TheOriginand Evolution
of MicrobialLife:Prokaryotes
and Protists
Objectives
Introduction
Describe the formation of stromatolites and explain the significance of the organisms that
produce them.
Early Earth and the Origin of Life
16.1 Describethe conditionsunderwhich the first life likely formedand the nature of those
first living organisms.
16.2 Describethe timing andlikely eventsthat led to the origin of life on Earth.
16.3 Describethe experiments
of Dr. StanleyMiller and their significancein understanding
how life might havefirst evolvedon Earth.
16.4 Explain the potentialrole of clay particles in the early evolution of life on Earth.
16.5 Describethe rolesof RNA in the early evolutionof life on Earth.
16.6 Describethe natureof the first cooperativeassociations
of moleculesenclosedby
membranes.
Prokaryotes
16.7
16.E
16.9
16.10
16.11
t6.12
16.13
16.14
16.15
16.16
t6.17
Describethe history and diverseroles of prokaryotic life.
Comparethe characteristics
of BacteriaandArchaea.
Comparethe differentshapesof prokaryotes.
Describethe nutritionaldiversityof prokaryotes.
Describethe diversetypesof Archaealiving in extremeenvironments.
Describethe structuresand functions of the diversefeaturesof prokaryotes.
Explain the natureandcausesof "blooms" of growth in pondsand lakes.
Describesomeof thediseases
associated
with bacteria.
DescribeKoch'spostulates
and explaintheir significanceto science.
Describethe history of bioterrorismand the effectivenessof anthraxas a weapon.
Describethe importantpositive natural roles and human usesof prokaryotes.
Protists
16.18 Explain how the first eukaryoticcells likely originatedas a communityof prokaryotes.
16.19 Describethe basictypesof protists.Explain why biologiststhink that they represent
many kingdoms.
16.20 Describethe characteristics
of the four most commongroupsof protozoa.
16.21,16.22 Describeand comparecellularslime molds and plasmodialslime molds.
of algae,including seaweeds.
16.23,l6.U Describethe characteristics
Comparedinoflagellates,
diatoms,and greenalgae.
t47
148
Instuctor's Guide to Textand Media
16.25 Explainhow multicellularlife may have evolvedfrom protists'
16.26 Createa shorttimeline noting the first evolutionof multicellularlife and the first movementof life onto land.
KeyTerms
stromatolite
ribozyme
RNA world
Bacteria
Archaea
peptidoglycan
coccus
bacillus
autotroph
photoautotroph
chemoautotroph
heterotroph
photoheterotroph
chemoheteronoph
extremehalophile
extremethermophile
methanogen
prokaryoticflagellum
pilus
endospore
actinomycete
cyanobacterium
pathogen
exotoxin
endotoxin
Lyme disease
Koch's postulates
bioremediation
membraneinfolding
endosymbiosis
symbiosis
protist
protozoan
flagellate
amoeba
pseudopodium
aPicomPlexan
ciliate
cellular slime mold
plasmodialslimemold
Plasmodium
alga
dinoflagellate
diatom
greenalga
brown alga
kelp
red alga
multicellular greenalgae
alternationof generations
gametophyte
sporophyte
WordRoots
chemo- : chemical;hetero. : different (chemoheterotruph:an organismthat must consumeorganic
moleculesfor both energyand carbon)
endo- : inner, within (endotoxin:a componentof the outer membranesof certaingram-negativebacteria
responsiblefor generalizedsymptomsof fever and ache)
exo- : outside(exotoxin:a toxic protein secretedby a bacterial cell that producesspecific symPtoms
evenin the absenceof the bacterium)
gamet- : a wife or husband(gametophyte:the multicellular haploid form in organismsundergoingalternationof generations,which mitotically produceshaploid gametesthat unite and grow into the sporophytegeneration)
halo- : salt; -philos = loving (halophile: microorganismsthat live in unusuallyhighly salineenvironmentssuch as the Great Salt Lake or the Dead Sea)
light
photo- : [ght; auto- : self; -troph : food, nourish Qrhotoautotropft;an organismthat harnesses
dioxide)
carbon
from
organic
compounds
of
energyto drive the synthesis
pseudo- = false; -podium : foot Qtseudopodium:a cellular extensionof amoeboidcells usedin moving and feeding)
sporo- : a seed;= -phyto = a plant (sporophyte:the multicellular diploid form in organismsundergoing alternationof generationsthat results from a union of gametesand that meiotically produceshaploid
sporesthat gtow into the gametophytegeneration)
stromato- : somethingspreadout; -lite : a stone (stromatolite.'rocks madeof bandeddomesof sedimentin which are found the most ancient forms of life)
Chapter 16 The Origin and Evolution of Microbial Lift
L49
LectureOutline
Introduction
How Ancient Bacteria Changed the World
A. The evolution of life has had a profound effect on the Earth.
1. Photosynthetic prokaryotes (cyanobacteria) evolved very early in the history of life
and left unique fossilized communities as stromatolites.
2. Modern-day cyanobacteria'of this type, less cornmon becauseof predation,are vittually indistinguishable from the early forms found in stromatolites(Figure 16.0).
