28 protists

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 28

Protists


• 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


• These amazing organisms

– Belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists

• Advances in eukaryotic systematics

– Have caused the classification of protists to change significantly


• Concept 28.1: Protists are an extremely diverse assortment of eukaryotes

• 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 multicellular


• 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)


• Reproduction and life cycles

– Are also highly varied among protists, with both sexual and asexual species


• A sample of protist diversity

Table 28.1


Endosymbiosis in Eukaryotic Evolution

• There is now considerable evidence

– That much of protist diversity has its origins in endosymbiosis


• 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


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

onad

s

Par

abas

alid

s

Kin

etop

last

ids

Eug

leni

ds

Din

ofla

gella

tes

Api

com

plex

ans

Cili

ates

Oom

ycet

es

Dia

tom

s

Gol

den

alga

e

Bro

wn

alga

e

Chl

orar

achn

ioph

ytes

Fora

min

ifera

ns

Rad

iola

rians

Gym

nam

oeba

s

Ent

amoe

bas

Pla

smod

ial s

lime

mol

ds

Cel

lula

r slim

e m

olds

Fung

i

Cho

anof

lage

llate

s

Met

azoa

ns

Red

alg

ae

Chl

orop

hyte

s

Cha

roph

ycea

ns

Pla

nts

Ancestral eukaryote

Chl

orop

hyta

Plan

tae

Rho

doph

yta

Ani

mal

ia

Fung

i

(Opisthokonta) (Viridiplantae)Dip

lom

onad

ida

Para

basa

la

Eugl

enoz

oa

Alveolata Stramenopila Cer

cozo

a

Rad

iola

ria

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

Flagella 0.2 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 28.7 9 m


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

Flagellum Alveoli0.2 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 µm

Flagella


• 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


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


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


• The micronuclei

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

• Conjugation is separate from reproduction

– Which generally occurs by binary fission


Figure 28.12

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

KeyConjugationReproduction

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


• 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


Oomycetes (Water Molds and Their Relatives)

• Oomycetes

– Include water molds, white rusts, and downy mildews

– Were once considered fungi based on morphological studies


• Most oomycetes

– Are decomposers or parasites

– Have filaments (hyphae) that facilitate nutrient uptake


• 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


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


• The ecological impact of oomycetes can be significant

– Phytophthora infestans causes late blight of potatoes


Diatoms

• Diatoms are unicellular algae

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

Figure 28.15 3 µm


• Diatoms are a major component of phytoplankton

– And are highly diverse

Figure 28.16 50 µm


• Accumulations of fossilized diatom walls

– Compose much of the sediments known as diatomaceous earth


Golden Algae

• Golden algae, or chrysophytes

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

• The cells of golden algae

– Are typically biflagellated, with both flagella attached near one end of the cell


• Most golden algae are unicellular

– But some are colonial

Figure 28.17

25 µm


Brown Algae

• Brown algae, or phaeophytes

– Are the largest and most complex algae

– Are all multicellular, and most are marine


• 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


Human Uses of Seaweeds

• Many seaweeds

– Are important commodities for humans

– Are harvested for food

Figure 28.20a–c

(a) The seaweed is grown on nets in shallow coastal waters.

(b) A worker spreadsthe harvested sea-weed on bambooscreens to dry.

(c) Paper-thin, glossy sheetsof nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.


Alternation of Generations

• A variety of life cycles

– Have evolved among the multicellular algae

• The most complex life cycles include an alternation of generations

– The alternation of multicellular haploid and diploid forms


• The life cycle of the brown alga Laminaria

Figure 28.21

Sporophyte(2n) Zoospores

Female

Gametophytes(n)

MEIOSIS

FERTILIZATION

Developing sporophyte

Zygote(2n)

Mature femalegametophyte

(n)

Egg

Sperm

Male

Sporangia

Key


The sporophytes of this seaweedare usually found in water just belowthe line of the lowest tides, attachedto rocks by branching holdfasts.

1

In early spring, at the end ofthe main growing season, cells onthe surface of the blade developinto sporangia.

2

Sporangia producezoospores by meiosis.3

The zoospores are allstructurally alike, butabout half of them developinto male gametophytesand half into femalegametophytes. Thegametophytes looknothing like the sporo-phytes, being short, branched filaments thatgrow on the surface ofsubtidal rocks.

