Bauman Chapter 14 Answers to Critical Thinking Questions
p. 406
Corals are small colonial animals that feed by filtering small microbes from seawater in
tropical oceans worldwide. Biologists have discovered that the cells of most (if not all)
corals are hosts to microscopic algae called zooxanthellae. Design an experiment to
ascertain whether corals and zooxanthellae coexist in a mutual, commensal, or parasitic
relationship.
Use a method that kills the zooxanthellae in the corals: if the corals do poorly or die, the
relationship is probably a mutual one; if the corals seem unaffected, it is a commensal
relationship; and if the corals grow more vigorously without the zooxanthellae, the
relationship is a parasitic one. Isolating the zooxanthellae from the corals and growing
them independently is required to determine if the relationship is truly mutual: It is
mutual if the zooxanthellae do poorly on their own; It is not mutual if the zooxanthellae
grow as well in isolation as in the coral.
p. 411
If a mutation occurred in Escherichia coli that deleted the gene for an adhesin, what
effect might it have on the ability of E. coli to cause urinary tract infections?
E. coli lacking adhesin is unlikely to cause urinary tract infections because it will be
flushed out by the movement of fluid through the system.
p. 436
1. Explain why patient Q, a menopausal woman, may have developed gingivitis from
normal microbiota.
One of the results of the hormonal changes during menopause is a thinning of mucous
membranes and often a decline in secretion of mucus. As the mucosal defenses of the
oral cavity decline, some of the microbes of the oral cavity may have an opportunity to
breach those defenses and establish in new areas like the gingiva.
2.
Patient W died of E. coli infection after an intestinal puncture. Explain why this
microbe, which normally lives in the colon, could kill this patient.
E. coli is a normal inhabitant of the intestine and in that environment E. coli growth is
controlled by the immune system and by the other microbial members of the community;
also, the mucous layer of the intestine blocks E. coli invasion into the underlying tissue.
When the intestine was punctured, E. coli was able to enter the body cavity and grow in
a part of the body where the defenses against this bacterium are poor.
3.
Examine the following graphs of the RED epidemic and the BLUE epidemic.
Neither RED disease nor BLUE disease is treatable. A person with either disease is
ill for only 1 day and recovers fully. Both epidemics began at the same time. Which
epidemic affected more people during the first 3 days? What could explain the short
time course for epidemic RED? Why was epidemic BLUE longer lasting?
The RED epidemic affected more people during the first 3 days. The RED epidemic has
a short incubation time, and is much more contagious resulting in the susceptible
population being infected in a short time. The BLUE epidemic has a longer incubation
time than RED resulting in a longer time until cases show up and a longer time over
which new infections are occurring.
4.
A 27-year-old female came to her doctor’s office with a wide-spread rash, fever,
malaise, and severe muscle pain. The symptoms had begun with a mild headache
3 days previously. She reported being bitten by a tick 1 week prior to that.
The doctor correctly diagnosed Rocky Mountain spotted fever (RMSF) and
prescribed tetracycline. The rash and other signs and symptoms disappeared in a
couple of days, but she continued on her antibiotic therapy for 2 weeks.
Draw a graph showing the course of disease and the relative numbers of pathogens
over time. Label the stages of the disease.
illness
decline
convalescence
Pathogens
Incubation
prodromal
5.
1
2
3
Weeks
Over 30 children younger than 3 years of age developed gastroenteritis after visiting
a local water park. These cases represented 44% of the park visitors in this age
group on the day in question. No older individuals were affected. The causative
agent was determined to be a member of the bacterial genus Shigella. The disease
resulted from oral transmission to the children.
Based only the information given, can you classify this outbreak as an epidemic?
Why or why not? If you were an epidemiologist, how would you go about
determining which pools in the water park were contaminated? What factors might
account for the fact that no older children or adults developed disease? What steps
could the park operators take to reduce the chance of future outbreaks of
gastroenteritis?
Yes, this is an epidemic. Shigella is still relatively rare in the US, and 44% is a fairly high
incidence even for Shigella. If possible, I would interview as many of the families with
sick kids as possible and try to narrow down the possibilities, then sample the suspect
pools for fecal contamination. Older children and adults are unlikely to have accidental
oral contact with non-potable water, whereas children under 3 are not careful about what
goes into their mouths. The park operators should treat the pools with hyperchlorate
and then flush them, then maintain acceptable levels of hyperchlorate in the future.
6.
Review lichen biology in Chapter 12. Describe the relationship between the
photosynthetic member of the lichen and the fungus in terms of the type of
symbiosis.
The relationship between the fungus and its photosynthetic symbiotic partner is a mutual
one; both members benefit.