Microbiology: An Evolving Science Fourth Edition Test Bank

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CHAPTER 1: Microbial Life: Origin and DiscoveryMULTIPLE CHOICE1.Viruses area.infectious agents that infect exclusively multicellular organisms.b.noncellular particles that take over the metabolism of a cell to generate more virusparticles.c.pathogens that replicate in complex growth media.d.cellular particles that belong to the archaea domain.e.microbes that consist of lipid membrane–enclosed genomes.ANS:BDIF:EasyREF:1.1OBJ:1.1a Recall the definition of a microbe | 1.1b List examples of microbesMSC:Remembering2.Analysis of DNA sequences revealsa.the ancient convergence of two cell types (i.e., prokaryotes and eukaryotes).b.that prokaryotes and eukaryotes evolved from a common ancestral cell.c.that bacteria share a common ancestor with archaea but not with eukarya.d.that prokaryotes are cells with a nucleus.e.that the genome ofHaemophilus influenzaehas about 2 billion base pairs.ANS:BDIF:EasyREF:1.1OBJ:1.1d Explain the implications of microbial genome sequencingMSC:Understanding3.Which of these groups are considered to be microbes but NOT considered to be cells?a.virusesd.protistsb.bacteriae.filamentous fungic.archaeaANS:ADIF:EasyREF:1.1OBJ:1.1a Recall the definition of a microbe | 1.1c Describe some problems with the definition ofa microbeMSC:Understanding4.A microbe is commonly defined as a ________ that requires a microscope to be seen.a.virusd.multicellular eukaryoteb.bacteriume.living organismc.single-cellular prokaryoteANS:EDIF:EasyREF:1.1OBJ:1.1a Recall the definition of a microbeMSC:Remembering5.Which one of the following statements regarding microbial cells is FALSE?a.Microbial cells acquire food, gain energy to build themselves, and respond toenvironmental change.b.Most single-celled organisms require a microscope to render them visible, but somebacterial cells are large enough to be seen with naked eyes.c.Microbes function as individual entities.d.Many microbes form complex multicellular assemblages.e.Viruses are not considered microbial cells.ANS:CDIF:EasyREF:1.1

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OBJ:1.1a Recall the definition of a microbeMSC:Understanding6.Which of the following statements is FALSE?a.A genome is the total genetic information contained in an organism’s chromosomal DNA.b.If a microbe’s genome includes genes for nitrogenase, that microbe probably can fixnitrogen.c.By comparing DNA sequences of different organisms, we can figure out how closelyrelated they are.d.Fred Sanger developed the first applicable DNA sequencing method.e.Fred Sanger completed the sequences ofHaemophilus influenzae.ANS:EDIF:EasyREF:1.1OBJ:1.1d Explain the implications of microbial genome sequencingMSC:Remembering7.The first cellular genomes to be sequenced were those ofa.humans.d.prions.b.bacteria.e.fungi.c.viruses.ANS:BDIF:EasyREF:1.1OBJ:1.1d Explain the implications of microbial genome sequencingMSC:Remembering8.The environment of early Earth may have contained all of the following EXCEPTa.ferrous iron.d.oxygen.b.methane.e.hydrogen gas.c.ammonia.ANS:DDIF:MediumREF:Special Topic 1.1OBJ:1.1a Recall the definition of a microbeMSC:Remembering9.The development of the theory of the “RNA world” resulted from the discovery ofa.archaea.d.ribozymes.b.prions.e.endosymbionts.c.bacteria.ANS:DDIF:MediumREF:1.6OBJ:1.6b Explain how studies on microbes fostered our knowledge of DNA function andenhanced DNA technologyMSC:Remembering10.What is the evidence that living cells existed on Earth up to 3.8 billion years ago?a.microfossilsd.Martian folded rock formationsb.16S ribosomal RNAe.diatom shellsc.Miller and Urey’s experimentsANS:ADIF:MediumREF:Special Topic 1.1OBJ:1.5a Explain why microbes can be challenging to classify taxonomically | 1.5b Outline howmicrobial classification has changed over timeMSC:Remembering11.What did van Leeuwenhoek discover using microscopic observations before and after drinking hotbeverages?a.Heat did not kill microbes.b.Heat killed microbes.c.Heat did not kill algae.

