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The Protists

A diverse assemblage of eukaryotesthat ARENʼT

fungi, plants, or animals

In what ways are protists important?

Base of many “food chains” - especiallyin aquatic settings

Clarify water by filtering out smallparticles

Some are parasites that causediseases in other organisms

Some have economic uses for humansSome are involved in important

symbiotic relationships…

Why can termites eat wood?

Because ofsymbiotichypermastigotes(a group ofparabasilids) livingin the termite gutworking togetherwith Archaeanmethanogens Fig 28.26 (SEM)

And… they are a spectacular groupof organisms

Where Did Eukaryotic Cells come from?

First found in fossil record about 2.1billion years ago

(Prokaryote fossils to 3.5 BYA)Two major features to explain:

- membrane-bounded organelles(mitochondria and plastids)

- internal membrane systems

Origin of Organelles

Idea is that the ancestors ofeukaryotic cells were symbioticconsortiums of prokaryotic cells

Has come to be called the“endosymbiont theory”

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Lynn Margulis

Person who led the development of the endosymbiont theory

The Ideas of the EndosymbiontTheory (Fig 25.9)

Mitochondria are the descendents ofaerobic heterotrophic bacteria

Chloroplasts are the descendants ofphotosynthetic bacteria - very likelycyanobacteria

Origin ofEukaryotes

Fig.25.9

Evidence that Supports theEndosymbiont Theory

Endosymbiotic relationships exist inthe modern world, e.g., somespecies of dinoflagellates areendosymbiotic in corals

Plastids and mitochondria about thesame size as typical prokaryoticcells

Evidence (cont.)

Similar membrane proteins (innermembrane)

Reproduce by a process similar tobinary fission

Contain circular DNA moleculesRibosomal RNA sequences in

organelles more similar toprokaryotes

What organisms have eukaryotic cells?

Animals (mitochondria) Plants (mitochondria and plastids) Fungi (mitochondria) Protists (mitochondria, some have

plastids)

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The ProtistsIncredible diversity of organisms -

your text recognizes 21 clades atprobably the Phylum or Kingdomlevel

Typically found in aquatic or dampenvironments, or in body fluids,tissues, or cells of host organisms

Most have flagella or cilia at somestage in their life cycle

Flagella and Cilia (Fig 6.23)

Structurallydistinct fromthe flagella ofprokaryotes

Eukaryoticflagella andcilia have asimilarstructureinvolvingmicrotubules

Human sperm

Ciliate

Cilia and Flagella in Action

Cilia and Flagella

Protist Size

Most are single-celled, but their cellstructure can be very complex

Ciliates (e.g., Paramecium,Vorticella) are among the mostcomplex of all cells

Some are multicellular andindividuals can be as large as 60meters in length - the “kelps”(brown algae)

Kelp (Brown Algae)

Definitely donʼt need a microscope to see this protist!

Protist Nutrition

Nutritionally diverse- photoautotrophs- chemoheterotrophs

Also are“mixotrophs”e.g., Euglena

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Nutrition

Three major means of obtainingnutrition amongst protists:

- Ingestive (“animal-like”), sometimescalled “protozoa”

- Absorptive (“fungus-like”) - Photosynthetic (“plant-like”),

sometimes called “algae”Distinct nutritional mechanisms may be

found within one Clade

Protistan Phylogeny“Kingdom Protista” was a diverse group of

organisms that were, in many cases, notclosely related

Phylogeny is currently in a “state of flux”DNA sequence data have been, and will

continue to be, very helpfulSplitting of “Kingdom Protista” into 21

clades (Phyla? Kingdoms?) has beenproposed

These clades have been placed into 5“supergroups” in your text

Fig 28.3

Protistan Diversity

A quick look at 9 of the 21 protistclades described in Campbell et al.

Why not look at ALL 21 clades?

Getting a Ph.D. - Thatʼs where you learnmore and more about less and less untilyou know everything about nothing

Intro Bio Course - Thatʼs where you learnless and less about more and more untilyou know nothing about everything

I want you to know something aboutsomething...

Supergroup Excavata

Evidence:- Excavated feeding groove- DNA sequence similarities

Evidence supporting this “supergroup” israther weak and investigation is on-going

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The Parabasalids

Have modified mitochondria called“hydrogenosomes”

Most familiar member Trichomonasvaginalis - cause of a commonsexually transmitted disease

Trichomonas Fact Sheet at the CDC Each cell possesses 4 flagella

Trichomonas vaginalis(Fig. 28.4)

The Euglenozoans

Two major groups: the kinetoplastids

the euglenids

The KinetoplastidsOne large mitochondrian per cellOrganized mass of DNA inside the

mitochondrian - called the “kinetoplast”Genus Trypanosoma cause of “African sleeping sickness”Disease is vectored by the “Tsetse fly”

(Glossina spp.) Invariably fatal if left untreated

Tsetse Fly

Red blood cell Trypanosome

Fig.28.6

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Supergroup Chromalveolata

Evidence:- DNA sequence similarities- Chloroplast structure similarities

Highly controversial “supergroup”

The Alveolates

Characterized by the presence ofsmall membrane-bounded cavitiesunder their cell membrane

Three major groups: Dinoflagellates Apiocomplexans Ciliates

The DinoflagellatesBoth marine and freshwaterMost species unicellularImportant component of “plankton”About 50% of known species are

photosyntheticMost species have elaborate cell

walls

Dinoflagellates

Ceratium (lightmicroscope)

