Question 1

Which of the following best describes why viruses are considered to exist in a 'borrowed life' state?

Accepted Answer

They require a host cell to replicate and cannot carry out metabolism on their own.

Question 2

Which experiment led to the discovery that the infectious agent causing tobacco mosaic disease was not a bacterium?

Accepted Answer

Infecting healthy plants with sap filtered through a porcelain filter that traps bacteria.

Question 3

Which of the following structures is NOT found in all viruses?

Accepted Answer

Membranous envelope

Question 4

A bacteriophage that can alternate between the lytic and lysogenic cycles is called a:

Accepted Answer

Temperate phage

Question 5

Which of the following best explains why antibiotics are ineffective against viral infections?

Accepted Answer

Viruses do not have metabolic pathways targeted by antibiotics.

Question 6

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

Accepted Answer

Attachment → Entry of DNA → Synthesis of viral components → Self-assembly → Release

Question 7

What is the role of restriction enzymes in bacterial defense against phages?

Accepted Answer

They cut up foreign phage DNA, preventing infection.

Question 8

Which of the following statements about the CRISPR-Cas system is TRUE?

Accepted Answer

It allows bacteria to destroy invading phage DNA using RNA-guided nucleases.

Question 9

Which of the following best describes a retrovirus?

Accepted Answer

A virus that uses reverse transcriptase to copy its RNA genome into DNA.

Question 10

Why are emerging viruses such as Ebola and Zika of particular concern to public health?

Accepted Answer

They often arise from mutation, animal reservoirs, or environmental changes, making them unpredictable and difficult to control.

Question 11

Which of the following is a key difference between a prophage and a provirus?

Accepted Answer

A prophage is integrated into a bacterial genome and can exit, while a provirus is integrated into an animal genome and remains permanently.

Question 12

Which of the following best explains why the H5N1 influenza strain is considered highly dangerous?

Accepted Answer

It is genetically very different from circulating human influenza strains, making immune response difficult.

Question 13

Which of the following is a plausible reason why normal seasonal flu viruses are not considered emerging viruses?

Accepted Answer

They have been circulating among humans for a long time, so the population has some immunity.

Question 14

Which of the following is TRUE about prions?

Accepted Answer

They are infectious proteins that can cause degenerative brain diseases.

Question 15

A plant virus is most likely to spread horizontally when:

Accepted Answer

It enters through a wound in the plant cell wall caused by an insect.

Question 16

Which of the following best describes the process by which prions propagate?

Accepted Answer

They convert normal proteins into the misfolded prion form, which then aggregate.

Question 17

Which of the following is a correct statement about viral envelopes?

Accepted Answer

They are derived from host cell membranes and contain both viral and host molecules.

Question 18

Which of the following is a reason why influenza viruses can cause pandemics?

Accepted Answer

They have segmented RNA genomes that allow for genetic reassortment and high mutation rates.

Question 19

Which of the following is a function of viral glycoproteins found on the envelope of animal viruses?

Accepted Answer

They bind to specific receptor molecules on the surface of a host cell.

Question 20

Which of the following best explains why vaccines are effective in preventing certain viral diseases?

Accepted Answer

They stimulate the immune system to recognize and mount a defense against the pathogen.

Viruses: Structure, Replication, and Impact on Living Organisms

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