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d.Caffeine in coffee killed microbes.e.The existence of spiral-shaped microbes.ANS:BDIF:MediumREF:1.2OBJ:1.2b Explain why the microscope is an important tool in the field of microbiology | 1.2cIdentify the contributions of the following individuals: Nightingale, Hooke, van Leeuwenhoek,Pasteur, and TyndallMSC:Analyzing12.Tyndall’s spontaneous generation experiments occasionally failed due toa.nutrient chirality.d.lack of oxygen.b.dust.e.endospores.c.fermentation.ANS:EDIF:EasyREF:1.2OBJ:1.2d Compare and contrast Spallanzani’s, Pasteur’s, and Tyndall’s experiments that testedspontaneous generationMSC:Analyzing13.The discovery of microbes occurred in the ________ century?a.seventeenthd.twentiethb.eighteenthe.twenty-firstc.nineteenthANS:CDIF:EasyREF:1.2OBJ:1.2b Explain why the microscope is an important tool in the field of microbiologyMSC:Remembering14.Robert Koch won the Nobel Prize for his contribution to medical bacteriology regardinga.Escherichia coli.d.rabies.b.Bacillus subtilis.e.smallpox.c.Mycobacterium tuberculosis.ANS:CDIF:MediumREF:1.3OBJ:1.3b List Koch’spostulatesMSC:Remembering15.How did European invaders to North America kill much of the native population?a.tuberculosisd.HIVb.leprosye.bubonic plaguec.smallpoxANS:CDIF:MediumREF:1.2OBJ:1.2a List both positive and negative impacts that microbes have had on human historyMSC:Understanding16.Florence Nightingalea.is best known as the founder of professional nursing.b.was the first to use disinfectant to demonstrate the significance of aseptic technique.c.developed the pie chart of mortality data during the Crimean War.d.performed the first controlled experiment on the chemical conversion of matter, knowntoday as chemotherapy.e.argued that the environment of early Earth contained mainly reduced compounds.ANS:ADIF:EasyREF:1.2OBJ:1.2a List both positive and negative impacts that microbes have had on human history | 1.2cIdentify the contributions of the following individuals: Nightingale, Hooke, van Leeuwenhoek,Pasteur, and TyndallMSC:Remembering

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17.Who developed the concept of medical statistics?a.Francis Crickd.Louis Pasteurb.Florence Nightingalee.Alexander Flemingc.Edward JennerANS:BDIF:EasyREF:1.2OBJ:1.2c Identify the contributions of the following individuals: Nightingale, Hooke, vanLeeuwenhoek, Pasteur, and TyndallMSC:Remembering18.The first person to visualize individual microbial cells wasa.Antonie van Leeuwenhoek.d.Lady Montagu.b.Robert Hooke.e.Edward Jenner.c.Louis Pasteur.ANS:ADIF:EasyREF:1.2OBJ:1.2c Identify the contributions of the following individuals: Nightingale, Hooke, vanLeeuwenhoek, Pasteur, and TyndallMSC:Remembering19.Semmelweis and Lister noted that many of their patients’ deaths were due toa.fungi.d.pathogen transmission by doctors.b.Escherichia coli.e.Staphylococcus.c.chlorine.ANS:DDIF:MediumREF:1.3OBJ:1.3a Describe what constitutes a pure culture and how to obtain oneMSC:Understanding20.What is the standard sterilization method for the controlled study of microbes?a.boilingd.autoclavingb.pasteurizatione.irradiationc.filter sterilizationANS:DDIF:MediumREF:1.2