3. In addition to being the ancestors of today's cyanobacteria,thesefirst photosynthetic
cyanobacteriaproduced the Earth's first oxygen-rich atmosphere.
4. Photosynthetic prokaryotes were dominant for about 2 billion years, from nearly 3
billion years ago (bya) to about 1 bya.
5. This chapter begins a survey of all of Earth's life forms in an evolutionary context,
beginning with the evolution of life itself.
NOTE: The earliest organisms were ancestorsof modern prokaryotes.They and the
first eukaryotes (early protists) have inhabited our planet for a much longer time
than have members of any other kingdom. Through the evolutionary eventsthat
resulted in their great diversity, all existing metabolic reactionsevolved,at least in
an early form.
I. Early Earth and the Origin of Life
Module 1.6.1 Life began on a young Earth.
A. The age of the universe is estimated to be between 10 and 20 billion years old, while
Earth coalescedfrom gathering interstellar matter about 4.5 bya.
B. The first atmospherewas likely to have been dominated by hot hydrogen gas. However,
the Earth's gravity was not strong enough to hold onto the light H2.
C. Studies of modern volcanoes suggeststhat the Earth's secondearly atmospherewas
composed of water vapor, carbon monoxide, carbon dioxide, nitrogen, and possibly
some methane and ammonia.
D. Earth's crust cooled and solidified about 4.1 bya, condensingwater vapor into early
seas.The early Earth was also subject to intense lightning, volcanic activity, and ultraviolet radiation (Figure 16.1A).
NOTE: It is ironic that life arose under conditions that included bombardmentby UV
radiation and now a major environmental concern is the depletion of the ozone layer
that protects the planet from this radiation (Modules 7.14 and 38.3).
E. Fossil evidence shows that photosynthetic prokaryotes existed by 3.5 bya (Figures
1 6 . 1 B ,D ) .
NOTE: The immensity of geological time and the very early events discussedcan be
made more meaningful by putting them in perspective. Borrowing an idea used by
"life-on-Earth year." On such a scale,
many, use a geologic time scale divided into a
prokaryotic life evolves in mid-March, eukaryotes first appearedaround September 1,
dinosaurs flourished around Christmas, and the typical human life span of 70 years is
representedby the last half-second on December 31.
F. Because cyanobacterialphotosynthesis is complex and advanced,the first cells likely
evolved earlier, perhaps as early as 3.9 bya (Figure 16.1C).
150
Instructor'sGuideto Tbxtand Media
Module 16.2 How did life originate?
generation.
A. Early ideason the origin of life held that life aroseby spontaneous
B. Experimentsin the 1600sshowedthat largerorganismscouldn't arisespontaneously
from nonliving matter.
C. In the 1860s,FrenchscientistLouis Pasteurconfirmedthat all life today,including
microbes,arisesonly from preexistinglife. However,Pasteur'sexperimentsdid not deal
with the questionof the origin of life.
D. It is very likely that life on Eartharosebetween4.1 and 3.5 bya.
that the earliestlife forms were simplerthan
E. Most biologistssubscribeto the hypothesis
nonliving matter.
from
they
evolved
that
and
today,
any that exist
F. Although extraterrestrialorganicmoleculescould have seededEarth's early environment,most scientiststhink that life arosefrom nonorganicmoleculespresentin Earth's
early oceansand atmosPhere.
G. A possiblescenario:Organicmonomersevolvedfirst, then polymers,then aggregates
that eventuallyformed in the particulararrangementthat allowed simple metabolism
and self-replication.Data supportingthe likelihoodof many of thesestepsexist from a
numberof exPeriments.
NOTE: The following modulesdetail someof the experimentalevidenceand theory
supponingthe stepsin this scenario.No one has completedall the stepsin order.
Today's environment(evenin laboratories)is very different from the environmentof the
early Earth. Huge amountsof time are neededfor thesecomplex developmentsto occur'
Module 16.3 TalkingAbout Science:StanleyMiller's experimentsshowedthat organicmoleculescould havearisenon a lifelessEarth.
A. In the 1920s,Oparinand Haldaneproposedthat organicchemistrycould haveevolved
it containedno oxygenand was reducing.
in the early Earth'senvironmentbecause
B. An oxidizing environment(like Earth'sO2-richenvironmenttoday) is corrosive,tending
arisetoday on Earth'
to break molecularbonds.Thus,life couldnot spontaneously
C. A reducing environmenttendsto add electronsto molecules,building more complex
forms from simpleones.
using an artificial mixture of inorganicmoleD. In 1953,Dr. Miller testedthis hypothesis
cules (H2O, H2, CHa,and NHr) in a laboratoryenvironmentthat simulatedconditions
on the early Eanh (Figure 16.3A,B).
E. Within days, the mixture producedaminoacids,some of the 20 amino acids that are
found in organismstoday (seeModule3.12).
usingmodificationsof Miller's setupto more closelymimic
F. More recentexperiments,
the early Earth'senvironment(lessH2, CHa,and NH3 and more CO, CO2,and N),
haveproducedall 20 naturally occurringamino acids, sugars,lipids, and nitrogenous
basesof nucleotides.
G. Rather than the early atmosphere,many scientiststhink that deep-seavents and submergedvolcanoesprovidedthe chemicalsrequiredfor the origin of life.
