Chapter 28 Protista

• Overview: A World in a Drop of Water

• Even a low-power microscope– Can reveal an astonishing menagerie of

organisms in a drop of pond water

Figure 28.150 m

Movie

• Protista- single or colonies of eukaryotic cells (Ameoba, Paramecium)

Animal-Like Protists

8-14

Fig. 8.22

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Cladogram of Protozoa Relationships

Animal-Like Protists: The Protozoa

and Colonial Eukaryotes

Unicellular

Figure 8.3

These amazing organismsBelong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists

• 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

• Protist habitats are also diverse in habitat• And including freshwater and marine species

Figure 28.2a–d

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)

• A sample of protist diversity

Endosymbiosis in Eukaryotic Evolution

Cyanobacterium

Heterotrophiceukaryote

Primaryendosymbiosis

Red algae

Green algae

Secondaryendosymbiosis

Secondaryendosymbiosis

Plastid

Dinoflagellates

Apicomplexans

Ciliates

Stramenopiles

Euglenids

Chlorarachniophytes

Plastid

Alv

eola

tes

Figure 28.3

• Diversity of plastids produced by secondary endosymbiosis

• Concept 28.2: Diplomonads and parabasalids have modified mitochondria

• A tentative phylogeny of eukaryotes– Divides eukaryotes into many clades

Figure 28.4

Dip

lom

ona

ds

Par

aba

salid

s

Kin

etop

last

ids

Eug

leni

ds

Din

ofla

gel

late

s

Api

com

ple

xan

s

Cili

ate

s

Oo

myc

ete

s

Dia

tom

s

Go

lden

alg

ae

Bro

wn

alg

ae

Ch

lora

rach

nio

phy

tes

Fo

ram

inife

ran

s

Ra

dio

laria

ns

Gym

nam

oeba

s

Ent

amoe

bas

Pla

smo

dia

l slim

e m

olds

Ce

llula

r sl

ime

mo

lds

Fu

ngi

Ch

oan

ofla

ge

llate

s

Met

azo

ans

Re

d al

gae

Ch

loro

phyt

es

Ch

aro

phy

cea

ns

Pla

nts

Ancestral eukaryote

Ch

loro

ph

yta

Pla

nta

e

Rh

od

op

hyt

a

An

ima

lia

Fu

ng

i

(Opisthokonta) (Viridiplantae)Dip

lom

on

ad

ida

Par

aba

sal

a

Eu

gle

no

zoa

Alveolata Stramenopila Ce

rco

zoa

Ra

dio

lari

a

Amoebozoa

• Diplomonads and parabasalids– Are adapted to anaerobic environments– Lack plastids– Have mitochondria that lack DNA, an

electron transport chain, or citric-acid cycle enzymes

Diplomonads

• Diplomonads– Have two nuclei and multiple flagella

Figure 28.5a5 µm

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

Parabasalids• Parabasalids include trichomonads

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

Figure 28.5b (b) Trichomonas vaginalis, a parabasalid (colorized SEM)

Flagella

Undulating membrane 5 µm

• Concept 28.3: Euglenozoans have flagella with a unique internal structure

• Euglenozoa is a diverse clade that includes– Predatory heterotrophs, photosynthetic

autotrophs, and pathogenic parasites

• 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 microtubulesFigure 28.6

Kinetoplastids

• 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

• The parasitic kinetoplastid Trypanosoma– Causes sleeping sickness in humans

Figure 28.79 m

8-6

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Fig. 8.9

Life Cycle of Trypanosoma Brucei

Figure 8.8 (b)

Phylum Sarcomastigophora

• Chars: Flagella, pseudopodia, or both; single type of nucleus; no spores formed.

• Subphylum Masigophora– Chars: One or more Flagella– Autotrophic (cl. Phytomastigophora)– Heterotrophic (cl. Zoomastigophora) or both;– Reproduction usually by fission

8-4

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Fig. 8.7

Structure of Euglena

Subphylum Mastigophora

(cl. Phytomastigophora)

Euglenids• Euglenids

– Have one or two flagella that emerge from a pocket at one end of the cell

– Store the glucose polymer paramylon

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

• Concept 28.4: Alveolates have sacs beneath the plasma membrane

• Members of the clade Alveolata– Have membrane-bounded sacs (alveoli) just

under the plasma membrane

Figure 28.9

FlagellumAlveoli0.2 µm

Dinoflagellates

• Dinoflagellates– Are a diverse group of aquatic

photoautotrophs and heterotrophs– Are abundant components of both marine and

freshwater phytoplankton

• Each has a characteristic shape– That in many species is reinforced by internal

plates of cellulose

• Two flagella– Make them spin as they move through the

water

Figure 28.10 3 µ

m

Flagella

Figure 8.6

Phylum Dinozoa: Dinoflagellates

• Rapid growth of some dinoflagellates– Is responsible for causing “red tides,” which

can be toxic to humans

Apicomplexans• 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 nonphotosynthetic plastid, the apicoplast

Phylum Apicomplexa

• Chars: All parasites

• Apical complex used for penetrating host cells

• Lack cilia and flagella, except in certain reproductive stages

• Coccidians or apicomplexans are named based upon the presence of apical complex

Most important Coccidians are members of the class

Sporozoea

• Chars: intracellular parasites of animals• Form spores or oocysts following sexual

reproduction• Complex life cycle that involve both

vertebrate and invertebrate hosts

• Example- Plasmodium the sporozoan that causes malaria.

