bio 110 lecture 1/31

Introduction to Protists

  • Definition of Protists:

    • All are eukaryotic organisms.

    • Eukaryotes have a nucleus.

  • Eukaryotic vs. Prokaryotic Cells:

    • Eukaryotic cells are generally larger and contain organelles, while prokaryotic cells do not.

    • Prokaryotes lack a nucleus and have simpler structures.

Eukaryotic Cells

  • Key Characteristics of Eukaryotes:

    • Presence of a nucleus and membrane-bound organelles.

    • Larger body size compared to prokaryotes.

  • Etymology:

    • Eukaryote: "eu" means true, and "karyon" means kernel, referring to the nucleus.

    • Prokaryote: "pro" means before, signifying cells that predate the nucleus.

Evolution of Eukaryotes

  • Primary Endosymbiosis:

    • Theory that eukaryotes evolved through engulfing prokaryotic cells.

    • Examples include the origin of mitochondria and chloroplasts.

  • Mitochondria:

    • Result from eukaryotic cells capturing aerobic bacteria.

  • Chloroplasts:

    • Result from capturing photosynthetic cyanobacteria.

  • Secondary Endosymbiosis:

    • Subsequent engulfing of eukaryotic cells.

    • Notable in some photosynthetic organisms.

Evidence Supporting Endosymbiosis

  • Genetic Evidence:

    • Mitochondria and chloroplasts have their own circular DNA, similar to bacterial DNA.

  • Ribosomes:

    • Ribosomes in chloroplasts and mitochondria are similar to bacterial ribosomes, indicating their prokaryotic origins.

  • Replication:

    • Mitochondria and chloroplasts replicate through binary fission, akin to bacterial reproduction.

The Kingdom of Protista

  • Characteristics of Protists:

    • Protists do not fit into other kingdoms: plants, animals, fungi, or bacteria.

    • Great diversity in form and function.

    • Can be unicellular, colonial, or multicellular.

  • Metabolism Types:

    • Autotrophic (photosynthetic).

    • Heterotrophic (depend on other organisms).

    • Mixotrophic (can alternate between photosynthesis and feeding).

Movement and Reproduction in Protists

  • Methods of Movement:

    • Motility through cilia, flagella, pseudopodia.

    • Example: Diatoms use a specialized groove for movement.

  • Reproduction:

    • Asexual methods (e.g., binary fission).

    • Sexual reproduction following the haplodiplontic life cycle.

Ecological Habitats

  • Habitats of Protists:

    • Found in diverse environments: marine, freshwater, terrestrial, and extreme habitats like thermal vents.

Phylogeny of Eukaryotes

  • Eukaryotic Family Tree:

    • Common ancestor leading to multiple lineages, including protists, fungi, plants, and animals.

    • Protists classification:

      • Protists are paraphyletic, as they do not include all descendants from a common ancestor.

Notable Groups of Protists

  • Archaeplastida:

    • Basal group leading to land plants, includes red and green algae.

  • Opisthokonta:

    • Group that includes fungi and animals, characterized by a posterior flagellum.

    • Choanoflagellates:

      • Closest relatives to animals.

  • Chromalveolates:

    • Include photosynthetic and non-photosynthetic groups, characterized by secondary endosymbiosis.

    • Examples: Dinoflagellates, diatoms, brown algae.

  • Amoebozoa:

    • Includes amoebas and slime molds.

Conclusion

  • Final Thoughts:

    • The protists group showcases a vast diversity of life forms.

    • Understanding the evolutionary relationships among them is key to grasping eukaryotic biology.