Module 16.4 The first polymersmay haveformedon hot rocks or clay.
A. Review:Polymerizationoccursby dehydrationsynthesis(Module 3.3).
B. Although biologicalpolymerizationoccursenzymaticallyin organismstoday,the reactions can alsooccurwhen dilute solutionsof monomersare drippedon hot mineral
_l
Chapter 16 The Origin and Evolution of Microbial Lifu
151
surfaces (heat forces the dehydration synthesis) or on clays (electric chargesconcentrate
monomers, and metallic atoms act as catalysts).
C. American biochemist Sidney Fox has made polypeptides from mixtures of amino acids
dripped on hot mineral surfaces.
Module 16.5 The first genetic material and enzymes may both have been RNA.
A. Review:The flow of geneticinformation from DNA to RNA to protein is intricate and
probablydid not evolveas such(seeModule 10.15).
B . The essentialdifferencebetweencells and nonliving matteris replication.
c.
A numberof lines of reasoningand someexperimentssupportthe hypothesisthat the
first genesmay havebeenmadeof RNA. Short RNA moleculescan assemblespontaneously,without cells or enzymes,from precursornucleotides.Someof thesesequences
will self-replicateif placedwith additionalmonomernucleotides.Further,someRNAs
can act as enzymes(ribozymes),even one that catalyzesRNA polymerization(Figure
16.5;Module10.10).
D. The hypotheticalperiodin the evolutionof life, when RNA playedthe role of both
geneticmaterial and enzyme,is termed the RNA world.
Module L6.6 Molecular cooperatives
enclosedby membranesprobably precededthe first real
cells.
A. Life requiresthe closeand intricate cooperationof many different polymers.Macromolprior to the developmentof membranes(Figure 16.6A).
eculesmay havecooperated
B . Experimentalevidenceshowsthat polypeptidesand lipids self-assembleinto microspheres,fluid-filled dropletswith semipermeable,membranelikecoatings.Though not
grow by the attraction of additionalpolypeptidesor lipids and
alive, thesemicrospheres
divide when they reacha certainmaximum size (Figure 16.68).
c.
Early molecularcooperationmay have involved a primitive form of translationof
polypeptidesdirectlyfrom genesin RNA. If thesecooperatingmoleculeswere incorporated into a microsphere,the basic structuresfor self-replicatingcells would be present
(Figure 16.6C).
D. At this point, a primitive form of natural selectionwould favor thosemolecular co-ops
that were most efficient at growing and replicating.
II. Prokaryotes
Module 16.7 ProkaryoteshaveinhabitedEarth for billions of years.
Revia,v:Prokaryoticcells(Module4.4).
A. Fossilevidenceshowsthatprokaryoteswere abundant3.5 bya, and they evolvedalone
for the following 1.5billion years.
B . Prokaryotesare ubiquitous,numerous,and small, surviving in environmentsthat are too
hot, cold, acidic,salry or alkalinefor any eukaryote(Figure 16.7).
c.
Despitebeingsmall,prokaryotes
influenceall other life-as the causeof diseaseand
otherproblems,as benigninhabitantsof all environments,and, morecommonly,in beneficial relationshipswith all other living things.
D. Probablythe most essentialactivitiescarried out by prokaryotesare the numerousways
they functionin the decomposition
of the deadremains(cellularand molecular)of
otherorganisms.
152
Instructor's Guide to Textand Media
Module 16.8 Archaeaand Bacteria are the two main branchesof prokaryotic evolution.
NOTE: When viewed througha microscope,thesetwo groupslook similar.
Review:Classificationof prokaryotesis first discussedin Module 15.14.
A. The main differencesbetweenthesetwo groupsare summarizedon Table 16.8.Many
RNA polymerase,and
of thesedifferencesconcerntheir nucleicacids (rRNA sequences,
presence
of
introns).
the
B. OtherdifferencesbetweenArchaea and Bacteria concernthe structureof their cell
walls and cell membranes.
C. In most featuresarchaeaare more similar to eukaryotesthan to bacteria.
D. Review:Currently, it is thought that modem archaeaand eukaryotesevolvedfrom a
commonancestor(Figure 15.148).
Module 16.9 Prokaryotescome in a variety of shapes.
A. Cocci (singular,coccus)are sphericaland often occur in defined groups of two or more
(Figure 16.9A).Thosethat occur in clustersare called staphylococci.Thosethat occur
in chainsare called streptococci.
(Figure
B. Bacilli (singular,bacillus) are rod-shapedand usually occur unaggregated
chains.
16.98).Diplobacilli occur in pairs and streptobacillioccur in
C. Vibrios resemblecommas(Figure 16.9C).
Spirilla are shorterand less flexiblethan
D. Spirilla and spirochetesare spiral-shaped.
spirochetes(Figure 16.9D).
Module 16.10 Prokaryotesobtain nourishmentin a variety of ways.
A. Review:Cellular respiration(Chapter6) and photosynthesis(Chapter7).
B. Modesof nutrition refer to how organismsobtain energyand carbon(Table16.10).
"self-feeders"that make carbon compoundsfrom the carbonin CO2
C. Autotrophs are
and the energy in sunlight (photoautotrophs) or inorganic compoundssuch as hydrogen sulfide (chemoautotrophs).
