Origins of Eukaryotic Diversity - Protists

"Protists" is artificial grouping

Evolutionary relationships have historically been unclear. In past, were often classified by mode of nutrition: heterotrophs by ingestion (called Protozoa) (Fig 28.1a) and amoeba, the movie, heterotrophs by absorbtion (Fig 28.1c), and autotrophs through photosynthesis (called algae) (Fig 28.1b and Fig 28.1d)and Euglena, the movie. Recent DNA studies have determined some monophyletic groups. (Fig 28.8)

Most are unicellular (Fig 28.3), some colonial, some multicellular. At cellular level many are very complex.

EVOLUTION OF EUKARYOTIC CELLS - A chimera of prokaryotic ancestors.

Origins of eukaryotes - Endosymbiotic theory. (Fig 28.4). And 2 more. (OH1 and OH2). See a slide show here.

cells with membrane-bound organelles
newest evidence from Australia indicates they originated 2.7 billion years ago

Autogenous event

- Nuclear membrane
- endoplasmic reticulum

Endosymbiotic event - serial endosymbiosis

- Mitochondria
- Chloroplasts

Evidence for the endosymbiont theory is that mitochondria and chloroplasts:

- Are appropriate size to be descendants of eubacteria.
- Have inner membranes similar to those on prokaryotic plasma membranes.
- Replicate by splitting, as in prokaryotes.
- DNA is circular and different from the DNA of the cell's nucleus.
- Contain their own components for DNA transcription and translation into proteins .
- Have ribosomes similar to prokaryotic ribosomes.
- Molecular systematics lend evidence to support this theory.
- Many extant organisms are involved in endosymbiotic relationships.

Protists are eukaryotic organisms having:

- true nuclei (Fig. 7.9)
- membrane-enclosed organelles (Figs. 7.7 and 7.8)
- "9+2" flagella and cilia. Most have flagella or cilia (Figs 7.24 and 7.23). See cilia on Vorticella, the movie. Cilia, the movie!

Many protists are parasites of humans:

Giardia (Fig 28.9)
Trichomonas vaginalis (Fig 28.10)
Trypanosoma spp. cause sleeping sickness (Fig 28.11)
Plasmodium spp. cause malaria (Fig 28.13)

Table 28.1 provides a summary of the Kingdoms of protists, but does NOT cover ALL the protists. You are NOT responsible for learning the various groups.