CHAPTER 1: Microbial Life: Origin and Discovery
MULTIPLE CHOICE
1. Viruses are
a. infectious agents that infect exclusively multicellular organisms.
b. noncellular particles that take over the metabolism of a cell to generate more virus
particles.
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: B DIF: Easy REF: 1.1
OBJ: 1.1a Recall the definition of a microbe | 1.1b List examples of microbes
MSC: Remembering
2. Analysis of DNA sequences reveals
a. 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 of Haemophilus influenzae has about 2 billion base pairs.
ANS: B DIF: Easy REF: 1.1
OBJ: 1.1d Explain the implications of microbial genome sequencing
MSC: Understanding
3. Which of these groups are considered to be microbes but NOT considered to be cells?
a. viruses d. protists
b. bacteria e. filamentous fungi
c. archaea
ANS: A DIF: Easy REF: 1.1
OBJ: 1.1a Recall the definition of a microbe | 1.1c Describe some problems with the definition of
a microbe MSC: Understanding
4. A microbe is commonly defined as a ________ that requires a microscope to be seen.
a. virus d. multicellular eukaryote
b. bacterium e. living organism
c. single-cellular prokaryote
ANS: E DIF: Easy REF: 1.1
OBJ: 1.1a Recall the definition of a microbe MSC: Remembering
5. Which one of the following statements regarding microbial cells is FALSE?
a. Microbial cells acquire food, gain energy to build themselves, and respond to
environmental change.
b. Most single-celled organisms require a microscope to render them visible, but some
bacterial 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: C DIF: Easy REF: 1.1

OBJ: 1.1a Recall the definition of a microbe MSC: Understanding
6. 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 fix
nitrogen.
c. By comparing DNA sequences of different organisms, we can figure out how closely
related they are.
d. Fred Sanger developed the first applicable DNA sequencing method.
e. Fred Sanger completed the sequences of Haemophilus influenzae.
ANS: E DIF: Easy REF: 1.1
OBJ: 1.1d Explain the implications of microbial genome sequencing
MSC: Remembering
7. The first cellular genomes to be sequenced were those of
a. humans. d. prions.
b. bacteria. e. fungi.
c. viruses.
ANS: B DIF: Easy REF: 1.1
OBJ: 1.1d Explain the implications of microbial genome sequencing
MSC: Remembering
8. The environment of early Earth may have contained all of the following EXCEPT
a. ferrous iron. d. oxygen.
b. methane. e. hydrogen gas.
c. ammonia.
ANS: D DIF: Medium REF: Special Topic 1.1
OBJ: 1.1a Recall the definition of a microbe MSC: Remembering
9. The development of the theory of the “RNA world” resulted from the discovery of
a. archaea. d. ribozymes.
b. prions. e. endosymbionts.
c. bacteria.
ANS: D DIF: Medium REF: 1.6
OBJ: 1.6b Explain how studies on microbes fostered our knowledge of DNA function and
enhanced DNA technology MSC: Remembering
10. What is the evidence that living cells existed on Earth up to 3.8 billion years ago?
a. microfossils d. Martian folded rock formations
b. 16S ribosomal RNA e. diatom shells
c. Miller and Urey’s experiments
ANS: A DIF: Medium REF: Special Topic 1.1
OBJ: 1.5a Explain why microbes can be challenging to classify taxonomically | 1.5b Outline how
microbial classification has changed over time MSC: Remembering
11. What did van Leeuwenhoek discover using microscopic observations before and after drinking hot
beverages?
a. Heat did not kill microbes.
b. Heat killed microbes.
c. Heat did not kill algae.