Preview: Chemoautotrophicprokaryotesliving in hydrothermal vents are discussedin
the introduction to ChaPter34.
D. Cyanobacteriaare photoautotrophicprokaryotesthat use H2O as a sourceof electrons
and release02 as a wasteProduct.
"other-feeders"that make carbon compoundsfrom the carbonin
E. Heterotrophs are
existing organic compoundsand obtain energy from those samecompounds(chemo'
hetenotrcphs) or from sunlight (photoheterotrophs).
F. E. coli is an important chemoheterotrophthat lives in the human intestine,that can live
on simple sugarsalone(Figure 16.10).
G. With generationtimes as short as severalhours or less, prokaryotic populationscan
multiply exponentiallyas long as there is a ready supply of nutrients.
H. There are two hypothesesregardingthe evolution of nutrition.
obtainedthe necessarycarbonand
1. The first hypothesisis that chemoheterotrophs
in which they evolved.
molecules
and
of
ions
soup
the
rich
energyfrom
2. The secondhypothesisis that chemoautotrophsobtainedthe carbon from dissolved
CO2 and the energyfrom chemicalreactionsinvolving sulfur, iron, and deep-sea
hYdrothermalvents.
Chapter16 TheOrigin and Evolutionof Microbial Lifu
153
Module 16.11 Archaeathrivein extremeenvironments-andin the ocean.
A. Extreme halophilesthrive in salty placessuchas the GreatSalt Lake (Figure 16.114).
aboveboiling
B. Someextremethermophilesthrive in hot springs,evenat temperatures
vents).Otherextremethermophilesthrive in very low pH
(for example,deep-ocean
suchas thosefound in YellowstoneNationalPark (Figure 16.11B).
environments
bacteriathat thrive in
C. The methanogensare a group of anaerobic,methane-producing
of
swamps.
in
the
mud
intestinesand
somevertebrate
arethe organismsresponsiblefor the productionof marshgas and are a
D. Methanogens
major contributorto flatulencein humans.Methanogensalsodigestcellulosein the gut
of animalssuchas cattleand deer.
E. Archaeaare turning up in environmentsthat are not so extreme.They are found at all
depthsin the oceanand are in equalproportionsto bacteriaat depthsbelow 1000
meters.More researchneedsto be conductedon this new domain.
Module 16.12 Diversestructuralfeatureshelp prokaryotesthrive almost everywhere.
A. Review:The size,structure,and function of prokaryotic flagella differ from those
aspectsof eukaryoticflagella(Module 4.18).
B. Flagellacanbe eitherscatteredover a cell or in bunchesat one or both ends.They are
filamentsand rotatcomposedof proteinin two parts:external,nonmembrane-bounded
in the plasmamembraneand cell wall. Motion is producedas they
ing rings embedded
spin on their axeslike propellers.(Figure 16.12{)
C. Review:The role of sexpili in conjugation(Module 12.2).
D. Pili are proteinfilamentsthinner than bacterialflagella(Figure16.128).Pili help bacteria stick to eachother or to surfacesin their environments.
E. Somebacteriacansurviveadverseenvironmentalconditionsby producingthick-walled
endosporesinsidethe parentcell walls arounda replicatedcopy of DNA (Figure
are extremely resistantto decompositionand disintegration.
l6.l2c). Endospores
is illustratedby thoseof Clostridiumbotu'
F. An exampleof the toughnessof endospores
such as poorly
linum, a bacteriumthat grows in anaerobic,low-acid environments,
causesbotulism
bacterium
of
this
colonies
released
by
toxin
The
vegetables.
canned
by humans.
when consumed
G. Actinomycetesare constructedfrom branchingfilamentsof cells. They are
soil bacteriathat break down organic molecules.Some
chemoheterotrophic
arecoilrmercialsourcesof antibiotics(for example,streptomycinfrom
actinomycetes
bacteria;Figure 16.l2D).
Streptomyces
sometimes"bloom" in aquaticenvironments.
Module 16.13 Connection:Cyanobacteria
A. Bloomsarepopulationexplosionsof microorganisms.
B. Largebloomsof cyanobacteriaindicatepollutedwaterconditions(Figure 16.144, B).
Suchbloomsoftenindicatepollution by organicwastes,suchas phosphatesand
nitrates,from agriculturalrunoff.
can releaselarge amountsof toxins that kill fish.
NOTE: Bloomsof cyanobacteria
can use up Oz during nighftime respiration and
of
microorganisms
Blooms of all sorts
suffocateotherO2-requiringorganisms.Relatethe informationin this module to the
in Chapter38 concerningthe humanimpacton the biosphere.
materialpresented
C. The lake picturedin Figure 16.13Amay look very much like the conditionsin which
dominated(=3.0 bya to 1.5 bya).
cyanobacteria
154
Instructor's Guide to Textand Media
may be very similar to that which
D. The photosyntheticapparatusof thesecyanobacteria
first releasedoxygen into Earth'satmosphere.
Module 16.L4 Connection:Somebacteriacausedisease.
A. Bacterialpathogenscauseabouthalf of all known humandiseasesand are responsible
for diseasesin all other eukaryotes.
