Question 1

Which of the following best describes the structure of a typical icosahedral virus capsid?

Accepted Answer

A roughly spherical structure composed of 20 equilateral triangles, each made of capsomeres

Question 2

A virus is found to have a lipid bilayer surrounding its capsid. What is the most likely origin of this envelope?

Accepted Answer

It is derived from the host cell membrane during viral release

Question 3

Which enzyme is commonly found inside the nucleocapsid of retroviruses and is essential for their replication?

Accepted Answer

Reverse transcriptase

Question 4

A researcher performs a plaque assay and counts 50 plaques on a plate after inoculating with 0.1 mL of a 10⁻⁶ dilution of a viral stock. What is the titer of the original viral stock in plaque-forming units (PFU) per mL?

Accepted Answer

$$5 	imes 10^8$

Question 5

Which of the following statements about viral genomes is correct?

Accepted Answer

Viral genomes can be composed of either DNA or RNA, and can be single- or double-stranded

Question 6

Why are bacterial viruses generally easier to culture and quantify than plant viruses?

Accepted Answer

Bacterial hosts can be grown as lawns on agar plates, allowing for easy visualization of plaques

Question 7

Which of the following best explains why viruses are considered obligate intracellular parasites?

Accepted Answer

They require host cell metabolic machinery for replication

Question 8

A virus with helical symmetry will have its length determined by which of the following?

Accepted Answer

The length of the viral nucleic acid

Question 9

Which of the following is a key difference between enveloped and nonenveloped viruses?

Accepted Answer

Enveloped viruses acquire their outer membrane from the host cell

Question 10

Which of the following best describes the function of lysozyme in bacteriophage T4?

Accepted Answer

It degrades the bacterial cell wall to allow viral entry or release

Question 11

A scientist is studying a virus that is inert outside the host but becomes metabolically active inside the host cell. Which property of viruses does this observation illustrate?

Accepted Answer

Viruses exist in both extracellular (inert) and intracellular (active) forms

Question 12

Which of the following is NOT a typical method for quantifying animal viruses?

Accepted Answer

Plaque assay using a bacterial lawn

Question 13

Which of the following best explains why plant viruses are more difficult to quantify than bacterial viruses?

Accepted Answer

Plant cells cannot be grown as lawns on agar plates

Question 14

Which of the following is a real-world application of the plaque assay technique?

Accepted Answer

Estimating the concentration of infectious virus particles in a vaccine preparation

Question 15

Which of the following statements about capsomeres is correct?

Accepted Answer

Capsomeres are protein subunits that make up the capsid

Question 16

A virus is found to have a complex structure with a head, tail, and tail fibers. Which type of host is this virus most likely to infect?

Accepted Answer

Bacterial cells

Question 17

Which of the following best describes the process of calculating viral titer using a plaque assay?

Accepted Answer

Counting the number of clear zones (plaques) formed on a host cell lawn and adjusting for dilution and volume

Question 18

Which of the following is a function of RNA replicase in RNA viruses?

Accepted Answer

Synthesizing RNA from an RNA template

Question 19

Which of the following is a plausible reason why viral envelopes are sensitive to detergents and alcohols?

Accepted Answer

The envelope is a lipid bilayer derived from the host cell membrane, which is disrupted by detergents and alcohols

Viruses: Structure, Morphology, and Cultivation

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