Figure 28.11

Inside mosquito Inside human

Sporozoites(n)

Oocyst

MEIOSIS

Liver

Liver cell

Merozoite(n)

Red bloodcells

Gametocytes(n)

FERTILIZATION

Gametes

Zygote(2n)

Key

Haploid (n)Diploid (2n)

Merozoite

Red blood cell

Apex

0.5 µm

• Most apicomplexans have intricate life cycles – With both sexual and asexual stages that often

require two or more different host species for completion

An infected Anopheles mosquito bites a person, injecting Plasmodium sporozoites in its saliva.

1 The sporozoites enter the person’s liver cells. After several days, the sporozoites undergo multiple divisions and become merozoites, which use their apical complex to penetrate red blood cells (see TEM below).

2

The merozoites divide asexually inside the red blood cells. At intervals of 48 or 72 hours (depending on the species), large numbers of merozoites break out of the blood cells, causing periodic chills and fever. Some of the merozoites infect new red blood cells.

3

Some merozoites form gametocytes.4

Another Anopheles mosquitobites the infected person and picksup Plasmodium gametocytes alongwith blood.

5 Gametes form from gametocytes.Fertilization occurs in the mosquito’sdigestive tract, and a zygote forms.The zygote is the only diploid stagein the life cycle.

6

An oocyst developsfrom the zygote in the wall of the mosquito’s gut. Theoocyst releases thousands

of sporozoites, whichmigrate to the mosquito’s

salivary gland.

7

8-10

Fig. 8.15

Life Cycle of Plasmodium

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Ciliates

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

feed– Have large macronuclei and small micronuclei

Phylum Ciliophora

• Chars: Cilia, macronuclei, and micronuclei usually present

• Ciliates are the largest most complex and diverse group of the protozoans

• Nearly occupy all aquatic habitats• Some are symbiotic• Reproduction can be asexual through

fission or sexual through conjugation

Example of a Ciliophora: Paramecium

• Common freshwater ciliate

• Observe live sample using methylcellulose solution

• Other Ciliophora: Colpidium, Vorticella and Stentor

Figure 28.12

50 µmThousands of cilia cover

the surface of Paramecium.

The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore.

Paramecium, like other freshwater protists, constantly takes in water

by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate

excess water from radial canals and periodically expel it through the plasma membrane.

Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell.

Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis.

Oral groove

Cell mouth

Micronucleus

Macronucleus

FEEDING, WASTE REMOVAL, AND WATER BALANCE

• Exploring structure and function in a ciliate

Contractile Vacuole

CONJUGATION AND REPRODUCTION

8 7

2

MICRONUCLEARFUSION

Diploidmicronucleus

Diploidmicronucleus

Haploidmicronucleus

MEIOSIS

Compatiblemates

Key

Conjugation

Reproduction

Macronucleus

Two cells of compatiblemating strains align sideby side and partially fuse.

1 Meiosis of micronuclei produces four haploidmicronuclei in each cell.

23 Three micronuclei in each cell

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

The cells swap one micronucleus.

4

The cellsseparate.

5

Micronuclei fuse,forming a diploid micronucleus.

6Three rounds of mitosis without cytokinesis produce eight micronuclei.

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

8Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells.

9

Asexual Reproduction in Protozoa - ciliophora

Binary Fission of Ciliated Stentor

Stentor ciliophora

• Concept 28.5: Stramenopiles have “hairy” and smooth flagella

• The clade Stramenopila– Includes several groups of heterotrophs as

well as certain groups of algae

• Most stramenopiles– Have a “hairy” flagellum paired with a

“smooth” flagellum

Smoothflagellum

Hairyflagellum

5 µmFigure 28.13

• The life cycle of a water mold

Figure 28.14

Cyst

Zoospore(2n)

ASEXUALREPRODUCTION

Zoosporangium(2n)

Germ tube

Zygotegermination

FERTILIZATIONSEXUALREPRODUCTION

Zygotes(oospores)(2n)

MEIOSIS

OogoniumEgg nucleus(n) Antheridial

hypha withsperm nuclei(n)

Key

Haploid (n)Diploid (2n)

Encysted zoosporesland on a substrate andgerminate, growing intoa tufted body of hyphae.

1 Several days later,the hyphae begin toform sexual structures.

2 Meiosis produceseggs within oogonia(singular, oogonium).

3 On separate branches of thesame or different individuals, meiosisproduces several haploid sperm nucleicontained within antheridial hyphae.

