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Review of Life Domains

• The three domains of life include the following:

  • Domain Eukarya

  • Includes organisms with eukaryotic cells, which have a nucleus.

  • Notable groups: Plants, Fungi, Animals, and various protists such as Euglenozoans, Forams, Diatoms, Ciliates, Red algae, and Green algae.

  • Domain Bacteria

  • Composed of prokaryotic organisms.

  • Includes diverse groups like Proteobacteria, Chlamydias, Spirochetes, Gram-positive bacteria, and Cyanobacteria.

  • Domain Archaea

  • Prokaryotic organisms, often extremophiles.

  • Subgroups include Euryarcheotes, Thaumarchaeotes, and Crenarcheotes.

• Connection:

  • Common ancestor of all life is a focal point from which these domains diverged.

  • Polytomy: A branch point leading to multiple lineages, representing an unresolved pattern of divergence.

Supergroups of Eukaryotes

• Four Supergroups Identified:

  1. Excavata

  • Notable for a feeding groove used to capture and ingest small particles.

  • Examples include Diplomonads, Parabasalids, Euglenozoans.

  1. SAR

  • Composed of Stramenopiles, Alveolates, Rhizarians; grouped based on DNA sequence similarities.

  • Examples include Diatoms, Brown algae, Ciliates, Dinoflagellates.

  1. Archaeplastida

  • Includes plants and red/green algae.

  1. Unikonta

  • Inclusion of animals, fungi, and various amoeboids.

Overview of Protists

• Protists defined:

  • They do not form a true phylogenetic group. Instead, they consist of a diverse assemblage of mostly unicellular organisms that do not fit into the categories of plants, animals, or fungi.

Excavata Supergroup

• Characteristics of Excavata:

  • Many members possess a unique feeding groove utilized for capturing and ingesting small particles.

Example: Euglenozoans

• Euglenozoans:

  • Feature crystalline rods within their flagella.

Kinetoplastids

• An example of Euglenozoans, characterized by:

  • A single, large mitochondrion containing an organized mass of DNA known as a kinetoplast, which consists of multiple copies of the mitochondrial genome.

  • Example organism: Trypanosoma brucei gambiense, responsible for West African sleeping sickness, transmitted by the tsetse fly.

Euglenids

• Another example of Euglenozoans:

  • Possess two flagella: Long flagellum and a short flagellum.

  • The chloroplasts are of secondary origin, containing chlorophylls a and b, and are surrounded by three membranes.

  • Some are mixotrophic, photosynthesizing in sunlight but capable of heterotrophic nutrition when it is unavailable.

  • Unique features: An eyespot (functional light detector), a contractile vacuole, and a pellicle (provides strength and flexibility).

  • Euglena commonly found in pond water, demonstrating movement towards light, enhancing photosynthesis.

SAR Supergroup

• Supergroup SAR contains:

  • Stramenopiles, Alveolates, Rhizarians

  • Grouped based on genetic similarities.

Stramenopiles

• Represents a group that includes Diatoms and Brown Algae.

  • Characterized by their flagella; typically have a paired hairy and smooth flagella during development.

Diatoms

• Major component of phytoplankton, recognized for:

  • Highly diverse, unicellular algae with a unique two-part, glass-like silica wall.

  • Male gametes possess hairy flagella.

Brown Algae (Phaeophyta)

• Commonly referred to as seaweeds; noted for:

  • Complex multicellular anatomy (e.g., kelps).

  • Spores and male gametes having hairy flagella and the presence of the pigment fucoxanthin, which gives a brown hue.

  • Contains edible mucilaginous polysaccharide, alginate, with structural features such as blades and stipes.

Alveolates

• Common characteristics include:

  • Presence of membrane-enclosed sacs (alveoli) beneath the plasma membrane.

  • Some members are heterotrophic, while others are photosynthetic

Ciliates

• Notable for dual nuclei:

  • Macronuclei (polyploid and transcriptionally active) and micronuclei (transcriptionally inactive, essential for sexual reproduction).

Dinoflagellates

• A diverse category of aquatic organisms, examples include:

  • Characterized by two flagella, with one transverse, enabling a spinning movement.

  • Some species reinforced by internal cellulose plates. Notable for phenomena such as red tides and bioluminescence.

  • Example: Zooxanthellae, symbiotic dinoflagellates crucial for coral reef productivity.

Apicomplexans

• Group of single-celled parasites involved in diseases, e.g., malaria caused by Plasmodium falciparum

  • Characteristic structure: At least one life stage possesses an apical complex, specialized for host cell penetration.

Rhizarians

• Characterized by:

  • Amoebas that have threadlike pseudopodia often supported by microtubules.

Foraminifera (Forams)

• Noted for:

  • Multi-chambered, calcium carbonate tests or shells, often hosting photoautotrophic algae.

Radiolarians

• Recognized for:

  • Axopodia that are reinforced by bundles of radiating microtubules for capturing food and locomotion. Unicellular and spherical forms that can exist in colonies.

Conclusion

• Key Points to Remember:

  • Distinguish different groups of protists based on unique morphological characteristics.

  • Familiarize yourself with specific examples from each group.

  • Understand important human pathogens discussed, especially Trypanosoma and Plasmodium.

  • Recognize organisms presented through various images or slides as part of your study guide for comprehensive knowledge and understanding of eukaryotic diversity.