d. Caffeine in coffee killed microbes.
e. The existence of spiral-shaped microbes.
ANS: B DIF: Medium REF: 1.2
OBJ: 1.2b Explain why the microscope is an important tool in the field of microbiology | 1.2c
Identify the contributions of the following individuals: Nightingale, Hooke, van Leeuwenhoek,
Pasteur, and Tyndall MSC: Analyzing
12. Tyndall’s spontaneous generation experiments occasionally failed due to
a. nutrient chirality. d. lack of oxygen.
b. dust. e. endospores.
c. fermentation.
ANS: E DIF: Easy REF: 1.2
OBJ: 1.2d Compare and contrast Spallanzani’s, Pasteur’s, and Tyndall’s experiments that tested
spontaneous generation MSC: Analyzing
13. The discovery of microbes occurred in the ________ century?
a. seventeenth d. twentieth
b. eighteenth e. twenty-first
c. nineteenth
ANS: C DIF: Easy REF: 1.2
OBJ: 1.2b Explain why the microscope is an important tool in the field of microbiology
MSC: Remembering
14. Robert Koch won the Nobel Prize for his contribution to medical bacteriology regarding
a. Escherichia coli. d. rabies.
b. Bacillus subtilis. e. smallpox.
c. Mycobacterium tuberculosis.
ANS: C DIF: Medium REF: 1.3 OBJ: 1.3b List Koch’s
postulates
MSC: Remembering
15. How did European invaders to North America kill much of the native population?
a. tuberculosis d. HIV
b. leprosy e. bubonic plague
c. smallpox
ANS: C DIF: Medium REF: 1.2
OBJ: 1.2a List both positive and negative impacts that microbes have had on human history
MSC: Understanding
16. Florence Nightingale
a. 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, known
today as chemotherapy.
e. argued that the environment of early Earth contained mainly reduced compounds.
ANS: A DIF: Easy REF: 1.2
OBJ: 1.2a List both positive and negative impacts that microbes have had on human history | 1.2c
Identify the contributions of the following individuals: Nightingale, Hooke, van Leeuwenhoek,
Pasteur, and Tyndall MSC: Remembering

17. Who developed the concept of medical statistics?
a. Francis Crick d. Louis Pasteur
b. Florence Nightingale e. Alexander Fleming
c. Edward Jenner
ANS: B DIF: Easy REF: 1.2
OBJ: 1.2c Identify the contributions of the following individuals: Nightingale, Hooke, van
Leeuwenhoek, Pasteur, and Tyndall MSC: Remembering
18. The first person to visualize individual microbial cells was
a. Antonie van Leeuwenhoek. d. Lady Montagu.
b. Robert Hooke. e. Edward Jenner.
c. Louis Pasteur.
ANS: A DIF: Easy REF: 1.2
OBJ: 1.2c Identify the contributions of the following individuals: Nightingale, Hooke, van
Leeuwenhoek, Pasteur, and Tyndall MSC: Remembering
19. Semmelweis and Lister noted that many of their patients’ deaths were due to
a. fungi. d. pathogen transmission by doctors.
b. Escherichia coli. e. Staphylococcus.
c. chlorine.
ANS: D DIF: Medium REF: 1.3
OBJ: 1.3a Describe what constitutes a pure culture and how to obtain one
MSC: Understanding
20. What is the standard sterilization method for the controlled study of microbes?
a. boiling d. autoclaving
b. pasteurization e. irradiation
c. filter sterilization
ANS: D DIF: Medium REF: 1.2

OBJ: 1.2c Identify the contributions of the following individuals: Nightingale, Hooke, van
Leeuwenhoek, Pasteur, and Tyndall MSC: Remembering
21. 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 highly
reduced 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: E DIF: Easy REF: 1.4
OBJ: 1.4a List Winogradsky’s contributions to microbial culture technique | 1.4b Define what
distinguishes lithotrophs from other organisms MSC: Understanding
22. Suppose Pasteur’s swan-necked flasks containing boiled broth became cloudy twenty-four hours
after boiling. Which choice could best explain the turbidity or cloudiness in the broth without
supporting 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 broth
cooled.
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: A DIF: Difficult REF: 1.2
OBJ: 1.2c Identify the contributions of the following individuals: Nightingale, Hooke, van
Leeuwenhoek, Pasteur, and Tyndall | 1.2d Compare and contrast Spallanzani’s, Pasteur’s, and
Tyndall’s experiments that tested spontaneous generation MSC: Applying
23. Which of the following is NOT considered to be an extremophilic condition for bacteria?
a. high alkalinity d. high nutrients
b. high salinity e. high temperature
c. high acidity
ANS: D DIF: Medium REF: 1.4
OBJ: 1.4c Explain the role of microbes in geochemical cycling, especially that of nitrogen
MSC: Remembering
24. The use of agar as a more robust gelling agent in solid media was suggested by
a. Robert Koch. d. Louis Pasteur.
b. Ignaz Semmelweis. e. Richard Petri.
c. Angelina Hesse.
ANS: C DIF: Easy REF: 1.3
OBJ: 1.3a Describe what constitutes a pure culture and how to obtain one | 1.3c Assess some of
the practical obstacles in applying Koch’s postulates MSC: Remembering
25. It took the advent of the polymerase chain reaction to detect the presence of the causative agent for
which disease?
a. anthrax d. rabies
b. tuberculosis e. smallpox
c. AIDS
ANS: C DIF: Difficult REF: 1.3

