Biology Lecture 6: Cell Structure and Function

Unit 5 / Concept 28: Protists

Learning Objectives

• Define Protists and their four supergroups.
• Identify Excavata, the protists with unique flagella.
• Demonstrate the diversity of the SAR group.
• Understand Archaeplastida and its two clades.
• Briefly explain the Unikonta supergroup.
• Enrichment Links:
  • Chagas Disease
  • Plasmodium, The Malaria Parasite
  • Foraminifera: Hard on The Outside, Squishy on the Inside
  • Green Algae

Overview of Protists

• Protists: Mostly unicellular eukaryotes, diverse in structure and function.
• Protists carry out all biological functions within organelles in each cell.
• They can be unicellular, colonial, or multicellular.

Four Supergroups of Eukaryotes

1. Excavates
2. SAR (Stramenopiles, Alveolates, Rhizarians)
3. Archaeplastida
4. Unikonta

• Clades: Groups of biological taxa sharing a common ancestor.

Supergroup Details

1. Excavates

• Protists with modified mitochondria and unique flagella.
• Characterized by cytoskeleton and sometimes an excavated groove.
• Includes:
  • Diplomonads: Lack plastids, have mitosomes, live anaerobically, often parasites (e.g., Giardia intestinalis).
  • Parabasalids: Reduced mitochondria called hydrogenosomes, e.g., Trichomonas vaginalis.
  • Euglenozoans: Includes kinetoplastids and euglenids.

2. SAR

• Defined by DNA similarities, highly diverse.
• Stramenopiles: Phototrophs and heterotrophs, includes diatoms, golden algae.
• Alveolates: Have alveoli under the plasma membrane, includes dinoflagellates, apicomplexans, ciliates.
• Rhizarians: Amoebas with threadlike pseudopodia, includes radiolarians, forams.

3. Archaeplastida

• Closest relatives to plants.

• Red Algae: Multicellular, reddish due to phycoerythrin.

• Green Algae: Grass-green chloroplasts, includes chlorophytes and charophytes.

• Economic Importance of Algae:

  • Food chain link, fish culture, sewage treatment, space research, food, fodder, fertilizers, medicine.

4. Unikonta

• Includes animals, fungi, and protists.
• Divided into amoebozoans and opisthokonts.
• Amoebozoans: Amoebas with lobe- or tube-shaped pseudopodia, includes slime molds.

Summary

• Protists are the most nutritionally diverse eukaryotes, with photoautotrophs, heterotrophs, and mixotrophs.
• Reproduction can be asexual or sexual.

End of Lecture Notes