B. Diseasescan be causedby bacterialgrowth on, and.destructionof, tissues,but theyare
more likely to be causedby the releaseof exotoxins (exotoxinsare madeof glycolipids) from growing bacteriaor the presenceof endotoxins on the surfaces(cell walls)
of thesebacteria.
aureusis a normal skin bacterium,but when it growsinside a person,
C. Staphylococcus
the exotoxinsit producescan causeseriousdisease,suchas toxic shocksyndrome(Figure 16.14A).
D. Harmlessbacteriacan developpathogenicstrains.For example,E. coli O157:H7,normally found in cattle, producean exotoxin that causesbloody diarrheaand may even
lead to kidney failure. The best prevention is to avoid undercookedmeat.
E. Speciesof Salmonella prduce endotoxinsthat causefood poisoning and typhoid fever.
F. Sanitation,the use of antibiotics, and educationare three of our defensesagainstbacterial diseases.
G. However, antibiotic-resistantbacteria have evolved and are now a major health issue
(Module 13.22\.
H. The causeof Lyme disease,Borrelia burgdorferi, is carried by a tick and elicits a distinctive set of symptomsand potential disorders(Figure 16.148).
bacteria.
Module 16.1.5Connection:Koch'spostulatesare usedto identify disease-causing
A. Discovering the causeof diseaseis the first step in preventingor curing the disease.
B. In 1876,Koch presenteddiagnosticcriteria proving Bacillus anthracisto be the cause
of anthrax:
1. The samepathogenmustbe found in eachhost.
2. The pathogenmust be isolatedinto pureculture.
3. The original diseasemustbe producedin new hostsinoculatedwith the culture.
4. The samepathogenmustbe isolatedagainfrom the new host (Figure 16.158).
C. Revia,v:Koch's postulatesprovide a goodexampleof the processof science
(Module 1.2).
D. For somepathogens,Koch'spostulatescannotbe usedbecausethe organismcannotbe
cultured outside the host. The causeof syphilis, the spirocheteTreponemapallidurn, is
such an organism,but the first postulate is true, and other evidenceleavesno doubtthat
this bacteriumis the causeof the disease.
Module 16.16 Connection:Bacteriacan be used as biological weapons.
A. Use of biological organismsas weaponshaveplayed a part throughouthistory.Victims
of bubonic plague (the causativeagent of which is Yersiniapestis)were hurled into the
ranks of opposingarmiesduring the Middle Age of Europe.Other examplesabound.
B. The United Statesstartedits own biological weaponsprogramin 1943and after developing high-qualitybioweaponsdecidedthat the programwas too repulsiveto continue.
The programwas dismantledin 1969 and in 1975the U.S. signedthe Biological
WeaponsConventionthat bannedany future bioweaponprograms.
lI
l
Chapter 16 The Origin and Evolution of Microbial Life
155
C. The anthrax scarewe experienced in the fall of 2001 was horrifying (five Americas
died) yet it could have been worse. Anthrax is not as deadly as some other infectious
diseasessuch as Ebola or smallpox. The route of infection determinesthe mortality
rate. Cutaneousanthrax is relatively easy to treat, while pulmonary anthraxis treatable
if detected early; however, it can be deadly becauseit is usually ignored as a common
cold and then it's too late.
D. An anthrax vaccine is available for personnel in harm's way, military and foreign diplomats. Widespreadvaccination programs would be too expensive and impractical. The
solution is diplomacY.
Module 16.17 Connection: Prokaryotes help recycle chemicals and clean up the environment.
A. Because of the variety of metabolic capabilities, prokaryotes play many beneficial roles
in cycling elementsamong living and nonliving components of environments.
B. Preview: Chemical cycles are discussedmore fully in Chapter 36.
C. Only prokaryotes are capable of nitrogen fixation, the conversion of N2 gas to nitrogen
in amino acids. Important nitrogen fixers include many cyanobacteriaand many chemoheterotrophs in the soil.
Preview: Many plants depend on prokaryotes for nitrogen (Modules 32.13 and 32.14).
D. The breakdown of organic wastes by decomposersis one of the most common beneficial roles of prokaryotes.
E. hokaryotic decomposers are part of the aerobic and anaerobic communities of organisms functioning in sewage-treatmentplants (Figure 16.17A).
F. Natural bacteria are encouraged, or recombinant strains are used, to decomposeaway
the remains of oil spills on beaches (Figure 16.178).
G. Species of Thiobacil/lzs,autotrophs that obtain energy from oxidizing ions in minerals,
can be used to help remove toxic metals from old mine and industrial wastesites. However, their use in this role is limited since their metabolism adds sulfuric acid to the
water.
III. Pnotists
Module 16.1E The eukaryotic cell probably originated as a community of prokaryotes.
A. The fossil record indicates that the first eukaryotes evolved more than 2.0 bya.
B. The endomembrane system is thought to have evolved by membrane infolding and
resulted in the specialization of internal membranes into membrane-boundedorganelles
(Figure 16.18A), except mitochondria and chloroplasts.
Review: The endomembranesystem is described in Modules 4.64.L4.