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OBJ:1.2c Identify the contributions of the following individuals: Nightingale, Hooke, vanLeeuwenhoek, Pasteur, and TyndallMSC:Remembering21.How does the Winogradsky column differ from Koch’s plate media?a.Koch’s media creates a gradient from oxygen-rich conditions at the surface to highlyreduced conditions below.b.The Winogradsky column is used for culturing viruses.c.The Winogradsky column is used for growing extremophiles.d.The Winogradsky column uses the kinds of nutrients that feed humans.e.The bacteria that Winogradsky isolated can grow only on inorganic minerals.ANS:EDIF:EasyREF:1.4OBJ:1.4a List Winogradsky’s contributions to microbial culture technique | 1.4b Define whatdistinguishes lithotrophs from other organismsMSC:Understanding22.Suppose Pasteur’s swan-necked flasks containing boiled broth became cloudy twenty-four hoursafter boiling. Which choice could best explain the turbidity or cloudiness in the broth withoutsupporting spontaneous generation?a.Endospores in the broth survived boiling and grew after the broth cooled.b.Contaminating organisms in the broth killed by boiling became alive again after the brothcooled.c.Chemicals in the broth came together to form living organisms.d.The broth allowed light to pass through it with less interference after boiling.e.Solid material in the broth dissolved during boiling.ANS:ADIF:DifficultREF:1.2OBJ:1.2c Identify the contributions of the following individuals: Nightingale, Hooke, vanLeeuwenhoek, Pasteur, and Tyndall | 1.2d Compare and contrast Spallanzani’s, Pasteur’s, andTyndall’s experiments that tested spontaneous generationMSC:Applying23.Which of the following is NOT considered to be an extremophilic condition for bacteria?a.high alkalinityd.high nutrientsb.high salinitye.high temperaturec.high acidityANS:DDIF:MediumREF:1.4OBJ:1.4c Explain the role of microbes in geochemical cycling, especially that of nitrogenMSC:Remembering24.The use of agar as a more robust gelling agent in solid media was suggested bya.Robert Koch.d.Louis Pasteur.b.Ignaz Semmelweis.e.Richard Petri.c.Angelina Hesse.ANS:CDIF:EasyREF:1.3OBJ:1.3a Describe what constitutes a pure culture and how to obtain one | 1.3c Assess some ofthe practical obstacles in applying Koch’s postulatesMSC:Remembering25.It took the advent of the polymerase chain reaction to detect the presence of the causative agent forwhich disease?a.anthraxd.rabiesb.tuberculosise.smallpoxc.AIDSANS:CDIF:DifficultREF:1.3

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OBJ:1.3c Assess some of the practical obstacles in applying Koch’s postulates | 1.3fDescribehow viruses were discoveredMSC:Understanding26.The word “vaccination” is derived from the Latin wordvacca, which meansa.inject.d.cow.b.smallpox.e.pustule.c.immunize.ANS:DDIF:EasyREF:1.3OBJ:1.3d Recall the contributions of various individuals to the discovery and implementation ofvaccination | 1.3e Compare the roles of immunization, antiseptics, and antibiotics in human diseasetreatment and preventionMSC:Remembering27.What was the basis for the original smallpox vaccine?a.chickenpox virusd.smallpox virusb.cowpox viruse.anthraxc.rabies virusANS:BDIF:MediumREF:1.3OBJ:1.3d Recall the contributions of various individuals to the discovery and implementation ofvaccinationMSC:Remembering28.Penicillin was first used to save the lives of many people during which war?a.the U.S. Civil Ward.World War Ib.the Korean Ware.World War IIc.the Vietnam WarANS:EDIF:EasyREF:1.3OBJ:1.3e Compare the roles of immunization, antiseptics, and antibiotics in human diseasetreatment and preventionMSC:Remembering29.How do many animal endosymbionts grow?a.on the surface of the hostd.on inorganic mineralsb.on low nutrientse.in biofilmsc.by reducing iron oxideANS:EDIF:MediumREF:1.4OBJ:1.4d Compare the roles of animal endosymbionts and plant endosymbiontsMSC:Remembering

