CHAPTER 28: The Origins of Eukaryotic Diversity
I. Introduction to the Protists
A. Protists are the most diverse of all eukaryotes
Arose 1 billion years before emergence of other eukaryotes
There are about 60,000 extant species
Are considered the simplest eukaryotic organisms
Nearly all are aerobic; anaerobic forms lack mitochondria
Photosynthetic forms called “algae/ingestive forms called “protozoa”/absorptive forms called
“slime molds”
Most protists have flagella or cilia
Life cycles quite variable: some reproduce asexually, others sexually, others use synqamy
(fusion of gametes), others form resistant cysts
B. Symbiosis was involved in the genesis of eukaryotes from prokaryotes Hypothesis of serial
endosymbiosis proposes that certain prokaryotic
species, called endosymbionts, lived within larger prokaryotes; i.e, chloroplasts descended
from endosymbiotic photosynthesizing prokaryotes, such as cyanobacteria, living in larger
cells, whereas mitochondria are postulated to be descendants of prokaryotic aerobic
heterotrophs.
II. Protist Systematics and Phylogeny
A. Members of candidate kingdom Archaezoa lack mitochondria Exs. Giardia and Trichomonas
B. Candidate kingdom Euglenozoa includes both autotrophic and heterotrophic flagellates, which
fall into two groups: Euglenoids (ex. Euqlena) and Kinetoplastids (ex. Trypanosoma and
African sleeping sickness)
C. Subsurface cavities (alveoli) are diagnostic of candidate kingdom Alveolata Small membrane—
bound cavities, or alveoli, under their cell surfaces may help to stabilize the cell surface or
regulate water/ion transport
1. Dinoflagellates
Components of phytoplankton that may cause red tides and paralytic shellfish poisoning
2. Apicomplexans (formerly called sporozoans)
Animal parasites such as Plasmodium, which causes malaria; Anopheles mosquitoes are the
vectors
3. Ciliates (Ciliophorans)
Exs. Stentor and Paramecium; contain two types of nuclei: macronucleus controls everyday
functions and micronucleus functions in conjugation
D. A diverse assemblage of unicellular eukaryotes move by pseudopodia
1. Rhizopods (amoebas)
2. Actinopods: heliozoans (fresh water) and radiolarians (marine)
3. Foraminiferans
E. Slime molds
1. Plasmodial slime molds (Myxomycota) with coenocytic plasmodia
2. Cellular slime molds (Acrasiomycota) with cAMP—activated swarm cells
F. Candidate kingdom Stramenopila
1. Diatoms (Bacillariophyta) with overlapping glasslike walls of silica
2. Golden algae (Chrysophyta)
3. Water molds and their relatives (Oomycota)
4. Brown algae (Phaeophyta) the largest and most complex of algae. All multicellular; most
marine; fucoxanthin; laminarin; agar
