Eukaryotes and Protists Overview

Protists Overview

• Protists form a diverse and heterogeneous group of eukaryotes that are distinct from fungi, land plants, and animals.
• Classified as a paraphyletic group, protists include primarily simple, mostly single-celled organisms.
• Major types include protozoa, plankton, and various macro algae.

Terminology

• Flagellum: Whip-like structure in eukaryotic and prokaryotic cells, used for movement.
• Amoebae-like: Variable cell shape with protruding extensions (pseudopodia) for movement and nutrient uptake.
• Symbiotic: Mutual benefit relationship with another organism.
• Parasitic: One organism benefits at the expense of another.
• Autotrophic: Organisms that produce their own energy-rich compounds, often via photosynthesis.
• Heterotrophic: Organisms that consume other organisms for energy.
• Pathogen: Organism that causes disease in another.

Importance of Protists

• Act as essential functional groups in ecosystems, including:
  • Photosynthesizing plankton in aquatic environments.
  • Decomposers of organic matter.
  • Parasites and pathogens.
• Some protists represent early evolutionary forms of multicellular fungi, plants, and animals, providing insights into evolutionary processes.

Super-Groups of Eukaryotes

• Excavata: Includes diverse flagellates, some with modified mitochondria (e.g., diplomonads, parabasilids, euglenozoans).
• Rhizaria: Composed of amoeba-like plankton with calcareous or silicon shells (e.g., Foraminifera and Radiolaria).
• Chromalveolata: Contains significant plankton groups such as:
  • Dinoflagellates (important primary producers).
  • Diatoms (contribute a large proportion of global photosynthesis).
  • Brown algae.
• Archaeplastida: Comprises land plants, red algae, and green algae.
• Unikonta: Encompasses organisms such as:
  • Amoebozoa (true amoebas and slime molds).
  • Opisthokonta (close relatives of animals and fungi).

Excavata Group

• Free-living and symbiotic protists, including key human parasites.
• Diplomonads: Have modified mitochondria and include parasites like Giardia lamblia.
• Parabasilids: Contain hydrogenosomes and include Trichomonas vaginalis causing genital infections.
• Euglenozoans: Flagellates including free-living and parasitic species like Trypanosoma, which causes sleeping sickness.

Chromalveolata Group

• Encompasses important single-celled plankton:
  • Dinoflagellates: Photosynthetic and bioluminescent, some cause harmful algal blooms (red tide).
  • Diatoms: Major contributors to global photosynthesis.
  • Apicomplexa: Exclusively parasitic protozoa (e.g., malaria-causing Plasmodium).
  • Ciliates: Characterized by cilia.

Archaeplastida Group

• Mostly multicellular, including:
  • Red Algae: Rely on phycoerythrin for photosynthesis in deeper waters and contribute to coral reef formation.
  • Green Algae: Comprised of Chlorophytes and Charophytes, believed to be ancestors of land plants.

Unikonta - Amoebozoa

• Consists of lifecycle-complex organisms, important in evolutionary studies:
  • Slime Molds: Fungus-like, forming mobile plasmodium during part of their life cycle.
  • Gymnamoeba: Free-living amoebas mostly found in soil and aquatic habitats.
  • Entamoeba: Notable for infections, causing diseases like amoebic dysentery.

Unikonta - Opisthokonta

• Includes animals and fungi, along with some related single-celled protists.
• Emphasis on evolutionary relationships connecting these organisms.