Bi 213 (2010)                        Protists                     Dr. Dutton


Study Strategy

•    The classification and systematics of the Protists is in flux.  Therefore, we will …

–  Use the term clade to describe a group that is monophyletic (e.g., clade Euglenozoa)

–  Use the term group to describe an assemblage of organisms whose monophyly is certain

–  “Groups” can be either, or both, subordinate or superordinate depending on the context

–  Be certain you know group names

–  Consider making comparison charts

•    Figure 28-03a



•    Are primarily …

•    unicellular.  However, some ..



•    Diversity in cellular anatomy, ecological roles, and life histories is greater in this group than in any other

•    Even though they are unicellular, these cells are …



Modes of Obtaining Nutrients

•    Nearly all are …

•    aerobic & use mitochondria for their respiration

•    They can be:







•    Three Convenient Categories (not phylogenetically based) are:



•    ____________________  (plant-like) protists AKA algae,



•    ____________________  (animal-like) protists AKA protozoa, and



•    ____________________  (fungus-like) protists


Locomotion & Reproduction

•    Most have …




•    All can reproduce asexually

•    Some also have sexual reproduction or at least undergo meiosis & syngamy

•    This allows for?



•    Many form resistant cysts

•    See Figure 13.6 and REVIEW IT!


Alternation of Generations

•    A variety of life cycles have evolved among the multicellular algae



•    The most complex life cycles include an ____________________  of generations, the alternation of multicellular haploid and diploid forms



•    ____________________  generations are structurally different, while



____________________  generations look similar (Figure 28.16)



•   Almost anywhere there is water









•   They form an important part of plankton


Evolution of Eukaryotes

•    How did complex eukaryotic cells evolve from simpler prokaryotic cells?

•    Important developments in complexity & organization  that led to Eukaryotic Cells:

•    Compartmentalization of different functions within a cell

•    We have already discussed …



•    ____________________  (Chapter 25)



•    Eukaryotic cells evolved from symbiotic “combinations” of prokaryotic cells



•    ____________________  :

•    developed from aerobic heterotrophic prokaryotes that entered larger cells as prey or parasites



•    ______________________________________  :


•    descendents of photosynthetic prokaryotes that became endosymbionts within larger cells (Figure 25.9)





•    similarities between modern bacteria and the chloroplasts and mitochondria of eukaryotes

– size

– membrane enzymes

– transport systems

– circular DNA without associated proteins

– process of replication

– ribosomes


Secondary Endosymbiosis & Algal Diversity

•    Algal plastids are structurally more diverse than plants and green algae

•    Result of …



•    Additional membranes are added through acquisition of additional plastids

•    These plastids eventually retain the vacuole membrane

•    In addition, some protists contain vestigial cytoplasm and nucleomorphs …

–  vestiges of the nucleus of the eukaryotic ancestor of the plastid

•    Figure 28.2


Systematics & Phylogeny

•    Protists were formerly treated as …

•    the garbage dump into which all the “misfits” fit

•    Protists were …

•    a polyphyletic group

•    Molecular phylogenetics is helping to resolve phylogeny

•    Currently (Figure 28.3):

•    5 broadly defined protistan clades are recognized


Supergroup: Excavates



•    The clade Excavata is characterized by its ____________________  

•    It includes protists with modified mitochondria and protists with unique flagella



•    Some members have a feeding ____________________  

•    This controversial group includes the diplomonads, parabasalids, and euglenozoans


Supergroup: Excavates
Diplomonads and Parabasalids

•    These 2 groups live in anaerobic environments, lack plastids, and have modified mitochondria

•    Diplomonads

–  Have modified mitochondria called ____________________  

–  Derive energy anaerobically, for example, by glycolysis

–  Have two equal-sized nuclei and multiple flagella

–  Are often parasites, for example, Giardia intestinalis

•    Parabasalids


–  Have reduced mitochondria called ____________________  that generate some energy anaerobically

–  Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females (Figure 28.4)


Supergroup: Excavates

•    Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

•    The main feature distinguishing them as a clade is a spiral or crystalline __________  of unknown function inside their flagella