C. Endosymbiosis is the likely basis of the origin of mitochondria and chloroplasts(Figure 16.188), with mitochondria evolving first. The ancestralmitochondria may have
been small heterofiophic prokaryotes and, similarly, the ancestral chloroplasts may have
been small photosynthetic prokaryotes.
D. Several lines of evidence support the endosymbiotic hypothesis. Mitochondria and
chloroplasts are similar in size and shape to prokaryotes and include bacterial-type
DNA, RNA, and ribosomes. These organelles replicate in eukaryotic cytoplasmin a
manner resemblingbinary fission. The inner, but not the outer, membranesof these
organelles contain erzymes and electron transport molecules characteristicof prokaryotes, not eukarYotes.
NOTE: Endosymbiosisis common today between protists and/or prokaryotes.
156
Instructor's Guide to Tbxt and Media
andtheir closemulticellularrelatives-probably
Module 16.19 Protists-unicellular eukaryotes
representmultiPlekingdoms.
A. Protists are diverse and likely representseveralkingdoms within Domain Eukarya.
protistsare referredto as
B. As a group,protistsare nutritionallydiverse.Photosynthetic
"ilgae," a term with no taxonomicmeaning.Heterotrophicprotistsare referredto as
protozoans.
C. Colonial and multicellularprotistswhoseimmediateancestorswere unicellularare also
consideredprotists.
D. Protistsare found in all habitatsbut aremost commonin aquaticones(Figure 16.19).
E. As eukaryotes,their cells are morecomplexthan prokaryotes',with many kinds of
organelles.
it was ancestralprotiststhat evolvedinto
F. Evolutionarily,protistswerepivotalbecause
ancestralplants,fungi, and animals.
provideevidencethat suggeststhat these
G. Studiesof protistannucleicacid sequences
eukaryotic cells evolvedfrom severaldifferentprokaryotic ancestors.
by lifestyle,not by taxon.
H. In the surveythat follows, protistsareconsidered
Module 16.20 Protozoaareprotiststhat ingesttheir food.
A few are causesof
of wateryenvironments.
A. Most speciesare free-livinginhabitants
into four
are
divided
Protozoa
other
animals.
and
humans
dangerousdiseasesof
grcups: flagellates, amoebas,apicomplexans,ciliates.
NOTE: Most protozoanshavecellsthatlack cell walls, althoughsomehaverelatively
rigid protein skeletonsbelow their plasmamembranes.
B. Flagellatesmove by one or moreflagella.Giardia is a flagellatethat can causeabdominal crampsand severedialrhea(Figure16.20A.1).What makesGiardia particularly
interestingis its two haploid nuclei andlack of mitochondria.The presenceof vestiges
that it oncehad mitochondria.
of mitochondrialgenesin its genomesuggests
that is spreadby tsetseflies
of Trypanosoma
C. Another interestingflagellateis a species
grows
among
blood cells. Trypanosomes
when
it
sickness
and causesAfrican sleeping
escapea host's immuneresponseby changingthe molecularappeifanceof the proteins
in the membranes(Figure 16.204.2).
D. Amoebasmove and feed by meansof pseudopodia(Figure 16'208).
E. Apicomplexansare all parasites,somecausingserioushumandisease.Plasmodium
speciesare spreadby mosquitoesandcausemalaria when they reproduceinside red
blood cells (Figure 16.20C).
Review:The relationshipbetweenthe sickle-cellallele and malaria(Module 9.14)
F. Ciliates are common, free-living forms that use cilia to move and feed. Daily activity is
and sexualrecombinationinvolves as many as
controlled by a polyploid macronucleus,
80 diploid micronuclei(Figure16.20D).
Review: Cilia are definedas numerous,short,flagellaJike structuresarrangedin more
complexpatternsthan flagella(Module4'18).
Module 16.21 Cellular slime moldshavebothunicellularand multicellularstages.
A. The unicellular stageexistsas individual,amoeboidcells that feed on bacteriain rotting
by mitotic cell division (Figure 16.21).
vegetation,increasingtheir populations
Chnpter16 TheOrigin and Evolutionof Microbial Lift
157
B. When their food supplyrunsout, the individualcells massinto a sluglike,multicellular
colony.
C. The slugswanderabout,movingto an advantageous
locationto reproduce.Some cells
form a stalk below, and othersform reproductivesporesabove.
with a simpledevelopmental
D. Becausethey are eukaryotes
sequence,
cellular slime
played
molds have
a role in researchon cellulardifferentiation.
E. Cellular slime moldshavelittle in commonwith true molds.
Module 16.22 Plasmodialslimemoldsform brightly colored"supercells"with many nuclei.
A. Theseprotistsexist in severaldifferentforms, includingsingle cells,multinucleatefeeding webs,resistantbodies,andmulticellularreproductivestructures.
B. They are commoninhabitantsof moist,rotting leavesand deadlogs.
C. Life startsas individualamoeboidor flagellatedcells (that can changeback and forth,
dependingon the availabilityof water).As thesecells ingestbacteria,they grow into an
amoeboidplasmodium(a singleundividedmassof protoplasmcontainingmany nuclei)
(Figure 16.22A).
D. When food runs out, the plasmodium moundsup into reproductivestructures@igure
16.228).