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30.All of the following are true about penicillin EXCEPT that ita.was discovered by Alexander Fleming.b.was an accidental discovery.c.is produced by a bacterium.d.was the first antibiotic used by humans.e.was purified by Florey and Chain.ANS:CDIF:DifficultREF:1.3OBJ:1.3e Compare the roles of immunization, antiseptics, and antibiotics in human diseasetreatment and preventionMSC:Remembering31.Which of the following statements regarding viruses is FALSE?a.Most are too small to be seen by a light microscope.b.They are “filterable agents” that can pass through porcelain filters that have a pore sizethat blocks microbes.c.Their genomes could be composed of DNA or RNA.d.They are smaller than plasmids and prions.e.Viral particles, when pure enough, can be crystallized.ANS:DDIF:MediumREF:1.3OBJ:1.3f Describe how viruses were discoveredMSC:Analyzing32.You have isolated a bacterium that you believe to be the causative agent of a new disease in frogs.How would you test the third of Koch’s postulates?a.Determine the shape of the bacterial cells.b.Inject the bacteria into a healthy frog.c.Isolate the bacterium from a sick frog.d.Show that the bacterium is not present in healthy frogs.e.Grow a pure culture of the bacterium outside the frog.ANS:BDIF:DifficultREF:1.3OBJ:1.3b List Koch’spostulatesMSC:Applying33.How did Sergei Winogradsky grow lithotrophs?a.enrichment cultured.endosymbiosisb.organic mediae.chain of infectionc.pure cultureANS:ADIF:EasyREF:1.4OBJ:1.4a List Winogradsky’s contributions to microbial culture technique | 1.4b Define whatdistinguishes lithotrophs from other organismsMSC:Understanding34.Organisms that live symbiotically inside a larger organism are known asa.organelles.d.endosymbionts.b.cyanobacteria.e.chloroplasts.c.mitochondria.ANS:DDIF:EasyREF:1.4OBJ:1.4d Compare the roles of animal endosymbionts and plant endosymbiontsMSC:Remembering35.Animal microbiomes are NOT significant ina.digesting plant fibers.d.converting ammonia to nitrate.b.bioluminescence.e.providing nutrients to the host.

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c.protection from pathogens.ANS:DDIF:EasyREF:1.4OBJ:1.4d Compare the roles of animal endosymbionts and plant endosymbiontsMSC:Applying36.Carl Woese’s discovery replaced the classification scheme of five kingdoms with a scheme ofthreea.phyla.d.orders.b.domains.e.genera.c.classes.ANS:BDIF:EasyREF:1.5OBJ:1.5b Outline how microbial classification has changed over time | 1.5d Describe theimportance of DNA sequencing in classificationMSC:Remembering37.The gene expression machinery of archaea is MOST similar toa.monera.d.eukaryotes.b.prokaryotes.e.mitochondria.c.bacteria.ANS:DDIF:MediumREF:1.5OBJ:1.5e Compare and contrast archaea, bacteria, and eukaryotesMSC:Understanding38.In the three-domain model, the bacterial ancestor of mitochondria derives from ancienta.fungi.d.archaea.b.cyanobacteria.e.protists.c.respiring bacteria.ANS:CDIF:MediumREF:1.5OBJ:1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplastsMSC:Remembering39.Which of the following organelles are thought to be of prokaryotic origin?a.chloroplastd.chloroplast and mitochondriab.mitochondriae.chloroplast and nucleusc.nucleusANS:DDIF:MediumREF:1.5OBJ:1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplastsMSC:Understanding40.In the three-domain model, the bacterial ancestor of chloroplasts derives from ancienta.fungi.d.archaea.b.cyanobacteria.e.protists.c.proteobacteria.ANS:BDIF:MediumREF:1.5OBJ:1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplastsMSC:Remembering41.Which commonly used microbial classification advancement led to the tree by Carl Woese in1977?

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a.comparative genomicsd.protein sequencingb.microscopye.16S rRNA sequencingc.X-ray diffractionANS:EDIF:MediumREF:1.5OBJ:1.5b Outline how microbial classification has changed over time | 1.5d Describe theimportance of DNA sequencing in classificationMSC:Understanding42.Electron microscopes use what to focus the beam of electrons?a.electromagnetsd.X-ray diffractionb.a condenser lense.glassc.light raysANS:ADIF:EasyREF:1.6OBJ:1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing ourknowledge of cell structure and functionMSC:Remembering43.Peter Mitchell and Jennifer Moyle discovered the ________ theory in the 1960s.a.germplasmd.DNA synthesisb.evolutione.polymerase chain reactionc.chemiosmoticANS:CDIF:EasyREF:1.6OBJ:1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing ourknowledge of cell structure and functionMSC:Remembering44.The X-ray diffraction studies by which of the following scientists concluded that DNA was adouble helix?a.James Watsond.Maurice Wilkinsb.Rosalind Frankline.Kary Mullisc.Francis CrickANS:BDIF:EasyREF:1.6OBJ:1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing ourknowledge of cell structure and functionMSC:Remembering45.What feature of bacteria facilitated the DNA revolution in the 1970s?

