Study Guide: Protists and Plant-Like Protists

Study Guide: Protists and Plant-Like Protists

I. Introduction to Eukarya and Protists

  • The Eukarya Supergroups: All eukaryotic organisms are classified into four major supergroups:
      1. Excavata
      2. SAR Clade (Stramenopiles, Alveolates, Rhizarians)
      3. Archaeplastida
      4. Unikonta
  • What are Protists?
      - Protists are a diverse group of eukaryotes that span all four supergroups.
      - They exhibit structural and functional diversity.
      - Protistic cells are more complex than prokaryotic cells.
  • Important to Note:
      - Most organisms in eukaryotic lineages are protists (highlighted in yellow on phylogenetic trees).
      - Most protists are unicellular, but some exist in groups and some are multicellular.

II. The SAR Clade

  • Definition: The SAR clade is a highly diverse group of protists defined by DNA similarities.
  • Name Origin: "SAR" is an acronym for its three major clades:
      1. Stramenopiles
      2. Alveolates
      3. Rhizarians
A. Stramenopiles
  • Diatoms:
      - Unicellular algae with a unique two-part, glass-like wall made of silicon dioxide.
      - Major components of aquatic ecosystems and are highly diverse.
      - Found in both oceans and lakes.
      - Fossilized diatom walls form much of what is known as diatomaceous earth.
  • Brown Algae (e.g., Laminaria):
      - Characterized by large, complex multicellular structures known as "giant seaweeds".
      - Exhibit plant-like structures such as:
        - Holdfast: Anchors the algae.
        - Stipe: Supports the blade (leaf-like structure).
      - Life Cycle: Involves the alternation of multicellular haploid and diploid forms.
        - Heteromorphic generations: Structurally different forms (e.g., sporophyte and gametophyte look distinct).
        - Isomorphic generations: Structurally similar forms.
      - Example: Laminaria (brown alga) exhibits heteromorphic generations.
  • Golden Algae:
      - Characterized by yellow and brown carotenoids.
      - Generally have a simple structure; mostly unicellular organisms that form groups.
B. Alveolates
  • Dinoflagellates:
      - Body is made up of phytoplankton.
      - Known for causing 'red tide' blooms (explosive growth).
      - Produce toxins that can lead to massive kills of invertebrates and fish.

III. Archaeplastida

  • Includes both red algae and green algae.
  • Diverse habitats: Freshwater, marine, and terrestrial.
A. Green Algae
  • Unicellular Examples:
      - Chlamydomonas: A model single-celled algal system.
        - Gametes of different mating types (+/-) are morphologically identical.
        - Mature cells develop into gametes under environmental stress (e.g., nitrogen stress).
        - The zygote is the only diploid state in its life cycle.
      - No alternation of generations: Not multicellular in its life cycle; its main form is haploid.
      - Volvox: A colonial freshwater green alga.
B. Multicellular Examples of Green Algae
  • Ulva (sea lettuce)
  • Caulerpa
  • Closest relatives of land plants.
  • Algal Cell Structure:
      - Cell Wall: Composed of cellulose and some carbohydrates/proteins; rigid when mature, permeable to water, gases, and minerals.
      - Water Content Regulation: Regulates water content, with water movement exerting outward pressure (turgor pressure).
      - Chloroplasts: Site of starch synthesis.
  • Algal Goliath: Chlorophyte (Acetabularia jalakanyakae):
      - A single-celled green alga with a single nucleus found in its rhizoid.
      - Discovered in the Andaman and Nicobar Islands of India and published in 2021.
C. Red Algae
  • Color: Reddish due to the presence of phycoerythrin.
  • Primarily multicellular.
  • No flagellate structures in their life cycle.
  • Economic Importance: Thin, glossy sheets of nori (red algae, Porphyra) are used to make mineral-rich wraps for sushi.

Key Terms to Remember:

  • Eukarya Supergroups
  • Protists
  • SAR Clade
  • Stramenopiles
  • Diatoms
  • Diatomaceous Earth
  • Brown Algae
  • Holdfast, Stipe, Blade
  • Alternation of Generations
  • Heteromorphic Generations
  • Isomorphic Generations
  • Golden Algae
  • Alveolates
  • Dinoflagellates
  • Red Algae
  • Phycoerythrin
  • Nori (Porphyra)
  • Acetabularia jalakanyakae

Review Questions for Self-Study:

  1. List the four supergroups of Eukarya. Which ones contain protists?
  2. Define what a protist is. What are some key characteristics of protists?
  3. What does "SAR" stand for in the SAR clade?
  4. Describe the unique features of diatoms. What are diatomaceous earths?
  5. Explain the concept of "alternation of generations" in brown algae. How do heteromorphic and isomorphic generations differ?
  6. What causes "red tides" and what are their ecological impacts?
  7. Identify two examples of unicellular green algae and two examples of multicellular green algae.
  8. Why is Chlamydomonas considered a model organism? Describe its life cycle.
  9. What gives red algae their characteristic color?
  10. What is a significant commercial use of red algae?
  11. What makes Acetabularia jalakanyakae an "Algal Goliath"?