NOTE: Becausethe nucleiin the feedingstageall divide by mitosisat exactly the same
time, someplasmodial slime molds were usedin early researchon the chemistry of
mitosis.
Module 16.23 Photosyntheticprotistsare called algae.
with chlorophylla, as do plants(Module 7.6).
A. Most algaehavechloroplasts
NOTE: The variety of accessoryphotosyntheticpigmentscausesmany algae to be other
colors than the typical gpss-greencolor of chlorophylla.
B. Someheterotrophicprotistsareconsideredalgae.
from singlecells to colonial filaments
C. The morphologyof speciesvariesconsiderably,
(seaweeds).
plantlike
bodies
to
D. Dinoflagellates are uniquelyshapedand move by two flagella in perpendiculargrooves.
Some dinoflagellatesareresponsiblefor toxin-releasingblooms in warm coastal waters
that are known as red tides (Figure 16.23A).Nutritionally, somedinoflagellatesare phoand otherschemoheterotrophs.
toautotrophs,otherschemoautotrophs,
E. Diatoms are unicellular,with uniquely shapedand sculpturedsilica walls. They are
common componentsof wateryenvironments(Figure 16.238).In terms of being a food
soluce, diatomsare to marineanimalswhat plants are to land animals.Fossilized
diatoms make up thick sedimentsof diatomaceousearth, which can be used either for
filtering or as an abrasive.
F. The green algae are conmon inhabitantsof fresh water and include a large variety of
forms. Greenalgaesharesomefeatureswith higher plants and are consideredto be
either the plant kingdom'sancestorsor membersof the plant kingdom (Figure 16.23C).
aremulticellularmarinealgae.
Module L6.24 Seaweeds
protists.Somehavecomplex bodare the mostcomplexof the photosynthetic
A. Seaweeds
ies with leaflike, stemlike,and rootlike structures,all analogousrather than homologous
to similar structuresin higherplants.
Review:The differencebetweenanalogyand homologyis discussedin Module 15.11.
158
Instructor'sGuideto Textand Media
B. Molecularand cellular studiessuggestthat there may be threegroupsof seaweeds;
brown algae,red algae,and multicellular green algae are eachplacedin a different
kingdom.
C. Brown algae includethe most complexseaweeds.Somecan grow to lengthsof 100m,
forming kelp "forests" that are rich with other life (Figure 16.24A).Similaritiesof molsuggestthat brown algaeand diatomsmay be membersof
eculesusedin photosynthesis
the samekingdom.
D. Red algae are most cornmonin tropical marine waters.Most are soft-bodied,but
encrustedspeciesare important in building coral reefs (Figure L6.248\.
E. Somemulticellular gneenalgae are seaweeds,such as Ulva. ThLereproductivepattern
of this alga involves alternationof generations,alternating betweenhaploid gametophytes that give rise to gametesdirectly by mitosis and diploid sporophytesthat give
rise to sporesby meiosis(Figure 16.24C).
Preview:An alternation of generations is found irmong many,but not all, algaeand all
plant evolution (Module 17.4).
plantsand is importantin understanding
Module 16.25 Multicellular life may haveevolvedfrom colonial protists.
A. Most multicellularorganisms,including seaweeds,slime molds,fungi, plants,andanimals, are characteizedby the differentiation of cells that perform different activities
within one organism.
B. Multicellularity undoubtedlyevolved severaltimes within the kingdom Protista.Some
of theseorganismsevolved further into ancestorsof the plant, fungus,and animal
kingdoms.
C. A hypothetical scenariofor the evolution of a multicellular plant or animal from an
early protist is presentedbelow:
1. Formationof ancestralcolonies,with all cells the same.
2. Specializationand cooperationamong different cells within the colony.
3. Differentiation of sexualcells from the somatic cells (Figure 16.25).
Module 16.26 Multicellular life has diversified over hundredsof millions of years.
A. Throughthe use of fossil recordsand moleculartechniques,the earliestmulticellular
organismsare thought to have beenpresenton Earttr about 1.2 billion yearsago
(Figure 16.26).
B. The fossil recordsindicate an abundanceof multicellular organisms(red algaeand
invertebrateanimals)dating from 600 to 700 mya. Theseorganismswere red algaeand
animalsresemblingcorals,jellyfish, and worms. Other kinds of multicellularalgae
probably existed as well, but their remains are yet to be found in the fossil record.
C. A massextinction occurredbetweenthe Precambrianand Paleozoiceras.
by diverseanimalsand
D. Up until 5@ mya to 475 mya,life was aquaticand represented
prokaryotes.
multicellular algae,along with ancestralprotists and
I
Chapter 16 The Origin and Evolution of Microbial Life
159
ClassActivities
1.
Based on the information in the text (and additional outside sourcesif you so desire) ask your students
to first consider the basis ofthe recognition ofprotists and then have them develop a phylogenetictree
of the protistan groups discussedin the text. Have them consider the questionof whether or not the
different types of seaweedsshould be classified as protists.
