Kingdom Protista

Protists

50 m

Even a low-power microscope

–Can reveal an astonishing menagerie of organisms in a drop of pond water

•Protists are more diverse than all other eukaryotes

–And are no longer classified in a single kingdom

•Most protists are unicellular

–And some are colonial or multi-cellular

Protist Diversity

Protist Diversity

• Organisms that range in size from single cells to complex structures more than 100 meters long.

• They show a variety of reproductive and nutritional strategies.

Protist Diversity

•Protists, the most nutritionally diverse of all eukaryotes, include

–Photoautotrophs, which contain chloroplasts

–Heterotrophs, which absorb organic molecules or ingest larger food particles

–Mixotrophs, which combine photosynthesis and heterotrophic nutrition

100 m

100 m

4 cm

500 m

The freshwater ciliate Stentor, a unicellular protozoan (LM)

Ceratium tripos, a unicellular marine dinoflagellate (LM)

Delesseria sanguinea, a multicellular marine red alga

Spirogyra, a filamentous freshwater green alga (inset LM)

(a)

(b)

(c)

(d)

Protists are also diverse in habitat

•Including freshwater and marine species

•There is now considerable evidence

–That much of protist diversity has its origins in endosymbiosis

ProtistA Evolution

•The plastid-bearing lineage of protists

–Evolved into red algae and green algae

•On several occasions during eukaryotic evolution

–Red algae and green algae underwent secondary endosymbiosis, in which they themselves were ingested

ProtistA Evolution

Cyanobacterium

Heterotrophiceukaryote

Primaryendosymbiosis

Red algae

Green algae

Secondaryendosymbiosis

Secondaryendosymbiosis

Plastid

Dinoflagellates

Apicomplexans

Ciliates

Stramenopiles

Euglenids

Chlorarachniophytes

Plastid

Alv

eola

tes

2˚ Endosymbiosis

•Have modified mitochondria

–Are adapted to anaerobic environments

–Lack plastids

–Have mitochondria that lack DNA, an electron transport chain, or citric-acid cycle enzymes

•A tentative phylogeny of eukaryotes

–Divides eukaryotes into many clades

Diplomonadida and parabasala

Diplomonads

–Have two nuclei and multiple flagella

5 µm(a) Giardia intestinalis, a diplomonad (colorized SEM)

ZooflagellatesZooflagellates

· Move by flagella

· They may enter into symbiotic relationships with other organisms.

Parabasalids-include trichomonads

–Which move by means of flagella and an undulating part of the plasma membrane

Euglenozoa

•Have flagella with a unique internal structure

•Euglenozoa is a diverse clade that includes

–Predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

•2 Types

–Kinetoplastids & Euglenids

Euglenozoa•The main feature that distinguishes protists in this clade

–Is the presence of a spiral or crystalline rod of unknown function inside their flagella

Flagella0.2 µm

Crystalline rod

Ring of microtubules

Kinetoplastids–Have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast

–Include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems

Trypanosoma

9 m

–Causes sleeping sickness in humans

Tsetse fly

Euglenids

Figure 28.8

Long flagellum

Short flagellum

Nucleus

Plasma membrane

Paramylon granule

Chloroplast

Contractile vacuole

Light detector: swelling near thebase of the long flagellum; detectslight that is not blocked by theeyespot; as a result, Euglena movestoward light of appropriateintensity, an important adaptationthat enhances photosynthesis

Eyespot: pigmentedorganelle that functions

as a light shield, allowinglight from only a certain

direction to strike thelight detector

Pellicle: protein bands beneaththe plasma membrane that

provide strength and flexibility(Euglena lacks a cell wall)

Euglena (LM)5 µm

EuglenidsEuglenids

EuglenidsEuglenids

Only one third of the species of Euglenoids are photosynthetic.

·   Euglena stores glucose in a polymer called Paramylon

·       

An eyespot with a photoreceptor is capable of detecting the presence of light.·       

Reproduction is asexual.

