Chapter 28
The Origins of Eukaryotic Diversity
I. Introduction to the protists
A. Systematists split protists into many kingdoms
1. In the five kingdom system, anything that wasn’t a
prokaryote, plant, animal, or fungus was grouped as a protist.
2. Systematists now divide protists into as many as 20
separate kingdoms.
Figure 28.2 (p. 547) – The kingdom Protista problem.
B. Protists are the most diverse of all eukaryotes
Figure 28.1 (p. 546) – Too diverse for one
kingdom: a small sample of protists.
General Description of Protists
1. Very few general characteristics can be cited without
many exceptions.
2. Most protists are unicellular, but some are colonial or
even multicellular.
- Many protist cells are very complex  individual cell
must perform all the basic functions performed by
specialized cells of plants and animals.
3. Nutrition
- Protists may be autotrophic, heterotrophic, or mixotrophic
organisms. Mixotrophic organisms combine
photosynthesis and food ingestion
a. Photosynthetic: algae (plant-like)
b. Ingestive: protozoa (animal-like)
c. Absorptive: fungus-like
4. Motility
a. Most protists are motile; they have either flagella or
cilia.  Eukaryotic and prokaryotic flagella are not
homologous structures.
5. Life Cycle
a. Some protists are asexual.
b. Some reproduce sexually by meiosis and then go on to
reproduce asexually.
c. Cysts form at some point during the life cycle of many
protists. Cysts are resistant cells that are capable of
surviving harsh conditions.
6. Habitat
a. Most protists are aquatic.
b. Plankton are organisms that drift or swim near the surface
of the water  Phytoplankton are responsible for half of the
world’s photosynthesis and O2 production.
The following Figure (28.3) gives details for a common Protist
(Euglena) and should be a model for what you remember of
single-celled Protists
II. Origin and early diversification of eukaryotes
A. Endomembranes contributed to larger, more
complex cells
-Endomembranes evolved from infoldings of prokaryotic
membranes.
- Endomembranes allowed for compartmentalization of
cellular functions. This contributed to the evolution of
increasing complexity and development of new functions 
This is a great example of the development of emergent
properties!
Figure 28.4 (p. 549) – A model of the origin of eukaryotes.
B. Mitochondria and chloroplasts evolved from
endosymbiotic bacteria
1. Heterotrophic prokaryotes were engulfed and function as
mitochondria.
2. Photosynthetic prokaryotes were engulfed and function as
chloroplasts.
C. Eukaryotic cell is a chimera of prokaryotic ancestors 
The term chimera refers to the mixture of three prokaryotes.
a. Original contributes genome
b. One becomes mitochondrion
c. One becomes chloroplast
Figure 28.5 (p. 551) – Secondary endosymbiosis and the
origin of algal diversity. Note: Chloroplast is called a plastid
2. After the first eukaryotes formed, there was a great wave
of diversification.
Figure 28.8 (p. 554) – A tentative phylogeny of eukaryotes.
III. Protistan diversity
A. Diplomonadida and Parabasala
1. Lack mitochondria
- Examples of eukaryotes that evolved
without acquiring endosymbiotic heterotrophic bacteria. 
Most systematists think they lost them.
2. Giardia lamblia  example of Diplomonad
- Humans ingest cysts by drinking feces-contaminated water.
- Parasite absorbs body fluids from host (Huge outbreaks
occurred in Wisconsin and Pennsylvania recently that
required heavy chlorination of water supplies.)
Question: Why doesn’t Giardia need mitochondria?
Figure 28.9 (p. 555) – Giardia lamblia, a diplomonad.
3. Trichomonas vaginalis  example of Parabasalid
- Parasite of the vagina.
**Note: These organisms live as parasites and they don’t
need to have mitochondria and respire on their own.**
B. Euglenozoa
1. Characterized by one or two flagella and
paramylon which is a glucose polymer. Example: Euglena!
2. Most members of this group are
photosynthetic (autotrophs). However,
3. Kinetoplastids (Trypanosoma) cause
sleeping sickness. It’s symbiotic. By which type of
symbiosis does it live?
Figure 28.11 (p. 556) – Trypanosoma, the kinetoplastid that
causes sleeping sickness.
C. Alveolata
1. Characterized by small cavities under the
cell surface (alveola).
2. Dinoflagellate (phytoplankton) blooms cause
“red tide” and produce toxins. Example:
- Pfisteria acts as a carnivore: kills fish, feeds on flesh.
-Others form the basis of many food chains in the oceans
and function as photosynthetic plankton.
-Others are bioluminescent and produce light when
disturbed to attract fish that eat predators that eat the
Dinoflagellates.
3. Apicomplexa are animal parasites
- e.g. Plasmodium causes malaria.
Figure 28.13 (p. 557) – The two-host life history of
Plasmodium, the apicomplexan that causes malaria.
4. Ciliophora
- Use cilia for movement.
- e.g. Stentor and paramecium. These
ciliates have one macronucleus and several micronuclei
Figure 28.14 (p. 558) – Ciliates.
D. Stramenopila
1. Diverse group of heterotrophs and phototrophs (algae)
- Usually have “hairy” flagella
Four taxa are within the stramenopila:
2. Oomycota are water molds; primarily heterotrophs.
The remaining members of this taxon are called Heterokont
algae. They are photosynthetic and contain endosymbiotic
plastids (chloroplasts). The taxa within the group are:
3. Bacillariophyta (diatoms) have glass-like walls and exist
as phytoplankton.
- e.g. Pinnularia
Figure 28.17 (p. 561) – Diatoms.
4. Chrysophyta are golden algae that live in colonies
- e.g. Dinobryon
Figure 28.18 (p. 562) – A golden alga
5. Phaeophyta are brown algae
- Kelp (seaweed) grow up to 60 meters per year and are
harvested for food.
Figure 28.20 (p. 563) – A kelp forest.
6. Algal life cycle
- Alternation of generations
**Need to know this!!**
Figure 28.21 (p. 564) – The life cycle of
Laminaria: an example of alternation of generations.
E. Rhodophyta (red algae)
1. No flagella
- Porphyra
Figure 23.22 (p. 565) – Red algae.
F. Chlorophyta (green algae)
1. Characterized by green chloroplasts, similar
to those found in plants.
Exist as unicellular (Chlamydomonas), colonial (Volvox) and
multicellular (Caulerpa) organisms.
Figure 28.23 (p. 566) – Colonial and multicellular
chlorophytes.
These are the forerunners of early plants Colonies and
multicellular chlorophyta evolved to become the higher
plants. Again, an example of emergent properties.
G. Some protists use pseudopodia for movement and
feeding. The examples that follow are of uncertain phylogeny.
1. Pseudopodia are cellular extensions that
may bulge from almost anywhere on the cell.
2. Typically heterotrophs
3. Best known examples are amoebas
(Rhizopoda).
Figure 28.26 (p. 569) – Use of pseudopodia for
feeding.
H. Mycetozoa are slime molds
**Know this life cycle!!**
Figure 28.29 (p. 571) – The life cycle of a
plasmodial slime mold, such as Physarum.
**Note: Table 28.1 (p. 573) is a good place to begin
memorizing clades and features.**