U E S T I O N S

4. All of the following are known mechanisms of avoiding the effects of antibodies except

A. antigenic variation.

B. mimicking "self."

C. synthesis of an Fc receptor.

D. synthesis of IgG protease.

E. remaining intracellular.

5. Which of the following statements about diphtheria toxin is false? It

A. is an example of an endotoxin.

B. is produced by a species of Corynebacterium.

C. inhibits protein synthesis.

D. can cause local damage to the throat.

E. can cause systemic damage (that is, to organs such as the heart).

6. Which of the following statements about botulism is true?

A. It is caused by Bacillus botulinum, an obligate aerobe.

B. The toxin is resistant to heat, easily withstanding temperatures of 100°C.

C. The organism that causes botulism can cause disease without avoiding the immune response.

D. Vaccinations are routinely given to prevent botulism.

E. Symptoms of botulism include uncontrolled contraction of muscles.

7. Superantigens

A. are exceptionally large antigen molecules.

B. cause a very large antibody response.

C. elicit a response from a large number of T cells.

D. attach non-specifically to B-cell receptors.

E. assist in a protective immune response.

8. Which of the following statements about endotoxin is true? It

B. is a component Gram-positive bacteria.

C. is highly antigenic.

D. is heat-stable.

E. causes T cells to release cytokines.

484 Chapter 19 Host-Microbe Interactions

9. The tissue damage caused by Neisseria gonorrhoeae is primarily due to

A. cross-reactive antibodies.

B. exotoxins.

C. hydrolytic enzymes.

D. the inflammatory response.

E. all of the these.

10. Which of the following statements about viruses is false? They may

A. colonize the skin.

B. enter host cells by endocytosis.

C. enter host cells by fusion of the viral envelope with the cell membrane.

D. induce apoptosis in infected host cells.

E. suppress expression of MHC class I molecules on host cells.

Applications

1. A group of smokers suffering from the outcome of severe

Staphylococcus aureus infections are suing the cigarette companies for extent of their injuries. They claim that the disease was aggravated by cigarette smoking. The group is citing studies indicating that phagocytes are inhibited in their action by compounds in cigarette smoke. A statement prepared by their lawyers states that the S. aureus would not have caused such a severe disease if the phagocytes and immune system overall were functioning properly. During the proceedings, a microbiologist was called in as a professional witness for the court. What were her conclusions about the validity of the claim?

2. A microbiologist put forth a grant proposal to study the molecules bacteria use to communicate. His principal rationale was that the damaging effects of many pathogenic microorganisms could be prevented by inactivating the molecules these bacteria use to communicate. Is this a reasonable proposal? Why or why not?

Critical Thinking

1. A student argued that no distinction should be made between commensalism and parasitism. Even in commensalism, the microorganisms are gaining some benefit (such as nutrients) from the host and this represents a loss to the host. In this sense the host is being damaged. Does the student have a valid argument? Why or why not?

2. A microbiologist argued that there is no such thing as "normal" flora in the human body, since the population is dynamic and is constantly changing depending on diet and external environment. What would be an argument against this microbiologist's view?

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