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OBJ: 1.3c Assess some of the practical obstacles in applying Koch’s postulates | 1.3f Describe
how viruses were discovered MSC: Understanding
26. The word “vaccination” is derived from the Latin word vacca, which means
a. inject. d. cow.
b. smallpox. e. pustule.
c. immunize.
ANS: D DIF: Easy REF: 1.3
OBJ: 1.3d Recall the contributions of various individuals to the discovery and implementation of
vaccination | 1.3e Compare the roles of immunization, antiseptics, and antibiotics in human disease
treatment and prevention MSC: Remembering
27. What was the basis for the original smallpox vaccine?
a. chickenpox virus d. smallpox virus
b. cowpox virus e. anthrax
c. rabies virus
ANS: B DIF: Medium REF: 1.3
OBJ: 1.3d Recall the contributions of various individuals to the discovery and implementation of
vaccination MSC: Remembering
28. Penicillin was first used to save the lives of many people during which war?
a. the U.S. Civil War d. World War I
b. the Korean War e. World War II
c. the Vietnam War
ANS: E DIF: Easy REF: 1.3
OBJ: 1.3e Compare the roles of immunization, antiseptics, and antibiotics in human disease
treatment and prevention MSC: Remembering
29. How do many animal endosymbionts grow?
a. on the surface of the host d. on inorganic minerals
b. on low nutrients e. in biofilms
c. by reducing iron oxide
ANS: E DIF: Medium REF: 1.4
OBJ: 1.4d Compare the roles of animal endosymbionts and plant endosymbionts
MSC: Remembering

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30. All of the following are true about penicillin EXCEPT that it
a. 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: C DIF: Difficult REF: 1.3
OBJ: 1.3e Compare the roles of immunization, antiseptics, and antibiotics in human disease
treatment and prevention MSC: Remembering
31. 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 size
that 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: D DIF: Medium REF: 1.3
OBJ: 1.3f Describe how viruses were discovered MSC: Analyzing
32. 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: B DIF: Difficult REF: 1.3 OBJ: 1.3b List Koch’s
postulates
MSC: Applying
33. How did Sergei Winogradsky grow lithotrophs?
a. enrichment culture d. endosymbiosis
b. organic media e. chain of infection
c. pure culture
ANS: A DIF: Easy REF: 1.4
OBJ: 1.4a List Winogradsky’s contributions to microbial culture technique | 1.4b Define what
distinguishes lithotrophs from other organisms MSC: Understanding
34. Organisms that live symbiotically inside a larger organism are known as
a. organelles. d. endosymbionts.
b. cyanobacteria. e. chloroplasts.
c. mitochondria.
ANS: D DIF: Easy REF: 1.4
OBJ: 1.4d Compare the roles of animal endosymbionts and plant endosymbionts
MSC: Remembering
35. Animal microbiomes are NOT significant in
a. 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: D DIF: Easy REF: 1.4
OBJ: 1.4d Compare the roles of animal endosymbionts and plant endosymbionts
MSC: Applying
36. Carl Woese’s discovery replaced the classification scheme of five kingdoms with a scheme of
three
a. phyla. d. orders.
b. domains. e. genera.
c. classes.
ANS: B DIF: Easy REF: 1.5
OBJ: 1.5b Outline how microbial classification has changed over time | 1.5d Describe the
importance of DNA sequencing in classification MSC: Remembering
37. The gene expression machinery of archaea is MOST similar to
a. monera. d. eukaryotes.
b. prokaryotes. e. mitochondria.
c. bacteria.
ANS: D DIF: Medium REF: 1.5
OBJ: 1.5e Compare and contrast archaea, bacteria, and eukaryotes
MSC: Understanding
38. In the three-domain model, the bacterial ancestor of mitochondria derives from ancient
a. fungi. d. archaea.
b. cyanobacteria. e. protists.
c. respiring bacteria.
ANS: C DIF: Medium REF: 1.5
OBJ: 1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplasts
MSC: Remembering
39. Which of the following organelles are thought to be of prokaryotic origin?
a. chloroplast d. chloroplast and mitochondria
b. mitochondria e. chloroplast and nucleus
c. nucleus
ANS: D DIF: Medium REF: 1.5
OBJ: 1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplasts
MSC: Understanding
40. In the three-domain model, the bacterial ancestor of chloroplasts derives from ancient
a. fungi. d. archaea.
b. cyanobacteria. e. protists.
c. proteobacteria.
ANS: B DIF: Medium REF: 1.5
OBJ: 1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplasts
MSC: Remembering
41. Which commonly used microbial classification advancement led to the tree by Carl Woese in
1977?