Peridinium(SEM)

“Red Tide”

Dead FishBoat

Red Tide

Dinoflagellate population explosionsWater stained brownish-red

(xanthophylls)Toxins produced by the

dinoflagellates can kill fish,invertebrates, seabirds

Some types of toxins canaccumulate in shellfish - causingpoisoning in humans

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Karenia brevis

One species of dinoflagellate thatcauses red tides

Produces a toxin that kills fish andinvertebrates

Human exposure to the toxin maycause a variety of symptoms,including death - Called “neurotoxicshellfish poisoning”

Karenia brevis (SEM)

Location of Karenia blooms(data from December 2004)

Unit 1 Exam

Available Monday 15 Septemberthrough Tuesday 23 September

READ: “COLL Testing Facility Policiesand Procedures” in the CourseIntroduction Learning Module

Go to Center for On-Line Learning,room 60 Carver Hall to take the exam

The Cilates

Many beautiful freshwater speciesUse cilia to move and feedHave very complex cells, e.g., each

cell has one micronucleus and onemacronucleus

Micronuclei participate in sexualreproduction; macronuclei incontrolling cell functions

Ciliates

Stentor spp. Paramecium spp.

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Paramecium feeding

The Stramenopiles

Some species are photoautotrophic,some are heterotrophic

Characterized by the presence hair-like projections on one of their(typically) two flagella

Stramenopile Flagella (Fig 28.12)Four major groups: Diatoms Brown algae (includes “kelp”) Golden algae Oomycetes (water molds)

The Diatomsglass-like cell walls - made of

hydrated silicaimportant photosynthetic organisms

in “plankton”fresh water and marinelarge number of species (estimated

to be ~ 100,000)

Diatoms

Diatom Diversity(Fig 28.3)

Diatom Art

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Diatomaceous Earth

Huge amounts of ancient diatom cell wallsVarious uses:

filtering medium metal polishes reflective paint pesticide nanotechnology

SEM of Diatom

Supergroup Archaeplastida

Evidence:- DNA sequence similarity- Chloroplast structure similarities

This “supergroup” is well supportedby the available evidence

The Red Algae

No flagella present at any stage of thelife cycle

Most abundant in tropical oceansMost are multicellular~ 6,000 described speciesSome species are heterotrophic

Red Algae (Fig 28.19)

Red Algae

Accessorypigments allowphotosynthesisat great depths -as deep as 260meters

Effective atabsorbing bluelight

Human Uses

Cell wall extracts: carageenan - commonly

eaten by people… agar - microbiological

culturing media

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How do you feel about sushi?

Fig. 28.19

The Green AlgaeMost species (~7,000) found in fresh

waterCell walls with a relatively high

percent of celluloseCan be unicellular,

colonial/filamentous, or multicellularCan be motile (flagella) or non-motile

Single-celled Green Alga -Eremosphaera viridis

Nucleus

Chloroplasts

Chlamydomonas

Unicellular and motile green alga Important model genetic system - much

research is done with this organism

Colonial Green Alga - Volvox (Fig. 28.3)

Volvox

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Filamentous Green Alga - Ulothrix spp.

MulticellularGreen Alga -

Ulva spp.(Fig. 28.21)

Green Algal Life CyclesCan be quite complex with both sexual

and asexual reproductionMost gametes have two flagellaGametes may be isogamous or

anisogamousSome multicellular species exhibit

alternation of generations (as do allplants)

- may be heteromorphic or isomorphic

An example of a green algallife cycle

Oedogonium is a genus offilamentous green algae

Oedogonium Life Cycle Oedogonium life cycle

AnisogamousMeiosis leads to production of

“zoospores” (not gametes)Gametes are produced by mitosisAsexual “macrozoospores” are also

produced by mitosis

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Supergroup Unikonta

Evidence:- DNA sequence similarities

This “supergroup” is well supported bythe available evidence

The Amoebozoans

Four major groups: Plasmodial slime molds Cellular slime molds Gymnamoebas (free-living) Entamoebas (parasitic)

Plasmodial Slime Molds

Feeding stage is an called a“plasmodium” (Fig. 28.24)

The plasmodium is a“coenocytic mass”

Multinucleatecytoplasm undividedby walls ormembranes

Live in moist habitats,e.g., rotting logs

The plasmodiumengulfs food by“phagocytosis” as doameobas

Cool Slime Mold Slime mold in “action”

Planet Earth - Jungles 23:20

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Response to the Environment

Growth away from detergent

Start End ~ 48 hours

Slime Mold Reproduction

If available water or food insufficient,produces resistant spores throughmeiosis

Eachsporangiumproducesmany spores(Fig. 28.24)

Gymnamoebas

UnicellularFound in soil, freshwater, and marine

habitatsHeterotrophs that often consume

prokaryotes and other protists astheir food

Move by producing pseudopodia

Amoeba spp. (Fig. 28.3)

Attack of the Killer Amoeba

Studying organisms too small to seewithout a microscope is…

1. Boring beyondhuman tolerance

2. Very boring3. More interesting

than I expected - butstill boring

4. Remarkablyinteresting

5. More interestingthan any previousexperience in my life

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The most interesting (or least boring)group weʼve studied so far is

1. Archaea2. Bacteria3. Excavata4. Chromalveolata5. Archaeplastida6. Unikonta