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Chapter 1
Living in a Microbial World
1. Which of the following is not an example of a microorganism?
a. a bacterium
b. a protozoan
c. a flea
d. a virus
e. a single-celled fungus
2. Which of the following statements is true?
a. All living things are unicellular.
b. All living things are multicellular.
c. Most microorganisms are multicellular.
d. Living things are composed of one or more cells.
3. Which of the following statements is true?
a. Most microorganisms have eukaryotic cells.
b. Most microorganisms have cells containing organelles.
c. Many microorganisms have cells in which the genetic material is not surrounded
by a nuclear membrane.
d. Animals have prokaryotic cells.
e. Plant cells do not contain organelles.
4. Cells have the ability to maintain internal conditions within ranges compatible with life.
This ability is called:
a. homeostasis.
b. evolution.
c. metabolism.
d. environmental response.
5. Which of the following are not composed of cells?
a. Bacteria and archaea
b. Fungi and protozoa
c. Viruses and prions
6. Metabolism refers to:
a. the transfer of genetic information from generation to generation.
b. the changes in the characteristics of living things over time.
c. the response of living things to chemical signals in their environment.
d. the ability to reproduce.
e. the ability to assimilate and use energy.
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7. Which of the following is an example of basic science?
a. a study to determine the mechanism used by bacteria to adhere to the lining of the
intestine
b. the development of a new anti-tuberculosis drug
c. the use of microorganisms to digest oil released during an oil spill
d. a study to determine how to prevent corrosion of water pipes by microorganisms
e. research into the use of microorganisms as a source of biofuel
8. Which of the following statements about model organisms is true?
a. They tend to be slow growing.
b. They tend to have unique biological properties, very different from other organisms.
c. They tend to reproduce quickly.
d. They tend to be more complex and harder to study than other living things.
e. They are used regularly in applied science, but not in basic science.
9. Which of the following statements about a hypothesis is true?
a. A hypothesis is an explanation for a scientific phenomenon that has been repeatedly
tested for many years and never disproved.
b. A hypothesis can never be disproved. It can only be proved.
c. A hypothesis is the initial observation of a natural phenomenon that leads to a
question.
d. A hypothesis is the question that stems from the observation of a natural
phenomenon.
e. A hypothesis is used to make a prediction about a future event that can later be
observed or tested experimentally.
10. Those factors that are kept the same in the experimental group and the control group are
called:
a. control variables.
b. experimental variables.
c. manipulated variables.
d. observed variables.
11. What are the primary differences between prokaryotic and eukaryotic cells? Which
groups of microorganisms have which cell type?
12. Which typical characteristics of living things are not observed in viruses?
13. Why are control groups necessary in a proper scientific experiment?
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Chapter 1 Answers
1. c
2. d
3. c
4. a
5. c
6. e
7. a
8. c
9. e
10. a
11. Prokaryotic cells are simpler and usually smaller in size than eukaryotic cells. In
prokaryotic cells, membrane-bound organelles, including the nuclear membrane, are not
present. In eukaryotic cells, cellular processes occur in organelles, with different
activities taking place in discreet locations within the cell. Bacteria and Archaea have
prokaryotic cells. Fungi, protozoa, and algae all have eukaryotic cells.
12. Viruses are not composed of cells. They are unable to replicate outside the cells of other
organisms and they have little if any independent metabolism.
13. In a proper experiment, the effect of the experimental variable, if any, is compared
between the experimental group and the control group. Without the control group, in
which the experimental variable was not manipulated, there would be no way to evaluate
the effect of the experimental variable.
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Chapter 2
The Chemistry of Life
1. Which of the following is a mismatched pair?
a. electrons: negative charge
b. neutrons: no charge
c. protons: positive charge
d. atomic mass number: protons plus electrons
e. uncharged atom: the number of electrons = the number of protons
2. If an atom X has an atomic number of 18, then:
a. there are 18 protons.
b. there are 9 protons and 9 electrons.
c. there are 18 neutrons.
d. there are 9 protons and 9 neutrons.
e. it also has a mass number of 18.
3. When one atom donates electrons and another atom accepts those electrons, a(n)
________ bond forms.
a. polar covalent
b. hydrogen bond
c. nonpolar covalent
d. ionic
4. An atom has 1 electron in an outer shell that holds a maximum of eight electrons. This
atom:
a. is most likely an inert gas.
b. will most likely form polar covalent bonds.
c. will most likely gain electrons to achieve stability.
d. will most likely become a negatively charged ion to achieve stability.
e. will most likely lose its outer electron to achieve stability.
5. Which of the following compounds will not dissolve in water?
a. one consisting largely of non-polar covalent bonds
b. one consisting largely of polar covalent bonds
c. one consisting largely of ionic bonds
d. one that readily forms hydrogen bonds
e. one in which many of the atoms have partial charges
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6. Which of the following statements is correct?
a. A base is a H+ ion donor.
b. Pure water is completely neutral and has a pH of 0.
c. As the concentration of H+ goes up, the pH also goes up.
d. If the hydroxyl ions outnumber the H+ ions, the pH will be less than 7.0.
e. Bases reduce the concentration of H+ in water.
7. When two monosaccharides are joined together, ________ is formed through ________
synthesis.
a. a disaccharide; hydrolysis
b. a polysaccharide; hydrolysis
c. glucose; condensation
d. a disaccharide; condensation
e. starch; condensation
8. The building blocks of ________ are ________ .
a. polysaccharides; fatty acids
b. DNA; nucleotides
c. nucleic acids; amino acids
d. polysaccharides; glycerol
e. fats; monosaccharides
9. Enzymes function by ________, which speeds up the rate of a chemical reaction.
a. increasing the stability of the reactants
b. multiplying the number of active sites on the reactants
c. lowering the energy of activation
d. increasing the energy of activation
e. keeping the pH constant
10. The purines of nucleic acids are ________ and ________.
a. thymine; guanine
b. adenine; guanine
c. adenine; cytosine
d. thymine; cytosine
e. cytosine; guanine
11. Describe the relationship between an atom’s stability and its energy. How does this
impact an atom’s reactivity?
12. What factors determine if a substance will or will not dissolve in water?
13. Why do proteins become less active as they lose their three-dimensional shape?
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Chapter 2 Answers
1. d
2. a
3. d
4. e
5. a
6. e
7. d
8. b
9. c
10. b
11. There is an inverse relationship between an atom’s stability and its energy level. They are
more likely to interact with other atoms (they are more reactive) when their energy is
greater and their stability is lower.
12. Water is a highly polar molecule, because of the polar covalent bonds between oxygen
and hydrogen atoms. These polar covalent bonds result in partial charges on each atom in
a water molecule; partial negative on the oxygen and partial positive on the hydrogen
atoms. These partial charges can attract charges, either partial or full, on other molecules,
allowing the water to hydrogen bond with these charged molecules. Consequently, any
molecule with charges (ionic compounds or compounds consisting of largely polar
covalent bonds) will hydrogen bond with water, and the collective force of many
hydrogen bonds causes the molecule to dissolve. Molecules that are composed of mainly
nonpolar covalent bonds lack charges, and therefore cannot hydrogen bond with water.
They therefore do not dissolve in water.
13. The ability of a protein to carry out its specific functions is dependent on its precise threedimensional folding, which allows the protein to interact with other molecules in a highly
specific manner. Anything that interferes with the protein’s complex three-dimensional
shape reduces the ability of the protein to properly interact with other molecules and
therefore reduces its activity. As proteins lose their three-dimensional shape, they are said
to be denatured. High temperature and pH extremes are common causes of protein
denaturing.
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Chapter 3
The Cell: Where Life Begins
1. As cells increase in size:
a. their surface/volume ratio increases, and they become more metabolically efficient.
b. their surface/volume ratio decreases, and they become more metabolically efficient.
c. their surface/volume ratio increases, and they become less metabolically efficient.
d. their surface/volume ratio decreases, and they become less metabolically efficient.
2. Bacteria which have a spherical shape are called ________.
a. bacilli
b. spirochetes
c. vibrio
d. spirilla
e. cocci
3. Which of the following extracellular structures allows some bacteria to resist
phagocytosis by phagocytic cells?
a. capsule
b. fimbriae
c. sex pili
d. flagella
4. ________ bacteria lose their crystal violet when the decolorizer alcohol is added during
the Gram stain procedure.
a. Gram-negative
b. Gram-positive
c. Acid-fast
d. Both Gram-negative and Gram-positive
5. Penicillin:
a. prevents the linkage between N-acetyl-glucosamine and N-acetylmuramic acid.
b. breaks the bonds between N-acetyl-glucosamine and N-acetylmuramic acid.
c. prevents the formation of pentaglycine bridges.
d. breaks pentaglycine bridges.
e. perforates the plasma membrane of Gram-positive bacteria.
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6. Which of the following is released by dying Gram-negative bacteria, whereupon it acts as
endotoxin?
a. peptidoglycan
b. O-polysaccharides
c. porin proteins
d. pentaglycine
e. lipopolysacharides
7. Membrane phospholipids:
a. are highly hydrophobic.
b. are highly hydrophilic.
c. have hydrophobic phosphate heads and hydrophilic fatty acid tails.
d. have hydrophilic phosphate heads and hydrophobic fatty acid tails.
e. are found in prokaryotic, but not eukaryotic, cells.
8. ________ is/are composed of long, slender protein filaments and act(s) as a type of
scaffolding for eukaryotic cells.
a. The cilia
b. The cytoskeleton
c. The endoplasmic reticulum
d. The endomembrane system
e. The endospore
9. Which of the following describes the correct pathway used by eukaryotic cells for the
synthesis of proteins transported out of the cell?
a. endoplasmic reticulum » ribosomes » Golgi apparatus » plasma membrane
b. plasma membrane » ribosomes; Golgi apparatus » endoplasmic reticulum
c. Golgi apparatus; ribosomes » endoplasmic reticulum » plasma membrane
d. ribosomes » endoplasmic reticulum » Golgi apparatus » plasma membrane
10. Which of the following organelles found in eukaryotic cells is most likely to have been
acquired by endosymbiosis?
a. the nucleus
b. the smooth endoplasmic reticulum
c. the Golgi apparatus
d. the lysosome
e. the mitochondrion
11. What is taxis as it applies to bacteria? What structure does bacteria that are capable of
taxis possess?