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a. comparative genomics d. protein sequencing
b. microscopy e. 16S rRNA sequencing
c. X-ray diffraction
ANS: E DIF: Medium REF: 1.5
OBJ: 1.5b Outline how microbial classification has changed over time | 1.5d Describe the
importance of DNA sequencing in classification MSC: Understanding
42. Electron microscopes use what to focus the beam of electrons?
a. electromagnets d. X-ray diffraction
b. a condenser lens e. glass
c. light rays
ANS: A DIF: Easy REF: 1.6
OBJ: 1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing our
knowledge of cell structure and function MSC: Remembering
43. Peter Mitchell and Jennifer Moyle discovered the ________ theory in the 1960s.
a. germplasm d. DNA synthesis
b. evolution e. polymerase chain reaction
c. chemiosmotic
ANS: C DIF: Easy REF: 1.6
OBJ: 1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing our
knowledge of cell structure and function MSC: Remembering
44. The X-ray diffraction studies by which of the following scientists concluded that DNA was a
double helix?
a. James Watson d. Maurice Wilkins
b. Rosalind Franklin e. Kary Mullis
c. Francis Crick
ANS: B DIF: Easy REF: 1.6
OBJ: 1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing our
knowledge of cell structure and function MSC: Remembering
45. 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: B DIF: Medium REF: 1.6
OBJ: 1.6b Explain how studies on microbes fostered our knowledge of DNA function and
enhanced DNA technology MSC: Understanding
46. This scientist first discovered the process of transformation.
a. Francis Crick d. Louis Pasteur
b. Robert Koch e. Frederick Griffith
c. Edward Jenner
ANS: E DIF: Difficult REF: 1.6
OBJ: 1.6b Explain how studies on microbes fostered our knowledge of DNA function and
enhanced DNA technology MSC: Remembering
47. Taq polymerase forms the basis of a technique for
a. comparative genomics. d. DNA amplification.
b. recombinant DNA. e. protein synthesis.
c. X-ray diffraction.
ANS: D DIF: Easy REF: 1.6
OBJ: 1.6c State some uses of microbes in medicine and industry
MSC: Understanding
48. In 1975, scientists held a conference at Asilomar to regulate and restrict the field of
a. recombinant DNA. d. DNA amplification.
b. comparative genomics. e. forensic microbiology.
c. DNA sequencing.
ANS: A DIF: Medium REF: 1.6
OBJ: 1.6c State some uses of microbes in medicine and industry
MSC: Understanding
49. The study of and cause of disease in humans, animals, and plants is called
a. microbiology. d. epidemiology.
b. phylogeny. e. forensics.
c. genomics.
ANS: D DIF: Medium REF: 1.6
OBJ: 1.6c State some uses of microbes in medicine and industry
MSC: Remembering
50. The ultracentrifuge is a high-speed centrifuge ideally suited for separating individual
a. cellular proteins and nucleotides. d. secondary metabolites.
b. microbial cells. e. base pairs.
c. mold spores.
ANS: A DIF: Medium REF: 1.6
OBJ: 1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing our
knowledge of cell structure and function MSC: Understanding
SHORT 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 for
comparison. This field is referred to as comparative genomics. Comparisons have revealed that
there is a set of core genes shared by all organisms.
DIF: Difficult REF: 1.1 | 1.5
OBJ: 1.1d Explain the implications of microbial genome sequencing | 1.5b Outline how microbial
classification has changed over time MSC: Analyzing
2. How are prokaryotes and eukaryotes different?
ANS:
A prokaryote lacks a nucleus and membrane-bounded organelles, whereas a eukaryote has a
nucleus and membrane-bounded organelles.
DIF: Easy REF: 1.1 | 1.5 OBJ: 1.1a Recall the definition of a microbe
MSC: Remembering
3. How do microbes help in the extraction of minerals?
ANS:
Several lithotrophic bacteria help in the rapid oxidation of minerals, which generates strong acids
that 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: Medium REF: 1.2
OBJ: 1.2a List both positive and negative impacts that microbes have had on human history
MSC: Applying
4. Antonie van Leeuwenhoek worked as a cloth draper, inspecting the quality of cloth. How did this
lead to his interest in microscopy?
ANS:
His work introduced him to magnifying lenses. He began the hobby of grinding lenses, ultimately
making a microscope that enabled him to observe single-celled microbes.
DIF: Medium REF: 1.2
OBJ: 1.2c Identify the contributions of the following individuals: Nightingale, Hooke, van
Leeuwenhoek, Pasteur, and Tyndall MSC: Understanding
5. What was the major complaint about Lazzaro Spallanzani’s experiment to disprove spontaneous
generation, 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’s
swan-neck flasks did not allow organisms to enter the flask but did allow oxygen to enter. Growth
was still not observed.
DIF: Medium REF: 1.2
OBJ: 1.2c Identify the contributions of the following individuals: Nightingale, Hooke, van
Leeuwenhoek, Pasteur, and Tyndall MSC: Evaluating