Alveolates

Members of the clade Alveolata

–Have membrane-bounded sacs (alveoli) just under the plasma membrane

FlagellumAlveoli0.2 µm

Includes:

•Dinoflagellates

•Apicomplexans

•Ciliates

Dinoflagellates–Are a diverse group of aquatic photoautotrophs and heterotrophs

–Are abundant components of both marine and freshwater phytoplankton

•Shape is reinforced by internal plates of cellulose

•Two flagella

–Make them spin as they

–move through the water

DinoflagellatesDinoflagellatesSome species are responsible for red tides that kill fish and shellfish

Toxins released can kill aquatic & terrestrial animals (aerosols)

Apicomplexans–Are parasites of animals and some cause serious human diseases

–Are so named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues

–Have a non-photosynthetic plastid, the apicoplast

ApicomplexansMost apicomplexans have intricate life cycles

–With both sexual and asexual stages that often require two or more different host species for completion

–Plasmodium causes malaria

PlasmodiumAnopheles mosquito

SporozoansSporozoans

• Parasitic

• Complicated life cycle that usually involves the formation of infective spores.

e.g. malaria - The parasite is injected into

a human by a mosquito. The parasite then invades red blood cells and ruptures them.

Ciliates–Are named for their use of cilia to move and feed

–Have large macronuclei and small micronuclei•The micronuclei

–Function during conjugation, a sexual process that produces genetic variation

•Conjugation is separate from reproduction

–Which generally occurs by binary fission

CiliatesCiliates• Example - Paramecium• The outer covering of paramecium is

covered with hundreds of cilia

• They have numerous organelles including a gullet (oral groove) and an anal pore

• The macronucleus controls the cell's activities.

• The micronucleus is involved in cell reproduction (sexual & asexual).

CONJUGATION AND REPRODUCTION

8 7

2

MICRONUCLEARFUSION

Diploidmicronucleus

Diploidmicronucleus

Haploidmicronucleus

MEIOSIS

Compatiblemates

Key

ConjugationReproduction

Macronucleus

The original macro-nucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei.

Micronuclei fuse,forming a diploid micronucleus.

Three rounds of mitosis without cytokinesis produce eight micronuclei.

Meiosis of micronuclei produces four haploidmicronuclei in each cell. 3 micronuclei in each cell

disintegrate. The remaining micro-nucleus in each cell divides by mitosis

The cells swap one micronucleus

The cellsseparate

Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells.

ParameciumParamecium

http://www.ittiofauna.org/webmuseum/invertebrati/microinvertebrati/pg_07_big.htm

50 µm

FEEDING, WASTE REMOVAL, AND WATER BALANCE

Stentor (Type of ciliate)Stentor (Type of ciliate)

Stramenopila

•Stramenopiles have “hairy” and smooth flagella

•The clade Stramenopila Includes:

–Water molds

–Diatoms

–Golden algae

–Brown algae

Smoothflagellum

Hairyflagellum

5 µm

Oomycetes–Include water molds, white rusts, and downy mildews

–Were once considered fungi based on morphological studies

–Are decomposers or parasites

–Have filaments (hyphae) that facilitate nutrient uptake

–Have cell walls made of cellulose

Diatoms •Are unicellular algae

–With a unique two-part, glass-like wall of hydrated silica

–major component of phytoplankton

3 µ

m

DiatomsDiatoms·  Most numerous unicellular algae in the oceans and are an important source of food and

oxygen. ·    Also important in freshwater environments.

·    Glucose stored as polysaccharide laminarin (Same as golden & brown algae)

·    Their remains form diatomaceous earth.

DiatomsDiatoms

50 µm

~ 100 000 species

•Or chrysophytes

–Are named for their color, which results from their yellow & brown carotenoids

•The cells of golden algae

–Are typically bi-flagellated, with both flagella attached near one end of the cell

Golden Algae

25 µm

Brown algae

•Or phaeophytes

–Are the largest and most complex algae

–Are all multicellular, and most are marine

–Include many of the species commonly called seaweeds

•Seaweeds

–Have the most complex multi-cellular anatomy of all algae

Brown AlgaeBrown AlgaePhotosynthetic & multicellular ·  Range in size. Many are 50-100 m long.·  Found along rocky shores

The thalus (plant like body) contains:·     Holdfasts for attachment·     Blades and air bladders that function in floatation ·     A stem-like structure that holds the blades is called a stipe.FucusCommon "seaweed" found along the rocky coast.

