Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 27
Test Yourself Questions
1.
Which of the following features is common to prokaryotic cells?
a.
a nucleus, featuring a nuclear envelope with pores
b.
mitochondria
c.
plasms membranes
d.
mitotic spindle
e.
none of the above
Answer: c. Cell membranes are common to all living things, including archaea and bacteria. Nuclei
having envelopes with pores, mitochondria, and mitotic spindles are features that distinguish eukaryotes
from archaea and bacteria.
2.
The bacterial phylum that produces oxygen gas as the result of photosynthesis is:
a.
b.
c.
d.
e.
the proteobacteria.
the cyanobacteria.
the Gram-positive bacteria.
all of the above.
none of the above.
Answer: b. The cyanobacteria are the only bacteria that produce oxygen as the result of photosynthesis.
3.
The Gram stain is a procedure that microbiologists use to
a.
determine if a bacterial strain is a pathogen.
b.
determine if a bacterial sample can break down oil.
c.
infer the structure of a bacterial cell wall and bacterial response to antibiotics.
d.
count bacteria in medical or environmental samples.
e.
all of the above.
Answer: c. The Gram stain allows microbiologists to infer the structure of bacterial cell walls and
bacterial responses to antibiotics. The Gram stain could also be used to make bacteria more readily
visible in order to count them, but different and faster counting methods are normally used.
4.
Place the following steps in the correct order, according to Koch’s postulates:
I. Determine if pure cultures of bacteria cause disease symptoms when introduced to a healthy
host.
II. Determine if disease symptoms correlate with presence of a suspected pathogen.
III. Isolate the suspected pathogen and grow it in pure culture, free of other possible pathogens.
IV. Attempt to isolate pathogen from second-infected hosts.
a.
b.
c.
d.
e.
II, III, IV, I
II, IV, III, I
III, II, I, IV
II, III, I, IV
I, II, III, IV
Answer: e. Koch’s postulates specify that the microbiologist must first observe correlation between
disease symptoms and occurrence of a suspected pathogen, then isolate the suspected pathogen and
grow it in pure culture. The microbiologist should then inoculate a healthy host with the pure culture and
watch for development of disease symptoms. If disease develops, the pathogen should be isolated from
the infected host.
5.
Cyanobacteria play what ecological role?
a.
producers
b.
consumers
c.
decomposers
d.
parasites
e.
none of the above
Answer: a. Cyanobacteria are photosynthetic, so they function as producers, providing other organisms
with organic compounds. Although some cyanobacteria produce toxins that harm other organisms,
these toxins do not play roles in an infection process.
6.
Bacterial structures that are produced by pathogenic bacteria for use in attacking host cells
include:
a.
Type III and IV secretion systems.
b.
magnetosomes
c.
gas vesicles.
d.
thylakoids.
e.
none of the above.
Answer: a. Type III secretion systems evolved from flagella in some pathogenic bacteria; Type IV
secretion systems evolved from pili and other mating system components in other pathogenic bacteria.
Both systems are used to transfer proteins, DNA, or other infectious material into host cells.
7.
The structures that enable some Gram-positive bacteria to remain dormant for extremely long
periods of time are known as:
a.
akinetes.
b.
endospores.
c.
biofilms.
d.
lipopolysaccharide envelopes.
e.
pili.
Answer: b. Endospores are produced within bacterial cells, and are enclosed by a tough protein
covering, which aids survival during long periods of dormancy.
8.
By means of what process do populations of bacteria or archaea increase their size?
a.
mitosis
b.
meiosis
c.
conjugation
d.
transduction
e.
none of the above
Answer: e. Bacterial populations increase by binary fission, the simple division of one bacterial cell into
two progeny cells.
9.
By what means do bacterial cells acquire new DNA?
a.
by conjugation, the mating of two cells of the same bacterial species
b.
by transduction, the injection of viral DNA into bacterial cells
c.
by transformation, the uptake of DNA from the environment
d.
all of the above
e.
none of the above
Answer: d. Conjugation, transduction, and transformation are all ways in which bacterial cells acquire
new DNA.
10.
How do various types of bacteria move?
a.
by the use of flagella composed of motor, hook, and filament
b.
by means of pili, which help cells twitch or glide along a surface
c.
by using gas vesicles to regulate buoyancy in water bodies
d.
all of the above are correct
e.
none of the above is correct
Answer: d. Bacterial flagella, pili, and gas vesicles are all structures that foster bacterial movement,
depending on the species.
Conceptual Questions
1. Explain why many microbial populations grow more rapidly than do eukaryotes, and how bacterial
population growth influences the rate of food spoilage or infection.
Answer: Small cell size and simple division processes allow many bacteria to divide much more rapidly
than eukaryotes. This helps to explain why food can spoil so quickly and why infections can spread very
rapidly within the body. Other factors also influence these rates.
2. Why does the overuse of antibiotics in medicine and agriculture result in widespread antibiotic
resistance?
Answer: Pathogen populations naturally display genetic variation in their susceptibility to antibiotics.
When such populations are exposed to antibiotics, even if initially only a few cells are resistant, the
numbers of resistant cells will eventually increase and could come to dominate natural populations.
3. What organisms are responsible for toxic blue-green blooms that often occur in warm weather on lake
surfaces?
Answer: Humans. Only when humans pollute natural waters with high levels of fertilizers originating
from sewage effluent or crop field runoff are cyanobacterial populations able to grow large enough to
produce harmful blooms.
Experimental Questions
1. What feature of Deinococcus radiodurans attracted the attention of researchers?
Answer: Deinococcus radiodurans has the ability to survive levels of ionizing radiation that would kill
most other organisms, and for periods of time that are not tolerated by other organisms. Investigators
wanted to know why D. radiodurans was so resistant to radiation.
2. What hypothesis did Daly and associates develop to explain radiation resistance in D. radiodurans?
Answer: Daly and associates suggested that cellular levels of manganese ion might play a role in
radiation resistance.
3. As shown in the Feature Investigation in Figure 27.20, bacterial cells were grown in media having
various levels of manganese ion, which they absorbed. Later, some of these bacteria were exposed to
high levels of ionizing radiation, while control bacteria were not exposed. What results of this experiment
support the hypothesis that cellular manganese plays a role in radiation resistance?
Answer: Bacteria that had been grown on media containing higher levels of manganese ion were better
able to resist radiation than those grown on media containing lower levels of manganese ion.
Collaborative Questions
1. How would you go about cataloging the phyla of bacteria and archaea that occur in a particular
place?
Answer: Take samples. Try to grow bacteria from the samples on many types of nutrient media. When
colonies grow, isolate different types and perform Gram-staining. Use a microscope to observe cells
from samples and cultures, looking for variations in cell shape, aggregation, cell wall features, and
flagella. Use references to classify different bacteria into phyla. Extract DNA from samples, and
sequence ribosomal RNA gene regions. Use references to classify the ribosomal gene sequences into
phyla.
2. How would you go about developing a bacterial product that could be sold for remediation of a site
contaminated with materials that are harmful to humans?
Answer: Collect samples from the contaminated sites. Try to grow bacteria from the sites on media that
contain relatively small amounts of the nutrients generally needed by bacteria, but also small amounts
of the materials to be degraded. If bacteria grow, transfer the colonies to media containing larger
amounts of the material in question. Cells that grow on such media could be further studied to
determine if they are degrading the substance while using it as a carbon source.