•    This clade includes the kinetoplastids and euglenids


Supergroup: Excavates
Group Euglenozoa

•    Kinetoplastids have a single mitochondrion with an organized mass of DNA called a




•    They include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems

•    This group includes Trypanosoma, which causes sleeping sickness in humans

•    Another pathogenic trypanosome causes Chagas’ disease (Figure 28.6)


Supergroup: Excavates
Group Euglenozoa



•     Euglenids have one or two ____________________  that emerge from a pocket at one end of the cell


•     Some species can be ____________________  autotrophic and heterotrophic (Figure 28.7)


Supergroup: Chromalveolates

•    Some data suggest that the clade Chromalveolata is monophyletic and originated by



a secondary ____________________  event

•    The proposed endosymbiont is a red alga

•    This clade is controversial and includes the alveolates and the stramenopiles


Supergroup: Chromalveolates
Group: Alveolates

•    Members of the clade Alveolata have membrane-bounded sacs



(____________________  ) just under the plasma membrane

•    The function of the alveoli is unknown

•    Alveolata includes the dinoflagellates, apicomplexans, and ciliates (Figure 28.8)


Supergroup: Chromalveolates
Group: Alveolates

•    Dinoflagellates are a diverse group of aquatic mixotrophs and heterotrophs

•    They are abundant components of both marine and freshwater phytoplankton

•    Each has a characteristic shape that in many species is reinforced by internal plates



of ____________________  

•      Two flagella make them spin as they move through the water



•      Dinoflagellate blooms are the cause of toxic “____________________   



____________________  ”

Figure 28.9


Supergroup: Chromalveolates
Group: Alveolates

•    Apicomplexans are parasites of animals, and some cause serious human diseases

•    One end, the apex, contains a complex of organelles specialized for penetrating a host

•    They have a nonphotosynthetic plastid, the ____________________  

•    Most have sexual and asexual stages that require two or more different host species for completion

•    Plasmodium is an apicomplexan parasite that causes malaria

•    Plasmodium requires both mosquitoes and humans to complete its life cycle

•    Approximately 2 million people die each year from malaria

•    Efforts are ongoing to develop vaccines that target this pathogen

Figure 28.10


Supergroup: Chromalveolates
Group: Alveolates

•    Ciliates, a large varied group of protists, are named for their use of cilia to move and feed


•    They have large ____________________  and small ____________________  

•    The micronuclei function during conjugation, a sexual process that produces genetic variation

•    Conjugation is separate from reproduction, which generally occurs by binary fission

Figure 28.11


Supergroup: Chromalveolates
Group: Stramenopiles

•    The clade Stramenopila includes several groups of heterotrophs as well as certain groups of algae

•    Most have a “____________________  ” flagellum paired with a



“____________________  ” flagellum (Figure 28.12)


Supergroup: Chromalveolates
Group: Stramenopiles

•    Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated




•    Diatoms usually reproduce asexually, and occasionally sexually

•    Diatoms are a major component of phytoplankton and are highly diverse

•    Fossilized diatom walls compose much of the sediments known as



____________________  earth (Figure 28.13)


Supergroup: Chromalveolates
Group: Stramenopiles
Golden Algae

•    Golden algae are named for their color, which results from their yellow and brown




•    The cells of golden algae are typically biflagellated, with both flagella near one end

•    All golden algae are photosynthetic, and some are also heterotrophic

•    Most are unicellular, but some are colonial (Figure 28.14)


Supergroup: Chromalveolates
Group: Stramenopiles
Brown Algae

•    Brown algae are the largest and most complex algae

•    All are multicellular, and most are marine

•    Brown algae include many species commonly called “seaweeds”



•    Brown algae have the most ____________________  multicellular anatomy of all algae

•    Giant seaweeds called kelps live in deep parts of the ocean



•    The algal body is plantlike but ____________________  true roots, stems, and leaves and is called a thallus

•    The rootlike holdfast anchors the stemlike stipe, which in turn supports the leaflike blades (Figure 28.15)


Supergroup: Chromalveolates
Group: Stramenopiles Oomycetes (Water Molds and Their Relatives)