Blade

Stipe

Holdfast

Brown AlgaeBrown Algae

•Kelps, or giant seaweeds

–Live in deep parts of the ocean

–Can grow as long as 60m

Cell walls are composed of cellulose and gel forming polysaccharides which cushion the algae in the intertidal zone

Brown Algae - Brown Algae - Macrocystis Macrocystis and Nereocystisand Nereocystis (Deep water (Deep water

Kelp)Kelp)

Macrocystis

Nereocystis

•The most complex life cycles include an alternation of generations

–The alternation of multi-cellular haploid and diploid forms

Sporophyte(2n)

Zoospores

Female

Gametophytes(n)

MEIOSIS

FERTILIZATION

Developing sporophyte

Zygote(2n)

Mature femalegametophyte

(n)

Egg

Sperm

Male

Sporangia

Key

Haploid (n)Diploid (2n)

A variety of life cyclesHave evolved among the multi-cellular

algae

Cercozoans

•Cercozoans and radiolarians have threadlike pseudopodia

•A newly recognized clade, Cercozoa

–Contains a diversity of species that are among the organisms referred to as amoebas

•Amoebas were formerly defined as protists

–That move and feed by means of pseudopodia

•Cercozoans are distinguished from most other amoebas

Foraminiferans, or forams

–Are named for their porous, generally multichambered shells, called tests

20 µm

Pseudopodia extend through the pores in the test

Radiolarians•Marine protists

–Whose tests are fused into one delicate piece, which is generally made of silica

–Phagocytize microorganisms with their pseudopodia

•The pseudopodia of radiolarians, known as axopodia

–Radiate from the central body

200 µm

Axopodia

RadiolariansRadiolarians

Marine plankton (float in marine environments) with a skeleton composed of silica, and numerous needle-like pseudopodia.

Amoebozoans• Have lobe-shaped pseudopodia

–rather than threadlike, pseudopodia

–Include gymnamoebas, entamoebas, and slime molds

ProtozoansProtozoans·  Do not have a cell wall

· Heterotrophic

·  Usually motile ·  Food vacuoles

·  Contractile vacuole (water elimination)

Reproduction is usually asexual but many also reproduce sexually during some part of their life cycle.

Gymnamoebas

–Are common unicellular amoebozoans in soil as well as freshwater and marine environments

•Most are heterotrophic

–And actively seek and consume bacteria and other protists

Pseudopodia

40 µm

Entamoeba

–Are parasites of vertebrates and some invertebrates

•Entamoeba histolytica

–Causes amebic dysentery in humans

AmoeboidsAmoeboids

Amoeba

Move by cytoplasmic extensions called pseudopodia.

Feed by phagocytizing (engulfing) their prey.

Most amoeboids are marine organisms;

Amoeba proteus is found in freshwater

AmoeboidsAmoeboids

Slime molds, or mycetozoans

–Were once thought to be fungi

•Molecular systematics

–Places slime molds in the clade Amoebozoa

–Plasmodial & Cellular types

The plasmodium–Is undivided by membranes and contains many diploid nuclei

–Extends pseudopodia through decomposing material, engulfing food by phagocytosis

Protists that are Decomposers Protists that are Decomposers (Saprotrophs)(Saprotrophs)

·     Slime molds play an ecological role similar to that of fungi. ·      They are decomposers, feeding on dead organic material. ·      They differ from fungi in that slime molds ingest their food.

·      Slime molds are masses that creep along the substrate and phagocytize dead organic material and microorganisms.

·        The mass is one large cell referred to as a plasmodium.

·        Spores are resistant to environmental extremes (Food and moisture) and germinate when environmental conditions become favorable

·        Saprotrophic; they live off of dead organic matter.

