenopiles

  • Brown algae

  • Golden algae

  • Ancestral eukaryote

  • Forams

  • Rhizarians

    • Actinopods

    • Red algae

    • Archaeplastids

    • Green algae

    • Land plants

    • Amoebas

    • Plasmodial slime molds

    • Cellular slime molds

    • Unikonts

    • Opisthokonts

    • Fungi

    • Choanoflagellates

    • Animals

Eukaryotic Group Distinctions

  • Prokaryotes: Separate lineage from eukaryotes

  • Unikonta:

    • One-tailed lineage containing more fungi-like groups

    • Includes Kingdoms Fungi and Animalia

  • Bikonta:

    • Two-tailed lineage

Major Lineages of Protists

  • Seven major Eukarya lineages each characterized by morphological distinctiveness

  • Distinctive cell structures led to diversification in lifestyles

  • Features may also evolve independently in various lineages, illustrating convergent evolution

Amoebozoa

  • Lobose Amoebae:

    • Lack cell walls

    • Engulf food for nourishment via amoeboid movement using lobe-like pseudopodia

    • Exhibits cytoplasmic streaming

    • Highly abundant in aquatic habitats and wet soils

    • Some species are internal parasites in humans and animals

    • Relevance: Influences nutrient cycling through microorganism feeding

    • Example: Dictyostelium discoideum as a model organism in cell biology

Slime Molds (Mycetozoans)

  • Previously classified as fungi

  • DNA reveals resemblances due to convergent evolution rather than a common ancestry

  • Divided into two main lineages:

    • Plasmodial slime molds

    • Cellular slime molds

Life Cycle of Plasmodial Slime Molds

  • At the feeding stage, forms a mass called a plasmodium:

    • Not multicellular; undivided by plasma membranes

    • Contains many diploid nuclei

    • Extends pseudopodia for food engulfment via phagocytosis

    • Does not have chitinous cell walls

Life Cycle of Cellular Slime Molds

  • Forms multicellular aggregates with cells separated by membranes

  • Individual cells feed, but they can also aggregate together to migrate and form a fruiting body

  • Dictyostelium discoideum: significant for understanding evolution of multicellularity

Excavata Group

  • Characterized by an excavated feeding groove on one side

  • Some may be mitochondria-less, though ancestors likely possessed them

    • Some retain vestigial mitochondria and others show mitochondrial genetic material

  • Predominantly unicellular heterotrophs

  • Locomotion via whiplike flagella

Major Groups within Excavata

  • Parabasalids:

    • Possess reduced mitochondria called hydrogenosomes for energy generation

    • Includes Trichomonas vaginalis, a pathogen causing yeast infections

  • Diplomonads:

    • Deep oral groove direct feeding behavior

    • Contain mitochondria known as mitosomes; energy derived from anaerobic processes

    • Characterized by two nuclei and multiple flagella

    • Example: Giardia intestinalis, a common intestinal pathogen

Lifecycle of Giardia

  • Cyst forms when contaminated:

    1. Ingestion of Giardia cyst through contaminated water, food, or contact

    2. Transforms into trophozoite in the small intestine, where it multiplies and absorbs nutrients

    3. Cysts excreted, existing in the environment for extended periods

Euglenozoans

  • Highly diverse clade consisting of:

    • Predatory heterotrophs

    • Photosynthetic autotrophs

    • Mixotrophs

    • Parasites

  • Key distinction: spiral or crystalline structure present in flagella

Euglenids

  • Can display dual flagella emerging from a pocket at one end

  • Exhibit both autotrophic and heterotrophic capabilities

  • Contains structures like eyespot facilitating light detection

Kinetoplastids

  • Many are obligate parasites, requiring host organisms for survival

  • Utilize flagella and an undulating membrane for movement

    • Notable examples include trypanosomes

Phylogenetic Analyses

  • A comprehensive diagram illustrates seven major lineages of eukaryotes with associated key subgroups:

    • Amoebozoa: Lobose amoebae, cellular slime molds, plasmodial slime molds

    • Opisthokonta: Fungi and Animals

    • Excavata: Parabasalids, Diplomonads, Euglenids

    • Plantae: Glaucophytes, Red algae, Green algae, and Land plants

    • Rhizaria: Foraminiferans, Actinopods, Chlorarachniophytes

    • Alveolata: Ciliates, Dinoflagellates, Apicomplexans

    • Stramenopila: Water molds, Diatoms, Brown algae

Conclusion

  • The study of protists provides insights into evolutionary biology, ecological interactions, and the mechanisms of disease and symbiosis, showcasing their vital role across various ecosystems.