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a.They are very small.d.All of their genes were known.b.They readily recombine DNA.e.They do not cause disease.c.They have very large genomes.ANS:BDIF:MediumREF:1.6OBJ:1.6b Explain how studies on microbes fostered our knowledge of DNA function andenhanced DNA technologyMSC:Understanding46.This scientist first discovered the process of transformation.a.Francis Crickd.Louis Pasteurb.Robert Koche.Frederick Griffithc.Edward JennerANS:EDIF:DifficultREF:1.6OBJ:1.6b Explain how studies on microbes fostered our knowledge of DNA function andenhanced DNA technologyMSC:Remembering47.Taq polymerase forms the basis of a technique fora.comparative genomics.d.DNA amplification.b.recombinant DNA.e.protein synthesis.c.X-ray diffraction.ANS:DDIF:EasyREF:1.6OBJ:1.6c State some uses of microbes in medicine and industryMSC:Understanding48.In 1975, scientists held a conference at Asilomar to regulate and restrict the field ofa.recombinant DNA.d.DNA amplification.b.comparative genomics.e.forensic microbiology.c.DNA sequencing.ANS:ADIF:MediumREF:1.6OBJ:1.6c State some uses of microbes in medicine and industryMSC:Understanding49.The study of and cause of disease in humans, animals, and plants is calleda.microbiology.d.epidemiology.b.phylogeny.e.forensics.c.genomics.ANS:DDIF:MediumREF:1.6OBJ:1.6c State some uses of microbes in medicine and industryMSC:Remembering50.The ultracentrifuge is a high-speed centrifuge ideally suited for separating individuala.cellular proteins and nucleotides.d.secondary metabolites.b.microbial cells.e.base pairs.c.mold spores.ANS:ADIF:MediumREF:1.6OBJ:1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing ourknowledge of cell structure and functionMSC:UnderstandingSHORT ANSWER

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1.What is the MOST recent evidence suggesting that all life on Earth shares a common ancestry?ANS:Many genomes have now been sequenced, and those sequences are available in databases forcomparison. This field is referred to as comparative genomics. Comparisons have revealed thatthere is a set of core genes shared by all organisms.DIF:DifficultREF:1.1 | 1.5OBJ:1.1d Explain the implications of microbial genome sequencing | 1.5b Outline how microbialclassification has changed over timeMSC:Analyzing2.How are prokaryotes and eukaryotes different?ANS:A prokaryote lacks a nucleus and membrane-bounded organelles, whereas a eukaryote has anucleus and membrane-bounded organelles.DIF:EasyREF:1.1 | 1.5OBJ:1.1a Recall the definition of a microbeMSC:Remembering3.How do microbes help in the extraction of minerals?ANS:Several lithotrophic bacteria help in the rapid oxidation of minerals, which generates strong acidsthat expedite the breakdown of mineral ore. Currently, approximately 20% of the world’s copper,as well as some uranium and zinc, is produced by bacterial leaching.DIF:MediumREF:1.2OBJ:1.2a List both positive and negative impacts that microbes have had on human historyMSC:Applying4.Antonie van Leeuwenhoek worked as a cloth draper, inspecting the quality of cloth. How did thislead to his interest in microscopy?ANS:His work introduced him to magnifying lenses. He began the hobby of grinding lenses, ultimatelymaking a microscope that enabled him to observe single-celled microbes.DIF:MediumREF:1.2OBJ:1.2c Identify the contributions of the following individuals: Nightingale, Hooke, vanLeeuwenhoek, Pasteur, and TyndallMSC:Understanding5.What was the major complaint about Lazzaro Spallanzani’s experiment to disprove spontaneousgeneration, and how did Louis Pasteur’s swan-neck flasks overcome this?ANS:Spallanzani’s flasks were plugged so as not to let organisms accidentally enter the boiled medium.Opponents argued that no growth was observed simply due to the lack of oxygen. Pasteur’sswan-neck flasks did not allow organisms to enter the flask but did allow oxygen to enter. Growthwas still not observed.DIF:MediumREF:1.2OBJ:1.2c Identify the contributions of the following individuals: Nightingale, Hooke, vanLeeuwenhoek, Pasteur, and TyndallMSC:Evaluating