12. Why is peptidoglycan such an attractive target for antibiotic drugs?
13. Provide a basic description of the fluid mosaic model of membrane structure.
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Chapter 3 Answers
1. d
2. e
3. a
4. a
5. c
6. e
7. d
8. b
9. d
10. e
11. Taxis refers to the ability of many bacteria to move toward favorable conditions (positive
taxis) or away from unfavorable conditions (negative taxis). Only motile bacteria are
capable of taxis. In an almost all cases, motile bacteria rely on flagella.
12. Almost all bacteria are protected from environmental hazards by a cell wall.
Peptidoglycan is a key component of the cell wall, and it is especially abundant in Grampositive bacteria. Antibiotics that interfere with peptidoglycan structure make affected
cells vulnerable to various environmental hazards, such as an influx of water which can
cause cell lysis. Peptidoglycan is a unique bacterial molecule, and therefore, antibiotics
that interfere with peptidoglycan pose little risk to eukaryotic cells.
13. According to the fluid mosaic model of membrane structure, the plasma membrane is
largely composed of lipid and protein. Much of the lipid is phospholipid, which is
composed of a hydrophilic phosphate “head” and two hydrophobic fatty acid “tails”. The
phosphates orient themselves toward water on both the extracellular and cytoplasmic
sides of the membrane, with the hydrophobic fatty acids occupying the membrane
interior. This double layer of phospholipids is referred to as a bilayer. Various membrane
proteins are embedded in the bilayer. Some of these proteins (transmembrane proteins)
span the membrane from the extracellular to the cytoplasmic side. Other proteins are
embedded only part way through the bilayer. The phospholipids in the bilayer are not
bound to each other. The bilayer is the result of the way in which the phospholipids
interact with water. The membrane is therefore not a rigid structure, with both the
phospholipids and the membrane proteins continually changing position.
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Chapter 4
A Field Guide to the Microorganisms
1. Which of the following are the most closely related?
a. Two animals that are in the same phylum
b. Two plants that are in the same class
c. Two fungi that are in the same order
d. Two bacteria that are in the same family
2. The bacteria that causes diphtheria is called corynebacterium diphtheria.
Which of the following has the name of this bacterial species written in proper scientific
form?
a. corynebacterium diphtheria
b. Corynebacterium Diphtheria
c. Corynebacterium diphtheria
d. corynebacterium Diphtheria
3.
The classification of living things according to their evolutionary relationships
is called:
a. taxonomy.
b. phylogenetics.
c. taxonomic hierarchy.
d. the five-kingdom system of classification.
e. the three-domain system of classification.
4. Which of the following is true about photosynthetic bacteria?
a. They are the most primitive of all bacteria.
b. Photosynthesis appears to have evolved several separate times.
c. Photosynthetic bacteria all appear to be closely related.
d. A comparison of rRNA genes in different lineages of photosynthetic bacteria would
reveal that the genes are almost identical in all lineages.
e. All photosynthetic bacteria appear to have evolved relatively recently.
5. Which of the following statements is true about archaea?
a. They are in the domain Bacteria.
b. They have cells walls identical to those of bacteria.
c. They have eukaryotic cells.
d. They often are found in extreme environments.
e. All known archaea require oxygen for survival.
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6. The feeding and reproducing stage of many protozoa is known as a:
a. trophozoite.
b. cyst.
c. vector.
d. protista.
e. mastigophora.
7. Fungi that grow on dead material are called:
a. autotrophs.
b. saprophytes.
c. filamentous fungi.
d. fleshy fungi.
e. Zygomycota.
8. Viruses go through a series of defined steps in their replicative cycle. In which of the
following are these steps listed in proper order?
a. attachment » uncoating » penetration » synthesis » release » assembly
b. penetration » attachment » uncoating » assembly » synthesis » release
c. uncoating » attachment » penetration » synthesis » assembly » release
d. attachment » penetration » uncoating » synthesis » assembly » release
e. penetration » synthesis » assembly » attachment » release » uncoating
9. Which of the following is true about viral penetration?
a. All non-enveloped and enveloped viruses enter host cells via endocytosis.
b. All non-enveloped and enveloped viruses enter host cells via fusion.
c. All non-enveloped viruses enter cells by endocytosis. All enveloped viruses enter
cells by fusion.
d. All non-enveloped viruses enter cells by fusion. All enveloped viruses enter cells by
endocytosis.
e. Non-enveloped viruses enter cells by endocytosis. Some enveloped viruses also enter
by endocytosis, while others enter by fusion.
10. In which of the following ways are prions believed to differ from all other infectious
agents?
a. Unlike any other infectious agents, they are acellular.
b. Unlike any other infectious agents, they can infect many different species of hosts.
c. Unlike any other infectious agents, are able to reproduce without any nucleic acid.
d. Prions appear to be unusual viruses that have both DNA and RNA.
e. Unlike other infectious agents, which are found only in specific host tissues, prions
have the ability to infect any tissue in a host’s body.
11. How are rRNA genes used to deduce evolutionary relationships?
12. What are mycorrhizial relationships? Provide an example.
13. What is different about the synthesis stage in a plus- and a minus-strand RNA virus?
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Chapter 4 Answers
1. d
2. c
3. b
4. b
5. d
6. a
7. b
8. d
9. e
10. c
11. All genes experience mutations (changes in their nucleotide sequences) over time.
Ribosomal RNA (rRNA) genes mutate slowly and at a fairly constant and predictable
rate. By comparing the nucleotide sequence in rRNA genes of any two species, scientists
can deduce how long ago the two species shared a common ancestor. Only after the
common ancestor split into separate lineages will rRNA mutations accumulate
independently in different lineages. Consequently, many differences in the rRNA genes
between two species indicate that they diverged long ago. Fewer differences indicate a
more recent common ancestor, meaning that the organisms being compared are more
closely related.
12. Mycorrhizal associations are relationships between plant roots and associated fungi that
grow on the roots. Because both the plant and the fungus benefits from the relationship,
this is an example of a mutualistic relationship. In the Zygomycota, the fungus supplies
the plant with phosphorus, while the fungus obtains necessary sugars from the plant.
Basidiomycota also frequently form mycorrhizal associations, in which the plant obtains
nitrogen from the fungus in return for sugars provided by the plant.
13. Both plus- and minus-RNA viruses carry RNA rather than DNA in their capsid. Plusstrand viruses carry DNA that can immediately be used to make proteins, once the virus
has gained entry into a host cell. This same RNA is also used as a template to produce
complementary minus-strand RNA. This minus-strand RNA is then used to produce
many copies of plus-strand RNA, which will be incorporated into newly formed capsids
during assembly. In minus-strand viruses, following penetration, the minus-strand RNA
is used as a template to make plus-strand RNA, which is then used to make necessary
viral proteins. This plus-strand RNA also acts as a template to make many new copies of
minus-strand RNA, which will be incorporated into newly formed capsids during
assembly.
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Chapter 5
The Microbiology of History
and the History of Microbiology
1. Which of the following was not cited as a possible partial explanation for the decline of
the Roman Empire?
a. pressure from Germanic tribesman along the Empire’s northern border
b. declining agricultural production near the capital at Rome
c. the difficulties involved in administrating such a large geographic area
d. epidemic malaria in and around Rome
e. incursions into the empire by Arabic tribesmen from North Africa
2. A serious disease outbreak that affects a large portion of the world is called a(n):
a. epidemic.
b. pandemic.
c. endemic.
d. zoonosis.
e. nosocomial infection.
3. Which of the following factors was cited as a contributing cause to the end of the English
feudal system?
a. a labor shortage caused by high mortality due to the “black death”
b. a disruption of transport in England caused by a fear of smallpox
c. a still unidentified disease outbreak that preferentially killed landowners
d. a series of very wet years that promoted increased mosquito numbers, and therefore
an epidemic of malaria
e. an outbreak of a serious plant pathogen that caused crops to fail, initiating a famine
4. Which of the following diseases played the biggest part in defeating Napoleon in his
attempt to conquer Russia?
a. typhus
b. typhoid
c. bubonic plague
d. malaria
e. smallpox
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5. Which of the following statements about the Weil-Felix test for typhus is false?
a. It relies on the fact that antibodies generated against Rickettsia do not react with
Proteus OX19.
b. It relies on cross-reactivity between the pathogen and the soil bacterium.
c. When blood serum is drawn from a person to be tested, the serum is mixed with a
solution containing Proteus OX19.
d. Humans are not normally infected with Proteus OX19.
e. If the individual being tested is positive, clumping will be seen on the test slide.
6. What was the important contribution to microbiology made by Anton Van Leeuwenhoek
in the 1600s?
a. He invented the microscope.
b. He was the first to observe microorganisms.
c. He disproved spontaneous generation.
d. He was the first to show that a disease could be caused by a microorganism.
e. He was the first to describe fermentation.
7. Four flasks are prepared with a broth that supports microbial growth. Broth A is boiled
and then sealed to prevent the entry of air. Broth B is boiled and left open to the air.
Broth C is boiled and left open, but the flask is fitted with an S-shaped neck. Broth D is
boiled, left open to the air, and fitted with an S-shaped neck, but after two days the neck
is removed. If the broths are examined after four days, which ones will contain living
microorganisms?
a. All broths will contain microorganisms.
b. None of the broths will contain microorganisms.
c. broths B & D
d. broths A & C
e. broths B, C & D
8. Which of the following early contributors to the development of microbiology as a
science is not paired up properly with his or her accomplishment?
a. Louis Pasteur: demonstrated that contaminating bacteria were responsible for wine
spoilage
b. Joseph Lister: developed aseptic technique
c. Florence Nightingale: introduced the idea of sanitation to hospitals
d. Ignaz Semmelweis: was the first to show that a specific microbe could cause a
specific disease
e. Robert Koch: developed pure culture technique
9. Which of the following is not a vector-borne disease?
a. bubonic plague
b. yellow fever
c. malaria
d. typhus
e. anthrax
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10. The principle of attenuation discovered by Pasteur had important implications for:
a. antibiotic development.
b. vaccine development.
c. aseptic surgery.
d. pure culture technique.
e. the development of variolation as a defense against smallpox.