4

Male gametophytes release sperm, and female gametophytesproduce eggs, which remainattached to the female gameto-phyte. Eggs secrete a chemicalsignal that attracts sperm of thesame species, thereby increasingthe probability of fertilization inthe ocean.

5

Sperm fertilizethe eggs.6

The zygotesgrow into newsporophytes,

starting lifeattached to

the remains ofthe female

gametophyte.

7


• 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 tests

Figure 28.22

20 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


Slime Molds

• Slime molds, or mycetozoans

– Were once thought to be fungi

• Molecular systematics

– Places slime molds in the clade Amoebozoa


Plasmodial Slime Molds

• Many species of plasmodial slime molds

– Are brightly pigmented, usually yellow or orange

Figure 28.25

4 cm


• At one point in the life cycle

– They form a mass called a plasmodium

Figure 28.26

Feedingplasmodium

Matureplasmodium(preparing to fruit)

Youngsporangium

Maturesporangium

Spores(n)

Germinatingspore

Amoeboid cells(n)

Zygote(2n)

1 mm

Key


MEIOSIS

SYNGAMY

StalkFlagellated cells(n)

The feeding stageis a multinucleateplasmodium that liveson organic refuse.

1 The plasmodiumtakes a weblike form.2 The plasmodium erects

stalked fruiting bodies (sporangia)when conditions become harsh.

3

Within the bulboustips of the sporangia,meiosis produces haploidspores.

4 These cells areeither amoeboid orflagellated; the twoforms readily convertfrom one to the other.

6 The cells unitein pairs (flagellatedwith flagellatedand amoeboid withamoeboid), formingdiploid zygotes.

7 The resistant spores dispersethrough the air to new locationsand germinate, becoming activehaploid cells when conditionsare favorable.

5


• The plasmodium

– Is undivided by membranes and contains many diploid nuclei

– Extends pseudopodia through decomposing material, engulfing food by phagocytosis


Cellular Slime Molds

• Cellular slime molds form multicellular aggregates

– In which the cells remain separated by their membranes


• The life cycle of Dictyostelium, a cellular slime mold

Spores(n)

Emergingamoeba

Solitary amoebas(feeding stage)

ASEXUALREPRODUCTIONFruiting

bodiesAggregatedamoebas

Migratingaggregate

SYNGAMY

MEIOSIS

SEXUALREPRODUCTION

Zygote(2n)

Amoebas

600 µm

200 µm

KeyHaploid (n)Diploid (2n)Figure 28.27

In the feedingstage of the lifecycle, solitary haploidamoebas engulf bacteria.

1 During sexual repro-duction, two haploidamoebas fuse andform a zygote.

2

The zygotebecomes a giantcell (not shown)by consuminghaploid amoebas.After developing aresistant wall, thegiant cell undergoesmeiosis followed byseveral mitoticdivisions.

3

The resistantwall ruptures,releasing newhaploid amoebas.

4

When food is depleted,hundreds of amoebascongregate in response to achemical attractant and forma sluglike aggregate (photobelow left). Aggregateformation is the beginningof asexual reproduction.

5

The aggregate migrates for awhile and then stops. Some of the

cells dry up after forming a stalk thatsupports an asexual fruiting body.

6

Othercells crawl

up the stalkand developinto spores.

7

Sporesare released.

8

In a favorableenvironment, amoebasemerge from the sporecoats and begin feeding.

9


• Dictyostelium discoideum

– Has become an experimental model for studying the evolution of multicellularity


• 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


Red Algae

• Red algae are reddish in color

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


• Red algae

– Are usually multicellular; the largest are seaweeds

– Are the most abundant large algae in coastal waters of the tropics

Figure 28.28a–c(a) Bonnemaisonia hamifera. This red alga

has a filamentous form.

Dulse (Palmaria palmata). This edible species has a “leafy” form.

(b)

A coralline alga. The cell walls ofcoralline algae are hardened by calcium carbonate. Some coralline algae aremembers of the biological communities around coral reefs.

(c)


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


Figure 28.31

Flagella

Cell wall

Nucleus

Regionsof singlechloroplast

Zoospores

ASEXUALREPRODUCTION

Mature cell(n)

SYNGAMY

SEXUALREPRODUCTION Zygote

(2n)

MEIOSIS

1 µm

Key


++

+

+

• 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

Technology

28 protists