Slime MoldsSlime Molds

Feedingplasmodium

Matureplasmodium(preparing to fruit)

Youngsporangium

Maturesporangium

Spores(n)

Germinatingspore

Amoeboid cells(n)

Zygote(2n)

1 mm

Key

Haploid (n)Diploid (2n)

MEIOSIS

SYNGAMY

StalkFlagellated cells(n)

Plasmodial Slime mold life cycle

Cellular slime molds

•Form multicellular aggregates

–In which the cells remain separated by their membranes

–Has become an experimental model for studying the evolution of multi-cellularity

Cellular Slime Mold Life Cycle

Spores(n)

Emergingamoeba

Solitary amoebas(feeding stage)

ASEXUALREPRODUCTIONFruiting

bodies

Aggregatedamoebas

Migratingaggregate

SYNGAMY

MEIOSIS

SEXUALREPRODUCTION

Zygote(2n)

Amoebas

600 µm

200 µm

Key

Haploid (n)Diploid (2n)

Algae

The word algae refers to aquatic (freshwater or marine) protists.

       

Algae photosynthesize like plants. They produce much of the oxygen in the atmosphere.

·  Algae provide food for aquatic food chains.

Red & Green Algae

•Are the closest relatives of land plants

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

–And the photosynthetic descendants of this ancient protist evolved into red algae and green algae

Red Algae• Are reddish in color

–Due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll

Red Algae

• Red algae are found mainly in warmer, tropical oceans.

• Accessory photosynthetic pigments are called phycobilins which allow some species to survive in deep waters where blue and green light predominates.

• Some species are filamentous but most have a complex pattern of branching.

• Some coralline forms deposit calcium carbonate in their cell walls, making coral reefs.

Green Algae–Are named for their grass-green chloroplasts

–Are divided into two main groups: chlorophytes and charophyceans

–Are closely related to land plants

Green AlgaeGreen Algae

Single-celled and multicellular forms.

·   

Ancestors of the first plants, both have the following characteristics in common:

They have a cell wall that contains cellulose.They have chlorophyllThey store their food as starch inside the

chloroplast.

Chlorophytes (green algae)

•Include:

–Unicellular, colonial, and multi-cellular forms

(a)

)

20 µm50 µm

UlvaUlva

• Multicellular with a leaf-like body that is two cells thick but up to one meter long

• Common name: Sea lettuce

VolvoxVolvox

· Colonial green algae

· They divide asexually to produce a daughter colony.

Notice the daughter colonies within the larger colonies.

VolvoxVolvox

• Some cells are specialized to produce sperm and eggs for sexual reproduction which is a characteristic of multicellular organisms.

• Considered to be a colony because it appears to be intermediate between a group of individual cells and a multicellular organism.

SpirogyraSpirogyra

·  Filamentous form of green algae.

·  Has a ribbonlike spiral-shaped chloroplast.

·  Sexual reproduction occurs by conjugation. ·       

The zygote is resistant and overwinters.

SpirogyraSpirogyra

Conjugation

Flagella

Cell wall

Nucleus

Regionsof singlechloroplast

Zoospores

ASEXUALREPRODUCTION

Mature cell(n)

SYNGAMY

SEXUALREPRODUCTION Zygote

(2n)

MEIOSIS

1 µm

Key

Haploid (n)

Diploid (2n)

++

+

+

Chlorophyte Life CycleHarsh environmental conditions

Normal environmental conditions

Protists Compared to Plants, Protists Compared to Plants,

Animals, and FungiAnimals, and Fungi • Characteristics resemble plants, animals, or fungi.

• Photosynthetic protists differ from plants in that they do not have structures that protect the gametes or zygote. 

• Plants and animals undergo a period of embryonic development but protists do not.

• Fungi have cell walls composed of chitin; protists do not have chitin in their cell walls

• Fungi do not have cilia or flagella. Many kinds of protists have cilia or flagella.

Trophic Levels

Autotrophs:·        green algae·        brown algae·        red algae·        diatoms·       

dinoflagellates·        euglenoids

Heterotrophs:·        amoeboids·        ciliates·        zooflagellates·        sporozoans·        slime molds