Question 1

Which of the following statements best describes a key difference between viruses and bacteria?

Accepted Answer

Viruses lack cellular organelles and must use host machinery for replication.

Question 2

A virus that consists only of nucleic acid and a protein capsid is called a:

Accepted Answer

Naked virus (nucleocapsid)

Question 3

Which of the following best explains why viruses are considered to have both living and non-living characteristics?

Accepted Answer

They can mutate and reproduce, but only inside living host cells.

Question 4

During the lytic cycle of a bacteriophage, what is the primary function of the enzyme lysozyme?

Accepted Answer

To degrade the bacterial peptidoglycan for genome injection and cell lysis

Question 5

Which step in the lytic cycle is responsible for the appearance of plaques on a bacterial lawn?

Accepted Answer

Release

Question 6

A student performs a plaque assay and counts 45 plaques on a plate inoculated with a $$10^{-5}$$ dilution using 0.1 ml of sample. What is the PFU/ml in the original sample? Use the formula $$	ext{PFU/ml} = \frac{	ext{Number of plaques}}{	ext{Volume plated (ml)}} 	imes 	ext{Dilution factor}.$$

Accepted Answer

$$4.5 	imes 10$$^{6}$$ PFU/ml

Question 7

Which of the following best describes viral specificity?

Accepted Answer

A specific virus will only attach to and infect a specific strain of a susceptible host bacterium.

Question 8

In a phage typing experiment, which result would indicate that a bacterial strain is sensitive to a particular phage?

Accepted Answer

The appearance of clear plaques in the sector where the phage was applied.

Question 9

Which of the following is NOT a component of a typical bacteriophage structure?

Accepted Answer

Mitochondria

Question 10

Why are enveloped viruses generally more sensitive to disinfectants than naked viruses?

Accepted Answer

Their lipid envelope, derived from the host cell membrane, is easily disrupted.

Question 11

Which of the following best describes the role of capsomeres in a virus?

Accepted Answer

They are protein subunits that make up the capsid.

Question 12

A bacteriophage infects a bacterium and shuts down the host's macromolecular synthesis. Which stage of the lytic cycle does this describe?

Accepted Answer

Biosynthesis

Question 13

Which of the following is a correct statement about the genetic material of viruses?

Accepted Answer

Viruses contain either DNA or RNA, but never both.

Question 14

In a laboratory experiment, you observe that only one of four bacterial strains is lysed by Coliphage T4. What does this demonstrate?

Accepted Answer

Coliphage T4 is specific to certain bacterial strains.

Question 15

Which of the following best describes a plaque observed on a bacterial lawn after bacteriophage infection?

Accepted Answer

A clear area where bacteria have been lysed by phages.

Question 16

Which laboratory technique is used to determine the number of infectious bacteriophage particles in a sample?

Accepted Answer

Plaque assay

Question 17

A student prepares serial dilutions of a phage sample and plates 0.1 ml of a $$10^{-4}$$ dilution, counting 120 plaques. What is the PFU/ml in the original sample? Use $$	ext{PFU/ml} = \frac{	ext{Number of plaques}}{	ext{Volume plated (ml)}} 	imes 	ext{Dilution factor}.$$

Accepted Answer

$$1.2 	imes 10$$^{6}$$ PFU/ml

Question 18

Which of the following best explains why phage typing can be used to identify unknown bacteria?

Accepted Answer

Phages are specific to certain bacterial strains, so lysis indicates susceptibility.

Question 19

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

Accepted Answer

Attachment → Penetration → Biosynthesis → Maturation → Release

Bacteriophages and Viral Specificity: Lab Study Guide

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