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

Protists

• 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)

Habitat

• 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)

Endosymbiosis

• 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)

Evidence

•

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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
Forams

• 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
Radiolarians

• 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

• 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

• 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)