11. Why is a large population of hosts more important for the maintenance of a “crowd
disease” than it is for other types of diseases?
12. What is the danger associated with agricultural monocultures?
13. What are Koch’s Postulates? Explain how they are used to determine the cause of a
particular disease.
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Chapter 5 Answers
1. e
2. b
3. a
4. a
5. a
6. b
7. c
8. d
9. e
10. b
11. “Crowd diseases” are acute in nature. Once a host is infected, the pathogen replicates
rapidly, symptoms appear quickly, and the host usually either recovers relatively quickly
and develops immunity to the disease, or dies. For the pathogen causing the disease, this
means that if it spreads through a population, it can quickly “use up” its potential hosts,
since most individuals are now either immune to a subsequent infection or dead. To
survive, therefore, the pathogen requires a large population (a “crowd”) of hosts, to insure
there are always an adequate number of susceptible individuals in the population, in
which the pathogen can reproduce. Other, chronic diseases do not necessarily require
such large populations of hosts, because when a pathogen causing such a disease infects a
host, the infection can last indefinitely, reducing the need for the pathogen to quickly find
new hosts to infect.
12. Monocultures are highly susceptible to crop diseases because if an appropriate pathogen
invades the crop, the pathogen will rapidly spread throughout the monoculture, causing
complete crop failure. A human population that depends on this monoculture is then at
risk for famine. Such total destruction of a plant community is rare in natural ecosystems
because such ecosystems generally consist of many plant species. It is unlikely that any
plant pathogen can attack more than a few plant types. The danger of monocultures in
agriculture can be mitigated by growing a variety of crops in the same area, since it is
unlikely that any one plant pathogen can damage all crops.
13. Koch’s postulates are a series of steps developed by Robert Koch to be used to determine
the exact cause of a particular disease. When animals are sick or dying from a disease of
unknown cause, potential causative agents are isolated from sick individuals. These
potential causative agents are then grown in pure culture. Next, experimental animals are
exposed to each of the potential causative agents. If one of the potential agents is the
genuine cause of the disease, animals exposed to this agent should develop a disease that
appears the same as the original disease under consideration. Microorganisms that are
isolated out of these now-sick experimental animals should be identical to those to which
the experimental animals were exposed. This confirms that the suspect organism is
indeed the causative agent of the disease.
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Chapter 6
Microbial Genetics
1. Which of the following components is not normally found as part of a DNA nucleotide?
a. a nitrogenous base
b. a phosphate group
c. uracil
d. a deoxyribose sugar
2. The term used to describe the orientation of the two strands of DNA is:
a. polarity.
b. complementary.
c. antiparallel.
d. 5’ to 3.’
e. forked.
3. ________ use(s) codons to specify which amino acid should be added to the growing
polypeptide chain during protein synthesis.
a. DNA
b. mRNA
c. tRNA
d. rRNA
e. operons
4. Protein synthesis occurs on ________, which are composed of proteins and ________.
a. ribosomes; mRNA
b. operons; mRNA
c. promoters; rRNA
d. ribosomes; rRNA
e. active sites; DNA
5. The region of the DNA to which RNA polymerase binds during transcription is known as
the ________.
a. promoter
b. codon
c. anticodon
d. operator
e. origin of replication
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6. In the lac-operon, under which of the following conditions will the repressor protein be
bound to its binding site?
a. when the environment contains abundant lactose
b. when the environment is very low in lactose
c. when the inducer is bound to the repressor
d. when RNA polymerase is most able to bind to the promoter
e. when the structural genes of the operon are being transcribed at a maximum rate
7. The uptake of naked DNA by some bacterial cells is called ________.
a. transduction
b. conjugation
c. an insertion
d. transformation
e. a point mutation
8. Which of the following mutations is most likely to prove beneficial to the cell
experiencing the mutation?
a. samesense mutation
b. missense mutation
c. nonsense mutation
d. frameshift mutation
e. spontaneous mutation
9. Which of the following statements is true?
a. Individuals of the same species have the same genes, but may have different alleles
of those genes.
b. Individuals of the same species have different genes but the same alleles.
c. Individuals of the same species have the same genes and alleles as each other.
d. Individuals of the same species have different genes and alleles from each other.
10. Which of the following is not a difference in the way gene expression occurs in bacteria
and in eukaryotes?
a. In bacteria, but not eukaryotes, RNA polymerase binds the promoter directly.
b. Bacteria, but not eukaryotes, have non-coding regions called introns in their genes,
which must be removed from mRNA following transcription.
c. In bacteria, but not eukaryotes, translation can begin on a particular mRNA, before
transcription of that same mRNA molecule is complete.
d. The ribosomes used by bacteria in translation are smaller and somewhat different in
structure than those used by eukaryotes.
e. Gene expression is generally quicker in bacteria than it is in eukaryotes.
11. Explain how RNA differs in structure from DNA.
12. How does “proofreading” by DNA polymerase occur during DNA replication?
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13. Identify and describe three distinct ways in which genetic recombination occurs in
bacteria.
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Chapter 6 Answers
1. c
2. c
3. b
4. d
5. a
6. b
7. d
8. b
9. a
10. b
11. RNA nucleotides contain the sugar ribose, whereas in DNA the sugar deoxyribose is
used. RNA is typically a single-stranded molecule, whereas DNA is a double-stranded
molecule. In RNA the nitrogenous base uracil is used in place of thymine. Because RNA
is transcribed from only a portion of the DNA, an RNA molecule is typically much
shorter, composed of many fewer nucleotides, than a DNA molecule is.
12. During DNA replication, DNA polymerase occasionally inserts the wrong nucleotide in
the growing daughter DNA strand. Subsequently, the enzyme is often unable to proceed
past the point of this mistake, because the aberrant base cannot properly hydrogen bond
to the nucleotide on the adjacent parental strand. In such situations, DNA polymerase
moves in reverse (in the 3’ to 5’ direction) and cuts out the last nucleotide that was added.
Following removal of this incorrect nucleotide, the enzyme then proceeds once again in
the 5’ to 3’ direction, essentially having a second chance to insert the proper nucleotide
into the growing daughter strand.
13. In transformation, DNA released by dead bacteria is taken up by living bacteria. This new
DNA may be incorporated into the bacterial chromosome of the recipient cell, altering
the genotype of the cell. The recipient cell is consequently said to be “transformed”. Only
certain bacterial species are capable of transformation. In transduction, a donor bacterial
cell becomes infected with a bacteriophage. During new bacteriophage assembly in the
cytoplasm of the host cell, some newly assembled phage particles incorporate fragments
of host bacterial DNA into their phage heads, instead of viral DNA. If these
bacteriophage subsequently infect new bacterial cells, they may erroneously introduce
bacterial DNA into newly infected host cells. Because such aberrant phage do not contain
a proper viral genome they will not kill the host bacterial cell, but if they release the
bacterial DNA from their nucleocapsid into the new recipient cell, and if the recipient cell
incorporates this DNA into their chromosome, the recipient bacterial cell will be
genetically altered, having acquired foreign DNA, with the bacteriophage acting as a
carrier. In conjugation, the donor bacterial cell has a small extrachromosomal loop of
DNA called a plasmid. A gene on the plasmid allows the donor to construct a sex pilus,
which can physically connect the donor cell to a recipient cell lacking a plasmid. The sex
pilus then contracts, pulling the donor and recipient cells together. This induces the donor
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cell to replicate its plasmid. As the two strands of plasmid DNA separate, one of the two
strands is transferred to the recipient cell, which then copies the single strand into its own
double-stranded plasmid. The recipient cell has now been genetically altered, as it has
obtained any genes found on the plasmid.
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Chapter 7
Metabolism and Growth
1. In a coupled reaction:
a. a catabolic exergonic reaction supplies the energy needed for an anabolic endergonic
reaction to occur.
b. a catabolic endergonic reaction supplies the energy needed for an anabolic exergonic
reaction to occur.
c. an anabolic endergonic reaction supplies the energy for a catabolic exergonic reaction
to occur.
d. an anabolic exergonic reaction supplies the energy for a catabolic endergonic reaction
to occur.
2. A photoautotroph is a microorganism that uses ________ as its carbon source and
________ as its energy source.
a. organic molecules; organic molecules
b. inorganic molecules; organic molecules
c. CO2 ; inorganic molecules
d. CO2; sunlight
3. A bacterial species never uses oxygen as a final electron acceptor. However, it has the
enzymes necessary to degrade toxic forms of oxygen. Such a bacterial species is an
example of:
a. an obligate aerobe.
b. an obligate anaerobe.
c. a facultative anaerobe.
d. an aerotolerant anaerobe.
e. a microaerophile.
4. In a particular redox reaction, when an electron pair is transferred from molecule X to
molecule Y:
a. the transferred electrons were at greater energy and reduced stability with molecule
X.
b. the electrons have greater energy and reduced stability with molecule Y.
c. the electrons had greater energy and stability with molecule X.
d. the electrons have greater energy and stability with molecule Y.
e. molecule X is reduced.
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5. Why is pyruvate reduced during fermentation?
a. to regenerate NAD+, permitting glycolysis to continue
b. to produce additional NADH, which can be oxidized in electron transport
c. to produce additional ATP by coupling ATP production to the reduction of pyruvate.
The now reduced form of pyruvate can then enter the Krebs Cycle.
d. Pyruvate is toxic to cells. It is therefore reduced to a non-toxic form.