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6.Describe the discoveries of Louis Pasteur while working with the French beer and winemanufacturers in assessing alcohol versus vinegar production during fermentation.ANS:Previously, it was believed that the conversion of grapes and grain to wine and beer was aspontaneous chemical process. Pasteur discovered that this fermentation was caused by livingyeast, which did not require oxygen for growth. He also discovered that when the grapes or grainare contaminated with bacteria instead of yeast, acetic acid is produced instead of alcohol.DIF:MediumREF:1.2OBJ:1.2c Identify the contributions of the following individuals: Nightingale, Hooke, vanLeeuwenhoek, Pasteur, and TyndallMSC:Understanding7.Describe the effects of three microbial diseases that have significantly affected human populationsthroughout history.ANS:Answers may vary. Some examples include bubonic plague, which killed one-third of Europe’spopulation in the fourteenth century; tuberculosis, which was common in the nineteenth century;AIDS, which affects many people today; and smallpox, which killed a large number of nativeNorth Americans.DIF:MediumREF:1.2OBJ:1.2a List both positive and negative impacts that microbes have had on human history | 1.2cIdentify the contributions of the following individuals: Nightingale, Hooke, van Leeuwenhoek,Pasteur, and TyndallMSC:Applying8.Why did it take so long for humans to determine that microbes cause infectious diseases?ANS:Microbes are too small to be seen with the naked eye, so until powerful-enough microscopes wereinvented, humans did not know that microbes existed. Even after humans were aware of thepresence of microbes, they did not suspect them of causing disease until people such as JosephLister and Ignaz Semmelweis performed experiments that showed antiseptics decrease theincidence of infection.DIF:DifficultREF:1.2 | 1.3OBJ:1.2b Explain why the microscope is an important tool in the field of microbiologyMSC:Understanding9.Robert Koch’s postulates have not been used to prove HIV as the causative agent of AIDS. Whynot?ANS:Answers may vary, but a major reason is that humans cannot be injected with HIV to see if theydevelop AIDS, and a suitable animal host doesn’t exist for testing.DIF:MediumREF:1.3OBJ:1.3c Assess some of the practical obstacles in applying Koch’s postulatesMSC:Understanding10.Define “attenuation” and describe some mechanisms used to attenuate pathogens.

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ANS:Attenuation results in a weakened organism that will not produce full-blown disease but willgenerate immunity. Answers for mechanisms may vary, but heat treatment or aging for variousperiods or natural attenuation in the host are mentioned in the chapter.DIF:MediumREF:1.3OBJ:1.3d Recall the contributions of various individuals to the discovery and implementation ofvaccination | 1.3e Compare the roles of immunization, antiseptics, and antibiotics in human diseasetreatment and preventionMSC:Applying11.What is the significance of the work of Ignaz Semmelweis and Joseph Lister?ANS:They showed that use of antiseptics on doctors’ hands and medical instruments drastically reducedthe mortality rate of hospital patients. They made these observations before Robert Koch’s germtheory of disease.DIF:MediumREF:1.3OBJ:1.3e Compare the roles of immunization, antiseptics, and antibiotics in human diseasetreatment and preventionMSC:Understanding12.How would you use Robert Koch’s postulates to prove that a specific organism causes a newdisease in mice?ANS:See Figure 1.17 in the textbook:(1)The suspected organism is found in all diseased mice, but is absent from healthy mice.(2)The suspected organism is isolated from the diseased mice and grown in pure culture.(3)When the suspected organism is introduced into a healthy mouse, the same disease occurs.(4)The same strain of microbe is obtained from the newly diseased mouse.DIF:DifficultREF:1.3OBJ:1.3b List Koch’s postulatesMSC:Applying13.Explain why the organisms that were studied by Sergei Winogradsky could not be grown onRobert Koch’s plate media containing agar or gelatin.ANS:The organisms studied by Winogradsky were lithotrophs, which feed solely on inorganicsubstances. Koch’s plate media contained organic nutrient sources, which may even be toxic to theorganisms he was attempting to grow.DIF:MediumREF:1.4OBJ:1.4a List Winogradsky’s contributions to microbial culture techniqueMSC:Analyzing14.Is it true that only culturable bacteria contribute to ecology? Explain your answer.ANS:No, this is not a true statement. It is estimated that barely 0.1% of microbial species can becultured. The work of Winogradsky and later microbial ecologists showed that bacteria arenecessary for geochemical cycling. Many of these organisms can’t be grown in pure culture onlaboratory media but can be grown in enrichment culture such as a Winogradsky column.

