$$ \text{Viral titer (PFU/mL)} = \frac{\text{Number of plaques}}{\text{Dilution factor} \times \text{Volume plated (mL)}} $$

Question 1

Which of the following best describes why viruses are classified as nonliving microbes?

Accepted Answer

They are unable to reproduce outside of a host cell and do not carry out metabolic processes independently.

Question 2

A virus with a helical capsid and an envelope is most likely to:

Accepted Answer

Budge off the host cell, acquiring part of the host membrane as its envelope.

Question 3

Which viral structure is primarily responsible for determining the shape of a free virus particle?

Accepted Answer

Capsid

Question 4

A bacteriophage infects a bacterial cell and its DNA becomes integrated into the host genome. What is this stage called?

Accepted Answer

Prophage

Question 5

Which of the following is NOT a criterion used by the International Committee on Taxonomy of Viruses to classify viruses?

Accepted Answer

Type of host cell infected

Question 6

During the lytic replication cycle of a bacteriophage, which step immediately follows the injection of genetic material into the host?

Accepted Answer

Synthesis of viral components using host machinery

Question 7

Which equation best represents the calculation of viral titer using plaque assay results?

Accepted Answer

$$ 	ext{Viral titer (PFU/mL)} = \frac{	ext{Number of plaques}}{	ext{Dilution factor} 	imes 	ext{Volume plated (mL)}} $$

Question 8

Which of the following best explains why some viruses are oncogenic?

Accepted Answer

They stimulate uncontrolled cell division and/or decrease cell responsiveness to death signals.

Question 9

A virus infects only human respiratory epithelial cells and not other tissues. This specificity is referred to as:

Accepted Answer

Tropism

Question 10

Which of the following statements about viral genomes is correct?

Accepted Answer

A virus can have either DNA or RNA as its genetic material, but not both.

Question 11

Which step in animal virus replication involves the removal of the capsid coat to release the viral genome?

Accepted Answer

Uncoating

Question 12

Which of the following viruses is known to be oncogenic and associated with human cancer?

Accepted Answer

Human papillomavirus (HPV)

Question 13

Which of the following best describes the difference in cultivation techniques for bacteriophages versus animal viruses?

Accepted Answer

Bacteriophages are grown on bacterial lawns, while animal viruses require cell culture or live animals.

Question 14

Which viral structure is most likely to be targeted by vaccines designed to prevent viral attachment to host cells?

Accepted Answer

Spike proteins

Question 15

A temperate bacteriophage confers new pathogenic properties to a bacterium by integrating its genome. This process is called:

Accepted Answer

Lysogenic conversion

Question 16

Which of the following is a correct sequence of steps in the lytic replication cycle of a bacteriophage?

Accepted Answer

Attachment → Entry → Synthesis → Assembly → Release

Question 17

Which of the following best explains why naked viruses are more resistant to environmental stress than enveloped viruses?

Accepted Answer

They lack a lipid envelope, making them less susceptible to desiccation and detergents.

Question 18

A patient is diagnosed with a persistent viral infection that shows periods of activity and inactivity. Which virus is most likely responsible?

Accepted Answer

Herpes virus

Question 19

Which of the following is a plausible reason why membrane filters that trap bacteria are unable to trap viruses?

Accepted Answer

Viruses are much smaller than bacteria, often ranging from 20-400 nm.

Question 20

Which of the following best describes the role of neuraminidase (NA) and hemagglutinin (HA) spike proteins in influenza viruses?

Accepted Answer

They facilitate viral attachment and entry into host cells and are frequently mutated.

Viruses: Structure, Classification, and Replication (Microbiology Study Notes)

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