6. In the presence of the final electron acceptor, what happens to the NADH that is
producedin glycolysis?
a. It is further reduced in the Krebs Cycle.
b. It is oxidized in electron transport.
c. It is converted into pyruvate.
d. It is released as a metabolic waste product.
e. It is converted into FADH2.
7. If the final electron acceptor is not present, which of the following still occurs?
a. the pumping of protons across a membrane
b. the production of ATP by the ATP synthase complex
c. the final oxidation of biological molecules in the Krebs cycle
d. the release of electrons to components of the electron transport chain by NADH and
FADH2
e. fermentation
8. Bacteria that grow well only at very low temperatures are termed:
a. extreme thermophiles.
b. mesophiles.
c. thermophiles.
d. psychrophiles.
e. psychotolerant.
9. A chemically defined medium is often required to grow ________ bacteria
in the laboratory.
a. fastidious
b. non-fastidious
c. acidophilic
d. halophilic
e. microaerophilic
10. During the stationary phase of microbial growth:
a. cells are preparing to divide.
b. production of new cells exceeds cell death.
c. production of new cells is approximately equal to cell death.
d. there is no production of new cells or cell death.
e. cell death exceeds the production of new cells.
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11. When cells catabolize biological molecules for the purposes of ATP production, energy
in the biological molecule is released in a large number of small steps, rather than in a
single large step. Why is this necessary?
12. Describe how ATP is produced in electron transport.
13. Describe differences that would be seen in the growth curve of a facultative anaerobe that
is grown in the presence of oxygen, and the same facultative anaerobe grown in the
absence of oxygen.
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Chapter 7 Answers
1. a
2. d
3. d
4. a
5. a
6. b
7. e
8. d
9. a
10. c
11. When energy is released slowly in a series of small steps, the cell can efficiently use the
energy to produce ATP. If energy were released all at once in a single large step, much of
the energy would be wasted because cells are not capable of harvesting so much energy
at once. Furthermore, much of this wasted energy would be released in the form of heat,
which would no doubt raise the temperature of the cell to the point where it could not
survive.
12. When NADH and FADH2 are oxidized by the early components of the electron transport
chain, the electrons are passed along a series of carriers, ultimately being used to reduce
the final electron acceptor, which is subsequently released as a respiratory waste. As the
electrons are passed between the various components in the chain, energy is released as
the electrons become progressively more and more stable. At certain components in the
chain, the released energy is used to pump protons across a membrane. This causes a
proton gradient to build up on one side of the membrane. The protons return to their
original position by flowing through the ATP synthase complex, which extends through
the membrane. As the protons flow back through this complex, the released energy is
used by the ADP and P-binding “head” of the ATP synthase complex, to bind P to ADP,
forming ATP.
13. Facultative anaerobes are able to grow in the presence or absence of oxygen. When
oxygen is present, oxygen serves as the final electron acceptor in electron transport. ATP
yield is relatively high. When oxygen is absent, facultative anaerobes rely on alternative
final electron acceptors or on fermentation to produce ATP. ATP yield is relatively low.
Because growth rate is to some degree dependent on ATP production, growth rate will be
faster in the presence of oxygen than in its absence. Consequently, if growth curves were
constructed for the facultative anaerobe growing in the presence or absence of oxygen,
the lag phase would be longer and the log phase would be less steep when oxygen is not
present.
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Chapter 8
Microbial Evolution:
The Origin and Diversity of Life
1. An experiment by Stanley Miller in the 1950s demonstrated that abiotic synthesis of
organic molecules could occur:
a. in a reducing environment.
b. in an oxidizing environment.
c. on the ocean floor.
d. at extremely high temperatures.
e. at extremely low temperatures.
2. Molecules composed of RNA that have enzymatic activity are known as:
a. ribosomes.
b. RNases.
c. catalases.
d. ribozymes.
e. nucleases.
3. Which of the sequences below is believed to be correct for the order in which the
following evolved?
a. liposomes » first heterotrophic prokaryotes » first oxygen-yielding photosynthetic
prokaryotes » first eukaryotes
b. first heterotrophic prokaryotes » first oxygen-yielding photosynthetic
prokaryotes » liposomes » first eukaryotes
c. first oxygen-yielding photosynthetic prokaryotes » first heterotrophic
prokaryotes » first eukaryotes » liposomes
d. eukaryotes » first heterotrophic prokaryotes » first oxygen-yielding photosynthetic
prokaryotes » liposomes
e. liposomes » first oxygen-yielding photosynthetic prokaryotes » first heterotrophic
prokaryotes » eukaryotes
4. Which of the following is believed to be the correct sequence for the order in which the
following metabolic processes evolved?
a. glycolysis » aerobic respiration » photosynthesis
b. photosynthesis » aerobic respiration » glycolysis
c. aerobic respiration » glycolysis » photosynthesis
d. photosynthesis » glycolysis » aerobic respiration
e. glycolysis » photosynthesis » aerobic respiration
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5. Which of the following facts provides evidence for endosymbiosis?
a. Mitochondria and chloroplasts have their own DNA, which replicates independently
of the nuclear DNA.
b. Ribosomes in mitochondria and chloroplasts have a structure similar to bacterial
ribosomes.
c. Chloroplasts have certain gene sequences in their DNA, which indicate a relationship
with cyanobacteria.
d. Both “a” and “b” above provide such evidence.
e. All of the above provide such evidence.
6. One hypothesis of viral origin suggests that viruses began as parasitic prokaryotes that
gradually lost most of their genetic information and ultimately became completely
dependent on host cells. This hypothesis is called:
a. the regressive hypothesis.
b. the escaped gene hypothesis.
c. the coevolved hypothesis.
d. the transposon hypothesis.
e. the parasitic hypothesis.
7. Which of the following points is not part of the theory of natural selection?
a. Under ideal conditions, all populations can grow exponentially if all individuals
survive and reproduce.
b. As environmental resources become limited, some individuals within a population
are more likely to reproduce than others.
c. Individuals within a population are not genetically identical.
d. Those with a genetic makeup that results in the best adaptation to a particular set of
environmental conditions are those most likely to reproduce. They will then pass on
genes for these adaptations to their offspring.
e. Specific environmental conditions can cause specific favorable mutations to occur,
resulting in better adaptation to those environmental conditions.
8. Under which of the following conditions would resistance to a specific antibiotic most
likely evolve?
a. when the antibiotic is not commonly used
b. when the antibiotic is routinely used, even in inappropriate situations
c. when the antibiotic is used, but only in carefully controlled and appropriate situations
d. when the use of the antibiotic is suddenly curtailed
e. when several antibiotics, including the specific antibiotic under consideration, are
used together
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9. We might expect virulence of a particular human pathogen to decrease:
a. when opportunities for transmission are limited.
b. when opportunities for transmission are abundant.
c. when animal reservoirs for the pathogen are scarce.
d. in very large human populations, such as a large city.
e. when it uses insect vectors for transmission.
10. The idea that sexual reproduction evolved as a way to increase genetic diversity in a
population, rendering that population less vulnerable to pathogens, is called:
a. the sexual selection hypothesis.
b. the artificial selection hypothesis.
c. the red queen hypothesis.
d. the white rabbit hypothesis.
e. the pathogen vs. host hypothesis.
11. Explain the rationale for the “RNA world” hypothesis.
12. Why is it that natural selection can never result in organisms that are perfectly adapted to
their environment?
13. It is believed that mitochondria were acquired by primitive eukaryotic cells before
chloroplasts were. What is the evidence for this?
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Chapter 8 Answers
1. a
2. d
3. a
4. e
5. e
6. a
7. e
8. b
9. a
10. c
11. All living things must reproduce, and reproduction requires genetic material to transmit
information from one generation to the next. For all modern prokaryotes and eukaryotes,
this genetic material is DNA. Yet if the original genetic material when early life was first
evolving was DNA, there is a problem: DNA can replicate itself, but it requires enzymes
to do so. Proteins can function as enzymes, but they cannot replicate. So did DNA, which
codes for all proteins, including enzymes, come first, or did the enzymes necessary for
DNA replication come first? Ribozymes, which are enzymes made of RNA, may provide
an answer to this question. Ribozymes, discovered in the 1980s, were found to be
involved in certain processes, including the synthesis of RNA. And since RNA, as a
sequence of nucleotides, can also encode genetic information, it has been suggested that
the first cells used RNA both as their genetic material and for the enzymes needed to
replicate the genetic material. This “RNA world” was eventually replaced by a “DNA
world”, because as cells became more complex, DNA was superior for encoding larger
amounts of information.
12. All organisms must be able to do many different things, and a characteristic that is
valuable for one task is often much less valuable or even a hindrance for a different task.
An organism’s various characteristics represent a compromise between the competing
demands with which all living things must contend.
13. Virtually all eukaryotic cells contain mitochondria, whereas only certain groups of
eukaryotic cells have chloroplasts. It is therefore assumed that mitochondria were
acquired before the eukaryotes diverged into the separate lineages that gave rise to
animals, plants, fungi, and the single-celled protists. Later, after this diversification had
begun, photosynthetic bacteria were acquired only by the branch that gave rise to
photosynthetic eukaryotes.
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Chapter 9
An Ecologist’s Guide to Microbiology
1. Which of the following represents a producer in a food web?
a. a fungus that is parasitic on plants
b. a herbivore
c. a carnivore
d. bacteria that break down organic material and return inorganic nutrients to the
environment
e. photosynthetic cyanobacteria
2. Which of the following statements is true?
a. The biomass of producers in an environment will be greater than the mass of primary
consumers.
b. The biomass of secondary consumers will be greater than that of primary consumers.
c. The biomass of tertiary consumers will be greater than that of quaternary consumers.
d. Both “a” and “c” are true.
e. Both “b” and “c” are true.
3. In aquatic environments, the ________ zone represents the part of the environment where
sunlight reaches the bottom.
a. photic zone
b. littoral zone
c. profundal zone
d. benthic zone
e. pelagic zone
4. Mycorrhizal associations would most likely be found in:
a. benthic marine environments.
b. a freshwater lake.
c. a stream or river.
d. the soil environment.
e. microbial biofilms.