•    Oomycetes include water molds, white rusts, and downy mildews

•    They were once considered fungi based on morphological studies

•    Most oomycetes are decomposers or parasites



•    They have ____________________  (hyphae) that facilitate nutrient uptake

•    Their ecological impact can be great, as in Phytophthora infestans causing potato blight


Supergroup: Rhizaria

•    DNA evidence supports Rhizaria as a monophyletic clade

•    They are a diverse group of protists defined by DNA similarities



•    Amoebas move and feed by ____________________  ; some but not all belong to the clade Rhizaria

•    Rhizarians include forams and radiolarians


Supergroup: Rhizaria

•    Foraminiferans, or forams, are named for porous, generally multichambered shells,



called ____________________  

•    Pseudopodia extend through the pores in the test

•    Foram tests in marine sediments form an extensive fossil record


Supergroup: Rhizaria

•    Marine protists called radiolarians have tests fused into one delicate piece, usually made of silica

•    Radiolarians use their pseudopodia to engulf microorganisms through




•    The pseudopodia of radiolarians radiate from the central body

Figure 28.18


Supergroup: Archaeplastida
Red algae and Green algae are the closest relatives of land plants

•    Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont

•    The photosynthetic descendants of this ancient protist evolved into red algae and green algae

•    Land plants are descended from the green algae

•    Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants


Supergroup: Archaeplastida
Red Algae

•    Red algae are reddish in color due to an accessory pigment called



____________________  , which masks the green of chlorophyll

•    The color varies from greenish-red in shallow water to dark red or almost black in deep water


•    Red algae are usually ____________________  ; the largest are seaweeds

•    Red algae are the most abundant large algae in coastal waters of the tropics

Figure 28.19


Supergroup: Archaeplastida
Green Algae

•    Green algae are named for their grass-green chloroplasts

•    Plants are descended from the green algae

•    The two main groups are chlorophytes and charophyceans

•    Most chlorophytes live in fresh water, although many are marine

•    Other chlorophytes live in damp soil, as symbionts in lichens, or in snow

•    Chlorophytes include unicellular, colonial, and multicellular forms

•    Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages

Figure 28.21


Supergroup: Unikonta

•    The supergroup Unikonta includes animals, fungi, and some protists

•    This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists)

•    The root of the eukaryotic tree remains controversial

•    It is unclear whether unikonts separated from other eukaryotes relatively early or late


Supergroup: Unikonta
Group: Amoebozoans

•      Amoebozoans are amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia

•      They include gymnamoebas, entamoebas, and slime molds


Supergroup: Unikonta
Group: Amoebozoans
Slime Molds

•      Slime molds, or mycetozoans, were once thought to be fungi

•      Molecular systematics places slime molds in the clade Amoebozoa


Supergroup: Unikonta
Group: Amoebozoans
Plasmodial Slime Molds



•      Many species of plasmodial slime molds are brightly ____________________  , usually yellow or orange

•      At one point in the life cycle, plasmodial slime molds form a mass called a



____________________  (not to be confused with malarial Plasmodium)

•      The plasmodium is undivided by membranes and contains many diploid nuclei

•      It extends pseudopodia through decomposing material, engulfing food by phagocytosis

Figure 28.24


Supergroup: Unikonta
Group: Amoebozoans
Cellular Slime Molds

•      Cellular slime molds form multicellular aggregates in which cells are separated by their membranes

•      Cells feed individually, but can aggregate to form a fruiting body

•      Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity

Figure 28.25


Supergroup: Unikonta
Group: Amoebozoans

•    Gymnamoebas are common unicellular amoebozoans in soil as well as freshwater and marine environments

•    Most gymnamoebas are heterotrophic and actively seek and consume bacteria and other protists


Supergroup: Unikonta
Group: Amoebozoans

•    Entamoebas are parasites of vertebrates and some invertebrates

•    Entamoeba histolytica causes amebic dysentery in humans


You should now be able to:

•       Explain why Protistan taxonomy is in “flux”

•       Explain the process of endosymbiosis and state what living organisms are likely relatives of mitochondria and plastids

•       Distinguish between endosymbiosis and secondary endosymbiosis

•       Name the five supergroups, list their key characteristics, and describe some representative taxa (See Figure/Table at the end of Chapter 28)