Acetates
Transparency
Figure16.1C
Figure16.38
Figure16.5
Figure16.6A
Table16.8
Table16.10
Figure16.12A
Figure16.158
Figure16.17A
Figure16.18A
Figure16.188
FigureI6.24C
Figure16.25
Figure16.26
Major episodesin the earlyhistory of life
The synthesisof organicmoleculesin the Miller-Urey apparatus
A hypothesisfor the origin of the first genes
the absence
of membranes
The beginningsof cooperationamong macromolecules'in
Differencesbetweenbacteriaand archaea
Nutritionalclassificationof organisms
Prokaryoticflagella
The usualprocedurefor demonstratingKoch'spostulates
The trickling filter systemat a sewagetreatmentplant
reticulumanda
Infolding of a prokaryoticplasmamembrane,giving riseto endoplasmic
nuclearenvelope
Endosymbioticbacteriagiving rise to mitochondriaandchloroplasts
A multicellulargreenalga;UIva (sealettuce)andits life cycle
A modelfor the evolutionof a multicellular organismfrom a unicellularprotist
A timelineof early multicellularlife
Media
Seethe beginningof this book for a completedescription of all media availablefor instructorsand students.Animationsand videos are availablein the Campbell Image PresentationLibrary. Media Activities
andThinking as a Scientistinvestigationsare availableon the studentCD-ROMand web site.
Animations and Videos
hokaryotic Flagella(Salmonella
typhimurium)Video
OscillatoriaVideo
OscillatoriaVideo
EuglenaMotion Video
EuglenaMotion Video
EuglennVideo
EuglenaVideo
Arnoeba Pseudopodia
Video
File Name
I 6- I 2A-ProkFlagellaVideo-S.mov
I 6-138-OscillatoriaVideo-B.mov
I 6- 138-OscillatoriaVideo-S.mov
16- 19-EuglenalVideo-B.mov
16- I 9-EuglenaI Video-S.mov
I 6- I 9-Euglena2Video-B.mov
I 6- 19-Euglena2Video-S.mov
I Video-B.mov
16-208-AmoebaPseud
160
Instructor's Guide to Tbxt and Media
Video
Amoeba Pseudopodia
AmoebaVideo
AmoebaVideo
StentorYideo
StentorYideo
StentorYideo
StentorYideo
VorticellaCilia Video
VorticellaCilia Video
Vorti cella Detail Video
Vorticella Detail Video
Vorti cella Habitat Video
Vorticella Habitat Video
PlasmodialSlime Mold SneamingVideo
PlasmodialSlime Mold StreamingVideo
PlasmodialSlime Mold Video
PlasmodialSlime Mold Video
DinoflagellateVideo
DinoflagellateVdeo
DiatomsMoving Video
DiatomsMoving Video
VariousDiatoms Video
VariousDiatoms Video
VolvoxColony Video
VolvoxColony Video
VolvoxDaughterVideo
VolvoxDaughterVideo
VolvoxFlagella Video
VolvoxFlagella Video
ChlamydomonasYideo
Video
Chlnmydomonas
I Video-S.mov
16-208-AmoebaPseud
-AmoebaPseud2Video-B.
mov
16-208
-AmoebaPseud2VideoS.mov
16-208
Video-B.mov
16-20D-Stentorl
Video-S.mov
16-20D-Stentorl
16-20D-Stentor2Video-B.mov
16-20D-Stentor2Video-S.mov
Video-B.mov
16-20D-Vorticellal
1Video-S.mov
I 6-20D-Vorticella
I 6-20D-Vorticella2Video-B.mov
16-20D-Vorticella2Video-S.mov
16-20D-Vorticella3Video-B.mov
I 6-2OD-Vorticella3Video-S.mov
I 6-22A-SlimeMoldSrVideo-B.mov
I 6-22A-SlimeMoldStrVideo-S.mov
16-22A-SlimeMoldVideo-B.mov
I 6-22A-SlimeMoldVideo-S.mov
16-23A-DinoflagellateVideo-B.mov
16-23A-DinoflagellateVideo-S.mov
1Video-B.mov
16-238-MiscDiatoms
1Video-S.mov
16-23B-MiscDiatoms
16-23B-MiscDiatoms2Video-B.mov
I 6-238-MiscDiatoms2Video-S.mov
I 6-23C-VolvoxColonyVideo-B.mov
16-23C-VolvoxColonyVideo-S.mov
I 6-23C-VolvoxDaughtrVideo-B.mov
16-23C-VolvoxDaughtrVideo-S.mov
I 6-23C-VolvoxFlagellaVideo-B.mov
I 6-23C-VolvoxFlagellaVideo-S.mov
I 6-24C-ChlamydomonasVideo-B.mov
16-24C-ChlamydomonasVideo-S.mov
ActivitiesandThinkingas a Scientist
ModuleNumber
Web/CDActivity 16A: TheHistory of Ltfe
Web/CDThinking as a Scientist:How Might Conditionson
Early Earth Have CreatedLife?
Web/CDThinking as a Scientist: WhatAre the Modesof
Nutrition in Proknryotes?
Web/CDActivity 168: ProknryoticCeIIStructureand Function
16.1
Web/CDActivity l6C: Diversityof Prol<aryotes
Web/CDThinking as a Scientist: WhatKinds of ProtistsAre
Foundin VariousHabitats?
16.3
16'10
16.12
16.13
16.26