5. Most of the bacteria that live in lakes can be classified as:
a. oligotrophs.
b. eutrophs.
c. Gram-positive.
d. Gram-negative.
e. thermophiles.
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6. Which of the following statements comparing freshwater and marine environments is
true?
a. The marine environment is generally far more stable than the freshwater
environment.
b. A seasonal thermocline may develop in a marine environment, but not a freshwater
environment.
c. Benthic zones occur in marine environments, but not in freshwater environments.
d. In a marine environment, the pelagic zone usually has the highest species diversity,
while in freshwater environments, diversity in the pelagic zone is usually low.
e. In marine environments, phosphorus is usually the principal factor limiting microbial
growth. In freshwater environments, iron is usually the most principal limiting
factor.
7. Which process in the nitrogen cycle, carried out by certain microorganisms, converts
atmospheric nitrogen into ammonia, which can then be utilized by plants?
a. nitrogen fixation
b. ammonification
c. nitrification
d. denitrification
8. Which of the following processes directly require the activity of microorganisms?
a. release of organic carbon into the environment from animal and plant remains
b. absorption of sulfate from the environment by green plants
c. release of organic nitrogen into the environment by dead plants and animals
d. conversion of organic phosphorus in animal and plant remains into inorganic
phosphorus
e. All of the above require microbial activity.
9. Consider two organisms, X and Y, which are involved in a type of ecological interaction.
Which of the following statements is false?
a. If X and Y are mutualists, both organisms have a positive effect on the growth of the
other.
b. If X is a commensal organism on Y, X has a positive effect on Y, but Y has no effect
on X.
c. If Y is a commensal organism on X, X has a positive effect on Y, but Y has no effect
on X.
d. If X and Y are competitors, both organisms have negative effects on each other’s
growth.
e. If X is a predator and Y is prey, X has a negative effect on Y, but Y has a positive
effect on X.
10. Which of the following statements about competition is true?
a. Compared to plants or animals, competition between microorganisms is a rare event.
b. The principle of competitive exclusion suggests that two organisms in competition
will eventually reach a stable equilibrium, where both organisms can coexist and
survive.
c. A commensial relationship is an example of competition.
d. If you take an environmental sample, and find numerous microbial species within
that sample, it suggests that none of these species are in competition with each other.
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e. Compared to animals and plants, the resolution of competition between
microorganisms is rapid.
11. What exactly is a biofilm? Where are biofilms found?
12. Why does the addition of extra nutrients into a lake often result in a die-off of fish and
other animals?
13. Describe why decomposers are so important in ecosystems.
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Chapter 9 Answers
1. e
2. d
3. b
4. d
5. a
6. a
7. a
8. d
9. b
10. e
11. A biofilm is a microbial community is which the cells are encased in a layer of
polysaccharide, secreted by the cells. The cells within a biofilm may or may not be of the
same species. The biofilm is generally organized in such a way that water can circulate
through the biofilm. Biofilms can be found on any hard surface such as rocks in a stream,
pipes, or dental enamel.
12. When extra nutrirents enter a freshwater ecosystem such as lake, due to agricultural
runoff, or other forms of pollution, these extra nutrients, combined with warmer
temperatures, can permit explosive growth of aquatic producers such as algae and
photosynthetic bacteria. These producers release oxygen into the water, which stimulates
the growth of aerobic bacteria. As these aerobes increase in number and continue to
deplete the oxygen in the water, the oxygen levels begin to fall, to the point where fish
and other large invertebrates cannot survive. Anaerobic bacteria now increase in number,
and as they release metabolic wastes, the water becomes increasing inappropriate for the
survival of large animals. This series of events is known as eutrophication.
13. Decomposers, primarily bacteria and fungi, are organisms that absorb organic material in
the environment and covert this material into inorganic substances, which are then
released into the environment. They are essential in ecosystems, because these inorganic
substances are required by producers.
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Chapter 10
The Nature of Disease:
A Pathogen’s Perspective
1. In terms of how a pathogen might affect a host, which of the following is the correct
sequence of events?
a. contamination » disease » infection
b. disease » contamination » infection
c. infection » contamination » disease
d. infection » disease » contamination
e. contamination » infection » disease
2. If a disease is described as a “zoonosis”, what type of reservoir do we expect the
pathogen causing the disease to utilize?
a. human
b. animal
c. environmental
d. both “a” and “b”
e. both “b” and “c”
3.
Eradication of any pathogen is very unlikely unless that pathogen uses:
a. human reservoirs only.
b. animal reservoirs only.
c. environmental reservoirs only.
d. human or animal reservoirs.
e. animal or environmental reservoirs.
4. For a given pathogen:
a. the ID50 will always be lower than the LD50.
b. the ID50 will always be higher than the LD50.
c. the ID50 and the LD50 will always be equal.
d. the ID50 may be lower or higher than the LD50.
5. The time period between infection and the onset of symptoms is called:
a. an inapparent infection.
b. the period of disease.
c. the incubation period.
d. the recovery period.
e. the threshold period.
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6. Which of the following statements is true about endotoxins?
a. They all work in different ways.
b. They are all proteins.
c. They are only produced by Gram-negative bacteria.
d. They are only produced by Gram-positive bacteria.
e. They interfere with host ribosomes, blocking protein synthesis by host cells.
7. Which of the following is false about exotoxins?
a. Part of the exotoxin called the “A subunit” binds to receptors on the surface of certain
host cells.
b. The combined exotoxin (both the A & B subunits) enter the host cell by endocytosis.
c. They may be produced by either Gram-positive or Gram-negative bacteria.
d. They are generally more toxic than endotoxins at low concentration.
e. They are composed of protein.
8. In a latent viral infection:
a. there is rapid viral replication in an infected cell.
b. there is slow viral replication in an infected cell.
c. there is no viral replication in an infected cell.
d. numerous inclusion bodies are visible in the cytoplasm of an infected cell.
e. we expect oncogenes to be activated, leading to tumor formation.
9. The portal of exit for pathogens:
a. is always the same as the portal of entry.
b. is always different from the portal of entry.
c. may or may not be the same as the portal of entry.
d. is a critical requirement if the pathogen is to cause disease.
e. is lacking in almost all human diseases.
10. Streptokinase, coagulase, and hemolysins are all examples of:
a. exotoxins.
b. endotoxins.
c. tissue degrading enzymes.
d. viral cytopathic effects.
11. How does our normal flora protect us from some infections by pathogens?
12. What is the difference between biological vector transmission and mechanical vector
transmission?
13. Why are symptoms in a host, such as diarrhea in the case of intestinal disease, or
sneezing and coughing in the case of respiratory disease, beneficial from the perspective
of some pathogens that cause these diseases?
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Chapter 10 Answers
1. e
2. b
3. a
4. a
5. c
6. c
7. a
8. c
9. c
10. c
11. Normal flora for a particular host organism are generally highly adapted to their
particular host, and they are very good at colonizing and adhering to that host. In their
preferred location, these well-adapted normal flora are usually capable of outcompeting
any pathogens which arrive, because the pathogens are unlikely to be as well adapted.
Many normal flora also secrete chemical compounds that inhibit the growth of potential
pathogens.
12. In biological vector transmission, the arthropod vector is an essential part of the
pathogen’s lifecycle, in which reproduction and/or essential development occurs.
Consequently, in most cases, the biological vector is absolutely essential if the pathogen
is to achieve transmission. Biological vectors usually infect hosts as the vector takes a
blood meal on the host, injecting the pathogen directly into the host. In mechanical vector
transmission, the vector is not actually infected with the pathogen. The pathogen merely
sticks to the body of the vector, and the pathogen does not necessarily reproduce or
develop while on the vector. Transmission occurs when the mechanical vector lands on
food or otherwise contaminates food or water that is later ingested by the host. Pathogens
that use mechanical vector transmission almost always use other modes of transmission
as well.
13. For many pathogens, symptoms such as coughing, sneezing, or diarrhea are beneficial
because such symptoms facilitate transmission. In such cases, the symptoms are
associated with the portal of exit, and by provoking such symptoms, the pathogen is
released from the portal of exit in larger numbers.
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Chapter 11
Host Defense
1. Which of the following cell types can be considered to be part of the innate immune
system?
a. red blood cells
b. neutrophils
c. helper T cells
d. cytotoxic T cells
e. B cells
2. Toll-like receptors:
a. permit certain innate immune system cells to recognize certain molecules that are
unique to microorganisms.
b. are found on the surface of cytotoxic T cells, and are used to recognize infected cells.
c. present foreign antigens on the surface of macrophages and dendritic cells.
d. are found on the surface of helper T cells, where they recognize antigens presented
by antigen presenting cells.
e. are used by macrophages and dendritic cells to signal helper T cells that an infection
is under way.
3. Which of the following is true about interferon?
a. It is released by uninfected cells during a viral infection.
b. It is produced by virally infected cells during a viral infection, whereupon it inhibits
further viral replication within the cells where it is made.
c. It is produced by virally infected cells to activate helper T-cells.
d. It is released by virally infected cells to induce an antiviral state in uninfected cells.
e. It is released by cells in lymph nodes to attract T cells to the lymph node.
4. Which of the following immune system structures and their associated function is not
correct?
a. thymus: maturation of T-cells
b. lymph node: generation of adaptive immune responses in tissues
c. spleen: generation of adaptive immune responses in the blood
d. liver: maturation of B-cells
e. skin: a barrier to entry
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5. Which of the following is not a correct and necessary step in the generation of a cellmediated response?
a. Antigen presenting cells are activated by pattern recognition.
b. Antigen presenting cells present antigen to helper T cells.
c. Antigen presenting cells activate cytotoxic T cells.
d. Helper T cells release cytokines that stimulate activate cytotoxic T cells.
e. Cytotoxic T cells recognize their specific antigen on the surface of infected cells.