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6. Describe the discoveries of Louis Pasteur while working with the French beer and wine
manufacturers 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 a
spontaneous chemical process. Pasteur discovered that this fermentation was caused by living
yeast, which did not require oxygen for growth. He also discovered that when the grapes or grain
are contaminated with bacteria instead of yeast, acetic acid is produced instead of alcohol.
DIF: Medium REF: 1.2
OBJ: 1.2c Identify the contributions of the following individuals: Nightingale, Hooke, van
Leeuwenhoek, Pasteur, and Tyndall MSC: Understanding
7. Describe the effects of three microbial diseases that have significantly affected human populations
throughout history.
ANS:
Answers may vary. Some examples include bubonic plague, which killed one-third of Europe’s
population 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 native
North Americans.
DIF: Medium REF: 1.2
OBJ: 1.2a List both positive and negative impacts that microbes have had on human history | 1.2c
Identify the contributions of the following individuals: Nightingale, Hooke, van Leeuwenhoek,
Pasteur, and Tyndall MSC: Applying
8. 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 were
invented, humans did not know that microbes existed. Even after humans were aware of the
presence of microbes, they did not suspect them of causing disease until people such as Joseph
Lister and Ignaz Semmelweis performed experiments that showed antiseptics decrease the
incidence of infection.
DIF: Difficult REF: 1.2 | 1.3
OBJ: 1.2b Explain why the microscope is an important tool in the field of microbiology
MSC: Understanding
9. Robert Koch’s postulates have not been used to prove HIV as the causative agent of AIDS. Why
not?
ANS:
Answers may vary, but a major reason is that humans cannot be injected with HIV to see if they
develop AIDS, and a suitable animal host doesn’t exist for testing.
DIF: Medium REF: 1.3
OBJ: 1.3c Assess some of the practical obstacles in applying Koch’s postulates
MSC: Understanding
10. 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 will
generate immunity. Answers for mechanisms may vary, but heat treatment or aging for various
periods or natural attenuation in the host are mentioned in the chapter.
DIF: Medium REF: 1.3
OBJ: 1.3d Recall the contributions of various individuals to the discovery and implementation of
vaccination | 1.3e Compare the roles of immunization, antiseptics, and antibiotics in human disease
treatment and prevention MSC: Applying
11. 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 reduced
the mortality rate of hospital patients. They made these observations before Robert Koch’s germ
theory of disease.
DIF: Medium REF: 1.3
OBJ: 1.3e Compare the roles of immunization, antiseptics, and antibiotics in human disease
treatment and prevention MSC: Understanding
12. How would you use Robert Koch’s postulates to prove that a specific organism causes a new
disease 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: Difficult REF: 1.3 OBJ: 1.3b List Koch’s postulates
MSC: Applying
13. Explain why the organisms that were studied by Sergei Winogradsky could not be grown on
Robert Koch’s plate media containing agar or gelatin.
ANS:
The organisms studied by Winogradsky were lithotrophs, which feed solely on inorganic
substances. Koch’s plate media contained organic nutrient sources, which may even be toxic to the
organisms he was attempting to grow.
DIF: Medium REF: 1.4
OBJ: 1.4a List Winogradsky’s contributions to microbial culture technique
MSC: Analyzing
14. 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 be
cultured. The work of Winogradsky and later microbial ecologists showed that bacteria are
necessary for geochemical cycling. Many of these organisms can’t be grown in pure culture on
laboratory media but can be grown in enrichment culture such as a Winogradsky column.

