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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.

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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 à 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 à 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 vaginalisà 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.**