4

Antheridial hyphae grow likehooks around the oogonium anddeposit their nuclei throughfertilization tubes that lead to theeggs. Following fertilization, thezygotes (oospores) may developresistant walls but are alsoprotected within the wall of theoogonium.

5

A dormant periodfollows, during which theoogonium wall usuallydisintegrates.

6

The zygotes germinateand form hyphae, and thecycle is completed.

7

The endsof hyphae

form tubularzoosporangia.

8

Each zoospor-angium produces

about 30biflagellated

zoosporesasexually.

9

Diatoms• Diatoms are unicellular algae

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

Figure 28.15 3 µ

m

• Diatoms are a major component of phytoplankton– And are highly diverse

Figure 28.16 50 µm

• Most golden algae are unicellular– But some are colonial

Figure 28.17

25 µm

• Brown algae– Include many of the species commonly called

seaweeds

• Seaweeds– Have the most complex multicellular anatomy of

all algae

Figure 28.18

Blade

Stipe

Holdfast

• Kelps, or giant seaweeds– Live in deep parts of the ocean

Figure 28.19

• Concept 28.6: 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– By their threadlike pseudopodia

Foraminiferans (Forams)

• Foraminiferans, or forams– Are named for their porous, generally

multichambered shells, called tests20 µm

• Pseudopodia extend through the pores in the test

• Foram tests in marine sediments– Form an extensive fossil record

Radiolarians

• Radiolarians are marine protists– Whose tests are fused into one delicate piece,

which is generally made of silica– That phagocytose microorganisms with their

pseudopodia

• The pseudopodia of radiolarians, known as axopodia– Radiate from the central body

Figure 28.23200 µm

Axopodia

• Concept 28.7: Amoebozoans have lobe-shaped pseudopodia

• Amoebozoans– Are amoeba that have lobe-shaped, rather

than threadlike, pseudopodia– Include gymnamoebas, entamoebas, and

slime molds

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

Figure 28.24

Pseudopodia

40 µm

Entamoebas

• Entamoebas– Are parasites of vertebrates and some

invertebrates

• Entamoeba histolytica– Causes amebic dysentery in humans

8-7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 8.10

Variations in Pseudopodia

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Fig. 8.11b

Subphylum Sarcodina: Superclass Rhizopoda, Class Lobosea

Other Sarcodina-“Not naked” sarcodines

• Arcella, Difflugia, and Actinospaerium and marine radiolarians and foraminifera form test.

• Test can be formed from sand grains, calcium carbonate and silica

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Fig. 8.12

Freshwater Amoeba (Difflugia Oblongata)

• Concept 28.8: Red algae and 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

Green Algae

• Green algae– Are named for their grass-green chloroplasts– Are divided into two main groups:

chlorophytes and charophyceans– Are closely related to land plants

• Most chlorophytes– Live in fresh water, although many are marine

• Other chlorophytes– Live in damp soil, as symbionts in lichens, or

in snow

Figure 28.29

• Chlorophytes include– Unicellular, colonial, and multicellular forms

Volvox, a colonial freshwater chlorophyte. The colony is a hollowball whose wall is composed of hundreds or thousands of biflagellated cells (see inset LM) embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm;if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “daughter” colonies within them (LM).

(a)

Caulerpa, an inter-tidal chlorophyte.The branched fila-ments lack cross-walls and thus are multi-nucleate. In effect,the thallus is onehuge “supercell.”

(b)

Ulva, or sea lettuce. This edible seaweed has a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against turbulent waves and tides.

(c)

20 µm50 µm

Figure 28.30a–c

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Fig. 8.8

Volvox, A Colonial Flagellate

Figure 28.31

Flagella

Cell wall

Nucleus

Regionsof singlechloroplast

Zoospores

ASEXUALREPRODUCTION

Mature cell(n)

SYNGAMY

SEXUALREPRODUCTION Zygote

(2n)

MEIOSIS

1 µm

Key

Haploid (n)

Diploid (2n)

++

+

+

• Most chlorophytes have complex life cycles– With both sexual and asexual reproductive

stages In Chlamydomonas,mature cells are haploid and contain a single cup-shaped chloroplast (see TEM at left).

1 In response to ashortage of nutrients, dryingof the pond, or some otherstress, cells develop into gametes.

2

Gametes of opposite mating types (designated + and –) pair off and cling together. Fusion of the gametes (syngamy) forms a diploid zygote.

3

The zygote secretes a durable coat that protects the cell against harsh conditions.

4

After a dormant period, meiosis produces four haploid individuals (two of each mating type) that emerge fromthe coat and develop into mature cells.

5

When a mature cell repro-duces asexually, it resorbs its flagella and then undergoes two rounds of mitosis, forming four cells (more in some species).

6

These daughter cells develop flagella and cell walls and then emerge as swimming zoospores from the wall of the parent cell that had enclosed them. The zoospores grow into mature haploid cells, completing the asexual life cycle.

7