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DIF: Difficult REF: 1.4
OBJ: 1.4c Explain the role of microbes in geochemical cycling, especially that of nitrogen
MSC: Analyzing
15. Define the term “endosymbiont” and give an example of an endosymbiotic relationship found in
nature.
ANS:
An endosymbiont is an organism living symbiotically inside a larger organism. Examples may
vary, but include the following: Rhizobium in a leguminous plant, bioluminescent bacteria in the
light organs of fish and squid, and photosynthetic algae and coral.
DIF: Medium REF: 1.4
OBJ: 1.4d Compare the roles of animal endosymbionts and plant endosymbionts
MSC: Applying
16. 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 that
interbreed. Microbes typically reproduce asexually. When they do exchange genes, they may do so
with distantly related species.
DIF: Medium REF: 1.5
OBJ: 1.5a Explain why microbes can be challenging to classify taxonomically
MSC: Analyzing
17. Briefly explain the endosymbiosis theory and the evidence that supports it.
ANS:
The endosymbiosis theory proposes that mitochondria and chloroplasts evolved from bacteria that
were engulfed by pre-eukaryotic cells, and that over time these endosymbiotic prokaryotic cells
lost the ability to survive outside of the host cell but were maintained as organelles. Evidence
supporting the endosymbiosis theory includes the fact that mitochondria and chloroplasts possess
circular DNA with similarity to modern bacteria.
DIF: Medium REF: 1.5
OBJ: 1.5c Appraise endosymbiosis as an explanation for mitochondria and chloroplasts
MSC: Understanding
18. What were Rosalind Franklin’s contributions toward discovering the structure of DNA, and why
wasn’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 micrographs
showed for the first time that DNA was a double helix. A colleague showed her micrographs to
James Watson, who was also studying the structure of DNA. Watson and Francis Crick published
their model of the structure of DNA in the journal Nature and denied that they had used Franklin’s
micrographs. Franklin also died before the awarding of the prize.
DIF: Medium REF: 1.6

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OBJ: 1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing our
knowledge of cell structure and function MSC: Understanding
19. 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 Svedberg
calculated that the particle sizes could be determined based on the rate of sedimentation of the
particles in an ultracentrifuge.
DIF: Medium REF: 1.6
OBJ: 1.6a Describe the roles of the electron microscope and the ultracentrifuge in advancing our
knowledge of cell structure and function MSC: Understanding
20. If you want to produce DNA polymerases like those used in polymerase chain reaction (PCR) for
amplification 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 PCR
reactions, would be searching for microbes in an environment where the temperature is extremely
high.
DIF: Difficult REF: 1.6
OBJ: 1.6c State some uses of microbes in medicine and industry
MSC: Applying

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