6. B-cells are able to recognize antigens because they have specific receptors on their
surfaces that bind specific antigens. These receptors are called ________.
a. toll-like receptors
b. pattern recognition receptors
c. MHC
d. IgG
e. IgM
7. Which of the following is a good example of how innate and adaptive immunity depend
on each other?
a. the release of perforin by cytotoxic T cells
b. presentation of the antigen by virally infected cells
c. phagocytosis of pathogens by neutrophils
d. the activation of humoral immunity by helper T cells
e. the ability of antibodies to function as opsonins
8. Which antibody type is usually produced in the greatest amount during a humoral
reponse?
a. IgA
b. IgD
c. IgM
d. IgE
e. IgG
9. During a successful secondary immune response:
a. the inductive period will be longer than it was during a primary response.
b. greatly increased levels of IgM are produced.
c. long-lived plasma cells immediately begin secreting antibody.
d. the number of pathogens should remain below the threshold of disease.
e. there will be a stronger cell-mediated response, but a less vigorous humoral response.
10. Which of the following vaccine types best mimics a genuine infection?
a. a vaccine made with an attenuated pathogen
b. a vaccine made with an inactivated pathogen
c. a subunit vaccine
d. Both “a” and “c” closely mimic a genuine infection.
e. Both “b” and “c” closely mimic a genuine infection.
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11. Describe how cells of the innate immune system activate the adaptive immune system
under certain circumstances.
12. In what way can the fever response be used to illustrate the point that response to
pathogens can both be protective and harmful?
13. How does HIV reduce immune function?
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Chapter 11 Answers
1. b
2. a
3. d
4. d
5. c
6. e
7. e
8. e
9. d
10. a
11. An adaptive response will only occur if innate immune responses alone are unable to
contain an infection. When an adaptive response is necessary, certain cells considered to
be part of the innate immune system, specifically macrophages and dendritic cells,
continue to ingest pathogens. These pathogens are degraded into small fragments within
vesicles, and are then bound to the major histocompatibility complex (MHC) proteins.
The small pathogen fragments can act as antigens, and the complex of MHC and antigen
is transported to the surface of the macrophage or dendritic cell, which function as
antigen presenting cells (APCs). The APCs migrate to lymphatic structures such as
lymph nodes, and they release chemical messengers (cytokines) that attract helper T cells.
Once in the lymph nodes, the helper T cells can interact with the MHC/antigen
complexes with their T-cell receptors. If the T-cell receptor of a helper T cell does not
recognize its specific antigen it remains inactive. If it does recognize its specific antigen
on the surface of an APC, the helper T-cell becomes activated, whereupon it replicates
into many mature effector helper T-cells. These effector helper T-cells can now stimulate
a full adaptive response by activating both cell mediated immunity (through the
activation of cytotoxic T-cells) and humoral immunity (through the activation of B cells).
12. In many infections, certain cytokines released by various cells act on a specific part of the
brain to elevate body temperature. In other words, these cytokines stimulate fever. A
fever can be a beneficial part of an innate immune response. At elevated body
temperature, phagocytic cells are more efficient, and some pathogens are less able to
reproduce. Fever, however, is uncomfortable, and is often recognized as one of the
symptoms of many diseases. It fever gets too high, it can actually be dangerous or even
life-threatening. Thus, while part of a protective immune response, fever, like many
aspects of immunity, actually contributes to the symptoms observed during infectious
disease.
13. HIV infects and kills helper T-cells. These cells are central to a proper adaptive immune
response. Helper T cells are the component of adaptive immunity that is stimulated by
antigen presenting cells during an infection. Once activated, helper T-cells can activate
cytotoxic T-cells to initiate a cell mediated response and B cells to initiate a humoral
response. Over time, an HIV infection can result in a greatly reduced number of helper T
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cells. Consequently, although healthy populations of cytotoxic T-cells and B-cells
remain, without enough helper T-cells they cannot be activated properly, and both cell
mediated and humoral responses decline, opening the door to the opportunistic infections
that are characteristic of advanced AIDS.
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Chapter 12
Control of Microbial Growth
1.
What is a nosocomial infection?
a. an infection contracted at one’s place of work, or at school
b. an infection contracted from an animal
c. an infection contracted from improperly prepared food
d. an infection contracted during a stay in the hospital
e. an infection that a health care worker contracts from a patient
2. Pasteurization:
a. is a technique used to sterilize liquids.
b. relies on high temperature and high pressure to kill microorganisms.
c. can be considered to be a bacteriotatic control measure.
d. selectively kills thermophiles in liquids.
e. selectively kills mesophiles in liquids.
3. Which of the following would be most appropriate to reduce microorganisms
in a wound?
a. an antiseptic
b. a disinfectant
c. UV Radiation
d. alcohol
e. any sterilization technique
4. If the number of microorganisms must be reduced in a beverage that cannot be subjected
to high temperatures, ________ would be an effective control method.
a. pasteurization
b. autoclaving
c. filtration
d. the addition of heavy metals
5. Sulfa drugs:
a. act by interfering with cell wall synthesis.
b. bind to and interfere with bacterial ribosomes.
c. interfere with bacterial DNA replicaton.
d. interfere with the activity of a bacterial enzyme.
e. disrupt the production of mycolic acids by acid-fast bacteria.
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6. In which of the following situations might a bacteriostatic drug be preferable to a
bactericidal drug?
a. when a patient is infected with an unknown pathogen
b. when the patient is immunocompromised
c. when antibiotics are being used prophylactically
d. when an infection is in a well-oxygenated region of the body
e. when Gram-negative bacteria have infected an ordinarily sterile region of the body
7. In which of the following situations might a broad spectrum drug be preferable to
a narrow spectrum drug?
a. when the patient is infected with an unknown pathogen
b. when the patient is immunocompromised
c. when Gram-negative bacteria have infected an ordinarily sterile region of the body
d. in a well-oxygenated region of the body
e. when the patient is in danger of going into shock from endotoxin poisoning
8. Which of the following statements is true?
a. Selective toxicity is harder to achieve when developing drugs against eukaryotic
pathogens than it is against bacteria.
b. Compared to antibiotics, antifungal drugs usually have limited side effects.
c. To date, drug resistance has not been a problem with antimalarial drugs.
d. Drugs against eukaryotic pathogens generally act by interfering with ribosomes.
e. An advantage of most drugs against eukaryotic pathogens is that they tend to be
extremely narrow spectrum.
9. Which of the following most accurately describes the activity of acyclovir?
a. It prevents uncoating by viral particles.
b. It is phosphorylated by a viral enzyme, producing a false nucleotide, which is then
incorporated into replicating viral DNA.
c. It prevents the release of newly replicated influenza viral particles from an infected
cell.
d. It interferes with the activity of the viral enzyme reverse transcriptase.
e. It binds to and inhibits the viral protease enzyme, which cleaves large viral proteins
into the smaller proteins needed for viral assembly.
10. Why are antibiotics often added to animal feed?
a. to reduce disease transmission among domestic animals
b. to increase the growth rate of domestic animals
c. to reduce the likelihood of drug resistance
d. All of the above are correct.
e. Both “a” and “b” are correct.
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11. In what situations would UV radiation be an appropriate method for microbial control?
12. What are some of the problems associated with the development of antiviral drugs?
13. How does stopping an antibiotic prescription prematurely contribute to the development
of drug resistance?
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Chapter 12 Answers
1. d
2. e
3. a
4. c
5. d
6. e
7. a
8. a
9. b
10. e
11. UV radiation is used most frequently to reduce the numbers of organisms on surfaces or
in the air. It is especially useful in places such as operating rooms, where organisms in
the air might otherwise contaminate surgical patients. Because UV radiation can damage
human tissue, UV lights would only be used in an operating room, prior to surgery; not
when people are actually in the room. UV lights can be used in a similar fashion in places
where crowding increases the likelihood of airborne pathogen transmission. Prisons,
nursing homes and child care facilities are examples. UV radiation is also often employed
to purify water in water-treatment facilities.
12. A problem in the development of antiviral drugs is that viral replication is tied so
intimately to the host. Because they use the host’s replicative machinery to replicate,
viruses offer fewer unique targets for antiviral drugs than other microorganisms do.
Additionally, when viruses are outside the host cell, they are metabolically inactive,
meaning there are few if any viral processes to attack with drugs. As a further
complication, since viruses only replicate inside host cells, any effective antiviral drug
must be able to penetrate host cells without harming them.
13. When a prescription is completed, the entire infection is ordinarily eliminated. If
treatment is stopped prematurely, some bacteria may still be alive, and they are likely to
be more resistant organisms. Consequently, if they resume growth, the now expanded
population of bacteria will all have descended from the more resistant survivors, meaning
that the infection will now be composed of more resistant organisms. When many people
fail to complete prescriptions, the incremental increase of resistance in each instance
ultimately can be a major contributor to the problem of drug resistance.
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Chapter 13
Epidemiology:
Who, What, When, Where, and Why?
1. The incidence of disease:
a. is the total number of cases of a particular disease during an epidemic.
b. is calculated by subtracting the number of recovered individuals from the number of
sick individuals.
c. is the number of new cases of a particular disease during a specified time period.
d. is the period of time measured in days, weeks, or years, during which an epidemic
occurs.
e. is the average number of new cases infected by a single sick individual for a specific
disease.
2. Which of the following is a characteristic of a commonsource epidemic?
a. Once the source is identified and controlled the last cases will occur approximately
one incubation period later.
b. Once the source is identified and controlled there should be no additional cases.
c. The time between identification and control, and the last cases, depends on the
transmission rate between sick and susceptible individuals.
d. When a common source epidemic begins, the number of cases rises slowly relative to
a host-to-host epidemic.
e. When a common source epidemic ends, the number of cases falls slowly relative to a
host-to-host epidemic.