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DIF:DifficultREF:1.4OBJ:1.4c Explain the role of microbes in geochemical cycling, especially that of nitrogenMSC:Analyzing15.Define the term “endosymbiont” and give an example of an endosymbiotic relationship found innature.ANS:An endosymbiont is an organism living symbiotically inside a larger organism. Examples mayvary, but include the following:Rhizobiumin a leguminous plant, bioluminescent bacteria in thelight organs of fish and squid, and photosynthetic algae and coral.DIF:MediumREF:1.4OBJ:1.4d Compare the roles of animal endosymbionts and plant endosymbiontsMSC:Applying16.Give two reasons why microbes have been difficult to classify.ANS:First, even with the use of light microscopes, only the basic shape of microbes can be determined,and many microbes have similar shapes even though they are very different in other ways. Second,microbes do not fit the classic definition of a species, which is a group of organisms thatinterbreed. Microbes typically reproduce asexually. When they do exchange genes, they may do sowith distantly related species.DIF:MediumREF:1.5OBJ:1.5a Explain why microbes can be challenging to classify taxonomicallyMSC:Analyzing17.Briefly explain the endosymbiosis theory and the evidence that supports it.ANS:The endosymbiosis theory proposes that mitochondria and chloroplasts evolved from bacteria thatwere engulfed by pre-eukaryotic cells, and that over time these endosymbiotic prokaryotic cellslost the ability to survive outside of the host cell but were maintained as organelles. Evidencesupporting the endosymbiosis theory includes the fact that mitochondria and chloroplasts possesscircular DNA with similarity to modern bacteria.DIF:MediumREF:1.5OBJ:1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplastsMSC:Understanding18.What were Rosalind Franklin’s contributions toward discovering the structure of DNA, and whywasn’t she one of the recipients of the Nobel Prize for this discovery?ANS:She was an X-ray crystallographer who studied the structure of DNA. Her X-ray micrographsshowed for the first time that DNA was a double helix. A colleague showed her micrographs toJames Watson, who was also studying the structure of DNA. Watson and Francis Crick publishedtheir model of the structure of DNA in the journalNatureand denied that they had used Franklin’smicrographs. Franklin also died before the awarding of the prize.DIF:MediumREF:1.6

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OBJ:1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing ourknowledge of cell structure and functionMSC:Understanding19.Briefly describe how the ultracentrifuge is used to determine the sizes of cellular macromolecules.ANS:The ultracentrifuge uses centrifugal forces to separate cell components. Theodor Svedbergcalculated that the particle sizes could be determined based on the rate of sedimentation of theparticles in an ultracentrifuge.DIF:MediumREF:1.6OBJ:1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing ourknowledge of cell structure and functionMSC:Understanding20.If you want to produce DNA polymerases like those used in polymerase chain reaction (PCR) foramplification of DNA, from which natural environment would you try to isolate the producers?ANS:Since DNA polymerase in PCR must survive many rounds of cycling to near-boiling temperatures,the most conducive environment for finding DNA polymerase, such as the enzymes used in PCRreactions, would be searching for microbes in an environment where the temperature is extremelyhigh.DIF:DifficultREF:1.6OBJ:1.6c State some uses of microbes in medicine and industryMSC:Applying

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