Question 1

Which of the following best distinguishes a virus from a bacterium?

Accepted Answer

Viruses lack cellular structure and metabolic enzymes, while bacteria are cellular and metabolically active.

Question 2

A nonenveloped polyhedral virus with spikes is most likely to use its spikes for which function?

Accepted Answer

Attachment to host cell receptors

Question 3

Which of the following best describes the difference between a viral species and a bacterial species?

Accepted Answer

Viral species are defined by their host range and genetic material, while bacterial species are defined by phenotypic and genotypic characteristics.

Question 4

The plaque method is used to culture bacteriophages. What is the principle behind this method?

Accepted Answer

Bacteriophages infect bacterial cells on an agar plate, creating clear zones called plaques where bacteria have been lysed.

Question 5

Continuous cell lines are preferred over primary cell lines for culturing animal viruses because:

Accepted Answer

Continuous cell lines can be maintained for longer periods and provide a consistent environment for viral growth.

Question 6

Which of the following is NOT a technique used to identify viruses?

Accepted Answer

Gram staining

Question 7

During the lytic cycle of T-even bacteriophages, how do the phages obtain nucleotides and amino acids for replication?

Accepted Answer

They use the host cell's metabolic machinery to obtain nucleotides and amino acids.

Question 8

Vibrio cholerae produces toxin and causes cholera only when it is lysogenic. What does this imply?

Accepted Answer

The bacterium must be infected by a bacteriophage carrying the toxin gene, which is integrated into its genome.

Question 9

Which of the following best describes the principal events in the multiplication cycle of an enveloped DNA-containing animal virus?

Accepted Answer

Attachment, entry by endocytosis or fusion, uncoating, biosynthesis of viral DNA and proteins, maturation, and release by budding.

Question 10

How can an RNA virus cause cancer if it does not have DNA to insert into a cell’s genome?

Accepted Answer

RNA viruses can use reverse transcriptase to convert their RNA into DNA, which can then integrate into the host genome.

Question 11

Which of the following is an example of a latent viral infection?

Accepted Answer

Shingles (herpes zoster)

Question 12

Which statement best differentiates persistent viral infections from latent viral infections?

Accepted Answer

Persistent infections involve continuous or slow viral production over time, while latent infections involve periods of inactivity with occasional reactivation.

Question 13

Which of the following best describes the difference between a virus, a viroid, and a prion?

Accepted Answer

Viruses contain nucleic acids and protein, viroids are infectious RNA without protein, and prions are infectious proteins without nucleic acids.

Question 14

The LD50 of botulinum toxin is $$0.03\ ng/kg$$ and the LD50 of Salmonella toxin is $$12\ mg/kg. $$Which toxin is more potent?

Accepted Answer

Botulinum toxin, because it has a lower LD50.

Question 15

A drug that binds mannose on human cells would most likely affect pathogenic bacteria by:

Accepted Answer

Preventing bacterial adherence to host cells.

Question 16

Which of the following is a function shared by capsules and M proteins in pathogenic bacteria?

Accepted Answer

Both inhibit phagocytosis by host immune cells.

Question 17

Why doesn’t the influenza vaccine offer more than a few months of protection?

Accepted Answer

Influenza virus undergoes antigenic variation, frequently changing its surface antigens.

Question 18

Which of the following best describes the function of siderophores in bacterial pathogenicity?

Accepted Answer

Siderophores bind iron from the host, making it available for bacterial growth.

Question 19

Which of the following statements correctly differentiates exotoxins from endotoxins?

Accepted Answer

Exotoxins are secreted proteins with specific effects, while endotoxins are lipopolysaccharides released from the outer membrane of Gram-negative bacteria.

Comprehensive Study Guide: Viruses, Pathogenicity, Immunity, and Epidemiology (Chapters 13–17)

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