3. The likelihood of a host-to-host epidemic is highest when:
a. the proportion of immune individuals in a population is below the epidemic
threshold.
b. the proportion of immune individuals in a population is above the epidemic
threshold.
c. the proportion of immune individuals in a population is at the epidemic threshold.
d. anytime the proportion of immune individuals in a population rises above 50%.
e. the second time a pathogen is introduced into a particular population.
4. In which of the following types of viruses is antigenic shift most likely?
d. RNA viruses
e. DNA viruses
f. enveloped viruses
g. non-enveloped viruses
h. viruses with a segmented genome
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5. A particular type of virus occasionally undergoes antigenic shift. In which of the
following situations is antigenic shift most likely?
a. when RNA polymerase makes a mistake, introducing an incorrect nucleotide
b. when the proofreading ability of RNA polymerase does not function properly
c. when a particular host cell is infected by a single strain of the virus
d. when a particular host cell is infected by two strains of the virus at the same time
e. when the proportion of immune individuals in the population is low
6. When a new disease appears, which of the following is developed first?
a. a case-control study
b. personal characteristics of the disease
c. place characteristics of the disease
d. time characteristics of the disease
e. a case definition
7. In the 1999 West Nile virus outbreak in New York City, which of the following pieces of
evidence suggested that the pathogen under investigation was not St. Louis encephalitis
(SLE)?
a. The time characteristic was not suggestive of SLE.
b. There was no mosquito involvement in this disease, as there would have been
for SLE.
c. The viral particles were too small to be SLE.
d. Control measures initiated to control a SLE outbreak were not effective.
e. The case-control study indicated that this was not SLE.
8. Epidemic paralytic polio:
a. was more likely when newborns were exposed to the virus.
b. was more likely when exposure was delayed beyond infancy.
c. was most commonly seen in situations where sanitation was poor.
d. was eradicated in the United States as routine sanitation became commonplace.
e. has not been observed since the 19th century in developed countries.
9. Into which category of emergent diseases would dengue be placed?
a. Category 1: invasion of a new host population by a known pathogen
b. Category 2: appearance of a completely new, previously unknown pathogen
c. Category 3: association of a well-known disease with a new pathogen
d. Category 4: increased virulence, or a renewed problem, with a well-known but
previously less virulent or well-controlled pathogen
10. Which of the following pathogens would most likely be used as a bioterrorism agent?
a. Pathogen A: an obligate anaerobe
b. Pathogen B: an obligate aerobe
c. Pathogen C: a Gram-positive bacterial species
d. Pathogen D: a RNA virus
e. Pathogen E: a spore-former
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11. How can a vaccine program prevent epidemics?
12. What is antigenic drift? Why are RNA viruses more prone to this phenomenon than DNA
viruses are?
13. Describe the design of a case-control study and how it is used to identify the cause of an
epidemic.
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Chapter 13 Answers
1. c
2. a
3. a
4. e
5. d
6. e
7. c
8. b
9. a
10. e
11. For many diseases, a vaccine program can effectively reduce the risk of an epidemic by
maintaining immunity in a population above the epidemic threshold. Once the immunity
is above the epidemic threshold, there are too few susceptible individuals in the
population to sustain increasing transmission. Even unvaccinated individuals are at less
risk of infection, because if the proportion of vaccinated individuals is high enough, there
are fewer transmission routes to unvaccinated individuals, and consequently their
likelihood of exposure to the pathogen declines.
12. Antigenic drift refers to the gradual change in a virus’ antigens, due to the accumulation
of point mutations in the virus’ genome. RNA viruses are especially prone to antigenic
drift because the key enzyme involved in genome duplication, RNA polymerase, is
incapable of proofreading. The DNA polymerase of DNA viruses, on the other hand, can
detect and replace most of the point mutations it may introduce, greatly reducing the
number of mutations that enter the genome. Consequently, changes in viral antigens are
far less likely.
13. In a case-control study, each individual affected with a disease (a “case”) is paired with
an individual that is unaffected by the disease (a “control”). Each case-control pair should
be as similar as possible in terms of age, sex, place of residence, and other factors that the
investigators consider important. The only significant difference should be whether or not
they are affected by the disease. Investigators then look for an additional characteristic or
behavior that is common to all the cases, but is not observed in the controls. If such a
factor is found, it can suggest to investigators why the cases were at risk for the disease
while the controls were not. This information might suggest characteristics of the disease
such as its mode of transmission that can help investigators narrow down the search for
the disease agent.
Chapter 14
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The Future is Here:
Microorganisms and Biotechnology
1. A restriction enzyme that recognizes relatively rare base sequences in the DNA will:
a. cleave DNA into a relatively large number of small fragments.
b. cleave DNA into a relatively small number of small fragments.
c. cleave DNA into a relatively large number of large fragments.
d. cleave DNA into a relatively small number of large fragments.
2. When DNA fragments are separated by gel electrophoresis:
a. smaller fragments migrate further on the gel than larger fragments.
b. larger fragments migrate further on the gel than smaller fragments.
c. fragments that contain larger amounts of purines, relative to pyrimadines,
migrate further.
d. fragments that contain many G-C pairs, relative to A-T pairs, migrate further.
e. all fragments containing genes with related functions migrate to an identical spot on
the gel.
3. Southern blotting can be used to:
a. insert donor DNA into recipient DNA.
b. determine if a specific gene is present in a DNA molecule.
c. separate DNA fragments based on size.
d. make many copies of a particular gene.
e. determine the exact nucleotide sequence in a DNA molecule.
4. Which of the following is not added to the reaction mix in the polymerase chain reaction?
a. a DNA polymerase enzyme
b. appropriate primers
c. target DNA
d. a supply of DNA nucleotides
e. a gene probe
5. If a gene of interest is inserted into a plasmid, and the plasmid also has a lethal gene and
an antibiotic resistance gene, to later identify those plasmids:
a. the inserted gene must not disrupt either the resistance or the lethal gene.
b. the inserted gene must interrupt the resistance gene.
c. the inserted gene must interrupt the lethal gene.
d. the inserted gene must interrupt both the resistance gene and the lethal gene.
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6. The sequencing of the human genome has shown us that:
a. the number of genes in the human genome is much smaller than previously thought.
b. the number of genes in the human genome is much larger than previously thought.
c. the number of genes in the human genome is about the same number as previously
thought.
d. the DNA of humans is much different from that of even our closest nonhuman
ancestors.
7. A foreign gene is incorporated into a virus, creating a recombinant virus. The virus is
now allowed to infect certain cells, with the hope that the foreign gene carried by the
virus will be incorporated into the DNA of the cells. Which of the following is true?
a. The virus is the cloning vector.
b. The cells are the cloning vectors.
c. The virus is the cloning host.
d. Both “a” and “c” are correct.
e. Both “b” and “c” are correct.
8. Which of the following is an important obstacle to the routine use of gene therapy?
a. It has proven difficult to produce recombinant viruses carrying normal copies of a
particular human gene.
b. It has proven difficult to get human host cells to express foreign genes in adequate
amounts.
c. It has proven difficult to identify the human genes involved in genetic disorders.
d. None of the above is currently an obstacle. Gene therapy is now routine.
e. All of the above are important obstacles.
9. What is bioremediation?
a. the production of genetically modified foods
b. the use of recombinant microorganisms to produce pharmaceutical products
c. the production of transgenic animals
d. the sequencing and study of entire genomes
e. the use of microorganisms to degrade harmful chemicals or otherwise detoxify
environmental pollutants
10. Genome analysis of bacteria has revealed:
a. that intracellular pathogens have the largest genomes of all bacteria.
b. nonfastidious bacteria have smaller genomes than fastidious bacteria.
c. that the genomes of different bacteria are remarkably similar.
d. bacteria can, at least on occasion, transfer virulence genes to each other.
11. What is the polymerase chain reaction? Briefly state how it works.
12. What exactly is a DNA library? What is a genomic library?
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13. One of the concerns about genetically modified plants is how they might affect wild
plants. In what way? Why is this worrisome?
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Chapter 14 Answers
1. d
2. a
3. b
4. e
5. c
6. a
7. a
8. b
9. e
10. d
11. The polymerase chain reaction (PCR) is a technique used by researchers to quickly
amplify a specific sequence of DNA. The DNA to be copied (the target DNA) is placed
in a tube along with short DNA sequences called primers, which are complementary to
the ends of the target DNA. A supply of A,G,C and T nucleotides is also added to the
mixture, as is a DNA polymerase enzyme that is capable of withstanding high
temperatures (Taq polymerase). The mixture is then placed in a thermocycler—a device
that can be programmed to alternate among various temperatures.
In PCR there are three temperature stages. The first stage heats the DNA up to the
point where it separates into single strands. In the second stage, the temperature is
lowered, allowing the primers to attach to the ends of the target DNA. In the third stage,
the Taq polymerase copies each of the single strands into double stranded DNA, doubling
the amount of the original target DNA. The process is then repeated, usually around 30
times, doubling the amount of target DNA each time. The final result can be billions of
copies of the original target DNA.
12. Once genes have been identified they can be inserted into cloning vectors, which can then
be used to introduce the gene into cloning hosts. These cloning hosts, carrying certain
introduced genes can be maintained indefinitely. A group of cloning hosts, all carrying
different introduced genes from the same organism, is called a DNA library. If a DNA
library is complete—if it contains cloning hosts that carry all of the DNA of the organism
in question—the DNA library can be termed a genomic library for that organism.
13. A major concern regarding genetically modified plants is that many cultivated plants can
hybridize with wild plants. If this occurs, it is possible that foreign genes that were
present in the genetically modified plants could end up in wild plants. These plants might
now express the foreign gene, with possibly serious and unpredictable consequences.
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Chapter 15
Guess Who’s Coming to Dinner:
Microorganisms and Food
1. Microbial fermentation of food products occurs when the microorganisms are allowed to
grow:
a. in an anaerobic environment.
b. in an aerobic environment.
c. in an acidic environment.
d. at low temperatures.
e. at high temperatures.
