Q: Which of the following equations correctly represents the calculation of viral titer in a plaque assay?

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

Question 1

Which of the following best distinguishes viruses from prokaryotic and eukaryotic cells?

Accepted Answer

Viruses lack cellular structure and cannot replicate without a host cell.

Question 2

A scientist is studying a new virus and observes that it contains only RNA as its genetic material, is surrounded by a protein coat, and has surface spikes. Which of the following correctly identifies the main components of this virus?

Accepted Answer

RNA, capsid, and spikes

Question 3

Which of the following statements about antigenic shift and antigenic drift in influenza viruses is correct?

Accepted Answer

Antigenic drift involves gradual accumulation of mutations, while antigenic shift can result in pandemics due to reassortment of gene segments.

Question 4

A virus infects only a specific species and a particular cell type within that species. This specificity is best described as:

Accepted Answer

Host range and tropism

Question 5

Which of the following is a key feature of bacteriophage lytic replication?

Accepted Answer

Release of new phages by lysis of the bacterial cell

Question 6

During the lysogenic cycle of a bacteriophage, which of the following events occurs?

Accepted Answer

The phage DNA integrates into the host genome and is replicated along with it.

Question 7

A patient is diagnosed with a viral infection that causes rapid onset of symptoms, followed by complete recovery and elimination of the virus. This infection is best described as:

Accepted Answer

Acute infection

Question 8

Which of the following best explains how viruses drive evolution by selective pressure and innovation?

Accepted Answer

Viruses introduce new genes into host populations through horizontal gene transfer.

Question 9

How does phage conversion impact bacterial pathogens?

Accepted Answer

It can result in bacteria acquiring new traits, such as toxin production, through lysogenic phage genes.

Question 10

In a laboratory, a researcher uses a plaque assay to quantify bacteriophages. Which of the following best describes a plaque in this context?

Accepted Answer

A clear zone on a bacterial lawn caused by lysis of bacteria by phages.

Question 11

Which of the following antiviral drugs inhibits viral DNA synthesis and is commonly used to treat herpes simplex virus infections?

Accepted Answer

Acyclovir

Question 12

A virus with a segmented RNA genome infects a host cell that is simultaneously infected by a different strain of the same virus. What is the most likely evolutionary outcome?

Accepted Answer

Antigenic shift due to reassortment of genome segments

Question 13

Which of the following equations correctly represents the calculation of viral titer in a plaque assay?

Accepted Answer

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

Question 14

Which of the following best describes the difference between lytic and lysogenic cycles in bacteriophages?

Accepted Answer

The lytic cycle results in destruction of the host cell, while the lysogenic cycle allows the phage genome to persist in the host without killing it.

Question 15

A patient is infected with a virus that remains dormant in nerve cells and can reactivate years later. This is an example of:

Accepted Answer

Latent infection

Question 16

Which of the following is NOT a component of a typical virus particle?

Accepted Answer

Ribosome

Question 17

Which of the following best explains why viruses are not considered living organisms?

Accepted Answer

They cannot carry out metabolism or reproduce independently.

Question 18

A researcher observes that a bacterium acquires the ability to produce a toxin only after infection by a specific bacteriophage. This phenomenon is best explained by:

Accepted Answer

Phage conversion (lysogenic conversion)

Question 19

Which of the following best describes the function of viral surface spikes?

Accepted Answer

They facilitate attachment to specific host cell receptors.

Question 20

Which of the following statements about the cultivation of animal viruses in the laboratory is correct?

Accepted Answer

Animal viruses require living cells, such as cell cultures or embryonated eggs, for propagation.

Microbiology Study Guide: Viruses, Bacteriophages, and Viral Evolution

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