2. The fermentation of most bread and alcoholic beverages relies on:
a. fermentation by Gram-positive bacteria.
b. fermentation by Gram-negative bacteria.
c. fermentation by single-celled fungi.
d. fermentation by filamentous fungi.
3. Which of the following is an example of single-cell protein?
a. yogurt
b. cheese
c. Spirulina
d. beer
e. summer sausage
4. Of the following pairs of organisms, which two are most closely related to each other?
a. Brewers’ yeast and Spirulina
b. Brewer’s yeast and the Lactobacillus used in yogurt production.
c. Brewer’s yeast and mushrooms
d. Penicillium camemberti and Lactobacillus
e. Penicillium camemberti and the Gram-positive bacteria used to make pickles.
5. When baking bread, all of the following steps occur. In which answer are the steps
presented in the correct order?
a. yeast is kneaded into dough » loaf is baked » yeast ferments » bread rises
b. loaf is baked » yeast is kneaded into dough » yeast ferments » bread rises
c. yeast is kneaded into dough » yeast ferments » loaf is baked » bread rises
d. loaf is baked » bread rises » yeast is kneaded into dough » yeast ferments
e. yeast is kneaded into dough » yeast ferments » bread rises » loaf is baked
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6. In which of the following products does fermentation of the must occur?
a. cheese
b. bread
c. beer
d. wine
e. sauerkraut
7. If you make homemade wine, which of the following accurately describes the
relationship between sweetness and alcohol content?
a. The sweeter the wine, the higher the alcohol content.
b. The sweeter the wine, the lower the alcohol content.
c. The dryer the wine, the lower the alcohol content.
d. There is no specific relationship between sweetness and alcohol content.
8. What is whey?
a. the semisolid milk product produced as a first step in cheese making
b. the remaining liquid following production of a semisolid milk product in cheese
making
c. the sprouted barley used in beer making
d. the sugar-rich liquid portion that is produced in beer making, once starch has been
degraded and remaining solids removed
e. the acid that is produced by bacteria during the production of sauerkraut
9. In what way are microorganisms used in the production of coffee?
a. Extracts of coffee beans are fermented by bacteria.
b. Extracts of coffee beans are fermented by yeast.
c. Extracts of coffee beans are first fermented by yeast. Fermentation waste products
released by the yeast are then converted in different products by aerobic bacteria.
d. Microorganisms that grow naturally on coffee beans provide the coffee with desirable
flavors.
e. Bacteria are used to remove the coating of coffee beans prior to roasting.
10. Probiotics are:
a. any microbially fermented food.
b. food items that are produced by aerobic bacteria.
c. hormones that are produced by bacteria.
d. products that contain living microorganisms, thought to be beneficial.
e. antibiotics added to animal feed to encourage more rapid growth.
11. Microbial fermentation only occurs under certain environmental conditions. Why, in
terms of metabolism, do these organisms ferment under such conditions?
12. In what way is the production of vinegar different from the production of the fermented
food products discussed in this chapter?
13. Provide a biochemical explanation for why bread rises during its production.
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Chapter 15 Answers
1. a
2. c
3. c
4. c
5. e
6. d
7. b
8. b
9. e
10. d
11. Fermentation occurs when bacteria are in an anaerobic environment. Without oxygen,
such bacteria must rely on glycolysis alone for ATP production, because under such
conditions they are unable to oxidize pyruvate (the final product of glycolysis) further.
Consequently, they must reduce, rather than oxidize, pyruvate in order to oxidize NADH.
The oxidized form of the NADH (NAD+) is required to continue glycolysis. When
pyruvate is reduced in this way, the reduced form of pyruvate represents a fermentation
waste product. It is these waste products that protect the food item from further
contamination, lend desirable flavors, or change the texture of the food product being
produced.
12. Unlike many of the products discussed in this chapter, vinegar is not a fermentation
waste. Rather, a sugar containing liquid is first fermented by yeast. The yeast release
ethyl alcohol as a fermentation waste. The ethyl alcohol is then converted to vinegar
(acetic acid) by aerobic bacteria in the genus Acetobacter.
13. In bread making, yeast, most commonly of the genus Saccharomyces, is kneaded into
the dough to provide an anaerobic environment. Because the yeast are facultative
anaerobes, they can now survive on fermentation alone, producing all the ATP they need
to survive via glycolysis. When pyruvate is reduced in fermentation, the waste products
are ethyl alcohol and carbon dioxide gas. It is the carbon dioxide gas that causes the
bread dough to rise. Ethyl alcohol will later be evaporated off during baking of the
dough.
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Chapter 16
Better Living With Microorganisms:
Industrial and Applied Microbiology
1. The easiest step when it comes to developing a new antibiotic is:
a. finding a microorganism that produces an antibiotic.
b. determining the optimum growth conditions for the microorganism in question.
c. the scale-up process.
d. improving the bacterial strain so that commercially valuable quantities of the
antibiotic are produced.
2. Metabolites are:
a. the substrate that is converted into a useful product by microorganisms.
b. an intermediate compound in a biochemical pathway, the final product of which is a
useful product.
c. the final product in a biochemical pathway.
d. either “a” or “c” above
e. either “b” or “c” above
3. Which of the following statements about primary and secondary metabolites is true?
a. Primary metabolites are produced maximally during the lag phase of growth.
b. Secondary metabolites are produced maximally during the lag phase of growth.
c. Primary metabolites are produced maximally during the log phase of growth.
d. Secondary metabolites are produced maximally during the log phase of growth.
e. Primary metabolites are produced maximally during the stationary phase of growth.
4. If bacteria that have undergone strain improvement are introduced into a natural
environment:
a. they will usually outcompete and replace naturally occurring, wild-type strains.
b. they will usually be outcompeted by naturally occurring wild-type strains.
c. they will usually act as predators on naturally occurring wild-type strains.
d. they will usually serve as prey for naturally occurring wild-type strains.
e. they will usually act as commensals with naturally occurring, wild-type strains.
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5. Microorganisms to be used commercially usually are developed in a series of defined
steps. Which of the following has those steps in the correct order?
a. laboratory flask » pilot plant fermentor » laboratory fermentor » industrial fermentor
b. laboratory fermentor » laboratory flask » pilot plant fermentor » industrial fermentor
c. industrial fermentor » pilot plant fermentor » laboratory fermentor » labortory flask
d. laboratory flask » laboratory fermentor » pilot plant fermentor » industrial fermentor
e. pilot plant fermentor » labortory flask » industrial fermentor » laboratory fermentor
6. Which of the following is an example of an extremozyme?
a. a microorganism that is isolated from a very hot, thermal pool of water
b. the Taq polymerase, isolated from Thermus aquaticus, which is used in PCR
c. a cellulase enzyme, which can digest cellulose, used in a stain remover
d. a biopesticide used to control insect pests in the garden
e. a microorganism used in nanotechnology
7. Which type of organism would be most promising if you were seeking an organism that
can digest hydrocarbons, to help clean up oil spills?
a. a nonfastidious organism
b. a fastidious organism
c. an obligate anaerobe
d. an extreme thermophile
e. an acidophile
8. When bacteria are used in wastewater treatment plants to convert hydrogen sulfide into
hydrogen sulfate, why are the bacteria grown on biofilms?
a. To protect them from damage to their cell walls caused by the waste water.
b. The bacteria that make this conversion can only grow in biofilms.
c. The biofilms increase the time during which the bacteria can metabolize the
hydrogen sulfide.
d. The hydrogen sulfate adheres to the biofilm, reducing the amount of this chemical
released in treated water.
e. Only bacteria growing in biofilms produce the enzyme necessary to make this
conversion.
9. Which of the following statements about landfills is true?
a. Decomposition of garbage is slowed by anaerobic conditions.
b. Decomposition of garbage is slowed by aerobic conditions.
c. Decomposition of garbage is slowed by toxic chemicals, which kill microorganisms.
d. Decompostion of garbage is slowed by the release of methane.
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10. Some bacteria release electrons, which can then be bound to an electrode, generating
electricity. This process may be used:
a. to produce cellulosic ethanol.
b. to produce biodegradable plastics.
c. to create microbial fuel cells.
d. to separate valuable minerals from rock deposits.
e. as a biologically produced hydrocarbon.
11. In what way does metabolite production by a microorganism often depend on other
microorganisms that may be found in the same environment?
12. What exactly is the biopesticide Bt? Why is this product, which kills garden pests, not a
danger to humans, pets, or other animals?
13. Why does compost tend to heat up over time? Why is it beneficial to periodically turn the
compost?
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Chapter 16 Answers
1. a
2. e
3. c
4. b
5. d
6. b
7. a
8. c
9. a
10. c
11. Microorganisms in the environment often live in complex species assemblages, and
sometimes a particular metabolite of interest is only produced when certain species are in
close proximity to each other. It is common for one species to produce a metabolic waste
that is used by a second species as a substrate for metabolite synthesis. In this case, the
second species will not produce this particular metabolite in the absence of the first
species.
12. The biopesticide Bt consist of the endospores of Bacillus thuringiensis mixed with inert
compounds. The endospores contain a protein that is highly toxic to many types of
insects, including many of those that cause problems for home gardeners. When dusted
onto plants, the spores may be ingested by insect pests, whereupon the protein toxin
enters the insect’s blood. The result is paralysis and ultimately death of the insect.
Humans and pets are not at risk, because unlike insects which generally have a basic pH
in their digestive system, mammals and birds have digestive systems with an acidic pH.
This acidity denatures the protein toxin, rendering it harmless.
13. Aerobes, because of their more efficient metabolism, are able to degrade organic waste
much faster than anaerobes. In well-oxygenated organic material, the rapid growth and
metabolism of these aerobes causes the organic material to heat up. Once all oxygen is
used up, the growth rate of these aerobes slows down and the temperature of the waste
material falls. Turning the compost aerates the soil, promoting the continued growth of
the aerobes, and the faster breakdown of organic material. By turning the compost and
introducing oxygen, the growth of obligate anaerobes such as methanogens is also
inhibited. With less methane being released, the risk of compost fires decreases.
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